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Residential Accessory Buildings

Can I build an accessory building on my property?

You can build an accessory building if it meets the following requirements:

  • It meets the minimum zoning requirements as noted in the table below
  • It will not be constructed on an easement (check the survey of your property)
  • The structure will be at least 1.5 metres (5 feet) from an underground septic tank or 5 metres (16.4 feet) from a septic field (greater clearances may be required)

Do I need to check for zoning compliance?

Yes. The height, size, and location of an accessory building of any size is determined by the Zoning By-law. For the zoning requirements for a particular property, please see Residential Zoning Requirements.

View the City of Thunder Bay Zoning Map for more information on your areas requirements.

A minimun separation distance of 2m (6.6 ft) shall be maintained between an Accessory Building and the Dwelling (not including deck). Eaves shall be a minimun of 300 mm (1 ft) away from property lines in R1 and R2 Zones.

* “All Buildings” includes decks greater than 0.6m (23 5/8 in) in height. Coverage may be increased to 40% for undersized lots in certain cases (see Planning Division)

** If a rear yard abuts an adjacent side yard, other requirements may govern.

Do I need to hire a professional designer?

Yes, if the building is more than 9.8 metres (32 feet) wide, you will need to engage the services of a professional engineer.

No, if the building is less than 50 square metres (538 square feet) AND you yourself have the required skills to prepare design drawings that provide enough information to verify that you have met the requirements of the Ontario Building Code and Thunder Bay’s Zoning By-law.

Do I need a building permit?

Yes, if the area of the accessory building is more than 10 square metres (108 square feet) or contains plumbing. Download a Building Permit Application Form Adobe PDF, 3 pages, 69 KB

What do I need to provide to the City in addition to the completed Building Permit application?

  • Schedule 1: Designer information, completed, with designer’s signature 
  • Written authorization from the owner of the building
  • Proof of ownership (either a property deed or tax notice)
  • Two sets of working drawings (floor plans) designed by a Registered Designer or by the owner or
  • Current site plan or survey, indicating existing buildings and the proposed structure.   
    Required fee: set at $10 per $1,000 of construction value, minimum fee is $50
  • Other approvals as needed (e.g. Thunder Bay Hydro) – see below for more information

What other information do I need?

  • If there are overhead electrical wires near the building site, contact Thunder Bay Hydro at (807) 343-1176 to review and approve your plans. The clearance requirements depend on the voltage of the line involved.
  • If there is a septic tank or septic field near the building site, contact the Thunder Bay District Health Unit, Sewage Systems and Land Development Program, at (807) 625-7991 for information on clearances.
  • If you are carrying out electrical work as part of the project, you must contact the Electrical Safety Authority at or call 1-877-372-7233 for information and inspections.

Excavations - call before you dig!

Ontario One Call logoAt least five days before you start digging, contact Ontario One Call to arrange for the location of underground utilities.

Dig safe - it's the law.

More information on Ontario One Call.


Once you receive a building permit, it is your responsibility to arrange for building inspections.

Call (807) 625-2570 (North Ward) or 807-625-3124 (South Ward) at least 48 hours in advance to book an appointment. You can call at any time to leave a message.

In most cases, there will be only one structural inspection when the building has been roofed and enclosed with exterior sheathing, doors and windows, but no interior finish.

Any electrical work must be inspected by Electrical Safety Authority ( call 1-877-372-7233.
City of Thunder Bay
Building Services Division

Address: Victoriaville Civic Centre
111 Syndicate Avenue S
P.O. Box 800
Thunder Bay ON P7C 5K4
Tel: (807) 625-2574
Fax: (807) 623-9344
Office Hours: Monday to Friday - 8:30 am to 4:30 pm