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Old 06-17-2010, 03:05 PM   #1
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insulate (mostly) above grade concrete wall


I'd appreciate some advice on the best way to insulate the wall pictured. 75% of the concrete section is above grade...the house is on a slope so 3' in the back corner is below grade and none of the concrete is below grade in the front. The wall is West facing and the house is in Seattle. The black area is tar paper that had previously been glued to the concrete.

Any thoughts on how to tackle this?

thanks.....Brett


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Old 06-18-2010, 12:56 AM   #2
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insulate (mostly) above grade concrete wall


A common way is to fir out w/ 2 by whatevers, then fill w/ insulation. I am no longer a fan of fiberglass AT ALL. Rock wool, cellulose, or cotton is better stuff. This assumes, of course, that that block wall is well sealed outside and will remain dry. Some folks simply glue X" thick XPS (blue or pink board) to the walls, which gives a continuous break from cold and is more robust if you get moisture on the walls. Fasten 1x strips over that to hang sheet rock to. GL. j

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Old 06-18-2010, 05:10 AM   #3
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insulate (mostly) above grade concrete wall


i'm still having trouble seeing the conc - all's i see is block what conc ? ?

ambient earth temp's about 67f,,, insulation ?
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Old 06-18-2010, 10:00 AM   #4
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insulate (mostly) above grade concrete wall


The back wall is block, but the other wall is 8" poured concrete and extends from the back corner to a framed wall (where you can see I've added batts).

I was going to do just what jklingel said and attach foam then furring strips and sheet rock, but I wasn't sure whether this was o.k. since part of the wall is below grade and part above.

I'm wondering whether the best solution is to build a 2X4 wall an inch away from the concrete and fill with batts. The wall is in a walk-out basement and although I just moved into the house, it appears to be dry.
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Old 06-18-2010, 11:35 AM   #5
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insulate (mostly) above grade concrete wall


Why a gap between the new and old walls?
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Old 06-18-2010, 12:29 PM   #6
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insulate (mostly) above grade concrete wall


So that the fiberglass doesn't touch the concrete.

I've seen lots of info online about insulating a below grade basement wall (glue on foam+stud wall with fiberglass+vapor barrier+sheet rock) but I can't find anything about an above ground wall. I think in my situation I need to allow the moist inside air to dry to the outside. I was thinking that the foam glued to the concrete would block the moisture, that's why I suggested just building the 2X4 wall with batts minus the foam.
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Old 06-18-2010, 02:57 PM   #7
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insulate (mostly) above grade concrete wall


First off, I am not sure there is "Verdict One" for basements, and the more I learn the more I wonder about vapor barriers with concrete walls, esp below grade. I thought your gap may be for that reason, so I'll ask what touching hurts. If the walls get moisture condensing on them (hence, "no wall touching the insulation") I suspect you will have wet insulation and mold/rot anyway; don't see how you can stop it. If you've got air going out there, carrying water vapor, then you will have convective currents minimizing the effect of your insulation, too. (S-can that fiberglass, IMO, too.) Below grade, I don't think you want a vapor barrier because any vapor that enters the wall sits in the wall cavity. Above grade, I believe the best place for insulation on block is outside, to keep the blocks warm and thus from condensing, if you do have moisture leakage. I'd sure read more, and I wish I had a pat answer for you. Greenbuildingadvisor.com is a good place to read. Google Joe Lstiburek, too; often cited on the gba site. GL. j
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Old 06-19-2010, 07:39 PM   #8
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insulate (mostly) above grade concrete wall


Quote:
Originally Posted by jklingel View Post
First off, I am not sure there is "Verdict One" for basements, and the more I learn the more I wonder about vapor barriers with concrete walls, esp below grade. I thought your gap may be for that reason, so I'll ask what touching hurts. If the walls get moisture condensing on them (hence, "no wall touching the insulation") I suspect you will have wet insulation and mold/rot anyway; don't see how you can stop it. If you've got air going out there, carrying water vapor, then you will have convective currents minimizing the effect of your insulation, too. (S-can that fiberglass, IMO, too.) Below grade, I don't think you want a vapor barrier because any vapor that enters the wall sits in the wall cavity. Above grade, I believe the best place for insulation on block is outside, to keep the blocks warm and thus from condensing, if you do have moisture leakage. I'd sure read more, and I wish I had a pat answer for you. Greenbuildingadvisor.com is a good place to read. Google Joe Lstiburek, too; often cited on the gba site. GL. j

Ditto. The more I learn about this stuff, the less clear-cut it is. I read a bunch of Joe Lstiburek (sp?) papers over at the buildingscience.com site that has a lot of his writing-- it's VERY informative.

I'd think insulation in your case would be best on the outside if at all practicable. If the concrete isn't getting super cold, then you have less of an issue with condensate accumulation.

Otherwise, I'd just think it through based on most likely needs for vapor control/transport and heat flow/mitigation.

In Seattle you have neither the brutal cold temps nor the blazing heat of other locales. I, too, am wondering if you'd need or want a vapor barrier at all. How likely is it in summer that your exterior will be so hot and humid that you get a massive vapor push into the cooler, drier conditioned space? Conversely, would you have a super-dry (bitter cold) winter which would create an extremely different environment indoors vs outdoors?

IMO, vapor barriers are for locations where there is a massive difference in heat and humidity between outdoors and conditioned space. Think Louisiana or North Dakota for two extremes. In Louisiana, you'd want the vapor barrier as far outside as you can (massive vapor push inward in summer). In North Dakota, you'd want the barrier on the inside (massive outward vapor push in winter).

In Seattle, I don't think the pluses of any vapor control measures outweigh the serious potential negatives.

JMO

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