How to fill crawl space insulation between 20" on center floor joists?

My house is elbow shaped. Kitchen, den, living room on one side of the bend and bedrooms, baths on the other. The floor joists under the bedroom side are 2x8 12" on center. I am cutting a 23" wide roll of insulation in half lengthwise to insulate under the house. This gives a tight fit to the insulation.
However under the den side of the house, the joist spacing is 20" on center. I have a 19" space to fill and insulation at Lowe's, Home Depot only comes in 15", 16", 23", and 24" widths. I don't particularly want to use the 23" rolls since that would be a waste of 4" from each roll.
Does anyone have any ideas of how to efficiently fill this space?
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snipped-for-privacy@removethis.com wrote:

Just get the 23" wide rolls or batts and cut them down to 19". Yes, it's a pain, but the only other alternative I can think of is to use blown-in insulation somehow. And if its the underside of the floor joist in the crawl space you are insulating, then adding something to hold the blown-in insulation in place is more trouble than cutting down wider rolls.
I've been doing this in our attic that has random roof joist spacing, ranging from 18" to 22" (old house built in 1925). Find a place to store all the little scraps to use for something else. I store my scraps behind one of the knee walls in the attic.
Ken
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wrote:

4x8 foot sheets of solid insulation. Cut them across the 4 foot side in 19 inch widths. This will give you five pieces of 4'x19" insulation. Tape the joints with aluminum tape. I used two inch thick foam with aluminum on both sides when I remodeled my kitchen. Cuts easily with a handsaw or a radial arm saw. Dust is nasty so wear a mask if you use a power saw.
--
"De inimico non loquaris sed cogites."

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I don't know if this will work, up to code, etc, but what about tacking the 4x8 sheet to the *bottom* of the joists leaving an air gap?
I think this would significantly reduce air infiltration... especially if you used a good seal where ther meet/terminate. (possible spray foam?) you might be able to incorperate a radiant barrier as well.
Also, what are you doing for vapor barrier? If you can get a continuous sheet it will also help with air infiltration. Anyone know if it's not a good idea to use a single large sheet which gets tucked up into the space before the insulation? (kinda like wide accordian folds)
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