Technology in Architectural Practice

This message has been cross posted to the following Discussion Forums: Technology in Architectural Practice and Committee on the Environment .
-------------------------------------------

The debate over allowing a house to "breathe" a little or to seal it up as tight as possible has been argued ever since the advent of sick building syndrome. I attend the local Green Conferences every year. I've been very interested in sustainability since my professor introduced it to me in 1990. After listening to the building scientists, the theory of total air sealing with controlled ventilation sounds very logical, especially coming from a Canadian building scientist describing their climate conditions. I do have a problem with relying on a quiet fan of an ERV to not break down and cause the building to get sick. In the South East, we have one of the most difficult environments to build in. The humidity is relentless, the termites and carpenter bees are hungry, and in Atlanta, we have a very intense topography being at the foothills of the North GA mountains. Air sealing is becoming a requirement here and everyone's hardwoods are cupping. The blower door test is now required (or will be) on all residences in the metro area. I have used several different strategies recommended by building scientists for applying the air sealing, insulation, and building configuration to provide better efficiency yet we keep having the same problems.

The "greenest" house I designed has a ground source heat pump (geothermal), tons of insulation, and we sealed the crawlspace with a heavy duty waterproofing membrane that welds together like a TPO roof. This house boasts $50/ month electric bills, until the hardwoods started cupping and the crawl became too humid. Now they have to run a dehumidifier 24/7 that costs $50/ month. All of these houses have ERVs, another piece of equipment wasting energy, just to be "sealed" so we can save energy. The builder is well versed in green design/ installation. We made every precaution recommended, yet you can't keep humidity out of a crawlspace no matter how hard you try to seal it. In this assembly, the one vulnerability I can think of is the required termite check strip at the top of the masonry wall where the wood begins. Our water table is high and so is our frost line, so the earth stays pretty damp. It's possible that the vapor is pushing it's way through that 1" strip.

I have a house on a sealed crawl with closed cell spray foam on the underside of the floor. This cupped the worst. We were warned not to use open cell as it let's the vapor leak through. Maybe the humidity is mostly coming from the inside, not the crawl?

I have another house with a basement instead of a crawl that has the same problems. This basement is conditioned, yet we're trapping the humidity in the house and it simply can't escape. We have tried everything to keep the flooring from cupping. Our solution to our energy efficient air tight construction is to run a dehumidifier 24/7 at $50/ month.

I have a house that is built on a slab on grade. This one has less cupping in the flooring, but you can't build a slab on grade house in most places in Atlanta as our topography is so intense. The advantage is that you're only dealing with moisture coming through the horizontal plane of the floor, not the side walls as well. The average lots have enough slope to make slab on grade too expensive and not enough slope or a low enough water table to do a basement. This why we end up with crawl spaces. Even when built as a perfectly sealed, short basement, they still get moist.

The houses that are built on naturally ventilated crawl spaces with R-30 batts in the floor are staying the driest and have no problems with the floor cupping. They may be a little less efficient, but they aren't relying on ERVs and dehumidifiers to stay comfortable and healthy. What happens when we have the next ice storm and the electric is out for a week? What happens during the next Summer brown out when the electricity is out for a day or two?

My theory is that you can't humidity seal a Southern crawl space, even with the best materials available. This makes crawl spaces and basements a humidity trap/ generator. In each case of blower door approved construction, the overall humidity in the living space is higher than "normal". I think the humidity that we create from breathing, showering, and other activities is being trapped as well. The AC can't remove it all, even when running all day. In the summer, these sealed crawls are much warmer than the interior of the climate controlled house, so this humidity is going to be attracted to the cold side of the surfaces straddling the temperature differential between interior and exterior. In our case, this is the hardwood flooring. Since wood is dry and highly absorbent, you don't see the condensation on the surface. You eventually see it cup. If you're trapping enough humidity, then you're not helping your efficiency. If you need dehumidifiers and ERVs to make your more efficient house air tight and healthy, then what's the difference in letting it breathe enough to not require this energy consuming equipment and worry about quiet fans quitting or power outages? As the brilliant Canadian building scientist put it, "If you have a theoretically perfectly sealed building, then where do you put the holes?" These are the crossroads we're at right now as policy is resulting in problems that will have to be solved. The ever evolving theories of sustainable design. The more complicated we make it, the more problems we have to solve. Too bad our lifestyles keep evolving beyond our means to keep up.

-------------------------------------------
Eric Rawlings AIA
Owner
Rawlings Design, Inc.
Decatur GA
-------------------------------------------

It is important to understand which direction the wood flooring cupping is taking: concave, or convex, with respect to the finished side. The cupping will be convex on the more humid side of the wood, which is expanding. I assume the more humid (convex, expanded) side in your case is the side of the flooring facing the crawlspace.

It seems the theoretical solution to the cupping hardwood flooring problem will have to center on establishing the same humidity level on both sides of the flooring material. Accomplishing that over a crawlspace is difficult; the dynamics of water vapor movement through the floor structure aren't easy to grasp. The wood products themselves have varying properties - some laminated, others solid wood. Some flooring products are impregnated, and all will be either factory- or site- finished with materials that may or may not serve as vapor retarders on one side of the wood only. The flooring underlayments may also affect vapor movement, as may the subfloor sheathings. 

I continue to wonder whether installing a separate $1,000 crawlspace dehumidifier (plus the $50 per month) in these sealed houses is really the answer, or whether it would make more sense to induce a modest air change rate throughout the house, using the crawlspace as an exhaust plenum to the exterior. Running a 100 cfm bathroom exhaust fan continuously in a 6000 cu. ft. crawlspace designed to draw conditioned air from the house above gives the crawlspace 1 air change per hour - perhaps enough to start equalizing the humidity between the house and the crawlspace. This of course adds to the overall air conditioning load of the house, but the load can be met by the much more efficient 15 SEER heat pump, and unless you like the smell of two day old cooked broccoli, you do want some fresh make-up air in the house anyway, which can be introduced through the HVAC return air system to allow for the crawlspace exhaust negative air pressure. Just a thought.

The termite observation strip is a possible target for improvement in sealed crawlspaces. I have seen a clear acrylic or polycarbonate sheet used at this location, with the vapor retarder materials sealed to both sides of it. That might help, although the idea that you can completely vapor seal a crawlspace, or a house for that matter, is a bit fanciful.

-------------------------------------------
Philip Kabza AIA
Partner and Dir Technical Services
SpecGuy
Charlotte NC
-------------------------------------------






Original Message:
Sent: 03-20-2012 08:02
From: Eric Rawlings
Subject: Let it breathe or seal it tight?

This message has been cross posted to the following Discussion Forums: Technology in Architectural Practice and Committee on the Environment .
-------------------------------------------

The debate over allowing a house to "breathe" a little or to seal it up as tight as possible has been argued ever since the advent of sick building syndrome. I attend the local Green Conferences every year. I've been very interested in sustainability since my professor introduced it to me in 1990. After listening to the building scientists, the theory of total air sealing with controlled ventilation sounds very logical, especially coming from a Canadian building scientist describing their climate conditions. I do have a problem with relying on a quiet fan of an ERV to not break down and cause the building to get sick. In the South East, we have one of the most difficult environments to build in. The humidity is relentless, the termites and carpenter bees are hungry, and in Atlanta, we have a very intense topography being at the foothills of the North GA mountains. Air sealing is becoming a requirement here and everyone's hardwoods are cupping. The blower door test is now required (or will be) on all residences in the metro area. I have used several different strategies recommended by building scientists for applying the air sealing, insulation, and building configuration to provide better efficiency yet we keep having the same problems.

The "greenest" house I designed has a ground source heat pump (geothermal), tons of insulation, and we sealed the crawlspace with a heavy duty waterproofing membrane that welds together like a TPO roof. This house boasts $50/ month electric bills, until the hardwoods started cupping and the crawl became too humid. Now they have to run a dehumidifier 24/7 that costs $50/ month. All of these houses have ERVs, another piece of equipment wasting energy, just to be "sealed" so we can save energy. The builder is well versed in green design/ installation. We made every precaution recommended, yet you can't keep humidity out of a crawlspace no matter how hard you try to seal it. In this assembly, the one vulnerability I can think of is the required termite check strip at the top of the masonry wall where the wood begins. Our water table is high and so is our frost line, so the earth stays pretty damp. It's possible that the vapor is pushing it's way through that 1" strip.

I have a house on a sealed crawl with closed cell spray foam on the underside of the floor. This cupped the worst. We were warned not to use open cell as it let's the vapor leak through. Maybe the humidity is mostly coming from the inside, not the crawl?

I have another house with a basement instead of a crawl that has the same problems. This basement is conditioned, yet we're trapping the humidity in the house and it simply can't escape. We have tried everything to keep the flooring from cupping. Our solution to our energy efficient air tight construction is to run a dehumidifier 24/7 at $50/ month.

I have a house that is built on a slab on grade. This one has less cupping in the flooring, but you can't build a slab on grade house in most places in Atlanta as our topography is so intense. The advantage is that you're only dealing with moisture coming through the horizontal plane of the floor, not the side walls as well. The average lots have enough slope to make slab on grade too expensive and not enough slope or a low enough water table to do a basement. This why we end up with crawl spaces. Even when built as a perfectly sealed, short basement, they still get moist.

The houses that are built on naturally ventilated crawl spaces with R-30 batts in the floor are staying the driest and have no problems with the floor cupping. They may be a little less efficient, but they aren't relying on ERVs and dehumidifiers to stay comfortable and healthy. What happens when we have the next ice storm and the electric is out for a week? What happens during the next Summer brown out when the electricity is out for a day or two?

My theory is that you can't humidity seal a Southern crawl space, even with the best materials available. This makes crawl spaces and basements a humidity trap/ generator. In each case of blower door approved construction, the overall humidity in the living space is higher than "normal". I think the humidity that we create from breathing, showering, and other activities is being trapped as well. The AC can't remove it all, even when running all day. In the summer, these sealed crawls are much warmer than the interior of the climate controlled house, so this humidity is going to be attracted to the cold side of the surfaces straddling the temperature differential between interior and exterior. In our case, this is the hardwood flooring. Since wood is dry and highly absorbent, you don't see the condensation on the surface. You eventually see it cup. If you're trapping enough humidity, then you're not helping your efficiency. If you need dehumidifiers and ERVs to make your more efficient house air tight and healthy, then what's the difference in letting it breathe enough to not require this energy consuming equipment and worry about quiet fans quitting or power outages? As the brilliant Canadian building scientist put it, "If you have a theoretically perfectly sealed building, then where do you put the holes?" These are the crossroads we're at right now as policy is resulting in problems that will have to be solved. The ever evolving theories of sustainable design. The more complicated we make it, the more problems we have to solve. Too bad our lifestyles keep evolving beyond our means to keep up.

-------------------------------------------
Eric Rawlings AIA
Owner
Rawlings Design, Inc.
Decatur GA
-------------------------------------------

I appreciate your 2 cents. The flooring is pointing up on the edges (concave on top) and I assumed the same thing about the direction of vapor drive. This doesn't explain the floor with closed cell foam over a crawl nor does it explain the high humidity readings in all of the interiors. Typically, wood will want to cup in the opposite direction of the curve of the grain (in section) if exposed to humidity on both sides. These consistent problems are happening to different builders with different subs. Could it be possible that the closed cell foam is trapping the humidity at the bottom side of the flooring, thus making it appear that the vapor is coming in from the crawl? Since the foam is under the subfloor, it's the over the thickness of the plywood that the temperature differential is swinging from hot in the crawl to cold in the house (summer) and the opposite in the winter. Regardless, condensation would want to occur under the flooring on the surface of the plywood. Those grooves in the flooring provide a little space for it to collect. If water vapor and condensation are allowed to collect under the flooring, this may explain the closed cell foamed floor and the direction of cupping. 

I'm a believer in simple is better. The more we complicate our solutions, the more potential for problems we create. I'm still on the fence here when it comes to fanatical tightening of buildings. ERVs are expensive and have a moderate operating cost. Dehumidifiers can be as expensive to run as the entire building in the case of my Example #1. Would that client's house cost more than $100 a month to run if we removed the ERV and Dehumidifier and drilled some holes in his wall and crawl to achieve enough ventilation to keep humidity down to the levels of our "leakier" houses from a few years ago? The argument down in the South is that a leaky house draws moist outside air into the building causing the AC to run all day, just to remove humidity. Our leaky houses aren't the ones with the obnoxiously high humid readings, it's the tight houses. The argument and solution to remove humidity to make AC more efficient actually makes humidity worse and we just spent more money on gadgets to boot. This is the kind of stuff that turns off the skeptic.

If we ventilate the crawl and spray foam the floor, then we have to relocate the mechanical equipment powering the first floor, which costs money in terms of interior sf and how much we can sell the house for. With zoning requirements of an old in-town neighborhood, our floor area is very precious. This scenario may be our next option, but I really hate experimenting on my clients. At what point will an owner get angry enough for litigation for being convinced to spend all this extra money on gadgets and such only to get what they perceive as worse results?

I always tell my clients, especially the spec builders, that a solution to a problem isn't a solution if it creates two more problems to solve and unfortunately many of the "scientific" solutions that are suggested come with many components and complications that could very well open us up to many, many more problems to solve. Here I present the humidity problem and look at how my problems domino from that one issue. For a three or four part solution, how do we know which part of the solution was effective or which one is the next problem generator?

-------------------------------------------
Eric Rawlings AIA
Owner
Rawlings Design, Inc.
Decatur GA
-------------------------------------------






Original Message:
Sent: 03-21-2012 07:05
From: Philip Kabza
Subject: Let it breathe or seal it tight?

It is important to understand which direction the wood flooring cupping is taking: concave, or convex, with respect to the finished side. The cupping will be convex on the more humid side of the wood, which is expanding. I assume the more humid (convex, expanded) side in your case is the side of the flooring facing the crawlspace.

It seems the theoretical solution to the cupping hardwood flooring problem will have to center on establishing the same humidity level on both sides of the flooring material. Accomplishing that over a crawlspace is difficult; the dynamics of water vapor movement through the floor structure aren't easy to grasp. The wood products themselves have varying properties - some laminated, others solid wood. Some flooring products are impregnated, and all will be either factory- or site- finished with materials that may or may not serve as vapor retarders on one side of the wood only. The flooring underlayments may also affect vapor movement, as may the subfloor sheathings. 

I continue to wonder whether installing a separate $1,000 crawlspace dehumidifier (plus the $50 per month) in these sealed houses is really the answer, or whether it would make more sense to induce a modest air change rate throughout the house, using the crawlspace as an exhaust plenum to the exterior. Running a 100 cfm bathroom exhaust fan continuously in a 6000 cu. ft. crawlspace designed to draw conditioned air from the house above gives the crawlspace 1 air change per hour - perhaps enough to start equalizing the humidity between the house and the crawlspace. This of course adds to the overall air conditioning load of the house, but the load can be met by the much more efficient 15 SEER heat pump, and unless you like the smell of two day old cooked broccoli, you do want some fresh make-up air in the house anyway, which can be introduced through the HVAC return air system to allow for the crawlspace exhaust negative air pressure. Just a thought.

The termite observation strip is a possible target for improvement in sealed crawlspaces. I have seen a clear acrylic or polycarbonate sheet used at this location, with the vapor retarder materials sealed to both sides of it. That might help, although the idea that you can completely vapor seal a crawlspace, or a house for that matter, is a bit fanciful.

-------------------------------------------
Philip Kabza AIA
Partner and Dir Technical Services
SpecGuy
Charlotte NC
-------------------------------------------






Original Message:
Sent: 03-20-2012 08:02
From: Eric Rawlings
Subject: Let it breathe or seal it tight?

This message has been cross posted to the following Discussion Forums: Technology in Architectural Practice and Committee on the Environment .
-------------------------------------------

The debate over allowing a house to "breathe" a little or to seal it up as tight as possible has been argued ever since the advent of sick building syndrome. I attend the local Green Conferences every year. I've been very interested in sustainability since my professor introduced it to me in 1990. After listening to the building scientists, the theory of total air sealing with controlled ventilation sounds very logical, especially coming from a Canadian building scientist describing their climate conditions. I do have a problem with relying on a quiet fan of an ERV to not break down and cause the building to get sick. In the South East, we have one of the most difficult environments to build in. The humidity is relentless, the termites and carpenter bees are hungry, and in Atlanta, we have a very intense topography being at the foothills of the North GA mountains. Air sealing is becoming a requirement here and everyone's hardwoods are cupping. The blower door test is now required (or will be) on all residences in the metro area. I have used several different strategies recommended by building scientists for applying the air sealing, insulation, and building configuration to provide better efficiency yet we keep having the same problems.

