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Exterior Below Grade Spray Foam

Hello,

I'm curious what the group thinks about exterior below grade spray foam. The current proposed basement insulation solution is to apply 3" of Closed Cell Spray Foam directly to the exterior of the poured concrete foundation wall. The foam will be protected with drainage mat prior to back filling.

Thanks!

Asked by Howard Road
Posted May 8, 2014 1:01 PM ET

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3 Answers

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1.

Almost all closed cell foam in N. America is blown with HFC245fa, which has a significant lifecycle environmental impact, including a global warming potential (GWP) about 1000x that of CO2.

4-5" of Type-II EPS (blown with pentane, GWP about 7x CO2) yields about the same performance but at a lower cost, and much lower environmental impact.

Answered by Dana Dorsett
Posted May 8, 2014 4:55 PM ET

2.

Howard,
Dana is correct concerning the environmental impact of closed-cell spray foam.

To answer your question: closed-cell spray foam works well below grade in this application. Of course, the above-grade portion of the cured spray foam needs to be protected from physical abuse and UV radiation (sunlight).

Answered by Martin Holladay, GBA Advisor
Posted May 12, 2014 6:27 AM ET

3.

spraying the exterior of your concrete wall will insulate & work OK, except that if you do not insulate around and under the footing, you will lose a lot of heat through that thermal bridge. in other words, heat will go through the concrete and through the footing, bypassing the insulation and cooling off the bottom of the wall. I saw this first hand in a passive solar earth bermed home we built years ago - works pretty well except that the bottom of the interior of the concrete wall stays cold and moist.

Insulating the interior of the concrete and isolating the slab will prevent that from happening.

Answered by Bob Irving
Posted May 12, 2014 7:27 AM ET

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