Investment

Adding an Accessory Dwelling Unit in Quebec: The Framework

By Georges Matar · September 21, 2026 · 9 min read

An empty basement, an attached garage used as a shed, a lot deeper than the others on the street. The reflex is to calculate a rent. The useful order is the reverse: what the by-law allows at your address, what the authorization costs, then what a lender and an insurer agree to see in it. Here are the three steps, with the figures published by Laval, by Montreal and by CMHC.

A lot’s potential is read in the zoning grid

Two documents decide before you do: the zoning sheet for your address and a recent certificate of location. The tax bill decides nothing.

In Laval, the check is done online. The Info-reglements tool allows a search by lot or by address. You enter the address, you click Voir les details, then you scroll below the map. If the notice “Attention! Des dispositions particulieres s’appliquent a votre zone” appears, a site planning and architectural integration programme applies and additional requirements are added. Without the notice, the file follows the standard process.

In Montreal, there is no single rule. The urban planning by-law is the borough’s, and the City names it in its procedures: by-law 01-274 for Ahuntsic-Cartierville, for example. Fees, documents and timelines vary from one permit counter to the next. A high land value on the assessment roll is never an authorization, and reading the roll and the grid explains why.

Adding an accessory dwelling unit in Laval: what is allowed

Laval publishes a dedicated procedure. The official vocabulary speaks of an unite d’habitation accessoire, the UHA, and a permit must be obtained before fitting out an additional dwelling inside an existing single-family home. Four limits shape the project:

The conversion is authorized only in an already existing 1 dwelling home.
Creating a UHA entirely detached from the principal residence is not permitted anywhere on the territory.
The main configurations are the addition, the attached garage converted into a dwelling, and the basement fitted out as a bachelor unit.
Access is flexible: a door opening onto the main dwelling or a shared hall, a connecting door locked or not, a separate entrance possible on any facade.

One detail matters for the budget: adding an extra parking space is not mandatory.

Among the advantages it lists, the City names rental income and the possibility of occupying the additional dwelling while renting out the main portion. The municipal authorization therefore does not lock you into a family use in Laval. Elsewhere, the answer is read on the zoning sheet for the address, never by analogy with a neighbouring city.

The permit, the documents and the bill

The fees are published. They get budgeted before the plans.

Item	Laval	Montreal
Permit	$732 for an additional dwelling, plus $92 for the first $20,000, then $2.50 per $1,000 bracket	$9.80 per $1,000 of work, minimum $167.40 residential
Service connection	$450 for the first dwelling, $20 per additional dwelling	Depends on the borough
Work in the street right of way	$300 for 1 to 4 dwellings	Depends on the borough
Announced timeline	30 days	30 to 60 days in Saint-Laurent

In Montreal, the estimate must include all costs related to the work, taxes included, and the review fees are not refundable. The permit for a building of four storeys or less stays valid for 18 months, and the work must begin within 12 months.

The file is heavier than the bill. For an addition, a second storey or the conversion of the attached garage, Laval requires a complete architect’s plan, signed and sealed by an architect under section 16 of the Loi sur les architectes where that applies, a recent certificate of location from a land surveyor, and a service connection sheet. In a flood plain or on a waterfront lot, add the shoreline, the flood elevations, the zone d’intervention speciale and the highest known water levels. In Montreal: certificate of location, building sheet, cost quotation and complete plans of every level.

What a lender counts as income from an accessory dwelling unit

This is where projects get revised: the projected rent does not enter the lender’s calculation in full, and the rule depends on the number of dwellings and on occupancy. CMHC publishes the approaches it accepts in mortgage loan insurance. For an owner occupied building covered by the loan application: with two dwellings, the gross rental income approach allows up to 100% of gross rents to be added to gross annual income, and the taxes and heating of the subject building may be excluded from the ratio calculation. With three or four dwellings, only two choices: up to 50% of gross rents, or net rental income, meaning gross rents less operating expenses. If the owner does not occupy the building, the range also drops to 50% of gross or to net income.

