Ottawa’s current additional-unit guidance describes up to two additional dwelling units on a lot with a principal home, where the applicable rules permit them. The City lists two arrangements: two apartments within the principal dwelling, or one apartment within the principal dwelling plus one coach house in an accessory building. That is a maximum of three dwelling units including the principal home; the two arrangements are alternatives, not an invitation to add both combinations.
The City describes a coach house as a separate dwelling in its own building on the same lot as the principal home. The layout and unit count are only part of the answer. Zoning permissions and exceptions, lot conditions, water and wastewater servicing, building and fire requirements, and permit and occupancy records can affect a project.
Check which zoning rules apply
Ottawa is transitioning to Zoning By-law 2026-50, and the City’s by-law page provides current information about its effect and appeal status. Check that page and the applicable zoning provisions for the property and application date. Do not rely on older summaries that describe a single secondary unit by detached, semi-detached, or duplex form as the City’s current full unit-count rule.
Start with the address and current zoning map. Confirm the principal building’s legal classification, the permitted unit arrangement, and any site-specific or transition provision. If considering a coach house, confirm its location and the rules for accessory structures and services as well as those for the additional dwelling unit.
Verify approvals separately
Ask the City to confirm the applicable zoning provisions and permit requirements for the proposed layout. Then check building and fire approvals, service capacity and connections, inspections, and occupancy status. A zoning summary does not establish that a unit was lawfully built or is ready for occupation.
Rental, short-term-rental licensing, title, and private financing or association restrictions are separate questions. Confirm the current requirements with the responsible offices and review the property’s actual records. This guide describes Ottawa’s published general pathway; it does not determine the result for a particular lot.