Walk-In Shower Conversions: Plumbing Essentials Before You Tear Out Your Tub
Tub to Shower Conversion Plumbing Requirements
Converting an underutilized, traditional bathtub into a sleek, modern walk-in shower is one of the single most popular bathroom remodeling projects among Eastside homeowners. Removing a high tub wall creates a safer, accessible bathing area, modernizes your bathroom’s aesthetic, and can make a compact master or guest bathroom feel twice its size.
However, swapping a bathtub for a walk-in shower is far more complex than simply tearing out tile and dropping in a new shower pan. Behind the drywall and under the subfloor, bathtubs and showers operate under completely different mechanical, drainage, and water flow demands.
Before you grab a sledgehammer to start demolition, understanding the critical tub to shower conversion plumbing requirements will help you avoid costly mid-project surprises, structural re-work, and water damage down the line. Here are the essential plumbing factors you must plan for before converting your tub.
1. Upgrading the Drain Pipe Size (The 1.5-Inch vs. 2-Inch Rule)
The single biggest technical hurdle during a tub-to-shower conversion involves your underground drain line.
Standard residential bathtubs rely on a 1.5-inch drain pipe. Because a bathtub holds standing water and drains slowly after you open the plug, a 1.5-inch line is sufficient.
Walk-in showers, however, have no tall perimeter walls to contain water—they depend on rapid, continuous drainage to prevent water from overflowing the shower curb and flooding your bathroom floor. Universal plumbing code mandates that walk-in shower enclosures must connect to a 2-inch drain pipe.
Connecting a new walk-in shower to an un-upgraded 1.5-inch tub drain creates a major flood risk and violates local building codes. Upgrading to a 2-inch drain line requires cutting into the subfloor, replacing the drain trap assembly beneath the floor, and connecting to the main waste branch.
2. Re-Centering and Relocating the Drain Hole
Bathtub drains are almost always located at one far end of the fixture footprint (left-hand or right-hand tub layouts). Walk-in shower pans and custom tiled curbed bases, on the other hand, usually require a centered drain to ensure proper floor slope and water shedding from all four corners.
Converting the space requires re-routing the subfloor drain pipe from the end wall to the exact center of the new shower footprint. This involves carefully re-framing subfloor joists, establishing a precise 1/4-inch per foot slope toward the new drain opening, and securing proper support below.
3. Water Pressure and Supply Line Sizing
Modern walk-in shower designs often feature high-end fixtures like body sprayers, dual rain showerheads, and hand-held wands. While these luxurious features elevate your daily routine, they demand higher water volume and steady water pressure.
Supply Pipe Sizing: Older homes across Bellevue and Issaquah often feature 1/2-inch copper or galvanized supply lines feeding the bathtub valve. Operating multiple showerheads simultaneously often requires upgrading feed lines to 3/4-inch piping to maintain adequate volume.
Valve Upgrades: Bathtub valves are designed to divert water back and forth between a tub spout and a single overhead showerhead. Walk-in conversions require installing a modern pressure-balancing shower valve or a thermostatic mixing valve equipped with a multi-port diverter.
4. Waterproofing and Shower Pan Preparation
A bathtub acts as a self-contained waterproof vessel. Once removed, your bare studs, floor joists, and subflooring are completely exposed to moisture.
Whether you install a pre-fabricated acrylic shower pan or build a custom tiled shower floor, proper waterproofing is critical. Professional installers construct a multi-layer waterproofing system utilizing pre-sloped mortar beds, flexible pan liners, and waterproof membrane backer boards (such as Schluter-KERDI or cement board with liquid membrane coatings) extended at least 72 inches up the wall studs.
Trust Rudy’s for Seamless Walk-In Shower Conversions
Converting a tub to a walk-in shower is an exciting upgrade, but cutting corners on hidden plumbing causes leaks, mold growth, and failed building inspections. At Rudy’s Plumbing Inc., Jason, Curtis, and our licensed plumbing team help local homeowners navigate the technical mechanics of bathroom remodeling with precision.
We handle drain line upsizing, valve rough-ins, line re-routing, and fixture installations, providing clear flat-rate pricing and backing all of our work with a full 2-year warranty.
Whether you are planning a full shower repair and installation conversion, adding a matching toilet installation and repair, installing a modern vanity faucet repair and installation, or securing non-invasive leak detection and repair, Rudy’s Plumbing is your dependable local partner.
Plan Your Bathroom Remodel Right. Contact Rudy’s Plumbing Inc. Today:
Phone Lines: (425) 643-6900 or (206) 232-8500
Email Address: rudysplumbingsvc@gmail.com
Office Location: 160 NW Gilman Blvd Ste 306, Issaquah, WA 98027