10-15-12, 12:48 PM | #1 |
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Whole wall thermal performance
I came across this paper today by the Oak Ridge National Laboratory. Its quite interesting and shows actual tested whole wall r-values. This means they take into account the thermal bridging of the wall studs and everything. They even show a larsen truss type all, but with fiberglass batting, not cellulose (boo).
Whole Wall Thermal Performance Content Page Here is the chart that shows the different wall types tested:
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10-15-12, 03:03 PM | #2 | ||
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That Oak Ridge study is awesome. Recently BSC has been working on something similar.
Air Leakage Degrades the Thermal Performance of Walls | GreenBuildingAdvisor.com
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10-15-12, 03:08 PM | #3 |
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Yeah, I read that too and was going to post info on it later. Its very interesting to see the difference between the insulations when there is in/exfiltration.
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10-17-12, 12:12 PM | #4 |
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I'm just adding some of the pretty charts from the article S-F posted because they are really good information.
•Wall 2: 2x4 studs, 16 inches o.c., with inset-stapled kraft-faced fiberglass batts; •Wall 3: 2x4 studs, 16 inches o.c., with face-stapled kraft-faced fiberglass batts; •Wall 4: 2x4 studs, 16 inches o.c., with damp-sprayed cellulose; •Wall 6: 2x4 studs, 16 inches o.c., with R-13 open-cell spray polyurethane foam; •Wall 6: 2x4 studs, 16 inches o.c., with R-13 closed-cell spray polyurethane foam; •Wall 7: 2x4 studs, 16 inches o.c., with R-13 friction-fit fiberglass batts plus 1-inch-thick exterior XPS rigid foam; •Wall 8: 2x6 studs, 16 inches o.c., with R-21 friction-fit fiberglass batts. So, this chart is showing us the amount of air transfer in a wall with +10 pascals and -10 pascals of pressure. The first half of the chart labeled [42] is done at 42C or 108F. The second half of the chart labled [-18] is done at -18C or 0F. As you can see, at colder temperatures a wall is much more leaky for the same pressure. Also note, that fiberglass quite a bit more air than cellulose, and spray foam being the best. Its also interesting to note that a 2x4 wall with cellulose performs better air leakage wise than a 2x6 wall filled with fiberglass, and also better than a 2x4 wall with 1" thick XPS over the exterior in most cases.
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10-17-12, 01:52 PM | #5 |
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on the fiberglass batt walls do they have a vapour barrier or is it just plywood, 2x4's/fiberglass, drywall?
I'd assume that with a properly sealed vapour barrier, all joints taped you'd be just as good as the foam's. |
10-17-12, 02:00 PM | #6 |
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The article doesn't mention any vapor barrier anywhere which is odd IMO since its a pretty big deal in cold climates. Good point.
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10-17-12, 02:13 PM | #7 | |
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Their points at the end of the article are also quite good and summarize the article pretty well.
Quote:
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11-05-12, 10:15 AM | #8 |
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attic: cellulose or fiberglass in cold climates
In case you all haven't seen this, it applies to anyone's decision whether to blow in cellulose or fiberglass in cold climates:
"There is a problem with loose-fill fiberglass attic insulation is cold climates. It appears that, as attic temperature drops below a certain point, air begins to circulate into and within the insulation, forming "convective loops" that increase heat loss and decrease the effective R-value. At very cold temperatures (-20F), the R-value may decrease by up to 50%." In full-scale attic tests at Oak Ridge national Laboratory, the R-value of 6 inches of cubed loose-fill attic insulation progressively fell as the attic air temperature dropped. At -18 F, the R-value measured only R-9. The problem seems to occur with any low-density, loose-fill fibrous insulation. Nisson, J.D. Ned, JLC, "Attic Insulation Problems In Cold Climates" March 1992, pp 42-43 |
The Following User Says Thank You to bizboy For This Useful Post: | Daox (11-05-12) |
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