The "greenest" house I designed has a ground source heat pump (geothermal), tons of insulation, and we sealed the crawlspace with a heavy duty waterproofing membrane that welds together like a TPO roof. This house boasts $50/ month electric bills, until the hardwoods started cupping and the crawl became too humid. Now they have to run a dehumidifier 24/7 that costs $50/ month. All of these houses have ERVs, another piece of equipment wasting energy, just to be "sealed" so we can save energy. The builder is well versed in green design/ installation. We made every precaution recommended, yet you can't keep humidity out of a crawlspace no matter how hard you try to seal it. In this assembly, the one vulnerability I can think of is the required termite check strip at the top of the masonry wall where the wood begins. Our water table is high and so is our frost line, so the earth stays pretty damp. It's possible that the vapor is pushing it's way through that 1" strip.

I have a house on a sealed crawl with closed cell spray foam on the underside of the floor. This cupped the worst. We were warned not to use open cell as it let's the vapor leak through. Maybe the humidity is mostly coming from the inside, not the crawl?

I have another house with a basement instead of a crawl that has the same problems. This basement is conditioned, yet we're trapping the humidity in the house and it simply can't escape. We have tried everything to keep the flooring from cupping. Our solution to our energy efficient air tight construction is to run a dehumidifier 24/7 at $50/ month.

I have a house that is built on a slab on grade. This one has less cupping in the flooring, but you can't build a slab on grade house in most places in Atlanta as our topography is so intense. The advantage is that you're only dealing with moisture coming through the horizontal plane of the floor, not the side walls as well. The average lots have enough slope to make slab on grade too expensive and not enough slope or a low enough water table to do a basement. This why we end up with crawl spaces. Even when built as a perfectly sealed, short basement, they still get moist.

The houses that are built on naturally ventilated crawl spaces with R-30 batts in the floor are staying the driest and have no problems with the floor cupping. They may be a little less efficient, but they aren't relying on ERVs and dehumidifiers to stay comfortable and healthy. What happens when we have the next ice storm and the electric is out for a week? What happens during the next Summer brown out when the electricity is out for a day or two?

My theory is that you can't humidity seal a Southern crawl space, even with the best materials available. This makes crawl spaces and basements a humidity trap/ generator. In each case of blower door approved construction, the overall humidity in the living space is higher than "normal". I think the humidity that we create from breathing, showering, and other activities is being trapped as well. The AC can't remove it all, even when running all day. In the summer, these sealed crawls are much warmer than the interior of the climate controlled house, so this humidity is going to be attracted to the cold side of the surfaces straddling the temperature differential between interior and exterior. In our case, this is the hardwood flooring. Since wood is dry and highly absorbent, you don't see the condensation on the surface. You eventually see it cup. If you're trapping enough humidity, then you're not helping your efficiency. If you need dehumidifiers and ERVs to make your more efficient house air tight and healthy, then what's the difference in letting it breathe enough to not require this energy consuming equipment and worry about quiet fans quitting or power outages? As the brilliant Canadian building scientist put it, "If you have a theoretically perfectly sealed building, then where do you put the holes?" These are the crossroads we're at right now as policy is resulting in problems that will have to be solved. The ever evolving theories of sustainable design. The more complicated we make it, the more problems we have to solve. Too bad our lifestyles keep evolving beyond our means to keep up.

-------------------------------------------
Eric Rawlings AIA
Owner
Rawlings Design, Inc.
Decatur GA
-------------------------------------------

Important discussion, as builders throughout the south and southeast are concerned with how to integrate current building science and sustainability with sound construction practice.

We stopped putting vapor retarders in the walls in southeast US warm humid climate buildings a decade ago. We have since concentrated on utilizing carefully installed air barriers that prevent massive moisture movement, while allowing the HVAC system to handle the water vapor diffusion through wall materials. This appears to work - the incidence of moisture and mold issues in building walls has dropped as a result.

It seems we forgot to consider the floors. Sheathings, underlayments, building paper, and some wood finish products are vapor retarders. I believe we need to work with the flooring manufacturers to identify conditions under which their products will work. They are the ones with the most to lose, so perhaps would be interested in contributing to studies that can provide more than anecdotal evidence of the moisture dynamics of wood subfloor assemblies in warm, humid climates.

Anyone who spends much time in a warm, humid climate unlined crawlspace quickly looks for an easier gig. They are dirty, wet, moldy, and bug-ridden places. The "traditional" southern crawlspace house (you know, the one we say "breathes") is slowly self-composting in the crawlspace, so it is not a solution, it is a slow, long term failure, full of occupants loading up on Allegra and bug spray and wondering why.

The lined and sealed crawlspace, with careful details carefully carried out, appears to be a good alternative to this, although we'll likely go through the same learning curves with this technology that we did with barrier EIFS. The big lesson with EIFS was that low bid contractors with untrained temporary laborers are not the folks to entrust with the well being of your buildings and occupants.

Where I am right now:  Seal the crawlspace at the perimeter. DO NOT spray the underside of the subfloor with foam (which is a highly questionable practice due to code-related combustion issues.) Eliminate vapor retarders in the subfloor assembly (is anyone using Tyvek as flooring underlayment in lieu of building paper?) Dehumidify the crawlspace with a separate expensive dehumifier or by inducing conditioned air to ventilate and exhaust. Monitor the humidity levels in the occupied spaces and the crawlspace, and establish the crawlspace humidity control levels so that all humidity levels are approximately equal, with limited temperature differentials. Do that for a while, and we'll start to know what we're doing and how to solve this problem.

-------------------------------------------
Philip Kabza AIA
Partner and Dir Technical Services
SpecGuy
Charlotte NC
-------------------------------------------






Original Message:
Sent: 03-22-2012 08:18
From: Eric Rawlings
Subject: Let it breathe or seal it tight?

I appreciate your 2 cents. The flooring is pointing up on the edges (concave on top) and I assumed the same thing about the direction of vapor drive. This doesn't explain the floor with closed cell foam over a crawl nor does it explain the high humidity readings in all of the interiors. Typically, wood will want to cup in the opposite direction of the curve of the grain (in section) if exposed to humidity on both sides. These consistent problems are happening to different builders with different subs. Could it be possible that the closed cell foam is trapping the humidity at the bottom side of the flooring, thus making it appear that the vapor is coming in from the crawl? Since the foam is under the subfloor, it's the over the thickness of the plywood that the temperature differential is swinging from hot in the crawl to cold in the house (summer) and the opposite in the winter. Regardless, condensation would want to occur under the flooring on the surface of the plywood. Those grooves in the flooring provide a little space for it to collect. If water vapor and condensation are allowed to collect under the flooring, this may explain the closed cell foamed floor and the direction of cupping. 

I'm a believer in simple is better. The more we complicate our solutions, the more potential for problems we create. I'm still on the fence here when it comes to fanatical tightening of buildings. ERVs are expensive and have a moderate operating cost. Dehumidifiers can be as expensive to run as the entire building in the case of my Example #1. Would that client's house cost more than $100 a month to run if we removed the ERV and Dehumidifier and drilled some holes in his wall and crawl to achieve enough ventilation to keep humidity down to the levels of our "leakier" houses from a few years ago? The argument down in the South is that a leaky house draws moist outside air into the building causing the AC to run all day, just to remove humidity. Our leaky houses aren't the ones with the obnoxiously high humid readings, it's the tight houses. The argument and solution to remove humidity to make AC more efficient actually makes humidity worse and we just spent more money on gadgets to boot. This is the kind of stuff that turns off the skeptic.

If we ventilate the crawl and spray foam the floor, then we have to relocate the mechanical equipment powering the first floor, which costs money in terms of interior sf and how much we can sell the house for. With zoning requirements of an old in-town neighborhood, our floor area is very precious. This scenario may be our next option, but I really hate experimenting on my clients. At what point will an owner get angry enough for litigation for being convinced to spend all this extra money on gadgets and such only to get what they perceive as worse results?

I always tell my clients, especially the spec builders, that a solution to a problem isn't a solution if it creates two more problems to solve and unfortunately many of the "scientific" solutions that are suggested come with many components and complications that could very well open us up to many, many more problems to solve. Here I present the humidity problem and look at how my problems domino from that one issue. For a three or four part solution, how do we know which part of the solution was effective or which one is the next problem generator?

-------------------------------------------
Eric Rawlings AIA
Owner
Rawlings Design, Inc.
Decatur GA
-------------------------------------------






Original Message:
Sent: 03-21-2012 07:05
From: Philip Kabza
Subject: Let it breathe or seal it tight?

It is important to understand which direction the wood flooring cupping is taking: concave, or convex, with respect to the finished side. The cupping will be convex on the more humid side of the wood, which is expanding. I assume the more humid (convex, expanded) side in your case is the side of the flooring facing the crawlspace.

It seems the theoretical solution to the cupping hardwood flooring problem will have to center on establishing the same humidity level on both sides of the flooring material. Accomplishing that over a crawlspace is difficult; the dynamics of water vapor movement through the floor structure aren't easy to grasp. The wood products themselves have varying properties - some laminated, others solid wood. Some flooring products are impregnated, and all will be either factory- or site- finished with materials that may or may not serve as vapor retarders on one side of the wood only. The flooring underlayments may also affect vapor movement, as may the subfloor sheathings. 

I continue to wonder whether installing a separate $1,000 crawlspace dehumidifier (plus the $50 per month) in these sealed houses is really the answer, or whether it would make more sense to induce a modest air change rate throughout the house, using the crawlspace as an exhaust plenum to the exterior. Running a 100 cfm bathroom exhaust fan continuously in a 6000 cu. ft. crawlspace designed to draw conditioned air from the house above gives the crawlspace 1 air change per hour - perhaps enough to start equalizing the humidity between the house and the crawlspace. This of course adds to the overall air conditioning load of the house, but the load can be met by the much more efficient 15 SEER heat pump, and unless you like the smell of two day old cooked broccoli, you do want some fresh make-up air in the house anyway, which can be introduced through the HVAC return air system to allow for the crawlspace exhaust negative air pressure. Just a thought.

The termite observation strip is a possible target for improvement in sealed crawlspaces. I have seen a clear acrylic or polycarbonate sheet used at this location, with the vapor retarder materials sealed to both sides of it. That might help, although the idea that you can completely vapor seal a crawlspace, or a house for that matter, is a bit fanciful.

-------------------------------------------
Philip Kabza AIA
Partner and Dir Technical Services
SpecGuy
Charlotte NC
-------------------------------------------






Original Message:
Sent: 03-20-2012 08:02
From: Eric Rawlings
Subject: Let it breathe or seal it tight?

This message has been cross posted to the following Discussion Forums: Technology in Architectural Practice and Committee on the Environment .
-------------------------------------------

The debate over allowing a house to "breathe" a little or to seal it up as tight as possible has been argued ever since the advent of sick building syndrome. I attend the local Green Conferences every year. I've been very interested in sustainability since my professor introduced it to me in 1990. After listening to the building scientists, the theory of total air sealing with controlled ventilation sounds very logical, especially coming from a Canadian building scientist describing their climate conditions. I do have a problem with relying on a quiet fan of an ERV to not break down and cause the building to get sick. In the South East, we have one of the most difficult environments to build in. The humidity is relentless, the termites and carpenter bees are hungry, and in Atlanta, we have a very intense topography being at the foothills of the North GA mountains. Air sealing is becoming a requirement here and everyone's hardwoods are cupping. The blower door test is now required (or will be) on all residences in the metro area. I have used several different strategies recommended by building scientists for applying the air sealing, insulation, and building configuration to provide better efficiency yet we keep having the same problems.

The "greenest" house I designed has a ground source heat pump (geothermal), tons of insulation, and we sealed the crawlspace with a heavy duty waterproofing membrane that welds together like a TPO roof. This house boasts $50/ month electric bills, until the hardwoods started cupping and the crawl became too humid. Now they have to run a dehumidifier 24/7 that costs $50/ month. All of these houses have ERVs, another piece of equipment wasting energy, just to be "sealed" so we can save energy. The builder is well versed in green design/ installation. We made every precaution recommended, yet you can't keep humidity out of a crawlspace no matter how hard you try to seal it. In this assembly, the one vulnerability I can think of is the required termite check strip at the top of the masonry wall where the wood begins. Our water table is high and so is our frost line, so the earth stays pretty damp. It's possible that the vapor is pushing it's way through that 1" strip.

I have a house on a sealed crawl with closed cell spray foam on the underside of the floor. This cupped the worst. We were warned not to use open cell as it let's the vapor leak through. Maybe the humidity is mostly coming from the inside, not the crawl?

I have another house with a basement instead of a crawl that has the same problems. This basement is conditioned, yet we're trapping the humidity in the house and it simply can't escape. We have tried everything to keep the flooring from cupping. Our solution to our energy efficient air tight construction is to run a dehumidifier 24/7 at $50/ month.

I have a house that is built on a slab on grade. This one has less cupping in the flooring, but you can't build a slab on grade house in most places in Atlanta as our topography is so intense. The advantage is that you're only dealing with moisture coming through the horizontal plane of the floor, not the side walls as well. The average lots have enough slope to make slab on grade too expensive and not enough slope or a low enough water table to do a basement. This why we end up with crawl spaces. Even when built as a perfectly sealed, short basement, they still get moist.

The houses that are built on naturally ventilated crawl spaces with R-30 batts in the floor are staying the driest and have no problems with the floor cupping. They may be a little less efficient, but they aren't relying on ERVs and dehumidifiers to stay comfortable and healthy. What happens when we have the next ice storm and the electric is out for a week? What happens during the next Summer brown out when the electricity is out for a day or two?

My theory is that you can't humidity seal a Southern crawl space, even with the best materials available. This makes crawl spaces and basements a humidity trap/ generator. In each case of blower door approved construction, the overall humidity in the living space is higher than "normal". I think the humidity that we create from breathing, showering, and other activities is being trapped as well. The AC can't remove it all, even when running all day. In the summer, these sealed crawls are much warmer than the interior of the climate controlled house, so this humidity is going to be attracted to the cold side of the surfaces straddling the temperature differential between interior and exterior. In our case, this is the hardwood flooring. Since wood is dry and highly absorbent, you don't see the condensation on the surface. You eventually see it cup. If you're trapping enough humidity, then you're not helping your efficiency. If you need dehumidifiers and ERVs to make your more efficient house air tight and healthy, then what's the difference in letting it breathe enough to not require this energy consuming equipment and worry about quiet fans quitting or power outages? As the brilliant Canadian building scientist put it, "If you have a theoretically perfectly sealed building, then where do you put the holes?" These are the crossroads we're at right now as policy is resulting in problems that will have to be solved. The ever evolving theories of sustainable design. The more complicated we make it, the more problems we have to solve. Too bad our lifestyles keep evolving beyond our means to keep up.

-------------------------------------------
Eric Rawlings AIA
Owner
Rawlings Design, Inc.
Decatur GA
-------------------------------------------

A recent issue of Fine Hombuilding magazine carried the story of the near hermetic sealing of a crawl space of a Southern home. The article included photographs of the crawl space at the beginning of constructioin, and then throughout. The pictures at the start of the article showed a crawl space that appeared to be bone-dry, to the point that it appeared moisture had never been an issue. In fact, the article never mentioned that dampness inside the house or the crawl space was an issue. It was apparently assumed that sealing the space would be better.

Without practical reason, the space was sealed tight with heavy membranes. sealed up all walls and piers to the floor support system, and sealed at all penetrations.

Naturally, we have no idea how the house has changed since this "improvement".

All this, including this forum, causes me to wonder if insulating the floor, but leaving the crawl space open, would be a viable solution. It seems almost politically incorrect to try such a solution.

Our predecessors, who constructed so many residences in the 19th and early 20th centuries did seem to know what they were doing, as far as ventilation is concerned. Now, with the overbearing availablity of electricity, it seems we just keep thinking up ways to justify evem more ways to consume power, that is power to operate fans, monitors, closures, etc.

