Plumbing Rough-In: The Hidden Infrastructure of Your New Bathroom
Plumbing rough-in is the critical phase where all drain lines, water supply lines, and venting are installed before walls are closed up. This work determines where every fixture will sit and how well your bathroom will function for decades to come. Getting it right now prevents expensive tearouts later.
Quick Summary
Time needed
1-3 days
Difficulty
Professional required
Cost
$1,000 - $4,000
Why Plumbing Rough-In Matters
The rough-in phase is your one chance to get the plumbing infrastructure right. Once walls are closed and tile is installed, making changes becomes exponentially more expensive and disruptive. This hidden work directly impacts every fixture's performance, from shower water pressure to toilet flushing power to how quickly your vanity drains.
- Determines fixture placement: Drain and supply line locations lock in where your toilet, vanity, and shower will sit. Changes after rough-in mean opening walls.
- Affects long-term performance: Proper pipe sizing ensures adequate water pressure. Correct drain slopes prevent slow draining and clogs for the life of the bathroom.
- Must pass inspection: Rough-in work requires an inspection before walls are closed. Failing means delays and rework at your expense.
- Impacts resale value: Properly permitted and inspected plumbing work adds confidence for future buyers and appraisers.
What Happens During Plumbing Rough-In
Plumbing rough-in involves installing all the pipes that will be hidden inside walls and floors. Here's what your plumber will tackle:
Drain Line Installation
Drain lines carry wastewater from each fixture to the main sewer or septic line. This is typically the most labor-intensive part of rough-in because drains must be precisely sloped and often require cutting through floor joists or concrete.
Key drain line requirements:
- • Toilet drain: 3-inch or 4-inch pipe (check local code)
- • Shower drain: 2-inch pipe minimum
- • Vanity drain: 1.5-inch pipe
- • Bathtub drain: 1.5-inch pipe
- • Slope: 1/4 inch per foot toward the main drain
Water Supply Lines
Hot and cold water lines run to each fixture location. Modern installations typically use PEX tubing, which is flexible, freeze-resistant, and faster to install than copper. Some areas still require copper, so check local codes.
Supply line sizing:
- • Main supply line: 3/4-inch
- • Branch lines to fixtures: 1/2-inch
- • Shower valve: 1/2-inch hot and cold
- • Toilet: 1/2-inch cold only
Supply line heights:
- • Vanity faucet: 20-24 inches above floor
- • Toilet supply: 6-8 inches above floor
- • Shower valve: 48 inches above floor
- • Showerhead: 78-80 inches above floor
Venting
Every drain needs a vent to work properly. Vents allow air into the drain system, preventing siphoning of water from traps and ensuring smooth drainage. Poor venting causes slow drains, gurgling sounds, and sewer gas entering the bathroom.
Venting requirements:
- • Vents must connect within specified distances from trap (varies by fixture and pipe size)
- • Vent pipes must slope upward toward the main vent stack
- • Minimum vent size is typically 1.5 inches (check code)
- • Air admittance valves (AAVs) may be permitted as alternatives in some areas
Shower/Tub Valve Installation
The shower valve is the heart of your shower system. It must be installed at the correct height, depth, and orientation. Getting this wrong affects both function and aesthetics.
Critical measurements:
- • Height: 48 inches from floor to valve center (standard)
- • Depth: Per manufacturer specs for your wall thickness
- • Showerhead drop: 78-80 inches from floor
- • Tub spout: 4 inches above tub rim
Valve considerations:
- • Pressure-balancing or thermostatic mixing valve
- • Must have blocking/backing for secure mounting
- • Account for tile thickness in depth setting
- • Test before closing walls
Toilet Flange Positioning
The toilet flange is a critical connection point that must be precisely positioned. Mistakes here lead to wobbly toilets, leaks, and potential water damage.
Flange requirements:
- • Distance from wall: 12 inches from finished wall to flange center (standard). Some toilets require 10-inch or 14-inch rough-in.
- • Side clearance: Minimum 15 inches from flange center to any side wall or fixture.
- • Height: Flange should sit flush with or up to 1/4 inch above the finished floor level.
- • Secure mounting: Flange must be firmly anchored to the subfloor.
Key Code Requirements and Inspection Points
Plumbing codes exist to protect health and safety. While codes vary by location, here are the most common requirements inspectors will check:
Drain System
- Proper pipe sizing for each fixture
- Correct slope (1/4" per foot minimum)
- Cleanout access where required
- No S-traps (only P-traps)
- Watertight connections
Vent System
- Every trap properly vented
- Vent within required distance of trap
- Correct vent pipe sizing
- Vents rise above flood level rim
- Proper connection to vent stack
Water Supply
- Proper pipe sizing (pressure/flow)
- Secure pipe support and hangers
- Pressure test passes (no leaks)
- Correct hot/cold orientation
- Backflow prevention where required
Fixtures
- Toilet rough-in at correct distance
- Shower valve at proper height/depth
- Anti-scald valve required
- Proper blocking for wall-mount fixtures
- Access panels where needed
Common Inspection Failures:
- • Insufficient drain slope causing pooling water during test
- • Missing or improperly placed vents
- • Failed pressure test (leaks in supply system)
- • Toilet flange at wrong height or distance from wall
- • No permit or wrong permit scope
Working with Your Plumber: What to Discuss
Clear communication before rough-in begins prevents problems. Here's what to cover with your plumber:
Before Rough-In Starts
- • Share the final floor plan and fixture locations
- • Provide specifications for all fixtures (toilet, vanity, shower valve)
- • Discuss any special features (rainfall showerhead, body sprays, handheld)
- • Confirm the rough-in dimensions for your specific toilet model
- • Review wall thickness (affects shower valve depth setting)
Important Questions to Ask
- • Will the existing main drain handle the new fixture configuration?
