Plumbing Rough-In: Complete Guide

Overview

• Typical Duration: 1-2 weeks
• DIY Difficulty: ⭐⭐⭐⭐☆ (4/5)
• Typical Cost: $8,000-$15,000 (2,000 sq ft house)
• When to Hire: Most owner-builders hire this out or get help
• Required Inspection: Yes - must pass before covering walls

Plumbing rough-in installs all water supply and drain-waste-vent (DWV) pipes before walls are closed. This is one of the most code-intensive phases, requiring knowledge of proper sizing, slopes, and venting requirements.

I've seen many owner-builders successfully DIY their plumbing rough-in, but it requires studying code requirements and planning carefully. Mistakes here mean cutting open walls later - expensive and frustrating.

When This Phase Happens

Plumbing rough-in happens after house is weathertight.

Must be complete first:

• Roof complete
• Windows and doors installed
• House is weathertight
• Under-slab plumbing complete (if slab foundation)

Can happen in parallel:

• Electrical rough-in
• HVAC rough-in
• All three rough-in trades can work simultaneously

What comes after:

• Rough-in inspection (all three trades)
• Insulation
• Drywall

Should You DIY This Phase?

DIY If:

• Comfortable with PEX or CPVC (easier than copper)
• Can learn code requirements (IRC P2900 series)
• Have access to code-required tools (pressure tester, etc.)
• Simple layout with straightforward runs
• Have time to study and plan carefully
• Local code allows owner-builder plumbing

Hire Out If:

• Complex multi-story plumbing
• Copper piping required (harder to work with)
• Uncomfortable with code requirements
• Want liability protection
• Need speed (pros do in 3-5 days vs 1-2 weeks DIY)

My recommendation: Hire a plumber for planning and inspection prep, DIY the installation under guidance. This ensures code compliance while saving 40-60% of labor costs.

Many codes require licensed plumber for testing and inspection, even if you do the work. Verify local requirements before starting.

Materials Needed

Water Supply System (PEX example - 2,000 sq ft home)

Drain-Waste-Vent (DWV) System

Tools Required

Essential:

• PEX crimping tool or expansion tool
• Tubing cutter (for PEX and CPVC)
• Hacksaw or reciprocating saw
• Drill with hole saw kit (1/2" to 2")
• Tape measure
• Level (torpedo and 4-foot)
• Marker and pencil

Nice to have:

• Inspection camera (see inside walls)
• Pressure test pump (required for inspection)
• Drain test equipment
• Pipe threading equipment (if using threaded pipe)

Code-required:

• Pressure test gauge (test to 50+ PSI)
• Smoke or peppermint test for DWV

Step-by-Step Process

Days 1-2: Planning and Layout

Review plans and code

• Study fixture locations on plans
• Calculate fixture units (determines drain sizing)
• Plan vent routing (every fixture needs venting)
• Identify main stack location (straightest path to roof)
• Plan water supply routing (minimize long runs)
• Mark all penetrations on framing

Fixture unit calculations (determines pipe sizing):

• Toilet: 3 fixture units
• Shower: 2 fixture units
• Lavatory: 1 fixture unit
• Kitchen sink: 2 fixture units
• Dishwasher: 2 fixture units
• Clothes washer: 3 fixture units

Pipe sizing based on fixture units:

• 1.5" drain: up to 2 fixture units (lavatory)
• 2" drain: up to 6 fixture units (sinks, showers)
• 3" drain: up to 20 fixture units (toilets, multiple fixtures)
• 4" main drain: building drain (preferred for main)

Days 3-5: DWV Rough-In (Do This First!)

Always rough-in DWV before water supply. DWV pipes are larger and less flexible in routing.

