Has anyone ever heard of fiberglass insulation batts that are 29"
wide? I'm trying to insulate the floor of my 1860 house and I'm
stumped by the joists, which are set 30" OC. I can't seem to find
anything wider than 24", or anything (like rigid foam board) which
could be cut to that width reasonably efficiently.
There are lot of these houses around -- I figure there must a solution
out there. But so far no luck. Ideas?
I've never heard of wider batts than 24". What I would do is take a
24" roll of fiberglass insulation and cross cut it into 29" pieces or
whatever and install them crosswise in the joist space. Alternatively
you can cut a little strip, to add to your 24" batts, though this can
be a PITA if you are relying on friction to hold the batts in place.
Lots of labor, but then that's an old house for you.
There's no reason the batt has to run parallel to the joists. Cut narrower
batts into lengths that would fit between your joists.
For instance, You could buy 24" wide insulation, and cut it into 29"
lengths. With eight foot batts, that would give you about three sections
per batt. However, with four foot batts, you would have a lot of waste.
I've also seen 4x8 sheets of rigid foam insulation at Home Depot. You could
cut three 29"x48" sections out of each sheet.
Another option would be to attach some kind of barrier to the underside of
your joists (1/4 inch hardware mesh, for instance), then blow in loose fill
insulation. Just don't use a vapor barrier like plastic sheeting that would
Another option, add a joist in-between your existing joists. They wouldn't
need to be the same depth as your existing joists (they wouldn't bear any
weight), just deep enough to span the distance without sagging. This should
let you install regular 15" batts fairly easy. However, if you did make
them the same depth as your current joists, you would end up with sturdier
floors as well.
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