Shower Valve Types and What the Rough-In Depth Depends On

Why this matters

A shower valve gets two decisions at rough-in that cannot be changed cheaply once the tile is up: what kind of valve it is, and how deep in the wall its body sits. Get the type wrong and the customer gets scalded or chilled when a toilet flushes. Get the depth wrong and the trim does not fit: the handle stem falls short of the finished wall, or the escutcheon stands off it with a gap water runs into. Both errors are found by the tile setter or the customer, never by the plumber who made them, and both are fixed by opening a finished wall. This card covers what the two valve families do, what the listings mean, and how wall finish thickness sets the depth.

The two families, by what they sense

Pressure balancing (ASSE 1016 type P). A spool or diaphragm in the cartridge sits between the hot and cold supplies and moves to keep the pressures entering the mixing chamber in balance. When someone flushes a toilet and cold pressure drops, the spool closes down the hot side to match, so the mix stays near where it was. It responds to a change in pressure. It does not know the outlet temperature. If the hot water itself gets hotter or colder, for example as a tank heater runs down or a tankless unit modulates, a pressure balancing valve passes that change straight through. Single handle, controls temperature only; flow is full on in most designs.

Thermostatic (ASSE 1016 type T, or type T/P). A wax or bimetal element in the cartridge senses the mixed water temperature and moves the hot and cold ports to hold the setting. It responds to a change in temperature, which covers both a pressure drop on one supply and a change in supply temperature. Type T/P combines both mechanisms. Thermostatic valves usually have separate controls for temperature and volume, and often feed several outlets through separate volume controls or a diverter.

Which one, when. A pressure balancing valve is the default in a single-shower bathroom on a tank heater; it is code compliant, simple and serviceable. Thermostatic earns its place where the customer wants volume control separate from temperature, where there are multiple outlets (body sprays, a hand shower plus a head), or where the hot supply temperature moves, as it does on many tankless systems at low flow. Check each valve's listed minimum flow against the heads and sprays the customer chose. A pressure balancing cartridge feeding a head well below the flow it was tested at can hunt or fail to balance, and a tankless heater that drops out at low flow will make any valve look bad.

The listings and what they bind

ASSE 1016 covers individual automatic compensating valves for showers and tub-shower combinations: type P, type T and type T/P. The IPC and UPC (IPC 2021 and UPC 2021, as adopted) require, in substance, that shower and tub-shower valves be of this kind and that they carry a high-limit stop set so the outlet does not exceed 120 F. That is the shelf default: shower and tub outlets limited to 120 F by an ASSE 1016 or 1070 device. See The Pressure and Temperature Numbers on Every Residential Call.

ASSE 1070 covers water temperature limiting devices, a mixing device installed at or near the fixture that limits the outlet temperature. It is the usual way a tub filler, which is not a shower valve, gets its 120 F limit. It does not provide the pressure-drop protection a 1016 valve gives a person standing in a shower.

The high-limit stop is set on site, not at the factory. The stop limits how far the handle can rotate toward hot, and the outlet temperature at full hot depends on the house's hot water temperature. Set it with the water running at full hot, a thermometer in the stream, adjusting until the reading is at or below 120 F. A valve that leaves the factory "set to 120" only does so if the house hot water happens to match the test bench.

The listing marks are on the valve body or the box. The maker's instructions are part of the listing, so a cartridge from another valve, or a cartridge installed without the limit stop, voids what the listing promised.

What sets the depth: the guard and the finished wall

Every rough valve body ships with a plaster guard (also called a mud guard or rough guard), a plastic shroud over the cartridge that protects it during finish work and marks the allowable range for the finished wall surface. The guard is the maker's depth gauge. Most guards show a minimum and a maximum line; the finished face of the tile or panel has to land between them. Inside that range the trim's stem extension and escutcheon will reach and seal. Outside it, they will not without an extension kit, if the maker offers one.

That means the rough-in depth is set by the total finish thickness, measured from the face of the stud or blocking the valve mounts to, out to the finished surface:

• Drywall or a direct-to-stud panel: the panel thickness.
• Tile on cement board: board + waterproofing membrane where it is a separate layer + thinset bed + tile.
• Stone or large-format tile: the same stack with a thicker tile and often a thicker bed.

Find out what is going on the wall before you rough. A plumber who roughs to "the usual" and leaves the tile choice to later has decided the depth without the one number it depends on.

