Insulating I-joists in a garage ceiling
Hello. I have been doing some research to insulate a 2 car attached garage with a room on top. Size is approximately 27×27, new construction. This is in zone-6, Augusta Maine region, and code is R30 for floors.
The ceiling/floor is built with 16″ wood I-Joists set at 12″ on center. There are no plumbing or ducts in the space, only electrical wiring. I have air sealed the rim joist with caulking, then 2″ of Tuff-R using Great-stuff foam. With I-joists there is 16″ between the Advantech subfloor and the future sheetrock ceiling, and 13″ in the web area as chords are 2×4’s, with slightly under 12″ between the plywood webs.
Current plan is to use Roxul batts cut in half to fit between the joists. Options range from min R30 at 7.25″ thick to max R53 at 12.75″ thick. I am thinking that R46 will be acceptable, which is two layers of R23 at 11″ thick. The insulation will be installed so that it sits on the bottom chord, so there will be 3.5″ of dead air space above the insulation below the subfloor.
Also planning to put a vapor barrier below the insulation before the ceiling sheetrock, mostly to keep garage moisture from getting to the upstairs.
Not sure if I missed any information that would be important. Are there any issues with this plan, or anything that I have missed? Thank you for any hints and tips.
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