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Vented attic insulation detail

pmartens | Posted in Plans Review on

I asked about a 2 component attic insulation package with storage space in between a few weeks ago and was thoroughly dissuaded from pursuing that design.  We are doing a remodel on an 1879 victorian in zone 5, the roof and exterior vinyl siding were done about 9 years ago so an exterior wrap is not in the cards, unfortunately.

I am wondering what you all think of the attached design detail.  I have access to the 4×8 foil faced polyiso as seconds, usually with an uneven edge or damage to the foil, at about 1/2 price.  There is a lumberyard near here that stocks this material and I have used it in several large projects with good luck.

At the juncture between stud bay and ceiling I would intend to have the SPF contractor seal the foam board into the wall spf to create a near continuous envelope all the way around the house (except for the rims joists)

My rough math puts this at about an R21+R22.4+R16.8 so a total of R60.2 which would have me well over our local new build requirement of R49.

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