Baffles, Venting, and Insulating Over Top of Exterior Wall in Attic
Sorry I am unfamiliar with terminology here.
I live in Southern Ontario, and this will be an unfinished attic with insulation batts on the attic floor.
From inside to out, The roof deck has truss, then horizontally oriented spaced 1 x 3 boards, then solid plywood, then shingles. So the 1×3 boards sort of act like furring for the plywood?
Our roof has a large overhang outside, but no soffit. Inside, At the angle where the exterior wall joins the plane of the roof deck, there is a vertical oriented board about 3 inches tall (where we had thought to add soffit venting), then under that, a 3inch board oriented horizontally over top the exterior wall. This horizontal board is flush with the floor of the rest of the attic.
I’ve read how important it is to insulate over the walls, but also how important it is to not allow the insulation to touch the roof deck. Also read that it’s important to leave the vented area clear for air flow, yet provide a wind wash block.
I can’t do all of that in this small space. If I vent where we intended, the top of the exterior walls cannot be insulated because of the space needed for wind block and baffles.
The other option for venting is: the space at which the vertical board and the roof deck meet has a gap 1/8- 1/4” in several places. We were thinking of using a saw and making sure this small gap exists consistently along the top of that vertical board.
I bought Pink Styrofoam Attic Baffles (Raft-R-Mate). I can butt those to the top 1/3 of the vertical board, just inferior to the gap and this will provide the vent/baffling and wind wash.
But will it be worth it all? Such a small gap… will it provide enough venting? We do have a large mechanical roof vent and ridge vents.
If you a agree with the “gap” alternative, would I then spray foam the baffle into place? So I can get a seal and some insulation over the wall? It is very difficult to maneuver to get any seal in place in order to then place only 2-2.5 inches of batt insulation between baffle and wall plate.
Your guidance is very much appreciated!
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