The plumbing plan for a secondary suite looks simple right up until the new toilet is below the old building drain, the vent has nowhere polite to go, and somebody has already poured the floor. Planning is cheaper when the concrete is still hypothetical.
What does the suite need at minimum?
Ontario's official second-unit guide lists hot and cold water, a kitchen sink, bathroom fixtures including a sink, bathing fixture and toilet (or qualifying composting toilet), and access to laundry. It also says second units need separate water shutoff valves so work in one unit does not interrupt the other.
The permit drawing has to show the plumbing
Toronto's current secondary-suite permit guide requires floor plans showing plumbing fixtures and a plumbing data sheet when plumbing, drains, or water service are involved. Other municipalities use their own forms and submission rules. The useful principle is universal: show the route before burying the route.
- Existing and proposed fixtures on every affected level
- Sanitary drain sizes, slopes, cleanouts, and connection points
- Vent routing and roof or stack connections
- Hot and cold water distribution and separate shutoffs
- Laundry connection and drainage
- Backwater valve or sewage-ejection equipment when required
Ask the elevation question early
Before laying out the bathroom, confirm the building drain's elevation and condition. A fixture below the available gravity connection may need a different layout or engineered pumping approach. Camera inspection and measured elevations are much more persuasive than everyone staring thoughtfully at the floor drain.
Backwater protection is property-specific
Ontario's second-unit guide says a backwater valve may be required where flooding or sewer backup is a concern. Local requirements and subsidy programs differ. Read our GTA basement flooding subsidy guide before buying equipment or starting work, because application and inspection timing can control eligibility.
Plumbing is one piece of a legal suite
A working toilet does not settle zoning, fire separation, exits, ceiling height, heating, ventilation, smoke and carbon monoxide alarms, or electrical approval. Use our Ontario legal secondary-suite guide for the full sequence. The suite becomes legal as a system, not fixture by fixture.
The tidy handoff file
Keep approved plans, permit and inspection records, plumber invoices, fixture specifications, photographs before close-in, drain-camera footage if obtained, and the locations of shutoffs and cleanouts. Label the shutoffs. Future emergencies do not enjoy scavenger hunts.
