What the plumbing for a shower actually includes
Every shower has four plumbing parts. There is a supply side with hot and cold lines feeding a valve, an outlet side that sends water up to the head, a drain with a trap, and a vent so the drain can move water without gurgling.
Most remodels keep the existing supply and drain locations when they can, because moving them costs more than any tile upgrade. A shower that sits where the old tub did often reuses the drain in the floor, though the drain size and trap may still need to change.
| Part | Typical spec | Why it matters |
|---|---|---|
| Drain and trap | 2-inch drain with a 2-inch trap | A 1.5-inch tub drain is often too small for a shower |
| Drain slope | 1/4 inch per foot toward the vent stack | Too flat and the line holds water, too steep and solids get left behind |
| Mixing valve | Pressure-balancing or thermostatic | Keeps a toilet flush from turning the shower scalding |
| Supply lines | 1/2-inch copper or PEX | Smaller lines starve a body spray or rain head |
| Showerhead flow | 2.5 gpm federal maximum | Multiple heads need enough supply to run at once |
Setting the valve and head heights before the wall closes
The valve body mounts to blocking in the stud wall, and its depth has to match the trim kit you buy. Brands differ, and a valve set half an inch too deep or too shallow will not accept the trim plate. Read the rough-in sheet that comes with the valve before you set it.
A common valve height is about 48 inches from the floor, with the head arm near 78 to 80 inches. Tall users sometimes raise the head. Decide this before the plumber closes the wall, since the stub for the head arm sits behind the tile backer.
Run a pressure test on the supply lines before any board goes up. We cap the lines, bring them to pressure and watch a gauge. A drop means a bad joint, and finding it now costs minutes instead of a torn-out wall.
Step by step: the order the work goes in
- Open the floor and wall. Strip to studs and subfloor so the drain, vent and supply lines are visible.
- Set the drain and trap. Connect to the branch line with the right slope, then confirm the vent is not blocked or too far away.
- Mount the valve and run supplies. Fasten the valve to blocking, run hot and cold, and set the head arm stub.
- Pressure test the supply. Hold the test long enough to see a slow leak, not just a quick check.
- Build and flood test the pan. Fill the shower pan with water and mark the level. A level that stays put for the test period means the liner and drain flange are sealed.
- Close up, tile and trim. Only then do the backer, tile and trim kit go on.
The flood test is the step people skip. A pan that leaks into the subfloor shows up months later as a stained ceiling below or a soft floor, and tile has to come out to fix it.
Permits and licensing for shower work in Hazelwood
Hazelwood contracts with St. Louis County for plumbing permits and inspections, and plumbing work is done under a St. Louis County license. For you, that means a shower that moves or adds a drain should go through the county, so the inspector sees the rough-in before the wall closes. Ask any plumber for proof of a county license before you sign.
A neighboring city, Florissant, allows owners of detached single-family homes to pull a homeowner plumbing permit for their own work, but not for underground or slab-enclosed piping. A shower drain in a concrete slab falls in the excluded group, so plan on a licensed plumber for it and confirm your own city's rules at 314-513-5034 for Hazelwood inspections and permits.
The International Plumbing Code (IPC) calls for a 2 inch trap and drain on a shower, and valves should meet ASME A112.18.1 and ASSE 1016 for pressure balance or temperature control. Check the valve's box for both marks before you commit to a rough-in.
What drives the price of a shower install
We do not publish a price for shower remodels because the plumbing scope varies too much from house to house. A clear price comes after a plumber sees the walls, the floor and the existing drain.
Tile, glass and fixtures are priced separately from the plumbing. Ask your remodeler to split the plumbing line out so you can compare.
Checklist before you demolish
- Know where your main water shutoff is and that it still closes.
- Pick the valve and trim kit first, then read its rough-in depth.
- Decide the showerhead height and any extra outlets.
- Confirm the drain size and where the branch line runs.
- Ask who pulls the permit and who schedules the inspection.
- Plan a flood test and pressure test before tile.
If you plan to add a new bathroom rather than redo an old one, the same list applies, plus a vent and a branch line that may not exist yet. That is plumbing installation work, and it is easier to price once a plumber sees the framing.
When to call a plumber instead of doing it yourself
Swapping a showerhead or a trim kit on an existing valve is a fair weekend job. Setting a new valve, cutting into drain lines or working inside a slab is not. A mistake behind tile is expensive to reach, so a pro earns the fee on the rough-in.
Call a plumber if the shower valve will not shut off, if the drain gurgles when another fixture runs, or if you see moisture around a shower that was recently installed. A leaking shower may also show up as a water stain on the ceiling below, which can be tracked with leak detection before more of the wall comes out.
If your shower drain backs up with water from the main line, treat that as a sewer problem instead and see our drain cleaning page. We serve homes in Florissant and Bridgeton along with Hazelwood.
Frequently asked questions
Often yes. The drain is usually in the right spot, but a tub drain is commonly smaller than the 2-inch drain a shower needs, so the drain and trap may need to be replaced. The valve and wall framing also change.
A 2-inch drain and trap is the standard residential size. A smaller drain can still carry water but clogs sooner and may not meet code.
Hazelwood contracts with St. Louis County for plumbing permits and inspections, so work that adds or moves piping typically needs one. Call Hazelwood Inspections and Permits at 314-513-5034 to confirm what your project needs.
Yes. A supply pressure test and a flood test on the pan both take little time and catch leaks while the wall is open. Both are far cheaper than removing tile later.
A valve at about 48 inches and a head arm near 78 to 80 inches are common. Choose the head height for the tallest person using the shower before the wall is closed.
Yes. The plumbing rough-in and tests happen first, then the tile crew takes over. We can finish the trim after tile is set, and we give a clear price before work starts.
Questions about your situation? A licensed plumber is on the line any hour.
Call (855) 575-2890