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Building envelope and floor deck in the south

  • 1.  Building envelope and floor deck in the south

    Posted 04-24-2017 08:52

    Looking for some feedback on designing a single family residence in Florida. I have only done SFR work in the northeast. Here is what I was thinking...

    Exterior Envelope (from outside-in) - Stucco finish on CMU. 1" closed cell spray foam, metal studs with mineral wool insulation, drywall.
    Questions - Do I have the insulation in the correct location? What R Value above code is optimal? Thoughts on type of window frames in this hot and humid condition?

    I notice that many homes have CMU walls on the first floor and wood frame for the second floor deck and exterior walls. What would be the pros/cons of going with a concrete deck on the second floor?

    Appreciate any feedback and good supplemental reading materials.

    Graham Ruggie
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  • 2.  RE: Building envelope and floor deck in the south

    Posted 04-25-2017 17:40
    Have you looked at Building Science  Corpration website?  They typically have "ideal wall" sections for just about every climate in the country.  There's a lot of information on their site, and it may take some digging to find something to fit your situation, but I find them to be a great resource:

    Phil Terzis AIA, LEED AP
    VP Project Planning
    Acorn Holdings LLC 
    One Gateway Center, Suite 805
    Newton, MA  02458

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  • 3.  RE: Building envelope and floor deck in the south

    Posted 04-27-2017 10:19



    I agree with Phil. 


    A couple of BSC resources I would recommend include the Builders Guide to Hot-Humid Climates and ETW: Building Profiles.  There is a profile for Orlando but it focuses on SIPS.  What I've found beneficial is looking at profiles in both similar and different climate zones to arrive at a decision.


    Bob Magoon


    Coastal Residential Design PLLC


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  • 4.  RE: Building envelope and floor deck in the south

    Posted 06-02-2017 13:46

    Hello Graham,


    I worked in the Orlando area as a licensed Architect for 23 years.  The members in ArCH (Architects Creating Homes), who are licensed Architects who specialize in the design of residential architecture would likely try to be nice, but the short answer is "No."  While what you're proposing is much better than the old-school CMU with insulation poured into its cells, I believe you can do far better.  All the leading pundits of insulation (including Building Science Corporation) and all of my 2017 CEU providers (and the latest IECC) have a consensus that you really should be using C.I. (Continuous Insulation) over the exterior most hard structural layer (which in your case is the CMU).  They all say that the tendency for moisture to collect inboard of that location often results in mold, of which there is an epidemic in this Country (and the world).  And what stops the dew point from occurring inside the CMU or the stud cavities is the presence of Continuous Insulation outboard of the structural sheathing/CMU. What you are proposing would probably work just fine as far as the studs are concerned, because you have the foam outboard of that, but I'd bet that your dew point will end up inside the CMU cells, generating possible mold and even moisture leakage at the base of the wall.  I'm going to suggest that you consider putting rigid insulation (like polyisocyanurate) screwed or adhered directly to the exterior face of the CMU, then adhere or screw 15# asphaltic felt as a water barrier (without which, most stucco finishes eventually leak), then screw a 1/4" synthetic drainage plane (See Benjamin Obdyke) with weeps at the bottom (and insect screening), over than, then screw galvanized metal lath to that (if you want stucco), or even the newer breed of synthetic laths, then stucco over that, if you really want stucco.  Make sure you use SCJ (Stucco Control Joints) more frequently than you think you need to, as stucco cracks, just about anywhere.  And make your stucco at least 7/8" thick.  After curing, use an elastomeric paint over it. You could also then use a less expensive wall section, with fiberglass batts in the stud wall (see below).  The key difference to the troubled Dryvit-like materials was the lack of a drainage plane and the inherent tendency for the exposed face of the stucco to leak over time.


    However, I'd have to ask you, if you're doing to all that trouble, why even use the CMU at all?  Probably less costly to just go with a stud wall (with fiberglass insulation), with 15/32" OSB glued and screwed structural sheathing, then the CI rigid foam insulation over that, then the asphaltic felt (water barrier, with joints taped so it also functions as an air barrier), then the Ben Obdyke drainage plane, then the lath, the stucco, and quality paint.


    CMU was a material of choice in FL dating back into the 1950s.  Just because a lot of people did it back then, doesn't mean it can't be improved upon these days.  Unless you're trying to make an architectural statement with exposed block (Like Nils Schweizer, FAIA did on his Winter Park HQ), you might be better with stud construction, as long as you get it up above the termite zone.  I think the key here is the CI, which is what Energy Codes are trying to pound into our heads.  But do what works for you.  I'm sure there's going to be a diversity of opinions on this subject.


    Rand Soellner  Architect     ArCH /NCARB /LHI /MA Arch


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