Committee on the Environment

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 watching a video during my lunch hour that addresses many of the issues you're raising in your email, Eric, so I thought it might be worth it to share:

http://vimeo.com/37815679 - USGBC National Speaker Series: Craig, Fugate, FEMA Administratior

He speaks very eloquently about the total cost of ownership of buildings, avoiding sick building syndrome and building for resiliency.  I think you will appreciate the breadth of his arguement.

Cheers,

Ludmilla

-------------------------------------------
Ludmilla Pavlova-Gillham AIA
Senior Facilities Planner
University of Massachusetts
Amherst 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
-------------------------------------------

-------------------------------------------
Lawrence Maxwell AIA
Spacecoast Architects, P.A.
Indialantic FL
-------------------------------------------
Hi Eric, I may have some answers to the excellent questions and comments that you have raised.  First, I do want to say that i have read many of your posts on design value and appraisals and you have raised many very good issues.  I am an architect on the east central coast of Florida so am VERY familiar with humidity issues.  I also used to be a researcher on buildings in hot humid climates (there is plenty of information of heating load dominated climates, but much less on cooling load dominated climates), and unfortunately that is where us southerners get most of the information that eventually gets us into problems.

The two issues that I see here is crawl space (and maybe basements), and residential construction ventilation and sealing.  First the ventilation and sealing issue.  All things being equal, it is important to build envelopes as tightly as possible and be able to control "where the holes are" as stated by the Canadian research scientist (and I know of who you speak).  If you do not "control where the holes (in the envelope) are" it is guaranteed they will be where you least want them.  We are not building rocket ships, so even with our best efforts, there will be "holes".   One of the "holes" that we might create is for the ERV (Energy Recovery Ventilator) to bring ventilation into the house and also exhaust "bad" air from the house.  Here in may actuality lie a part of the problem.  There is actually two types of ERVs.  The common one is an "air to air heat exchanger" in that air being brought into the house, and the air being exhausted from the house passes against opposite sides of a "membrane" usually a metal, that strips heat from the warmer air and conducts it across the membrane to the be extracted from the membrane by the cooler air, as of course heat is energy, cold is just the absence of heat energy and heat energy always moves to a situation of less heat energy.  Now, in cold climates during the heating season, the air being exhausted from the house by the ERV contains the heat that was generated by the house, and uses it to warm the outside (cold, and importantly DRY) ventilation air being brought in.  Usually in those heating load dominated climates, they do not even need to run the ERV in the summer time as they can just open the windows w/o the need for AC, therefore no need to run the ERV.  When this type of ERV is used in your situation, the opposite is actually taking place.  Most of the time that you are using the ERV is during the cooling season with the AC running.  The warm air is actually the air from the outside that is being brought in and it is hot and HUMID.  You are receiving benefit from the ERV as it is stripping heat from the incoming hot air and transferring it to the outgoing cooler air so that the incoming air will not require as much cooling to reach comfort conditions.  HOWEVER, it has not removed ANY of the humidity that is in that incoming air stream BECAUSE IT CAN'T.  Therefore the incoming air is not only humid, it has even higher relative humidity as of course the relative humidity is based on the level of moisture in the air relative to its temperature.  The second type of ERV is an EERV or Enthalpy Energy Recovery Ventilator.  This exchanger removes moisture (humidity) from the incoming air stream while also transferring heat.  if you had the EERV, most likely you would not have the humidity issues.  Another important thing to remember is that dehumidification during AC season is based strictly on AC RUN TIME.  It is very important in hot humid climates to Never oversize an AC unit as the run times are reduced, therefore the dehumidification potential is also reduced.  it is important to remember that Air conditioners do not bring cooling into a house (as "cool" is only the absence of heat energy) but rather extracts heat from the house.  In an air to air air conditioner, it extracts heat energy from the inside air, "compresses" that energy so that transfer medium (the refrigerant) is raised to a higher temperature than the outside air so that the heat energy can be discharged into the warm outside air (heat energy flowing to a lesser heat energy situation).  The only difference between an air to air AC unit and a "geo-thermal" heat pump is that the heat exchange is to a "cooler" situation, therefore a more efficient heat exchange.  A  heat pump is just an air conditioner that can reverse itself so that it can discharge heat to the outside air in cooling mode or reverse itself and extract heat from the outside air and bring it into the house in heating mode.  Geo-thermal heat pumps were created because while an AC unit is a very efficient heat transfer mechanism, if there is very little available heat energy in the outside air to collect and bring into the home during the heating season, they are not very effective in many places other than say Florida.  The Geo-thermal units just tap into a ground or ground water source that has a more constant temperature throughout the entire year.  more cooling efficiency capabilities in summer, and more heating capabilities in winter.  The dehumidifiers that you mentioned are nothing more than very small air conditioners that create a cooling coil to pass humid air across cooling it to the point that the humidity condenses on the coils and drains into the bucket, and the heat that this mini air conditioner generates as part of the cooling cycle is just discharged back into the room that the unit is sitting in.  As the unit is not 100% efficient, it generates more heat as part of the function of the system and also discharges this into the room that now the home AC unit must also remove.

