Fiberglass insulation support conundrum


Old 04-13-10, 12:21 PM
Thread Starter
Join Date: Jan 2010
Location: North Carolina
Posts: 55
Fiberglass insulation support conundrum

Hi there - I was wondering why the fiberglass batts in our crawl space were hanging down so badly. The Kraft paper does not touch the floor above, which can't be good.

So I determined the on-center distance between the joists to be 16" and got myself a bunch of wire insulation supports. When I tried to put them up, I found out - to my surprise - that the wires are not long enough for our joists. It looks like the joists are thinner than normal with a thicker strip attached to the bottom of them (if that makes sense). The installer simply put 16" wires in there, but they don't hold squat, and many have fallen out over the years.

In any case, I need to get me longer supports. There are 24" wires, which I will have to cut off at the appropriate length. Is there a particularly appropriate cutter that will make a chisel-type cut, so that the wire ends will dig into the wood? Since I also need to dig out some old fence in our backyard, I was hoping to get a cutter that can handle both jobs well. Any recommendations?

Thanks! MM
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Old 04-13-10, 01:48 PM
Join Date: Oct 2008
Location: New England
Posts: 9,997
Those are called "I" joists and do present the problem that not only are the wires too short, but the insulation is not wide enough. Most insulation is cut 15" to be tight in a 14.5" cavity. Your cavities are, I'm assuming, 15.5" and thus the insulation will perform very poorly. And given the difficulty in getting those floors warm, heat rises, you need the best job possible. A couple of options, both involve replacing the fuberglass that is there, are commercial batts which are wider or mineral wool which can be cut to 16" lengths and installed cross wise. Just some thoughts.

Old 04-13-10, 03:43 PM
Join Date: Aug 2009
Location: USA
Posts: 4,941
Perhaps filling in the spaces with 1/2" plywood or foam would be a good idea.
Old 04-15-10, 09:24 AM
Thread Starter
Join Date: Jan 2010
Location: North Carolina
Posts: 55
Thanks for the input!

Filling the space between the joists with 1/2"-1" rigid foam strips sounds like a great idea, because I won't have to get completely new insulation ($$$). I'd rather invest my money in insulating the entire crawl space after turning it into an unvented version once the current HVAC system needs to be replaced. It's 10 years old and only very basic equipment, so it'll probably go within a few years...

Thanks again! MM

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