How many units can one lot have?
Usually the house and two more. The City's ADU team reviews permits for existing single family dwellings including up to two internal units & one detached unit
(City of Hamilton, Additional Dwelling Units, read November 5, 2026). The City's ADU page puts the maximum at four units on some lots, and the ADUs page lists the three ways to build one.
What decides whether my lot qualifies?
| Check | What it decides | Where to look |
|---|---|---|
| The zoning by-law | Which rules apply: the city-wide 05-200, or a former town's by-law | The areas page |
| Room for a detached unit | Distances from the lot lines and the house, height, size, the path to the street | Basement unit or garden suite |
| Rural land | A detached ADU on rural land needs a lot of at least 1.5 hectares | By-law 24-039 |
| Heritage | A heritage permit before a building permit | City Cultural Heritage Planning |
| A creek, valley or the escarpment | A conservation authority or Niagara Escarpment Commission approval first | Building near the escarpment or a creek |
| The house itself | Whether a basement can meet the Building Code for a home: ceiling height, exits, fire separation | The building permit review |
The rural rule is By-law 24-039 (City of Hamilton By-law 24-039, read November 5, 2026). Since November 2024 Ontario's regulation 462/24 has also overridden some local limits on additional units, which is why Hamilton cut the distance between a house and a rear-yard unit to 4.0 metres and raised lot coverage to 45%.
What if the plan misses a rule?
A minor variance from the Committee of Adjustment, at the routine fee of $745 for a secondary dwelling unit in 2026; see when you need a minor variance. If it is refused, the plan changes: often a smaller unit or a different spot on the lot.
Who should build it?
A unit inside the house is a renovation. A new detached unit is different: Ontario's home construction regulator says coach, laneway and tiny homes generally require licensing and warranty coverage
(Home Construction Regulatory Authority, read November 5, 2026). Who may build a new home explains what that means. Whether there is money to help is in money for an ADU in Hamilton.