Thinking about swapping your old bathtub for a sleek, modern shower? You’re not alone—over 68% of U.S. homeowners choose to convert tubs to showers during bathroom renovations, according to the National Association of Home Builders (2023). But one of the trickiest parts? How to plumb a shower drain when replacing a tub. Done wrong, it leads to leaks, mold, or costly rework. Done right, it’s the foundation of a functional, long-lasting shower. This guide walks you through every step—safely, correctly, and confidently—even if you’ve never touched a pipe wrench before.
Why Is Plumbing a Shower Drain Different from a Tub Drain?
Tubs and showers may both use water, but their drainage systems serve different purposes:
- Tub drains are typically located near the center or end of the tub and handle large volumes of water slowly.
- Shower drains must manage continuous, fast-flowing water over a flat surface and require a precise slope (¼ inch per foot) toward the drain.
“A shower pan without proper slope or drain alignment is a recipe for standing water—and eventual structural damage,” says licensed plumber Marcus Lee of Plumbing Today magazine.
This difference means you can’t just reuse your tub’s existing drain setup. You’ll need to adjust the drain location, pipe size, and often the trap configuration.
Tools & Materials You’ll Need
Before you start tearing out that tub, gather these essentials:
| Category | Items |
|---|---|
| Tools | Adjustable wrench, pipe cutter, level, tape measure, screwdriver, utility knife, drill |
| Materials | Shower drain kit (with flange and strainer), PVC or ABS pipes (2″ diameter), P-trap, plumber’s putty or silicone sealant, cement (for mortar bed if using traditional pan), waterproofing membrane (e.g., Schluter-Kerdi) |
| Safety Gear | Gloves, safety goggles, dust mask |
💡 Pro Tip: Always check local plumbing codes. Most U.S. jurisdictions require a 2-inch drain line for showers (vs. 1.5-inch for tubs) to handle flow rates up to 10 gallons per minute.
Step-by-Step: How to Plumb a Shower Drain When Replacing a Tub
Step 1: Remove the Old Tub & Expose Subfloor
- Turn off water supply and disconnect any supply lines.
- Carefully remove the tub—often secured with screws or adhesive.
- Once removed, inspect the subfloor for rot or damage. Replace compromised wood before proceeding.
Step 2: Locate & Adjust the Drain Position
- Most tub drains sit 15–17 inches from the back wall. Shower drains should be centered in the new stall area.
- If your existing drain isn’t centered, you’ll need to relocate the waste line.
- Cut into the subfloor to access the drain pipe. Use a 2-inch PVC or ABS pipe to reroute if necessary.
⚠️ Warning: Never reduce pipe size. A 2-inch drain is required by the International Plumbing Code (IPC) for showers to prevent overflow.
Step 3: Install the New P-Trap & Drain Assembly
- Connect a new P-trap directly below the planned drain location. Ensure it’s vented within 5 feet (per IPC).
- Dry-fit the shower drain body (flange) into the opening. It should sit flush with the finished floor level.
- Apply plumber’s putty or silicone around the underside of the flange before securing it to prevent leaks.
🔗 For more on trap types and venting rules, see Wikipedia’s page on plumbing traps.
Step 4: Create Proper Slope for the Shower Base
- Whether using a pre-sloped pan or building a custom mortar bed, the floor must slope ¼ inch per foot toward the drain.
- Example: In a 36″ x 36″ shower, the perimeter should be ¾ inch higher than the drain center.
- Use a laser level or long straightedge to verify slope before installing tile or base.
Step 5: Waterproof the Area
- Install a waterproofing membrane (like RedGard or Schluter-DITRA) over the entire shower floor and up the walls at least 3 inches.
- Seal seams and corners with manufacturer-approved tape or liquid membrane.
- Let cure fully before tiling or installing a prefab base.
Step 6: Test for Leaks Before Closing Up
- Plug the drain and fill the shower pan with 2 inches of water.
- Mark the water level and wait 24 hours.
- If the level drops, you have a leak—recheck seals and joints before proceeding.
Common Mistakes to Avoid
| Mistake | Consequence | Fix |
|---|---|---|
| Using a 1.5″ drain pipe | Slow drainage, overflow risk | Upgrade to 2″ pipe |
| Skipping pre-slope | Water pools, mold growth | Build proper mortar bed |
| Poor waterproofing | Subfloor rot, ceiling damage below | Use full membrane system |
| Ignoring venting | Gurgling drains, sewer odors | Install vent within code limits |
Should You Hire a Pro or DIY?
If you’re comfortable with basic plumbing and have tools, this project is doable for intermediate DIYers. However, consider hiring a licensed plumber if:
- You need to reroute multiple pipes
- Your home has cast iron or galvanized steel plumbing
- Local codes require permits or inspections
According to HomeAdvisor (2025), the average cost to convert a tub to a shower ranges from $1,200 to $8,000, with labor making up 40–60% of the total. Doing the plumbing yourself can save $500–$1,500—if done correctly.
FAQ Section
Q1: Can I use the same drain pipe from my tub for the shower?
A: Only if it’s 2 inches in diameter and properly vented. Most tub drains are 1.5″, which is insufficient for showers per modern plumbing codes. You’ll likely need to replace or upgrade the pipe.
Q2: Do I need a new P-trap when converting to a shower?
A: Yes. Even if the old trap is intact, it’s best practice to install a new P-trap to ensure a reliable water seal and prevent sewer gases from entering your bathroom.
Q3: How far should the shower drain be from the wall?
A: For curbless or standard stalls, the drain is usually centered. In linear drain systems, it runs along the front or back wall. Always plan based on your shower base or tile layout.
Q4: What’s the minimum slope for a shower floor?
A: The IPC requires a minimum slope of ¼ inch per foot toward the drain. Less slope = standing water; more slope = awkward footing.
Q5: Can I install a shower pan without mortar?
A: Yes—many prefab fiberglass or acrylic pans come with built-in slope and don’t require mortar. Just ensure they align with your drain location and are properly sealed.
Q6: How long does it take to plumb a shower drain?
A: For a DIYer, 1–2 days (including drying/curing time). Professionals can often complete it in a single day, assuming no major rerouting is needed.
Conclusion
Converting a tub to a shower is a smart, space-saving upgrade—but how to plumb a shower drain when replacing a tub is the make-or-break step. With the right planning, materials, and attention to slope, sealing, and code compliance, you’ll create a shower that’s safe, efficient, and built to last.
Don’t let fear of plumbing hold you back. Follow this guide, double-check your work, and enjoy the satisfaction of a job well done.
Found this helpful? Share it with a friend who’s tackling a bathroom remodel! 🛠️🚿 #DIYBathroom #ShowerConversion #HomeRenovation
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