What is the difference between an ADU and an SDU?

ADU (Accessory Dwelling Unit) and SDU (Secondary Dwelling Unit) are essentially the same thing in Ontario - just different terminology used by various municipalities and professionals. Both refer to self-contained residential units that are secondary to the main dwelling on a property.

In Ottawa specifically, the City officially uses the term "secondary dwelling unit" in their zoning bylaws and permit applications. However, you'll often hear contractors, real estate professionals, and homeowners use "ADU" interchangeably, as this term has become popular across North America. The Ontario Building Code also references "secondary suites" when discussing the technical requirements for these units.

Regardless of the terminology used, the requirements remain identical in Ottawa. Your secondary dwelling unit must meet the same standards whether you call it an ADU, SDU, or secondary suite. This includes minimum unit sizes (28 square meters for a bachelor, 37 square meters for one-bedroom), separate entrance requirements, proper fire separation between units, and compliance with R4 zoning where permitted.

The confusion often arises because different regions use different terms. Some Ontario municipalities prefer "additional residential unit" (ARU), while others stick with "secondary dwelling unit." In the United States, "ADU" is the predominant term. Real estate listings might use any of these terms, but they're all describing the same type of housing.

What matters most for Ottawa homeowners is understanding the City's specific requirements rather than getting caught up in terminology. When applying for permits through ottawa.ca/building or speaking with City staff, use "secondary dwelling unit" to avoid any confusion. The Building Code Services department at 613-580-2424 will know exactly what you're referring to.

For your basement conversion project, focus on the actual requirements: proper ceiling height (minimum 6'5"), adequate natural light, separate entrance access, fire-rated separation from the main house, and compliance with your property's zoning. These technical standards are what determine project feasibility and cost, typically ranging from $80,000 to $200,000 for a complete basement secondary dwelling unit in Ottawa.

Want to discuss converting your basement into a secondary dwelling unit? We offer free consultations to assess your space and explain the specific requirements for your property.