EPS Exterior Basement Insulation
I recently had the final inspection done on a basement waterproofing project that included rigid foam insulation. The inspector noticed that I used 4in of EPS foam which he referred to as “beadboard” and he mentioned the most recent code requires a vapor barrier on the exterior side of the insulation if it is not “draining.” The insulation I used is Diversifoam Raylight Type IX 25HD which is a high density foam and is 0.6-2.5 perm in. and rated for exterior foundation use. I haven’t seen a detail anywhere that includes a vapor barrier (poly sheet) on the exterior side of the foam but maybe i missed something…
Inside of the foam is a Miri-drain board, and then elastomeric waterproofing membrane rolled on the CMU wall. Is this a safe and effective; code compliant assembly?
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Replies
Andy,
Codes are very much a local issue. (One of the GBA's professional members may have specific feedback on your issue.) Did the inspector fail your project or just comment on how it was completed?
While you are waiting for input, you might want to read this article on best practices for insulating a basement: https://www.greenbuildingadvisor.com/article/how-to-insulate-a-basement-wall.
Thanks for the link to the article! I will take a look. Inspector didn't fail it. He noted "OK" and signed it but left the following note. "Confirm foam is ok without vapor barrier at exterior."
The elastomeric waterproofing is a vapor barrier. You wouldn't need or want an additional vapor barrier on the outside of the foam, although the insulation would perform better if it were drainable like fiberglass board or mineral wool or covered by drainable backfill. You want it to dry out quickly and not absorb too much water for optimum R value.
A vapor barrier on the outside would not only not keep the insulation dry, it would ensure that it stays wet. Your assembly sounds just fine.