Detailing an Overhanging Floor
This may be an easy one. Half of the second story of the house I am designing and building will be overhanging the first floor and will be posted down to bedrock. This is zone 6. I have a very tight and well insulated (R-40 walls/r-60 roof) design in mind and am considering air barriers, moisture barriers, insulation and enclosure of the part of the floor that overhangs.
I will deck with advantec, so I imagine that is my moisture barrier. I don’t plan on using rigid foam or spray foam. The rest of the house will be dense pack cellulose, so I would like to use this in the floor if I can. I would also consider rock wool. If the floor framing is 2×10, I will have 9 inches of insulation. I would then add a thermal break in the form of rockwool comfort board, for example. I hope to leave it unskirted. My questions are…
1. Is R-40 enough in this situation?
2. Should I then add another air or moisture barrier (tyvek?) on the outside of the comfort board?
3. Would strapping it out and applying metal roofing be an advisable enclosure
Thanks!
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Replies
Have you taken a look at GBA articles like this one?
https://www.greenbuildingadvisor.com/article/insulating-a-wood-framed-floor-assembly
stephenr,
1. R-40, with the rockwool as a thermal break should be fine. The comfort will depend a lot on how conductive the finished floor you choose is.
2. I don't see much benefit to having a WRB on the underside.
3. Metal roofing would work well. Some concealed faster types (like snap-lock) may sag a bit and need intermediate screws.