Accessory Dwelling Units

Accessory Dwelling Units (ADU)

Accessory Dwelling Units (ADU) are permitted in The Town of Gravenhurst, subject to local regulations. The Zoning By-law outlines the requirements for this use. Below is a summary of some of the requirements, but also see Sections 5.1 and 5.2 of the Zoning By-law (page 40) for more details regarding Accessory Dwelling Units.

1. ADUs are permitted within the primary dwelling and in an accessory building in Urban, Community, or Rural Areas, specifically permitted in R-1, R-2, R-3, RM-1, RM-2, RC-4, RR-5 provided the lot meets the minimum lot area frontage requirement of the zone.  Please note that ADUs are not permitted in the Waterfront Residential (WR) Zone. Refer to Zoning Map: GeoHub
2. Municipal or private services are required.
3. ADUs cannot be severed from the primary dwelling in the Rural Area.
4. Maximum ADU size in a primary dwelling or in an accessory building is 45% gross floor area of the structure, excluding any deck or unenclosed porch.
5. Where an ADU is to be located in an accessory structure, the min setback requirements listed for the principal building in the applicable zone apply.         
6. One parking spot is required for each ADU.
7. ALL Accessory Dwelling Units must meet the requirements of the Ontario Building Code as needed.

• Accessory Dwelling Unit built on-site:
  • The Ontario Building Code sets out minimum room sizes in all dwelling units including accessory dwelling units, including but not limited to: living areas, dining areas bedroom, kitchen and bathrooms. Room sizes depend on whether or not the rooms and spaces in a unit are open-concept or separated by walls. Generally, where units have separated living spaces the minimum required room sizes are greater than units having combined living spaces.
  • Notwithstanding this, any dwelling unit containing combined living spaces containing sleeping accommodation, shall have a minimum combined living space of 13.5 square metres (145sq. ft.) for not more than two persons. In addition, the Ontario Building Code has regulations in relation to, but not limited to: stairs, minimum ceiling heights, hallway and door width requirements, windows, plumbing, lighting and other requirements that all ADU would have to meet. It is also important to note that all homes including ADUs must be attached securely to the ground through a foundation.
  • In addition, ADUs whether built on-site or factory-built must take into account climate conditions such as temperature, wind, snow, rain & energy efficiency.
  • Accessory Dwelling Units must be accessible if there is a fire or medical emergency. Firefighters must be able to access all dwelling units at all times.  The Ontario Building Code requires each building to have access for fire department vehicles by a public street, a private road or a yard.  Private roads or yards are only an acceptable option if certain conditions are met such as, a connection to a public thoroughfare, location of fire hydrants and proper overhead clearance.
  • A list of all Building Code requirements for dwelling units can be found in the Ontario Building Code 
  • Factory-built Tiny Homes or Mobile Manufactured Homes must meet one of the two key CSA certification standards in the Building Code for factory-built buildings (CSA-Z240.2.1-09; CSA A277-08).

1. Building permits and inspections are required prior to the start of construction. Contact the Building Department.
2. Other regulations may apply.

Development Charges

Reports to Town of Gravenhurst

• April 2022 Planning Council Report

Accessory Dwelling Unit Brochure

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