Questions on creating a conditioned attic
I’ve been reading through the other questions and articles by Martin and I think I have something of a handle on my options, but I really feel like I need some expert advice before I proceed. I’m in a suburb of Chicago (Zone 5a) and just bought a house with a attic that was basically built as a 3rd floor complete with a set of stairs coming up to it. It has 8″ rafters and is currently vented. As it is, it’s pretty hot in the summer, easily over 120 degrees. The floor of the attic is insulated and has plywood over it so the current thermal envelope is to the ceiling of the 2nd floor. I would like to insulate it with spray foam to make it a conditioned attic and seal the vents as well. I have had a couple of contractors come out, both have said they would prefer to use open cell in this situation. With open cell they believe if there is a leak I would be able to quickly find out versus if I go with closed cell.
My question to everyone is what is the best way to insulate this space with the understanding that I would want to finish it in the near future? Additionally, I would want to diminish any thermal bridging and provide a thermal break by installing 2″ foam board (is 2″ necessary? can I do 1″?) on the rafters after the spray foam goes in and before the dry wall goes on, maybe in a 2nd phase before I put up drywall. Would an ignition barrier be needed right away? What is the most scientifically sound way to insulate here? Would using closed cell on the knee walls (3.5″ deep) be advisable? I’ve provided pictures below and also have provided pictures of what looks like a metal chimney pipe, I read somewhere on here that there needs to be a gap around the pipe of an inch or more? I’m not actually sure if it’s used as the furnaces and hot water heaters vent outside. Bonus question on finishing, it probably makes sense to run any electric for lighting and outlets/switches before I spray foam, correct? Thanks in advance for your responses!
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