A way to resolve all of this is to either incorporate an EERV in lieu of the ERV, or better yet, eliminate the ERV and pipe or duct air from the outside directly to the return side of the AC unit.  In many cases this can be a small "pipe" of 2" or less (sized by the mechanical engineer), it is not all that much.  When the AC turns on air coming to the unit from the house will also have air introduced from the outside via this pipe or duct condition and dehumidify it and circulate it through out the house.  No extra fans, filters, concerns about the ERV not operating etc.  As you mentioned about a potential loss of electricity, if the ERV can't operate, NEITHER can the AC, and if for more than a short period of time, no matter how hot and humid it is outside, the house will have to be opened up or it will be come stifling inside anyway.

Now, what to do with that "extra" air that has been brought into the house?  Create small "holes" between the house and various areas of the crawl space, and a "hole" between the crawl space and the exterior (with a back draft damper).  When the AC turns on and while cooling and dehumidifying the house brings in air from the outside, the air to be ejected passes through the crawl space and helps to keep it dry.  This keeps the crawl space "ventilated" and dry, and you control "where the holes are".  I suspect that most of your moisture problem is actually not coming up from the crawl space, but rather the hardwood is just the material that is most susceptible to high humidity levels and is most likely the flooring (hence it seems that the problem is from below).  However, if there is no way to provide some way to ventilate the crawl space of basement, it will have moisture issues also.  

Hope this is helpful.

Sincerely,
Lawrence Maxwell AIA
President
Spacecoast Architects PA
Indialantic, FL


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

You must of heard Gordy's "holes" speech too. I very much appreciate your explanation/ solution and it all makes perfect sense. The damper in the crawl was the missing piece of the puzzle for me, as we talked about a similar scenario to get rid of the ERV and dehumidifier. The damper gives us the one way movement of air. I'll pass this on to the builders...

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






Original Message:
Sent: 03-22-2012 12:08
From: Lawrence Maxwell
Subject: Let it breathe or seal it tight?



-------------------------------------------
Lawrence Maxwell AIA
Spacecoast Architects, P.A.
Indialantic FL
-------------------------------------------
Hi Eric, I may have some answers to the excellent questions and comments that you have raised.  First, I do want to say that i have read many of your posts on design value and appraisals and you have raised many very good issues.  I am an architect on the east central coast of Florida so am VERY familiar with humidity issues.  I also used to be a researcher on buildings in hot humid climates (there is plenty of information of heating load dominated climates, but much less on cooling load dominated climates), and unfortunately that is where us southerners get most of the information that eventually gets us into problems.

