Bathroom Plumbing Rough-In
This is where your new bathroom layout becomes reality. Relocating supply lines, installing drain pipes, and adding proper venting creates the foundation for reliable plumbing that will serve for decades.
Quick Summary
Time required
1-3 days
Typical cost
$2,000-5,000
Difficulty
Pro required
What Plumbing Rough-In Involves
Rough-in plumbing is the behind-the-walls work that makes your fixtures functional. This phase happens after demo and before walls are closed up, giving access to install everything properly.
Drain Lines (DWV - Drain, Waste, Vent)
All wastewater must flow downhill to the main sewer line. Drain pipes are installed with precise slopes to prevent clogs and ensure proper drainage.
- •Toilet drain: 3\" PVC pipe connecting to main stack
- •Shower drain: 2\" pipe with P-trap, sloped 1/4\" per foot
- •Sink drain: 1.5\"-2\" pipe with P-trap under vanity
- •Main stack: 3\"-4\" vertical pipe connecting to sewer
Supply Lines (Hot and Cold Water)
Fresh water pipes run from main supply to each fixture. Modern installations use PEX for flexibility and ease, though copper is still common.
- •Hot and cold lines to sink, shower, tub
- •Cold water line to toilet fill valve
- •Shut-off valves at each fixture for maintenance
- •Pipes secured to studs every 32\" to prevent sagging
Vent Stack (Critical for Proper Drainage)
Vents allow air into drain lines, preventing siphoning and enabling smooth wastewater flow. Without proper venting, drains gurgle, drain slowly, or siphon water from P-traps.
- •Connects to drain lines and extends through roof
- •Typically 1.5\"-2\" PVC pipe
- •Required by code for all plumbing fixtures
- •Must be inspected and approved before covering
Professional Rough-In Process
Mark Fixture Locations
Before cutting any pipes, mark exact locations for toilet flange, shower drain, sink drain, and all supply line outlets. Measurements must be precise.
Standard rough-in dimensions: Toilet center to wall: 12\" (sometimes 10\" or 14\"). Sink height: 31\"-36\". Shower valve height: 38\"-48\". Shower head height: 72\"-78\". These are starting points—adjust for your specific fixtures.
Install Drain Lines First
Drains are installed before supply lines because they're larger and less flexible. Proper slope is critical—too flat and waste doesn't flow, too steep and liquids outrun solids.
Run and Connect Vent Lines
Each fixture needs proper venting. The vent connects to the drain line and rises vertically through the roof, allowing air in and sewer gases out.
Common vent configurations: Individual vents run from each fixture up through roof. Wet vents serve multiple fixtures using one vent pipe. AAV (Air Admittance Valves) can sometimes replace roof vents where code allows. Most bathrooms use wet venting with the toilet stack serving as main vent.
Install Supply Lines
With drains complete, run hot and cold supply lines. Modern PEX is easier to work with than copper and less likely to freeze or corrode.
PEX Installation Tips:
- •Red PEX for hot water, blue for cold (not required but helpful)
- •Secure to studs with plastic clips every 32 inches
- •Use crimp rings or expansion fittings—both are code compliant
- •Install shut-off valves at each fixture for future maintenance
- •Keep hot and cold lines separated to prevent heat transfer
Pressure Test All Supply Lines
Before inspection, the system must be pressure tested to prove there are no leaks. This is required by code and critical for preventing future water damage.
Pressure test procedure: Cap all supply line openings. Attach air compressor or hand pump with gauge. Pressurize system to 50-80 PSI. Mark gauge level and wait 24 hours. If pressure drops, there's a leak. Find and fix before inspection. Some jurisdictions require water testing instead of air.
Schedule Rough-In Inspection
A building inspector must approve all plumbing before walls are closed. Schedule this inspection as soon as rough-in is complete and pressure tested.
Inspector checks:
- Correct pipe sizes for each fixture type
- Proper drain slopes (1/4\" per foot minimum)
- Adequate venting for all fixtures
- Secure pipe supports and hangers
- Shut-off valves at fixture locations
- Pressure test results or witness new test
- Proper distances and clearances
Key Code Requirements
Drain pipe sizing
Toilet: 3\" minimum. Shower: 2\" minimum. Sink: 1.5\" minimum. Tub: 1.5\" minimum. Main stack: 3\"-4\" depending on fixture count.
Venting required
All fixtures must be vented. Maximum distance from trap to vent varies by pipe size and local code (typically 3.5\'-6\'). Vent must extend through roof minimum 6\" above surface.
Shut-off valves mandatory
Every fixture must have accessible shut-offs for supply lines. This allows maintenance without shutting off water to entire house. Ball valves preferred over gate valves.
Support spacing
Horizontal pipes must be supported every 32\" (PEX) or 6\' (copper, PVC). Vertical pipes every 10\'. Use proper hangers and straps—no wire or rope.
Frequently Asked Questions
What is plumbing rough-in for a bathroom?
Plumbing rough-in is the installation of all water supply lines, drain pipes, and vent stacks before walls are closed. This includes running new pipes to fixture locations, connecting to main drains and water supply, installing shut-off valves, and ensuring proper drainage slopes. It's called "rough-in" because pipes are exposed and accessible for inspection before being covered by drywall and tile.
Can I do bathroom plumbing rough-in myself?
While physically possible for experienced DIYers, most jurisdictions require licensed plumbers for rough-in work that requires permits and inspections. Mistakes can cause major water damage, mold, and code violations. Unless you have plumbing experience and understand local codes, hire a professional. Cost typically ranges from $2,000-5,000 for a full bathroom, which is a fraction of potential repair costs from improper installation.
What size pipes are required for bathroom drains?
Standard drain pipe sizes: 1.5\"-2\" for bathroom sinks, 2\" for shower drains, 3\" for toilets, and 3\"-4\" for main waste stacks. Vent pipes are typically 1.5\"-2\". All drains must slope at least 1/4 inch per foot toward the main stack. Using undersized pipes causes slow drainage and clogs. These sizes are specified by plumbing code and must be followed.
How long does bathroom plumbing rough-in take?
A professional plumber typically completes bathroom rough-in in 1-3 days depending on complexity. Simple fixture replacement in existing locations: 1 day. Relocating fixtures or adding new ones: 2-3 days. This includes running pipes, installing valves, pressure testing, and making adjustments. Factor in additional time for inspection scheduling and any required corrections.
What is the pressure test requirement for rough-in plumbing?
After installing supply lines, the system must be pressurized to 50-80 PSI and hold pressure for 24 hours without leaks. Cap all openings, attach a pressure gauge, and pump air or water into lines. If pressure drops, there's a leak that must be found and fixed. This test is required for inspection approval before walls can be closed.
Rough-In Complete
With plumbing approved by inspection, you're ready to move forward with electrical rough-in. Both must be complete before closing up walls.