How To Run Plumbing For A New Bathroom: A Step-by-Step Guide for Homeowners

Why Running Plumbing for a New Bathroom Feels Overwhelming (And How to Fix It)

You’ve dreamed of a spa-like bathroom. New tiles, a freestanding tub, maybe even heated floors. But then you hit the wall—literally. How do you run plumbing for a new bathroom? Where do the pipes go? Do you need a permit? Can you even do this yourself?

You’re not alone. According to a 2023 HomeAdvisor survey, 68% of homeowners who attempted DIY plumbing for a new bathroom encountered unexpected issues—from low water pressure to code violations that forced costly redo’s. The good news? With the right plan, you can avoid those pitfalls.

This guide breaks down exactly how to run plumbing for a new bathroom—from layout to rough-in to final inspection—using clear, step-by-step instructions backed by plumbing professionals and real-world examples. No jargon. No fluff. Just what works.

1. What Are the Key Plumbing Fixtures You Need to Plan For?

Before you cut a single hole in the floor, you need to know what you’re plumbing in. Every bathroom requires these core fixtures:

“A poorly planned layout is the #1 reason DIY bathroom projects fail,” says Mike Reynolds, Master Plumber with 22 years in New England. “You can’t just guess where the pipes go. You need to think like a plumber—gravity and slope are law.”

Pro Tip: Use graph paper or free apps like SketchUp Free or RoomSketcher to sketch your layout. Measure your space exactly. A 1-inch mistake can mean a $500 rework.

2. Where Should You Place Fixtures for Optimal Plumbing Flow?

The magic of good plumbing isn’t just pipes—it’s distance and slope. Here’s the golden rule: the closer your fixtures are to the main stack (the vertical drain pipe), the better your drainage and the cheaper your job.

✅ Ideal Layouts (Based on Building Code & Best Practices)

• Toilet: Place it closest to the main sewer stack (usually in the center or back wall).
• Shower & Sink: Group them together on the same wall. This lets you share a single vent and drain line, saving materials and labor.
• Bathtub: Avoid placing it far from the shower if they’re both in the same room. Shared plumbing = fewer penetrations.

💡 Real Case Study: In a 2024 remodel in Austin, TX, homeowners moved their bathroom 8 feet from the original stack. Result? They needed an additional 22 feet of drain pipe, a new vent, and a $1,200 sump pump just to handle slow drainage. Grouping fixtures saved them $3,400.

Avoid this mistake: Don’t run drain lines uphill. Every inch of horizontal pipe must slope ¼ inch per foot toward the main stack. Use a laser level to check.

3. How Do You Rough-In Plumbing Before Drywall? (The Critical Step)

Rough-in means installing all pipes, drains, and supply lines before walls and floors are finished. This is when mistakes become expensive.

✅ Step-by-Step Rough-In Process:

1. Turn off main water and drain lines.
2. Mark locations for all fixtures using chalk or tape.
3. Cut openings in subfloor and wall studs (use a reciprocating saw).
4. Install drain lines using PVC (for drains) or copper/PEX (for water).
   • Toilet drain: 3″–4″ PVC, sloped ¼”/ft toward main stack.
   • Sink & shower drains: 1.5″–2″ PVC.
5. Install water supply lines:
   • Use ½” PEX tubing (flexible, freeze-resistant, easy to install).
   • Run hot and cold lines to each fixture location. Leave 6–8″ of excess pipe sticking out.
6. Install vents: Every drain needs a vent to prevent suction and gurgling.
   • Vents must rise vertically at least 6″ above the flood rim of the highest fixture.
   • Use 1.5″–2″ PVC for vents.
7. Cap all openings with plastic caps to keep debris out until final installation.

🔧 Expert Tip: “Always pressure-test your water lines before closing walls,” says Lisa Tran, licensed plumber and instructor at the Plumbing & HVAC Institute. “Use 80 PSI for 15 minutes. If the pressure drops, you have a leak. Fix it now—not after drywall.”

4. Do You Need a Permit? What Happens If You Don’t Get One?

Yes. You absolutely need a permit.

In the U.S., 94% of municipalities require a plumbing permit for new bathroom installations (per the International Residential Code, IRC). Skipping it isn’t just risky—it’s illegal.

