What's involved in relocating the toilet or shower drain to change the bathroom layout?

Relocating a toilet or shower drain is one of the most involved — and expensive — aspects of a bathroom renovation because it requires modifying the drain-waste-vent (DWV) system below the floor, which must meet Ontario Building Code requirements for pipe sizing, slope, and venting. It's absolutely doable, but it adds significant cost and complexity compared to keeping fixtures in their existing positions, and it always requires a building permit from the City of Toronto.

The reason drain relocation is so much more complex than moving a supply line is gravity. Supply lines are pressurized — water is pushed through the pipes regardless of direction or slope, so rerouting them is relatively straightforward. Drain pipes rely on gravity to move waste water, which means they must maintain a consistent downward slope (typically 1/4 inch per foot for most residential drain sizes) from the fixture to the main stack. Moving a drain means rerouting this sloped pipe path while maintaining the correct fall, which often means cutting into or modifying the floor structure.

Relocating a Toilet

The toilet is the most challenging fixture to relocate because it connects to a 3-inch or 4-inch drain line (the largest drain in the bathroom) and must maintain adequate slope to the main soil stack. The standard toilet rough-in measurement is 12 inches from the finished wall to the centre of the drain flange, though 10-inch and 14-inch rough-ins exist in some Toronto homes.

Moving a toilet 6–12 inches (for example, shifting it to create more clearance from the vanity) is a moderate plumbing task. The plumber cuts the existing drain, extends or redirects the pipe beneath the subfloor, and installs a new flange at the new location. Cost for this minor relocation is typically $800–$2,000 in the GTA, depending on floor construction and accessibility.

Moving a toilet several feet (to a different wall or a completely new position) is a major plumbing modification. The new drain path must maintain proper slope over the longer distance, which may require lowering the pipe's connection point at the stack or even modifying floor joists. In older Toronto homes with shallow floor joist cavities (2x8 joists are common in pre-war and early post-war construction), there may not be enough vertical space between the subfloor and the ceiling below to accommodate the required slope over a long run. This is why many bathroom layout changes in two-storey GTA homes include a raised floor section (a platform of 2–4 inches) to create the clearance needed for the new drain slope. Cost for a major toilet relocation runs $2,000–$5,000 including permit, plumbing, and subfloor modifications.

Relocating a Shower Drain

Shower drains are typically 2-inch lines, which are easier to work with than toilet drains but still require proper slope to the stack. Moving a shower drain to convert from a tub/shower combo to a standalone walk-in shower, or to reposition a shower within the room, involves removing the existing shower base or tub, cutting into the subfloor, rerouting the drain pipe, and installing a new drain assembly.

For a curbless or linear drain shower (increasingly popular in GTA renovations), the entire bathroom floor area around the shower needs to be sloped toward the drain, which may require modifying the subfloor with a pre-sloped mortar bed or a pre-fabricated shower tray system like Schluter Kerdi-Shower. This adds complexity and cost beyond the plumbing itself. A shower drain relocation with a standard centre drain runs $500–$1,500 for the plumbing work; a curbless shower conversion with linear drain and floor modification runs $2,000–$5,000 for the plumbing and substrate work before tile.

Venting Requirements

Every drain fixture must be properly vented to prevent siphoning of the P-trap, which would allow sewer gas into the bathroom. When you relocate a drain, the existing vent connection may no longer serve the new fixture location, requiring a new vent line to be run up through the wall to connect to the vent stack. In some cases, an air admittance valve (AAV) can serve as the vent for a relocated fixture, but Ontario Building Code limits where AAVs can be used — your plumber will determine whether an AAV is acceptable for your specific situation or whether a traditional vent pipe must be run.

Condo Considerations

In GTA condos, drain relocation is significantly more restricted. The main plumbing stack is shared among all units on the vertical line, and its location is fixed. You can typically move a toilet or shower drain within a limited radius of the stack connection, but any relocation that changes the connection point to the stack may require engineering approval from the condominium corporation and may not be permitted at all. Moving a toilet more than a few inches in a condo typically requires building a raised floor platform, which reduces ceiling height — a significant concern in standard-height condo units. Always consult with your condo board and a licensed plumber before planning any drain relocation in a condo bathroom.

Permits and Professional Requirements

All drain relocation work requires a plumbing permit from the City of Toronto or your local municipality, and must be performed by a licensed plumber. The work must be inspected before the floor is closed up. Budget $150–$300 for permit fees, and ensure the inspection is scheduled before your contractor closes the subfloor — reopening a finished floor for a missed inspection is costly and frustrating. This is never a DIY project; improper drain work causes sewer gas leaks, slow drains, backups, and water damage that far exceed the cost of doing it right the first time.