Another wall-plan-question thread
Situation: Fairbanks, Alaska, heating degree days of 14,000. Building a two-story addition onto an existing house, built in ‘80.
Walls will be double-stud, filled w/ dense packed cellulose, 10” to 12” wide. Exterior siding will be T-111, as the boss wants to match the T-111 on the old house. My old walls have a 6 mil poly VB, 13” of ‘glass, then T-111.
Now for the questions:
(1) An inspector said “We only accept 6 mil poly as a VB.” Upon asking, he then said “One perm or less”, but was not familiar w/ ADA. I can fix that. Thus, a poly VB would probably be OK, but I would like to eliminate one. Given my conditions, is ADA advisable instead of poly, or is the ADA and MemBrain perhaps a better alternative? Membrain almost sounds SciFi.
(2) The bigger question is what to do on the outside. The old house has the fiberglass right against the T-111, but reading threads here indicate that I should have a WRB like Typar between the T-111 and the cellulose. If so, obviously the Typar will sit right against the T-111 and may hold liquid water against the plywood, either because of a leak or melting condensation. Too, the plywood is going to get cold; will winter condensation likely be a problem if the T-111 is stained to be vapor permeable?
(1) (a) ADA, or ADA and MemBrain for the inside.
(b) Tenoarm VB on the inside.
(2) For the outside, here are some choices.
(a) 12” of dense-packed cellulose, Typar, then T-111. Optional: Nail 8’ x 1x2s, on edge, on the T-111, one per stud bay. Leave the Typar a tad loose. The 1x2s pushing the Typar in a tad will give a little breathing room. ???
(b) 10” of dense-packed cellulose, 2” of non-foiled EPS, Typar, T-111.
(c) 12” of dense-packed cellulose, 1/2” CDX, Typar, vertical 1/2” strips on the studs, then alum, vinyl or wood siding, and live alone.
If I have the T-111 two inches from the studs because of EPS, I assume it would be wise to either have plywood sheets, inlet 1x4s, or metal cross bracing at the corners. A stain that is vapor permeable; suggestions there?
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