Converting a Tub-Shower Combo into a Walk-In Shower: Plumbing and Drain Relocation

The 1.5-Inch vs. 2-Inch Drain Line Mandate

The single biggest plumbing trap in tub-to-shower conversions is the drain line diameter.

Standard bathtubs drain through a 1 1/2-inch drain pipe. Because a tub has deep sides, it acts as a reservoir that can hold water while it slowly drains.

A walk-in shower, especially one with a low 2-inch curb or a curbless threshold, has virtually no water storage capacity. Under the North Carolina Plumbing Code (Section 709), shower drains are legally required to be a minimum of 2 inches in diameter.

Connecting a walk-in shower to an existing 1.5-inch tub drain will fail building inspection and risks immediate floor flooding when shampoo or hair slows drainage.

Relocating the Drain to Center

Bathtub drains are located at one end of the alcove (left or right hand). Most pre-sloped shower pans and custom tile floors require a centered or linear drain.

Moving the drain requires cutting the subfloor, removing the old 1.5-inch trap, and running a new 2-inch PVC drain line with a new 2-inch P-trap back to the main plumbing stack.

Plumbers must ensure the new horizontal run maintains a minimum 1/4 inch per foot downward slope and does not compromise existing floor joists by improper notching or oversized drilling.

Waterproofing: Why Prefab Pan Liners Fail

Traditional shower construction used PVC vinyl pan liners loosely folded into corners and tacked to studs. Punctures from roofing nails or leaking curb corners were common.

AGCS installs modern, bonded, waterproof shower systems (such as Schluter-KERDI or Hydro Ban bonded sheet membranes). The waterproof membrane is applied directly beneath the tile surface, ensuring that water cannot saturate the mortar bed or wood subfloor.

Mixing Valve Height and Showerhead Placement

Standard tub valves are installed roughly 28 to 32 inches above the subfloor, comfortable for someone sitting in a bath.

For a walk-in shower, the pressure-balanced or thermostatic mixing valve must be relocated to 44 to 48 inches above finished floor height for convenient standing operation, while showerheads are typically raised to 78 to 84 inches.