Insulating timber extention

[Djks]

Hi redoing kitchen half of which leads on to a timber frame extension built maybe 25 years ago.

There's been a hotchpotch of work done over the years so I'm renewing everything on the timber extention. Ceiling is also down, it had 1 inch insulation, didnt realise anything that thin would exist which would explain why it is so cold!

Whats best to insulate walls and ceiling - celotex? Insulated plasterboard? Mineral wool?

 

[JP_]

Celetox (or similar), I think you'd want about 12.5-15cm if possible - maybe 100mm between studs overlaid with 25 or 50mm.
Boarded over with fire proof plasterboard in a kitchen.

There is a minimum standard / building reg for such work, but probably best to go beyond that to keep bills down in future.

Some good advice here
https://www.homebuilding.co.uk/advice/how-to-insulate-a-wall