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Batting for non-standard width

I'm trying to insulate the attic in a 100-year-old house. The bays between the joists are 20" wide, but I can't find any rolls of batting at that width.

My first thought is to buy 23" batting and slice off the extra 3" with a utility knife, but that seems like it might be both messy and time-consuming. I'm looking for 6 1/2" deep fiberglass insulation, the higher R-value the better.

Any ideas on the best approach are greatly appreciated. For instance, is there any way to get batting custom cut? Thanks in advance

Re: Batting for non-standard width

cutting 23" wide batts are pretty much all you can unless you want to use blown in cellulose or spend 3x more and get spray foam installed

A. Spruce
Re: Batting for non-standard width

Another option would be to use narrower insulation in the bays and then roll out the wider stuff perpendicular to the joists over the top of everything.

Re: Batting for non-standard width

this happens often. what we do is take a regular insulation bat and cut up a whole length into segments of 20" or whatever the width of the rafters are and install them all perpendicular to the rafters. so if you have a rafter bay and the between the rafter measurement is 20" (for example) and it's 12' long, then you cut 9-10 pieces of insulation 20 1/2" long and you'll need about 9-10 pieces to fill each bay.

make sense?

Re: Batting for non-standard width

Thanks everyone! This is exactly what I was looking for.

I've never done this before, and could only find basic instructions ("wear gloves") on the web.

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