spray foam slab insulation

[billconner]

Had not read of this here but saw this on another site and found it interesting.

"For the past 15 years or so we've been making the recommendation to install spray foam for any insulated concrete slabs. We prefer a tamped crushed stone base and the spray foam can be installed in a fraction of the time over the entire area as compared to conventional foam board insulation.

With our material there are no seams, breaks, joints, etc. that you'd experience with foam board so the install is much more reliable. Furthermore, in its inherent qualities, it provides the vapor retarder that is typically achieved by using poly/plastic.

The added benefit is that the spray foam has a strength that is more than enough to withstand the weight of the concrete and vehicles and for basement applications - it doubles as a radon barrier!'

 

[66Caprice]

It would be a nice way to insulate under there. But we need to see if closed cell spray foam really does have the strength to be under a slab. I am going to see if there is any information out there.

 

[ConCretin]

We've seen it done a handful of times over the years although it seems strange every time. The owners always say they've done the research and claim that it's superior to board insulation. It seems to stand up fine to construction traffic and I've never heard of any problems. There are obvious advantages over uneven grades such as thickened areas or haunches due to elimination of voids. Other than that, I don't really know too much about it.

 

[billconner]

I see at least 15 psi which is over 2000 psf so should be fine. Seems it may be available up to 80 psi.

 

[mike93lx]

I'd be curious to hear from a foam manufacturer on the application

 

[PCustoms]

Around here they'll dig out the perimeter of old rubble or fieldstone foundations and spray as part of waterproofing and insulation upgrades.

 

[jblnut]

I have built a few fish houses over the years and always used spray foam and have had to trim it to fit the cavity each time. I’d be concerned that no matter how skilled the applicator is that it’d still be uneven and cause potential thin spots in the concrete.

 

[Tbender78]

I did this when I built my garage. Only been down for a couple years and not heated yet. Time will tell.

 

[ConCretin]

I have built a few fish houses over the years and always used spray foam and have had to trim it to fit the cavity each time. I’d be concerned that no matter how skilled the applicator is that it’d still be uneven and cause potential thin spots in the concrete.

Great point. It does to be somewhat uneven so I'd take that into account when establishing grades.

 

[billconner]

I don't know how much the foam varied but does it really vary more than a gravel base? Of course depending on use of space - so you plan for a slab an 1" thicker than you need - plan for 5" and at the thinnest its 4"? If its just carpentry or living space, 3" is going to hold up.

It seems the virtues are speed and vapor barrier in one. Disadvantages may be cost and some uncertainty on thickness, though it would seem hard to use a laser and knock down really high spots.

 

[jrsavoie]

If you use board insulation, be careful what you use. I've used R Control high density white board. I believe it was 2 pound density, the same as foam I have hired sprayed.

The usual pink board and blue board are bad choices. They eventually soak up moisture like a sponge. Resulting in a zero R value.

 

[pcmeiners]

If it is uneven your going to have hundreds of stress points, not good for cracks...I would go with the flat sheets.

 

[billconner]

If it is uneven your going to have hundreds of stress points, not good for cracks...I would go with the flat sheets.

Not a pro but I had same thought. I've thought smooth surface and vapor barrier, and not restraini edges, would allow it to shrink with least chance of cracks.