Bonus room insulation
I have a bonus room (i.e over garage) that I would like to finish. I would prefer not to use any type of blown in foam. The roof is framed with 2×6’s (12/12 pitch) and the floor to the garage space underneath is 2×8’s. The space is located in a cold climate (6). The roof is not a hip or valley roof and there is clear access from the walls to the ridge. There are colar ties about 11′ up and that is where a flat ceiling would go with the remaining 6′ above being “attic”.
I plan on using mineral wool insulation for the floor (R28 batts) and comfortboard 80 (1″) under the floor joists then strapping it with 1×4’s and 5/8″ drywall.
The roof I would like to keep as a cold roof so I would like to build site built baffles using either xps or eps foam. The issue is that if I build the baffle (1″) and keep the desired 2″ air gap I cannot use batt insulation for the remainder of the 2×6. Compressing the batt this much would not be desirable. Do I fur out the missing 1″ or do I cut and coble something into this space? I would also like to use the comfortboard 80 (2″) underneath the rafters to increase the R value or would using a rigid insulation be a better approach? How much of an R value would I realistically get? Is there a better approach not using CC blown in insulation? The remaining flat section of the ceiling would be insulated with R60 batt insulation.
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