Ian_m wrote:

In an effort to make ignoring Part P easier (sorry re-wire kitchen) I have
removed the plasterboard ceiling which was 15mm plasterboard.

Should I just replace with plain 15mm or would moisture proof and/or sound
deadening (as my sons bedroom is directly above) be more suitable ?

What time does the kitchen close?

It aught to have fireproof stuff though. The pink faced.

If you want a modicum of sound proofing use rolls of rockwool supported
temporarily in between the joists with string or somesuch. Most people
usually feed it up into the spaces a bit at a time but it is time
consuming and itchyfying to do it that way.