Hi

I'm about to back-fill my new foundation and I am going to put EPS foam on the exterior and horizontally over the footings in part to protect them in my zone6/7 climate. I can get an extremely good deal directly from a large EPS manufacturer locally.

For this application is it necessary to have a minimum density like Type II or Type IX or is Type I good enough?
Is it necessary for the boards to be grooved or have special skins or facings like some specialty boards for below grade or is generic EPS good enough?
Any tips on back filling over the horizontal foam? I imagine it getting broken up by whatever stones are in the fill(mostly clay that was removed during excavation) and dropped by the the excavator bucket. The boards will be sitting on top of the gravel used to cover the weeping tile.
Related to the last question...I might be able to obtain a ton(not literally) of shredded EPS for free. Would there be any harm in back filling a little bit with shredded EPS? Would there be any gain? I figure it might provide a cushion over top of the horizontal boards and add even more insulation. I wonder though if it will just collect a whole bunch of water and do more harm than good.

I will likely later on use EPS under the slab as well. Is type II the minimum density for under slab?

I think I just broke the question per post limit...sorry about that :)

Thanks!
Dave

I would slope horizontal foam downwards, to direct water away from the wall.

Yes it will be sloped away

Type-II may be good enough- how deep is the soil going on top of it?

Under slabs Type-II is definitely good enough.

Backfilling with shredded EPS &/or low density EPS blocks is a fairly standard practice for insulating over the footings of large foundations/buildings and retaining walls.etc. Shredded EPS or loose EPS beads eliminates potential lateral frost heave loads by absorbing the mechanical strain, and drains very well. Putting landscaping fabric &/or a heavy vapor barrier (sloping away from the foundation) over the EPS back fill (under 1-3' of topsoil)  should work pretty well.  Unless you'll be putting a driveway over it, any density shred, Type-I or even loose EPS beads would be good enough for backfill. It's customary in commercial applications to mix the shred with sand to limit potential settling/compaction but that would be less of an issue here. If you take a EPS-shred backfill approach there is no point rigid EPS directly on the top of footing- you'll get a huge R value out of just the backfill even at ~R2/inch (R24/foot.)

Thanks for the reply Dana!

I wasn't expecting to get as much as R2 out of the shredded EPS. That would save me a lot of trouble if I just dump shredded EPS over the footings and skip the horizontal. It would save on vertical foam as well if I only insulate down to the top of the EPS fill. This seems like a great way to recycle/reuse EPS. Its strange I cant find more info/people doing it other than geoblocks(which would have to be produced and purchased). I have to assume there is a substantial advantage to using blocks over shredded? More R per inch? More stable for engineering projects?

Can I skip the vapour barrier/fabric and just make sure I have well sloped surface drainage. Id like to get the backfill done in one step and I dont think guy doing the backfill will wait for me to put down vapour barrier mid job. I have a lot of gravel and drainage tile which will be directly below the shredded EPS.

I dont have 1st hand experience with shredded EPS but my gut feeling is that it might fly all over the place when trying to dump it on the footings. It comes in bags...any harm in just throwing whole bags down there? I realize there will be gaps...and I guess when the bag eventually punctures at some point it will trap water like a balloon...but boy would it be easy to just walk around the foundation dropping bags of shredded EPS and backfilling. Maybe adding water to the shred might help. Thoughts?

I called the manufacturer of the boards today and unfortunately its only type I. Can I get away with Type I for slabs and walls? I assume even if the answer is yes it might be difficult to walk on when placing the vapour barrier and pouring the concrete. Is anyone doing this with type I?

Thanks again!

Just to follow up...I finished backfill today. I didn't use the shredded EPS. The 2" Type I EPS boards held up just fine to dropping clay and stones from an excavator... in case anyone else is considering using Type I horizontally over footings. They had a lot more flex than I thought which was good.

Still wondering if type I is ok for under slab....after having worked with this stuff for 3 days my gut feeling is that it will be fine.

There is a lot less pressure on the foam with only 4" of concrete on it compared to 6-7' of soil, eh?

I'm not convinced you won't have some amount of compression of the horizontal Type-I EPS atop the footings over time, due to the sheer mass of the soil overburden. At typical soil densities every foot of depth adds about 0.75 psi, but it can be as much as 2x that. if the top of the footing is 6' below grade you are looking at 4-5 psi static load. Type-I EPS is typically rated a 10 psi to hit 10% deformation per ASTM D 1621.

At 135 lbs per cubic foot, a 4" concrete slab comes in at about 0.25 psi. Even with dynamic loading methinks you have some margin there, as long as you aren't using it to support the house.

The other issue with Type-I EPS is that it can take on about 6% of water by volume into interstitial bead spacing, with a corresponding hit in thermal performance when fully wet, but with a well-drained slab that's not a problem until the tide rises to slab-level. When the tide goes out the performance is fully restored.