Insulating drylocked basement

percipOctober 17, 2008

I am doing a major renovation and have my basement stripped down to the concrete foundation blocks and studs on the walk-out side (wood framed). Unfortunately, the entire below-grade concrete blocks are covered with drylock which now acts as a water/vapor barrier to prevent the blocks from drying out. Anyway, I'm trying to identify the best insulation method for this space.

I will be caulking all seams, then will spray the wood-framed side with 2" of closed cell foam. On the concrete walls, I am thinking of using 2" styrofoam wallmate before attaching mold-resistant gypsum boards. I could go up to 3.5" on some walls by pairing 2" styrofoam and 1.5" wallmate. Is this the best option? Do I need a vapor barrier between the wallmate and the gypsum boards? Should I consider other approaches?

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Drylok is vapour permeable, which means water vapour can travel through but just not as water.

I'm not clear on your distinctions in wall type. Since you have a budget for ccSPF, just spray it on the concrete, frame and use your favourite fibrous insulation in the stud wall. Or you can use Wallmate, as you suggest. No vapour barrier is required in either case. Two other acceptable approaches are fibrous insulation and a "smart" vapour retarder and EPS foam board instead of XPS. Just be sure to use mechanical dehumidification in that case to keep relative humidity below 50%. Actually, I'd do that in any case.

Here is a link that might be useful: Drylok

    Bookmark   October 20, 2008 at 11:23PM
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I agree with worthy. A dehumidifier in your case could be the best investment. Beware of using anything organic, or made with organic compounds on the below grade walls. That include some types of insulation, drywall if you are planning to finish the space, and latex based paint.
You might want to consider "all-in-one" solutions, such as basement wall panel systems. They are finishing options, add insulation and moisture protection.

    Bookmark   October 21, 2008 at 8:46AM
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