Ready-made duplexes usually cost more than single homes, but converting a home into a duplex by adding a separate basement unit is common for affordability. Rental income can help qualify for mortgages, with lower down payments for owner-occupants. Ontario allows up to four units per lot with waived development charges for additional units. Conversions require separate entrances, kitchens, bathrooms, proper ceiling heights, and parking spots, with specific basement window and ceiling rules.