Basement insulating to avoid moisture problems

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Posted by: from Montreal
11/1/2015 at 11:35:04 AM


I'm finishing my basement and am getting conflicting info on how to frame and insulate. I have a poured concrete foundation. I'm using 2 inch xps. I'm sealing all the seams then framing my walls with 2x4's. I was then going to fill the cavities with fibreglass insulation to get my r value to the recommended 20.

My question is, is there an alternative to using pressure treated wood for my base plate? (The stuff is highly toxic.) Also, I understand the xps acts as a vapour barrier. Is it necessecary to also include a barrier between the insulation and drywall?

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Date/Time11/1/2015 at 1:08:54 PM

The xps when sealed with tuck tape provides a great vapour barrier. So after framing you can add whatever level of batt insulation you desire.

Regarding the base plates. You will find that the blue board will not be sold once the existing stock is sold at all building centers.

There is the brown board that acts much the same way as the old blue, but is much more eco friendly. Be sure to by a small can of the brown stain that goes with the product. And liberally soak any cut ends you make in the original boards. Also install a roll of the 4" wide foam under the base plates prior to ram-setting them in place. All of the lumber above the baseplates can be standard framing lumber if you follow those steps.

Enjoy your basement.


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Date/Time11/1/2015 at 4:07:13 PM

Hi, MTL. The xps is a great product but I would also ad a 6 ml vapour barrier between the drywall and the batt insulation. As you mentioned, there are several thoughts on this subject but by combining the products you'll gain the best over-all coverage. As to the base plate, you can get by with a plastic or foam barrier between the concrete and the wood. The primary reason is so the wood wond absorb the moisture and rot or mould over time.



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Date/Time11/2/2015 at 5:21:15 AM

A vapour barrier is needed to separate the cold area from the warm. Therefore there should always be 6mil used between the insulation and the drywall. A sill gasket should be used on your bottom plate as for using PT inside your home I would suggest reading the manufacturers suggestions on there product. If your basement is more than 4 years old you do not have to worry much about moisture destroying the bottom plate as long as you use a sill gasket. Unless you have moisture problems that should be all you need. I would also suggest that if you do have moisture issue and your home is more than 4 years old have that checked out before you finish your basement.

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