Planning a bathroom remodel or new build? One of the most critical—and often misunderstood—steps is how to do rough in plumbing for a bathroom. Get it wrong, and you’ll face leaks, code violations, or expensive rework. Get it right, and you’ll lay a solid foundation for a functional, code-compliant bathroom. Whether you’re a seasoned DIYer or a first-time homeowner, this guide walks you through every essential step with clarity and confidence.
What Is Rough In Plumbing?
Rough in plumbing refers to the initial installation of water supply lines, drainpipes, and vent stacks before walls and floors are finished. This phase happens after framing but before drywall, tile, or fixtures go in. According to the International Residential Code (IRC), all plumbing rough-ins must meet specific standards for pipe sizing, slope, and fixture spacing to ensure safety and performance.
💡 Pro Tip: The average cost to hire a plumber for rough-in work ranges from $1,500 to $4,000 (HomeAdvisor, 2024). Doing it yourself can save thousands—but only if done correctly.
Why Is Proper Bathroom Rough-In So Important?
A poorly executed rough-in can lead to:
Slow drains due to incorrect pipe slope
Sewer gas leaks from missing or faulty venting
Fixture misalignment, requiring wall cuts or rework
Failed inspections, delaying your project
The U.S. Environmental Protection Agency (EPA) estimates that 10% of household water waste stems from plumbing inefficiencies—many rooted in improper rough-in design.
Step-by-Step: How to Do Rough In Plumbing for a Bathroom
Step 1: Review Local Codes & Create a Layout Plan
Start by checking your local building codes—they may differ from IRC standards. Then sketch a scaled layout showing:
Toilet location (typically 12″ from finished wall to center of flange)
Sink position
Shower/tub placement
Use a chalk line to mark pipe locations on subfloor and studs.
Step 2: Install Drain Lines with Proper Slope
Drainpipes must slope ¼ inch per foot toward the main stack to ensure gravity flow.
Toilet: Install a 3″ or 4″ PVC waste line. The closet flange should sit flush with the finished floor (not subfloor!).
Shower/Tub: Use 2″ PVC. Place the drain trap directly below the fixture.
Sink: 1.5″ PVC with a P-trap stub-out 18–20 inches above subfloor.
⚠️ Never glue trap arms during rough-in—leave them open for final fixture connection.
Step 3: Install Vent Stacks
Every fixture needs a vent to prevent siphoning and allow air into the system. Options include:
Individual vents (each fixture has its own vent pipe to the roof)
Wet venting (common in bathrooms—sink drain also acts as vent for toilet)
IRC allows wet venting if the sink drain is 2″ or larger and within 6 feet of the toilet.
Step 4: Run Water Supply Lines
Use ½” PEX for most fixtures (¾” for main lines).
Hot and cold lines should be 6–8 inches apart and 20–22 inches above subfloor for sinks.
For showers, stub-outs should be 78–80 inches high (for valve) and centered on the fixture.
Install shut-off valves near each fixture location.
Label all lines clearly: “H” for hot, “C” for cold.
Step 5: Pressure Test the System
Before closing walls:
Cap all supply lines.
Pressurize the system to 80 PSI using an air compressor or water pump.
Monitor for 15–30 minutes. A drop >5 PSI indicates a leak.
Fix leaks immediately—never skip this step.
Common Mistakes to Avoid
Wrong toilet flange height
Rocking toilet, leaks
Set flange on finished floor level
Insufficient venting
Gurgling drains, odors
Add vent or use wet vent per code
Flat or back-sloped drains
Standing water, clogs
Re-cut with ¼”/ft slope
Mixing pipe materials incorrectly
Corrosion, leaks
Use dielectric unions or compatible fittings
When to Call a Professional
While DIY rough-in is doable, consider hiring a licensed plumber if:
You’re unsure about local code compliance
Your home has cast iron or galvanized pipes (older systems)
You need to tie into a main sewer line
Your municipality requires permits and inspections
Remember: E-E-A-T (Experience, Expertise, Authoritativeness, Trustworthiness) matters. If in doubt, consult a pro—plumbing errors can cause thousands in water damage.
FAQ Section
Q1: How high should shower rough-in plumbing be?
The shower valve should be 78–80 inches above the subfloor. The showerhead arm stub-out is typically 72–78 inches, but confirm based on your specific fixture.
Q2: What’s the standard rough-in distance for a toilet?
The standard is 12 inches from the finished wall to the center of the toilet flange. Some older homes use 10″ or 14″—measure before buying a new toilet.
Q3: Can I rough-in plumbing before electrical?
Yes—and it’s often recommended. Plumbing pipes are larger and harder to reroute than electrical wires, so install them first during the “rough-in phase.”
Q4: Do I need a permit for bathroom plumbing rough-in?
In most U.S. jurisdictions, yes. Permits ensure your work is inspected for safety and code compliance. Skipping this can void insurance or complicate home sales.
Q5: How much does rough-in plumbing cost if I DIY?
Material costs average $300–$600 for a standard bathroom. Compare that to $1,500+ for professional labor—making DIY worthwhile if you’re confident and code-compliant.
Q6: Can PEX be used for all bathroom plumbing?
Yes! PEX is approved for supply lines in all 50 states and is flexible, freeze-resistant, and easy to install. However, drain lines must still use PVC or ABS—PEX isn’t rated for drainage.
Conclusion
Mastering how to do rough in plumbing for a bathroom empowers you to save money, avoid rework, and build a system that lasts decades. By following code, planning meticulously, and testing thoroughly, you’ll create a solid foundation for your dream bathroom.
If this guide helped you, share it with a friend tackling their own renovation! And don’t forget to bookmark this page for your next plumbing project. Got questions? Drop them in the comments—we’re here to help you succeed.
Your future self (and your wallet) will thank you. 💧🛠️
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