I've got a crawl space that is about 3' high so you can get around under there pretty well. Above it is a terrazzo floor where the heated/cooled portion of the living quarters are. The dogs love the terazzo floor in the summer time. I have to go into the crawl space every now and then to resolve plumbing issues. I don't go under there without the dogs since I saw that water mocassin crawl out from the access door.

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Jim

Time for a little definition of terms.
The White Styrofoam beadboard is not acceptable in many jurisdictions because the bond between the beads can break down with exposure to moisture and that leaves a while mess that has very little insulation value.

The pink or blue are generally and extruded polystyrene board that are not subject to such weathering issues.
The beadboard is OK for interior uses, but not where it will get weathered. The pink or blue may be used anywhere, I think.

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1982 300SD " Wotan" ..On the road as of Jan 8, 2007 with Historic Tags

The beaded foam lets air and moisture flow through. Comes in 4X8 foot panels. The more ridgid styrofoam types are moisture and air proof I think. They usually come in 2 X 8 foot panels.

You have to be careful not to apply them as a vapour barrier where there should not be one.For thirty plus years I use the beadboard of a little better quality on the exterior of frame construction to reduce the studs, headers,outer edge joists, and top and bottom plate transfer of heat out of the dwellings. Covering it with a product like building wrap.

Care has to be taken to let any moisture that makes it's way into the walls a way to leave. Or rot is going to occur. Almost impossible to get a 100 percent vapour barrier. Plus even six mill plastic has a minute amount of moisture porosity.

Tuck tape the standard red tape for overlaping joints is just a joke. The glue on it separates from the tape a few years down the road. I caulk all inside overlaps with acoustic caulking including along the floor line. Never sets up totally and never loses its adhesive properties I believe. Outside overlaps get cartridge roofing cement. Glues tyback seams together like no tomorrow. As they say the devil is in the details.

The current housewraps also have some issues. Too many cases of removing the siding a few years later and some brands have turned to dust.