We're getting ready to put down site finished reclaimed heart pine 3/4" thick and 5" planks, some of which will be quite long. We know we have to lay them perpendicular to the joists.

We live in N. Mississippi where humidity reigns king. We've ripped up our carpeting, padding, and the 3/4" soundboard in the LR, DR, and hallway. Underneath was 15# felt paper and 1 x 8's running on diagonal over the joists. No hidden surprises, just one 1x8 that needs to be replaced because it has a large gouge in it and was probably that way when it was installed 20 yrs ago.

Our LR & hallway are over a large vented crawlspace (you can walk in it and joists are up about 10' from ground). The DR is over a finished walkout basement. The crawlspace is dry but it does get more humid in summer when temperature soars. Our gas furnace is located in the crawlspace.

I'm wondering if we should:

a. Remove old felt paper and use new 30# felt paper as an extra precaution for against possible humidity migration and then lay the new flooring on that or

b. Use new 15# felt paper, and lay 1/2" plywood first, rosin paper and then the new wood flooring or

c. use 15# felt paper only and then lay the new flooring on that?

Any suggestions from installers out there?

Thank you in advance!

Close the crawlspace. Use Aquabar.

http://www.fortifiber.com/pdf/install_guides/IG_aquabar_b.pdf

Hmmm, even AquaBar says in the link you provided that the crawlspace should be "properly ventilated" - which it is. Do we find AquaBar at HD or Lowe's or is this something that we need to special order somewhere? I've never heard of it before.

I agree with a closed and dehumidified crawl space!!!

A vented crawl space was speced before climate control inside the homes was invented and made affordable.

Just think if you have outside air with 80º@75%rH, and that air is vented into the crawl space and allowed to cool off. The rh is going to increase considerably. Meaning your subfloor is going to be wet in comparision to the flooring inside your home.... cupping!!