Fitting shower valve in 3" stud wall

Yes, get a surface mounted valve.

I managed to fit a flush Mira Excel in a 2.5" paramount board wall.

Thanks Andy. How did you attach it?

A U-shaped metal bracket screwed (*) through the 'front' plasterboard, and the plastic 'shoe' that supports the valve screws to that, then tiled over.

Thanks Andy. The plastic shoe you mention, did that come with the valve?

Mine is similar to this but with one 2 holes either side of the body to attach it to

yes

Looking at the current Mira built-in version (BIV), it doesn't appear to use one now

Normally I find that some ply "plates" of the appropriate thickness (i.e. may need combinations / layers of different plys), stuck to the inside of the plaster board at the back of the wall, then gives a solid surface you can screw the valve to.

Plumbing it up in copper also helps make it more rigid.

I did one recently with the ply backer, and found that was more than solid enough without needing to worry about supporting it from the front. (there was a chrome plate on mine that then sat over the tiles, and which would be siliconed in place. Hence you get some extra support from that if needed.

Or a lot of araldite and hope you never need to get at it! Brian

What?s on the other side of the stud wall? Can you put anything on the other side of the wall to Screw the valve into? I fitted a Grohe rapio T valve into a standard stud wall cavity but using 18mm ply on the other si de of the plasterboard (which was conveniently in a built in wardrobe). Som e photos here (but they don?t show the other side of the shower mix er)

Unfortunately it is my daughter's bedroom and that bit of the wall is in full view ie not behind a wardrobe or anything