Main drain installation:

1. Install cleanouts at base of stacks and every 100 feet
2. Slope main drain 1/4" per foot minimum toward sewer/septic
3. Support every 4 feet with proper hangers
4. Keep drain lines straight (no sags or bellies)
5. Test slope with level before cementing

Toilet drain installation:

1. Position flange at correct height (finished floor level)
2. Connect 3" or 4" drain to toilet flange
3. Vent within 6 feet of fixture (closer is better)
4. Secure flange to floor framing

Vent stack installation:

1. Run 3" main stack from main drain through roof
2. Keep stack as straight as possible (no more than 45° offsets)
3. Extend 12" above roof penetration
4. Flash at roof penetration (critical!)
5. Connect branch vents to main stack

Vent requirements (critical for passing inspection):

• Main vent stack: 3" minimum
• Branch vents: 1.5" minimum
• Wet venting allowed in some configurations (check code)
• All fixtures must be vented within maximum distance:
  • Toilet: 6 feet from vent
  • Sink/lav: 5 feet from vent
  • Shower: 5 feet from vent

Shower/tub drain:

1. Install drain at correct depth (varies by fixture - check specs)
2. P-trap should be accessible for service
3. Vent within 5 feet of trap
4. Test drain before installation (fill and check for leaks)

Days 6-8: Water Supply Rough-In

Main supply planning:

1. 3/4" main from water heater to distribution point
2. Branch to 1/2" for individual fixtures
3. Keep hot and cold parallel (easier for fixture installation)
4. Maintain proper spacing (6" between hot and cold)

PEX installation (easiest for DIY):

1. Run 3/4" trunk lines along main routes
2. Branch 1/2" lines to each fixture
3. Use proper fittings (crimp or expansion - not both!)
4. Support every 32" with plastic hangers
5. Protect from freezing in exterior walls
6. Leave loops at fixtures for flexibility during finish

Installation tips:

• Use red PEX for hot, blue for cold (not required but helpful)
• Label lines at panel for future reference
• Install shut-off valves for each fixture
• Install zone shut-offs for easier maintenance
• Keep lines away from heat sources (recessed lights, exhaust)
• Protect pipes where passing through framing (nail plates required within 1-1/4" of edge)

Water heater connection:

• 3/4" supply and return lines
• Install expansion tank on cold side
• Install shut-off valves for service
• Install drain valve at lowest point
• Follow manufacturer spacing requirements

Days 9-10: Testing and Inspection Prep

Pressure test (required):

1. Cap all outlets with test caps
2. Connect pressure test pump to system
3. Pressurize to 50 PSI (or code requirement - often 80 PSI)
4. Let sit for 30 minutes to 2 hours
5. Pressure should not drop (small drop OK, verify no leaks)
6. Identify and fix any leaks
7. Re-test until system holds pressure

DWV test (varies by jurisdiction):

1. Some require water test (fill system, check for leaks)
2. Some require smoke test (smoke reveals leaks)
3. Some allow peppermint test (smell reveals leaks)
4. Most common: water test of drain lines
5. Fill lines, check for leaks at all joints

Inspection preparation:

• All lines properly supported
• All penetrations have nail plates
• Pressure test complete and holding
• DWV test complete
• No kinked or damaged lines
• Proper slopes on drains verified
• All vents properly routed and sized
• All cleanouts accessible

Code Requirements

Key IRC plumbing requirements:

• IRC P2603 - Water supply: 3/4" minimum service, sized per fixture units

• IRC P2904 - Slope of horizontal drainage: 1/4" per foot for pipes under 3", 1/8" per foot for 3" and larger

• IRC P3104 - Vent required: Every fixture requires venting within prescribed distances

• IRC P3103 - Vent size: Based on fixture units and developed length

• IRC P2503.5 - Support: Horizontal piping every 6 feet for copper/CPVC, every 32" for PEX, every 4 feet for DWV

• IRC P2601 - Pressure: System must test to 50 PSI minimum for 15 minutes with no loss

• IRC P2503.6 - Nail plates: Required where pipes pass within 1-1/4" of framing edge

Subcontractor Considerations

If hiring plumbers:

Typical pricing:

• Complete rough-in: $4,000-$8,000 for 2,000 sq ft home
• Hourly rate: $75-$125 per hour
• Per fixture: $300-$600 per fixture rough-in

Timeline: 3-7 days for typical house

What to look for:

• Licensed plumber (required in most jurisdictions)
• Experience with residential new construction
• Familiar with local code requirements
• Will handle inspection
• Provides warranty on work
• Carries liability and workers comp insurance

Red flags:

• Not licensed (you're liable for code violations)
• Won't pull permit or handle inspection
• Can't explain vent requirements
• Pressure to skip testing

Common Mistakes

1. Inadequate Venting

Why it's a problem: Slow drains, gurgling, sewer gas, fails inspection. #1 plumbing rough-in failure. How to avoid: Study IRC P3100 venting requirements. Every fixture must be properly vented. Cost if you don't: $1,000-$5,000 to cut walls open and add vents.

