1/4″ Drywall for T&G Ceiling Air Barrier?
I have a log cabin and am replacing a sheetrock ceiling in a bedroom that was damaged from a leak in the old roof which has since been replaced. I would like to install whitewashed tongue and groove pine for the ceiling and in reading about proper installation I have come to the conclusion that taped and sealed drywall is by far the most recommended air barrier to use beneath the T&G. I need the ceiling to tuck over the top of the log walls which allows for just a hair over 1″ of total thickness for the ceiling material. Because of this, I am wondering if I can use 1/4″ sheetrock against the rafters, sealed and taped, then the 3/4″ T&G over the top of that. Everything I have read suggests using 1/2 or 5/8 sheetrock for ceilings because of sagging, but if covering with T&G pine, this shouldn’t be an issue. I’m asking the question to make sure I’m not missing something significant regarding code, etc. I live in the Front Range Mountains of CO (Right on the border between zone 5 & 7). This is a flat ceiling with a sloped roof and large attic above, insulated with some blown in insulation covered with fiberglass batts. The attic is thoroughly ventilated with soffit vents in every other bay and a full-length ridge vent.
Also, FWIW, the living room and kitchen have original (1984) T&G installed over black plastic sheeting which doesn’t seem to be a recommended material as it is likely vapor barrier that can cause condensation in the attic. I will likely redo these ceilings next as the T&G is poorly installed and I’d just like to make sure I’ve got the best method figured out before I tackle those larger rooms.
Replies
With your plan you should have no issues with 1/4 inch sheetrock. As you have pointed out the T&G will "support" the sheetrock or at the very least prevent it from sagging. There's no reason you couldn't use a smart vapor barrier though (one that allows moisture to transfer instead of trapping it like plastic would)
I had a similar situation a few years back, but in my situation I had very old T&G that needed to be air sealed from above (in the attic). The T&G, in my opinion, is plenty strong as it is. In order to air seal it, i went up in the attic and laid 1" polyisocyanurate foam cut to friction fit between the joists. I used spray foam where the foam sheets hit the joists and between 8' lengths of foam. Blown in cellulose on top of it. Plenty strong, no more drafts and much warmer room according to the customer.
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Yes, As Sawdust_Steve said, there will not be any issue with 1/4 inch sheetrock. It can manage the tension created and prevent it from sagging."