Two layers of EPS below grade around foundation wall acceptable?
I was stepping into my truck to pick up some EPS. Thickest I find at the big box store is 2″. Curious if it’s OK to stack two 2″ sheets of EPS around the perimeter of the basement wall for exterior insulation? I will have at least three feet of backfill washed stone behind it.
My concern is that if water seeps between the sheets it will never dry. Is this OK? Maybe I should drape it with dimpled drain wrap?
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2 layers is just fine. The constant moisture does no harm to EPS. With the washed stone for drainage, there is no need for dimpled wrap. You do still need a good waterproofing layer applied to the foundation.
A gap between sheets doesn’t matter. EPS is ok underground regardless, so the extra gap doesn’t change anything as far as the EPS is concerned. You’ll have a little extra installation labor is all, and it’s best to stagger the seams. Even if you were to put any kind of wrap or barrier around the EPS, water will eventually find a way in there. XPS has slightly better performance when exposed to long term water underground, but you should have good drainage with your stone so there should be no issues.