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Old 01-18-2011, 11:28 AM   #1
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Condensation behind xps?


When I removed the blanket insulation in our basement, there was frozen condensation behind it on the above ground areas of the wall. It was dry a day later. I put up 1/2" xps foam around the basment. Not so much for insulation, just a barrier between the studwall and the concrete. The temps have been up and down the past couple weeks as I finished the foam, from -10 to 40F. The other day I noticed a samll damp spot on the floor in the NW corner of the house. I assume this was condensation that formed during the really cold days and then melted and made its way to the floor. Since I will be caulking the gap at the floor and at the top, and eventually insulating everything, should I even worry about this?

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Old 01-19-2011, 11:55 AM   #2
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Condensation behind xps?


Well I borrowed a dehumidifier to see if that does anything. Since I know for sure its not a leakage problem and more than likely humidity I'm not going to worry about it. I still have to seal the top and bottom of the xps anyway.

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Old 01-19-2011, 11:21 PM   #3
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Condensation behind xps?


Once you air seal the foam board to the wall and add wood framing with air sealing the drywall, you should be fine; http://www.buildingscience.com/docum...ent-insulation

The 1/2" board sounds a little thin, where are you located?

Gary
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Old 01-20-2011, 09:27 AM   #4
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Condensation behind xps?


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Originally Posted by GBR in WA View Post
Once you air seal the foam board to the wall and add wood framing with air sealing the drywall, you should be fine; http://www.buildingscience.com/docum...ent-insulation

The 1/2" board sounds a little thin, where are you located?

Gary
Located in Omaha, NE. I decided to go with the 1/2" since I am also using R13 insulation in the studs.
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Old 01-20-2011, 10:22 AM   #5
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Condensation behind xps?


I did the exact opposite. I did not want to use any fiberglass insulation in the walls as once it gets wet, it tends to not dry out and will mold/mildew, whereas XPS is mold/mildew resistant.

I put 2" foam board up, then studded the walls with no additional insulation or vapor barrier.

I sealed all the seams between boards and then applied 600 linear feet of DIY spray foam insulation on the top of the XPS into the sill plate cavities to ensure no air penetration behind the XPS and a place for condensation to form.

Yes, I spent more on the 2" than 1/2" and batts, but long term, not having to worry about it, was what I was after.
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Old 01-20-2011, 12:29 PM   #6
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I did the exact opposite. I did not want to use any fiberglass insulation in the walls as once it gets wet, it tends to not dry out and will mold/mildew, whereas XPS is mold/mildew resistant.

I put 2" foam board up, then studded the walls with no additional insulation or vapor barrier.

I sealed all the seams between boards and then applied 600 linear feet of DIY spray foam insulation on the top of the XPS into the sill plate cavities to ensure no air penetration behind the XPS and a place for condensation to form.

Yes, I spent more on the 2" than 1/2" and batts, but long term, not having to worry about it, was what I was after.
I had thought about that but I didn't want to lose that addition 1.5" along the walls. I knew I was going to use xps but there are so many different ways you can do it. I think as long as I seal it well enough it will be good.
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Old 01-20-2011, 01:13 PM   #7
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Condensation behind xps?


With your annual heating degree days (6400) compared to Minnesota (7900), you need at least 2-1/2" of XPS (80%), page 9; http://www.eere.energy.gov/buildings...s/db/35017.pdf

Gary

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