Vapor Barrier when boarding cavity wall

[BeagleBob]

I am drylining a cavity wall as part of an understairs bathroom. The cavity is not insulated and I will be installing the plasterboard on a stud frame as there are quite a few surface run pipes that I can't move. Some pipes are cold water pipes, others are central heating pipes. Given that I will have a void behind the plasterboard that is being heated by the central heating pipe (and a cold water pipe to condense on) what should I be doing in terms of vapor control? I was thinking about using spray foam to add some insulation around the hot water pipes. Should I have a barrier directly behind the plasterboard or am I better having the foil type line applied directly to the cavity wall. Apologies for the basic question - just a keen diy-er. Thanks in advance for any advice

 

[Wayners]

I'll try and answer.
I'm no expert.
You just need to stop moisture penetrating wall which will cause condensation.
You need to lag pipes.
Foil backed plasterboard or insulation board has foil over.
Elements board is good to tile over.
This is worth a watch I think