The two issues that I see here is crawl space (and maybe basements), and residential construction ventilation and sealing.  First the ventilation and sealing issue.  All things being equal, it is important to build envelopes as tightly as possible and be able to control "where the holes are" as stated by the Canadian research scientist (and I know of who you speak).  If you do not "control where the holes (in the envelope) are" it is guaranteed they will be where you least want them.  We are not building rocket ships, so even with our best efforts, there will be "holes".   One of the "holes" that we might create is for the ERV (Energy Recovery Ventilator) to bring ventilation into the house and also exhaust "bad" air from the house.  Here in may actuality lie a part of the problem.  There is actually two types of ERVs.  The common one is an "air to air heat exchanger" in that air being brought into the house, and the air being exhausted from the house passes against opposite sides of a "membrane" usually a metal, that strips heat from the warmer air and conducts it across the membrane to the be extracted from the membrane by the cooler air, as of course heat is energy, cold is just the absence of heat energy and heat energy always moves to a situation of less heat energy.  Now, in cold climates during the heating season, the air being exhausted from the house by the ERV contains the heat that was generated by the house, and uses it to warm the outside (cold, and importantly DRY) ventilation air being brought in.  Usually in those heating load dominated climates, they do not even need to run the ERV in the summer time as they can just open the windows w/o the need for AC, therefore no need to run the ERV.  When this type of ERV is used in your situation, the opposite is actually taking place.  Most of the time that you are using the ERV is during the cooling season with the AC running.  The warm air is actually the air from the outside that is being brought in and it is hot and HUMID.  You are receiving benefit from the ERV as it is stripping heat from the incoming hot air and transferring it to the outgoing cooler air so that the incoming air will not require as much cooling to reach comfort conditions.  HOWEVER, it has not removed ANY of the humidity that is in that incoming air stream BECAUSE IT CAN'T.  Therefore the incoming air is not only humid, it has even higher relative humidity as of course the relative humidity is based on the level of moisture in the air relative to its temperature.  The second type of ERV is an EERV or Enthalpy Energy Recovery Ventilator.  This exchanger removes moisture (humidity) from the incoming air stream while also transferring heat.  if you had the EERV, most likely you would not have the humidity issues.  Another important thing to remember is that dehumidification during AC season is based strictly on AC RUN TIME.  It is very important in hot humid climates to Never oversize an AC unit as the run times are reduced, therefore the dehumidification potential is also reduced.  it is important to remember that Air conditioners do not bring cooling into a house (as "cool" is only the absence of heat energy) but rather extracts heat from the house.  In an air to air air conditioner, it extracts heat energy from the inside air, "compresses" that energy so that transfer medium (the refrigerant) is raised to a higher temperature than the outside air so that the heat energy can be discharged into the warm outside air (heat energy flowing to a lesser heat energy situation).  The only difference between an air to air AC unit and a "geo-thermal" heat pump is that the heat exchange is to a "cooler" situation, therefore a more efficient heat exchange.  A  heat pump is just an air conditioner that can reverse itself so that it can discharge heat to the outside air in cooling mode or reverse itself and extract heat from the outside air and bring it into the house in heating mode.  Geo-thermal heat pumps were created because while an AC unit is a very efficient heat transfer mechanism, if there is very little available heat energy in the outside air to collect and bring into the home during the heating season, they are not very effective in many places other than say Florida.  The Geo-thermal units just tap into a ground or ground water source that has a more constant temperature throughout the entire year.  more cooling efficiency capabilities in summer, and more heating capabilities in winter.  The dehumidifiers that you mentioned are nothing more than very small air conditioners that create a cooling coil to pass humid air across cooling it to the point that the humidity condenses on the coils and drains into the bucket, and the heat that this mini air conditioner generates as part of the cooling cycle is just discharged back into the room that the unit is sitting in.  As the unit is not 100% efficient, it generates more heat as part of the function of the system and also discharges this into the room that now the home AC unit must also remove.

A way to resolve all of this is to either incorporate an EERV in lieu of the ERV, or better yet, eliminate the ERV and pipe or duct air from the outside directly to the return side of the AC unit.  In many cases this can be a small "pipe" of 2" or less (sized by the mechanical engineer), it is not all that much.  When the AC turns on air coming to the unit from the house will also have air introduced from the outside via this pipe or duct condition and dehumidify it and circulate it through out the house.  No extra fans, filters, concerns about the ERV not operating etc.  As you mentioned about a potential loss of electricity, if the ERV can't operate, NEITHER can the AC, and if for more than a short period of time, no matter how hot and humid it is outside, the house will have to be opened up or it will be come stifling inside anyway.

Now, what to do with that "extra" air that has been brought into the house?  Create small "holes" between the house and various areas of the crawl space, and a "hole" between the crawl space and the exterior (with a back draft damper).  When the AC turns on and while cooling and dehumidifying the house brings in air from the outside, the air to be ejected passes through the crawl space and helps to keep it dry.  This keeps the crawl space "ventilated" and dry, and you control "where the holes are".  I suspect that most of your moisture problem is actually not coming up from the crawl space, but rather the hardwood is just the material that is most susceptible to high humidity levels and is most likely the flooring (hence it seems that the problem is from below).  However, if there is no way to provide some way to ventilate the crawl space of basement, it will have moisture issues also.  

Hope this is helpful.

Sincerely,
Lawrence Maxwell AIA
President
Spacecoast Architects PA
Indialantic, FL


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

-------------------------------------------
Mike Jackson FAIA
Springfield IL
-------------------------------------------

Eric,  I passed your comments on to Bill Rose, a research architect at the University of Illinois in Urbana-Champaign.  He made some observations about your particular projects, but then points everyone to a technical web site that addresses some of the major issues with crawl space design. 






Original Message:
Sent: 03-23-2012 07:15
From: Eric Rawlings
Subject: Let it breathe or seal it tight?


You must of heard Gordy's "holes" speech too. I very much appreciate your explanation/ solution and it all makes perfect sense. The damper in the crawl was the missing piece of the puzzle for me, as we talked about a similar scenario to get rid of the ERV and dehumidifier. The damper gives us the one way movement of air. I'll pass this on to the builders...

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






Original Message:
Sent: 03-22-2012 12:08
From: Lawrence Maxwell
Subject: Let it breathe or seal it tight?



