Thanks, As mentioned, im in UK, so not sure if all materials you guys are suggesting are available to me.
I intend to do the following:
6*2 stud wall frame,
staggered studs using 3*2
one half filled with:
https://www.insulationsuperstore.co....32m2-pack.html
the other with:
https://www.insulationsuperstore.co....-x-1200mm.html
side with rockwool will be finished with
https://www.insulationsuperstore.co....00-x-15mm.html
side with celotex will be lined with:
https://www.insulationsuperstore.co....00-x-15mm.html
Think that should give me enough protection for a washroom that shares the stud with a living space.