KarlOB1980

We're building a couple of semi detached bungalows and are wondering if anyone else has done something similar. Between each house we have 100 mm solid concrete clocks and 100mm cavity with sound insulation. The sound proofing guys have recommended we then need to come in 10mm on each side of the concrete blocks and construct a 100mm insulated stud wall with sound proof board. We have gone back to them to say sure just dot and dab sound proof board on either side should be sufficient (even if this is doubled up). Does this all sound normal?