- • Do we need to upgrade the water supply line size?
- • Are there any structural concerns (joists, beams) that affect routing?
- • What is the timeline for inspection after rough-in?
- • Is there anything I need to have on-site (valves, fixtures)?
Items to Have Ready
- • Shower valve body (rough-in must match the trim kit you'll use)
- • Toilet rough-in specifications
- • Vanity dimensions and sink type (vessel, undermount, drop-in)
- • Tub specifications if installing a freestanding or drop-in tub
- • Building permit posted and available for inspection
Timeline Considerations
Plumbing rough-in timing depends on several factors. Understanding these helps you set realistic expectations:
| Scenario | Typical Duration |
|---|---|
| Fixtures staying in same locations | 1 day |
| Moving fixtures within the bathroom | 1-2 days |
| Adding fixtures or significant reconfiguration | 2-3 days |
| Working in concrete slab | 2-4 days |
| Inspection scheduling | 1-5 business days (varies by location) |
Pro Tip: Schedule Smart
Schedule your plumbing inspection as soon as rough-in work is complete. Inspectors are often booked several days out. Waiting to call can add a week or more to your project timeline.
Common Mistakes to Avoid
These rough-in mistakes can haunt you for years. Make sure your plumber avoids them:
Wrong toilet rough-in distance
Consequence: Toilet won't fit or looks odd with a large gap behind it
Prevention: Verify your toilet's rough-in requirement before installation. Standard is 12 inches, but some are 10 or 14.
Shower valve at wrong depth
Consequence: Trim plate doesn't sit flush or valve handle is recessed too deep
Prevention: Account for cement board, waterproofing membrane, and tile thickness when setting valve depth.
Insufficient drain slope
Consequence: Slow draining, standing water, and eventual clogs
Prevention: Use a level to verify 1/4 inch per foot slope. Test with water before inspection.
Missing or undersized vents
Consequence: Gurgling drains, slow drainage, sewer gas entering bathroom
Prevention: Every fixture needs proper venting within code-specified distances.
Not pressure testing supply lines
Consequence: Hidden leaks discovered after walls are closed
Prevention: Always pressure test at 40-80 PSI for at least 15 minutes before inspection.
Forgetting access panels
Consequence: Future maintenance requires cutting open walls
Prevention: Plan access panels for shower valves, tub drains, and any shutoff valves.
How to Prepare for Rough-In Inspection
A little preparation ensures your inspection goes smoothly. Here's what to do before the inspector arrives:
- 1Ensure permit is posted and accessible
- 2Keep all work visible and accessible (no insulation covering pipes yet)
- 3Leave test caps on all open drain lines
- 4Have supply lines capped and under pressure
- 5Clear debris so inspector can easily see all work
- 6Have your plumber available (in person or by phone) to answer questions
- 7Know the scope of work covered by your permit
- 8Have approved plans available if inspector requests them
Frequently Asked Questions
How long does plumbing rough-in take for a bathroom remodel?
Typically 1-3 days depending on complexity. A simple remodel with fixtures in the same locations might take just one day. Moving fixtures, adding new ones, or working in concrete can extend this to 2-3 days or more.
What is the standard rough-in distance for a toilet?
The standard is 12 inches from the center of the toilet flange to the finished wall. However, some toilets are designed for 10-inch or 14-inch rough-ins, so always verify your specific model's requirements before installation.
What slope do drain pipes need?
Drain pipes need a minimum slope of 1/4 inch per foot (about 2% grade) toward the main drain. This ensures proper drainage while allowing solids to flow with the water. Too little slope causes slow drainage; too much can cause water to outrun solids.
Can I use PEX instead of copper for water supply lines?
Yes, PEX is approved in most jurisdictions and has become the preferred choice for many plumbers. It's more affordable, easier to install, and freeze-resistant. Check your local codes, as some areas have restrictions. PEX cannot be used where exposed to UV light.
What happens during a plumbing rough-in inspection?
The inspector verifies proper drain slopes, vent placement, supply line sizing, toilet flange positioning, and that pressure tests pass without leaks. All work must comply with local plumbing codes. The inspection must pass before walls can be closed.
Plumbing Rough-In Checklist
Use this checklist to verify all rough-in work is complete before scheduling your inspection:
Drain System
- All drain lines installed with proper slope
- P-traps in place for each fixture
- Toilet flange at correct height and distance
- Shower drain at correct location
- Cleanouts installed where required
Vent System
- All fixtures properly vented
- Vents connected to main stack or AAV
- Vent pipes rise above flood level rim
- Proper vent sizing throughout
Water Supply
- Hot and cold lines to each fixture
- Proper pipe sizing throughout
- Pipes secured with hangers
- Pressure test completed (no leaks)
- Test caps in place
Fixtures
- Shower valve at correct height and depth
- Blocking installed for wall-mount fixtures
- Access panels planned where needed
- Anti-scald valve verified
Ready for the Next Step?
Once your plumbing rough-in passes inspection, it's time to move on to electrical rough-in. This includes wiring for outlets, lighting, exhaust fans, and any heated floor systems.
Related Guides
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Schedule Rough-In Inspections
What inspectors look for and how to prepare.
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Protecting your bathroom with proper waterproofing systems.