Expand or Reconfigure Your Home? Costs and ROI in Montreal

Article by François Guida

President, CEO and Partner, Groupe Cartier

Published October 21, 2026 · 6 min read

In Montreal, a home addition costs $250 to $550 or more per square foot (typical budget of $100,000 to $300,000), while an interior reconfiguration runs between $100 and $300 per square foot. The right choice depends on your lot, your neighbourhood and the space you can actually recover: Groupe Cartier helps you decide with numbers, not guesses.

Every year, homeowners across Greater Montreal ask themselves the same question before starting a project: expand the house, or simply make better use of the space they already have? Both routes transform daily life, but their costs, timelines and resale returns differ considerably.

At Groupe Cartier, a general contractor and design firm founded in Montreal in 1998, we have guided this decision for more than 25 years, with an integrated team of APDIQ-member designers, project managers and site supervisors, all in-house. Here is how to weigh the two options objectively.

Home addition: what it really costs in 2026

An addition almost always involves structural work: a new foundation, framing, roofing, insulation, extended electrical and plumbing, then complete finishes. That is why the price per square foot climbs quickly beyond a simple interior renovation.

• Addition (new foundation or added storey): $250 to $550 or more per square foot.
• Typical overall budget: $100,000 to $300,000 for a complete residential project.

These ranges cover design, materials, CCQ-certified labour and site management, but exclude taxes (GST and QST, 14.975% combined) and a contingency of about 15% that is always wise to plan for.

Interior reconfiguration: recovering space without pushing the walls out

In many cases, the "missing" space already exists in the home, poorly distributed among compartmentalized rooms, a closed-off kitchen or an underused basement. An interior reconfiguration planned by an interior designer can recreate the equivalent of an extra room without touching the foundation.

The cost of a reconfiguration generally falls between $100 and $300 per square foot, depending on the scope of work (opening up walls, moving plumbing or electrical, new finishes). It is often the preferred option in dense neighbourhoods where the lot simply does not allow an addition. Our article on strategies to maximize space without expanding details nine concrete approaches used by our designers.

Neighbourhoods with large lots: an addition makes sense

In areas where lots are generous, an addition often remains the most logical option for gaining a primary bedroom, a closed-off office or a family room. This is particularly true in Boucherville, Saint-Bruno-de-Montarville, Laval, Rosemère, Lorraine and Blainville, where backyards and setbacks provide the room needed to build without compromising the landscaping.

These municipalities attract established families living in homes built between the 1970s and 1990s, whose addition potential remains largely untapped compared with today's needs (a larger kitchen island, a primary suite, a home office).

Dense neighbourhoods: reconfiguration is the way to go

Conversely, in central neighbourhoods such as the Plateau-Mont-Royal, Villeray and Outremont, narrow lots, strict borough bylaws and the proximity of neighbours severely limit the possibility of an addition. Interior reconfiguration (opening up walls, a rethought kitchen, a mezzanine or an optimized basement) then becomes the most profitable way to gain functionality.

Permits and regulations: an unavoidable step

Any residential addition in Montreal requires a building permit issued by the borough or the municipality concerned, in accordance with the applicable urban planning bylaws (those of the City of Montreal can be consulted on montreal.ca). Heritage areas such as Westmount, Outremont or the Town of Mount Royal apply additional architectural criteria (exterior materials, height, siting) that can lengthen approval times.

An interior reconfiguration that does not affect the load-bearing structure or the building footprint generally involves lighter procedures, but any load-bearing wall that is moved must be assessed by a professional. Our team, holder of RBQ licence No. 8264-6134-49 since May 2002, prepares the plans and coordinates all procedures with the city, with a single point of contact responsible for the project from start to finish. Our article on the RBQ, APCHQ and CCQ credentials explains what this licence concretely guarantees.

ROI: which option pays off more at resale?

Return on investment differs by type of work. A quality kitchen renovation delivers an ROI of 75% to 100% at resale, a return that is hard to match. A well-designed addition, for its part, usually recovers 60% to 80% of its cost, depending on the local market and the quality of execution.

• Custom kitchen renovation: ROI of 75% to 100%.
• Addition (storey or foundation): ROI of 60% to 80%.
• Targeted interior reconfiguration: often comparable to the cost of a kitchen, with a similar ROI when it affects rooms of high perceived value (kitchen, bathroom, open-plan area).

In many cases, the most profitable strategy combines both: a targeted reconfiguration of the high-impact rooms, complemented by a modest addition rather than a full extension. This is the kind of analysis our interior designers carry out at the very first visit.

How Groupe Cartier helps you decide

Before recommending a direction, our team assesses your lot, your borough's regulations, your budget and your real needs. Our turnkey renovation service covers design, plans, permits, construction and delivery, with in-house carpenters-joiners and cabinetmakers, and no unknown subcontractors.

Our work, such as the Piedmont project (production and installation of custom furniture, in collaboration with Zu Design et Architecture intérieure) or the Delorimier project, winner of the Concours Miralis (Cuisine Québec), illustrates our commitment to maximizing every square foot. See our projects for concrete examples. Our cabinetry comes notably from Miralis, a Quebec cabinetmaker founded in 1976 and a long-standing partner of Groupe Cartier.

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