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Can you add a basement apartment in Montreal?

Rosemont–La Petite-Patrie: building a dwelling entirely in the basement is prohibited everywhere (except large projects approved as a PPCMOI, a specific construction proposal); a habitable basement is still allowed if it extends the ground-floor unit and is less than 60% of its area.

Permit required
Basement apartment: check for my addressFree and no account needed: your lot, your zone and its grid on the map (in French)

A 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: building a dwelling entirely in the basement is prohibited everywhere (except large projects approved as a PPCMOI, a specific construction proposal); a habitable basement is still allowed if it extends the ground-floor unit and is less than 60% of its area. (By-law 01-279-81 (borough's official summary))
  • Rosemont–La Petite-Patrie: a sunken courtyard or an outside staircase down to the basement is prohibited in the front yard. (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

Basement apartment elsewhere: Côte Saint-Luc, 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

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