That's what i'm worried about. A few questions if you get a min.
You mentioned you decoupled your walls/ceiling - what system did you use?
It sounds like the main change you made was using rubber matting rather than green glue and adding an extra door - is that about right? Are you happy with it now?
Noted. I'm now leaning towards decent insulation, decoupled walls, two layers of plasterboard and some kind of mat (if budget allows) or green glue between them. I'm also going to ask the architectes what the cost would be in having 4 walls built inside the existing room and then decouple the ceiling. The floor i'm thinking insulation and as much mass as can be added.
Looking good, kungfuman. Did you find them pretty straight forward to install?
Yeah, the genie clips are very easy to install - plenty of guides / instructions around. Have a look on youtube too as I'm sure theres a few videos showing you how to put it together.