Building on uneven floor

[dr_penner]

Greetings to all forum users! I am delurking after a 1 month lurking period.

I am intending to build a music room/studio in the basement of my 1100 sq. foot residential home. The space I have to work with is 14'X 11'X 7' (small, I know).

One of the many problems that I have is that the floor is not evenly flat. I live in Winnipeg, Manitoba, Canada, where heaving floors are not unusual after the spring thaw. Our concrete floor has an obvious rise in the center of the building leaving my space with some mildly (but obviously) sloping grades. Fortunately it has not shifted in the 4 years that I have been here.

I initially thought that this was little concern; I would simply build my room-within-a-room (RWAR) using wood shims under the baseplates of the wall frames. Then my brother pointed out that most of the houses built in these parts deliberately raise the base plate off of the floor using a temporary spacer (later removed)to accomodate any rise of the floor. This is to prevent the wall frame from driving up into the ceiling joists pushing the ceiling up.

Alternately, some houses nail one baseplate 2x4 to the floor directly and then have a second baseplate a few inches above the first (separated by the temporary spacer). Any rise from the floor pushes up the lower base plate (sliding up the securing nails) while the upper baseplate remains at the same level. This seems somewhat like a shock absorber to me.

My problem is that all of the web info that I have read about constructing soundproof walls seems to assume that your floor will be perfectly flat and always remain so. I fear that trying to serve two masters (soundproof room and accomodate floor heave) will compromise my project. Certainly I can't have a big gap between the base plate of the wall and the floor to let air and sound through.

The second option listed above sounds more palatable, as I could seal the bottom baseplate and stuff the gap between it and the second upper baseplate with insulation. Then again I might just say screw it and build with my shims and hope that the floor never heaves again.

Does anyone have any words of advice for me? Has anyone dealt with this before? How did you deal with it? Am I worrying too much? I really don't want to build this room twice!

Kurt Penner

[John Sayers]

It's sort of out of my area Kurt as I live in the semitropics and don't have this sort of problem. But.. maybe you could consider pouring another slab ontop of the existing but with thick insulation between as per a floating floor construction.
Check out floating concrete slabs at
http://www.lis.net.au/~johnsay/Acous...Acoustics3.htm

cheers
john