Worked example: a tile shower in a 2x4 wall

A tub-to-shower conversion. The valve mounts on 2x4 blocking between studs. The finish stack, as stated by the tile contractor on the job:

• cement backer board, 1/2 in
• thinset, 1/8 in
• tile, 3/8 in

Total finish thickness: 1/2 + 1/8 + 3/8 = 1 in from the stud face to the finished tile face.

The guard on this valve (illustrative, read off the body in the box): with the valve mounted on its blocking, the guard's minimum finished wall line sits 1/2 in in front of the stud face and its maximum line 1 1/2 in in front. The window is 1 1/2 - 1/2 = 1 in wide.

Looking down on the wall, drawn to scale left to right:

 wall cavity       stud    min    tile    max
                   face    line   face    line
                    |       |       |       |
  valve body and    |board  |thinset|       |
  blocking sit here |       |+ tile |       |
                    |<-1/2->|       |       |
                    |<---- 1 in --->|       |
                    |<------ 1 1/2 in ----->|  shower

Setting it. The plumber measured from the stud face along the guard to confirm the 1 in finish would land between the lines. It sits centered in the window, 1/2 in inside each line. That margin matters because tile sets thicker than planned more often than thinner.

Fixing it in place. The body was strapped to the blocking so it cannot be pushed deeper when the board is screwed on, the guard was left on, and the outlet to the head was sweated to a drop ear elbow screwed to blocking at the head height from Standard Rough-In Heights and Clearances for a Bathroom. Supplies were pressure tested before the board went up, and the result was written on the stud for the inspector and the tile setter.

What the customer changed. Two weeks later the customer switched to a natural stone that sets at 3/4 in on a 3/8 in bed. New stack: 1/2 + 3/8 + 3/4 = 1 5/8 in. That is 1 5/8 - 1 1/2 = 1/8 in past the maximum line. Caught before board went up, the fix was to re-set the blocking 3/8 in toward the shower side, which moves both guard lines forward by the same 3/8 in: minimum 7/8 in, maximum 1 7/8 in in front of the stud face. The 1 5/8 in finish now sits 1 7/8 - 1 5/8 = 1/4 in inside the maximum line and 1 5/8 - 7/8 = 3/4 in out from the minimum. The supply and outlet piping was re-cut to suit. Caught after the tile, it would have been an extension kit if the maker offers one for that body, or an opened wall.

The lesson in the numbers. The original 1 in stack had 1/2 in of margin each way. The stone added 5/8 in to the stack and went through the maximum line by 1/8 in. Ask about the tile, and ask again before the board goes up.

Tub and shower ports, and other rough-in traps

• Tub-shower valves have a bottom port to the spout. On many bodies used shower-only, the bottom port is capped or plugged as the maker specifies; check the instructions, because on some diverter designs the cap is part of how the valve is meant to work.
• Inlets are marked. Hot on the left is the convention; most valves let you reverse a cartridge or have a reversible spool when the supply has to come in backwards on a back-to-back install. Correct it at rough, not with a handle that turns the wrong way.
• Integral stops. Many valves have service stops on the inlets behind the trim. They let the cartridge be changed without shutting off the house and are worth choosing on new work.
• The valve must be reachable from outside the spray. Valve location relative to the door or curtain, and the heights for the valve, head and tub spout, are owned by Standard Rough-In Heights and Clearances for a Bathroom.
• Access. Some jurisdictions and makers call for an access panel behind a valve with slip-joint or serviceable connections; a soldered or pressed valve generally does not need one, but check the adopted code and the maker.

When the valve is already in a finished wall

Replacing a cartridge is service work done from the front. Replacing a valve body in a finished, tiled wall means opening the wall from the back or the front and repairing the finish, and choosing a replacement whose guard range matches the existing wall depth. That access work is owned by Shower Valve Replacement in a Finished Wall; the install and replacement procedure itself is owned by How to Install or Replace a Shower Valve.

References

• ASSE 1016, performance requirements for automatic compensating valves for individual showers and tub-shower combinations, as referenced by the adopted plumbing code
• ASSE 1070, performance requirements for water temperature limiting devices, as referenced by the adopted plumbing code
• IPC 2021 and UPC 2021, as adopted, for the shower and bathtub valve requirements
• See related: How to Install or Replace a Shower Valve
• See related: Shower Valve Replacement in a Finished Wall