Kneewall Design


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Old 10-04-06, 09:31 PM
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Kneewall Design

Hello All,

I'm finishing a bonus room above our garage, and I'll begin framing here in a few weeks. My question is about the Kneewalls. I've been reading about "air sealing" and how important it is. My kneewalls will be constructed from 2x4's 16'' oc with a top and bottom plate and filled will r13.

I was wanting to put some type of sheeting on the backside of the kneewall to form somewhat of an air tight kneewall. The backside of my kneewall will exposed to all ambient temps and soffit vents, so I was just wanting to reduce the amount of air seeping in or out of those kneewalls.

Is this a good idea, and if so what type of sheeting? Does the sheeting need to be fire resistant?

Thanks for all of your help.

Dave
 
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Old 10-05-06, 01:07 PM
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I don't know that you need sheeting on the back side of the kneewalls - they would be treated just like the attic ceiling. You would put insulation batts between the studs, cover with a vapor barrier on the room side, then sheetrock (or whatever your finish wall is). Your attic ceiling is exposed to the same conditions as the back of your kneewall.
 
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Old 10-05-06, 02:01 PM
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I see your point Ubob,

I saw that idea on the US Dept of Energy's website and it just sounded like a good idea. I was wondering if people are doing this and does it help? It would definitely improve the "R" value of the kneewall. I'm just not sure if that sheeting would induce other problems.

Dave
 
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Old 10-05-06, 05:41 PM
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You could put sheetrock, or plywood on the backside, but neither is going to raise the R-value appreciably (maybe 1/2R?). I would avoid foam board or any sheathing that would act as a vapor barrier - since it would trap moisture in the wall. I could see a case made for something like Tyvek, as it would be a draft barrier, but let moisture through.

If you are set on the idea of having sheathing on the outside, and haven't insulated yet, consider sheathing first, then use blown-in celulose for insulation. It will seal tighter than the fiberglass, and might even be cheaper (not counting the cost of the sheathing). You could then cover it with a vapor barrier, then your sheetrock.
 
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Old 10-06-06, 12:38 PM
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Thanks Ubob!!

A draft barrier is exactly what I was trying to achieve. I definitely do not want to trap any moisture in the kneewall. I was just trying to prevent drafts and make the room as energy efficient as possible w/o breaking the bank. I'll look into the Tyvek. Thanks for the great tips.

Dave
 
 

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