How do you fix prevent moisture damage in a block foundation?

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How do you fix moisture problems in basement?

John rodrigues Nov. 27, 2020Last updated: Dec. 2, 2020

I am redoing a basement wall that has a lot of moisture and has rotted the studs I see you mentioned to do drywall, studs with mineral wood then 2" of rigid insulation attached to block foundation would it be ok if I put Delta MS against the block foundation then apply the rigind insulation Thanks for your help.

Responses (3)

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John rodrigues Dec. 2, 2020, 3:22 p.m.

Thanks Mike Im in Toronto zone 6 I see what you mean by the Delta membrane not having a place to drain to. Im going with the other  option on your site using 3" closed cell sprayed right onto the block wall then using PT wood for framing with FoamSealR 3-1/2 in. x 50 ft. Multi-Use Ridged Sill Plate Gasket do you think I should also put Roxul on the 2x4s or is that overkill? Also if the closed cell gets moist would it just evaporate to the inside and would that create any mildew on drywall really appreciate your help on this its very hard to find good information out there. Thanks jr

Mike Reynolds Dec. 3, 2020, 10:26 a.m.

Hey John,

My only concern would be the condition of the block wall and possible cracking. Is it in good shape? If so, and you go for it I would suggest the following - PT isn't really necessary, I would frame the stud wall an inch away from the concrete blocks and sit it up on small 1 inch high foam blocks (one cheap sheet of EPS from a local building supply store would be all you likely need) so the spray foam can get under and behind. That way your wood is prefectly protected. As for the spray foam, my other suggestion would be to choose a spray foam with more climate friendly blowing agents- read more here. There are a few companies that have switched to much less harmful blowing agents, they are also said to be a lot less toxic to humans. Below you can see what I mean by foam blocks, it just keeps the wood off the concrete. The wall isn't structural so the weight isnt't a problem. As for putting batts in the cavities, once you're already going with the spray foam you might want to just save myself the headache and labour of doing a how round of batt insulation and get them to thicken that to the desired R value you want. They charge by linear foot usually so adding an extra 2 inches of spray foam while they are already at it may actually be the cheapest solution, but price it out both ways I guess.