-------------------------------------------
Lawrence Maxwell AIA
Spacecoast Architects, P.A.
Indialantic FL
-------------------------------------------
Hi Eric, I may have some answers to the excellent questions and comments that you have raised.  First, I do want to say that i have read many of your posts on design value and appraisals and you have raised many very good issues.  I am an architect on the east central coast of Florida so am VERY familiar with humidity issues.  I also used to be a researcher on buildings in hot humid climates (there is plenty of information of heating load dominated climates, but much less on cooling load dominated climates), and unfortunately that is where us southerners get most of the information that eventually gets us into problems.

The two issues that I see here is crawl space (and maybe basements), and residential construction ventilation and sealing.  First the ventilation and sealing issue.  All things being equal, it is important to build envelopes as tightly as possible and be able to control "where the holes are" as stated by the Canadian research scientist (and I know of who you speak).  If you do not "control where the holes (in the envelope) are" it is guaranteed they will be where you least want them.  We are not building rocket ships, so even with our best efforts, there will be "holes".   One of the "holes" that we might create is for the ERV (Energy Recovery Ventilator) to bring ventilation into the house and also exhaust "bad" air from the house.  Here in may actuality lie a part of the problem.  There is actually two types of ERVs.  The common one is an "air to air heat exchanger" in that air being brought into the house, and the air being exhausted from the house passes against opposite sides of a "membrane" usually a metal, that strips heat from the warmer air and conducts it across the membrane to the be extracted from the membrane by the cooler air, as of course heat is energy, cold is just the absence of heat energy and heat energy always moves to a situation of less heat energy.  Now, in cold climates during the heating season, the air being exhausted from the house by the ERV contains the heat that was generated by the house, and uses it to warm the outside (cold, and importantly DRY) ventilation air being brought in.  Usually in those heating load dominated climates, they do not even need to run the ERV in the summer time as they can just open the windows w/o the need for AC, therefore no need to run the ERV.  When this type of ERV is used in your situation, the opposite is actually taking place.  Most of the time that you are using the ERV is during the cooling season with the AC running.  The warm air is actually the air from the outside that is being brought in and it is hot and HUMID.  You are receiving benefit from the ERV as it is stripping heat from the incoming hot air and transferring it to the outgoing cooler air so that the incoming air will not require as much cooling to reach comfort conditions.  HOWEVER, it has not removed ANY of the humidity that is in that incoming air stream BECAUSE IT CAN'T.  Therefore the incoming air is not only humid, it has even higher relative humidity as of course the relative humidity is based on the level of moisture in the air relative to its temperature.  The second type of ERV is an EERV or Enthalpy Energy Recovery Ventilator.  This exchanger removes moisture (humidity) from the incoming air stream while also transferring heat.  if you had the EERV, most likely you would not have the humidity issues.  Another important thing to remember is that dehumidification during AC season is based strictly on AC RUN TIME.  It is very important in hot humid climates to Never oversize an AC unit as the run times are reduced, therefore the dehumidification potential is also reduced.  it is important to remember that Air conditioners do not bring cooling into a house (as "cool" is only the absence of heat energy) but rather extracts heat from the house.  In an air to air air conditioner, it extracts heat energy from the inside air, "compresses" that energy so that transfer medium (the refrigerant) is raised to a higher temperature than the outside air so that the heat energy can be discharged into the warm outside air (heat energy flowing to a lesser heat energy situation).  The only difference between an air to air AC unit and a "geo-thermal" heat pump is that the heat exchange is to a "cooler" situation, therefore a more efficient heat exchange.  A  heat pump is just an air conditioner that can reverse itself so that it can discharge heat to the outside air in cooling mode or reverse itself and extract heat from the outside air and bring it into the house in heating mode.  Geo-thermal heat pumps were created because while an AC unit is a very efficient heat transfer mechanism, if there is very little available heat energy in the outside air to collect and bring into the home during the heating season, they are not very effective in many places other than say Florida.  The Geo-thermal units just tap into a ground or ground water source that has a more constant temperature throughout the entire year.  more cooling efficiency capabilities in summer, and more heating capabilities in winter.  The dehumidifiers that you mentioned are nothing more than very small air conditioners that create a cooling coil to pass humid air across cooling it to the point that the humidity condenses on the coils and drains into the bucket, and the heat that this mini air conditioner generates as part of the cooling cycle is just discharged back into the room that the unit is sitting in.  As the unit is not 100% efficient, it generates more heat as part of the function of the system and also discharges this into the room that now the home AC unit must also remove.

