Second Dwelling Unit Ottawa

You will see three different labels used for the same broad idea: a self-contained residential space on the same lot as an existing home, with its own kitchen, bathroom, sleeping area, and private entrance.

Additional Dwelling Unit (ADU) is the term the City of Ottawa uses in its zoning by-law, and it is the umbrella term on this site – it covers every type we build. In everyday conversation people tend to split it in two. Accessory dwelling unit usually describes a unit that stands on its own, detached and separate from the main house: a garden suite, a laneway suite, or a coach house. Secondary dwelling unit, or SDU, usually describes a unit created inside the primary structure: a basement apartment, a garage conversion, or a self-contained suite carved out of the existing house.

The difference is about construction and cost, not legality. A detached unit needs its own foundation, roof, and servicing, which is most of why it costs more per square foot. An internal conversion reuses what is already there. Either way, the unit needs a City of Ottawa building permit and has to meet the same egress, fire separation, and ceiling height requirements to be legal. We design, permit, and build both.

A legal second dwelling unit holds its value and stays code-compliant with the same routine maintenance any home needs: checking roof and gutter condition each spring and fall, testing smoke and carbon monoxide alarms, keeping the furnace or heat pump filter changed on schedule, and watching for water pooling near a detached unit’s foundation after heavy rain. For a basement apartment specifically, keeping the fire separation between units intact, with no unauthorized openings cut into a shared wall or ceiling, matters for both safety and for staying compliant with your occupancy permit.