I'm doing a nail down of engineered 1/2 inch wood floor onto wood subfloor on top story of a ranch over a walkout conditioned basement. I'm a novice. My research suggested that a complete vapor barrier was a bad idea because of the potential to trap moisture and rot the subfloor and to leave too uneven a humidity level on the top versus the underside of the flooring. A semipermeable layer to control the rate of moisture change and impede rather than block moisture transmission seemed to be the way to go.

I found nothing but positive reviews for Aquabar B from pro's who had switched from tar or rosin paper. I went to Home Depot, but it's apparently only an Internet order item. I was going to order when the employee showed me Roberts SVS. I think it's a newer product. The package says it certified by some flooring association (forget the acronym). But I can't find the permeability rating. I'll probably go with the Aquabar because it seems tried and true. But does anyone have experience with or opinion of the Roberts SVS?

I haven't seen the roberts but I'd stick to aquabar. Most Roberts stuff is meh.