Shower Plumbing Diagram: Rough-In Dimensions and Layout
A shower plumbing diagram maps four systems inside one wet wall: the 2-inch drain and P-trap below the floor, the two 1/2-inch hot and cold supply lines, the mixing valve set around 48 inches up, and the shower arm near 78 to 80 inches. Nail these rough-in numbers before tile goes on and the valve trim, arm, and head all drop in clean.
What does a shower plumbing diagram show?
A shower plumbing diagram shows how the drain, trap, supply lines, and valve connect behind the finished wall. Two 1/2-inch supply lines feed a single mixing valve, which sends blended water up to the shower arm. Waste drops through a 2-inch drain into a P-trap, then runs out a sloped, vented trap arm to the branch line.
Picture the wet wall from the front. The drain sits in the floor near the center of the pan. Straight up the wall, the cold line runs on the right and the hot on the left into the valve at roughly waist-to-chest height. From the valve, a single pipe climbs to the shower arm elbow near the ceiling. The P-trap and vent hide below and beside the drain.
If you are new to reading these layouts, our guide to residential plumbing diagrams shows how supply, drain, and vent lines stack across a whole house. This page zooms in on the shower and tub group only.
What are the standard shower rough-in dimensions?
The shower rough-in numbers below cover drain size, trap, valve height, head height, and supply layout in one place. They reflect common International Plumbing Code (IPC) and Uniform Plumbing Code (UPC) minimums, but your valve brand’s spec sheet and local code override them, so verify each figure before you cut pipe or set a stub.
| Element | Size | Standard rough-in number |
|---|---|---|
| Shower drain pipe | 2 in (1.5 in code minimum) | Centered 10 to 14 in from each finished wall |
| Shower P-trap | 2 in | Trap weir 6 to 10 in below finished floor |
| Trap arm slope | – | 1/4 in per foot toward the branch |
| Trap arm to vent | 2 in | Up to 8 ft (IPC), up to 5 ft (UPC) |
| Hot and cold supply | 1/2 in each | 8 in apart, hot left, cold right |
| Mixing valve height | – | 48 in for tub-shower, 42 to 45 in shower-only |
| Tub spout (combo) | 1/2 in | About 28 in above tub floor, 4 in above rim |
| Shower arm and head | 1/2 in | 78 to 80 in above floor (72 in minimum) |
| Pan slope to drain | – | 1/4 in per foot toward the drain |
The drain location is the one number people miss. It is not a fixed measurement off the wall like a toilet flange. It follows the drain hole molded into your shower base, or the low point of a sloped mortar bed on a tiled pan. Buy the pan first, then set the drain to match it, and always measure to finished wall surfaces rather than bare studs.
How is the shower drain and P-trap laid out?
The shower drain drops straight into a 2-inch P-trap sitting directly below the drain body. The trap holds a water seal that blocks sewer gas. From the trap, a 2-inch trap arm slopes 1/4 inch per foot to the branch drain and must reach a vent within 8 feet under the IPC or 5 feet under the UPC.
Keep the trap as close under the drain as the framing allows. A short vertical tailpiece is normal, but long horizontal offsets above the trap collect hair and soap and start to gurgle. In joist-framed floors, the trap weir usually lands 6 to 10 inches below the finished floor, which leaves room for the tailpiece and the drain body.
Every fixture trap needs air behind it or the seal siphons dry and lets gas in. For sizing the stack, branch vents, and air-admittance valves that serve the shower, see how the vent ties in. Rough the vent in with the drain, before the supply lines.
How high should the shower valve and showerhead be?
Set the mixing valve 48 inches above the finished floor for a standard tub-shower combo, or 42 to 45 inches for a shower-only stall so a seated or shorter user can still reach it. Rough the shower arm at 78 to 80 inches. Code allows a 72-inch head minimum, but 80 inches suits most adults.
These are centerline heights measured off the finished floor or tub base, not the subfloor, so account for the pan, backer board, and tile thickness. The valve depth in the wall matters too. Most pressure-balance and thermostatic valves want the plaster guard flush with the finished surface, so dry-fit the tile stack before you brace the valve.
How do the supply lines run to a shower?
