floorhardwood-floorinsulationmoisture
I am thinking about using a 6 mil poly and a thicker sound/water barrier to make walking on the floors a bit softer. I plan to tape (or use silicon) as a means to seal moisture.
My question is, is it a good strategy to completely seal the floor like this? Judging by my crawlspace (which is sealed with 6mil poly), droplets gather underneath. Wouldn't the same happen for my insulation under the hardwood? Would it damage the concrete?
No, there's no need to install a vapor barrier between two conditioned spaces. The purpose of a vapor barrier is to prevent warm moist air from traveling through the insulation and condensing on the cooler side, which can easily happen in cold climates. With a conditioned space on both sides, you can allow any moisture in the air to pass through.
There's also no need for insulation except for sound proofing (fires can pass through doors, as can any heat). For sound, make sure your insulation is designed for that, and also consider a resilient channel or similar product that will keep the drywall physically separate from the studs, which is how many sounds travel through walls.
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.
Best Answer
Use a combined moisture & sound deadening barrier like Roberts Unison 2-in-1. I put this under my engineered bamboo floor. It was an easy install and works great.