⚠️ Risks of No Permit:

• Failed home inspection when you sell (buyers walk away).
• Fines up to $5,000 in some states (e.g., California, New York).
• Insurance denial if water damage occurs from unpermitted work.
• Mandatory demolition if discovered during a neighbor’s remodel.

📚 Learn more about plumbing codes from the official International Residential Code (IRC) — the standard followed by nearly all U.S. jurisdictions.

How to get a permit:

1. Visit your city’s building department website.
2. Submit a plumbing plan (hand-drawn is fine).
3. Pay fee ($100–$300, depending on location).
4. Schedule inspections: rough-in, final.

Pro Tip: Many cities now offer online permit applications. Search: “[Your City] plumbing permit application.”

5. What Tools and Materials Do You Actually Need?

You don’t need a professional toolkit—but you do need the right basics.

Materials Checklist:

• ½” PEX tubing (for water supply)
• 1.5″–4″ PVC pipe (for drains)
• P-traps, cleanouts, vents
• Shutoff valves (one per fixture)
• Pipe hangers and clamps

💬 “Buy quality fittings. A $2 cheap valve can leak after 6 months. I’ve seen homes flooded because of it.” — Dave K., DIYer turned pro plumber in Ohio.

6. How Do You Vent a Bathroom Plumbing System Properly?

Venting is the silent hero of plumbing. Without it, water drains slowly, toilets bubble, and sewer gas enters your home.

✅ The 3 Rules of Venting:

1. Every drain needs a vent.
2. Vents must connect to the main vent stack (usually going through the roof).
3. Vents must be higher than the highest fixture’s flood rim.

Two Common Venting Methods:

✅ Best for DIYers: Use an AAV if your state allows it (most do, except CA, NY, and MA). Install it within 5 feet of the fixture, above the fixture’s flood rim. Brands like Studor are widely trusted.

FAQ Section: Your Top Plumbing Questions Answered

Q1: Can I run bathroom plumbing myself without a license?

A: Yes—in most states, homeowners can do plumbing on their own primary residence. But you still need a permit and must pass inspection. If you’re renting or doing it for someone else, you need a license. Always check your local building department.

Q2: How long does it take to run plumbing for a new bathroom?

A: For a DIYer with basic tools, plan for 2–4 days for rough-in, plus 1–2 days for inspections and final fixture installation. Professionals typically finish in 1 day for rough-in.

Q3: What’s the most common plumbing mistake in new bathrooms?

A: Improper slope on drain lines. Too flat = slow drainage. Too steep = solids get stuck. Always use a ¼” per foot slope. Use a laser level—you’ll thank yourself later.

Q4: Can I use PEX for both hot and cold water?

A: Absolutely. PEX is now the #1 choice for residential plumbing. It’s flexible, freeze-resistant, and doesn’t corrode like copper. Just use PEX-A (most flexible) and crimp or clamp fittings.

Q5: How far can a toilet be from the main stack?

A: Maximum horizontal distance is 6 feet for a 3″ drain line. Beyond that, you need a larger pipe (4″) or a mechanical ejector pump (expensive!). Keep it close.

Q6: Do I need a separate vent for the shower and sink?

A: No—if they’re on the same wall and within 5 feet of each other, you can use a wet vent. The sink drain can serve as the vent for the shower. This saves pipe and labor.

Conclusion: You’ve Got This—Now Go Make Your Dream Bathroom Real

Running plumbing for a new bathroom isn’t magic. It’s math, planning, and a little patience. By following this guide—grouping fixtures, ensuring proper slope, getting a permit, and testing your lines—you’re not just installing pipes. You’re building value, safety, and comfort into your home.

The average U.S. homeowner recoups 60–80% of bathroom remodel costs at resale (per Remodeling Magazine, 2024). But only if it’s done right.

Don’t let fear stop you. Start with a sketch. Call your city for a permit. Take your time. And when you flip that final switch and water flows cleanly—that’s the moment it all clicks.

👉 Found this guide helpful? Share it with a friend who’s dreaming of a new bathroom! Tag them on Pinterest, Facebook, or Instagram with #DIYBathroomPlumbing so others can learn too.

Final Pro Tip: Keep all permit documents, inspection receipts, and photos of your work in a folder. You’ll need them when you sell your home. Trust us—future buyers will thank you.