Insulating basement walls which have a waterproof membrane

5 years ago

We recently had a interior French drain installed along with a clean space wall system on the walls (photo attached for reference) which acts as a vapour barrier. My question is .. when insulating the basement walls, should we be leaving a gap between the insulation and the waterproof membrane or no gap at all? Should we also use rock wool instead of fibreglass insulation? Also assuming that the usual vapour barrier that would be between the insulation and drywall would be a bad idea as it would trap moisture?

Hoping somebody would have some experience with this!

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Comments (3)

worthy
5 years ago
last modified: 5 years ago
Water sensitive insulation in a basement wall is wonderful for mould. So "No" to fiber glass. The problem with foam board is that adhering it to the plastic membrane will damage the membrane.

Fiberglass insulation in basement.

Likewise for spray foam. So that leaves rockwool. And, of course, no vapour barrier between it and your finished wall. And no gap between the rockwool and the membrane, as the gap will cause condensation problems.
HU-238474569
Original Author
5 years ago
Thanks for the feedback! A little bit more info in regards to the air gap which I probably should have mentioned. We have also installed a subfloor using Dricore panels which seem to require a 1 inch air gap between stud and wall on unfinished walls. If we place insulation from top to bottom and from front of stud to the wall essentially closing that air gap, could we possibly have issues even though we have some finished interior walls with a 1/4 gap which would allow for air flow in some areas?

so greatful for thoughts on this.
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worthy
5 years ago
last modified: 5 years ago
The Dri-Core and framing has to be to the interior of the gravel channel--the basement living space. Otherwise, there is no level base for the DriCore; it would be on gravel.

For best results, Dri-Core says place the Dri-Core first, followed by the framing. (You will have to attach the framing to the floor joists above to keep it plumb.) Dri-Core calls for only a 1/4" gap to allow moisture under the Dri-Core to evaporate. You will have many inches behind the finished wall. That moisture will go to the drainage channel; the rockwool is unaffected by the moisture. Then pack the rockwool into space between the framing tight to the drainage membrane right down to the gravel.

If you're building the framing first, be sure to put the base on a water resistant material--preferably 1 inch thick strips of XPS foam board, which will protect the baseplate from water in case of minor flooding. Then, as Dri-Core instructs, leave a 1/4" gap between the finished wall and the Dri-core. This allows evaporation of moisture caught under the bottom of the Dri-Core. That gap doesn't affect the wall insulation's effectiveness.