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Old 10-07-2014, 02:19 PM   #1
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Insulating a faux exterior wall


I recently purchased a house with a gambrel roof that extends to the ground, and the interior walls follow the gambrel pitch creating a wall that leans approximately 15. I intend to build a new wall standing completely upright against the original exterior wall, but am not sure how to insulate it.

The original wall has R11 insulation, but I'd like to take the opportunity to add an additional R11 in my new wall, but will there be moisture problems? The existing insulation is paper faced and has no other vapor barrier. My new wall with have an air gap between it and the existing wall of approximately 10" at the bottom and 0" at the top.

Any thoughts???

New |\
wall | \
| \
| \ Existing
| \ wall
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| \
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Old 10-07-2014, 02:38 PM   #2
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I'm sure going back and adding your location to your profile will be a big help.
I see no way moistures going to be an issue.
What do you plan on using that's R-11?
A 2 X 4 wall with batts would be R-13 a 2 X 6 would be R-19.
No windows involved.
This house does not happen to be in Hartfield VA does it.
Reason I ask is I mow the lawn at a house built like that and it's coming up for sale.
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Old 10-07-2014, 03:10 PM   #3
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You are correct, it's a 4" wall (R-13). My only concern was the paper barrier on the original insulation will be behind my new layer and an air gap and I believe these are supposed to perform as some type of vapor barrier. And along that long, should I install a vapor barrier under my sheetrock and over my new insulation as usual?

I thought I might as well add another layer as Iowa (not VA) gets pretty extreme and the extra won't hurt.
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Old 10-07-2014, 03:14 PM   #4
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I see no reason for an added barrier. Want one anyway then just use faced batts.
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Old 10-07-2014, 05:34 PM   #5
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If I understand correctly, you will basically be constructing a kneewall. You can either leave the insulation on the underside of the roof making that unused space a part of the conditioned building envelope, or remove it and make the envelope at the new wall. I'd probably recommend the latter. Seal and insulate at the inner wall.
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Old 10-08-2014, 09:46 AM   #6
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Not really a kneewall, but a new separate wall away from the original exterior roof/wall. So if I understand you correctly, you feel removing the original insulation is best if I intend to insulate the new wall. Thus creating no air gap between the insulating panels.

The finished construction would create the following layers from the inside out.
Sheetrock - studs - air gap - studs - exterior sheeting. Currently the exterior wall has insulation and sheetrock which can be removed if necessary. I'm just trying to obtain the best R-value I can because of the extra space available. But I want to ensure I have no moisture problems when I do it.
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Old 10-08-2014, 10:14 AM   #7
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Insulating both walls and leaving air space between would be improper. Pick one wall or the other and either treat it as conditioned space or unconditioned space... I guess another alternative since it won't be very deep would be to just fill to whole cavity with insulation. Probably overkill though.
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Old 10-08-2014, 10:49 AM   #8
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I think I'll just "gut" the existing exterior wall and install R-19 in my new interior wall with a proper vapor barrier.

Thanks for all the input...
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Old 10-09-2014, 03:58 PM   #9
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If you're going to have a big cavity there once you've torn off the old drywall, why not just stuff the whole thing full of cellulose? It's cheap, it works, and you'll get continuous coverage unbroken by the studs, which you'll have to deal with if you only put batts between the studs. The cellulose may settle over time, but if you dense-pack it, that won't happen.
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