Planning a bathroom remodel or new build? One of the most critical—and often intimidating—steps is how to rough plumb a shower tub with PEX or copper. Get it wrong, and you’ll face costly rework, water damage, or failed inspections. But done right, your plumbing will be efficient, leak-free, and code-compliant for decades. Whether you’re a seasoned contractor or a confident DIYer, this guide breaks down everything you need to know—clearly, safely, and in line with modern plumbing standards.
What Does “Rough Plumbing” Mean for a Shower Tub?
Rough plumbing refers to the initial installation of water supply lines, drainpipes, and venting before walls and floors are finished. For a shower-tub combo, this includes positioning hot/cold supply lines, the shower riser, tub spout connection, and the drain-waste-overflow (DWO) assembly—all hidden behind drywall or tile.
According to the International Residential Code (IRC), all rough-in work must be inspected before enclosure. Skipping this step risks non-compliance and future leaks that are expensive to fix once walls are closed up.
PEX vs Copper: Which Is Better for Shower Tub Rough-In?
Choosing between PEX (cross-linked polyethylene) and copper piping is one of the first decisions you’ll make. Both are widely used, but they differ significantly in cost, installation ease, and longevity.
| Feature | PEX Pipe | Copper Pipe |
|---|---|---|
| Cost | $0.50–$1.50/ft | $2–$4/ft |
| Installation Time | Faster (no soldering) | Slower (requires torch/solder) |
| Freeze Resistance | High (flexes under pressure) | Low (can crack when frozen) |
| Lifespan | 40–50 years | 50+ years |
| Code Approval | Approved nationwide (IRC P2904) | Universally accepted |
💡 Pro Tip: Most modern residential projects now use PEX due to its flexibility, lower cost, and resistance to corrosion—especially in areas with hard water. However, some local codes still restrict PEX near water heaters or outdoors, so always check with your municipality.
For more on material science behind these pipes, see Wikipedia’s overview of plumbing materials.
Tools & Materials You’ll Need
Before cutting into walls, gather these essentials:
- PEX tubing (½” diameter for supply lines) or Type M copper pipe
- PEX crimp/expansion tools or propane torch, flux, and lead-free solder (for copper)
- Tub spout with built-in diverter (if using showerhead)
- Shower valve (pressure-balanced or thermostatic)
- Drain-waste-overflow (DWO) kit compatible with your tub
- Pipe cutter, deburring tool, measuring tape
- Level, stud finder, and masking tape (for marking)
- Shut-off valves (required by code within 6 ft of fixture)
Always shut off main water supply and drain lines before starting.
Step-by-Step: How to Rough Plumb a Shower Tub
Follow these steps carefully—precision here prevents headaches later.
Step 1: Locate Studs and Plan Layout
Use a stud finder to mark wall framing. The standard rough-in height for shower valves is 48–52 inches from the finished floor. Tub spouts typically sit 4 inches above the tub rim (usually 8–12″ from floor). Mark these locations with tape.
⚠️ Critical Note: Measure twice. A misaligned valve can’t be adjusted after tiling!
Step 2: Install the Drain-Waste-Overflow (DWO)
- Place the tub in its final position (even if temporary).
- Connect the DWO tailpiece to the tub’s drain outlet.
- Run 1½” PVC or ABS pipe from the DWO to the main waste stack, sloping ¼” per foot toward the drain.
- Include a vent within 5 feet of the trap (per IRC P3105).
Step 3: Run Supply Lines
- For PEX: Cut tubing to length, insert into valve ports, and secure with crimp rings or expansion fittings. Leave 6–8″ of extra pipe extending from the wall for final trim-out.
- For Copper: Solder joints before installing in-wall. Use dielectric unions if connecting to galvanized steel elsewhere.
Ensure hot and cold lines are correctly labeled (left = hot, right = cold—per plumbing code).
Step 4: Install the Shower Valve
Mount the valve body securely to a blocking stud. Test-operate the cartridge (if included) to confirm smooth function. Cap all open ends to prevent debris entry.
Step 5: Pressure Test the System
- Cap all supply ends.
- Pressurize lines to 80 psi (standard household pressure).
- Monitor for 15–30 minutes. Any drop indicates a leak.
- Fix leaks before calling for inspection.
📊 Industry Insight: A 2023 study by the Plumbing-Heating-Cooling Contractors Association (PHCC) found that 72% of rough-in failures were due to untested joints or incorrect slope on drains.
Common Mistakes to Avoid
Even experienced plumbers slip up. Watch out for:
- Incorrect valve height: Too high or low ruins ergonomics.
- Ignoring thermal expansion: PEX expands/contracts—use supports every 32″.
- Skipping the pressure test: Hidden leaks cause mold and structural damage.
- Using incompatible fittings: Mixing PEX brands can void warranties.
- Poor drain slope: Leads to slow drainage or gurgling.
FAQ Section
Q1: Can I use PEX for both hot and cold shower lines?
A: Yes! PEX is rated for temperatures up to 200°F (93°C), well above standard domestic hot water (120–140°F). Just ensure you use oxygen-barrier PEX if connected to a closed-loop hydronic system.
Q2: How far apart should hot and cold supply lines be?
A: Standard center-to-center distance is 8 inches, matching most shower valves and trim kits. Confirm your valve specs before cutting pipes.
Q3: Do I need a permit to rough plumb a shower?
A: In nearly all U.S. jurisdictions, yes. Plumbing work affecting health/safety requires a permit and inspection. Fines for unpermitted work can exceed $1,000.
Q4: Can I mix PEX and copper in the same rough-in?
A: Yes—but use a dielectric union or brass fitting to prevent galvanic corrosion where dissimilar metals meet.
Q5: What’s the minimum clearance needed behind the tub?
A: At least 12 inches of access space is recommended behind the tub for DWO maintenance. If enclosed, install an access panel (required by IRC R201).
Q6: How do I know if my rough-in passes code?
A: Key checks: correct valve height, proper venting within 5 ft of trap, ¼”/ft drain slope, pressure-tested lines, and shut-off valves nearby. Your local inspector will verify these.
Conclusion
Mastering how to rough plumb a shower tub with PEX or copper gives you control over one of the most vital phases of bathroom construction. With the right planning, materials, and attention to code, you’ll create a durable, efficient system that lasts decades—without callbacks or leaks.
Whether you choose the speed of PEX or the tradition of copper, this guide ensures you avoid costly errors and build with confidence.
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