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Exterior basement EPS insulation details

Chris_the_new_guy | Posted in Green Building Techniques on

I’m trying to figure out my exterior foundation insulation details.  I’m in zone 6 and building a 2 story over poured foundation basement. 

I’ve decided to put 2 inches EPS on the exterior of the foundation basically right up to the bottom of a structural iron ledge just below the sill.  All of the info I have read states that’s it’s a good idea to use a dimple mat along with damp proofing or perhaps waterproofing along with the EPS.  I’ve read that you can either put the dimple mat on the concrete side of the EPS or the dirt side.  Here are my questions:

1.  If I go with the dimple mat on the concrete side of the EPS won’t that leave a 3/4 inch air gap behind the EPS above the drainage mat (option 1 in the pic)?  Should I fill that gap in this case?  Any ideas on how I should attach the EPS to the dimple mat?  Should I cut the EPS above the dimple mat and put the rest of it flush against the concrete (option 2) with an adhesive foam?

2. If I go with the dimple mat on the dirt side of the EPS (not my preferred choice), would I just use longer fasteners to attach it through the 2 inch EPS?

3.  I have seen some EPS products with vertical drainage channels cut in them every 2 inches (called drainage boards).  Would this solve the problem completely and replace the dimple mat completely?

I am building in a clay soil of which some homes in the neighborhood have moisture issues in the basements (mostly 50+ year old homes).

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  1. drewintoledo | | #1

    It seems that if you have your dimple mat sandwiched between your foundation wall and your EPS then that dictates that water would travel past the EPS in order to drain. Why not put the dimple at on the outside of the EPS?

    1. Chris_the_new_guy | | #2

      What would be the best way to attach the EPS to the foundation and then the dimple mat to the eps?

      After posting I was thinking the best of both worlds would be to use the drainage board EPS against the foundation then the dimple mat on top of the EPS. That way there is 2 drainage methods.

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