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Fiberglas insulation around windows?

Posted by ajsmama (My Page) on
Wed, Mar 11, 09 at 8:44

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

Follow-Up Postings:

RE: Fiberglas insulation around windows?

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 "Breaktime" forum -- lots of insulation pros there.


RE: Fiberglas insulation around windows?

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!

RE: Fiberglas insulation around windows?

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.

RE: Fiberglas insulation around windows?

I wouldn't take the casing down, but I'd do the rest of the windows.

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