Should I use a 6 mil poly moisture barrier for engineered hardwood floor installed over concrete slab-on-grade?
For what it's worth, what I wound up doing is using the Floor Muffler underlayment, which is its own moisture barrier. As per the directions, I applied it over the subfloor and about 2" up the walls.



It's hard to see, but I have indeed left an appropriate half inch expansion gap between the wood and the drywall. And this is engineered hardwood so I don't expect it to move all that much.