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Westmount

What are the rules for a home extension in Westmount?

A building permit is required for an extension (By-law 1634, s. 38).

Permit required
Home extension: 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

  • The siting must comply with the zone's grid of physical and spatial specifications. (art. 4.5.1)
  • Side yard: open space of at least 2.13 m, or 0.46 m per 3.05 m of height (max. 6.10 m), whichever is stricter. (art. 5.3.2)
  • Rear yard: from 6.10 m (rear wall of 7.62 m or less) to 10.67 m (wall of more than 13.72 m). (art. 5.3.3 (table 2))
  • A semi-detached or row house cannot extend more than 3.50 m beyond its rear wall as it stood on July 9, 1993. (art. 5.3.6)
  • Home that does not meet today's setbacks (acquired rights): an extension is allowed if it does not worsen the non-conformity and meets the rest of the by-law; an added storey may be built in the side yard regardless of minimum setbacks if it stays on the perimeter of the existing foundations and respects the permitted height and number of storeys. (s. 8.3.5)

Summary by Radar Foncier, in our own words: the official French text of the by-law, linked above, prevails.

Applying in Westmount

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).

Home extension elsewhere: Dorval, Gatineau, Montreal, Sherbrooke, Vaudreuil-Dorion.

Version française de cette page

Source: Zoning By-law 1303 (administrative consolidation up to By-law 1641; accessory dwelling units: By-law 1657), French version, checked on October 25, 2026. Plain-English summary: the official French text prevails, and a by-law can change. Confirm with the Westmount 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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