Short answer
Some eligible detached homes may add one attached accessory dwelling under Québec's temporary statutory rule through August 20, 2029. You must confirm the borough, site eligibility, municipal exemptions and permits first.
Official-record update — October 13, 2026: Montréal cannot be assessed with one citywide backyard-suite answer. Borough regulations and any applicable conditional-use path must be checked for the exact address. A Québec temporary attached-unit entitlement does not itself legalize a detached backyard dwelling.
Evidence: borough specific / property unverified. Still unresolved: Borough-specific adopted text, maps, heritage protections, provincial opt-outs and permits. No parcel approval or final comprehensive legal signoff.
What local rules actually say
Québec's temporary autorisation de plein droit (August 21, 2024–August 20, 2029) may allow one attached additional dwelling in an eligible detached single-family house, even where ordinary municipal zoning would otherwise prohibit it. Montréal's boroughs regulate building form and permits separately. The temporary measure is not permission to construct any number of units or a detached backyard cottage.
An eligible project can involve subdividing the existing main house or constructing an addition attached to it; a standalone garden house or detached garage apartment is not covered by that provincial override.
Important exceptions and the next step
- Property type: The measure applies to a detached single-family home, not a duplex, row house or apartment building.
- Location: The lot must be inside the urbanization perimeter and outside certain mapped public-safety constraint areas.
- Heritage: Listed heritage protections and certain heritage sites exclude a property from the automatic rule.
- Local exclusions: A municipality can adopt a regulation excluding some or all of its territory from this temporary authorization; check whether the applicable exemption affects the project.
- Permits still matter: Building, layout, architectural, parking and servicing rules still apply. Contact the correct Montréal borough permit counter before work begins.
There is no trustworthy citywide maximum unit count for all Montréal parcels. For detached suites, duplex-to-multiplex conversion, or new multi-unit construction, use the adopted borough zoning and the specific property, not the provincial temporary attached-unit rule.
How to verify an individual property
- Look up the legal property address and zone on the official Montreal zoning map.
- Confirm the proposed dwelling type: internal suite, addition, detached garden home or multiplex; these can follow different rules.
- Verify zone exceptions, lot size, servicing, hazard/heritage limits, any registered restrictions and the current amending bylaws.
- Ask the local planning/building office for the required written zoning confirmation and building permits before commissioning construction.
Québec temporary attached-unit rule (2024–2029)
A separate Québec measure runs from 21 August 2024 through 20 August 2029. It can allow ONE additional attached dwelling in an eligible detached house within the urban perimeter, despite ordinary local zoning, subject to statutory exclusions and possible municipal opt-out. It does not authorize detached backyard cottages and does not waive municipal permits, architectural standards, building safety or hazard and heritage protections.