WPB Plywood for Stud Wall?

Hello -- I'm planning to build 4" stud wall between bedroom and bathrooms and 3" between that and outside wall between 2 bathrooms. The 3" in a kind of square "S" shape to create shower cubicles for each bathroom. The bedroom side will be skimmed and either painted or papered. The bathrooms side will be tiled.

I was thinking of using 12mm WPB Ply on the bathrooms side of the 4" and on both sides of the 3" between bathrooms. I think this will be stronger, less likely to degrade, and also have a heavy wall mounted bath filler which ply will support better than plasterboard (spigot through wall then back nut holds it in place).

Cost of boards is similar, ply slightly more but cost difference no issue. Can anybody see any disadvantages to doing this? If I fill void with insulation, would that meet building regs?

Thanks for any advice, Peter

Dont know what WPB ply is but WBP ply would be the better option

Should be OK I'd imagine, however I hope you dont plan on skimming on top of ply!?

Thanks -- No, planning to tile straight onto WBP (!) ply.

I wouldn’t use WBP in wet areas, you will still have to tank it before tiling or your tiles will probably fall off the wall; use a decent cement based tile backer board (Aquapanel) instead. Also be aware that any wall between a room with a w/c & another habitable room (but not the bedroom it serves) is subject to Building Regulations & must be sound insulated; I doubt if 12mm WBP meets those requirements but am unsure. For these areas use Sound Block Moisture Resistant boards;
http://www.british-gypsum.com/produ...ries/gyproc_acoustic/gyproc_soundbloc_mr.aspx

You can get Wallboard 10 which meets the sound requirements
http://www.british-gypsum.com/produ...ies/gyproc_acoustic/gyproc_wallboard_ten.aspx

it's not suitable for bathrooms although you can use it on the back (bedroom) side of the stud. The cement tile backer board already meets minimum sound insulation requirements. The gap inside the stud should be filled with sound insulation material - a minimum 25mm of mineral wool.

You can tile directly onto the Moisture resistant PB but where you need extra support to fix, stick a lump of plywood onto the back of the plasterboard &/or put in extra studs/noggins. If you use MR board in wet areas, tank before you tile.