Hi I would like to insulate between the floor joists in a crawlspace. Rigid foam and closed cell foam seem to have the same r-value but differ substantially in price. I would like to know if I could install 2-4 inches of rigid foam and then contract to seal the installation with 2″ of sprayed close cell foam? Appreciate your thoughts. Al
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If you are going to install rigid, why not just seal the rigid with Great Stuff or similar and call it a day?
I posted a similar question awhile ago. Got some good feedback. I'm now leaning towards just spraying the foam(leaning towards Tiger Foam based on recommendations). I might just go with 5-6 inches of spray. More than that might get costly without that much of an increase in insulating value. Looking forward to more comments.
My understanding is that Tiger Foam is rather expensive. Of course, it is also quick. So given a choice between rigid and Tiger, it appears the question is, "would you rather spend time or money?".
Before you make a final decision, buy a couple of sheets of foam, crawl into the crawl, and see how easy/hard it is to fit the stuff between the joists. Be sure to try some areas where there are wires and pipes.
I just did some polyisocyanate foam insulation between roof rafters with no plumbing or wiring in the way.
Twelve sheets of 1 1/2" thick X 4' X 8' sheets cost $200 at Home Depot. The cans of "Great Stuff" foam ended up costing over $100. I also installed furring strips to hold the foam in place while I used the Great Stuff foam to seal the gap around the perimeter of the foam sheets. It was about $400 for about 200 square feet.
The furring strips will also give me a place to screw into when I install the drywall "ceiling" between the rafters, so they are doing double duty.
I think the sheets of foam have a place - where you can lay them down as full sheets. If you slice and dice them to fit between rafters, you end up with so much perimeter that needs to be foamed you might as well just spray.
Installation was not difficult but it was time consuming. It did go very well and I think I did a good job. Go to the FH web site for a video tip on cutting the sheets with a sharpened-edge putty knife. It works really well.
If I had to do it again, I think I would just use spray. I used so much foam from the can it was almost silly. I say that now but recognize this, I have never used spray before. It just seems a lot simpler (overall less costly and faster). In a confined crawl space, though, it seems it would be a lot messier and difficult and might even be dangerous to do (suffocation/inhalation hazard).
I hope this helps in some way.
CC foam is about $1/bf installed typically. Rigid polyisocyanurate board is about $.65/bf for materials, plus cans of sealant and your labor. Pre-Packaged 2-part foam canisters are over $1/bf materials + labor. On most jobs, it's almost always most cost effective to sprayfoam the entire thing, assuming you have $1000+ in work for the spray foam crew to make it worthwhile to come out to the job.