Creating Legal Basement Apartments & Additional Units in Montreal: What Homeowners Need to Know
One of the most effective strategies is converting unused or underutilized space—especially basements—into legal dwelling units. Whether you want to build a new basement apartment, add a civic number, or even turn your triplex into a four-plex, the right planning and permitting process is essential.
Why add a legal basement apartment? A legal basement apartment can generate consistent rental revenue, increase property value, and help offset mortgage and renovation costs. In larger properties, converting a triplex into a four-plex is one of the most compelling opportunities—allowing owners to boost long-term income without purchasing a new property.
Our process is simple and streamlined: we visit the property to take precise measurements, then prepare clear existing plans of the space and proposed plans for the new unit layout. We verify compliance through code and zoning studies, complete and sign the required Fiche de bâtiment, and package everything needed for your permit submission. In most cases, this full set of documents is ready within about 10–14 days, so you can move quickly from idea to application.
While we provide services across the island of Montreal, a large portion of our basement planning projects are concentrated in areas like LaSalle, Montréal-Nord, Saint-Léonard, and Lachine. These neighbourhoods are filled with exactly the kinds of small multi-unit buildings that are ideal candidates for basement apartments and additional units. Whether it’s finishing a basement to create a new rental, regularizing an existing unit, or converting a triplex into a four-plex, we’re familiar with the building types, the borough expectations, and the permitting process.
