Should Retrofit Window install use insulation?

I'm having a window replaced with a vinyl replacement window. So the frame of the current window (steel) will be left and the new one has a lip on the outside that goes beyond the window to the stucco.
I still have to confirm this, but it appears that the company does not fill in the small gaps from the undersized replacement to the old frame with any insulation. They caulk the outside fin and then the inside trim.
Any opinions on if it is important to put some sort of insulation? One thing I realized was that there would be the vinyl and then about 3 inches of space then the trim vinyl sealing the other side. It occurred to me that the *glass* only has air in between it too, and a much smaller gap.
Actually, I am more concerned about noise than anything, and I seem to recall people in here saying fiberglass insulation does little if anything for noise.
Is this an issue in the install that I should even be concerned about?
-- John
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I had the same issue whwn I had windows installed last year. They did not include insulating the window weight spaces. I simply cut some fiberglass into strips and stuffed them into the weight pockets before the guy put the new windows in. The new windows are about 50% quieter than the old wooden ones with storm windows were. I hope to get more done this year and will try the foam and see which works better

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If the window is caulked correctly, inside and out, this will create a dead air space, which is a great insulator. That said, many installation instructions say to use fiberglass insulation or low- expansion foam in any gap wider that 1/8" and then caulk the seams. If you use insulation, you don't pack it tight because it losses R value.
Another thing to ask the installers about is backer rod. If there is nothing in the gap behind the caulk, it is very difficult to get a good 3 sided seal. Backer rod is a round foam strip that get's stuffed in the gap to - ready? - back up the caulk. The wider the gap (sideways, not deep) the more important the backer rod is. Try caulking a 1/4" gap with a 3" void behind it - you get the idea. Backer rod comes in various widths for various gaps sizes and is pretty cheap, like a nickel a foot in bulk.
Remember that once they reinstall the trim, you won't know how good a caulk job they did, so I'd make sure you get a good explanation as to how they are sealing the gap. You can spend thousands on a window job and be worse off than when you started if they do a lousy job of installing them.
Good luck!
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On Sun, 30 Mar 2008 06:12:20 -0700 (PDT), John Ross

I admit I'm very biased. Use the correct caulk on the vinyl nail fin. Butyl caulk is my choice. A proper moist wrap tucked around/under window and siding (stucco). Top piece goes on last. Imagine how water flows. Done correct the window won't leak from outside climates.
Before the inside finished trim is done and any trim caulk, fill the spaces around the window rough opening with the foam material from a hardware. (backer rod?) is a dense foam and comes in 1/2, 1, and larger diameters. Cut and pack the empty spaces.
This is the same type foam I use too insulate outside pipes: AC pipes, water pipes (PVC)....not the same application.
Borg may have a bag if the type for the window insulation.
It WILL insulate the window. It only takes a few minutes, but makes substantial comfort.
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use the expanding foam from a can, its costly but insulates great, seals and quiets things too. air infiltration carries noise.......
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snipped-for-privacy@aol.com wrote:

Make sure you use the LOW-expansion kind, where it says on the can, 'safe for windows'. The regular stuff, in a confined space, can push hard enough to jam the window solid. Note also that many retrofit window installers never touch the existing inside trim- in fact that is part of their sales pitch. The kit is sized to fit the existing casing exactly. Need to discuss all this with the guy that writes up the order- if there are weight pockets, etc, you want them filled before they are covered with the new material and inaccessible. Even if it costs a few bucks and they have to drill a few holes before they pop the new window in, it is worth it. If the installers don't do it, homeowner will have to pry off the inside casing later, and go in that way. Not a big deal, but if you have never done it before, trimming out a window without breaking the old trim and trashing the paint on the wall can be a challenge.
-- aem sends...
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