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.guys
why do they opt to use fiberglass for wide spaces?????? other than cost.
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
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.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?
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" 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.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
Either one works, and works well....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....