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Foam over Platon dimple mat on foundation

We are stumped at a stage in our building process. Winter is here and we need to deal with our foundation. Our site is dry dry dry, but we are not ready to just attach foam to the cement and backfill without any effort to damp/water proof the foundation.

We are essentially forced to use a mechanical system as the weather and temperatures (-10 degrees celcius and wet) are making any other sort of damp/water proofing impossible (as far as we know).

The main concerns with applying the Platon dimple mat is the difficulty of application and the question of what you do once you've reached the top of the dimple mat and you want to continue up the foundation/onto the rim joist with the foam. Should we just add a shim under the foam so that it remains in the same plane as the foam below (which is over the dimple mat)? Any other suggestions on damp/water proofing?

Asked by jessie pratt
Posted Dec 11, 2012 4:20 PM ET
Edited Dec 12, 2012 9:36 AM ET

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4 Answers

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1.

Jessie,
The simplest detail, it seems to me, would be to continue to Platon dimple mat right up to the top of the concrete foundation wall. That eliminates the need for shims.

Just be sure to complete the air barrier at the top of the dimple mat; canned spray foam might make sense at this location. If your wall plates aren't cantilevered over the concrete -- or if you aren't installing rigid foam on your above-grade walls equal in thickness to the rigid foam on your foundation -- you'll need Z-flashing at the top of the Platon dimple mat. The Z-flashing should also protect the top of the foundation foam.

Answered by Martin Holladay
Posted Dec 12, 2012 9:40 AM ET

2.

Thanks Martin!

Answered by jessie pratt
Posted Dec 12, 2012 9:44 AM ET

3.

I know this is old, but: as long as the dimple mat is air sealed, it won't reduce or get rid of the insulation value of the foam correct?

I am struggling to come up with an acceptable waterproof membrane for my exterior crawl space encapsulation. I am skeptical of liquids (staying attached over time and proper coverage) and peel and stick is pricey, so if I could use dimple mat and air seal to avoid loosing the insulating benefit of 4" of EPS, that would be great.

Answered by Joshua Terry
Posted Aug 17, 2017 8:49 PM ET

4.

Joshua,
Q. "As long as the dimple mat is air sealed, it won't reduce or get rid of the insulation value of the foam -- correct?"

A. Correct.

Answered by Martin Holladay
Posted Aug 18, 2017 6:11 AM ET

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