Drylock and basement insulation retro-fit
A follow up question after reading “RR-1108: Hybrid Foundation Insulation Retrofits: Measure Guidelines.” As detailed in one of the alternatives in that article, for my basement retro-fit I am planning on using foam panels installed directly to the foudation walls, as the first step towards coverting the basement to conditioned space (playroom). I will likely use foam panels or plywood with a bubble mat (like dry-core) for the floors.
The basement is basically dry, 80 year old house, poured concrete foundation (12″-18″ thick), no water leaks but some effloresence. House is just outside Boston, and we’ve had two major spring floods in the last 5 years, with no water in my basement at all. But my street has a very high water table and the basement gets quite humid in the summer. It’s just not financially feasible for me to water seal the outside of the foundation or install a curtain drain. The slope of the lot and the gutter drainage is quite good.
The question I have is whether I should use Drylock or any other sealing product on the walls or on the floor before attaching foam panels; none of the articles on GBA address this issue exactly. Although I know that the foam panels are impermeable, would Drylock offer some increased protection against moisture penetration? Or will further sealing the walls just trap more moisture in the concrete, and should I be more worried about making sure the panels have chanels to vent whatever moisture will make it trough the walls and floor? I am particularly worried about the floor, as it is only 3-4 inches thick, and shows the most effloresence –
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Replies
Rick,
Your concrete will be just fine at whatever moisture content it happens to have. It's been there for 80 years and willl keep doing what it's been doing all those years. If you provide a path for drying you will set yourself up for mold problems once the foundation is insulated (I.e. colder). Sounds to me like your situation is perfect for a spray foam job. It will cost you more than the board stock but it will solve your humidity problems, which back venting boards will not. For your slab, your optimum system combines a dimpled membrane and foam board insulation. The plywood and bubble mat panels may limit moisture flow but offer little insulation value. If you want your kids to be comfortable, go with the foam insulation.
I think you're fine to attach foam to the walls without using Drylok. It sounds like you have good drainage.
Take a look at the basement insulation article Andy Engel wrote in FHB 5 or so years ago. I suggest you use foam and plywood on the floor as he suggests, after you apply foam to the walls. Then build your stud wall. 20 gauge 1-5/8" steel studs work great if you want to save space and use something that won't support mold. Building this wall on top of the insulated floor keeps the steel studs away from the thermal drain of the concrete floor.
If you space the stud wall about 1" from the foam panels you can run electrical behind the studs. Plus you can shoot spray foam blobs between the studs and foam walls to mechanically keep the foam panels against the masonry (in case the glue fails in the future) and stiffen the stud wall.
See some photos below.
Billy
Another alternative is an insulated panel by LeeCor Systems that has non-thermal bridging light-guage steel studs. For your application, they have a split panel with steel only on one side. This alternative would allow you to install your framing in the same step as the insulation, air and vapor barriers.