A way to resolve all of this is to either incorporate an EERV in lieu of the ERV, or better yet, eliminate the ERV and pipe or duct air from the outside directly to the return side of the AC unit.  In many cases this can be a small "pipe" of 2" or less (sized by the mechanical engineer), it is not all that much.  When the AC turns on air coming to the unit from the house will also have air introduced from the outside via this pipe or duct condition and dehumidify it and circulate it through out the house.  No extra fans, filters, concerns about the ERV not operating etc.  As you mentioned about a potential loss of electricity, if the ERV can't operate, NEITHER can the AC, and if for more than a short period of time, no matter how hot and humid it is outside, the house will have to be opened up or it will be come stifling inside anyway.

Now, what to do with that "extra" air that has been brought into the house?  Create small "holes" between the house and various areas of the crawl space, and a "hole" between the crawl space and the exterior (with a back draft damper).  When the AC turns on and while cooling and dehumidifying the house brings in air from the outside, the air to be ejected passes through the crawl space and helps to keep it dry.  This keeps the crawl space "ventilated" and dry, and you control "where the holes are".  I suspect that most of your moisture problem is actually not coming up from the crawl space, but rather the hardwood is just the material that is most susceptible to high humidity levels and is most likely the flooring (hence it seems that the problem is from below).  However, if there is no way to provide some way to ventilate the crawl space of basement, it will have moisture issues also.  

Hope this is helpful.

Sincerely,
Lawrence Maxwell AIA
President
Spacecoast Architects PA
Indialantic, FL


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

If you are interested in hearing Bill Rose speak on moisture control, register for the free (for everyone) webinar:

Research, Building Science and Architecture

Earn 1 HSW CEH ' May 7th ' 12-1pm ET ' 9-10am PT ' Register Now at No Cost

The subject of the webinar is building science and research on buildings, and how building science has been accepted within the architecture community. The webinar will draw heavily on writings and examples from throughout the 20th century, with particular emphasis on research before and after World War II. It will track how the architecture literature of the time described the integration of science and research into architecture. It will touch on the variety of research, including behavioral, health, history, and technology.

The principal example will be the science and research that led to prescriptive measures of moisture control such as vapor barriers and attic ventilation. The webinar will trace how these measures were introduced (by an architect!), codified, applied, challenged, and changed over time. The example will be used to illustrate how architects participate in the research process, and how they apply the products of research.

This is a part of the AIA Housing Knowledge Community research webinar series. See the complete series archive at http://www.aia.org/housing. You may have already registered under its working title was "Behavioral and Technical Housing Research."

-------------------------------------------
Kathleen Simpson
Manager, Knowledge Communities
The American Institute of Architects
Washington DC
-------------------------------------------






Original Message:
Sent: 03-26-2012 16:44
From: Mike Jackson
Subject: Let it breathe or seal it tight?



-------------------------------------------
Mike Jackson FAIA
Springfield IL
-------------------------------------------

Eric,  I passed your comments on to Bill Rose, a research architect at the University of Illinois in Urbana-Champaign.  He made some observations about your particular projects, but then points everyone to a technical web site that addresses some of the major issues with crawl space design. 

Hello Eric,

Crawl spaces are historically quite troublesome. I am sorry that you have trouble with cupping floors. It's always risky to try to offer advice from a distance without seeing the actual conditions. Let me offer a few observations anyway.

Wood floors may cup for many reasons, and by seeing which floors are cupped and which are not can help with a diagnosis. "Cupping" may mean that the underside is swelled with respect to the top. Of all the things that could cause this, my guess is higher-than-desired humidity in the crawl space. This is usually verified with temperature and humidity loggers like the "hobo" loggers from Onset Corporation. You convert the temperature and relative humidity to a measure of absolute humidity such as vapor pressure or dewpoint, and compare the absolute humidity of the crawl space to the living space. Any website that describes psychrometric relations can guide how to do this conversion.

You say the crawl space is sealed with only a termite inspection strip exposed. Let me guess--the crawl space walls are block, and the sill plate is a pressure treated 2x6 which is exposed, and the cores of the block are open at the top into the crawl space. (I could be quite wrong on this, of course.) Exposed cores will feed a lot of humidity into the space. Open-cell insulation under the floor will allow the underside of the floor to "see" the crawl space humidity. If the cores are open, block them with closed-cell foam. See if there are any traces of water entering into the crawl space onto the top of the membrane--that could also be part of the problem.

It's far more economical to find the humidity source and stop it, than to run a dehumidifier or recovery ventilator. The terminology I use is HRV for a ventilator (aluminum core) which transfers heat only, and ERV for a ventilator (nylon core or desiccant wheel) that transfers humidity as well as heat. 

It's hard to justify putting holes of any kind in a house. I hope this helps.

