Hi Worthy. I have read and re-read Lstiburek's crawl space paper and I think I finally get it. Could you tell me if this is right? One can completely cover the wood joists with spray foam as long as one uses 3" high density foam? The reason the open pier approach works is because the crawl space isn't colder than the outside air?

If all this is true, would I be able to correct my flawed crawl space by

1) covering the floor with a 20 mil vapor barrier

2) remove batting then spray the wood with 3" of high denisty foam

3) continue to use SaniDry dehumidifier

I can't do the open pier approach because most of the crawl space is below grade.

I have read many of your posts recently they are so informative. Thanks for taking the time to share so much information.