To tape or not to tape. That is the question.
CZ 3A (mixed humid)
I am finalizing my wall design which current works like this from the sheathing out:
– 1/2″ OSB with taped seams and Knauf Eco-Seal Plus on the interior for air barrier (will do air-tight drywall inside for a belt and suspenders approach).
– Tyvek DrainWrap with taped seams (WRB and drain-plane)
– 1/2″ foli face polyiso R-3.6.(to make sure I move the dew point outside of the sheathing)
– air gap for radiant barrier to work (the foil on the poly iso is “free” so whiy not get another R-3?)
– siding (brick and stone veneer and some Hardie plank (or equivalent)
Dupont says to not tape foam board when placed over Tyvek since:
– The board will shrink and expand stressing the tape to eventual failure
– Leaving the tape off allows the wall assembly to dry faster
However, I am not sure I agree with Dupont…
From what I understand, some tapes (including Tyvek tape) hold up pretty well on foamboard. I would prefer the tape to be foil faced, but it is more important that it hold up “forever”. Also, while the Tyvek will serve as the primary drain plane, would it hurt to use the taped foam board as one as well?
However, foil faced polyiso only has a perm rating of <.3, vs 30-50 for Tyvek, so will Tyvek DrainWrap be able to “vent” properly? I want the radiant barrier properties, but not at the cost of the sheathing and wall having moisture issues. So, maybe I do agree with Dupont.., Your thoughts?
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