MrCrowbar, Andre, DanDan thanks for your replies.
The inner room structure would be decoupled from existing structure, standalone framing built a couple cm from existing walls. See attached picture. The only connection to outer room would be through the floor.
As this room is going to be built inside a garage with a concrete slab I was not planning to float the floor. As I read floating the floor, unless done properly, can be really bad. I was going to use 1 cm rubber foam under the frame and wood flooring to decouple the room from the slab.
RUBBER FOAM,
SPEC.
Does anybody have any suggestions about the air gap size? To provide decoupling a couple of cm would be necessary I think?
Thanks,