Methods for air sealing the ceiling
We are building in a cold climate, zone 7, using ICF walls. Because the walls are ICF, they act as an air barrier, but I’m trying to figure out the best way to air seal the ceiling. Based on what I’ve read on this site, I’m following a few guidelines:
- Ceiling will be flat, using energy heel trusses
- Using blown in cellulose, thinking around R-60
- No recessed lighting (thanks Martin)
We will obviously need J-boxes for ceiling lights along with ceiling fans, and I’d of course like these to penetrate the air barrier as little as possible. There will need to be a couple pipe penetrations for the plumbing stacks.
It seems to me like there are several methods for creating an air barrier, and I’m trying to weigh the pros/cons of each:
- Use a sheet of polyethylene above the drywall. This seems to be the most common method in this area (zone 7), although I’m not sure how well it really ends up sealing in practice because of punctures. How easy is it and what is the best method to seal around all the punctures from connecting the partition walls?
- Do the same thing but use a “newer” membrane product?
- Airtight drywall approach. Requires caulking around J-boxes.
- Use a wiring chase. Attach OSB to the underside of the roof trusses and tape the seams with Siga Wigluv or similar. The OSB is the air barrier. Affix 2x4s which the drywall attaches to and creates a 1.5″ ceiling wiring chase in which you don’t have to worry about air sealing. Would cost more in materials because of the extra layer of OSB and you would lose some headroom.
Any others? I’m looking to figure out what would be the easiest way to have someone do some good air sealing that will last for the long term. Thanks for the advice.
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