What is involved in legally converting a purchased single-family home into a duplex in Ontario?

Converting a single-family home into a legal duplex generally requires confirming the property's zoning actually permits a second unit, then obtaining the necessary building permits and meeting Ontario Building Code requirements for things like fire separation between units and proper means of egress, since these standards exist specifically to protect occupant safety in a multi-unit configuration. Depending on the municipality, additional approvals or registrations for the secondary unit may also apply.

This is not a quick or guaranteed process; requirements, permit timelines, and specific rules vary by municipality, and some properties or neighbourhoods may not permit an additional unit at all under current zoning, regardless of the physical layout of the home. Before committing to a purchase on the assumption that conversion will be straightforward, confirm with the municipal planning and building departments what is actually required for that specific property, and budget for the possibility that permits, inspections, and construction take longer and cost more than initially expected. A lawyer can help you understand any conditions or restrictions tied to the property before you rely on conversion plans.