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Old 12-09-2012, 02:04 PM   #1
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Does Fiberglass Insulation lose it's R value

Where it comes to heating and cooling your home you want to have it very will insulated to keep it warm in the Winter and cool in the Summer.
With my understand Fiberglass Insulation will loose it R value the colder it gets. Is this true?
And where it gets HOT out in the Summer it loses the elfishness of the R value and lets heat penetrate through it. Is this true?
There has been studies on this and this is what they say.
So I am asking you if there is anything to this.


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Old 12-10-2012, 07:52 AM   #2
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Fiberglass does not loose R-Value solely because of temperature but via convection as a result of the delta T across a given surface.

If you use high density batting, this potential for convection is minimized and if combined with and air tight envelope, fiberglass can work just fine.


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Old 12-12-2012, 12:29 AM   #3
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fwiw..... from

this is just a tiny excerpt from the intro; read the study to get the rest of the story, but i have also read in other places that the r value of fg batts is somewhat temperature dependent. (in my case, it was reported that the colder it gets, the more the r value drops. not good.) how much of a change in the r value, and whether it is of practical significance, i don't know. i am not interested in reading more on fg insulation because i hate the stuff and will never use it again regardless of its merits or lack thereof. i've read and handled it enough. p.e.o.s. "Building energy models usually employ a constant, room-temperature-measured value for the thermal resistance of fiberglass roof insulation. In summer, however, the mean temperature of roof insulation can rise significantly above room temperature, lowering the insulation’s thermal resistance by 10% to 20%."

Here is another link, showing the increase in thermal conductivity as the temp goes up.

Last edited by jklingel; 12-12-2012 at 12:34 AM.
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