Shower pipework duct construction

[Simon.Pieman]

 I'm getting conflicting information from the plumbers/builders in my local pub about construction of this. I need to create a half height duct against a bathroom wall to house the shower pipework running into a concealed tap unit. Nobody can seem to agree on the timber size and type for the frame, I could use studwork but timber is more easily obtainable. I'll be putting tiling backing board on the frame and 8mm tiles on top. So, would 1'' square be good enough or 1'' X 2"" perhaps? What type of timber? treated or not?
 

[caretaker]

mines buried in the concrete behind the tiles. hope its not leaking!

[chaz]

It depends on the wall, is it an internal wall, solid or stud, external solid or cavity? If the wall isn't an external solid wall then there should be no need to use treated timber.
What size pipe and fittings are you using? 15mm copper with soldered fittings take the least room up plastic fittings take much more room up?
why is it only half height that will leave a ledge for water to sit on?
You could use CLS 63x38 x2.4m long £2.77 from B&Q or they do treated timber 50x22 £3.12  38x25 £2.34 or 38x19 £1.86.
put timber to carry the shower head and rail and make a plan so you know where they are after tiling. It's not an electric shower is it?

good look with it, I used the CLS for mine but was building a new stud wall so put the pipe and wire in and then plasterboard and tiles been ok for 12 years.

[Simon.Pieman]

It depends on the wall, is it an internal wall, solid or stud, external solid or cavity? If the wall isn't an external solid wall then there should be no need to use treated timber.
What size pipe and fittings are you using? 15mm copper with soldered fittings take the least room up plastic fittings take much more room up?
why is it only half height that will leave a ledge for water to sit on?

Thanks for that Chaz. It's an internal block wall, I can't run pipes through it from the adjacent rooms so I have to build this duct, I'm not fitting an electric shower, the pipes are just 2m from the boiler and tank so feed and pressure is good enough to keep it a simple tap arrangement (with thermal cut out).
 The duct is half height so that I get a 'shelf' I thought about this at first because it could give probs if not constructed right of course, but as long as it has a fall and is watertight it should be ok, it's going to be 500mm away from the shower head. The duct width is going to be 110mm with a removable tile at the side so plenty of room for plastic fittings