Bathroom Rough-In Checklist: Vents, Drains, and Water Lines Done Right

Planning a Bathroom Rough-In? Start with This Field-Tested Checklist

If you’re framing a new bath or renovating an older one, a clean, code-compliant bathroom rough-in is what makes the finish work go smoothly. The right slopes, venting, and pipe sizing prevent gurgling drains, slow tubs, and failed inspections. Below is the same practical sequence our Western PA team uses to rough in bathrooms that pass the first time and perform for years.

1) Map the Layout Before You Cut

• Measure centerlines: Toilet (15" min. from side obstructions; 12" typical from finished wall to flange center), tub/shower valve height, and sink center.
• Account for finishes: Tile, backer board, and vanity depth change your final clearances. Rough to the finished surface, not bare studs.
• Plan vent locations: Keep vent takeoffs within code distance limits from traps to avoid siphoning.

2) Drain & Trap Sizing (Keep Water Moving)

• Toilet: 3" minimum drain.
• Tub/Shower: 2" drain and trap.
• Lavatory: 1-1/4" or 1-1/2" trap with 1-1/2" drain is typical; check local code for the final call.
• Cleanouts: Provide accessible cleanouts at changes in direction ≥ 135° and at the base of stacks.

Maintain a consistent slope of 1/4" per foot on horizontal runs (3" and larger may be allowed at 1/8" per foot—verify your jurisdiction). Flat spots create buildup; too steep can leave solids behind.

3) Venting That Actually Works

Every trap needs a vent that breaks siphon and admits air. Options include individual vents, wet venting (where permitted), and re-venting to a common stack.

• Distance to vent: Stay within the maximum trap-to-vent distance for your pipe size.
• Vertical first: Keep the vent rising vertical until 6" above the flood level rim before running horizontal.
• Wet vents: Common in bathroom groups; pipe sizing must support fixture units. Don’t undersize.

4) Water Supply Rough-In (Quiet & Balanced)

• Pressure balance/thermostatic valves: Rough at the manufacturer’s height. Add blocking now—tile later.
• Shutoffs: Install accessible stops for the toilet and lavatory; consider isolation valves for showers in multi-unit properties.
• Pipe protection: Use nail plates at stud penetrations; sleeve through framing to reduce noise and abrasion.
• Recirculation (optional): If long runs to a tankless heater, rough in a return line for faster hot water.

5) Toilet Flange & Closet Bend Basics

• Flange height: Top of flange sits on the finished floor, not on the subfloor.
• Bend selection: Use long-sweep fittings instead of hard 90s where possible to reduce clog risk.
• Vent connection: Vent the closet bend per code; keep fittings in the correct orientation for flow.

6) Tub/Shower Drains & Pans

• 2" trap and drain: Required for most showers; some codes allow exceptions for existing 1-1/2" with liners—verify locally.
• P-trap location: Directly below the drain; avoid drum or S-traps.
• Flood test: Water test pans and shower liners for 24 hours before covering.

7) Blocking, Backing, and Future-Proofing

• Blocking for accessories: Grab bars, heavy doors, and shower glass anchors.
• Access panels: Plan discreet access for whirlpool pumps, shutoffs, and mixing valves.
• Sound control: Add insulation in wet walls; it’s easier now than later.

8) Inspection-Ready Checklist

• Test DWV with a water head or air test per local code.
• Cap and pressure test water lines.
• Verify trap arm lengths, vent rises, and fitting orientation.
• Document photos before closing walls—future you will thank you.

When a Rough-In Reveals Bigger Issues

Renovations often expose hidden problems—corroded galvanized, undersized vents, or a main line with roots. If your camera shows cracked clay or offsets, trenchless options like LightRay UV spot repair or full lining can stabilize the line with minimal digging.

Need Help With a Bathroom Rough-In?

From code-compliant venting to spotless pressure tests, John Shelton Plumbing roughs in bathrooms the right way across the Alle-Kiski Valley and Western PA. Request a consultation and we’ll help you pass inspection the first time.