Hi Simon,
Every second stud is double because of the weight of the plaster.
16mm firecheck plaster is very heavy.It took 4 of us to lift each sheet into position. 40 sheets weighs 2.5 tonnes.So far we have used 156 sheets and still have to plaster the outside walls (approx another 55 sheets) Thats a lot of weight.
The rubber is both underneath and above the framework. We went to Clark rubber and purchased big sheets of 8x4 foam rubber then cut them down to 4 inch strips.By doing it this way saved at least $1800 (I'm showing my age I don't know metric)
The rockwool is R2.5 and comes in packs of 6, it is available from Bunnings wharehouses at approx $28 per bag. I've been buying it at 80 bags at a time, which is a truckload, I get it at a slightly better price,but not much. Rockwool is banned on all Victorian building sites ,so you will need some mates to help you install it, Don't get talked into using anything else!
Only the drum room and the vocal booth are on floating floors.The whole studio is on concrete slab (8 inches ) and is above a mechanics workshop. The room already floats-Can't wait to see it rock
If your in Melboune and wan't to check the place out let me know-
because this truly is the greatest place on earth
All the very best
Kev