Sloped ceilings from inside: Removing drywall
We just uncovered the final instance of corner-cutting by a local/franchised insulation contractor. (T Carlson, this is the same project you and I discussed, but the situation is messier than previously thought). Rather than insulate the entire sloped ceiling between the kneewall and the top attic, this group only insulated the top portion and left the lower 3 feet of sloped ceiling entirely uninsulated (and hidden). This unscrupulous crew made a conscious decision thinking we would never notice.
For solutions to insulate the sloped ceiling, we’ve explored working from the kneewall area up, which is impossible, and also from the top attic down, which is nearly impossible. (They foamed in 4″ of polyiso in the top of the sloped ceiling bays, and there is 18″ of cellulose in the top attic.)
This leaves removing drywall and working from the inside.
The rafter bays are 2×8″. At the bottom of sloped ceiling is foam board with a 1″ air channel, and at the top of the sloped ceiling is 4″ of polyiso (2×2″ boards), foamed into place and with uneven edges. Even if we had top access, removing the foamed in polyiso would be a project. So, whatever we do will need to be made continuous with what is currently in place at the top and bottom of the slopes.
Assuming that we open roughly 2-3′ of sloped ceiling along a 40′ run of closets and bedroom, what is our best approach to get this right once and for all? We are in CZ4.
1. Make baffles from rigid foam, air seal the edges, maintain the 1″ channel, and fill the bays with batts?
2. Make baffles from rigid foam or 1/4″ plywood, maintain the 1″ channel, and spray closed cell foam (either flash and batt or 4″ of foam)?
3. Some other approach?
If we use rigid foam, what kind?
Of course we could also dense packed the sloped ceilings, but 1) this incurs moisture risk, 2) wastes the 1″ air channel we worked so hard to maintain when we moved the thermal boundary in the kneewall, below, 3) isn’t that great R value, 4) will still involve drywall repair and painting to clean.
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