Is exterior foundation waterproofing and interior closed cell spray foam a double vapour barrier?
I am having my foundation waterproofed with blue seal which is an elastomeric rubber waterproofing coating. I am also going to have 3 inches of closed cell foam sprayed against the interior of my concrete foundation right up through the rim joists. I’m just wondering if that would create a double vapour barrier on both sides of the concrete wall? Wondering if the concrete would be able to dry if moisture happened to get in there.
Would damproofing instead of waterproofing the exterior foundation make any difference? I know that with CC spf on the interior there shouldn’t be any real drying towards the inside, so could the wall still dry to the outside?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
> Wondering if the concrete would be able to dry if moisture happened to get in there.
Concrete doesn't need to dry. Remember, concrete can be poured under water, cure, and stay forever.
> Would damproofing instead of waterproofing the exterior foundation make any difference?
Don't damp proof it. Water proof it.
Thanks
If this is new construction, make sure you have a capillary break on the top of the wall between the concrete and the wood framing. It's a good idea to install a capillary break between the footing and the bottom of the wall too. See Martin's article about that here:
https://www.greenbuildingadvisor.com/article/capillary-breaks-above-footings
If this is an existing structure, then you're obviously more limited. Ideally, you want a capillary break on the top of the wall to keep any "rising damp" from getting up to the wood framing. The concrete itself can stay wet forever without any trouble as Patrick mentioned, it's only the "wood stuff" that needs protection.
If you have no capillary break and can't install one, then you might want to consider making sure the rim joist area can dry. Even here though, it's limited risk.
You need that waterproofing on the basement wall, don't compromise that -- deal with any drying/wicking issues in other ways.
Bill