Multi level basement

I am going to finish my basement and think I have decided to save the money and do most myself. With that said I have a question:

This is a new home construction with a Slab floor. Code requirements require floating walls due to expansive soil. It is built with 9 ft ceilings as basmenet finishes are an option of the builder.

I am thinking about raising part of the basement 12" to make it 8ft cielings, this would give the main theater area a "sunken" feeling at 9ft and provide better viewing from the rec area above.

With that in mind can i use 2x12 and create a subfloor without tying it into the walls and then build my floating walls on top of that? In essence the floor would still be able to raise with the slab if needed. Will this meet code, or am i missing something? Thanks for any advice you can give...

 

Sounds like a plan to me! As far as code goes you will need to call the people in charge in your area. Some towns in the same county even have different rules.
Better to get that information from the "horse's mouth" so to speak. They should be able to answer any questions where you go to get the permit.