Insulating my basement

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Posted by: from Lindsay
10/29/2016 at 7:30:03 PM

I want to insulate my basement. It is currently bare concrete block wall not finished. I was going to install foil backed foam boards against the block wall then 2x4 stud wall filled with Roxul. However at this point I'm not sure whether to install a vapour barrier or not. The building code requires it however I have read many conflicting articles about this and I am concerned about creating a "vapour lock" that will actually trap moisture inside the wall cavity.

I have already begun the process with 3/4" foil backed rigid board and have started the framing and now I am rethinking my approach.

Any advice is greatly appreciated.

Thanks in advance.

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Date/Time10/29/2016 at 8:08:38 PM

Anytime your insulating a exterior wall or basement wall vapor barrier is required and if your worried about vapor lock, don't be because your supposed to build your wall 2 to 3 inches away from the foundation wall to allow air flow.

Hope this helps.

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Date/Time10/30/2016 at 11:00:54 AM


Assuming your block wall is water tight, your approach is fine. Here's the BUT, 3/4" foil is not great to use, little R value, and problems as a vapor barrier. The right way for your approach is.

1.5" or better, pink, blue, or other foam, rated as a vapor barrier not retarder. Glue to block, and seal with tape and foam or caulk at floor and floor above (this is your vapor barrier). Frame as normal, no space required. Insulate after your ESA inspection, with standard insulation, NO vapor barrier this allows any vapor to dry to the inside. Use mold resident drywall, and mix your own mud, don't use premixed.

Hope this helped.

John Miller

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Brad in Lindsay
Date/Time10/30/2016 at 2:11:58 PM

Thanks guys. Altho your replies were different they essentially end up at the same place - an insulated basement wall with rigid Styrofoam - one that acts as a vapour barrier and one that requires an additional product to create a vapour barrier.

I'm assuming that the reason that the thicker foam board acts as a vapour barrier is because it has a greater r value?

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Date/Time10/30/2016 at 5:27:51 PM

Johns comment was exactly correct. That is how my firm finishes the inside walls of all basements we finish. We generally use Tuck tape to close up all the seems on the foam.

Enjoy your basement.

James Fram

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