Insulating stud bays: Spray closed-cell foam directly on 1×6 diagonal sheathing or use asphalt felt with air gap?
We’re renovating a historic 1935 brick home. Once the interior paster was removed from the walls, we found 1×6 diagonal sheathing (in great shape). While the stud bays are open, we’d like to add insulation to the house.
The house is framed with 2×4 (1.75×3.75 actual) studs.
My original plan was to line the stud bays with asphalt felt, leaving 1/2 to 3/4 air gap to allow the stud bay to dry out, and seal it up with 1″ of closed cell foam, and fill the rest of the bay out with open cell foam.
I’m now wondering if I could spray the closed cell foam directly on the interior side of the 1×6 diagonal sheathing without creating a moisture issue. Skipping the asphalt felt would speed up the process, and allow a bit of extra open cell foam to be applied to the bay.
The fear would be that foam application directly to the sheathing would create a moisture issue, and the sheathing rot would go unnoticed behind brick and layers of foam.
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