-------------------------------------------
Charles Graham AIA
Architect
O'Neal, Inc.
Greenville SC
-------------------------------------------






Original Message:
Sent: 03-23-2012 09:29
From: Philip Kabza
Subject: Let it breathe or seal it tight?

Important discussion, as builders throughout the south and southeast are concerned with how to integrate current building science and sustainability with sound construction practice.

We stopped putting vapor retarders in the walls in southeast US warm humid climate buildings a decade ago. We have since concentrated on utilizing carefully installed air barriers that prevent massive moisture movement, while allowing the HVAC system to handle the water vapor diffusion through wall materials. This appears to work - the incidence of moisture and mold issues in building walls has dropped as a result.

It seems we forgot to consider the floors. Sheathings, underlayments, building paper, and some wood finish products are vapor retarders. I believe we need to work with the flooring manufacturers to identify conditions under which their products will work. They are the ones with the most to lose, so perhaps would be interested in contributing to studies that can provide more than anecdotal evidence of the moisture dynamics of wood subfloor assemblies in warm, humid climates.

Anyone who spends much time in a warm, humid climate unlined crawlspace quickly looks for an easier gig. They are dirty, wet, moldy, and bug-ridden places. The "traditional" southern crawlspace house (you know, the one we say "breathes") is slowly self-composting in the crawlspace, so it is not a solution, it is a slow, long term failure, full of occupants loading up on Allegra and bug spray and wondering why.

The lined and sealed crawlspace, with careful details carefully carried out, appears to be a good alternative to this, although we'll likely go through the same learning curves with this technology that we did with barrier EIFS. The big lesson with EIFS was that low bid contractors with untrained temporary laborers are not the folks to entrust with the well being of your buildings and occupants.

Where I am right now:  Seal the crawlspace at the perimeter. DO NOT spray the underside of the subfloor with foam (which is a highly questionable practice due to code-related combustion issues.) Eliminate vapor retarders in the subfloor assembly (is anyone using Tyvek as flooring underlayment in lieu of building paper?) Dehumidify the crawlspace with a separate expensive dehumifier or by inducing conditioned air to ventilate and exhaust. Monitor the humidity levels in the occupied spaces and the crawlspace, and establish the crawlspace humidity control levels so that all humidity levels are approximately equal, with limited temperature differentials. Do that for a while, and we'll start to know what we're doing and how to solve this problem.

-------------------------------------------
Philip Kabza AIA
Partner and Dir Technical Services
SpecGuy
Charlotte NC
-------------------------------------------






Original Message:
Sent: 03-22-2012 08:18
From: Eric Rawlings
Subject: Let it breathe or seal it tight?

I appreciate your 2 cents. The flooring is pointing up on the edges (concave on top) and I assumed the same thing about the direction of vapor drive. This doesn't explain the floor with closed cell foam over a crawl nor does it explain the high humidity readings in all of the interiors. Typically, wood will want to cup in the opposite direction of the curve of the grain (in section) if exposed to humidity on both sides. These consistent problems are happening to different builders with different subs. Could it be possible that the closed cell foam is trapping the humidity at the bottom side of the flooring, thus making it appear that the vapor is coming in from the crawl? Since the foam is under the subfloor, it's the over the thickness of the plywood that the temperature differential is swinging from hot in the crawl to cold in the house (summer) and the opposite in the winter. Regardless, condensation would want to occur under the flooring on the surface of the plywood. Those grooves in the flooring provide a little space for it to collect. If water vapor and condensation are allowed to collect under the flooring, this may explain the closed cell foamed floor and the direction of cupping. 

I'm a believer in simple is better. The more we complicate our solutions, the more potential for problems we create. I'm still on the fence here when it comes to fanatical tightening of buildings. ERVs are expensive and have a moderate operating cost. Dehumidifiers can be as expensive to run as the entire building in the case of my Example #1. Would that client's house cost more than $100 a month to run if we removed the ERV and Dehumidifier and drilled some holes in his wall and crawl to achieve enough ventilation to keep humidity down to the levels of our "leakier" houses from a few years ago? The argument down in the South is that a leaky house draws moist outside air into the building causing the AC to run all day, just to remove humidity. Our leaky houses aren't the ones with the obnoxiously high humid readings, it's the tight houses. The argument and solution to remove humidity to make AC more efficient actually makes humidity worse and we just spent more money on gadgets to boot. This is the kind of stuff that turns off the skeptic.

If we ventilate the crawl and spray foam the floor, then we have to relocate the mechanical equipment powering the first floor, which costs money in terms of interior sf and how much we can sell the house for. With zoning requirements of an old in-town neighborhood, our floor area is very precious. This scenario may be our next option, but I really hate experimenting on my clients. At what point will an owner get angry enough for litigation for being convinced to spend all this extra money on gadgets and such only to get what they perceive as worse results?

I always tell my clients, especially the spec builders, that a solution to a problem isn't a solution if it creates two more problems to solve and unfortunately many of the "scientific" solutions that are suggested come with many components and complications that could very well open us up to many, many more problems to solve. Here I present the humidity problem and look at how my problems domino from that one issue. For a three or four part solution, how do we know which part of the solution was effective or which one is the next problem generator?

-------------------------------------------
Eric Rawlings AIA
Owner
Rawlings Design, Inc.
Decatur GA
-------------------------------------------






Original Message:
Sent: 03-21-2012 07:05
From: Philip Kabza
Subject: Let it breathe or seal it tight?

It is important to understand which direction the wood flooring cupping is taking: concave, or convex, with respect to the finished side. The cupping will be convex on the more humid side of the wood, which is expanding. I assume the more humid (convex, expanded) side in your case is the side of the flooring facing the crawlspace.

It seems the theoretical solution to the cupping hardwood flooring problem will have to center on establishing the same humidity level on both sides of the flooring material. Accomplishing that over a crawlspace is difficult; the dynamics of water vapor movement through the floor structure aren't easy to grasp. The wood products themselves have varying properties - some laminated, others solid wood. Some flooring products are impregnated, and all will be either factory- or site- finished with materials that may or may not serve as vapor retarders on one side of the wood only. The flooring underlayments may also affect vapor movement, as may the subfloor sheathings. 

I continue to wonder whether installing a separate $1,000 crawlspace dehumidifier (plus the $50 per month) in these sealed houses is really the answer, or whether it would make more sense to induce a modest air change rate throughout the house, using the crawlspace as an exhaust plenum to the exterior. Running a 100 cfm bathroom exhaust fan continuously in a 6000 cu. ft. crawlspace designed to draw conditioned air from the house above gives the crawlspace 1 air change per hour - perhaps enough to start equalizing the humidity between the house and the crawlspace. This of course adds to the overall air conditioning load of the house, but the load can be met by the much more efficient 15 SEER heat pump, and unless you like the smell of two day old cooked broccoli, you do want some fresh make-up air in the house anyway, which can be introduced through the HVAC return air system to allow for the crawlspace exhaust negative air pressure. Just a thought.

The termite observation strip is a possible target for improvement in sealed crawlspaces. I have seen a clear acrylic or polycarbonate sheet used at this location, with the vapor retarder materials sealed to both sides of it. That might help, although the idea that you can completely vapor seal a crawlspace, or a house for that matter, is a bit fanciful.

-------------------------------------------
Philip Kabza AIA
Partner and Dir Technical Services
SpecGuy
Charlotte NC
-------------------------------------------






Original Message:
Sent: 03-20-2012 08:02
From: Eric Rawlings
Subject: Let it breathe or seal it tight?

This message has been cross posted to the following Discussion Forums: Technology in Architectural Practice and Committee on the Environment .
-------------------------------------------

The debate over allowing a house to "breathe" a little or to seal it up as tight as possible has been argued ever since the advent of sick building syndrome. I attend the local Green Conferences every year. I've been very interested in sustainability since my professor introduced it to me in 1990. After listening to the building scientists, the theory of total air sealing with controlled ventilation sounds very logical, especially coming from a Canadian building scientist describing their climate conditions. I do have a problem with relying on a quiet fan of an ERV to not break down and cause the building to get sick. In the South East, we have one of the most difficult environments to build in. The humidity is relentless, the termites and carpenter bees are hungry, and in Atlanta, we have a very intense topography being at the foothills of the North GA mountains. Air sealing is becoming a requirement here and everyone's hardwoods are cupping. The blower door test is now required (or will be) on all residences in the metro area. I have used several different strategies recommended by building scientists for applying the air sealing, insulation, and building configuration to provide better efficiency yet we keep having the same problems.

The "greenest" house I designed has a ground source heat pump (geothermal), tons of insulation, and we sealed the crawlspace with a heavy duty waterproofing membrane that welds together like a TPO roof. This house boasts $50/ month electric bills, until the hardwoods started cupping and the crawl became too humid. Now they have to run a dehumidifier 24/7 that costs $50/ month. All of these houses have ERVs, another piece of equipment wasting energy, just to be "sealed" so we can save energy. The builder is well versed in green design/ installation. We made every precaution recommended, yet you can't keep humidity out of a crawlspace no matter how hard you try to seal it. In this assembly, the one vulnerability I can think of is the required termite check strip at the top of the masonry wall where the wood begins. Our water table is high and so is our frost line, so the earth stays pretty damp. It's possible that the vapor is pushing it's way through that 1" strip.

I have a house on a sealed crawl with closed cell spray foam on the underside of the floor. This cupped the worst. We were warned not to use open cell as it let's the vapor leak through. Maybe the humidity is mostly coming from the inside, not the crawl?

I have another house with a basement instead of a crawl that has the same problems. This basement is conditioned, yet we're trapping the humidity in the house and it simply can't escape. We have tried everything to keep the flooring from cupping. Our solution to our energy efficient air tight construction is to run a dehumidifier 24/7 at $50/ month.

I have a house that is built on a slab on grade. This one has less cupping in the flooring, but you can't build a slab on grade house in most places in Atlanta as our topography is so intense. The advantage is that you're only dealing with moisture coming through the horizontal plane of the floor, not the side walls as well. The average lots have enough slope to make slab on grade too expensive and not enough slope or a low enough water table to do a basement. This why we end up with crawl spaces. Even when built as a perfectly sealed, short basement, they still get moist.

The houses that are built on naturally ventilated crawl spaces with R-30 batts in the floor are staying the driest and have no problems with the floor cupping. They may be a little less efficient, but they aren't relying on ERVs and dehumidifiers to stay comfortable and healthy. What happens when we have the next ice storm and the electric is out for a week? What happens during the next Summer brown out when the electricity is out for a day or two?

My theory is that you can't humidity seal a Southern crawl space, even with the best materials available. This makes crawl spaces and basements a humidity trap/ generator. In each case of blower door approved construction, the overall humidity in the living space is higher than "normal". I think the humidity that we create from breathing, showering, and other activities is being trapped as well. The AC can't remove it all, even when running all day. In the summer, these sealed crawls are much warmer than the interior of the climate controlled house, so this humidity is going to be attracted to the cold side of the surfaces straddling the temperature differential between interior and exterior. In our case, this is the hardwood flooring. Since wood is dry and highly absorbent, you don't see the condensation on the surface. You eventually see it cup. If you're trapping enough humidity, then you're not helping your efficiency. If you need dehumidifiers and ERVs to make your more efficient house air tight and healthy, then what's the difference in letting it breathe enough to not require this energy consuming equipment and worry about quiet fans quitting or power outages? As the brilliant Canadian building scientist put it, "If you have a theoretically perfectly sealed building, then where do you put the holes?" These are the crossroads we're at right now as policy is resulting in problems that will have to be solved. The ever evolving theories of sustainable design. The more complicated we make it, the more problems we have to solve. Too bad our lifestyles keep evolving beyond our means to keep up.

-------------------------------------------
Eric Rawlings AIA
Owner
Rawlings Design, Inc.
Decatur GA
-------------------------------------------

Mr. Graham does a good job of reminding us to maintain some professional objectivity and cynicism toward "the latest and greatest" solution to problems we may or may not have. I'm reminded though that our precursors were not necessarily wiser than us; they did the best they could with what they had. I've pulled apart enough rotting 100 year old construction to know that sometimes they were right, and sometimes they weren't. They lived in very simple drafty or uncomfortably hot structures without air conditioning, electricity, or plumbing, and certainly without copolymer air and vapor barriers and prefinished wood floors. They also probably didn't understand that you can't see water vapor in a photograph - once photographs came along - nor understand the increased load that crawlspace-sourced water vapor places on air conditioning systems.

Building scientist Joe Lstiburek is one of the few who has put together a rational case for the crawlspace sealing application, based upon metering of building performance factors; more information is located here:  www.buildingscience.com/resources/cond-crawlspaces 
 
In a way, we're stuck with increasing complexity in our buildings, at least until we enter the Long Emergency predicted by James Kunstler, at which point things will become simple again quickly, if not easily.

-------------------------------------------
Philip Kabza AIA
Partner and Dir Technical Services
SpecGuy
Charlotte NC
-------------------------------------------






Original Message:
Sent: 03-26-2012 19:43
From: Charles Graham
Subject: Let it breathe or seal it tight?

A recent issue of Fine Hombuilding magazine carried the story of the near hermetic sealing of a crawl space of a Southern home. The article included photographs of the crawl space at the beginning of constructioin, and then throughout. The pictures at the start of the article showed a crawl space that appeared to be bone-dry, to the point that it appeared moisture had never been an issue. In fact, the article never mentioned that dampness inside the house or the crawl space was an issue. It was apparently assumed that sealing the space would be better.

Without practical reason, the space was sealed tight with heavy membranes. sealed up all walls and piers to the floor support system, and sealed at all penetrations.

Naturally, we have no idea how the house has changed since this "improvement".

All this, including this forum, causes me to wonder if insulating the floor, but leaving the crawl space open, would be a viable solution. It seems almost politically incorrect to try such a solution.

Our predecessors, who constructed so many residences in the 19th and early 20th centuries did seem to know what they were doing, as far as ventilation is concerned. Now, with the overbearing availablity of electricity, it seems we just keep thinking up ways to justify evem more ways to consume power, that is power to operate fans, monitors, closures, etc.

-------------------------------------------
Charles Graham AIA
Architect
O'Neal, Inc.
Greenville SC
-------------------------------------------






Original Message:
Sent: 03-23-2012 09:29
From: Philip Kabza
Subject: Let it breathe or seal it tight?

Important discussion, as builders throughout the south and southeast are concerned with how to integrate current building science and sustainability with sound construction practice.

We stopped putting vapor retarders in the walls in southeast US warm humid climate buildings a decade ago. We have since concentrated on utilizing carefully installed air barriers that prevent massive moisture movement, while allowing the HVAC system to handle the water vapor diffusion through wall materials. This appears to work - the incidence of moisture and mold issues in building walls has dropped as a result.

It seems we forgot to consider the floors. Sheathings, underlayments, building paper, and some wood finish products are vapor retarders. I believe we need to work with the flooring manufacturers to identify conditions under which their products will work. They are the ones with the most to lose, so perhaps would be interested in contributing to studies that can provide more than anecdotal evidence of the moisture dynamics of wood subfloor assemblies in warm, humid climates.

Anyone who spends much time in a warm, humid climate unlined crawlspace quickly looks for an easier gig. They are dirty, wet, moldy, and bug-ridden places. The "traditional" southern crawlspace house (you know, the one we say "breathes") is slowly self-composting in the crawlspace, so it is not a solution, it is a slow, long term failure, full of occupants loading up on Allegra and bug spray and wondering why.

The lined and sealed crawlspace, with careful details carefully carried out, appears to be a good alternative to this, although we'll likely go through the same learning curves with this technology that we did with barrier EIFS. The big lesson with EIFS was that low bid contractors with untrained temporary laborers are not the folks to entrust with the well being of your buildings and occupants.

Where I am right now:  Seal the crawlspace at the perimeter. DO NOT spray the underside of the subfloor with foam (which is a highly questionable practice due to code-related combustion issues.) Eliminate vapor retarders in the subfloor assembly (is anyone using Tyvek as flooring underlayment in lieu of building paper?) Dehumidify the crawlspace with a separate expensive dehumifier or by inducing conditioned air to ventilate and exhaust. Monitor the humidity levels in the occupied spaces and the crawlspace, and establish the crawlspace humidity control levels so that all humidity levels are approximately equal, with limited temperature differentials. Do that for a while, and we'll start to know what we're doing and how to solve this problem.

