There is actually a house that is under construction in Rockford Illinois that have a Swedish inspired shallow foundation
http://blog.lamidesign.com/2012/03/all-about-swedish-standard-house.html

Have you guys done ANY seismic work on these types of foundations?

What are the "seismic issues"? My understanding is that a monolithic, thickened edge slab is common in California. Surrounding it with foam shouldn't change things.

we only have building codes for wind and snow to consider in sweden not earthquakes

My understanding is that a monolithic, thickened edge slab is common in California. Surrounding it with foam shouldn't change things.

I don't even know what happens to slabs in a good roller. In my mind, I see the friction coefficient between the smooth surfaced foam and the underlying small gravel as being much smaller than that between an aggregate slab and the underlying ground or gravel in the slabs we are familiar with.

"The best argument for using XPS under slabs comes from radiant heating contractors, because XPS has much better retention than EPS for the staples used for holding the PEX in place, which makes the heating installation easier. If it's not a radiant-slab, go with EPS and be happy!"

What about two layers, one EPS at ground and an XPS on top to staple to?

Wouldn't be worth the effort. The holding power of the staples are unimportant as soon as the slab is poured. The best argument for EPS is that XPS has a high greenhouse gas burden.

And that EPS costs less per R value.

Hi, guys. First post on here.

Is there a reason that no one's using PolyUrethane for underslab/footing insulation? Thanks.

yes; it absorbs water which lowers the R value. Use EPS which doesn't.

Thanks for answering, Bob.

Could you point me to some studies or something to substantiate that? Everything I read leads me to think that PUR is a no-brainer for above-ground wall insulation. It even mentions water permeability as one of its strengths vs EPS.

It therefore doesn't make sense that it's not used under basements, but it's not.

Any solid info to clear this up would help. I've emailed back and forth with RayCore about using their panels for under the basement, and they just said there's no study in place that would guarantee it's success.

Thanks a lot.

I think Bob was confusing PUR with PIR (Polyisocynurate). Both EPS and 2lb density or higher spray PUR have well defined closed cell structures, and none of the hygroscopic nature of PIR. EPS is more vapor permeable than PUR, but it's waterproof (it's used everywhere as a float material in marine applications), and cheap, clearly a cheaper way to go for under-slab insulation where there is no advantage to the higher R/inch of PUR.

I have gotten a couple of third hand reports in the past couple of years of problems with installing sprayed 2lb and 3lb density polyurethane directly on the gravel or dirt, but none of the details of how/what went wrong. To be sure it's an expensive and sticky mistake when that happens- not sure if it was operator error (likely), but wouldn't be an issue if using pre-foamed sheet goods. The OSB skins of RayCore SIPs are an issue for sub-slab apps though.

The HFC245fa blowing agent used for nearly all high density spray polyurethane make it a non-starter for most applications in my book. It has a lifecycle global warming potential about 1000x CO2, whereas EPS is blown with pentane, at about 7x CO2 GWP. For that reason alone RayCore is on my personal "don't use" list until & unless they will stipulate that only low a suitable GWP blowing agent such as (eg Honeywell Solstice ) is used in their manufacture, and NOT HFC245fa. YMMV.

Thanks, Dana1.

(BTW, what does YMMV mean?  EDIT:  I GOT IT!  Your Milage May Vary)  You alluded that polyurethane is more expensive.  Is THAT why EPS is more of the mainstream?  SIGNIFICANTLY more expensive?  RayCore's site gave a rough figure, right on their main page, that they'd 'only' be about 1300 bucks more on a 1500sq ft. home than stick-built.  How would your average EPS system compare?(I do realize how hard it is to just throw figures out, but...)

I wonder if there's some chemical reason that they do stick with such a bad blowing agent.  What if they used the same exact one as the EPS folk do?  Would it dissolve the PUR, or something?

I think Bob was confusing PUR with PIR (Polyisocynurate)
yes; mea culpa

Posted By Pokletu on 27 Jan 2014 07:18 PM
Thanks, Dana1.

(BTW, what does YMMV mean?  EDIT:  I GOT IT!  Your Milage May Vary)  You alluded that polyurethane is more expensive.  Is THAT why EPS is more of the mainstream?  SIGNIFICANTLY more expensive?  RayCore's site gave a rough figure, right on their main page, that they'd 'only' be about 1300 bucks more on a 1500sq ft. home than stick-built.  How would your average EPS system compare?(I do realize how hard it is to just throw figures out, but...)

I wonder if there's some chemical reason that they do stick with such a bad blowing agent.  What if they used the same exact one as the EPS folk do?  Would it dissolve the PUR, or something?

EPS as simple unbonded sheet goods runs about 10 cents per square foot per unit R (eg. R20 is $2.00/square foot, pretty much, more or less).  Mid density polyurethane (2lbs per cubic foot density) installed on site runs about 17-18 cents/R-foot, so R20 would run about $3.50 per square foot.

I have no idea what the real installed costs of RayCore's panel goods are.  EPS in SIP form bonded to OSB on both sides is considerably more expensive than the naked sheet goods, and I would presume the same to be the case for PUR core SIPs as well.  The RayCore statements of R-value are well in excess of reality (they completely ignore the thermal bridging effects of the splines and bottom/top plates, window framing, etc), but since they're selling a wall system and not insulation, they are still on the legal side in making those statements from an FTC perspective, and do NOT need to test to ASTM C 518. (Other SIP and ICF vendors have similarly fanciful numbers, some more excessive than others.)

HFC245fa is actually an IMPROVEMENT over the stuff than the CHFCs most commonly used for blowing PUR prior to the Montreal Protocol, since it doesn't destroy the ozone layer.  EPS and polyiso are blown with pentane, but it's a different chemistry, different polymer, and pentane would not work with polyurethane. There are some mid density polyurethane chemistry suitable for blowing with with water (the most common blowing agent for  low density open cell polyurethane).  Icynene MD-R-210 and MD-R200 are both water blown ~2lb density polyurethane foams but run about R5/inch to the HFC-blown goods' R6-7/inch, which becomes a marketing issue. The suite of products from Aloha Energy (a regional player in the northeast) is also water blown, and runs about R6/inch.

There are other much lower-impact HFC high-R blowing agents out there for blowing 2lb polyurethane such as Honeywell Solstice, DuPont FEA-1100, cyclopentane (which has flammability issues), Forane 1233zd, but to date none of these have garnered a significant market share, (and probably won't until HFC245fa is banned by regulators.)