OK, more information and a happy ending for us on this one
First up the Rockwall soundscreen bats we are using are R2 compared to the R1.5 that the builders are using in the walls, I should have been clearer in my post above. This difference is why the builder was concerned.
Wish we had known to ask about this at selection- lesson for others.
The bats we are using come in 75mm and 90mm thickness, our steel frame is 75mm so we are using 75mm thick bats. The SS made a point of telling me that using the wrong thickness will cause problems with the plaster board, so it must be a common mistake.
The bats are available in 580mm and 430mm width and most of our beams are 600mm wide so 580mm is the best size.
Today we heard back that the electrician had checked the wiring and as he only had 6 or 7 points on each circuit we would be ok to insulate.
So a lot of messing around but we are now good to insulate.
The wall insulation went in today and that combined with the acoustic bats make for a very quiet house. It is like putting on noise cancelling headphones.
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So hopefully all of this will be helpful to someone else here.
regards
sean