For basements, the usual for walls seems to be a pressure-treated
bottom plate attached directly to the concrete floor.

I'm using a (waterproof) subfloor material that channels water to the
floor drain. The perimeter concrete walls will be sheathed in XPS
styrofoam (any seepage through the concrete wall should drain to the
floor rather than through the XPS). The manufacturer of the subfloor
(OVRX Barricade) indicates that walls can be built on top of the
floor, but it is a floating floor so the idea of building finished
walls on top of it seems counter-intuitive...so I'm going with the
assumption that the walls shouldn't be built on top of the floor.

Is there any reason not to place the bottom plate for exterior walls
on top of 0.5" XPS styrofoam rather than directly on the concrete?
The idea is to cut the foam into 3.5" x 4' lengths (separated by small
gaps to allow moisture flow). Without the gaps, moisture may collect
behind the wall with nowhere else to go. With the gaps, moisture
could flow under the subfloor and to its final destination (the
drain).

Makes sense to me...but I haven't seen anyone else doing it. Thoughts?

"Borrall Wonnell" wrote in message
...
For basements, the usual for walls seems to be a pressure-treated
bottom plate attached directly to the concrete floor.

I'm using a (waterproof) subfloor material that channels water to the
floor drain. The perimeter concrete walls will be sheathed in XPS
styrofoam (any seepage through the concrete wall should drain to the
floor rather than through the XPS). The manufacturer of the subfloor
(OVRX Barricade) indicates that walls can be built on top of the
floor, but it is a floating floor so the idea of building finished
walls on top of it seems counter-intuitive...so I'm going with the
assumption that the walls shouldn't be built on top of the floor.

Is there any reason not to place the bottom plate for exterior walls
on top of 0.5" XPS styrofoam rather than directly on the concrete?
The idea is to cut the foam into 3.5" x 4' lengths (separated by small
gaps to allow moisture flow). Without the gaps, moisture may collect
behind the wall with nowhere else to go. With the gaps, moisture
could flow under the subfloor and to its final destination (the
drain).

Makes sense to me...but I haven't seen anyone else doing it. Thoughts?

I fear the weight of the wall will compress and distort your styro. Also I
am not sure what the life of that product it. You might combine it with my
suggestion below.

What I did in a old house with a rock foundation that sometimes had minor
water on the floor was to use treated 1x4 scabs with gaps along the sole
plate which was also treated. I kept the drywall 3/4" off the floor. I kept
the base 1/4" off the floor and did not use shoe molding. This allowed
water to follow its natural course.


--
Colbyt
Please come visit http://www.househomerepair.com

On Tue, 23 Feb 2010 09:51:03 -0800 (PST), Borrall Wonnell
wrote:

For basements, the usual for walls seems to be a pressure-treated
bottom plate attached directly to the concrete floor.

I'm using a (waterproof) subfloor material that channels water to the
floor drain. The perimeter concrete walls will be sheathed in XPS
styrofoam (any seepage through the concrete wall should drain to the
floor rather than through the XPS). The manufacturer of the subfloor
(OVRX Barricade) indicates that walls can be built on top of the
floor, but it is a floating floor so the idea of building finished
walls on top of it seems counter-intuitive...so I'm going with the
assumption that the walls shouldn't be built on top of the floor.

Is there any reason not to place the bottom plate for exterior walls
on top of 0.5" XPS styrofoam rather than directly on the concrete?
The idea is to cut the foam into 3.5" x 4' lengths (separated by small
gaps to allow moisture flow). Without the gaps, moisture may collect
behind the wall with nowhere else to go. With the gaps, moisture
could flow under the subfloor and to its final destination (the
drain).

Makes sense to me...but I haven't seen anyone else doing it. Thoughts?
Your "floating" floor is stronger than the XPS - building
"partitions" on top of the floating subfloor is standard practice.
Better than using PT wood on concrete.

On Feb 23, 5:56*pm, wrote:

*Your "floating" floor is stronger than the XPS - building
"partitions" on top of the floating subfloor is standard practice.
Better than using PT wood on concrete.- Hide quoted text -


My subfloor *IS* XPS (5/8" OSB laminated to 1/2" XPS)! They're built
in 2x2 panels, and the manufacturer recommends 1/2" gap to surrounding
walls.

Concerning building partition walls on top of the floating subfloor:

1) Won't the walls move as the subfloor expands/contracts (why the
1/2" gap required around the perimeter?).
Seems like it would break lots of plaster joints.

2) Alternately, if I secure the partition walls through the subfloor
to the concrete below (creating a 'fixed' wall), wouldn't I be risking
that the floor expand and then buckle? I've seen this happen with
laminate (finished) floors that were installed too close to a wall.

3) Admittedly, there would be a lot less work installing the floor
first. Might be a lot more work if I ever need to remove portions of
the subfloor.