-------------------------------------------
Philip Kabza AIA
Partner and Dir Technical Services
SpecGuy
Charlotte NC
-------------------------------------------






Original Message:
Sent: 03-22-2012 08:18
From: Eric Rawlings
Subject: Let it breathe or seal it tight?

I appreciate your 2 cents. The flooring is pointing up on the edges (concave on top) and I assumed the same thing about the direction of vapor drive. This doesn't explain the floor with closed cell foam over a crawl nor does it explain the high humidity readings in all of the interiors. Typically, wood will want to cup in the opposite direction of the curve of the grain (in section) if exposed to humidity on both sides. These consistent problems are happening to different builders with different subs. Could it be possible that the closed cell foam is trapping the humidity at the bottom side of the flooring, thus making it appear that the vapor is coming in from the crawl? Since the foam is under the subfloor, it's the over the thickness of the plywood that the temperature differential is swinging from hot in the crawl to cold in the house (summer) and the opposite in the winter. Regardless, condensation would want to occur under the flooring on the surface of the plywood. Those grooves in the flooring provide a little space for it to collect. If water vapor and condensation are allowed to collect under the flooring, this may explain the closed cell foamed floor and the direction of cupping. 

I'm a believer in simple is better. The more we complicate our solutions, the more potential for problems we create. I'm still on the fence here when it comes to fanatical tightening of buildings. ERVs are expensive and have a moderate operating cost. Dehumidifiers can be as expensive to run as the entire building in the case of my Example #1. Would that client's house cost more than $100 a month to run if we removed the ERV and Dehumidifier and drilled some holes in his wall and crawl to achieve enough ventilation to keep humidity down to the levels of our "leakier" houses from a few years ago? The argument down in the South is that a leaky house draws moist outside air into the building causing the AC to run all day, just to remove humidity. Our leaky houses aren't the ones with the obnoxiously high humid readings, it's the tight houses. The argument and solution to remove humidity to make AC more efficient actually makes humidity worse and we just spent more money on gadgets to boot. This is the kind of stuff that turns off the skeptic.

If we ventilate the crawl and spray foam the floor, then we have to relocate the mechanical equipment powering the first floor, which costs money in terms of interior sf and how much we can sell the house for. With zoning requirements of an old in-town neighborhood, our floor area is very precious. This scenario may be our next option, but I really hate experimenting on my clients. At what point will an owner get angry enough for litigation for being convinced to spend all this extra money on gadgets and such only to get what they perceive as worse results?

I always tell my clients, especially the spec builders, that a solution to a problem isn't a solution if it creates two more problems to solve and unfortunately many of the "scientific" solutions that are suggested come with many components and complications that could very well open us up to many, many more problems to solve. Here I present the humidity problem and look at how my problems domino from that one issue. For a three or four part solution, how do we know which part of the solution was effective or which one is the next problem generator?

-------------------------------------------
Eric Rawlings AIA
Owner
Rawlings Design, Inc.
Decatur GA
-------------------------------------------






Original Message:
Sent: 03-21-2012 07:05
From: Philip Kabza
Subject: Let it breathe or seal it tight?

It is important to understand which direction the wood flooring cupping is taking: concave, or convex, with respect to the finished side. The cupping will be convex on the more humid side of the wood, which is expanding. I assume the more humid (convex, expanded) side in your case is the side of the flooring facing the crawlspace.

It seems the theoretical solution to the cupping hardwood flooring problem will have to center on establishing the same humidity level on both sides of the flooring material. Accomplishing that over a crawlspace is difficult; the dynamics of water vapor movement through the floor structure aren't easy to grasp. The wood products themselves have varying properties - some laminated, others solid wood. Some flooring products are impregnated, and all will be either factory- or site- finished with materials that may or may not serve as vapor retarders on one side of the wood only. The flooring underlayments may also affect vapor movement, as may the subfloor sheathings. 

I continue to wonder whether installing a separate $1,000 crawlspace dehumidifier (plus the $50 per month) in these sealed houses is really the answer, or whether it would make more sense to induce a modest air change rate throughout the house, using the crawlspace as an exhaust plenum to the exterior. Running a 100 cfm bathroom exhaust fan continuously in a 6000 cu. ft. crawlspace designed to draw conditioned air from the house above gives the crawlspace 1 air change per hour - perhaps enough to start equalizing the humidity between the house and the crawlspace. This of course adds to the overall air conditioning load of the house, but the load can be met by the much more efficient 15 SEER heat pump, and unless you like the smell of two day old cooked broccoli, you do want some fresh make-up air in the house anyway, which can be introduced through the HVAC return air system to allow for the crawlspace exhaust negative air pressure. Just a thought.

The termite observation strip is a possible target for improvement in sealed crawlspaces. I have seen a clear acrylic or polycarbonate sheet used at this location, with the vapor retarder materials sealed to both sides of it. That might help, although the idea that you can completely vapor seal a crawlspace, or a house for that matter, is a bit fanciful.

-------------------------------------------
Philip Kabza AIA
Partner and Dir Technical Services
SpecGuy
Charlotte NC
-------------------------------------------






Original Message:
Sent: 03-20-2012 08:02
From: Eric Rawlings
Subject: Let it breathe or seal it tight?

This message has been cross posted to the following Discussion Forums: Technology in Architectural Practice and Committee on the Environment .
-------------------------------------------

The debate over allowing a house to "breathe" a little or to seal it up as tight as possible has been argued ever since the advent of sick building syndrome. I attend the local Green Conferences every year. I've been very interested in sustainability since my professor introduced it to me in 1990. After listening to the building scientists, the theory of total air sealing with controlled ventilation sounds very logical, especially coming from a Canadian building scientist describing their climate conditions. I do have a problem with relying on a quiet fan of an ERV to not break down and cause the building to get sick. In the South East, we have one of the most difficult environments to build in. The humidity is relentless, the termites and carpenter bees are hungry, and in Atlanta, we have a very intense topography being at the foothills of the North GA mountains. Air sealing is becoming a requirement here and everyone's hardwoods are cupping. The blower door test is now required (or will be) on all residences in the metro area. I have used several different strategies recommended by building scientists for applying the air sealing, insulation, and building configuration to provide better efficiency yet we keep having the same problems.

The "greenest" house I designed has a ground source heat pump (geothermal), tons of insulation, and we sealed the crawlspace with a heavy duty waterproofing membrane that welds together like a TPO roof. This house boasts $50/ month electric bills, until the hardwoods started cupping and the crawl became too humid. Now they have to run a dehumidifier 24/7 that costs $50/ month. All of these houses have ERVs, another piece of equipment wasting energy, just to be "sealed" so we can save energy. The builder is well versed in green design/ installation. We made every precaution recommended, yet you can't keep humidity out of a crawlspace no matter how hard you try to seal it. In this assembly, the one vulnerability I can think of is the required termite check strip at the top of the masonry wall where the wood begins. Our water table is high and so is our frost line, so the earth stays pretty damp. It's possible that the vapor is pushing it's way through that 1" strip.

I have a house on a sealed crawl with closed cell spray foam on the underside of the floor. This cupped the worst. We were warned not to use open cell as it let's the vapor leak through. Maybe the humidity is mostly coming from the inside, not the crawl?

I have another house with a basement instead of a crawl that has the same problems. This basement is conditioned, yet we're trapping the humidity in the house and it simply can't escape. We have tried everything to keep the flooring from cupping. Our solution to our energy efficient air tight construction is to run a dehumidifier 24/7 at $50/ month.

I have a house that is built on a slab on grade. This one has less cupping in the flooring, but you can't build a slab on grade house in most places in Atlanta as our topography is so intense. The advantage is that you're only dealing with moisture coming through the horizontal plane of the floor, not the side walls as well. The average lots have enough slope to make slab on grade too expensive and not enough slope or a low enough water table to do a basement. This why we end up with crawl spaces. Even when built as a perfectly sealed, short basement, they still get moist.

The houses that are built on naturally ventilated crawl spaces with R-30 batts in the floor are staying the driest and have no problems with the floor cupping. They may be a little less efficient, but they aren't relying on ERVs and dehumidifiers to stay comfortable and healthy. What happens when we have the next ice storm and the electric is out for a week? What happens during the next Summer brown out when the electricity is out for a day or two?

My theory is that you can't humidity seal a Southern crawl space, even with the best materials available. This makes crawl spaces and basements a humidity trap/ generator. In each case of blower door approved construction, the overall humidity in the living space is higher than "normal". I think the humidity that we create from breathing, showering, and other activities is being trapped as well. The AC can't remove it all, even when running all day. In the summer, these sealed crawls are much warmer than the interior of the climate controlled house, so this humidity is going to be attracted to the cold side of the surfaces straddling the temperature differential between interior and exterior. In our case, this is the hardwood flooring. Since wood is dry and highly absorbent, you don't see the condensation on the surface. You eventually see it cup. If you're trapping enough humidity, then you're not helping your efficiency. If you need dehumidifiers and ERVs to make your more efficient house air tight and healthy, then what's the difference in letting it breathe enough to not require this energy consuming equipment and worry about quiet fans quitting or power outages? As the brilliant Canadian building scientist put it, "If you have a theoretically perfectly sealed building, then where do you put the holes?" These are the crossroads we're at right now as policy is resulting in problems that will have to be solved. The ever evolving theories of sustainable design. The more complicated we make it, the more problems we have to solve. Too bad our lifestyles keep evolving beyond our means to keep up.

-------------------------------------------
Eric Rawlings AIA
Owner
Rawlings Design, Inc.
Decatur GA
-------------------------------------------

here in california, we have had to deal with the provisions of the state of california title 24 energy code for last 25 years or so.  one requirement has been to reduce air infiltration through the exterior envelope.  the result has been increased energy savings.  the downside is that mold is a more common occurrence...typically related to the lifestyle of the occupants.  i think in some instances an overall reduction in air quality has also occurred.  both of which are directly related to the building's inability to "breathe"...


-------------------------------------------
Stephen Angelo AIA
Architect
Offices of Stephen Michael Angelo, Architect AIA
Livermore CA
-------------------------------------------






Original Message:
Sent: 03-27-2012 07:41
From: Philip Kabza
Subject: Let it breathe or seal it tight?

Mr. Graham does a good job of reminding us to maintain some professional objectivity and cynicism toward "the latest and greatest" solution to problems we may or may not have. I'm reminded though that our precursors were not necessarily wiser than us; they did the best they could with what they had. I've pulled apart enough rotting 100 year old construction to know that sometimes they were right, and sometimes they weren't. They lived in very simple drafty or uncomfortably hot structures without air conditioning, electricity, or plumbing, and certainly without copolymer air and vapor barriers and prefinished wood floors. They also probably didn't understand that you can't see water vapor in a photograph - once photographs came along - nor understand the increased load that crawlspace-sourced water vapor places on air conditioning systems.

Building scientist Joe Lstiburek is one of the few who has put together a rational case for the crawlspace sealing application, based upon metering of building performance factors; more information is located here:  www.buildingscience.com/resources/cond-crawlspaces 
 
In a way, we're stuck with increasing complexity in our buildings, at least until we enter the Long Emergency predicted by James Kunstler, at which point things will become simple again quickly, if not easily.

-------------------------------------------
Philip Kabza AIA
Partner and Dir Technical Services
SpecGuy
Charlotte NC
-------------------------------------------






Original Message:
Sent: 03-26-2012 19:43
From: Charles Graham
Subject: Let it breathe or seal it tight?

A recent issue of Fine Hombuilding magazine carried the story of the near hermetic sealing of a crawl space of a Southern home. The article included photographs of the crawl space at the beginning of constructioin, and then throughout. The pictures at the start of the article showed a crawl space that appeared to be bone-dry, to the point that it appeared moisture had never been an issue. In fact, the article never mentioned that dampness inside the house or the crawl space was an issue. It was apparently assumed that sealing the space would be better.

Without practical reason, the space was sealed tight with heavy membranes. sealed up all walls and piers to the floor support system, and sealed at all penetrations.

Naturally, we have no idea how the house has changed since this "improvement".

All this, including this forum, causes me to wonder if insulating the floor, but leaving the crawl space open, would be a viable solution. It seems almost politically incorrect to try such a solution.

Our predecessors, who constructed so many residences in the 19th and early 20th centuries did seem to know what they were doing, as far as ventilation is concerned. Now, with the overbearing availablity of electricity, it seems we just keep thinking up ways to justify evem more ways to consume power, that is power to operate fans, monitors, closures, etc.

-------------------------------------------
Charles Graham AIA
Architect
O'Neal, Inc.
Greenville SC
-------------------------------------------






Original Message:
Sent: 03-23-2012 09:29
From: Philip Kabza
Subject: Let it breathe or seal it tight?

Important discussion, as builders throughout the south and southeast are concerned with how to integrate current building science and sustainability with sound construction practice.

We stopped putting vapor retarders in the walls in southeast US warm humid climate buildings a decade ago. We have since concentrated on utilizing carefully installed air barriers that prevent massive moisture movement, while allowing the HVAC system to handle the water vapor diffusion through wall materials. This appears to work - the incidence of moisture and mold issues in building walls has dropped as a result.

It seems we forgot to consider the floors. Sheathings, underlayments, building paper, and some wood finish products are vapor retarders. I believe we need to work with the flooring manufacturers to identify conditions under which their products will work. They are the ones with the most to lose, so perhaps would be interested in contributing to studies that can provide more than anecdotal evidence of the moisture dynamics of wood subfloor assemblies in warm, humid climates.

Anyone who spends much time in a warm, humid climate unlined crawlspace quickly looks for an easier gig. They are dirty, wet, moldy, and bug-ridden places. The "traditional" southern crawlspace house (you know, the one we say "breathes") is slowly self-composting in the crawlspace, so it is not a solution, it is a slow, long term failure, full of occupants loading up on Allegra and bug spray and wondering why.

The lined and sealed crawlspace, with careful details carefully carried out, appears to be a good alternative to this, although we'll likely go through the same learning curves with this technology that we did with barrier EIFS. The big lesson with EIFS was that low bid contractors with untrained temporary laborers are not the folks to entrust with the well being of your buildings and occupants.

Where I am right now:  Seal the crawlspace at the perimeter. DO NOT spray the underside of the subfloor with foam (which is a highly questionable practice due to code-related combustion issues.) Eliminate vapor retarders in the subfloor assembly (is anyone using Tyvek as flooring underlayment in lieu of building paper?) Dehumidify the crawlspace with a separate expensive dehumifier or by inducing conditioned air to ventilate and exhaust. Monitor the humidity levels in the occupied spaces and the crawlspace, and establish the crawlspace humidity control levels so that all humidity levels are approximately equal, with limited temperature differentials. Do that for a while, and we'll start to know what we're doing and how to solve this problem.

-------------------------------------------
Philip Kabza AIA
Partner and Dir Technical Services
SpecGuy
Charlotte NC
-------------------------------------------






Original Message:
Sent: 03-22-2012 08:18
From: Eric Rawlings
Subject: Let it breathe or seal it tight?

I appreciate your 2 cents. The flooring is pointing up on the edges (concave on top) and I assumed the same thing about the direction of vapor drive. This doesn't explain the floor with closed cell foam over a crawl nor does it explain the high humidity readings in all of the interiors. Typically, wood will want to cup in the opposite direction of the curve of the grain (in section) if exposed to humidity on both sides. These consistent problems are happening to different builders with different subs. Could it be possible that the closed cell foam is trapping the humidity at the bottom side of the flooring, thus making it appear that the vapor is coming in from the crawl? Since the foam is under the subfloor, it's the over the thickness of the plywood that the temperature differential is swinging from hot in the crawl to cold in the house (summer) and the opposite in the winter. Regardless, condensation would want to occur under the flooring on the surface of the plywood. Those grooves in the flooring provide a little space for it to collect. If water vapor and condensation are allowed to collect under the flooring, this may explain the closed cell foamed floor and the direction of cupping. 

