Retrofitting a Vented Roof for Insulation and Air-Sealing
I have been hired by a client to insulate a 3 season cottage (exposed studs and rafters) in Maine, zone 6. Basically, it was built and inspected, and now he wants to insulate it. Here are the details, followed by some questions.
It has been built traditionally with 2×4 walls, plywood sheathing, hydrogap wrap and clapboards. No tape or any modern air sealing measures were taken. The floor and rafters are 2×10 and the ceiling is cathedral (7/12) with a sleeping loft. We plan to use rock wool in the bays all the way around and call it good. The interior is to be finished with horizontal shiplap.
I plan to retrofit a vented roof by ripping one inch boards and installing a sheet product in between the bays creating 1 inch channels. I am thinking of using 3/8 plywood for this but am open to suggestions. I plan on caulking this plywood in to create an air seal to prevent moisture from migrating towards the sheathing from the interior. Would it also be wise to caulk the sheathing and blocking from the inside before I build the channels? I am pretty sure that the roofer laid ice and water shield on the entire roof before putting down architectural shingles on the 7/12 pitch. I will cut a ridge vent in in the spring and do soffit vents.
I am hoping not to have to hang drywall before I lay shiplap on the interior walls and ceiling. Would installing a smart membrane, or some other product, be a way to avoid having to do this?? Would the air sealing that I am doing with my venting channels protect the sheathing from getting wet from vapor from the interior and mean that I was safe to simply lay shiplap??
Thanks for your input.
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