2. Wrong Drain Slope

Why it's a problem: Standing water, slow drains, clogs, fails inspection. How to avoid: Maintain 1/4" per foot slope. Check with level. No sags or bellies. Cost if you don't: $500-$2,000 per drain to re-pipe.

3. Improper Pipe Support

Why it's a problem: Sagging lines, noise, leaks, fails inspection. How to avoid: Support every 32" for PEX, every 4 feet for DWV. Use proper hangers. Cost if you don't: Failed inspection, must expose and add supports.

4. Forgetting Cleanouts

Why it's a problem: Can't clear clogs, fails inspection, code violation. How to avoid: Install cleanout at base of each stack and every 100 feet of horizontal drain. Cost if you don't: $300-$800 per cleanout to add later (cut walls/floors).

5. No Pressure Testing

Why it's a problem: Leaks hidden in walls discovered after drywall. Expensive water damage. How to avoid: Pressure test to 50+ PSI for 30+ minutes before inspection. Cost if you don't: $1,000-$5,000 per leak to cut walls, repair, patch, repaint.

6. Wrong Pipe Sizing

Why it's a problem: Insufficient flow, pressure loss, fails inspection. How to avoid: Size pipes per code based on fixture units. When in doubt, go larger. Cost if you don't: Re-piping, failed inspection.

7. Forgetting Nail Plates

Why it's a problem: Drywall screws puncture pipes, leaks behind walls. How to avoid: Install 1/16" nail plates wherever pipes pass within 1-1/4" of framing edge. Cost if you don't: Leaks, water damage, emergency repairs.

8. Improper Toilet Flange Height

Why it's a problem: Toilet rocks, leaks at base, wax ring fails. How to avoid: Set flange at finished floor height (not subfloor). Account for tile or other flooring. Cost if you don't: $300-$600 to reset toilet, repair subfloor damage.

9. Mixing Pipe Types Incorrectly

Why it's a problem: Incompatible materials, leaks, corrosion, code violations. How to avoid: Use proper transition fittings between different materials (PEX to copper, etc.). Cost if you don't: Leaks, corrosion, failed joints.

10. No Expansion Tanks

Why it's a problem: Water hammer, damage to fixtures, shortened appliance life, code violation in many areas. How to avoid: Install expansion tank on cold water side near water heater. Cost if you don't: Fixture damage, noisy pipes, code violation.

Quality Checkpoints

Before rough-in inspection, verify:

• [ ] All fixtures have proper drain size (1.5", 2", or 3")
• [ ] All drains slope 1/4" per foot minimum
• [ ] All fixtures properly vented within code distances
• [ ] Main vent stack 3" minimum through roof
• [ ] Cleanouts installed at base of stacks
• [ ] Toilet flanges at finished floor height
• [ ] All DWV joints properly glued
• [ ] All supply lines properly crimped/connected
• [ ] Proper pipe support (every 32" PEX, 4' DWV)
• [ ] Nail plates installed where required
• [ ] Water supply pressure test passed (50+ PSI, 30+ min)
• [ ] DWV test complete (water, smoke, or peppermint)
• [ ] No kinked or damaged lines
• [ ] All lines labeled (hot/cold)
• [ ] Shut-off valves installed appropriately
• [ ] No leaks detected

Budget Breakdown

Example for 2,000 sq ft home, 2.5 baths:

Timeline Tips

Best season: Any time (interior work)

Scheduling:

• Coordinate with electrical and HVAC (all can work simultaneously)
• Schedule inspection for all three trades together
• Allow 1-2 weeks before inspection (time to test and fix issues)

What Comes Next

After plumbing rough-in inspection passes:

1. Complete all rough-in trades (electrical, HVAC)
2. Combined rough-in inspection
3. Insulation installation
4. Drywall installation

Link to: Electrical Rough-In Phase

Related Resources

• Plumbing Rough-In Inspection Guide
• Venting Requirements Guide
• Fixture Unit Calculator

Need Plumbing Help?

Plumbing rough-in is complex with strict code requirements. If you're unsure about venting or sizing, a consultation can save you from failed inspections.