Blown-in insulation over fiberglass batts
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Currently in the process of construction with R11 fiberglass batt insulation. When using thermal imaging, there are lots of voids and gaps, especially at the edges of the rooms. The plan is to use blown in R27 fiberglass on top to bring the total to R38.
Is there any utility in fixing the batts to fix the voids and gaps? Or will the blown-in fiberglass on top of everything fix all of that?
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I seem to recall a very similar post very recently?
Personally, I'd probably do a quick job of fixing the batts just because of OCD. The blown material probably won't work it's way down into the gaps, especially small gaps, since it will get stuck on the sides and build up a blockage before the lower part of the gap fets filled.
From a practical sense, you probably won't see a huge amount of thermal performance difference regardless, unless you have pretty large gaps. Note that I'm only talking about gaps on the SIDES of the batts, between the batts and the framing. Any depressions in the SURFACE of the batts are no problem, the blown fiberglass material will fill those depressions in without any trouble at all.
Bill
Thanks. Do you think blown-in cellulose would work better on top of the fiberglass batts than blown-in fiberglass?
If you can't air seal the ceiling under the attic, then yes, blown cellulose would probably be better since it's more restrictive to airflow than fiberglass is. Cellulose is also better in terms of radiant heat penetrating the material, which is a plus during cooling season. Cellulose is heavier though, so it will compress the batts more than fiberglass, but I don't think that will really cause any issues.
Bill
Thanks. The attic was air sealed. With that in mind, it sounds like there wouldn't be a substantial difference between blown-in fiberglass vs cellulose?
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You may find this discussion useful:
https://www.greenbuildingadvisor.com/question/densepack-and-loosepack-fiberglass-or-cellulose