Fiberglass vs solid??

[jdsackett]

Ladies and Gentlemen, how y'all doing?? Have a question about insulation. Many of you use solid board insulation for walls, etc. After researching costs involved, fiberglas come in tons cheaper and has a better R value. Plus it bends well and can be fitted easily on curved surfaces. Granted, there isn't a lot of depth in the space it needs to go. Now, Question: If a roll of R13 fiberglass is 6 inches thick, if it is compressed down to 2 inches, does it retain its R13 rating and if not how much does it lose?? In my mind, it has many desirable properties, but there must be a reason so many use the board. Thanks. Regards, J.D.

 

[Spaceman Spiff]

Question: If a roll of R13 fiberglass is 6 inches thick, if it is compressed down to 2 inches, does it retain its R13 rating and if not how much does it lose?? In my mind, it has many desirable properties, but there must be a reason so many use the board. Thanks. Regards, J.D.

No it does not retain R13.

http://www2.owenscorning.com/litera...ul Compressed R-Value Chart Tech Bulletin.pdf

The main reason closed cell insulation is used is that it does not absorb nor hold water; i.e. doesn't act like a sponge.

-- Spiff

 

[karl]

ah, the great insulation debate.....

Short answer- air between the fibers is the insulation, the more it is compressed- the less insulative value.

Among the reasons for not using fiberglass are;
it settles with movement
fibers migrate anywhere they can, including your living space.
absorbs moisture
mice love it.

That said, I have insulated difficult vans(Sprinters) with fiberglass, and sealed the walls with a continuous vapor barrier. http://www.amazon.com/gp/product/B000GFT7FI/ref=oh_aui_detailpage_o07_s00?ie=UTF8&psc=1

I prefer rigid closed cell foam in cases where access is more reasonable. Often covering the foam with painted cloth as a lightweight finish wall.

YMMV

 

[Willy]

I believe that fibreglass insulation has a LOWER per inch than foam insulation.. but is way cheaper. ..Willy.

 

[akrvbob]

All good responses! Yes, if you compress it it drastically loses it's R Value

No, it does not have as good an R value as Polyiso rigid foam boards:

3 1/2 inches of Fiberglass = R-14
3 1/2 inches of Polyiso = R-22
2 inches of Polyiso = R-12

By the time you compress that fiberglass, Polyiso will probably have triple it's R value.
Bob

 

[HarmonicaBruce]

I believe that squeezing 6 inches down to 2 inches will decrease the insulative properties by 2/3. It will conduct (at least) 3 times as much heat. This is based on my having been a physics major in college, but does not mean I'm correct.

 

[highdesertranger]

all good answers. way back when rocks were being formed and I did van conversions(1970's). about all that was available was fiberglass or foam rubber. while both insulated good if not compressed, both absorb water like a sponge. many times when converted vans came in for repairs. the insulation would be moldy and the sheet metal would be rusting from the inside out. so when Styrofoam became readily available most of your better conversion companies switch and with the newer ridged insulation the is really no reason for using fiberglass. highdesertranger

 

[jdsackett]

Well, I figured there had to be a reason no one was using it. Thanks for the input fellas. Regards, J.D.