Spray foam over shingles?
I am renovating a ca. 1840 timber frame house, with odd-spaced rafters, one layer of board sheathing, one layer of plywood sheathing, one layer of composition shingles, minimal overhangs, and ridges that have settled a few inches. I am planning to install new rafters over the existing roof, with larger overhangs, new zip decking, synthetic underlayment, and a snap-together standing seam roof. This approach gives me a straight roof, allows me to leave the ceilings below intact, allows me to match the rafter tails on the addition I built recently, and allows insulation to be installed on top of the existing roofing.
I had planned to use EPS for insulation in between the rafters, however I’m thinking I’ll get too many gaps and it will be labor intensive. Has anyone here used closed-cell spray foam in a similar situation? It would have the advantage of being continuous plus it would get under the rafters where they clear the existing roof. It would also be quick.
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