Rigid foam insulation on ceiling
I’m finishing off a new construction room above a garage. Currently into the insulation phase, and discussing this with a contractor friend, he told me to be cautious of my plan as it might not be best.
Room has scissor trusses with energy heals at 24” on center, strapped every 16”. Plan is this…
1. Two lifts of R23 Roxul batt insulation between the trusses laying on the strapping.
2. 1” (or 3/4”) of foil-faced polyiso rigid board insulation over the entire ceiling, taped and sealed
3. Re strap under the insulation, perpendicular to the original strapping
4. Ceiling finish will be T&G pine to the strapping
I believe that this will give me an R value of >51. (R46 batts + R5 foam + air space) This is in zone 6 (Maine), min required is R49. The taped up foam will be my vapor barrier, and it’s all good, right?
Walls are 2×6 and will have Roxul batts, and there are a couple of skylights that will be sealed with 5 to 7 inches of foam insulation all around.
My contractor friend told me to be careful of the foil face board due to possible moisture problems later on. Not sure why this is, I thought that the foam was an added benefit for thermal bridging, plus I need a vapor barrier anyway, right?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part