What's the best insulation to use with 2x4's?

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Hi,
My contractor told me to use R13 insulation on the walls framed out by 2x4's. He said that it won't fit thinkness-wise, but I would be able to compress it with drywall. Does that sound like good advice?
Many thanks in advance,
Aaron
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Google R13 fiberglass....looks to me like it's 3.5" thick......sounds like the right stuff for 2x4 const
are you sure he said "if won't fit"?
cheers Bob
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Agree, the R13 stuff is 3.5 inches thick and is designed for this application. It is the stuff to use for 2X4 framed walls. Get the kraft-faced kind and install it with the kraft paper on the inside. You unfold the little folded over strips of paper on each side and staple them to the stud. When you're done the wall looks like a continuous sea of brown kraft paper. Wear a dust mask while installing the insulation; when you see the layer of pink fuzz covering the mask at the end of the day, you'll be glad you did. Wear old clothes and at the end of the day, just throw them away. They will be scratchy ever after. -- H
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Heathcliff wrote:

Hint: Take a pair of old tube socks. Cut two finger-holes in the toes. Slip over your hands and forearms.
Discard when the project's done.
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Since it is the trapped air that does the insulating, I doubt if it would make much difference since compressing the R-13 insulation would reduce its insulating ability.

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Jeff wrote:

Hi, Wondering if amount of air trapped inside the batt is same whether it is compressed or loose? I understand R means resistance against air leak.
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The more you compress, the less air trapped, the less insulation value.
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I see this point but i would like to understand this. If you take this argument to the extreme, then the least amount of insulation is best, because that keeps the most amount of air inside the walls. So how come just having air between the walls is bad insulation?
Thanks,
Aaron
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I think you end up with wall space measurement of fiberglass R value , if wall is 4", fiberglass is 5", then compressed to 4 its the 4" R rating, or near to it.
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closed cell expanding foam insulation the best, it sealls all the nooks anbd cranies stopping air flow, and at R7 or so per inch much better than fiberglass, yes it costs more but gives saving forever
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Just air would be perfect except for one condition: it must be totally still, unable to circulate. With air movement you will have convection losses. This is the reason why storm windows are so inefficient. If you could tolerate a window being translucent instead of transparent, then materials could be used that have very low heat transmission like a closed cell polyethylene foam board. But as insulation numbers increase for such materials, the light transmission decreases. Looks like we're stuck with some trade offs for now.
Joe
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Because having just air means the air can move and readily transport heat from the warm wall to the cold wall. With insulation filling the cavity, there is still a lot of air there, but it's being held in place by the insulation, so it's far more difficult for an air molecule to go from one wall to the other.

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Because having just air means the air can move and readily transport heat from the warm wall to the cold wall. With insulation filling the cavity, there is still a lot of air there, but it's being held in place by the insulation, so it's far more difficult for an air molecule to go from one wall to the other.
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Exactly. There is an optimum for every insulation material, be it fiberglass, cellular foam, cellulose, etc. One big space is not so good. divide it into four and it is slightly better, divide again into four hundred it is better, but divide it into 40,000 spaces it is great, but then if you divide that into 80,000 spaces the solid material between the air cells is transmitting the heat again. That is why concrete walls are so poor compared to even thin layers of insulation.
Heat is always trying to move to the cooler places. With most materials it moves through liquids faster than solids where it moves faster than air.
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How do you divide foam
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ransley wrote:

My bartender just scrapes it off with a knife.
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How do you divide foam
*************************************** Cellular structure is self dividing
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-snip-

You understand incorrectly- it is "resistance to heat flow". Glass provides 100% resistance to air flow- but is a poor insulator, so it has a negligible r value.
Jim
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Aaron Fude wrote:

Hi, Your location?
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It will work but if it gets real cold or hot and utility bills are high, and whose are not, foam will do a much better job
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Just my opinion, but I use R-19, and while I have no way to measure it for insulating value, it does a good job of keeping the cool in in the summer and the warm in in the winter. The reason it works IMO is draft stop, filling the cavity completely works better (again IMO) than having a little something flopping around not even touching the studs, which is usually the case with R13.
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