CC Spray Foam is a vapor barrier, so for basement brick is it (a) ideal, or (b) a nightmare? Does brick need an air gap before foam?
[email protected]
| Posted in General Questions on
Some people say spray foam is great for basement brick because it is a vapor barrier.*
Other people say spray foam is a nightmare for basement brick because it is a vapor barrier.*
Other people say spray foam is a nightmare for basement brick because it is a vapor barrier.*
Who is right? / In what context is each true?
Would closed cell spray foam trap moisture so cause spalling?
(*closed cell, upon reaching a minimum thickness)
Rigid foam with spots of adhesive attaching it to the brick – and with spray foam at the perimeters – would have the same vapor-trapping effect.
Would it be better to attach rigid foam to the back of wooden wall framing, leaving an air gap between the brick and the foam?
—-
Toronto, double-brick 110-year-old house, no weepers.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
Despite popular opinion, closed cell foam isn't a complete vapor barrier, it's a vapor retarder, at somewhere around 1 perm at 2" and dropping the thicker it gets. But using it can definitely result in brick absorbing water, which then spalls in freezing temperatures. Martin wrote about the subject here: https://www.greenbuildingadvisor.com/article/insulating-old-brick-buildings.