Can't find the right width insulation for crawl space.

[adama]

Sorry if this doesn't belong here.

I am about to insulate my crawl space. The width between joists is 18 inches. I can only find 15 and 23 inch batts. I went ahead and bought the 23". Should I just fold the extra down the sides of the joists? Or would it be worth it to cut the extra 6" off and piece it together and use it? Would stuffing extra insulation between joists cause any negative effect from compressing the insulation?

[stvc]

Cut the extra off. fiberglass is only effective when properly installed, tight fitting and not compressed. If you buy the rolls, before you pop it open you can use a hand saw to cut the whole roll at once. You probably will find some spaces for the waste but don't piece it together. Fill all holes from pipes, wires etc. first with expanding foam, very important step.

[bobb25]

If it's a damp crawl space, you might want to consider spray foam. My cousin had a house built, and after two years, half the insulation had gotten wet enough to fall down. If you do cut the role while together, you'll have to use something other than the staple method.

[stvc]

Not sure but I think NC would require the vapor barrier toward the living space, they sell stiff wire that goes between the joists to hold it up. Moisture in craw space is always something that requires consideration though.

[karsthuntr]

If it's a damp crawl space, you might want to consider spray foam. My cousin had a house built, and after two years, half the insulation had gotten wet enough to fall down. If you do cut the role while together, you'll have to use something other than the staple method.

It would have been better to correct the moisture problem.

[cem-bsee]

save lots of man-hr = insulate walls!

but not the bottom 4- 6" of masonry at the earth -- need to see the termites!

[bobb25]

It would have been better to correct the moisture problem.

I tried to tell him that. His well tank and water lines were down there, always dripping with condensation. Lousy construction. They even put the well pump so far down that it was sucking sand. Only tankless coil I ever saw that was filled with solid glass from the sand being cooked.

[karsthuntr]

I tried to tell him that. His well tank and water lines were down there, always dripping with condensation. Lousy construction. They even put the well pump so far down that it was sucking sand. Only tankless coil I ever saw that was filled with solid glass from the sand being cooked.

I'll refuse to warranty a unit in the crawl unless they fix the moisture problem. I have seen 5yo furnaces that looked like they were installed in the 70's.

[teddy bear]

Insulating between the joist is risky bussiness. Best to cover the earth with plastic, close the vents, and insulate the walls with aluminum faced foam board. You will need some dehumidification for perfect control. If you must precede with your insulating the joist, the vapor barrier should be toward the high moisture side which is down in the SE US. Vapor barrier toward the floor allows condensation on the barrier under the insulation. The results is rotten joist and mold unless the crawlspace dew point is maintain <50%RH or <60^F dew point. Check buildingscience.comm
Regards, TB

[dandyme]

The width between joists is 18 inches.

What kind of dumbass builder put joist on that kind of center?

[bobb25]

I'll refuse to warranty a unit in the crawl unless they fix the moisture problem. I have seen 5yo furnaces that looked like they were installed in the 70's.

He had a Weil boiler with a tankless coil, but it wasn't in the crawl space. I've seen 5 year old steel boilers rust out just from turning them off in the summer.

[adama]

Insulating between the joist is risky bussiness. Best to cover the earth with plastic, close the vents, and insulate the walls with aluminum faced foam board. You will need some dehumidification for perfect control. If you must precede with your insulating the joist, the vapor barrier should be toward the high moisture side which is down in the SE US. Vapor barrier toward the floor allows condensation on the barrier under the insulation. The results is rotten joist and mold unless the crawlspace dew point is maintain <50%RH or <60^F dew point. Check buildingscience.comm
Regards, TB

Why do you say it is risky? Most houses around have the floors insulated, especially the new ones. Or am I misunderstanding something?

Also, I was under the impression that the vapor barrier was supposed to be toward the floor

What kind of dumbass builder put joist on that kind of center?

Who knows, it was built in 1925

[bobb25]

I agree with teddy, although not with the risky part. You'd be better off insulating the walls, and if you have dirt, cover it with plastic, which you should do anyway.