Could you use Tyvek as a moisture barrier? Would you use it alone or in conjunction with roofers' felt?

Tyvek is not considered a moisture barrier; even when used under siding. It has some moisture resistance but not that much. It's primary function is as an air infiltration barrier. Extensive testing has been done on many brands of house wraps and none were found to be better than 15 lb. asphalt felt for a water repellant. 6 to 8ml polyethylene should be installed on the ground over a crawl space as a moisture barrier. Then 15 lb asphalt felt on top of the subfloor, and under the hardwood, as a vapor RETARTDANT, not barrier. Forget the Tyvek.

Gary,

I have read a lot of press lately that Tyvek is nothing more than a marketing masterpiece. As you said, people are finding that it is no more effective than asphalt paper, and it is more expensive. One contractor was asked, "Why are you using Tyvek?". He responded, "Well, everyone else is".