The practical consequence: going from one dwelling to two is the most advantageous step from the calculation’s point of view, and the advantage is lost at the third. Run the cost of the work and the projected rent through the mortgage calculator, then have the ratios validated by a mortgage broker: he and the lender are the ones who decide.

Do not budget on help that does not exist yet. The Canada Secondary Suite Loan Program appears in Canada’s Housing Plan with the notation “in development”. It promises low interest loans. As long as it is not accepting applications, it is not part of your financing structure.

Subdividing rather than adding: the question comes before the plans

If your lot clearly exceeds the sector’s standard, severance is a distinct option, with its own entry door: the subdivision permit, then the cadastral operation. Laval handles these applications through an electronic service, and the cadastral documents attached must be valid according to the instructions of the minister responsible for the cadastre, with a prevalidation of the files done before the permit application. The file therefore begins at the land surveyor’s office, not at the counter. The rest of the route, from the parks contribution to the servitudes, is detailed in reading the roll and the zoning.

Taxes, assessment and insurance: what changes after the work

The roll moves. One more dwelling modifies the inventory of your assessment unit. When the modification gives rise to a notice, Montreal indicates that the application for review is filed within 60 days following the sending of that notice, or before the May 1 following the coming into force of the roll, whichever is later, with fees starting at $90 for a building of $500,000 or less. That deadline gets watched, it does not get discovered.

Insurance is settled before the first tenant. The Insurance Bureau of Canada is blunt: failing to disclose all information relating to occupancy can lead to the cancellation of a home insurance policy. Its example is exactly our scenario, the tenant who accidentally starts a fire in the basement while the insurer did not know he was there. The Bureau adds that ordinary home policies cover neither the contents nor the civil liability of tenants, and that landlord coverage can include loss of rental income and defence costs. Consult your representative before the work, keep written proof of the notice, require annual proof of insurance from the tenant.

On the tax side, renting out part of your principal residence opens the change of use regime, explained in the intergenerational home by-law. An accountant validates your case, not a broker.

Renting the accessory unit: the lease and setting the rent

As soon as there is a lease, you enter the jurisdiction of the Tribunal administratif du logement (Quebec’s rental board), and three rules get checked before setting a price.

The form is mandatory. The Tribunal’s lease has been required since September 1, 1996 for every new residential lease, whether it is a room, an apartment or a house.

The notice to the new tenant is not optional. The landlord must state the lowest rent paid during the 12 months preceding the start of the lease or, where applicable, the rent fixed by the Tribunal. If no rent was paid during those 12 months, the notice must state the last rent paid and its date. And no deposit may be required, whether for keys or furniture.

The restriction on the right to have rent fixed targets the building, not the dwelling. Neither the landlord nor the tenant may ask the Tribunal to fix the rent where the dwelling is located in a building erected five years ago or less, or in a building whose use for residential purposes results from a change of destination five years ago or less. A tenant who then refuses the increase must leave at the end of the lease. Since February 21, 2024, to invoke this restriction, the landlord must also state in the lease the maximum rent that may be imposed during the five years following the date on which the building was ready for habitation.

No source I consulted lets me say whether a dwelling added inside an already residential house falls into either of those two descriptions. Do not assume it does, and do not copy the clause into the lease “just in case”: have the question settled by a legal adviser. The other obligations that arrive with a first tenant are gathered in managing a rental property.

Frequently asked questions

Can I build a small detached dwelling at the back of my yard in Laval? No. The City writes that creating a UHA entirely detached from the principal residence is not permitted on its territory. What remains is the addition, the converted attached garage and the bachelor style basement.

Do I have to add a parking space? In Laval, adding an extra space is not mandatory in a single-family building. In Montreal, the number of parking spaces adjusts to the intended use: the answer comes from the borough.

How much does an accessory dwelling unit add to resale value? No official source lets me put a number on it. What can be demonstrated: a permitted, compliant dwelling with its lease in order gets financed, whereas an improvised dwelling will have to explain itself to the next buyer’s lender and insurer.

To go further, read the checks before investing in Laval and the checks before buying land.

Wondering what your address actually allows? Write to me. We pull out the zoning sheet and the certificate of location before talking about rent or plans.