Bill Rose

(principal author of the Technology Assessment Report at crawlspaces.org)

Original Message:
Sent: 03-23-2012 07:15
From: Eric Rawlings
Subject: Let it breathe or seal it tight?


You must of heard Gordy's "holes" speech too. I very much appreciate your explanation/ solution and it all makes perfect sense. The damper in the crawl was the missing piece of the puzzle for me, as we talked about a similar scenario to get rid of the ERV and dehumidifier. The damper gives us the one way movement of air. I'll pass this on to the builders...

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






Original Message:
Sent: 03-22-2012 12:08
From: Lawrence Maxwell
Subject: Let it breathe or seal it tight?



-------------------------------------------
Lawrence Maxwell AIA
Spacecoast Architects, P.A.
Indialantic FL
-------------------------------------------
Hi Eric, I may have some answers to the excellent questions and comments that you have raised.  First, I do want to say that i have read many of your posts on design value and appraisals and you have raised many very good issues.  I am an architect on the east central coast of Florida so am VERY familiar with humidity issues.  I also used to be a researcher on buildings in hot humid climates (there is plenty of information of heating load dominated climates, but much less on cooling load dominated climates), and unfortunately that is where us southerners get most of the information that eventually gets us into problems.

The two issues that I see here is crawl space (and maybe basements), and residential construction ventilation and sealing.  First the ventilation and sealing issue.  All things being equal, it is important to build envelopes as tightly as possible and be able to control "where the holes are" as stated by the Canadian research scientist (and I know of who you speak).  If you do not "control where the holes (in the envelope) are" it is guaranteed they will be where you least want them.  We are not building rocket ships, so even with our best efforts, there will be "holes".   One of the "holes" that we might create is for the ERV (Energy Recovery Ventilator) to bring ventilation into the house and also exhaust "bad" air from the house.  Here in may actuality lie a part of the problem.  There is actually two types of ERVs.  The common one is an "air to air heat exchanger" in that air being brought into the house, and the air being exhausted from the house passes against opposite sides of a "membrane" usually a metal, that strips heat from the warmer air and conducts it across the membrane to the be extracted from the membrane by the cooler air, as of course heat is energy, cold is just the absence of heat energy and heat energy always moves to a situation of less heat energy.  Now, in cold climates during the heating season, the air being exhausted from the house by the ERV contains the heat that was generated by the house, and uses it to warm the outside (cold, and importantly DRY) ventilation air being brought in.  Usually in those heating load dominated climates, they do not even need to run the ERV in the summer time as they can just open the windows w/o the need for AC, therefore no need to run the ERV.  When this type of ERV is used in your situation, the opposite is actually taking place.  Most of the time that you are using the ERV is during the cooling season with the AC running.  The warm air is actually the air from the outside that is being brought in and it is hot and HUMID.  You are receiving benefit from the ERV as it is stripping heat from the incoming hot air and transferring it to the outgoing cooler air so that the incoming air will not require as much cooling to reach comfort conditions.  HOWEVER, it has not removed ANY of the humidity that is in that incoming air stream BECAUSE IT CAN'T.  Therefore the incoming air is not only humid, it has even higher relative humidity as of course the relative humidity is based on the level of moisture in the air relative to its temperature.  The second type of ERV is an EERV or Enthalpy Energy Recovery Ventilator.  This exchanger removes moisture (humidity) from the incoming air stream while also transferring heat.  if you had the EERV, most likely you would not have the humidity issues.  Another important thing to remember is that dehumidification during AC season is based strictly on AC RUN TIME.  It is very important in hot humid climates to Never oversize an AC unit as the run times are reduced, therefore the dehumidification potential is also reduced.  it is important to remember that Air conditioners do not bring cooling into a house (as "cool" is only the absence of heat energy) but rather extracts heat from the house.  In an air to air air conditioner, it extracts heat energy from the inside air, "compresses" that energy so that transfer medium (the refrigerant) is raised to a higher temperature than the outside air so that the heat energy can be discharged into the warm outside air (heat energy flowing to a lesser heat energy situation).  The only difference between an air to air AC unit and a "geo-thermal" heat pump is that the heat exchange is to a "cooler" situation, therefore a more efficient heat exchange.  A  heat pump is just an air conditioner that can reverse itself so that it can discharge heat to the outside air in cooling mode or reverse itself and extract heat from the outside air and bring it into the house in heating mode.  Geo-thermal heat pumps were created because while an AC unit is a very efficient heat transfer mechanism, if there is very little available heat energy in the outside air to collect and bring into the home during the heating season, they are not very effective in many places other than say Florida.  The Geo-thermal units just tap into a ground or ground water source that has a more constant temperature throughout the entire year.  more cooling efficiency capabilities in summer, and more heating capabilities in winter.  The dehumidifiers that you mentioned are nothing more than very small air conditioners that create a cooling coil to pass humid air across cooling it to the point that the humidity condenses on the coils and drains into the bucket, and the heat that this mini air conditioner generates as part of the cooling cycle is just discharged back into the room that the unit is sitting in.  As the unit is not 100% efficient, it generates more heat as part of the function of the system and also discharges this into the room that now the home AC unit must also remove.

