How to Rough In Bathroom Plumbing

Learning how to rough in bathroom plumbing is the difference between a remodel that goes smoothly and one that stalls at inspection or, worse, behind finished tile. Rough-in is the phase where all the hidden plumbing goes in: drain pipes, vent pipes, and water supply lines, installed in the walls and floors before drywall, tile, and fixtures. Done right, every fixture lands exactly where it should, drains quietly, and passes inspection the first time. This guide covers the full sequence, from layout to testing, for a standard full bathroom with a toilet, sink, tub or shower.

What Rough-In Means

Plumbing work happens in two main stages. Rough-in is the first: pipes are run through framing, stub-outs poke out of walls and floors where fixtures will connect, and everything is tested. Finish plumbing is the second: after walls are closed and tile is set, the plumber installs the toilet, faucet, shower valve trim, and trap assemblies that connect to those stub-outs. The rough-in determines whether the finish stage is a quick install or a frustrating series of workarounds.

Rough-in also includes the inspection. In most US jurisdictions, a bathroom remodel that adds or moves plumbing requires a permit, and the rough-in inspection happens before insulation and drywall. The inspector checks pipe sizing, slope, venting, support, and materials. Failing inspection means opening walls again, so it pays to build to code the first time rather than hoping the inspector will not notice a flat drain run or a missing vent.

For a single fixture, such as a sink, the process is smaller in scope. Our guide to a bathroom sink drain rough in covers that job in detail. This guide covers the whole room.

Planning Your Bathroom Layout

Every successful rough-in starts on paper, not with a saw. Draw the bathroom to scale, including the finished wall thickness (drywall plus tile where applicable) and the finished floor height (subfloor plus underlayment plus tile). Mark each fixture centerline: toilet flange center, sink drain center, tub drain center, and shower drain center. Then mark the main drain stack and the vent stack, and plan how each fixture drain will reach them with proper slope.

Keep drain runs as short and straight as possible. Every bend is a potential clog point and a place where slope is easy to lose. Where possible, group fixtures on a shared wet wall — the wall that carries the most plumbing — so drains and vents share a common path. A toilet, sink, and tub on one wall can often share a vent arrangement that would be far more complex if the fixtures were scattered on three walls.

Check clearances while you plan. Code requires minimum clear space around fixtures: typically 15 inches from the toilet centerline to each side wall or fixture, 21 inches of clear space in front of the toilet, and similar clearances for sinks and tubs. A layout that looks fine on a sketch can fail inspection if the toilet ends up too close to the vanity. Measure twice, and confirm your local code, since some cities add to the national minimums.

Finally, decide on fixture models before roughing in. A wall-hung toilet, a freestanding tub, and a vessel sink each have different rough-in dimensions than standard models. Buying fixtures after the pipes are in is a recipe for adapters, offsets, and exposed pipes. Lock in your toilet, vanity, sink, tub or shower, and shower valve first, then rough in to their specs.

Drain and Vent Rough-In

Drains come first because they set the elevations for everything else. The main soil stack, usually 3 or 4 inch pipe, carries toilet waste and connects to the building drain. Branch drains run from each fixture to the stack: 3 inch for the toilet, 2 inch for a tub or shower, and 1-1/2 inch for a sink. Each branch must slope toward the stack at a minimum of 1/4 inch per foot for pipes 2-1/2 inches and smaller, and 1/8 inch per foot for 3 inch and larger pipe under many codes.

Install drains in this sequence: set the toilet flange location first, since the toilet has the least flexibility, then run the tub or shower drain, then the sink drain. Use long-sweep elbows for horizontal-to-horizontal changes of direction, and sanitary tees where a drain meets a vent. Avoid short 90-degree elbows on horizontal runs — they create turbulence and clog points. Support horizontal pipe every 4 feet and vertical stacks at each floor so the slope does not sag over time.

Venting is inseparable from draining. Every trap needs a vent, and the vent must rise vertically from the fixture drain and tie into the vent system that exits through the roof. Bathroom groups can often be wet vented, where one fixture drain serves as the vent for another, but the sizing and fixture order rules are strict. Our wet venting guide explains when that arrangement is allowed. If you are unsure, run individual vents — it costs a bit more pipe, but it removes all doubt at inspection.

Water Supply Rough-In

With drains and vents in place, run the water supply lines. Modern rough-ins use PEX tubing in most of the country, with copper still common in some areas. PEX is flexible, freeze-resistant, and fast to install, but it needs proper supports and protection where it passes through framing. Copper is durable and familiar to inspectors everywhere, but it costs more and takes longer to solder. Either way, use 1/2 inch lines to individual fixtures and 3/4 inch for main runs feeding a bathroom group.

Standard supply stub-out heights are roughly 21 inches above the finished floor for a toilet (cold only, with the shutoff valve), and about 20 to 22 inches for a vanity sink, with hot on the left and cold on the right when facing the fixture. Shower and tub valves sit at about 48 inches for a shower valve and 28 to 32 inches for a tub spout, but always follow the valve manufacturer specs — different valves have different depth requirements in the wall, and a valve set too deep or too shallow will not accept its trim plate cleanly.