Two 1/2-inch supply lines carry water to the shower: hot on the left, cold on the right, spaced about 8 inches apart into the mixing valve. PEX and copper both work. Half-inch pipe feeds a standard 1.8 to 2.5 gallon-per-minute head, though some builders run 3/4-inch line and reduce at the valve for longer runs.
The valve blends hot and cold, then a single riser carries mixed water up to the shower arm. On a tub-shower combo, that same valve body also feeds the tub spout below. Brace both supply lines and the valve solidly to blocking so the pipes do not move when someone turns the handle, which is a common source of water hammer.
How does a tub-shower diverter work?
A tub-shower diverter sends water either to the tub spout or up to the head from one valve. In most combos, the diverter is a pull-up gate built into the tub spout: lift it and back-pressure forces water up the riser to the head. Some systems use a separate diverter in the valve trim instead of the spout.
Because the diverter creates pressure to push water uphill, the riser to the head and the drop to the spout both tie into the same valve outlet. When a diverter wears out, water leaks from the spout while the shower runs, or head pressure drops. On a tub combo, once the trim is set, caulk the base and trim to seal the joint against the wall.
How do you plumb a shower step by step?
Plumbing a shower follows a fixed order: drain and trap first, then vent, then supply and valve, then a pressure test before the walls close. The sequence below covers a standard single-head shower or tub-shower combo. For the wider fixture group around it, see the full bathroom rough-in.
- Locate the drain to match the shower base or pan, centered 10 to 14 inches off the finished walls, and set a 2-inch drain body.
- Install the 2-inch P-trap directly below the drain, then run the trap arm at 1/4 inch per foot to the branch line.
- Tie the trap arm to a vent within the code limit, 8 feet under the IPC or 5 feet under the UPC.
- Run two 1/2-inch supply lines, hot left and cold right, and mount the mixing valve at 48 inches, braced to blocking.
- Extend the riser to the shower arm elbow at 78 to 80 inches, and, on a combo, drop the spout line to about 28 inches.
- Cap the stub-outs and pressure-test the supply and DWV lines, then call the rough-in inspection before drywall.
- After tile and finish, set the trim, arm, head, and handle, then run water and check every joint for leaks.
Frequently asked questions
What is the rough-in height for a shower valve?
Most plumbers set the shower mixing valve 42 to 48 inches above the finished floor, with 48 inches standard for a tub-shower combo and 42 to 45 inches common for a shower-only stall. A tub spout diverter valve sits lower, around 28 inches. Confirm the number on your valve brand’s spec sheet, since trim depth and handle style shift it.
How far should a shower drain be from the wall?
A shower drain usually centers 10 to 14 inches from each finished wall, roughly the middle of a standard 32 by 32 or 36 by 36 pan. The exact spot follows the shower base you buy, so match the drain hole in the pan or the slope of a mortar bed. Measure to finished wall surfaces, not bare studs.
What size drain pipe does a shower need?
A new shower drain must be at least 2 inches in most areas, and 2 inches is the standard. Code sets a 1.5-inch minimum outlet, but 2 inches drains a modern high-flow head without pooling. Older tubs and showers often used a 1.5-inch line, which you can keep on a like-for-like repair but should upsize on a full rebuild.
Does a shower need a P-trap?
Yes. Every shower drain needs a P-trap, almost always 2 inches, sitting directly below the drain body. The trap holds a water seal that blocks sewer gas from rising through the drain. The trap weir usually lands 6 to 10 inches below the finished floor in joist framing, and the trap arm past it must reach a vent within the code limit.
What size supply lines does a shower use?
A shower runs two 1/2-inch supply lines, one hot and one cold, into the mixing valve, typically in PEX or copper. Half-inch pipe carries enough flow for a standard 1.8 to 2.5 gallon-per-minute head. Some builders run 3/4-inch line to the valve and reduce to 1/2 inch at the stub-out for better pressure on long runs or multiple heads.
How high should a shower head be?
Rough in the shower arm 78 to 80 inches above the finished floor for a comfortable standing height. Code sets a 72-inch minimum, but 80 inches clears most adults and gives a natural spray angle. For taller households, 82 to 84 inches works. The arm drops down to the head, so the head itself hangs a few inches below the stub.
Last reviewed: September 2026.