A way to resolve all of this is to either incorporate an EERV in lieu of the ERV, or better yet, eliminate the ERV and pipe or duct air from the outside directly to the return side of the AC unit.  In many cases this can be a small "pipe" of 2" or less (sized by the mechanical engineer), it is not all that much.  When the AC turns on air coming to the unit from the house will also have air introduced from the outside via this pipe or duct condition and dehumidify it and circulate it through out the house.  No extra fans, filters, concerns about the ERV not operating etc.  As you mentioned about a potential loss of electricity, if the ERV can't operate, NEITHER can the AC, and if for more than a short period of time, no matter how hot and humid it is outside, the house will have to be opened up or it will be come stifling inside anyway.

Now, what to do with that "extra" air that has been brought into the house?  Create small "holes" between the house and various areas of the crawl space, and a "hole" between the crawl space and the exterior (with a back draft damper).  When the AC turns on and while cooling and dehumidifying the house brings in air from the outside, the air to be ejected passes through the crawl space and helps to keep it dry.  This keeps the crawl space "ventilated" and dry, and you control "where the holes are".  I suspect that most of your moisture problem is actually not coming up from the crawl space, but rather the hardwood is just the material that is most susceptible to high humidity levels and is most likely the flooring (hence it seems that the problem is from below).  However, if there is no way to provide some way to ventilate the crawl space of basement, it will have moisture issues also.  

Hope this is helpful.

Sincerely,
Lawrence Maxwell AIA
President
Spacecoast Architects PA
Indialantic, FL


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

Really enlightening postings Eric on the issues you have encountered, and Lawrence on ERV's and Crawlspaces!

The information appears to echo Advanced Energy's crawlspace information at http://www.crawlspaces.org/ 

Advanced Energy also addressed some ERV issues in this article.  http://www.advancedenergy.org/buildings/knowledge_library/ventilation/erv.pdf I did not see a publication date but I think I first read it a few years ago - maybe sometime in 2008 to 2010 - so it should still be relevant.

Reading this article in Home Energy http://www.homeenergy.org/show/article/nav/hvac/id/639 let me to David Butler at http://www.optimalbuilding.com/. I really like a quiet variable speed blower that runs almost continuously on low in the summer in the smallest sized system to meet the loads. David serves as an HVAC consultant on many of my residential design projects throughout the US. I knew about the issues with oversized AC systems as they especially relate to the inability to remove humidity, but David is better able to communicate that information directly to HVAC subcontractors that he may interact with in the course of his consulting.  He also enjoys getting into details directly with the technically-oriented clients.

-------------------------------------------
Debra Rucker Coleman, AIA
Architect
Sun Plans Inc.
Mobile, AL

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






Original Message:
Sent: 03-22-2012 12:08
From: Lawrence Maxwell
Subject: Let it breathe or seal it tight?



-------------------------------------------
Lawrence Maxwell AIA
Spacecoast Architects, P.A.
Indialantic FL
-------------------------------------------
Hi Eric, I may have some answers to the excellent questions and comments that you have raised.  First, I do want to say that i have read many of your posts on design value and appraisals and you have raised many very good issues.  I am an architect on the east central coast of Florida so am VERY familiar with humidity issues.  I also used to be a researcher on buildings in hot humid climates (there is plenty of information of heating load dominated climates, but much less on cooling load dominated climates), and unfortunately that is where us southerners get most of the information that eventually gets us into problems.

