Question from the field… performance after cutting spray foam
Steve Hull| Posted inGeneral Questionson
Hey all,
I’m a contractor interested in building performance. It’s common practice that after installing windows and doors, you spray foam to seal the rough opening. This then gets cut back to accept drywall/trim/siding.
I’ve always wondered if cutting the spray foam affects the spray foam’s performance? Before cutting, the foam develops a nice hard skin and it seems to me that doing away with this might be a bad thing. Is there any data on this?
Thanks,
Steve
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Replies
Steve,
I've heard builders express the opinion that you just shared, but I haven't seen any research or data to back up the theory.
Here's what I do know, however: even if you have a very careful trigger finger, and manage to install just the right amount of canned spray foam around a window so that it doesn't expand beyond the plane of your framing, so that no trimming is required, the spray foam still isn't airtight. You'll still get a little air leakage -- either through pores in the foam, or due to imperfect adhesion with the framing lumber and window frame.
That's why builders obsessed with airtightness use a belt-and-suspenders approach (canned spray foam plus European tape on the interior).
Steve,
Don't ignore chinking to air seal the window frame. The new formulations really are amazing materials:
http://www.sansin.com/product/timber-tec-chinking/
I like this product, a lot.