Should I share plumbing walls between Toronto bathrooms to save cost?

Sharing plumbing walls between bathrooms is one of the smartest cost-saving strategies in home renovation — when done right. By stacking or clustering bathrooms back-to-back or above each other, you can reduce your plumbing rough-in costs by 20–40% compared to running independent drain and supply lines across the house.

The core idea is simple: when two bathrooms share a common wall (or are stacked vertically), your plumber can tie into a single wet wall — the framed cavity that houses your drain stack, vent stack, and supply lines. Instead of running a second set of pipes across the house, you're just adding connections to an existing chase. Less pipe, less labour, less drywall patching, less disruption.

Where this strategy works best is in new builds, full gut renovations, or additions where you have flexibility in the layout. A classic Toronto example is a main floor powder room placed directly below a second-floor full bathroom — both sharing the same wet wall. Another common setup is two bathrooms on the same floor positioned back-to-back, sharing one plumbing wall between them. In older Toronto homes (think post-war bungalows in Scarborough or North York), this is often already how the house was built, and any renovation should respect and work with that existing layout.

What You Actually Save

In the current GTA market, plumbing rough-in for a new bathroom typically runs $3,500–$8,000+ depending on distance from the main stack and complexity. Sharing a wet wall can reduce that by $1,000–$3,000 per bathroom because you're cutting pipe runs, fittings, and labour hours significantly. Drain venting — which must comply with the Ontario Building Code (OBC) Part 7 — is also simplified when fixtures are clustered, since you may be able to wet-vent or common-vent fixtures rather than running individual vent stacks to the roof.

Toronto-Specific Considerations

In Toronto, any new bathroom or significant plumbing alteration requires a building permit through the City of Toronto Building Division (416-397-5330 or toronto.ca/building). Your plumber must be licensed under Ontario's plumbing trade regulations, and the rough-in will be inspected before walls are closed. In older homes — particularly century homes in The Annex, Leslieville, or Cabbagetown — cast iron drain stacks are common and may need upgrading to ABS or PVC when tying in new fixtures, which affects your budget.

One thing to watch: Toronto's older homes often have undersized drain stacks (3-inch instead of 4-inch). If you're adding a second bathroom to an existing wet wall, your plumber needs to confirm the stack can handle the additional load before you commit to the layout.

When to Hire a Pro

This is firmly in licensed-plumber territory. Drain slope, venting compliance, and stack sizing are not DIY decisions — improper venting causes sewer gas issues and failed inspections. A good plumber will review your floor plan and tell you within an hour whether your proposed layout works efficiently.

Your next step is to have a licensed plumber walk your space before you finalize any bathroom layout. Bring your rough floor plan and ask specifically about wet wall sharing and venting strategy — a 1–2 hour consultation (typically $150–$300 in the GTA) can save you thousands in the design phase. Browse licensed plumbing contractors in your area at the Toronto Construction Network to find local professionals who know Toronto's housing stock and permit process.