i'm installing a false ceiling in what will be a coffee shop. our
sitting room is directly above. so far we've put in a timber frame
with 100mm of acoustic rockwool flexi between the joists, there is an
airgap above that (150mm). above that the original lath and plaster
ceiling, above that is deadening, its a victorian house (no idea about
how in tact this is as in my experience lifting the floor when CH/
rewiring gets done a lot is removed), and finally floorboards (no
carpet)

i am attempting to take what *practical* measures i can to
soundproof. would an extra layer of plasterbaord be worth the effort?

also i'm confused about the fire rating. BC made no mention of a fire
rated ceiling when the plans were approved, however the ceiling does
seperate differnent "occupancies"... and what if we sold the shop or
house at a later date?

double layer of plasterboard - or not worth it?