How to attach 6" of foam to outside of walkout basement & protect at grade?

Cold climate, Teller County Colorado.

Thinking about next basement. 76' x 38' rectangle. Hole is already dug into hill. Decomposed granite, no soil except about 2" at undisturbed surface.

7' along entire rear will be below grade, both sides will go from the 7' down to about 2' at the front left & right corners.

Hope building inspector will allow FPSF?

Dry stack cement blocks surface bonded, lots of verticle & horizontal bondbeam rebar, all holes filled with mud.

I want to use 6" of XPS below grade & EPS above grade at exterior.

How to attach foam to cement & protect at grade?

 

Ah, yes, the good old, decomposed granite. Reminds me of my years in New Mexico, where a lot of ours was the real crumbly stuff, between the Rio Grande and the Sandias. Not easy to work with.

For bonding your foam to the block, I'd look into something not affected by water (after it sets)--possibly a polyurethane? To make sure, pick the brains of some experts down at your local mason's supply store, where they would know what others have been buying and using successfully in your area. Should be one or more such stores in the Springs. Same goes for a good exterior coating--Thoro Seal comes to mind, but check with someone knowledgeable.

 

Foam to concrete, special glue + a ram-set-nailgun using 3" nails that come with washers, you can set the depth.

How about copper roll flashing $$. It can be turned a nice green patina with a mixture of acid & salt (non-iodized)

 

Why the use of an excessive amount of XPS below grade where the minimum soil temperature is not that low and then shift to lower quality EPS foam above grade where the air temperature and exposure may be much more severe?

Even in northern MN, where the winter temperatures are much lower it is difficult or impossible to justify that amount of insulation below grade from an economic or comfort standpoint. There, winter minimum air temperatures temperatures may be as low as -40F, but often -15F, but the soil temperatures are much warmer. Do not get confused by the prescriptive frost depth which is for structural conditions and not heating, cooling or operational economics.

Dick

 

15 miles from my house site, about same altitude 8,800' Closest data I could find online.

Mean annual soil temperature: 37 to 42 degrees F.

I'm here to learn. I want the best results vs. cost.

I was thinking XPS below grade due to better moisture rejection & compression strength. Not so?

I could use 3" foam from 7' -> 3' below grade, then 6" on up the 10' wall to the top?

For above grade foam, how to attach outer layer to inner, just glue??

 

I tend to agree with Dick on this one. Use the lower cost EPS below grade and switch to XPS above but maybe there are reasons for your method I am not aware of. As for protecting the product above grade I have found a product that uses STYROFOAM insulation with a concrete mortar facing. The panels are tongue and groove to minimize thermal breaks. Google tech-crete.com out of canada (BC) for information. I believe this is the same basic product/system that Dow once carried but they dropped it. Not sure why.

 

For above grade, I could also use 6" Tapcon screws, countersink into foam 1" & use 1" washers?