Last summer I ripped out some disgusting shag carpeting in my ground level bedroom, covered the particleboard underlayment with 15lb asphalt roofing felt, and used a manual flooring nailer to install 5/8" engineered bamboo planks.

The room, which is subject to high levels of humidity, developed a horrible chemical odor which became so bad that I had to rip up the new floor and dispose of it. The guy at the flooring store claimed it was because I should have used "unsaturated felt" -- the "saturated" felt I used was reacting with the bamboo. I've never heard of this, I thought using asphalt-saturated 15lb roofing felt was standard procedure?

Now that I'm redoing the floor I want to make sure I don't make any mistakes. I'm going with 3/4" solid hardwood teak planks this time.

I've ripped out the crappy 1/2" particleboard underlayment and plan on replacing it with 3/4" CDX plywood. The old plywood subfloor (unknown thickness) seems flimsy; I can feel it sag when I stand between the joists. There's a few cracks in it too where I'm worried about moisture rising from below.

I don't want to use asphalt paper again because I'm worried about the smell returning. What is my best choice to retard moisture coming from below?

Right now I'm considering laying down 6 mil poly over the subfloor, then a new underlayment of 3/4" plywood, then red rosin paper, and finally the new hardwood.

Any comments or advice would be most appreciated.

The smell might have been the toxic chemicals used in some cheap bamboo manufactured in China. No regulation, and you will be surprised.

WRONG! The 6 mil poly needs to be laid on the ground, under the entire house in the crawl space, which should be DRY! Red rosin has ZERO vapor retardant properties. It just "cushions" the flooring. Try Aquabar B instead. I can't imagine having any problems with this material.
http://www.fortifiber.com/pdf/data_shee ... abar_b.pdf
Also, read this page # 2:
http://www.nofma.org/Portals/0/Publicat ... arders.pdf