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Braddiy 10-06-2012 08:47 PM

basement insulation in Toronto,
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I am renovating a basement laundry/bathroom and have a question on insulation. I have glued 1" foam board to exterior cement block walls and then tuck taped all seams. i then put up a regular 2x4 wall about 5" from the foam because i needed to run dryer ducting and water pipes, my question is should i also insulate 2x4 wall with roxul (like picture below)or would that create a moisture problem in the 5" gap between exterior wall and new framed wall

or should i not insulate new wall at all.

please see photo and excuse my wording as i am diy lol

Red Squirrel 10-06-2012 09:38 PM

I think you can insulate as there can never be too much insulation. However I think you do NOT put a vapor barrier because the foam acts as one. Though I'm curious to see what others say since I've been wanting to do my basement and I will probably do something similar. On the other hand the VB normally goes on the hot side, so really not sure what the rule is with something like this.

Gary in WA 10-08-2012 12:26 AM

The Roxul does not act as a vapor barrier. The air space between the foam/frame wall-insulation is bad for creating convective loops; In the U.S., it is against code as we fire-stop frame walls every 10' horizontally as well as at the top plate/ceiling joist cavity. Otherwise a wall outlet fire could spread quickly through the top plates gap along any of the ceiling joist cavities, up through a wiring/plumbing hole at the other side/end of the basement, even to the attic setting the sheathing/asphalt roofing on fire. Then the roof is burning down as the basement is burning up. Fire-blocking; #21;

As far as v.b., for you locally:

And in general;

P.S. I'll move this thread to "Insulation" unless you are making a "How to guide"?

Red Squirrel 10-08-2012 12:34 AM

I was talking mostly about the foam itself acting as VB, though I'm not sure if it does or not.

And good point on the fire consideration. That foam stuff burns quite nicely.

gregzoll 10-08-2012 12:47 AM

The problem with using the foil faced foam board before the Roxul, is just going to cause problems. For the OP, you really need to tear all of that down and start it from the beginning properly.

Gary in WA 10-08-2012 09:26 PM

Foil-faced foamboard is fine if:


gregzoll 10-09-2012 07:43 AM

For one a basement is not a wood framed structure, and 2 those rules only apply to the U.S., not the Canucks.

Gary in WA 10-10-2012 08:10 PM

Read my highlights from that link: "However, a Class I vapor control layer could be used in a below grade assembly under the following conditions: (a) no moisture-sensitive material is trapped between the concrete and the Class I vapor control layer, (b) this space is completely isolated from air communication with the interior, and (c) the Class I vapor control layer is protected from interior-sourced condensation. An example of this assembly would be foil-faced polyisocyanurate applied to the basement wall, with the gap between insulation and concrete isolated and air sealed from the interior." From;

In Canada, 3.4 under "Vapor diffusion control", #4- foam plastic is acceptable as a vapor barrier on concrete below grade on concrete walls; with or without a wood frame wall inboard.

Here is a study by BSC written by a Canadian about 4 Canadian cities, including the use of XPS;


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