Hey folks.  I'm currently having a house built with IntegraSpec ICF and after filling a few garbage bags with scrap foam I started to ponder a better use for the left-overs than a landfill graveyard.

Since my garage is an ICF structure also and will have insulated doors and roof, why not use the leftover foam underneath the slab?

I had contemplated putting EPS under the slabe but decided it was not worth the money, but since I've got this scrap foam from the walls, why not?

Since the pieces would be relatively small, my thinking is to place them on top of the sand back-fill and then cover with the clear stone before pouring the slab.

Any thoughts or comments on this would be appreciated.

May be ok, but typically I believe xps is used, not eps. EPS is not rated for underslab use.

 

Bunt

The IntegraSpec installation manual recommends EPS under the basement slab, and all the quotes I received specified EPS underneath the slab.

Either way, what are the consequences of using the EPS waste underneath the garage slab?

EPS is INDEED rated for under-slab use, and used in slab insulation apps all the time.  2lb/ft^3 stuff has similar compressive strength as the usual 2lb XPS. The arguments get bogged down on how much & how quickly water is absorbed & released, but it's all pretty-good stuff.  In low-load slabs the low density 1lb/ft^3 stuff often used as roofing insulation will handle it just fine.

I'm not sure what the density of stuff in SIPs usually is, but I'd be surprised if many were lower than 1.25lbs/ft^3 nominal, since it's strength factors into the structural rating of the whole shebang.  Under a garage slab I wouldn't sweat it a bit.  Under a footing holding up a 3 story building, I definitely would. YMMV.

A nice concept for less-structural cementitious EPS insulation,  bead-crete:

http://www.builditsolar.com/Projects/SpaceHeating/BeadFoamCrete.htm

I wouldn't worry too much about a bead-crete slab with a 1-2" hard-concrete top finish in a garage either.

You may find this thread of interest:

http://www.greenbuildingtalk.com/Forums/tabid/53/forumid/14/postid/63138/view/topic/Default.aspx

Oops! I'd somehow read "SIP", not "ICF". ICFs are usually 1.5lbs density & up- even LESS to worry about.

Putting the EPS on TOP of the drainage layers rather than below them will make it less likely to become water-saturated and lose R-value. If you only have enough to do part of the slab, the perimeter is far more important than the center. I'm assuming the footings were done in ICFs, and are thus insulated? (If not, start there!)

O.K., my bad. I always use xps under slab (the blue stuff). I read somewhere that eps wasn't rated for under slabs (for whatever reason). I have a 2 lb density quadlock panel in front of me right now. Feels just like the xps stuff I normally use. I think it all comes down to the compressive strength of the foam. Seems to me the xps always seems more dense. Bunt

ICF footings?  No, they were done the "old fashioned way" with 2 x 10 lumber, however the garage walls are ICF and the garage is filled with 5 feet of sand.  So I'll be putting the extra foam on top of the compacted sand, then cover with 6" clear stone, then 4" concrete slab.  There should be no water pooling at the foam level since it's 5 feet over the footings, and it's inside the garage.  I suppose I could put it on top of the 6" stone, however I would think it's easier for the slab to pour over stone than over foam pieces...

Right, but since I'm planning to put 6" of clear stone over the foam before the concrete slab, should be no problem?

Basically I'm just looking to do something more useful with the leftover foam than throw it in the landfill.  If this is too complicated and I need to put a membrane, etc. etc.  I won't bother.

Another use for the scrap is to put it in a chipper and spead it in the attic. That would give you some nice insulation up there, plus it is not harmfull if it touches your skin.

Methinks you'll run afoul of fire code issues doing that if you don't do it right...

Buried under the slab seems right.