Thanks, Worthy. I actually am quite familiar with the paper you linked and couldn't agree more with the author. I'm selling the house mentioned above so don't want to invest a lot of money to address this problem. All of the houses in the area are the same. But while I have your attention, perhaps you can give your opinion on the house we currently use. It, too, has a vented, unconditioned crawl space but has a sand floor and the A/C ducts run through it bringing the bad smells into the living space. However, we can close the louvers on the vents on this house because they are SmartVents, so the whole vent pivots open in the event of a storm surge. We closed the vents and installed a SaniDry dehumidifier, which has helped but not completely fixed the problem. We are going to have the floor covered in the next week. I would love to remove the batting under the floor above and insulate the walls and condition the space but I don't think the vents are sealed enough for this not to be a huge waste in energy. Opening the space more to the outside and treating it as pier construction is not an option due to the nature of the house construction. So, what are my options? I have an HVAC guy coming out next week for a full evaluation, replace any dirty vents and SEAL them well. This will improve indoor air quality but not moisture control in the space. Do you think it's possible to achieve RH

My energy rater just suggested laying visqueen all over my crawlspace. He said it should be sealed with caulking at all overlaps of pieces and where it meets the walls / supports. This would lock the moisture from the ground under the plastic. You could also seal the cement / concrete walls with a "paint on" moisture barrier, as well. Then you'd likely need to insulate those HVAC ducts better. According to the energy rater, a great deal more energy is wasted through the crawlspace than people realize. So this wouldn't be a wasted effort.

The crawl space treatment we used for the Habitat houses I helped build consisted of thick(6 mil) plastic sheets glued together(special glue) and then glued to the foundation(again special glue for the concrete in our homes) and glued around intrusions(pipes/etc.). Now, the actual reason for that installation was part of the radon mitigating system built into the house. But, it would work for your situation. We did the install using volunteers with minimal training---basically how to overlap the sheets and glue. There should be videos on You Tube illustrating the process. Look up passive radon mitigating systems.

I have a crawl space. Vents should be open all the time, except for winter months (in cold areas) Air circulation is important. A good thick plastic sheeting should be properly applied to the dirt floor to keep moisture from underneath out of the crawl space. No insualtion under the house itself, unless you have done other special work to keep it a conditioned space. Since up until several years ago, we had never had a crawl space, we thought about insulating the underside of the house, but, were told no, not a good idea by every insulation company we contacted. This is the second house with a crawl space we have owned now. It stays dry as a bone underneath, but, we also have proper drainage outside too.