Montreal
What are the rules for a home extension in Montreal?
An extension requires a permit from the borough.
Permit requiredA zone, a heritage area or a shoreline can have its own standards: with your address, the Radar reads your zone's grid and tells you what applies to your property.
The rules, in short
Rules of the Ahuntsic-Cartierville, Rosemont–La Petite-Patrie and Ville-Marie boroughs. Each Montreal borough has its own by-law: check your address.
- Rosemont–La Petite-Patrie: it is prohibited to extend or convert a floor to create living space below ground level, with some exceptions (By-law 01-279-81, in force since summer 2025). (By-law 01-279-81 (borough's official summary))
Summary by Radar Foncier, in our own words: the official French text of the by-law, linked above, prevails.
Applying in Montreal
- Processing time: Varies by borough (no general processing time published)
- Cost: Varies by borough; example shown on montreal.ca: $9.80 per $1,000 of work, with a minimum ($167.40 for a pool)
- Urban planning department: 311
- Permits on the municipality's website
For the permit application, you will often need a site plan (certificat d'implantation) drawn up by a land surveyor: certificate of location and site plan, what to know (in French).
Other projects in Montreal
Home extension elsewhere: Dorval, Gatineau, Sherbrooke, Vaudreuil-Dorion, Westmount.
Version française de cette page
Source: Borough urban planning by-laws: Ahuntsic-Cartierville (01-274), Rosemont–La Petite-Patrie (01-279) and Ville-Marie (01-282); rules taken from the montreal.ca how-to pages for these 3 boroughs only, checked on October 22, 2026. Plain-English summary: the official French text prevails, and a by-law can change. Confirm with the Montreal urban planning department before buying materials. Radar Foncier is an independent service, not affiliated with the municipality.
Radar Foncier in English. Permits and rules for Québec homeowners; the full site and the reports are in French. Version française