The two issues that I see here is crawl space (and maybe basements), and residential construction ventilation and sealing.  First the ventilation and sealing issue.  All things being equal, it is important to build envelopes as tightly as possible and be able to control "where the holes are" as stated by the Canadian research scientist (and I know of who you speak).  If you do not "control where the holes (in the envelope) are" it is guaranteed they will be where you least want them.  We are not building rocket ships, so even with our best efforts, there will be "holes".   One of the "holes" that we might create is for the ERV (Energy Recovery Ventilator) to bring ventilation into the house and also exhaust "bad" air from the house.  Here in may actuality lie a part of the problem.  There is actually two types of ERVs.  The common one is an "air to air heat exchanger" in that air being brought into the house, and the air being exhausted from the house passes against opposite sides of a "membrane" usually a metal, that strips heat from the warmer air and conducts it across the membrane to the be extracted from the membrane by the cooler air, as of course heat is energy, cold is just the absence of heat energy and heat energy always moves to a situation of less heat energy.  Now, in cold climates during the heating season, the air being exhausted from the house by the ERV contains the heat that was generated by the house, and uses it to warm the outside (cold, and importantly DRY) ventilation air being brought in.  Usually in those heating load dominated climates, they do not even need to run the ERV in the summer time as they can just open the windows w/o the need for AC, therefore no need to run the ERV.  When this type of ERV is used in your situation, the opposite is actually taking place.  Most of the time that you are using the ERV is during the cooling season with the AC running.  The warm air is actually the air from the outside that is being brought in and it is hot and HUMID.  You are receiving benefit from the ERV as it is stripping heat from the incoming hot air and transferring it to the outgoing cooler air so that the incoming air will not require as much cooling to reach comfort conditions.  HOWEVER, it has not removed ANY of the humidity that is in that incoming air stream BECAUSE IT CAN'T.  Therefore the incoming air is not only humid, it has even higher relative humidity as of course the relative humidity is based on the level of moisture in the air relative to its temperature.  The second type of ERV is an EERV or Enthalpy Energy Recovery Ventilator.  This exchanger removes moisture (humidity) from the incoming air stream while also transferring heat.  if you had the EERV, most likely you would not have the humidity issues.  Another important thing to remember is that dehumidification during AC season is based strictly on AC RUN TIME.  It is very important in hot humid climates to Never oversize an AC unit as the run times are reduced, therefore the dehumidification potential is also reduced.  it is important to remember that Air conditioners do not bring cooling into a house (as "cool" is only the absence of heat energy) but rather extracts heat from the house.  In an air to air air conditioner, it extracts heat energy from the inside air, "compresses" that energy so that transfer medium (the refrigerant) is raised to a higher temperature than the outside air so that the heat energy can be discharged into the warm outside air (heat energy flowing to a lesser heat energy situation).  The only difference between an air to air AC unit and a "geo-thermal" heat pump is that the heat exchange is to a "cooler" situation, therefore a more efficient heat exchange.  A  heat pump is just an air conditioner that can reverse itself so that it can discharge heat to the outside air in cooling mode or reverse itself and extract heat from the outside air and bring it into the house in heating mode.  Geo-thermal heat pumps were created because while an AC unit is a very efficient heat transfer mechanism, if there is very little available heat energy in the outside air to collect and bring into the home during the heating season, they are not very effective in many places other than say Florida.  The Geo-thermal units just tap into a ground or ground water source that has a more constant temperature throughout the entire year.  more cooling efficiency capabilities in summer, and more heating capabilities in winter.  The dehumidifiers that you mentioned are nothing more than very small air conditioners that create a cooling coil to pass humid air across cooling it to the point that the humidity condenses on the coils and drains into the bucket, and the heat that this mini air conditioner generates as part of the cooling cycle is just discharged back into the room that the unit is sitting in.  As the unit is not 100% efficient, it generates more heat as part of the function of the system and also discharges this into the room that now the home AC unit must also remove.

A way to resolve all of this is to either incorporate an EERV in lieu of the ERV, or better yet, eliminate the ERV and pipe or duct air from the outside directly to the return side of the AC unit.  In many cases this can be a small "pipe" of 2" or less (sized by the mechanical engineer), it is not all that much.  When the AC turns on air coming to the unit from the house will also have air introduced from the outside via this pipe or duct condition and dehumidify it and circulate it through out the house.  No extra fans, filters, concerns about the ERV not operating etc.  As you mentioned about a potential loss of electricity, if the ERV can't operate, NEITHER can the AC, and if for more than a short period of time, no matter how hot and humid it is outside, the house will have to be opened up or it will be come stifling inside anyway.

Now, what to do with that "extra" air that has been brought into the house?  Create small "holes" between the house and various areas of the crawl space, and a "hole" between the crawl space and the exterior (with a back draft damper).  When the AC turns on and while cooling and dehumidifying the house brings in air from the outside, the air to be ejected passes through the crawl space and helps to keep it dry.  This keeps the crawl space "ventilated" and dry, and you control "where the holes are".  I suspect that most of your moisture problem is actually not coming up from the crawl space, but rather the hardwood is just the material that is most susceptible to high humidity levels and is most likely the flooring (hence it seems that the problem is from below).  However, if there is no way to provide some way to ventilate the crawl space of basement, it will have moisture issues also.  

Hope this is helpful.

Sincerely,
Lawrence Maxwell AIA
President
Spacecoast Architects PA
Indialantic, FL


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