Almost finished excavating my crawl space. Down to 42" throughout.
The floor joists (some 6" some 8") are placed at irregular intervals. While
some are nearly 24" o.c., most of them are not. Spacing ranges anywhere
from 12" to around 19".
What is the easiest way to insulate (from below) these odd cavities. When I
did some of the walls, I simply used my 36" paper cutter to cut the
insulation and installed the small pieces 'side-ways'. If I made
longitudinal cuts there would be a lot of waste with long thin slivers of
insulation left over.
Somebody must have already solved this. Please don't tell me that
professionally installed foam is the answer. I cannot afford that
All replies appreciated.
We used this:
in several places recently. A lot of it went in exterior wall
in our small foyer, but we also sprayed it above the foundation,
between the joists in our basement and crawl space. (The
purpose there was to close up the voids in the top row of
block, to reduce the amount of air that was pulled up from
the ground into the house. It's a weirdly built house.)
My husband did most of it, but he got a friend from work to do
the crawlspace portion (because DH is pretty spherical and
didn't think he could effectively reach where he needed to in
our crawlspace that's roughly 24" high, and less where the
It wasn't cheap, but it was cheaper than hiring it done.
Purchase the widest width of fiberglass insulation you can find. For 24"
OC, it would be 22-1/2" or so wide. Sharpen the edge of a 4" or 6" drywall
knife to use for both tucking and cutting the insulation. Lay it on one
board and use another on top to compress the fiberglass insulation and then
cut along the board, using it as a straight edge, with the sharpened side of
the drywall knife. Personally, I'd cut it about 3/4" oversize for a better
friction fit. Use the knife to tuck the sides into the space between the
joists, since you want the entire surface to be against the floor sheathing
above. You can also purchase stiff wires, (called lightening rods) that you
jamb between the joists to support the insulation, hold it against the
decking and prevent it from sagging.
Save the pieces you cut off, and you'd be surprised at how you'll find
places they can be used, such as in corners and for tucking around windows
I've got somewhat random joists. I've got it help up by fence wire,
The most important part is to have no holes in the insulation
barrier. No airspaces to the floor. So stuffing is fine. I have one area
where I overlapped to rolls, one for each edge.
I bought a bunch or R30 cheap at the home despot. You can pull that
apart and lap it back together.
The floors are pretty tight now. We had the coldest winter in some time
and the heat loss through the floor was good. If you don't have an IR
spot thermometer, they are fabulous for looking for the weak spots in
the thermal envelope (during temp extremes) not to mention "cool"!
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