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Options for air and water barrier and local qualified builder for this roof system

pakrat1 | Posted in GBA Pro Help on

Well here’s my dilemma, Houston TX, 50s rancher, 3/12 pitch, plank deck, 2.5’ overhangs enclosed soffits.

No working room in attic, mostly filled up with ridged AC ducts, lots of alarm wireing, max height at ridge 30″ and very limited access to eve area, <2” rock wool batt insulation in bad shape.

So will change to “conditioned” attic, and go with 5” ISO above deck, vent channel above foam, OSB or PLY top deck, underlayment and OC cool shingles.

My only options for the WRB / AIR Barrier is on primary deck or middle layer of foam unless I site build the vent channel

The Dilemma:  wrb / vb locations ?? 

 Option 1:  peal and stick on primary deck. Least labor $$, quickest dry in.  Problem is I can’t find anyone who can honestly tell me if I will get an odor from the asphalt adhesive into the living area through the ship lap deck.

Option 2:  peal and stick over bottom 3” layer of foam with Thermacal 1 with 2” iso and 1.5” vent channel over that, a lot more labor $$$ but would eliminate odor from peal and stick. screws night not seal as well due to shredding of the sealent.

Option 3: site build vent channel and put peal and stick above both layers of foam under screeds, this would give the best screw sealing ability from the Peal & Stick.  A lot trickier to build, ( anybody know a builder in Houston with this kind of experience ) Labor $$$$

Top deck will be traditional roofing system, OSB or PLY, I&W, solar reflective OC Cool shingles

Any thoughts, suggestions, 

Thanks Mike

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  1. Expert Member
    Akos | | #1

    Since you attic is unfinished, I think something like this would be cheaper/easier (assuming 2x6 rafters):
    -rafters with mineral wool batts + radiant barrier
    -ship lap
    -peel and stick
    -1.5" polyiso

    This works out to R32 for the whole assembly.

    With 1.5" rigid, you can use 3 1/2 nails, no need for long screws, way quicker to install.

    If your rafters are not deep enough, you can strap them out to 5.5" with either wood of 2" strips of foam. Strapping would still be way less work than dealing with 7" screws through 5" foam.

    If you want more R value, increase the strapping thickness. Going up to 2x8 gets you to R38, 2x10 R45.

    My wife's studio is T&G walls with peel and stick on the outside with plywood interior, so not the most air tight on the inside. Never noticed any smells. Something on the roof will get hotter so more off gassing, usually these smell do go away after a while though.

    EDIT: I miscalculated, the embed, only 1" foam with 3 1/2 nails. For 1.5" foam you need 4"

  2. pakrat1 | | #2

    The attic is virtually in accessible, see pix. The whole attic is this crowded or worse, one section has a raised ceiling totaly excluding access. What peal and stick did you on your wife's studio

  3. Expert Member
    Akos | | #3

    That is a bit tight.

    It was VP100. All peel and stick smell, I would get a sample and see how long it takes for it to off gas in the house and weather you can live with the smell during this period.

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