12-15-11, 12:40 PM | #11 |
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Here is the spec sheet for the "150" XPS. They also have a 250 XPS which I'm not sure what the difference is (perhaps tongue and groove vs flat sides).
http://insulation.owenscorning.com/a...a29e2fd5bc.pdf With a 40°F temperature differential this stuff has an r-value of 5.5. At 75F differential it is R5.
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12-15-11, 02:05 PM | #12 |
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The spray foam I used is rated at R-7 per inch x 3 inches = 21, plus 5 more inches of cellulose at R-3 per inch = 15 + 21 = R-36. I added a second offset 2x4 stud wall for the extra thickness, so thermal bridging is minimal.
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12-15-11, 02:55 PM | #13 | |
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Quote:
Without a doubt, you are doing this the right way... possibly more right than you realize... Your 3" of foam on the outside walls not only gives excellent R-value, and a complete seal against infiltration, but it also sets up a thermal gradient, such that moist air will never reach the dew point inside your cellulose fill. Just couldn't be better. Had I started with the knowledge I have now, and the technologies that are available now, I would do exactly what you are doing. As it is I will probably do a variant of your method on the next room I tackle. My little house is only 700 square feet, and I'm trying to minimize intrusion into my living space... so some balance is called for here. The offset studs idea is great... I think I can do a version of that, next room. Great advice, great work! -AC_Hacker
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12-15-11, 04:08 PM | #14 |
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EPS has a lower R than XPS which is R 5. 4.something is about right for EPS.
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12-15-11, 07:18 PM | #15 |
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Thanks AC, for the kind words.
I think my wife took some pictures along the way. I hope to put up a build thread of the process some time soon. My house is only 800 sf too. We feel that if just right for the three of us. |
12-15-11, 08:02 PM | #16 | |
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-AC_Hacker P.S.: [Everybody tells me I should add onto my house, but for 35 years I have successfully resisted!]
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12-16-11, 01:02 AM | #17 |
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12-16-11, 06:40 AM | #18 |
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Dunno if you posted the right link. That guy is using polyiso in his wall, not EPS or XPS... Only one other guy mentions using XPS. I think polyiso would be the way to go since its indoors and has a significantly higher r-value.
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12-16-11, 10:31 AM | #19 | |
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I was mostly focused on the technique. -AC_Hacker
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12-16-11, 11:11 AM | #20 | ||
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Daox,
Gotta thank you on this one... Turns out that I can get the XPS at the same price or slightly cheaper locally, because there is a manufacturing plant close to my town. Quote:
Quote:
I went through the literature, and the companies do their best to make it difficult to do an apples-to-apples comparison. Polyiso is higher R-value, but is subject to "R creep." R-6.5/in. seems to be the spec. There is also a foil face that can be used with a dead air space to increase R-value. EPS is or should be cheaper, but for me, locally, it is not. They're coating one side with a metalized layer, and if you use it correctly, with the dead air space and all, it has higher R-value than XPS, but the EPS + dead air system takes up more space. No significant R creep. Disregarding the metalized layer and dead air space, R-3.8 to R-4+ per in. seems to be the spec. Otherwise, R-5.5 with the dead air space (3/4" to 3"). XPS has no foil, no R-creep and R-5 value. That's what I'll be using. Most people seem to be using saws with this stuff and the dust & debris from the sawing seems to be a real problem. I'm going to see if I can hack up some kind of a hot wire tool. Thanks for the XPS tip... -AC_Hacker
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