Spray foam

Sukhoi29SU

I just received some preliminary numbers for insulation on my home project. I told the insulation rep when he visited the job site about my plan for 2” XPS foam for under slab insulation for the radiant, and he was trying to convince me that spraying 2” of foam insulation would be rigid and about the same price. He just gave me numbers to spray 2” of closed cell foam on the floor and over the plumbing , which I’d staple the pex to. Has anyone ever done this? He claims it’s about the same price as getting the 2”xps foam board. I haven’t priced it out yet.

delta T

2" XPS comes in a few varieties. You can get anything from 15 PSI compressive strength up to 100 PSI compressive strength. The engineer/architecht/AHJ should tell you what exactly you need. Ask your insulation guy to supply you with manufacturer's data about the compressive strength of the spray foam and see if it matches what you need.

hot_rod

I tried spray foam under slab one time. I was not impressed with the evenness, or lack of. I'm not sure it was as water resistant as the board type. Seem like it would be expensive? The foam installer tried to tell the homeowner on my job that 1/2 spray was equal to 1-1/2' board type?

Maybe current foam versions are better. I see some pole builders are using a foam type product to put the posts in the hole, instead of dirt or concrete.

pecmsg

hot_rod said:

I tried spray foam under slab one time. I was not impressed with the evenness, or lack of. I'm not sure it was as water resistant as the board type. Seem like it would be expensive? The foam installer tried to tell the homeowner on my job that 1/2 spray was equal to 1-1/2' board type?

Maybe current foam versions are better. I see some pole builders are using a foam type product to put the posts in the hole, instead of dirt or concrete.

https://www.youtube.com/watch?v=-EfzBhUuNZU

pecmsg

Spray foam is used on Outdoor Walk In Coolers and freezers and talk the weight loads!
http://smithmeadows.com/farm/how-to-build-a-walk-in-freezer/

Zman

This is done regularly in the Rockies. The local contractors are pretty good at getting it even, I like that they can continue it up the wall and then cut it to grade with a saw. It makes a great edge detail. R value is about 6.9 per inch, weight rating is similar to blue board and it will resist water movement. You also do not get gaps underneath like with blue board. Make sure they are using the right product. Not all are appropriate for this application.

GroundUp

Do not like. I think it's probably a better envelope than board foam and better R-value and compressive strength at the same thickness, BUT the lack of a flat surface is a total PITA. Maybe spray foam is just spendy here, but for the R value I feel the board foam is much more cost effective all around