Do I need a permit for if I want to create/build Secondary Dwelling Unit (Additional Dwelling / Apartment)?

Yes, but first you need to check with the City/ Town whether the Zoning By-laws allow it, some Cities permit second suite dwelling units in detached dwellings, semi-detached dwellings and link house dwellings subject to certain zoning provisions.

Two-Unit Houses existing on or before November 16, 1995 are grandfathered by the Land Use Planning and Protection Act (bill 20) and are subject to the requirements of the Ontario Fire Code.

Existing Two-Unit Houses shall be registered with Building Services.