Tom Jordan is a painting contractor in northern New Jersey who’s at his wit’s end as he tries to figure out a remodeling job at his own home.
It seems simple enough. Jordan is turning a three-season room on his 1930s house into a fully conditioned space. The room measures 12 feet by 16 feet and has an 8-foot ceiling. The flat roof overhead is framed in full-depth 2x6s, finished with what Jordan believes is roll roofing (a type of asphalt roofing).
“My issue is how to correctly insulate the ceiling,” he writes in a Q&A post. “I’ve spent what seems like hundreds of hours online and had a few insulation contractors look at the room, and I can’t believe the inconsistencies that exist on this subject.”
In Climate Zone 5, the prescriptive table of the International Residential Code requires at least R-49 of ceiling insulation. With 2×6 rafters, that’s a tall order, and Jordan adds a couple of major caveats.
“The roof is only four years old, so removing it is not an option,” he says, ruling out a layer of exterior rigid foam. “The room does not have any venting, nor is it possible to vent … Before anyone suggests closed-cell spray foam, I’m ruling that out. I have no confidence in the ‘healthiness’ of the product. It might be a great product, but I don’t want it in my house.”
Those are the ground rules for this Q&A Spotlight.
You need exterior insulation
Convenient or not, Jordan will need exterior insulation over the roof sheathing in order to meet code minimums, says Ryan Lewis, advice that is seconded by GBA editor Martin Holladay. And it will be important to maintain the correct ratio of interior to exterior insulation.