Moving a Toilet, Shower or Sink: What Plumbing Changes Involve

A new layout is often the reason for a bathroom remodel: the toilet seen first from the door, a tub nobody uses where a shower should be, a single sink that should be two. Each of those means moving plumbing. Some moves are a few hours of work; others mean opening the floor and rerouting the drain to the main line. Knowing which is which keeps the design realistic and the budget honest.

What moves easily and what does not

The difference comes down to drains. Water supply lines are small, pressurized and can go almost anywhere. Drains rely on gravity: they need continuous slope toward the main line, a trap at each fixture and a vent that lets air in so the trap is not siphoned dry. Bigger drains are harder to move.

The toilet: flange, drain and rough-in

The toilet sits on a flange connected to its drain. Its position is measured as the rough-in: the distance from the finished wall to the center of the flange. Most toilets are made for a 12-inch rough-in, but older homes vary, so measure yours before choosing a toilet. Changing the rough-in by even a few inches means cutting the floor, moving the flange and reworking the drain below it.

Wherever the toilet ends up, Washington's plumbing code sets the minimum space around it: at least 15 inches from its centerline to any side wall or obstruction, 30 inches center to center from another toilet or bidet, and in a house at least 21 inches of clear space in front (WA UPC 402.5). Those numbers often decide whether a move is possible at all in a small room. The full list is on our bathroom plumbing code page.

Showers: drain size, slope and location

Washington requires showers to have a waste outlet and tailpiece of at least 2 inches (WA UPC 408.4). Bathtubs only need 1-1/2 inches (UPC 409.2), which matters for a tub-to-shower conversion. Washington has an exception: where a 2-inch waste is not readily available and the building official approves, the drain may stay 1-1/2 inch when an existing tub is replaced by a shower, but only where one showerhead rated at 1.8 gallons per minute is installed. Multiple heads or body sprays rule it out.

Moving a shower drain also changes how the floor is sloped and waterproofed. A linear drain along one wall and a center drain need different framing and slope. Curbless showers usually need the floor framing lowered under the shower. See tub-to-shower conversions and curbless showers.

Venting: the part you never see

Every fixture must be separately trapped, S-traps are prohibited, and each trap needs a vent within a maximum distance set by the plumbing code's trap arm table (UPC 1001.2, 1002.2). The vent pipe runs up through the wall and eventually through the roof or into an existing vent. When a fixture moves far from the existing vent, a new vent has to be routed up through a wall and attic, which is often the most disruptive part of the move. In a two-story house, a vent from a first-floor bath may have to pass through a finished room above.

Joists, slabs and crawl spaces

How your house is built decides how a drain gets from the new fixture location to the main line.

• Joist direction. A drain that runs parallel to the floor joists can travel between them. A drain that has to cross joists cannot simply be cut through them, because the residential code limits how much a joist may be notched or bored. Large drains crossing framing often need the floor reframed or the pipe dropped below the joists.
• Crawl space. A plumber can usually reach and reroute drains from below, which keeps a move manageable.
• Concrete slab. The slab must be cut, trenched and patched to move a drain, and the existing line underneath has to be located first. Slab moves cost more and take longer.
• Second floor. The ceiling below usually has to be opened to reroute drains, then repaired and refinished.

Permits and inspections

In the City of Vancouver, a building permit covers remodels and changes to walls, and "If the work is part of a remodel or new construction, then it is included in your RES (Residential Building Permit)." Standalone plumbing work goes on a trade permit through the city's Online Permit Center. The plumbing exemptions in the city's code cover leak repairs and removing and reinstalling the same fixtures, but not work that involves "the replacement or rearrangement of valves, pipes or fixtures." Moving a fixture is rearrangement.

In unincorporated Clark County, "A plumbing permit is required for installation of any plumbing fixtures." Camas, Battle Ground, Ridgefield and Washougal each have their own rules; see bathroom permits outside city limits.

Vancouver's inspection codes for this work include 405 Underfloor Plumbing, 410 Rough Plumbing, 420 Plumbing Fixture and 495 Final Plumbing. Pipes stay visible until the rough inspection passes. See plumbing permits for bathroom work for the details.

Who may do the work

In Washington, "No person may engage in or offer to engage in the trade of plumbing without having a journey level certificate, specialty certificate, residential service certificate, temporary permit, or trainee certificate" (RCW 18.106.020). L&I puts it simply: "Only L&I-certified plumbers can legally perform plumbing work on someone else's property." Owners may do plumbing on property they own without a certificate (RCW 18.106.150), but the permit and inspections still apply. Check any plumber's certificate on L&I's Verify tool before work starts.

What drives the cost

Moving plumbing costs more when:

• the toilet or shower moves, rather than the sink;
• a drain has to cross joists, run under a slab or pass through a finished ceiling;
• a new vent has to be routed up through the house;
• the existing drain and supply pipe is old enough that it makes sense to replace it while walls are open;
• the new location needs floor framing changes, as curbless showers often do.

A layout that keeps the toilet and shower drains roughly in place, and moves the sink, the vanity and the look of the room, often delivers most of the benefit for less. For planning numbers, see JDI's bathroom cost calculator. To see what your floor and walls allow, schedule a visit through our Vancouver bathroom remodeling page. JDI's free in-home consultation ends in an itemized plan and a 3D design layout, so you can compare a layout that moves fixtures with one that keeps them.