Replies

1. 
   nynick | Feb 09, 2024 12:37pm | #1

   Flash applications of SF and then batt installation is a normal practice these days, if that's what you mean. Many people hate SF in any form, however. I'm not one of them.

2. Expert Member
   Michael Maines | Feb 09, 2024 02:44pm | #2

   I avoid spray foam when I can for a few reasons: it's more expensive than most other options; it glues everything it touches together--which can be seen as a benefit, but having renovated many homes, I prefer to design for disassembly and repair; it has significantly higher (negative) impact on climate change than almost every other material we use in construction; it sometimes does not cure properly, which can be a complete nightmare for homeowners.

   If you are comparing equivalent R-values, there is no advantage of using it on some walls but not others. It does have slightly higher R/in than fluffy insulation such as cellulose, fiberglass or mineral wool, so when space is very tight you might find that spray foam makes sense. But R-21 spray foam has exactly the same thermal performance as R-21 of other types of insulation. (Despite advertised claims, closed cell foam will eventually be around R-5.6/in, once air displaces the blowing agents in the foam cells.)

   I do use it in specific situations, where it is far easier and more effective than alternatives. One is old foundations, whether crawl spaces or full basements, particularly ones that are made of rough stones or of concrete too rough to attach sheets of foam to.

   Another is when converting old attics into living space and the roofing does not need to be replaced in the near future; headroom is usually very tight so creating an unvented roof with spray foam is the most effective (and cost-effective) option. But I prefer venting roofs whenever possible.