I was wondering if there is an industry standard in terms of what depth to set shower mixer valve blocking at? In your traditional house the wall is only a 2×4 depth, meaning a block of 2×4 would only leave 2" of depth if the back side of the shower mixer wall was drywalled. I have read that the standard plastic ground is supposed to be flush with the finished surface of the shower wall, in my case, tile.
According to these instructions, that makes me have to bump my 2×4 blocking OUT of the 2×4 stud cavity. I have this luxury because that is not a finished wall surface. However, it seems odd – even backwards, and it seems like I would need the block to stick inward instead because I have a thicker wall than a normal precast shower enclosure. I'm going to have 1/2" tile board, the thinset, and 1/4" tile. These numbers don't add up and I am thinking I made a mistake. It's a Delta shower kit, meaning mixer valve, shower head, and trim rings all in one and not something universal.
Best Answer
Different brands and models of shower valves require different wall-depth installation. You should always follow the installation instructions that came with the valve assembly.
Most valves come with a temporary plastic or cardboard "plate" that illustrates the location of the finished wall surface in relation to the valve-body installation depth. If you do not have that "template" anymore, you can often estimate depth by assembling the trim to the valve and measuring from where the wall surface would be to the mounting holes. You need to locate the supply piping according to final installation depth of the valve, not the other way 'round (not an issue with flexible supply tube like PEX).
Except for special application products, they are made to fit a standard wood-frame wall but may not allow the use of 2 x 4 lumber as a mounting support; in fact, some recommend use of a manufacturer-specific mounting strap/stringer.
Example of depth mounting instructions for a random Delta valve model: