Poured-In foam for retrofit insulation of cathedral ceiling
I have a cathedral ceiling with pickled boards. The previous owner insulated the 2×8 rafters with fiberglass and vent baffles to the ridge vent, which means about 6″ of insulation. I’m trying to avoid removing all the boards to insulate. At the top of the ceiling is a horizontal area of about 3 feet wide. If I remove just those horizontal boards (and the soffits) I have access to the cavities. I’m thinking about removing the fiberglass (easy), laying down pieces of 4-6mil poly in the cavity (because the boards have slight gaps and knots), cutting 2″ polyiso sheets to fit the bays, minus an inch or so on each side, and using pour-in closed cell urethane on top of the polyiso, letting it run down the sides to fill the side gaps. I would block the bottom of the bays 1st and access the bays from the top (they’re only about 5′ long from the horizontal opening at the top). The poly sheets would prevent any foam from getting through board gaps, the polyiso would provide the bulk of insulation, and the pour-in foam would expand up the final couple of inches to the roof sheathing (and fill in the side gaps). Any thoughts, or better way to do it?
P.S. Local foam insulators aren’t interested in doing it because they don’t want to spray up into the enclosed cavity.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part