OK, frame’s up, siding’s on, insulation’s in, with well-detailed vapor retarder installed in the interests of minimizing air infiltration. Then the sheetrockers go to work.
In practice, just how good/bad are they at installing the sheetrock without mangling the vapor retarder while they cut holes for outlets, fit around windows, etc.? What steps does a GC take with them to protect the careful work done in installing the VR?
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If you are really concerned with the holes created by the rockers around the elec boxes, you are supposed to use guys like these:
http://www.lessco-airtight.com/
Scroll down for a picture.
Some areas have them as part of their energy code.
Every sheetrock crew I've ever seen work is brutal to vapor barriers. Punched holes from maneuvering big sheets in tight spaces, tears from forcing the rock into tight corners, slips of the knife while cutting rock adjacent to the plastic, etc. The worst thing about it, they either don't know or don't care and won't tell anyone. I had a guy tell me once, "ah the sheetrock will seal it up". Best thing you can do is brief the supervisor stay on the job and keep a close eye out. Actually, get as many sets of eyes as you can. Sheetrockers move fast and while you are at one end of the house some guy in another corner will be trashing the vapor barrier.
Ted, there is a great article in JLC this month describing the myths and facts about this very topic and ways you can help out the vapor barrier.
When I express concern about damage to the VR, I'm not so much concerned about how much water vapor diffusion will be increased by having a tiny fraction of the overall wall surface exposed by a slit in the VR. I'm more concerned about compromising the function of the VR as an air barrier. There is a difference.A foot-long slit in the VR won't result in any substantial fraction increase in water vapor migration by diffusion through the wall, but it could create a disastrous breach for transport of water vapor and heat by convective flow (a leak).I'm thinking that it would be prudent to assume the possibility (or probability) that some SR artist will bury all sorts of punctures behind the SR when supervision is elsewhere. To compensate, the air barrier would have to be elsewhere. This could be done by putting the VR on the outside edge of the inner wall studs if double wall construction. Or it could be by careful use of Tremco sealant between framing members and taping all seams on the WRB (a good idea anyway).Any other ideas?Edit: I haven't seen the JLC article yet. Perhaps it is part of Martin's article. I browsed the online copy. I'll look at the mag tonight.Edited 6/11/2008 4:52 pm ET by DickRussell OK, I looked. Martin is talking about the misconception that housewrap is automatically an air barrier. Well, air won't go through housewrap (unless it is perforated), but it will go around it easily enough. As usually installed, there are are plenty of places left for air to go around the wrap, like at the bottom of the sheathing, where the wrap typically stops. I'll go for the statement that the wrap can be part of an air barrier system, if properly integrated with other elements of sealing up things. I've seen some articles describing use of pieces of wrap installed under the sill, then brought up over the bottom of the sheathing and the main part of the wrap covering and taped to that smaller piece.I've seen other claims that the place for the air barrier is at the inside of the wall assembly, as in the airtight drywall system. Maybe it's a matter of who's doing the work and how careful he is.
Edited 6/12/2008 8:22 am ET by DickRussell