I'm a believer in simple is better. The more we complicate our solutions, the more potential for problems we create. I'm still on the fence here when it comes to fanatical tightening of buildings. ERVs are expensive and have a moderate operating cost. Dehumidifiers can be as expensive to run as the entire building in the case of my Example #1. Would that client's house cost more than $100 a month to run if we removed the ERV and Dehumidifier and drilled some holes in his wall and crawl to achieve enough ventilation to keep humidity down to the levels of our "leakier" houses from a few years ago? The argument down in the South is that a leaky house draws moist outside air into the building causing the AC to run all day, just to remove humidity. Our leaky houses aren't the ones with the obnoxiously high humid readings, it's the tight houses. The argument and solution to remove humidity to make AC more efficient actually makes humidity worse and we just spent more money on gadgets to boot. This is the kind of stuff that turns off the skeptic.

If we ventilate the crawl and spray foam the floor, then we have to relocate the mechanical equipment powering the first floor, which costs money in terms of interior sf and how much we can sell the house for. With zoning requirements of an old in-town neighborhood, our floor area is very precious. This scenario may be our next option, but I really hate experimenting on my clients. At what point will an owner get angry enough for litigation for being convinced to spend all this extra money on gadgets and such only to get what they perceive as worse results?

I always tell my clients, especially the spec builders, that a solution to a problem isn't a solution if it creates two more problems to solve and unfortunately many of the "scientific" solutions that are suggested come with many components and complications that could very well open us up to many, many more problems to solve. Here I present the humidity problem and look at how my problems domino from that one issue. For a three or four part solution, how do we know which part of the solution was effective or which one is the next problem generator?

-------------------------------------------
Eric Rawlings AIA
Owner
Rawlings Design, Inc.
Decatur GA
-------------------------------------------






Original Message:
Sent: 03-21-2012 07:05
From: Philip Kabza
Subject: Let it breathe or seal it tight?

It is important to understand which direction the wood flooring cupping is taking: concave, or convex, with respect to the finished side. The cupping will be convex on the more humid side of the wood, which is expanding. I assume the more humid (convex, expanded) side in your case is the side of the flooring facing the crawlspace.

It seems the theoretical solution to the cupping hardwood flooring problem will have to center on establishing the same humidity level on both sides of the flooring material. Accomplishing that over a crawlspace is difficult; the dynamics of water vapor movement through the floor structure aren't easy to grasp. The wood products themselves have varying properties - some laminated, others solid wood. Some flooring products are impregnated, and all will be either factory- or site- finished with materials that may or may not serve as vapor retarders on one side of the wood only. The flooring underlayments may also affect vapor movement, as may the subfloor sheathings. 

I continue to wonder whether installing a separate $1,000 crawlspace dehumidifier (plus the $50 per month) in these sealed houses is really the answer, or whether it would make more sense to induce a modest air change rate throughout the house, using the crawlspace as an exhaust plenum to the exterior. Running a 100 cfm bathroom exhaust fan continuously in a 6000 cu. ft. crawlspace designed to draw conditioned air from the house above gives the crawlspace 1 air change per hour - perhaps enough to start equalizing the humidity between the house and the crawlspace. This of course adds to the overall air conditioning load of the house, but the load can be met by the much more efficient 15 SEER heat pump, and unless you like the smell of two day old cooked broccoli, you do want some fresh make-up air in the house anyway, which can be introduced through the HVAC return air system to allow for the crawlspace exhaust negative air pressure. Just a thought.

The termite observation strip is a possible target for improvement in sealed crawlspaces. I have seen a clear acrylic or polycarbonate sheet used at this location, with the vapor retarder materials sealed to both sides of it. That might help, although the idea that you can completely vapor seal a crawlspace, or a house for that matter, is a bit fanciful.

-------------------------------------------
Philip Kabza AIA
Partner and Dir Technical Services
SpecGuy
Charlotte NC
-------------------------------------------






Original Message:
Sent: 03-20-2012 08:02
From: Eric Rawlings
Subject: Let it breathe or seal it tight?

This message has been cross posted to the following Discussion Forums: Technology in Architectural Practice and Committee on the Environment .
-------------------------------------------

The debate over allowing a house to "breathe" a little or to seal it up as tight as possible has been argued ever since the advent of sick building syndrome. I attend the local Green Conferences every year. I've been very interested in sustainability since my professor introduced it to me in 1990. After listening to the building scientists, the theory of total air sealing with controlled ventilation sounds very logical, especially coming from a Canadian building scientist describing their climate conditions. I do have a problem with relying on a quiet fan of an ERV to not break down and cause the building to get sick. In the South East, we have one of the most difficult environments to build in. The humidity is relentless, the termites and carpenter bees are hungry, and in Atlanta, we have a very intense topography being at the foothills of the North GA mountains. Air sealing is becoming a requirement here and everyone's hardwoods are cupping. The blower door test is now required (or will be) on all residences in the metro area. I have used several different strategies recommended by building scientists for applying the air sealing, insulation, and building configuration to provide better efficiency yet we keep having the same problems.

The "greenest" house I designed has a ground source heat pump (geothermal), tons of insulation, and we sealed the crawlspace with a heavy duty waterproofing membrane that welds together like a TPO roof. This house boasts $50/ month electric bills, until the hardwoods started cupping and the crawl became too humid. Now they have to run a dehumidifier 24/7 that costs $50/ month. All of these houses have ERVs, another piece of equipment wasting energy, just to be "sealed" so we can save energy. The builder is well versed in green design/ installation. We made every precaution recommended, yet you can't keep humidity out of a crawlspace no matter how hard you try to seal it. In this assembly, the one vulnerability I can think of is the required termite check strip at the top of the masonry wall where the wood begins. Our water table is high and so is our frost line, so the earth stays pretty damp. It's possible that the vapor is pushing it's way through that 1" strip.

I have a house on a sealed crawl with closed cell spray foam on the underside of the floor. This cupped the worst. We were warned not to use open cell as it let's the vapor leak through. Maybe the humidity is mostly coming from the inside, not the crawl?

I have another house with a basement instead of a crawl that has the same problems. This basement is conditioned, yet we're trapping the humidity in the house and it simply can't escape. We have tried everything to keep the flooring from cupping. Our solution to our energy efficient air tight construction is to run a dehumidifier 24/7 at $50/ month.

I have a house that is built on a slab on grade. This one has less cupping in the flooring, but you can't build a slab on grade house in most places in Atlanta as our topography is so intense. The advantage is that you're only dealing with moisture coming through the horizontal plane of the floor, not the side walls as well. The average lots have enough slope to make slab on grade too expensive and not enough slope or a low enough water table to do a basement. This why we end up with crawl spaces. Even when built as a perfectly sealed, short basement, they still get moist.

The houses that are built on naturally ventilated crawl spaces with R-30 batts in the floor are staying the driest and have no problems with the floor cupping. They may be a little less efficient, but they aren't relying on ERVs and dehumidifiers to stay comfortable and healthy. What happens when we have the next ice storm and the electric is out for a week? What happens during the next Summer brown out when the electricity is out for a day or two?

My theory is that you can't humidity seal a Southern crawl space, even with the best materials available. This makes crawl spaces and basements a humidity trap/ generator. In each case of blower door approved construction, the overall humidity in the living space is higher than "normal". I think the humidity that we create from breathing, showering, and other activities is being trapped as well. The AC can't remove it all, even when running all day. In the summer, these sealed crawls are much warmer than the interior of the climate controlled house, so this humidity is going to be attracted to the cold side of the surfaces straddling the temperature differential between interior and exterior. In our case, this is the hardwood flooring. Since wood is dry and highly absorbent, you don't see the condensation on the surface. You eventually see it cup. If you're trapping enough humidity, then you're not helping your efficiency. If you need dehumidifiers and ERVs to make your more efficient house air tight and healthy, then what's the difference in letting it breathe enough to not require this energy consuming equipment and worry about quiet fans quitting or power outages? As the brilliant Canadian building scientist put it, "If you have a theoretically perfectly sealed building, then where do you put the holes?" These are the crossroads we're at right now as policy is resulting in problems that will have to be solved. The ever evolving theories of sustainable design. The more complicated we make it, the more problems we have to solve. Too bad our lifestyles keep evolving beyond our means to keep up.

-------------------------------------------
Eric Rawlings AIA
Owner
Rawlings Design, Inc.
Decatur GA
-------------------------------------------

I've been out of the energy-efficient home design work for many years but 25-35 years ago I designed and consulted on hundreds of them in Alabama. As I read the comments below discussing high moisture levels in tight houses in the South, I wonder how the AC units were sized in comparison to the weather conditions under which the moisture problems show up. When I was working on passive solar, energy efficient houses during the 70's and 80's in Alabama, I saw so many oversized AC systems in tight, energy efficient houses that short-cycling AC units were my first place to look when the living spaces had high moisture levels.

Mechanical subcontractors always wanted to sell extra tonnage in big units and didn't believe that a house could require as little cooling as a tight house did. When the units were oversized, they'd drop the inside air temperature so fast to satisfy the thermostat that the coils didn't have time to remove any substantial moisture before the unit shut off. The moisture that had condensed on the oversized coils would sit there without ever forming droplets big enough to drain off. Then, when the unit came on again later, the fan evaporated the moisture that was still on the coils back into the house air before the coil temperature dropped enough to start dehumidifying again and the system proceeded to again rapidly cool the air without ever sufficiently dehumidifying it. With the older AC systems this would happen to varying degrees depending on the combination of indoor moisture generation, outdoor moisture levels, wind, infiltration, and thermal gain.

I came to the conclusion then that the only ways to solve the problem throughout the seasons and during the common Alabama warm rainstorms would be to use multiple units set to come on in stages as the temperatures and humidities changed or to design new systems that would have some combination of variable cooling capacity, variable fan speed configurations, and/or a fan delay strategy with proper computer controls. Are those or better AC solutions being used in any of these air conditioned houses with indoor moisture problems in the South?

Also, what is the logic behind sealing a crawl space at the subfloor with foam and not putting the barrier on the ground and on the exterior walls where the moisture is coming in? We typically sealed the crawlspaces at the dirt and at the exterior walls (which we also insulated with closed cell foam) and they stayed both dry and close to the indoor temperatures. Metal termite shields at the sill plates kept the bugs out and didn't create enough of a thermal break to cause any problems. No flooring problems were ever reported to me.

-------------------------------------------
James Terry AIA
Evan Terry Associates, PC
Birmingham AL
-------------------------------------------                                                                               





Original Message:
Sent: 03-28-2012 10:49
From: Stephen Angelo
Subject: Let it breathe or seal it tight?

here in california, we have had to deal with the provisions of the state of california title 24 energy code for last 25 years or so.  one requirement has been to reduce air infiltration through the exterior envelope.  the result has been increased energy savings.  the downside is that mold is a more common occurrence...typically related to the lifestyle of the occupants.  i think in some instances an overall reduction in air quality has also occurred.  both of which are directly related to the building's inability to "breathe"...


-------------------------------------------
Stephen Angelo AIA
Architect
Offices of Stephen Michael Angelo, Architect AIA
Livermore CA
-------------------------------------------






Original Message:
Sent: 03-27-2012 07:41
From: Philip Kabza
Subject: Let it breathe or seal it tight?

Mr. Graham does a good job of reminding us to maintain some professional objectivity and cynicism toward "the latest and greatest" solution to problems we may or may not have. I'm reminded though that our precursors were not necessarily wiser than us; they did the best they could with what they had. I've pulled apart enough rotting 100 year old construction to know that sometimes they were right, and sometimes they weren't. They lived in very simple drafty or uncomfortably hot structures without air conditioning, electricity, or plumbing, and certainly without copolymer air and vapor barriers and prefinished wood floors. They also probably didn't understand that you can't see water vapor in a photograph - once photographs came along - nor understand the increased load that crawlspace-sourced water vapor places on air conditioning systems.

Building scientist Joe Lstiburek is one of the few who has put together a rational case for the crawlspace sealing application, based upon metering of building performance factors; more information is located here:  www.buildingscience.com/resources/cond-crawlspaces 
 
In a way, we're stuck with increasing complexity in our buildings, at least until we enter the Long Emergency predicted by James Kunstler, at which point things will become simple again quickly, if not easily.

-------------------------------------------
Philip Kabza AIA
Partner and Dir Technical Services
SpecGuy
Charlotte NC
-------------------------------------------






Original Message:
Sent: 03-26-2012 19:43
From: Charles Graham
Subject: Let it breathe or seal it tight?

A recent issue of Fine Hombuilding magazine carried the story of the near hermetic sealing of a crawl space of a Southern home. The article included photographs of the crawl space at the beginning of constructioin, and then throughout. The pictures at the start of the article showed a crawl space that appeared to be bone-dry, to the point that it appeared moisture had never been an issue. In fact, the article never mentioned that dampness inside the house or the crawl space was an issue. It was apparently assumed that sealing the space would be better.

Without practical reason, the space was sealed tight with heavy membranes. sealed up all walls and piers to the floor support system, and sealed at all penetrations.

Naturally, we have no idea how the house has changed since this "improvement".

All this, including this forum, causes me to wonder if insulating the floor, but leaving the crawl space open, would be a viable solution. It seems almost politically incorrect to try such a solution.

Our predecessors, who constructed so many residences in the 19th and early 20th centuries did seem to know what they were doing, as far as ventilation is concerned. Now, with the overbearing availablity of electricity, it seems we just keep thinking up ways to justify evem more ways to consume power, that is power to operate fans, monitors, closures, etc.

-------------------------------------------
Charles Graham AIA
Architect
O'Neal, Inc.
Greenville SC
-------------------------------------------






Original Message:
Sent: 03-23-2012 09:29
From: Philip Kabza
Subject: Let it breathe or seal it tight?

Important discussion, as builders throughout the south and southeast are concerned with how to integrate current building science and sustainability with sound construction practice.

We stopped putting vapor retarders in the walls in southeast US warm humid climate buildings a decade ago. We have since concentrated on utilizing carefully installed air barriers that prevent massive moisture movement, while allowing the HVAC system to handle the water vapor diffusion through wall materials. This appears to work - the incidence of moisture and mold issues in building walls has dropped as a result.

It seems we forgot to consider the floors. Sheathings, underlayments, building paper, and some wood finish products are vapor retarders. I believe we need to work with the flooring manufacturers to identify conditions under which their products will work. They are the ones with the most to lose, so perhaps would be interested in contributing to studies that can provide more than anecdotal evidence of the moisture dynamics of wood subfloor assemblies in warm, humid climates.

Anyone who spends much time in a warm, humid climate unlined crawlspace quickly looks for an easier gig. They are dirty, wet, moldy, and bug-ridden places. The "traditional" southern crawlspace house (you know, the one we say "breathes") is slowly self-composting in the crawlspace, so it is not a solution, it is a slow, long term failure, full of occupants loading up on Allegra and bug spray and wondering why.

The lined and sealed crawlspace, with careful details carefully carried out, appears to be a good alternative to this, although we'll likely go through the same learning curves with this technology that we did with barrier EIFS. The big lesson with EIFS was that low bid contractors with untrained temporary laborers are not the folks to entrust with the well being of your buildings and occupants.

Where I am right now:  Seal the crawlspace at the perimeter. DO NOT spray the underside of the subfloor with foam (which is a highly questionable practice due to code-related combustion issues.) Eliminate vapor retarders in the subfloor assembly (is anyone using Tyvek as flooring underlayment in lieu of building paper?) Dehumidify the crawlspace with a separate expensive dehumifier or by inducing conditioned air to ventilate and exhaust. Monitor the humidity levels in the occupied spaces and the crawlspace, and establish the crawlspace humidity control levels so that all humidity levels are approximately equal, with limited temperature differentials. Do that for a while, and we'll start to know what we're doing and how to solve this problem.

-------------------------------------------
Philip Kabza AIA
Partner and Dir Technical Services
SpecGuy
Charlotte NC
-------------------------------------------






Original Message:
Sent: 03-22-2012 08:18
From: Eric Rawlings
Subject: Let it breathe or seal it tight?

I appreciate your 2 cents. The flooring is pointing up on the edges (concave on top) and I assumed the same thing about the direction of vapor drive. This doesn't explain the floor with closed cell foam over a crawl nor does it explain the high humidity readings in all of the interiors. Typically, wood will want to cup in the opposite direction of the curve of the grain (in section) if exposed to humidity on both sides. These consistent problems are happening to different builders with different subs. Could it be possible that the closed cell foam is trapping the humidity at the bottom side of the flooring, thus making it appear that the vapor is coming in from the crawl? Since the foam is under the subfloor, it's the over the thickness of the plywood that the temperature differential is swinging from hot in the crawl to cold in the house (summer) and the opposite in the winter. Regardless, condensation would want to occur under the flooring on the surface of the plywood. Those grooves in the flooring provide a little space for it to collect. If water vapor and condensation are allowed to collect under the flooring, this may explain the closed cell foamed floor and the direction of cupping. 

