Wall Framing and Flooring over Subfloor

[Schopsy]

As I mentioned on another thread, I am preparing to finish my basement. I am considering the following subfloor stackup:

• Existing Concrete Floor
• Delta FL Vapor Barrier
• 1" XPS
• 5/8" Plywood (Tongue and Groove)

The finish flooring will, most likely, be vinyl plank in the living areas and ditra/tile in the bathroom.

I have several questions:

1. Does this subfloor stackup look reasonable?
2. Can the Plywood be left floating in the living areas?
3. Should the Plywood be Tapcon'd through the XPS to the existing concrete in the bathroom?
4. Should the partition walls be built on top or next to the built up subfloor? (see sketch below). In either case the base plate would be fastened to the existing concrete floor.
   

In the sketch below, I've shown "on top" as A and "next to" as B. If A is used, to the left would be an unfinished utility room with a dehumidifier to pull any moisture from below the Delta FL. If B is used, any moisture below the Delta FL have to absorb back into the concrete or into the base plates (which would be treated, of course). The exterior stud walls are in, so B will be used around the perimeter of the basement regardless.



Thanks in advance for your replies!

[dlarrivee]

Don't use DELTA FL and XPS together.

Frame after you finish the floor, it will be much better that way.

You will need to tapcon the ply, it wont stay there floating perfectly without.

[Schopsy]

6 mil vapor barrier, then?

[Dana]

A 6 mil vapor barrier would be fine.

The foundation wall also needs foam between the concrete & studs, as well as between the concrete & sub-floor edge.

You have serious moisture trap risk to the plywood with vinyl flooring on top, which is also a strong vapor barrier. Using something more vapor open than vinyl for the finish floor is STRONGLY recommended.

[Schopsy]

Thanks for the replies. Are there any "non-carpet" flooring options that would be suitable below grade other than carpet? My thought with vinyl was that it would be moisture tolerable, but I've kind of eliminated that line of thought with the plywood in the subfloor stackup.

[Schopsy]

Dana, regarding the top vapor barrier, is the tile in the bathroom going to be a problem? Would I be better to use cement board rather than plywood in there?

Thanks again!

[Dana]

Tile is usually quite vapor permeable, despite being waterproof to liquid water. Cement board provides better rigidity and a better bonding surface for tiles than plywood, which is also important to consider.

Most laminate flooring is at least somewhat vapor permeable, but get specs on it. Standard hardwood & bamboo flooring also works, and with the foam & poly underneath would only have moisture issues if the basement has flooding problems, which would hopefully be addressed BEFORE you finish it out nicely.

With an inch of foam you'd have sufficient R under it to avoid summertime condensation/mold issues under the carpet, if you went with a carpeting solution. Without the foam carpet would be all but guaranteed to have rot/mold issues. (Not that I'm a fan of carpeted floors, in basements or anywhere else.)