XPS to Interior Drain on Basement Wall

twarocAugust 21, 2014

Frequent site reader, but first time poster.

I'm having an interior drain put around the perimeter of my basement walls. The lip of this is spaced 3/8" off the wall and rises slightly up off the floor. The contractor wanted to install a 90mil 0-perm vapor barrier that ran the full length of the wall and was cemented into the drain. I declined this because I think the concrete needs to "dry to the inside" as many posters have pointed out.

My plan is to install 2" XPS, glue to wall (with the foamboard specific stuff, vertical stripes of glue ... or fasten with those plastic fasteners, where do you get those?) tape the seams, etc. I'll also end up spray foaming the rim joist which will likely seal the top. The foam will control any water that gets through and direct it into the drain lip on the wall.

I'm seeking opinions on:
- Should I DryLoc the walls before I put the foam on? I can't decide given the pros and cons I've found.

- How to interface foam to the drain lip so any water that seeps through the concrete will run into that drain lip. Is there a specific flashing available? Do I set the foam on top of the lip? Notch the foam over the drain?

Here are two pictures of the Water Guard system that's going in to give you an idea of the lip I'm talking about (and a pic where that vapor barrier that I opted not to have).

Thanks for your time!



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First, basement walls do not have to dry to the interior, now says Dr. Joe Lstiburek, the building scientist who widely spread the notion that they did.

However, foam insulation on the interior basement wall is certainly an excellent energy savings choice. Especially if the wall is leaking, or is expected to leak. XPS is pretty much impervious to water. We use it in cottage country to keep docks buoyant.

I would just stop the foam a couple of inches above the drain.

Of course, I always waterproof from the outside to stop any damage to the walls and footings before it starts.

The best fasteners for the foam are all plastic. See photo. Or you can use 1x2s or 3s to hold a number of sheets of insulation tight to the wall.

This post was edited by worthy on Sat, Aug 23, 14 at 14:23

    Bookmark   August 23, 2014 at 10:34AM
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Thanks for the reply and providing that new link. I guess now it doesn't matter whether I put a 6mil vapor barrier behind the foam, drylock the wall w/ no vapor barrier, or just put the 2" foam against the wall.

I was leaning to power washing the wall, patching any digits, and putting xps up with no plastic, but now I guess it doesn't matter.

Where did you find that picture? What are those things called? I can't find them at the Depot.

    Bookmark   August 23, 2014 at 4:16PM
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There are a number of manufacturers. You can order on-line. Or try contacting Owens-Corning, for instance, which has a line of fasteners for attaching their foam boards to all kinds of substrates.

Locally, a building supply retailer as opposed to the Big Boxes should have these fasteners. There are even retail chains selling only fasteners.

    Bookmark   August 24, 2014 at 10:25AM
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