I'm a believer in simple is better. The more we complicate our solutions, the more potential for problems we create. I'm still on the fence here when it comes to fanatical tightening of buildings. ERVs are expensive and have a moderate operating cost. Dehumidifiers can be as expensive to run as the entire building in the case of my Example #1. Would that client's house cost more than $100 a month to run if we removed the ERV and Dehumidifier and drilled some holes in his wall and crawl to achieve enough ventilation to keep humidity down to the levels of our "leakier" houses from a few years ago? The argument down in the South is that a leaky house draws moist outside air into the building causing the AC to run all day, just to remove humidity. Our leaky houses aren't the ones with the obnoxiously high humid readings, it's the tight houses. The argument and solution to remove humidity to make AC more efficient actually makes humidity worse and we just spent more money on gadgets to boot. This is the kind of stuff that turns off the skeptic.

If we ventilate the crawl and spray foam the floor, then we have to relocate the mechanical equipment powering the first floor, which costs money in terms of interior sf and how much we can sell the house for. With zoning requirements of an old in-town neighborhood, our floor area is very precious. This scenario may be our next option, but I really hate experimenting on my clients. At what point will an owner get angry enough for litigation for being convinced to spend all this extra money on gadgets and such only to get what they perceive as worse results?

I always tell my clients, especially the spec builders, that a solution to a problem isn't a solution if it creates two more problems to solve and unfortunately many of the "scientific" solutions that are suggested come with many components and complications that could very well open us up to many, many more problems to solve. Here I present the humidity problem and look at how my problems domino from that one issue. For a three or four part solution, how do we know which part of the solution was effective or which one is the next problem generator?

-------------------------------------------
Eric Rawlings AIA
Owner
Rawlings Design, Inc.
Decatur GA
-------------------------------------------






Original Message:
Sent: 03-21-2012 07:05
From: Philip Kabza
Subject: Let it breathe or seal it tight?

It is important to understand which direction the wood flooring cupping is taking: concave, or convex, with respect to the finished side. The cupping will be convex on the more humid side of the wood, which is expanding. I assume the more humid (convex, expanded) side in your case is the side of the flooring facing the crawlspace.

It seems the theoretical solution to the cupping hardwood flooring problem will have to center on establishing the same humidity level on both sides of the flooring material. Accomplishing that over a crawlspace is difficult; the dynamics of water vapor movement through the floor structure aren't easy to grasp. The wood products themselves have varying properties - some laminated, others solid wood. Some flooring products are impregnated, and all will be either factory- or site- finished with materials that may or may not serve as vapor retarders on one side of the wood only. The flooring underlayments may also affect vapor movement, as may the subfloor sheathings. 

I continue to wonder whether installing a separate $1,000 crawlspace dehumidifier (plus the $50 per month) in these sealed houses is really the answer, or whether it would make more sense to induce a modest air change rate throughout the house, using the crawlspace as an exhaust plenum to the exterior. Running a 100 cfm bathroom exhaust fan continuously in a 6000 cu. ft. crawlspace designed to draw conditioned air from the house above gives the crawlspace 1 air change per hour - perhaps enough to start equalizing the humidity between the house and the crawlspace. This of course adds to the overall air conditioning load of the house, but the load can be met by the much more efficient 15 SEER heat pump, and unless you like the smell of two day old cooked broccoli, you do want some fresh make-up air in the house anyway, which can be introduced through the HVAC return air system to allow for the crawlspace exhaust negative air pressure. Just a thought.

The termite observation strip is a possible target for improvement in sealed crawlspaces. I have seen a clear acrylic or polycarbonate sheet used at this location, with the vapor retarder materials sealed to both sides of it. That might help, although the idea that you can completely vapor seal a crawlspace, or a house for that matter, is a bit fanciful.

-------------------------------------------
Philip Kabza AIA
Partner and Dir Technical Services
SpecGuy
Charlotte NC
-------------------------------------------






Original Message:
Sent: 03-20-2012 08:02
From: Eric Rawlings
Subject: Let it breathe or seal it tight?

This message has been cross posted to the following Discussion Forums: Technology in Architectural Practice and Committee on the Environment .
-------------------------------------------

The debate over allowing a house to "breathe" a little or to seal it up as tight as possible has been argued ever since the advent of sick building syndrome. I attend the local Green Conferences every year. I've been very interested in sustainability since my professor introduced it to me in 1990. After listening to the building scientists, the theory of total air sealing with controlled ventilation sounds very logical, especially coming from a Canadian building scientist describing their climate conditions. I do have a problem with relying on a quiet fan of an ERV to not break down and cause the building to get sick. In the South East, we have one of the most difficult environments to build in. The humidity is relentless, the termites and carpenter bees are hungry, and in Atlanta, we have a very intense topography being at the foothills of the North GA mountains. Air sealing is becoming a requirement here and everyone's hardwoods are cupping. The blower door test is now required (or will be) on all residences in the metro area. I have used several different strategies recommended by building scientists for applying the air sealing, insulation, and building configuration to provide better efficiency yet we keep having the same problems.

The "greenest" house I designed has a ground source heat pump (geothermal), tons of insulation, and we sealed the crawlspace with a heavy duty waterproofing membrane that welds together like a TPO roof. This house boasts $50/ month electric bills, until the hardwoods started cupping and the crawl became too humid. Now they have to run a dehumidifier 24/7 that costs $50/ month. All of these houses have ERVs, another piece of equipment wasting energy, just to be "sealed" so we can save energy. The builder is well versed in green design/ installation. We made every precaution recommended, yet you can't keep humidity out of a crawlspace no matter how hard you try to seal it. In this assembly, the one vulnerability I can think of is the required termite check strip at the top of the masonry wall where the wood begins. Our water table is high and so is our frost line, so the earth stays pretty damp. It's possible that the vapor is pushing it's way through that 1" strip.

I have a house on a sealed crawl with closed cell spray foam on the underside of the floor. This cupped the worst. We were warned not to use open cell as it let's the vapor leak through. Maybe the humidity is mostly coming from the inside, not the crawl?

I have another house with a basement instead of a crawl that has the same problems. This basement is conditioned, yet we're trapping the humidity in the house and it simply can't escape. We have tried everything to keep the flooring from cupping. Our solution to our energy efficient air tight construction is to run a dehumidifier 24/7 at $50/ month.

I have a house that is built on a slab on grade. This one has less cupping in the flooring, but you can't build a slab on grade house in most places in Atlanta as our topography is so intense. The advantage is that you're only dealing with moisture coming through the horizontal plane of the floor, not the side walls as well. The average lots have enough slope to make slab on grade too expensive and not enough slope or a low enough water table to do a basement. This why we end up with crawl spaces. Even when built as a perfectly sealed, short basement, they still get moist.

The houses that are built on naturally ventilated crawl spaces with R-30 batts in the floor are staying the driest and have no problems with the floor cupping. They may be a little less efficient, but they aren't relying on ERVs and dehumidifiers to stay comfortable and healthy. What happens when we have the next ice storm and the electric is out for a week? What happens during the next Summer brown out when the electricity is out for a day or two?

My theory is that you can't humidity seal a Southern crawl space, even with the best materials available. This makes crawl spaces and basements a humidity trap/ generator. In each case of blower door approved construction, the overall humidity in the living space is higher than "normal". I think the humidity that we create from breathing, showering, and other activities is being trapped as well. The AC can't remove it all, even when running all day. In the summer, these sealed crawls are much warmer than the interior of the climate controlled house, so this humidity is going to be attracted to the cold side of the surfaces straddling the temperature differential between interior and exterior. In our case, this is the hardwood flooring. Since wood is dry and highly absorbent, you don't see the condensation on the surface. You eventually see it cup. If you're trapping enough humidity, then you're not helping your efficiency. If you need dehumidifiers and ERVs to make your more efficient house air tight and healthy, then what's the difference in letting it breathe enough to not require this energy consuming equipment and worry about quiet fans quitting or power outages? As the brilliant Canadian building scientist put it, "If you have a theoretically perfectly sealed building, then where do you put the holes?" These are the crossroads we're at right now as policy is resulting in problems that will have to be solved. The ever evolving theories of sustainable design. The more complicated we make it, the more problems we have to solve. Too bad our lifestyles keep evolving beyond our means to keep up.

-------------------------------------------
Eric Rawlings AIA
Owner
Rawlings Design, Inc.
Decatur GA
-------------------------------------------

Actually, wood cupping is dependent on the growth rings, not the wet or dry side.

-------------------------------------------
Charles Graham AIA
Architect
O'Neal, Inc.
Greenville SC
-------------------------------------------






Original Message:
Sent: 03-22-2012 08:18
From: Eric Rawlings
Subject: Let it breathe or seal it tight?

I appreciate your 2 cents. The flooring is pointing up on the edges (concave on top) and I assumed the same thing about the direction of vapor drive. This doesn't explain the floor with closed cell foam over a crawl nor does it explain the high humidity readings in all of the interiors. Typically, wood will want to cup in the opposite direction of the curve of the grain (in section) if exposed to humidity on both sides. These consistent problems are happening to different builders with different subs. Could it be possible that the closed cell foam is trapping the humidity at the bottom side of the flooring, thus making it appear that the vapor is coming in from the crawl? Since the foam is under the subfloor, it's the over the thickness of the plywood that the temperature differential is swinging from hot in the crawl to cold in the house (summer) and the opposite in the winter. Regardless, condensation would want to occur under the flooring on the surface of the plywood. Those grooves in the flooring provide a little space for it to collect. If water vapor and condensation are allowed to collect under the flooring, this may explain the closed cell foamed floor and the direction of cupping. 

I'm a believer in simple is better. The more we complicate our solutions, the more potential for problems we create. I'm still on the fence here when it comes to fanatical tightening of buildings. ERVs are expensive and have a moderate operating cost. Dehumidifiers can be as expensive to run as the entire building in the case of my Example #1. Would that client's house cost more than $100 a month to run if we removed the ERV and Dehumidifier and drilled some holes in his wall and crawl to achieve enough ventilation to keep humidity down to the levels of our "leakier" houses from a few years ago? The argument down in the South is that a leaky house draws moist outside air into the building causing the AC to run all day, just to remove humidity. Our leaky houses aren't the ones with the obnoxiously high humid readings, it's the tight houses. The argument and solution to remove humidity to make AC more efficient actually makes humidity worse and we just spent more money on gadgets to boot. This is the kind of stuff that turns off the skeptic.

If we ventilate the crawl and spray foam the floor, then we have to relocate the mechanical equipment powering the first floor, which costs money in terms of interior sf and how much we can sell the house for. With zoning requirements of an old in-town neighborhood, our floor area is very precious. This scenario may be our next option, but I really hate experimenting on my clients. At what point will an owner get angry enough for litigation for being convinced to spend all this extra money on gadgets and such only to get what they perceive as worse results?

I always tell my clients, especially the spec builders, that a solution to a problem isn't a solution if it creates two more problems to solve and unfortunately many of the "scientific" solutions that are suggested come with many components and complications that could very well open us up to many, many more problems to solve. Here I present the humidity problem and look at how my problems domino from that one issue. For a three or four part solution, how do we know which part of the solution was effective or which one is the next problem generator?

-------------------------------------------
Eric Rawlings AIA
Owner
Rawlings Design, Inc.
Decatur GA
-------------------------------------------






Original Message:
Sent: 03-21-2012 07:05
From: Philip Kabza
Subject: Let it breathe or seal it tight?

It is important to understand which direction the wood flooring cupping is taking: concave, or convex, with respect to the finished side. The cupping will be convex on the more humid side of the wood, which is expanding. I assume the more humid (convex, expanded) side in your case is the side of the flooring facing the crawlspace.

It seems the theoretical solution to the cupping hardwood flooring problem will have to center on establishing the same humidity level on both sides of the flooring material. Accomplishing that over a crawlspace is difficult; the dynamics of water vapor movement through the floor structure aren't easy to grasp. The wood products themselves have varying properties - some laminated, others solid wood. Some flooring products are impregnated, and all will be either factory- or site- finished with materials that may or may not serve as vapor retarders on one side of the wood only. The flooring underlayments may also affect vapor movement, as may the subfloor sheathings. 

I continue to wonder whether installing a separate $1,000 crawlspace dehumidifier (plus the $50 per month) in these sealed houses is really the answer, or whether it would make more sense to induce a modest air change rate throughout the house, using the crawlspace as an exhaust plenum to the exterior. Running a 100 cfm bathroom exhaust fan continuously in a 6000 cu. ft. crawlspace designed to draw conditioned air from the house above gives the crawlspace 1 air change per hour - perhaps enough to start equalizing the humidity between the house and the crawlspace. This of course adds to the overall air conditioning load of the house, but the load can be met by the much more efficient 15 SEER heat pump, and unless you like the smell of two day old cooked broccoli, you do want some fresh make-up air in the house anyway, which can be introduced through the HVAC return air system to allow for the crawlspace exhaust negative air pressure. Just a thought.

The termite observation strip is a possible target for improvement in sealed crawlspaces. I have seen a clear acrylic or polycarbonate sheet used at this location, with the vapor retarder materials sealed to both sides of it. That might help, although the idea that you can completely vapor seal a crawlspace, or a house for that matter, is a bit fanciful.

-------------------------------------------
Philip Kabza AIA
Partner and Dir Technical Services
SpecGuy
Charlotte NC
-------------------------------------------






Original Message:
Sent: 03-20-2012 08:02
From: Eric Rawlings
Subject: Let it breathe or seal it tight?

This message has been cross posted to the following Discussion Forums: Technology in Architectural Practice and Committee on the Environment .
-------------------------------------------

The debate over allowing a house to "breathe" a little or to seal it up as tight as possible has been argued ever since the advent of sick building syndrome. I attend the local Green Conferences every year. I've been very interested in sustainability since my professor introduced it to me in 1990. After listening to the building scientists, the theory of total air sealing with controlled ventilation sounds very logical, especially coming from a Canadian building scientist describing their climate conditions. I do have a problem with relying on a quiet fan of an ERV to not break down and cause the building to get sick. In the South East, we have one of the most difficult environments to build in. The humidity is relentless, the termites and carpenter bees are hungry, and in Atlanta, we have a very intense topography being at the foothills of the North GA mountains. Air sealing is becoming a requirement here and everyone's hardwoods are cupping. The blower door test is now required (or will be) on all residences in the metro area. I have used several different strategies recommended by building scientists for applying the air sealing, insulation, and building configuration to provide better efficiency yet we keep having the same problems.

The "greenest" house I designed has a ground source heat pump (geothermal), tons of insulation, and we sealed the crawlspace with a heavy duty waterproofing membrane that welds together like a TPO roof. This house boasts $50/ month electric bills, until the hardwoods started cupping and the crawl became too humid. Now they have to run a dehumidifier 24/7 that costs $50/ month. All of these houses have ERVs, another piece of equipment wasting energy, just to be "sealed" so we can save energy. The builder is well versed in green design/ installation. We made every precaution recommended, yet you can't keep humidity out of a crawlspace no matter how hard you try to seal it. In this assembly, the one vulnerability I can think of is the required termite check strip at the top of the masonry wall where the wood begins. Our water table is high and so is our frost line, so the earth stays pretty damp. It's possible that the vapor is pushing it's way through that 1" strip.

I have a house on a sealed crawl with closed cell spray foam on the underside of the floor. This cupped the worst. We were warned not to use open cell as it let's the vapor leak through. Maybe the humidity is mostly coming from the inside, not the crawl?

I have another house with a basement instead of a crawl that has the same problems. This basement is conditioned, yet we're trapping the humidity in the house and it simply can't escape. We have tried everything to keep the flooring from cupping. Our solution to our energy efficient air tight construction is to run a dehumidifier 24/7 at $50/ month.

I have a house that is built on a slab on grade. This one has less cupping in the flooring, but you can't build a slab on grade house in most places in Atlanta as our topography is so intense. The advantage is that you're only dealing with moisture coming through the horizontal plane of the floor, not the side walls as well. The average lots have enough slope to make slab on grade too expensive and not enough slope or a low enough water table to do a basement. This why we end up with crawl spaces. Even when built as a perfectly sealed, short basement, they still get moist.

