Bathroom rough-in is the part of plumbing nobody sees and everyone pays for. A bathroom rough in sets the supply lines, drains, and vent stacks before drywall goes up — and a 1/2-inch error on a toilet drain costs $1,200 to fix once tile is down. Whether you’re adding a basement bath, expanding a master suite, or finishing new construction, understanding rough-in dimensions, IPC code requirements, and contractor pricing prevents the expensive surprises that derail bathroom remodels.
Part of our Bathroom Remodeling & Flooring guide — explore the full guide →
This guide covers standard rough-in measurements, the plumbing tree most contractors use, code-mandated clearances under the IPC and IRC, and realistic cost ranges from $2,500 for a simple half-bath to $9,000 for a full bath rough on a slab foundation.
What Rough-In Actually Includes
Rough-in is the second phase of new bathroom work, after framing and before drywall. It includes: setting drain-waste-vent (DWV) pipes in walls and floors, running hot and cold supply lines, installing the closet flange for the toilet, setting tub or shower drains, stubbing out supply lines for sinks and toilets, and running the vent stack through the roof. Electrical and HVAC are typically roughed in parallel but separately.
Building inspectors visit the site after rough-in is complete and before drywall covers anything. Failing rough-in inspection means re-doing work in already-tight wall cavities — a budget killer. Most jurisdictions require licensed plumbers to pull the permit; DIY rough-in is legal in some states but often voids homeowner’s insurance.
Standard Toilet Rough-In Dimensions
The most-discussed rough-in spec is the toilet rough-in distance — the measurement from the finished wall behind the toilet to the center of the closet flange. Three standard distances:
- 12 inches — the default for nearly all new construction in the US. Fits 95% of off-the-shelf toilets from Kohler, Toto, and American Standard.
- 10 inches — common in older homes, especially pre-1960 construction. Use 10-inch rough-in toilets like the Toto Drake CST744E or Kohler Cimarron 10″.
- 14 inches — rare, used when wall framing is unusually thick or to accommodate large floor drains. Fewer toilet models available.
Side clearance: minimum 15 inches from the toilet centerline to any side wall, vanity, or tub per IRC R307.1. Front clearance: minimum 21 inches in front of the toilet bowl, with 24 inches strongly preferred for comfort.
Sink and Vanity Rough-In Specs
Single-bowl vanity rough-in: drain at 18 to 20 inches above finished floor, centered under the bowl. Hot and cold supplies stub out at 20 to 22 inches above finished floor, spaced 8 inches apart on center for standard widespread faucets.
For double vanities, drop two separate drains — sharing a single drain through a sanitary tee saves a few dollars in pipe but fails IPC venting requirements in most jurisdictions. Run individual P-traps for each bowl, joined to a horizontal branch that vents back to the stack within 5 feet per IPC 909.1.
Shower and Tub Rough-In
Standard shower drain: centered in a 32×32, 36×36, or 60×32 footprint depending on shower pan. Drain stub-out is 2 inches in diameter for showers (1.5 inches no longer code-compliant under IPC 709.1). Set the drain rough-in 6 to 8 inches above the slab if running new drain lines, or break the slab to tie into existing drains.
Shower valve rough-in height: 38 to 48 inches above finished floor depending on user height and shower style. Center the valve on the long wall, 4 to 6 inches off-center if the shower head and valve aren’t stacked. Pressure-balance or thermostatic valves (Delta R10000-UNBX at $80, Moen 2510 at $85) are required by IPC 424 in nearly all jurisdictions to prevent scalding.
Tub drain rough-in: centered 16 inches from the back wall and 4 inches from the end wall for standard 60-inch alcove tubs. Overflow stub: 4 to 6 inches above tub floor.
Drain Sizing and Venting Requirements
IPC fixture unit calculations determine drain pipe sizes. For a typical full bath (toilet + sink + tub-shower):
- Toilet drain: 3-inch PVC or ABS, sloped 1/4 inch per foot
- Sink drain: 1.5-inch trap arm to 2-inch branch
- Tub-shower drain: 2-inch minimum
- Branch drain: 3-inch PVC, ABS, or cast iron carrying all fixtures to the main stack
- Vent stack: 1.5-inch minimum, transitioning to 3-inch where it passes through the roof in cold climates to prevent ice closure
Every fixture needs a vent within the maximum trap-arm distance specified in IPC Table 909.1 — typically 5 to 8 feet depending on drain size. Air admittance valves (Studor Mini-Vent, $30) are allowed in many jurisdictions as a substitute for through-roof venting, but check local code.
Supply Line Rough-In
Modern homes use PEX-A or PEX-B (Uponor or SharkBite) for water supply runs. Color-code red for hot and blue for cold. Use 3/4-inch trunk lines from the manifold to the bathroom, 1/2-inch branches to individual fixtures. Crimp connections with a Milwaukee M12 PEX Crimper ($200) or use SharkBite push-fit couplings for hand-tightenable joints.
Install mid-line shutoff valves where supply lines enter the bathroom — a Webstone PEX-EXP 1/2-inch ball valve ($12) lets you isolate the bathroom for future repairs without shutting off the whole house. Pressure-test all rough-in plumbing at 100 psi for at least 15 minutes before drywall — required by most inspectors per IPC 312.
Cost Tiers for Bathroom Rough-In
Pricing varies wildly by location and complexity:
Half-bath (toilet + sink): $1,800 to $3,500 in basement or first-floor locations with easy access to existing drains. Adds another $1,500 to $3,000 if you need to break a slab to tie into existing drain lines.
Full bath (toilet, sink, tub-shower): $3,500 to $6,500 for new construction or above-grade additions with stacked plumbing layout. $5,500 to $9,000 for slab-on-grade installations requiring concrete cutting, or for non-stacked layouts where each fixture needs its own vent.
Custom master bath (double vanity, separate shower and tub): $6,500 to $14,000. Multiple drains, longer supply runs, and often custom valve heights for body sprays add hours of labor.
Get three written bids and verify each contractor pulls a permit. Skipping the permit saves $200 to $600 upfront and costs $3,000 to $8,000 in retrofits if a future buyer’s inspector flags unpermitted work. Bathroom rough in is the foundation of every successful remodel — done right, it lasts 50 years; done wrong, it leaks at the worst possible time.