Shower valve depth deserves special attention. Most modern shower valves include a plaster guard or depth gauge that shows the finished wall plane. Set the valve so the guard sits flush with the finished tile surface, not the bare stud or backer board. A valve buried too deep means the handle and trim will not seat; a valve set too proud leaves a gap behind the trim plate. Take the extra ten minutes to mock up the finished wall thickness before soldering or crimping the valve in place.

Fixture-by-Fixture Measurements

Toilet: the flange center sits 12 inches from the finished wall for a standard toilet (10 inch and 14 inch rough-in models exist for tight or unusual layouts). The flange should sit on top of the finished floor, not below it, and it must be anchored to the floor. The water supply stub-out sits about 6 inches to the left of center and 21 inches above the floor, though exact placement varies by toilet model.

Sink: drain centerline 18 to 20 inches above the finished floor for a standard vanity, centered on the sink bowl. Supply stub-outs at 20 to 22 inches, hot left and cold right, roughly 4 inches to each side of center. Vessel and wall-mount sinks change these numbers — see the sink rough-in guide linked above.

Tub: drain centered under the tub drain outlet, which varies by tub model, so confirm from the tub spec sheet. The tub spout sits 4 to 6 inches above the tub rim, and the shower valve (for a tub-shower combo) sits about 48 inches above the finished floor. The showerhead arm for a combo unit sits at 72 to 78 inches.

Shower: drain centered in the shower pan or at the location specified by a linear drain. The valve sits at about 48 inches, and the showerhead arm at 72 to 78 inches, or higher for a rain head. For a curbless shower, the drain elevation is critical — the pan must slope to the drain at 1/4 inch per foot, and the rough-in drain height must match the pan system exactly.

These are standard dimensions, not a substitute for your fixture spec sheets. When the spec sheet and the rule of thumb disagree, the spec sheet wins.

Testing and Inspection

Never close a wall over untested plumbing. For drain, waste, and vent (DWV) lines, the standard test is a water test: plug all openings, fill the system with water to the highest fixture or to a 10-foot head, and hold it for at least 15 minutes while checking every joint for leaks. Some jurisdictions allow an air test instead, at around 5 psi. Either way, the test must hold without a pressure drop or visible leak.

For water supply lines, pressure-test at normal working pressure or higher — typically 60 to 80 psi, or the pressure specified by your local code — and hold for at least 15 minutes. Check every crimp, solder joint, and valve connection. A slow drip at a supply joint will not fix itself, and it will do far more damage behind drywall than it does during a test.

Schedule the rough-in inspection only after both tests pass. Have your permit card, your layout sketch, and your fixture spec sheets on site. Inspectors appreciate a clean, accessible job: pipes supported, penetrations fire-blocked where required, and no buried joints. If the inspector flags something, fix it and call for re-inspection before insulating or hanging drywall.

Common Mistakes to Avoid

The most expensive mistakes are measurement mistakes. Measuring from bare studs instead of finished surfaces shifts every stub-out. Forgetting the tile thickness on a shower wall buries the valve too deep. Centering a sink drain on the cabinet instead of the bowl creates a trap that will never line up cleanly. All three are avoided by one habit: mark finished surfaces on the framing before measuring anything.

The second category is slope and venting mistakes. A drain run that looks level to the eye can still be flat or back-pitched. Use a level on every run, not your eye. A missing or undersized vent causes gurgling drains, slow drainage, and sewer odor when traps siphon dry. When in doubt, add a vent or upsize it — vents are cheap compared to opening a finished wall.

The third category is material mistakes. Mixing ABS and PVC in the same glued joint, using the wrong cement, or using thin-wall tubing inside a wall all fail inspection and leak eventually. Use one DWV material consistently, use the matching cement, and use schedule 40 pipe inside walls.

Rough-In Cost in 2026

A full bathroom rough-in by a licensed plumber in 2026 typically runs $2,500 to $6,000 for a standard full bath with walls already open, depending on region, fixture count, and how far drains must run to reach the stack. Moving a toilet across the room, cutting concrete slab, or adding a new vent through the roof pushes the price toward the high end or beyond. A half bath or powder room rough-in runs less, often $1,200 to $3,000. Permit and inspection fees add $100 to $500 in most areas.

DIY rough-in saves labor but not materials, permits, or the cost of a failed inspection. If your project needs a permit, get quotes from at least two licensed plumbers before deciding. For help pricing your bathroom rough-in, call (877) 762-1902.

Roughing in a bathroom is methodical work, not fast work. Plan on paper, set drains with correct slope, vent every trap, pressure-test before closing walls, and the finish stage will feel easy. That is the whole secret: the rough-in is where a bathroom is won or lost, and it is won long before the first tile goes up.