The houses that are built on naturally ventilated crawl spaces with R-30 batts in the floor are staying the driest and have no problems with the floor cupping. They may be a little less efficient, but they aren't relying on ERVs and dehumidifiers to stay comfortable and healthy. What happens when we have the next ice storm and the electric is out for a week? What happens during the next Summer brown out when the electricity is out for a day or two?

My theory is that you can't humidity seal a Southern crawl space, even with the best materials available. This makes crawl spaces and basements a humidity trap/ generator. In each case of blower door approved construction, the overall humidity in the living space is higher than "normal". I think the humidity that we create from breathing, showering, and other activities is being trapped as well. The AC can't remove it all, even when running all day. In the summer, these sealed crawls are much warmer than the interior of the climate controlled house, so this humidity is going to be attracted to the cold side of the surfaces straddling the temperature differential between interior and exterior. In our case, this is the hardwood flooring. Since wood is dry and highly absorbent, you don't see the condensation on the surface. You eventually see it cup. If you're trapping enough humidity, then you're not helping your efficiency. If you need dehumidifiers and ERVs to make your more efficient house air tight and healthy, then what's the difference in letting it breathe enough to not require this energy consuming equipment and worry about quiet fans quitting or power outages? As the brilliant Canadian building scientist put it, "If you have a theoretically perfectly sealed building, then where do you put the holes?" These are the crossroads we're at right now as policy is resulting in problems that will have to be solved. The ever evolving theories of sustainable design. The more complicated we make it, the more problems we have to solve. Too bad our lifestyles keep evolving beyond our means to keep up.

-------------------------------------------
Eric Rawlings AIA
Owner
Rawlings Design, Inc.
Decatur GA
-------------------------------------------

First, let me commend you for exploring this issue. As one who grew up in Louisiana and spent 13 years in Alabama, I am well aware of the issues that arise with attempts to control humidity. I confess that our commercial projects don't have crawl spaces so my thoughts may not be entirely viable. It had been in the codes that ventilation was required for attics and crawl spaces so the idea of sealing the vertical crawl is surprising to me. I would be curious if you've ever over ventilated the crawl wspace while super sealing the horizontal floor? My understanding of the logic is that the air flow allows the humid crawl space to move rather than stagnate and force its way into your house. Similar to a pond with no outlet tending to attract scum, the crawl with no outlet causes the damaging effects you described. It used to be that the walls were also noted to have vapor retarders on the warm in winter side which didn't make sense in the south. Now the energy codes say to omit the retarder (for breathability) in climate zones 1 through 3 (the southeast). Unless the mechanical engineer advises otherwise. There are programs out there that can calculate the dew point location with various temp and humidity vs. Assembly to detemine the location of the dewpoint under various conditions. The object is to avoid condensation on an interior surface. This lends itself to designing the insulation toward the exterior with the retarder protecting the wall or floor assembly. Not so easy to do in reality without bringing a host of other issues (insects) into the equation. Suffice to say, there does not appear to be a single solution. It varies on building type, how it is used, and the cladding on it. The idea of sealing the thermal envelope seems to continue to be true though. You simply have to define where that envelope occurs and provide the ventilation everywhere else. Good luck ------------------------------------------- Jonathan Larson AIA Project Architect Goodwyn, Mills & Cawood, Inc. Nashville TN -------------------------------------------
Original Message: Sent: 03-20-2012 08:02 From: Eric Rawlings Subject: Let it breathe or seal it tight? This message has been cross posted to the following Discussion Forums: Technology in Architectural Practice and Committee on the Environment . ------------------------------------------- The debate over allowing a house to "breathe" a little or to seal it up as tight as possible has been argued ever since the advent of sick building syndrome. I attend the local Green Conferences every year. I've been very interested in sustainability since my professor introduced it to me in 1990. After listening to the building scientists, the theory of total air sealing with controlled ventilation sounds very logical, especially coming from a Canadian building scientist describing their climate conditions. I do have a problem with relying on a quiet fan of an ERV to not break down and cause the building to get sick. In the South East, we have one of the most difficult environments to build in. The humidity is relentless, the termites and carpenter bees are hungry, and in Atlanta, we have a very intense topography being at the foothills of the North GA mountains. Air sealing is becoming a requirement here and everyone's hardwoods are cupping. The blower door test is now required (or will be) on all residences in the metro area. I have used several different strategies recommended by building scientists for applying the air sealing, insulation, and building configuration to provide better efficiency yet we keep having the same problems. The "greenest" house I designed has a ground source heat pump (geothermal), tons of insulation, and we sealed the crawlspace with a heavy duty waterproofing membrane that welds together like a TPO roof. This house boasts $50/ month electric bills, until the hardwoods started cupping and the crawl became too humid. Now they have to run a dehumidifier 24/7 that costs $50/ month. All of these houses have ERVs, another piece of equipment wasting energy, just to be "sealed" so we can save energy. The builder is well versed in green design/ installation. We made every precaution recommended, yet you can't keep humidity out of a crawlspace no matter how hard you try to seal it. In this assembly, the one vulnerability I can think of is the required termite check strip at the top of the masonry wall where the wood begins. Our water table is high and so is our frost line, so the earth stays pretty damp. It's possible that the vapor is pushing it's way through that 1" strip. I have a house on a sealed crawl with closed cell spray foam on the underside of the floor. This cupped the worst. We were warned not to use open cell as it let's the vapor leak through. Maybe the humidity is mostly coming from the inside, not the crawl? I have another house with a basement instead of a crawl that has the same problems. This basement is conditioned, yet we're trapping the humidity in the house and it simply can't escape. We have tried everything to keep the flooring from cupping. Our solution to our energy efficient air tight construction is to run a dehumidifier 24/7 at $50/ month. I have a house that is built on a slab on grade. This one has less cupping in the flooring, but you can't build a slab on grade house in most places in Atlanta as our topography is so intense. The advantage is that you're only dealing with moisture coming through the horizontal plane of the floor, not the side walls as well. The average lots have enough slope to make slab on grade too expensive and not enough slope or a low enough water table to do a basement. This why we end up with crawl spaces. Even when built as a perfectly sealed, short basement, they still get moist. The houses that are built on naturally ventilated crawl spaces with R-30 batts in the floor are staying the driest and have no problems with the floor cupping. They may be a little less efficient, but they aren't relying on ERVs and dehumidifiers to stay comfortable and healthy. What happens when we have the next ice storm and the electric is out for a week? What happens during the next Summer brown out when the electricity is out for a day or two? My theory is that you can't humidity seal a Southern crawl space, even with the best materials available. This makes crawl spaces and basements a humidity trap/ generator. In each case of blower door approved construction, the overall humidity in the living space is higher than "normal". I think the humidity that we create from breathing, showering, and other activities is being trapped as well. The AC can't remove it all, even when running all day. In the summer, these sealed crawls are much warmer than the interior of the climate controlled house, so this humidity is going to be attracted to the cold side of the surfaces straddling the temperature differential between interior and exterior. In our case, this is the hardwood flooring. Since wood is dry and highly absorbent, you don't see the condensation on the surface. You eventually see it cup. If you're trapping enough humidity, then you're not helping your efficiency. If you need dehumidifiers and ERVs to make your more efficient house air tight and healthy, then what's the difference in letting it breathe enough to not require this energy consuming equipment and worry about quiet fans quitting or power outages? As the brilliant Canadian building scientist put it, "If you have a theoretically perfectly sealed building, then where do you put the holes?" These are the crossroads we're at right now as policy is resulting in problems that will have to be solved. The ever evolving theories of sustainable design. The more complicated we make it, the more problems we have to solve. Too bad our lifestyles keep evolving beyond our means to keep up. ------------------------------------------- Eric Rawlings AIA Owner Rawlings Design, Inc. Decatur GA -------------------------------------------

Very thoughtfully presented, Eric. And full of great real-world practical knowledge.
Let's consider a colder climate where humidity is not such a large problem, and distill the argument further.
Known: It takes a certain amount of BTU's to raise the temperature of a certain amount of cold air. Regardless of whether you do that with a wood stove, a gas furnace, or an oil-fired boiler.
Known: Humans require a certain amount of fresh air (oxygen vs. CO2) to stay healthy. Regardless of whether it comes in through a window, a sill crack, or a fan-assisted ERV.
An Example: The wood stove in my off-the grid cabin in Maine burns the oxygen inside the cabin. I like the cracks and gaps that let in a bit of fresh air. But it is probably not the most environmentally friendly way to stay warm. I cut my own wood supply (renewable) on my own property, but I worry about the particulates going up the flue.
Would it be 'better' if I installed a high-efficiency (LP?) gas heater, sealed the building, and installed an ERV that operated with power from the solar system?
Yes, I think it would, if done properly. The "if-done-properly" part of this is the kicker.  This would mean sizing the ERV properly, and controlling it so that it can vary it's delivery according to need, and distributing the fresh air evenly throughout the space.  My existing cracks do a great job of distributing fresh air evenly. This is the part where I worry that our sealed ERV buildings don't perform as well; the uneven distribution. "Done properly" would also mean contact points on the system controls to integrate with windows and doors (the unit does not need to run if a window is open), and to alert the occupants if the system breaks down. I believe we are still learning how to build well, but we are moving in the right direction.  Where we still need to advance our work is in the area of controls, in particular, in my opinion. (How we can build good buildings without having the HVAC systems controls integrated with windows and doors?)
Why is our newer way better? Again, if done properly, because it scientifically heats a certain amount of cold air while consuming the minimum required number of BTUs while delivering the required amount of fresh air, without excess. Thus, is more sustainable.
Humidity? A big concern in your area.  Would there be a way to power your dehumidification with renewable energy, and control it in a manner that is fully integrated with the rest of your system, without blowing your budget? A difficult task...
(Is your humidity really coming in from the crawl spaces? Or is it coming in through open windows and doors?)
PB
-------------------------------------------
Paul Brown AIA
Paul Spencer Brown, Architect
Needham MA
-------------------------------------------






Original Message:
Sent: 03-20-2012 08:02
From: Eric Rawlings
Subject: Let it breathe or seal it tight?

This message has been cross posted to the following Discussion Forums: Technology in Architectural Practice and Committee on the Environment .
-------------------------------------------

The debate over allowing a house to "breathe" a little or to seal it up as tight as possible has been argued ever since the advent of sick building syndrome. I attend the local Green Conferences every year. I've been very interested in sustainability since my professor introduced it to me in 1990. After listening to the building scientists, the theory of total air sealing with controlled ventilation sounds very logical, especially coming from a Canadian building scientist describing their climate conditions. I do have a problem with relying on a quiet fan of an ERV to not break down and cause the building to get sick. In the South East, we have one of the most difficult environments to build in. The humidity is relentless, the termites and carpenter bees are hungry, and in Atlanta, we have a very intense topography being at the foothills of the North GA mountains. Air sealing is becoming a requirement here and everyone's hardwoods are cupping. The blower door test is now required (or will be) on all residences in the metro area. I have used several different strategies recommended by building scientists for applying the air sealing, insulation, and building configuration to provide better efficiency yet we keep having the same problems.

The "greenest" house I designed has a ground source heat pump (geothermal), tons of insulation, and we sealed the crawlspace with a heavy duty waterproofing membrane that welds together like a TPO roof. This house boasts $50/ month electric bills, until the hardwoods started cupping and the crawl became too humid. Now they have to run a dehumidifier 24/7 that costs $50/ month. All of these houses have ERVs, another piece of equipment wasting energy, just to be "sealed" so we can save energy. The builder is well versed in green design/ installation. We made every precaution recommended, yet you can't keep humidity out of a crawlspace no matter how hard you try to seal it. In this assembly, the one vulnerability I can think of is the required termite check strip at the top of the masonry wall where the wood begins. Our water table is high and so is our frost line, so the earth stays pretty damp. It's possible that the vapor is pushing it's way through that 1" strip.

I have a house on a sealed crawl with closed cell spray foam on the underside of the floor. This cupped the worst. We were warned not to use open cell as it let's the vapor leak through. Maybe the humidity is mostly coming from the inside, not the crawl?

I have another house with a basement instead of a crawl that has the same problems. This basement is conditioned, yet we're trapping the humidity in the house and it simply can't escape. We have tried everything to keep the flooring from cupping. Our solution to our energy efficient air tight construction is to run a dehumidifier 24/7 at $50/ month.

I have a house that is built on a slab on grade. This one has less cupping in the flooring, but you can't build a slab on grade house in most places in Atlanta as our topography is so intense. The advantage is that you're only dealing with moisture coming through the horizontal plane of the floor, not the side walls as well. The average lots have enough slope to make slab on grade too expensive and not enough slope or a low enough water table to do a basement. This why we end up with crawl spaces. Even when built as a perfectly sealed, short basement, they still get moist.

The houses that are built on naturally ventilated crawl spaces with R-30 batts in the floor are staying the driest and have no problems with the floor cupping. They may be a little less efficient, but they aren't relying on ERVs and dehumidifiers to stay comfortable and healthy. What happens when we have the next ice storm and the electric is out for a week? What happens during the next Summer brown out when the electricity is out for a day or two?

My theory is that you can't humidity seal a Southern crawl space, even with the best materials available. This makes crawl spaces and basements a humidity trap/ generator. In each case of blower door approved construction, the overall humidity in the living space is higher than "normal". I think the humidity that we create from breathing, showering, and other activities is being trapped as well. The AC can't remove it all, even when running all day. In the summer, these sealed crawls are much warmer than the interior of the climate controlled house, so this humidity is going to be attracted to the cold side of the surfaces straddling the temperature differential between interior and exterior. In our case, this is the hardwood flooring. Since wood is dry and highly absorbent, you don't see the condensation on the surface. You eventually see it cup. If you're trapping enough humidity, then you're not helping your efficiency. If you need dehumidifiers and ERVs to make your more efficient house air tight and healthy, then what's the difference in letting it breathe enough to not require this energy consuming equipment and worry about quiet fans quitting or power outages? As the brilliant Canadian building scientist put it, "If you have a theoretically perfectly sealed building, then where do you put the holes?" These are the crossroads we're at right now as policy is resulting in problems that will have to be solved. The ever evolving theories of sustainable design. The more complicated we make it, the more problems we have to solve. Too bad our lifestyles keep evolving beyond our means to keep up.

-------------------------------------------
Eric Rawlings AIA
Owner
Rawlings Design, Inc.
Decatur GA
-------------------------------------------

Welcome to the world of attempting to put theory to practice.
-------------------------------------------
Charles Graham AIA
Architect
O'Neal, Inc.
Greenville SC
-------------------------------------------






Original Message:
Sent: 03-20-2012 08:02
From: Eric Rawlings
Subject: Let it breathe or seal it tight?

This message has been cross posted to the following Discussion Forums: Technology in Architectural Practice and Committee on the Environment .
-------------------------------------------

The debate over allowing a house to "breathe" a little or to seal it up as tight as possible has been argued ever since the advent of sick building syndrome. I attend the local Green Conferences every year. I've been very interested in sustainability since my professor introduced it to me in 1990. After listening to the building scientists, the theory of total air sealing with controlled ventilation sounds very logical, especially coming from a Canadian building scientist describing their climate conditions. I do have a problem with relying on a quiet fan of an ERV to not break down and cause the building to get sick. In the South East, we have one of the most difficult environments to build in. The humidity is relentless, the termites and carpenter bees are hungry, and in Atlanta, we have a very intense topography being at the foothills of the North GA mountains. Air sealing is becoming a requirement here and everyone's hardwoods are cupping. The blower door test is now required (or will be) on all residences in the metro area. I have used several different strategies recommended by building scientists for applying the air sealing, insulation, and building configuration to provide better efficiency yet we keep having the same problems.

The "greenest" house I designed has a ground source heat pump (geothermal), tons of insulation, and we sealed the crawlspace with a heavy duty waterproofing membrane that welds together like a TPO roof. This house boasts $50/ month electric bills, until the hardwoods started cupping and the crawl became too humid. Now they have to run a dehumidifier 24/7 that costs $50/ month. All of these houses have ERVs, another piece of equipment wasting energy, just to be "sealed" so we can save energy. The builder is well versed in green design/ installation. We made every precaution recommended, yet you can't keep humidity out of a crawlspace no matter how hard you try to seal it. In this assembly, the one vulnerability I can think of is the required termite check strip at the top of the masonry wall where the wood begins. Our water table is high and so is our frost line, so the earth stays pretty damp. It's possible that the vapor is pushing it's way through that 1" strip.

