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Discussion Starter · #1 ·
i see most guys using low expanding foam for windows. however, when there is a wide gap for whatever reason,they always use fiberglass. why is fiberglass insulation used for wide gaps?
 

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Expanding foam is for DIY home owners pros use fiberglass. Foam voids most all window warranties.
 

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Discussion Starter · #3 ·
i see most pro's around here using low expanding foam and only fiberglass when there is a wide gap. there has to be a reason why fiberglass is used for wider gaps.
 

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the warranty issue is they don't warranty damage cause by foam,not that you cant use it
just have to know how to use a low expansion foam and a foam gun
hilti makes the best imo
 

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Probably because of the cost!

I've always used the fiberglass for a few reasons


First is because it is less expensive.
I can pick up bags of cut-offs for free from my local insulation contractor.

Second is because when I saw the foam first used around here,it wasn't done right and the windows became inoperable.

Third reason is I'm an oldfrt and not subject to new ideas without seeing the results until the test of time has proven them viable.
 

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ive seen guys pack so much fiberglass that even that can bow the jambs

nothing will airseal around a unit better than foam,and thats what your looking to do around a unit imo fiberglass wont do it
 

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Since the advent of low expansion foam i'll pick that everytime over fiberglass because it's 100% air tight/water tight once it sets up. All the jambs should be shimmed accordingly anyhow, though i know many guys pack in fiberglass to be used in place of shimming so the sashes seal properly throughout the range of motion.

I've never had a call back for air coming in using either foam/fiberglass around the windows, and we used fiberglass for well over 20yrs now...i just personally prefer to use foam when i have the opportunity, and not all replacement window scenario's have enough gap to use foam for a full jamb seal...straws/wands are a lil too fat to fit in the gap between the old wood jamb and new window, so many times we still use fiberglass...i just make the call on each situation.
 

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guys
why do they opt to use fiberglass for wide spaces?????? other than cost.
Because foam is expensive and they probably low bid the job. Fiberglass provides very little insulation value when compacted. You would be better off stuffing old newspaper in the gap. Or better still, measure more carefully.
 

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just because your not called back dont mean air infiltation isnt happening

you pull the trim from a unit and see black streaks running thru the fiberglass air is just being filtered right thru it

you could also use the right sized foam backer rod and sealent to achive
a high degree of air sealing
 

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Discussion Starter · #12 ·
no, not a problem with measuring. i see it with some new construction on older homes. sometimes there are wide gaps around the sill or stool.
can foam be used for very wide or LARGE spaces?
 

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ive seen guys pack so much fiberglass that even that can bow the jambs

nothing will airseal around a unit better than foam,and thats what your looking to do around a unit imo fiberglass wont do it

Very true!
It has to be done right.

It shouldn't be stuffed in so tight that it loses it's intended use anyways.
Kind of like stuffing 6" insulation into a 2x4 wall.

It does work when done right.

Here is a shot of my exterior garage entry door.
I never finished the insulation ,so if you look at the black streak where I didn't put insulation compared to the area just above ,where I just pulled back the fiberglass you can see that the fiberglass was doing its job.

No black streaks where the fiberglass was.
 

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no, not a problem with measuring. i see it with some new construction on older homes. sometimes there are wide gaps around the sill or stool.
can foam be used for very wide or LARGE spaces?
Doesn't matter if it's new construction or not. In fact mismeasurement is usually more prevelent on new consruction than with replacement windows b/c new construction windows are made to certain sizes and carpenters dont aways get every window the same size. Foam is also very messy to use and a lot of window installers give up before they master it's use.

Can be used in large areas such as weight pockets, in fact we always use it there. I also agree on the right size backer rod, that's important.
 

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Discussion Starter · #15 ·
ok skydawggy i think i see your point. it can be used in very wide spaces,its just more expensive? i see so many guys using foam but then use fiberglass ONLY in a wide area..is that why?
dumb question but here goes, can you use fiberglass insulation in conjunction with foam in a gap; half and half?
 

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just because your not called back dont mean air infiltation isnt happening

you pull the trim from a unit and see black streaks running thru the fiberglass air is just being filtered right thru it

you could also use the right sized foam backer rod and sealent to achive
a high degree of air sealing
But if you do your job right, on replacement windows, with caulking the blind stops prior to setting new insert into place, technically there should'nt be air infiltration since that joint between the outside and the new window has a sealant creating a barrier...which if done right you should'nt have to use insulation at all and it falls back into that claim of "dead air space is the best insulator":rolleyes: I just like the foam since i KNOW there will never be air passing through, ever, it's impossible if you do the job right. And the same could be said for fiberglass. But after replacing hundreds of already new replacement windows homeowners and Hank the hack Handyman tried to install on Sunday...i as well as most of you other guys that do this know the job is rarely done right...most just slap'em in and go since the checks will be cashed long before they find out they have issues.
 

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for me seeing that insulation that pristine has not been my experience
air will follow the path of least resistance for sure and may be why the glass in the pics is as clean as that

usually fiberglass just slows down the speed at which air moves thru it
thats another reason you see it faced with foil or paper or plastic and shouldnt the glass you put the cavity also have it?

not saying i haven't insulated windows like that before,cause i have but given the option ill choose a good low exp foam

to say foam is diy well....:rolleyes:
 

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oh? were talking vinyl replacement? sorry i thought we were talking prime units sorry,and ill agree caulking those units is generally enough,i usually get them foam wrapped
 

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for me seeing that insulation that pristine has not been my experience
air will follow the path of least resistance for sure and may be why the glass in the pics is as clean as that

usually fiberglass just slows down the speed at which air moves thru it
thats another reason you see it faced with foil or paper or plastic and shouldnt the glass you put the cavity also have it?

not saying i haven't insulated windows like that before,cause i have but given the option ill choose a good low exp foam

to say foam is diy well....:rolleyes:
Either one works, and works well....
if it is done properly.
I have seen guys screw up
with both, I can make either one work.
The idea is to fill the cavity,
not stuff it.
The whole concept of fiberglass
is that it traps air.
The air does ot move through
it.
 

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i respectfully disagree with air not going thru fiberglass:notworthy
i dont think that r value is what your going for when you insulate around a window or door,which is why its said not to pack the glass so it mantains the stated value

but hey like i said if you pro's like it who am i to say:thumbup:
 
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