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Community and Q&A

Red-Pen Test for Air Barrier

timot1 | Posted in General Questions on

I’m building a single family residence in WA state (zone 4 Marine).

Stegohome vapor barrier under 2×4 sleepers and T&G subfloor.  This is over a poorly finished concrete slab that has R10 XPS underneath.  I will tape perimeter of plastic to 2×6 walls (might use siga’s rissan tape) and then use Prosoco on the exterior side of the wall sealing the bottom of the plywood to CMU blocks.

**Should I add additional insulation between 2×4 flooring joists?


Wall assembly from exterior:
Hardieplank, rain screen [non-PT 3/4″ utility lumber], 2″ Roxul Comfortboard 80, Prosoco Cat 5 (my air barrier with joint and seam for fenestrations), 15/32 CDX plywood, 2×6 stud walls, cavity filled with Roxul R23 Comfortbatt, Drywall, latex paint (my class iii vapor retarder).

Wall to Roof connection:
Tape prosoco covered wall to XPS

Roof assembly: (I have 32′ spanning room-in-attic trusses and I want R49)
Shingle, 30# felt, 19/32 CDX plywood, roof trusses in cavity [1.5″ air space from eave to ridge, unfaced R38 insulation batt to fill cavity, staggered 2.5″ of XPS inside ceiling joists with “Big Gap” spray foamed edges, 3/4 furring strips, drywall, latex paint.

Do you see any causes for concern?
Is there a better way to air seal the roof? Also concerned with wall to roof transition.  I really wanted to build Risinger’s “monopoly house” but I’d need to re-engineer the trusses.  The trusses also prevent me from adding exterior insulation.

Tried to make this post brief :/

Please let me know if you need any additional info.



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  1. user-2310254 | | #1


    I'll give your post a bump.

    1. timot1 | | #3

      Thank you

  2. Expert Member
    PETER G ENGLE PE | | #2

    ** In your climate zone, adding insulation between the 2x4 floor joists is probably unnecessary, but would nearly double the effective floor insulation. And, it won't hurt anything. Pretty cheap upgrade.

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