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Renewable Energy for the Home

Fiberglas insulation around windows?

15 years ago

I posted on the Remodeling forum and got conflicting responses. Everyone seems to agree that low-expanding foam is better than fiberglas around windows and doors but here's the problem. DH packed fiberglas in tightly around windows b/c he didn't think builder put enough. Then I hired carpenter to (in some cases recut) biscuit join the mitres on pre-cut casing, I stained and poly'd, got all the bedroom windows and 1 bath (9 windows) up then found the tight fiberglas downstairs. If DH did all the windows like this (I assume he did), should I pull off and prob. destroy the 9 window casings to put foam around instead?

We haven't caulked anything b/c the casings are stained and not painted. I asked DH if we should run a bead of caulk on back of casings b4 install (I didn't want to caulk after install and have it show), he said it would make a mess so we didn't. But should we do that with the remaining ones?

I was hoping people here would know more about insulating and caulking, but that I could also get reasonable answer about exisitng casings (only cost about $150 - $200 for work so far but to redo it would involve materials too and so figure at least $400 plus another couple weeks of my time more to redo those windows if I wreck the casing and have to buy/join/finish new). Thanks

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Comments (4)

solargary
15 years ago
Hi,
I think foam is better mainly because it does not allow air to circulate through it as fiberglass does.
But, if it were me (and I'm an energy saving freak), I'd not take the casings down and do it again.

It was not all that long ago when all windows were done with FG stuffed in.
I'd just must make sure you do a good job of caulking around the outside of the windows.

Once its all in place, you can use a smoke pencil to see if there is any airflow around the edges of the window and behind the casing. If there is, maybe a very very light bead of clear caulk where the casing meets the wall?

You might try posting the same question on the Taunton.com "Breaktime" forum -- lots of insulation pros there.

Gary
2ajsmama
Original Author
15 years ago
Thanks Gary. DH said this AM no way are we taking those casings down, though if I want to pull all the FG out of the open ones and spray foam instead I can (he won't). He also corrected me - it was the carpenter who said caulk on the backside of the casings would make a mess, but I can't see how it would be worse than caulking afterward. As far as the casings already up, since our walls aren't really flat (and jambs aren't level with walls - in some cases we've had to cut sheetrock and caulk anyway to get casing to lie flat b/c header is bowed), there are a few spots where there are small gaps at the sides. Carpenter was very neat caulking (white paintable) on tops and sides where he had to cut sheetrock, I can ask him to caulk sides of all the casings (clear this time) and maybe I won't have to paint all around the windows.

Our modular was built in 2007 by factory now LEED certified and they still stuffed (not that much) FG around openings. But DH said all the factory-installed windows had house wrap right up to them so shouldn't be any air infiltration so I don't know why DH had to put more FG in. We have 1 site-installed window in MBR that carpenter had to put new jamb in, it was so poorly done so wrap might have been cut way back for that, there was no insulation above the header so we tried to stuff more up there after new jambs were in (carpenter didn't put any in, at least we saw that b4 he put the casing on). Still have all the aprons to do - we can use foam under all the windows. Thanks again!
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Don't bother with removing those additional pieces unless they are covering some large void. Even in that case, you can drill a hole and fill (don't overfill) that section. Shop vac out all the old fiberglass that you can readily get to. The issue is not insulation as much as it is stopping the air (as you noted). That being the case, a small skim layer to seal the envelope would accomplish about 85-90% of the value of the retrofit. Do yourself a favor and get a foam gun. Don't bother with the straw stuff. It is more cumbersome and less controllable. Make sure the can is warm and slightly mist the area that you are going to apply the foam to. These low pressure foam are water based cures. Don't worry about making the substrates super clean. Once you work with the foam, you will quickly realize that it sticks to everything.....trust me. Do not try to fill the larger void in one pass. You will get over expansion and leave yourself with a mess inside, outside, or both. Fill the gaps with multiple passes of the foam if they require a larger fill. Get some disposable tips for the gun and don't remove the can from the gun unless you have another can going on the gun. This will prevent the foam from curing in the gun barrel. Thankfully these guns will still be available after the Executive orders. Good luck.
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klaire2001
15 years ago
You could do a blower door test (check for infiltration) or find someone with an IR camera. Either of these methods will let you KNOW if there is air leakage around the windows.
chris8796
15 years ago
I wouldn't take the casing down, but I'd do the rest of the windows.

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