On May 7, 2025, La Presse published an opinion piece titled “Unités d'habitation accessoires : la densification douce rendue possible” (Accessory dwelling units: gentle density made possible). The author defends a simple idea: adding a second dwelling on an already developed lot can transform our neighbourhoods profoundly without upsetting their character. The intuition is right, and it resonates with us. Before a reader, in the Laurentians or elsewhere, draws hasty conclusions for their own lot, a few clarifications are in order.
What the article gets right
The central idea is sound. An accessory dwelling unit (ADU), whether integrated into the main house, attached, or detached in the yard, adds housing where infrastructure already exists, in areas that are already built up. No new subdivision on the outskirts, no clear-cut forest. We call it gentle density because it fits into the existing landscape without distorting it.
The article also points out the possible uses: a home for a loved one, extra income, a transition to a smaller house. That is the human appeal of the formula, and it is real.
Bill 31 does not work on its own
The first shortcut to correct: people often talk about “Bill 31” as if it were a single text. In fact, two laws govern ADUs in Quebec, and they complement each other.
Bill 16, passed in 2023, gives municipalities a permanent power to allow and regulate ADUs through bylaws. Bill 31, passed in 2024, adds a temporary so-called “as-of-right” mechanism. Confusing the two gives a false picture of what is permitted.
Another nuance about dates is worth noting. The article cites March 25, 2024 as the starting point. According to documents from the Ministère des Affaires municipales, the as-of-right provision of Bill 31 applies instead from August 21, 2024 to August 21, 2029.
Attached, integrated or detached: the distinction that changes everything
This is the most important point, and the La Presse article does not expand on it. The as-of-right provision of Bill 31 does not cover every type of ADU.
Covered: units integrated into the main building (for example, a basement converted into a dwelling) and attached units (joined to the house).
Not covered by the as-of-right provision: detached units, the well-known backyard homes. Whether they are allowed depends on each municipality's bylaw, under Bill 16.
In other words, a neighbour building a small home at the back of their yard in Dunham does not mean the same project is possible on your lot. It all depends on your town.
And in the Laurentians, concretely?
The regional picture is a patchwork, and it is shifting.
Mont-Tremblant is among the municipalities cited in the La Presse opinion piece as having expressed interest in ADUs. Saint-Jérôme, for its part, already allows certain ADUs within its urban perimeter and is working to integrate them more broadly into its new urban plan, according to an investigation by Journal Le Nord published in October 2024.
Conversely, Sainte-Anne-des-Lacs held a public consultation in 2024 on adding detached ADUs to its urban plan, then withdrew that provision after strong opposition from residents, again according to Journal Le Nord. The concerns raised included traffic, septic tanks, tree clearing and short-term rentals.
The lesson is simple: even within the same RCM, the rules can vary significantly. The only way to know what applies to your lot is to check with your municipality's urban planning department.
Key takeaways
The opinion piece published in La Presse is right on the essentials: ADUs can add housing without abruptly transforming our neighbourhoods, and provincial law has indeed opened up new room. Three clarifications, however, should accompany that reading.
There are two laws, not just one. The as-of-right provision does not cover detached units. And the final decision remains, in most cases, in the hands of the municipality.