Q's about framing basement partition walls

Greetings all!
My wife and I are putting up two partition walls in our basement and have two construction questions we like some guidance on before we get started:
(1) Most of the rest of the framing in our house is 2X6. I presume the main advantage of 2X6 framing over 2X4 is strength. I can't imagine strength is much of an issue for our two partition walls, but still I was wondering if there are any other issues I am neglecting here (such as having adequate space to run electrical wire, using insulation, etc.)? What do people typically use for something like this -- 2X4 or 2X6? Offhand, I would think 2X4 would be easier to handle and work with, but perhaps there is greater general stability with 2X6.
(2) Secondly, under what circumstances would I use a floating partition (see http://www.asktooltalk.com/home/qanda/faq/foundations/floating-walls/floating-walls.htm )?. The floor of this basement is poured concrete (but I use the term "basement" loosely -- only one side of it is below grade and that is only four feet or so deep). Our soil is rather clay-ish, but our house is atop a fairly steep hill (where water can't easily pool). Since we live in Southern California, USA, we don't get tons of moisture, so I can't imagine there are huge fluctuations in the concrete as a function of moisture and temperature fluctuation. The foundation was poured about 20+ years ago, and although it has some cracks in it, it doesn't look as though the ravages of time have harmed it much. A floating partition seems like a huge nuisance, and I'd like to avoid it if possible.
Thanks for any advice!
Chuck
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The amount of rain you get and the position on a hill are definite factors, but the real indicator is the expansiveness of the soil which is indicated by cracks in the foundation. There could be clay in Southern California, but often it is adobe-type soil which absorbs plenty of water unlike clay. But actually we're talking about the kind of wall to build, and 2x4 is plenty unless you want extra thick sound insulation inside. 2x6 walls require slightly more expensive doors, too.

http://www.asktooltalk.com/home/qanda/faq/foundations/floating-walls/floating-walls.htm )?.
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You have no need whatsoever for 2x6. The reason they are used for some homes is not a matter of strength, but rather a matter of allowing more insulation, hence, higher R factor.
:You could use 1 1/2" metal studs. You would be restricted to shallow electrical boxes and not have much room for insulation if desired.
Your easiest install will be using 3 1/2" material, metal or wood (2x4). You will be able to use "normal" rough in boxes, insulation, and door jambs. I am very aware of Colorado builders using floating walls and have used them there myself. I do not think you are in expansive clay country, but I do not know. All clay is expansive, some is much more volatile than others.. What you are technically worried about has to do with the plastic index of the soil. Numbers above 30 raise eye brows. Numbers in the 40's demand respect and special modifications. I would think a simple call to your local building department would reveal whether it is a problem in your area. If they have never heard of floating walls, carton form floors, lime slurry injection, and post tension residential slabs I would not really worry about it.
Keep the whole world singing. . . Dan G
(remove the 7)
Dolchas wrote:

http://www.asktooltalk.com/home/qanda/faq/foundations/floating-walls/floating-walls.htm )?.
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