What can I build? ARU lot checker
This ARU lot checker uses the published rules for seven Ontario municipalities to estimate how many units your lot may allow and which types fit. It takes about 30 seconds. Rules checked October 26, 2026.
How the ARU checker works
The checker starts from Ontario's rule of up to three units on a serviced urban lot, then applies each municipality's published limits on units, detached buildings, size and rural lots. It does not read your zoning map, so treat the result as a starting point, not a permit decision.
Each answer links to the detailed city guide with official sources. When you are ready, run the money side through the ARU rent and incentive calculator, or see our secondary unit services.
Frequently asked questions
What can I build on my lot in Ontario?
If your lot is in a settlement area with municipal water and sewer and has a detached, semi or row house, Ontario allows up to three units as of right. Your municipality decides the details such as size, height and setbacks, and some allow four or more.
Is this checker a zoning decision?
No. It summarizes published municipal rules to give you a starting point. Zoning, servicing, easements, conservation authority limits and lot shape can all change the answer. We confirm the real answer for your address in a free property check.
Can I add a unit if I am on a well or septic?
Sometimes. The provincial three-unit rule only covers serviced lots. Some municipalities, such as Prince Edward County and Belleville, allow an extra unit on private services with a septic evaluation or hydrogeological study.
Want the real answer for your address?
We check your zoning map, servicing and lot dimensions and send you a plain-language summary. Free, usually within one business day.