Air ceiling edges of gypsum ceiling
I know you need to seal between the top plates and the edge of the gypsum board. On a wall perpendicular to the joists, there are obvious gaps to fill. Am I right to assume on a wall running parallel with the joists, where deadwood is employed, you need to foam between the edge of the deadwood and gypsum and possibly between pieces of deadwood if two pieces are employed for different sides?
My current insulation contractor caulks and foams all interior framing joints between and around multi-ply framing members, but, to my knowledge, they don’t seal the edges of ceilings because their sealing is done just before drywall. I read an article in JLC saying this is the lowest hanging fruit with the most bang for your buck, so I am wanting to do this on my own home and look into doing this on our future projects.
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tupchurch,
What is deadwood?
From the context I think he means blocking between joists to support an interior partition.
If the air barrier on the walls is the sheathing, and the air barrier for the ceilings is the drywall, you have to connect them somehow. The simplest way is to do it before the ceiling joists and rafters have been put on. You can run a 2' piece of Tyvek over the wall and tape it to the barrier on the wall and staple it up after the joists are in. Or you can put a 12" piece of 3/4" plywood over the top of the wall. I grew up in New England where ceilings are normally strapped with 1x3, so the plywood is the same thickness as the strapping. Either way, once the ceiling is in you go up into the attic and seal the edge to the drywall. Since the edge is about a foot out from the wall you have room to work.
But, as they say in the shipping business, and in the sailing business, that ship has sailed. The top plate of the wall is going to have to be your air barrier, and you have to seal the wall air barrier to it and also the drywall. It's not impossible, it's just more difficult because you have to get down into the eaves and the joists and rafters are in the way.