Insulating an open crawl space
Hi, I have a cabin in West Virginia that is on a foundation of cinder blocks that the floor joist is about 18 inches from the earth. The soil is a heavy clay content that is either hard as a rock when dry. Or moist because I am at the bottom of a holler. So putting skirting will bring on wood rot from the moisture. This cabin was build in 1984. The wood has no rot because it is exposed to air. However, the plywood on top of the floor joist is bare wood as are the joists. My question is this. Can I use styrofoam insulation in between the floor joists to insulate? Being that styrofoam is plastic, does that mean it will act as a moisture barrier from different temperatures of the structure as one would do with exterior walls using a moisture barrier to prevent moisture? Thanks
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Styrofoam is know as EPS (Expanded PolyStyrene) when used as insulation. How vapor open (or closed) it is depends on the thickness. Thinner material is more vapor open, so more drying potential, but also less R value, so less insulating value. You could use it between joists, but that would be a lot of work. It would be easier to fill the space between the joists with batts and put the rigid foam across the bottom of the joists, which would also help reduce the thermal bridging of the joists.
Have you considered a crawlspace encapsulation project here to block the moisture from getting to your home?
Bill
Bill the problem is I am in Low lying land with a creek about 20 feet away so there is a high water table and a crawl space is out of the question. As I said there is no wood rot because it is exposed to air. My question is , would styrofoam say 1 1/2" thick act as a moisture barrier if I installed it under the plywood flooring and in between the floor joists where it would be tight up against the plywood flooring. Or do I need a moisture barrier such as a plastic vapor barrier then install the styrofoam insulation.