Renovating · Extension · Montreal
In Montreal, an extension is a borough file, with nineteen different by-laws and a single fee. Here is what the city publishes, what the borough decides, the 2026 costs, and the extend-or-move calculation.
In Montreal, the extension permit is issued by the borough, not by the central city, and each borough applies its own siting, height, PIIA and delay rules; the fee, however, is published by the city: $9.80 per $1,000 of work cost, with a minimum of $167.40 for a strictly residential building ($491.70 for commercial, industrial or mixed), renewal at 25% of the price, possible additional review fees for a heritage building or a protected sector, and no refund in case of refusal (montreal.ca, April 2026). A $150,000 extension therefore costs $1,470 in permit fees. On the island, the extension often takes the form of a rear annex or a storey on a bungalow (Saint-Laurent, Ahuntsic, Rivière-des-Prairies, Pierrefonds, LaSalle), or a mezzanine and rear extension on a plex or a row house (Rosemont, Villeray, Verdun, Le Sud-Ouest), where lane, minimum rear yard and facade alignment rules are strict and PIIA sectors are numerous. The cost of the work follows the 2026 industry ranges ($250 to $450 per square foot on a full foundation, $200 to $400 for a storey), often at the top of the range in the city (site access, party walls, paid site parking). The value created is judged on closed sales on the street, where floor area is scarcest and pays best.
| Item | Rule (montreal.ca, "Renovations: how much does a permit cost", April 10, 2026) |
|---|---|
| Fee | Cost of work ÷ 1,000 × $9.80 (example: $150,000 of work, $1,470) |
| Minimum | $167.40 for a strictly residential building; $491.70 for commercial, industrial, institutional or mixed |
| Renewal | 25% of the initial permit price, same minimums |
| Additional fees | Possible for a heritage building or a protected sector, varying by borough |
| Refund | No refund in case of cancellation or refusal |
| Who issues it | The borough, online or at the permit counter; siting, height, rear yard, PIIA rules and delays specific to each of the nineteen boroughs |
| Documents | Certificate of location, scaled architectural plans (often signed), site plan, cost estimate, structural details and, in a PIIA, elevations and materials |
Before the plans, ask the borough for your lot's zoning sheet (lot coverage, height in storeys and metres, setbacks, minimum rear yard, alignment) and whether the sector is covered by a PIIA or a heritage-value sector: in Rosemont, Le Plateau, Villeray or Outremont, the rear extension of a plex almost always goes through a committee, which adds one to three months.
| Type of extension | Typical 2026 cost (Dessins Drummond estimates, August 2026) | Typical project |
|---|---|---|
| Ground-level extension on a full foundation (basement) | $250 to $450 per square foot | 400 sq ft at the back: $100,000 to $160,000 |
| Ground-level extension on piers or a slab | $200 to $390 per square foot | Cheaper, no basement |
| Second storey added on the existing house | $200 to $400 and more per square foot | 800 sq ft: $160,000 to $320,000 and more, depending on structure and roof |
| Attached garage | $180 to $240 per square foot | 400 sq ft: $72,000 to $96,000 |
| Four-season sunroom | $250 to $325 and more per square foot | 300 sq ft: $75,000 to $97,500 |
These ranges are industry estimates, before taxes, excluding plans ($2,000 to $8,000 depending on the architect or technologist), permits and contingencies (allow 10% to 15%); an extension that touches the roof, plumbing, electrical or load-bearing structure lands at the top of the range. Three detailed quotes from RBQ-licensed contractors, with a schedule and a holdback, remain the only way to get a price.
An extension is rarely recovered in full at resale: in a sector where comparable houses already have the added area, the value created comes close to the cost; in a sector of smaller houses, it caps at what the market pays for the best house on the street, and the excess is lost. The honest comparison: the cost of the extension (plus 6 to 14 months of work and municipal taxes that rise with the assessed value) against the cost of selling and buying bigger (commission, notary, welcome tax, moving: about 8% of the price, $50,000 to $60,000 on a $650,000 to $700,000 house) and the price gap between the two houses. A broker who knows the sector's closed sales can price both options within a week, before you pay for plans.
Yes, for any increase in floor area, including a storey, an attached garage, a sunroom or a veranda; the permit is obtained before the work and an inspector visits the site.
About $100,000 to $160,000 in 2026 for a ground-level extension on a full foundation, taxes, plans and permit extra, according to industry estimates.
Partly: the value created depends on the sector's comparable sales and caps at what the market pays for the best house on the street; compare with selling and buying bigger.
Six to fourteen months from plans to completion, including several weeks for the permit, longer if the project needs a minor variance or an architectural integration approval (PIIA).
Before extending, compare with the other option: the cost of selling, renovating before selling and the 2026 renovation grants.
The Loaa & Manseur team, led by Lotfi Manseur and Loaa Al Daow, is the number 1 team at RE/MAX Platine in 2024 and 2025, 6th RE/MAX team in Quebec, 15th in Canada and in the global top 50 of large residential teams according to the official RE/MAX ranking, computed on actual transactions. Its Google profile counts 221 reviews with a 4.9 rating. Its offices are at 55 avenue de l'Équinoxe in Brossard, one bridge from the island, and every broker's licence can be checked in the OACIQ public register. Three things to verify yourself before calling us, and to demand of any other broker.
Also available in French: version française de ce guide.
Published September 7, 2026 by the Loaa & Manseur team, the number 1 team at RE/MAX Platine in 2024 and 2025, 6th RE/MAX team in Quebec, 15th in Canada and in the global top 50 according to the official RE/MAX ranking. Tell us about your project.
Équipe no 1 de RE/MAX Platine en 2024 et en 2025, 6e au Québec, 15e au Canada et dans le top 50 mondial au classement officiel RE/MAX. Réponse en moins de 24 heures, sept jours sur sept.