How to best insulate a garage roof with storage truss?
Hello, I’m building a 16x44ft detatched garage and workshop that will be heated with a single 240v ceiling mount electric resistance heater periodically to 65 degrees and maybe kept at 40+ degrees through the winter. I’d like to insulate it as much as I reasonably can to cut down on the heating cost and limit the carbon footprint that comes with semi conditioning it in the first place. The garage will contain at least one high voltage electric car charger, but that’s another topic.
The walls are 2×6, so Im thinking standard fiberglass batting covered with drywall will be good there. The roof is half storage truss and half vaulted scissor truss. If you’re unfamiliar, the storage truss is framed using 2×4 with another interior triangle made of 2x3s and about 5ft headroom. I would like to insulate against the roof deck with vent chutes. It looks like that only leaves about 6in of insulation space at the peak, however, so the r38 Batts I was considering may be tough to fit. Is there any better option I should consider here, such as drywall and blown cell? Should I fir down the rafters to get the cathedral batting to fit, just go with 2×6 batting all around, or something else? Cost is a big condideration, but I’m willing to wait 10-20 years for any financial payback.
Last question, how much can I realistically air seal if the ceiling were left unfinished, and is that an argument to finish it with sheetrock? Should I consider a vapor barrier? I thought about running 1″ rigid foam on the truss and blowing cell behind it, but now I’m probably going overboard, and exposed foam might be a fire hazard with the ceiling heater, right? I know, it’s just a garage, but I want to do it right, and I enjoy the comfort factor too in the summer.
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