I have a house on a sealed crawl with closed cell spray foam on the underside of the floor. This cupped the worst. We were warned not to use open cell as it let's the vapor leak through. Maybe the humidity is mostly coming from the inside, not the crawl?

I have another house with a basement instead of a crawl that has the same problems. This basement is conditioned, yet we're trapping the humidity in the house and it simply can't escape. We have tried everything to keep the flooring from cupping. Our solution to our energy efficient air tight construction is to run a dehumidifier 24/7 at $50/ month.

I have a house that is built on a slab on grade. This one has less cupping in the flooring, but you can't build a slab on grade house in most places in Atlanta as our topography is so intense. The advantage is that you're only dealing with moisture coming through the horizontal plane of the floor, not the side walls as well. The average lots have enough slope to make slab on grade too expensive and not enough slope or a low enough water table to do a basement. This why we end up with crawl spaces. Even when built as a perfectly sealed, short basement, they still get moist.

The houses that are built on naturally ventilated crawl spaces with R-30 batts in the floor are staying the driest and have no problems with the floor cupping. They may be a little less efficient, but they aren't relying on ERVs and dehumidifiers to stay comfortable and healthy. What happens when we have the next ice storm and the electric is out for a week? What happens during the next Summer brown out when the electricity is out for a day or two?

My theory is that you can't humidity seal a Southern crawl space, even with the best materials available. This makes crawl spaces and basements a humidity trap/ generator. In each case of blower door approved construction, the overall humidity in the living space is higher than "normal". I think the humidity that we create from breathing, showering, and other activities is being trapped as well. The AC can't remove it all, even when running all day. In the summer, these sealed crawls are much warmer than the interior of the climate controlled house, so this humidity is going to be attracted to the cold side of the surfaces straddling the temperature differential between interior and exterior. In our case, this is the hardwood flooring. Since wood is dry and highly absorbent, you don't see the condensation on the surface. You eventually see it cup. If you're trapping enough humidity, then you're not helping your efficiency. If you need dehumidifiers and ERVs to make your more efficient house air tight and healthy, then what's the difference in letting it breathe enough to not require this energy consuming equipment and worry about quiet fans quitting or power outages? As the brilliant Canadian building scientist put it, "If you have a theoretically perfectly sealed building, then where do you put the holes?" These are the crossroads we're at right now as policy is resulting in problems that will have to be solved. The ever evolving theories of sustainable design. The more complicated we make it, the more problems we have to solve. Too bad our lifestyles keep evolving beyond our means to keep up.

-------------------------------------------
Eric Rawlings AIA
Owner
Rawlings Design, Inc.
Decatur GA
-------------------------------------------

I can't comment on the US and Canadian experiences outlined in the following discussions, however in Queensland Australia where I have been living and practicing for many years we would never contemplate the sealing of our buildings. It would be doomed exercise.

The Queensland climate is characterised by hot humid summers and cold dry winters in the South east corner. The northern parts of the state are warm and humid and then hot and humid!  The "traditional" Queensland house is raised off the ground, has plenty of flow-through ventilation and is made of lightweight materials. The downside of this approach is that the buildings in the SE are very cold in the winter. Contemporary practitioners have experimented with lightweight insulated walls and roofs with the ability to close the building up during winter and open it during summer. If adequate ventilation is not provided the result is mould and fungus growth. There is now a trend towards concrete and cmu (driven by client preference) however the lightweight materials tend to give us the best performance.

There is a a research unit attached to the Queeensland Insitute of Technology specialising in the study of Sub Tropical Design run by Rosie Kennedy who I am sure would love to make her research available to AIA members. http://www.subtropicaldesign.org.au

I am now working in Vietnam in both Danang and Ho Chi Minh City where the problems of mould and humidity pervade every building. We have adopted the principles of cross-flow ventilation in our Villas in Danang despite the requirement to construct them in concrete. Yes even the roofs are concrete with the tiles glued on.

-------------------------------------------
Edward Haysom AIA
Director
Haysom Architects
Fortitude Valley BC

-------------------------------------------






Original Message:
Sent: 03-20-2012 08:02
From: Eric Rawlings
Subject: Let it breathe or seal it tight?

This message has been cross posted to the following Discussion Forums: Technology in Architectural Practice and Committee on the Environment .
-------------------------------------------

The debate over allowing a house to "breathe" a little or to seal it up as tight as possible has been argued ever since the advent of sick building syndrome. I attend the local Green Conferences every year. I've been very interested in sustainability since my professor introduced it to me in 1990. After listening to the building scientists, the theory of total air sealing with controlled ventilation sounds very logical, especially coming from a Canadian building scientist describing their climate conditions. I do have a problem with relying on a quiet fan of an ERV to not break down and cause the building to get sick. In the South East, we have one of the most difficult environments to build in. The humidity is relentless, the termites and carpenter bees are hungry, and in Atlanta, we have a very intense topography being at the foothills of the North GA mountains. Air sealing is becoming a requirement here and everyone's hardwoods are cupping. The blower door test is now required (or will be) on all residences in the metro area. I have used several different strategies recommended by building scientists for applying the air sealing, insulation, and building configuration to provide better efficiency yet we keep having the same problems.

The "greenest" house I designed has a ground source heat pump (geothermal), tons of insulation, and we sealed the crawlspace with a heavy duty waterproofing membrane that welds together like a TPO roof. This house boasts $50/ month electric bills, until the hardwoods started cupping and the crawl became too humid. Now they have to run a dehumidifier 24/7 that costs $50/ month. All of these houses have ERVs, another piece of equipment wasting energy, just to be "sealed" so we can save energy. The builder is well versed in green design/ installation. We made every precaution recommended, yet you can't keep humidity out of a crawlspace no matter how hard you try to seal it. In this assembly, the one vulnerability I can think of is the required termite check strip at the top of the masonry wall where the wood begins. Our water table is high and so is our frost line, so the earth stays pretty damp. It's possible that the vapor is pushing it's way through that 1" strip.

I have a house on a sealed crawl with closed cell spray foam on the underside of the floor. This cupped the worst. We were warned not to use open cell as it let's the vapor leak through. Maybe the humidity is mostly coming from the inside, not the crawl?

I have another house with a basement instead of a crawl that has the same problems. This basement is conditioned, yet we're trapping the humidity in the house and it simply can't escape. We have tried everything to keep the flooring from cupping. Our solution to our energy efficient air tight construction is to run a dehumidifier 24/7 at $50/ month.

I have a house that is built on a slab on grade. This one has less cupping in the flooring, but you can't build a slab on grade house in most places in Atlanta as our topography is so intense. The advantage is that you're only dealing with moisture coming through the horizontal plane of the floor, not the side walls as well. The average lots have enough slope to make slab on grade too expensive and not enough slope or a low enough water table to do a basement. This why we end up with crawl spaces. Even when built as a perfectly sealed, short basement, they still get moist.

The houses that are built on naturally ventilated crawl spaces with R-30 batts in the floor are staying the driest and have no problems with the floor cupping. They may be a little less efficient, but they aren't relying on ERVs and dehumidifiers to stay comfortable and healthy. What happens when we have the next ice storm and the electric is out for a week? What happens during the next Summer brown out when the electricity is out for a day or two?

My theory is that you can't humidity seal a Southern crawl space, even with the best materials available. This makes crawl spaces and basements a humidity trap/ generator. In each case of blower door approved construction, the overall humidity in the living space is higher than "normal". I think the humidity that we create from breathing, showering, and other activities is being trapped as well. The AC can't remove it all, even when running all day. In the summer, these sealed crawls are much warmer than the interior of the climate controlled house, so this humidity is going to be attracted to the cold side of the surfaces straddling the temperature differential between interior and exterior. In our case, this is the hardwood flooring. Since wood is dry and highly absorbent, you don't see the condensation on the surface. You eventually see it cup. If you're trapping enough humidity, then you're not helping your efficiency. If you need dehumidifiers and ERVs to make your more efficient house air tight and healthy, then what's the difference in letting it breathe enough to not require this energy consuming equipment and worry about quiet fans quitting or power outages? As the brilliant Canadian building scientist put it, "If you have a theoretically perfectly sealed building, then where do you put the holes?" These are the crossroads we're at right now as policy is resulting in problems that will have to be solved. The ever evolving theories of sustainable design. The more complicated we make it, the more problems we have to solve. Too bad our lifestyles keep evolving beyond our means to keep up.

-------------------------------------------
Eric Rawlings AIA
Owner
Rawlings Design, Inc.
Decatur GA
-------------------------------------------

Hi Eric,
I contacted you directly, and wanted to commend you for addressing the issue of humidity in the SE USA such an orderly and responsible manner. I have seen issues without ventilation of wood, product high levels of moisture content, well about the 19% kiln dried. While areas of extreme cold, such as Canada, and the low humidity areas of the US, sprayed foam may be an excellent vapor barrier and insulation.

I question the placing a water based sprayed insulation, without any means of ventilation, directly in contact with the wood sheathing, subfloor, or roof sheathing. The wood floor solution may be resolved with a flat "purlin' between the hardwood floor and the subfloor, venting at the perimeter, likely accommodated at the baseboard in residential construction. The moisture during the curing process of the foam, may be sealed, by the non uniform process, curing, perhaps more quickly on the air exposed side, thus possibly trapping the residual moisture. This moisture may be drawn into the low moisture content of the hardwood and subfloor. Granted this is speculation, not knowing the specific chemical reaction in the curing process.


Consider the similarity of a gym hardwood (maple) floor system, and the neoprene blocks that elevate the plywood substrate in many systems from the concrete, often fully recess the thickness of the floor system. Wood and ventilation may provide  great symbiotic relationships in high humidity areas. (Incidentally, these 'pools' especially near exterior doors, may need to be 'drained, isolated' or otherwise addressed to minimize the collection of moisture, and water, in the concrete 'pool.')

Again, thank you for the posting of this issue, as you are likely not the only one impacted. Sealed spaces, while minimizing some environmental issues of radon, and mold, may have side affects needing attention. Consider moving the tempered air, and building in ventilation 'layers'.
 

-------------------------------------------
Archie Gupton AIA
Raleigh NC
-------------------------------------------

Being from Chicago, the land of basements, I do not know much about crawl spaces.  Therefore my response may be inappropriate or one that also generates more problems.

Have you tried putting a vapor barrier on the underside of the floor construction?  I am imagining on the underside of the joists.

-------------------------------------------
Joseph Stypka AIA
Vice President, Director Specifications
Murphy/Jahn Architects
Chicago IL
-------------------------------------------

-------------------------------------------
Kenneth Kruger AIA
Kruger Kruger Albenberg/Architects Engin
Cambridge MA
-------------------------------------------
I would think the flooring has a right to stay flat either way.  To parse the problem, some more data would be helpful.  Is the strip flooring buckling concave up or convex up?  Air sealing is addressed as if it might be incorporating vapor sealing.  Where are the vapor retarders, if any?   How are the basement or craw-space walls being treated regarding drainage and air, water and vapor sealing.  What are the boundary conditions of the WP membrane on the earthen floor?  Does any of the construction have a double vapor seal hindering venting in and out -- such as possibly that crawl space with a WP membrane and then closed-cell foam at the ceiling?

One also wonders if the ERVs are moving enough air.  Certainly in the event of mechanical malfunction, one should be able to open windows and other relief vents.

Lastly, current thinking for air-sealed homes is that attics and basements/crawlspaces should be part of the conditioned space.  For the flooring problem, that would have both sides of the wood see the same environment.







Original Message:
Sent: 03-20-2012 08:02
From: Eric Rawlings
Subject: Let it breathe or seal it tight?

This message has been cross posted to the following Discussion Forums: Technology in Architectural Practice and Committee on the Environment .
-------------------------------------------

The debate over allowing a house to "breathe" a little or to seal it up as tight as possible has been argued ever since the advent of sick building syndrome. I attend the local Green Conferences every year. I've been very interested in sustainability since my professor introduced it to me in 1990. After listening to the building scientists, the theory of total air sealing with controlled ventilation sounds very logical, especially coming from a Canadian building scientist describing their climate conditions. I do have a problem with relying on a quiet fan of an ERV to not break down and cause the building to get sick. In the South East, we have one of the most difficult environments to build in. The humidity is relentless, the termites and carpenter bees are hungry, and in Atlanta, we have a very intense topography being at the foothills of the North GA mountains. Air sealing is becoming a requirement here and everyone's hardwoods are cupping. The blower door test is now required (or will be) on all residences in the metro area. I have used several different strategies recommended by building scientists for applying the air sealing, insulation, and building configuration to provide better efficiency yet we keep having the same problems.

The "greenest" house I designed has a ground source heat pump (geothermal), tons of insulation, and we sealed the crawlspace with a heavy duty waterproofing membrane that welds together like a TPO roof. This house boasts $50/ month electric bills, until the hardwoods started cupping and the crawl became too humid. Now they have to run a dehumidifier 24/7 that costs $50/ month. All of these houses have ERVs, another piece of equipment wasting energy, just to be "sealed" so we can save energy. The builder is well versed in green design/ installation. We made every precaution recommended, yet you can't keep humidity out of a crawlspace no matter how hard you try to seal it. In this assembly, the one vulnerability I can think of is the required termite check strip at the top of the masonry wall where the wood begins. Our water table is high and so is our frost line, so the earth stays pretty damp. It's possible that the vapor is pushing it's way through that 1" strip.

I have a house on a sealed crawl with closed cell spray foam on the underside of the floor. This cupped the worst. We were warned not to use open cell as it let's the vapor leak through. Maybe the humidity is mostly coming from the inside, not the crawl?

I have another house with a basement instead of a crawl that has the same problems. This basement is conditioned, yet we're trapping the humidity in the house and it simply can't escape. We have tried everything to keep the flooring from cupping. Our solution to our energy efficient air tight construction is to run a dehumidifier 24/7 at $50/ month.

I have a house that is built on a slab on grade. This one has less cupping in the flooring, but you can't build a slab on grade house in most places in Atlanta as our topography is so intense. The advantage is that you're only dealing with moisture coming through the horizontal plane of the floor, not the side walls as well. The average lots have enough slope to make slab on grade too expensive and not enough slope or a low enough water table to do a basement. This why we end up with crawl spaces. Even when built as a perfectly sealed, short basement, they still get moist.

The houses that are built on naturally ventilated crawl spaces with R-30 batts in the floor are staying the driest and have no problems with the floor cupping. They may be a little less efficient, but they aren't relying on ERVs and dehumidifiers to stay comfortable and healthy. What happens when we have the next ice storm and the electric is out for a week? What happens during the next Summer brown out when the electricity is out for a day or two?

My theory is that you can't humidity seal a Southern crawl space, even with the best materials available. This makes crawl spaces and basements a humidity trap/ generator. In each case of blower door approved construction, the overall humidity in the living space is higher than "normal". I think the humidity that we create from breathing, showering, and other activities is being trapped as well. The AC can't remove it all, even when running all day. In the summer, these sealed crawls are much warmer than the interior of the climate controlled house, so this humidity is going to be attracted to the cold side of the surfaces straddling the temperature differential between interior and exterior. In our case, this is the hardwood flooring. Since wood is dry and highly absorbent, you don't see the condensation on the surface. You eventually see it cup. If you're trapping enough humidity, then you're not helping your efficiency. If you need dehumidifiers and ERVs to make your more efficient house air tight and healthy, then what's the difference in letting it breathe enough to not require this energy consuming equipment and worry about quiet fans quitting or power outages? As the brilliant Canadian building scientist put it, "If you have a theoretically perfectly sealed building, then where do you put the holes?" These are the crossroads we're at right now as policy is resulting in problems that will have to be solved. The ever evolving theories of sustainable design. The more complicated we make it, the more problems we have to solve. Too bad our lifestyles keep evolving beyond our means to keep up.

-------------------------------------------
Eric Rawlings AIA
Owner
Rawlings Design, Inc.
Decatur GA
-------------------------------------------