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How to insulate framed full wall in front of half concrete wall.

How to insulate framed full wall in front of half concrete wall.


Old 04-15-16, 06:26 PM
Thread Starter
Join Date: Oct 2010
Location: USA
Posts: 263
How to insulate framed full wall in front of half concrete wall.

I plan on constucting a full wall in front of the original half concrete wall in the basement (instead of doing a pony wall and shelf). On top of this concrete wall set back 4 inches is the house framed wall that is filled with fiberglass with a foil looking vapor barrier stapled to the inside. If I were to frame a full wall in front of this, how would I inslulate this 4 inch cavity behind the top section? Would I just remove the vapor barrier, fill with more fiberglass and then reattach the vapor barrier? Or should I pull it all out, cut foam to go against the sheething from the inside, foam spray seal it with great stuff, then stuff with fiberglass out to the new wall and not vapor barrier?
The bottom concrete and ledge are already covered with xps.

Secondly can xps be used in an "interior" basement wall. This interior wall is between the utility room that is not heated or finished and the finished heated side?

Last edited by hammerdown22; 04-15-16 at 07:24 PM.
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Old 04-15-16, 08:03 PM
Join Date: Oct 2008
Location: New England
Posts: 9,997
XPS should not be left exposed, studs and insulation if you need a wall.

The problem you want to avoid is humid air coming in contact with a cool or cold surface. In the winter the outside walls, both concrete and the insulated exterior wall will be cool. Your new wall will make the existing exterior wall cold by isolating it from the heat.

That is a lot of gap to fill, but probably not too much to do so. I would remove the existing foil facing and fill the gap and the new stud wall with high density batt insulation or mineral wool, Roxul. I like the Roxul. Enclose the top, air tight, and drywall the interior air sealing all penetrations and omit the vapor barrier.

The new understanding for vapor barriers is, they are rarely required and can cause more problems than they solve. Air sealing is the number one defense against moisture issues, assuming your walls aren't leaking.

The best use of the rigid is, as already exists, is against the concrete.


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