Short of space to store your tools, bikes and winter sports equipment? Do your two cars spend the winter outside and you're tired of scraping the windows at -15°C every morning?

You're thinking of adding an attached garage to your house.

It's a popular project in Longueuil and all over the South Shore. With real estate prices on the rise (+9.1 % in Montérégie in 2024), moving for more space is expensive. Adding a garage is often more logical and economical.

But building an attached garage isn't as simple as putting a garden shed in the backyard. There are permits to obtain, zoning rules to respect and construction standards to follow. Do it the wrong way, and you risk having your permit denied, being fined, or having structural problems that will cost you dearly down the road.

In this guide, we explain exactly how to build an attached garage in Longueuil: municipal bylaws, construction stages, actual costs in 2025, and mistakes to avoid. We also debunk common myths and answer questions we're often asked.

Why more and more homeowners are adding attached garages in Longueuil

An attached garage isn't just a luxury. For many families in Longueuil, it's become a necessity.

The reasons are simple: the need for space, comfort and added value to the home.

Save space without moving

Most homes built in the 60s, 70s and 80s in Longueuil have no garage, or just a small carport.

But needs have changed. Today, many families have two vehicles. Then there are bikes, gardening tools, lawnmowers, snowblowers, field hockey equipment, skis, kayaks... All these things take up space.

A 20' x 20' (approx. 400 sq. ft.) attached garage is the perfect space for parking one or two vehicles and storing everything else in an organized fashion. No need to leave bikes lying around in the yard or stack boxes in the basement.

And with Quebec winters, having a heated (or at least insulated) garage is a real comfort. You get into your car straight from home, without freezing your hands scraping the windows. Car batteries last longer. You can do odd jobs even in January.

Impact on resale value

A well-built, standard-compliant attached garage can increase the value of your home by 5 % to 10 %, depending on size, quality, and neighborhood.

In a market where the average price of a house in Longueuil is around 550,000 $ to 650,000 $, this represents between 27,500 $ and 65,000 $ of added value. Even if the garage costs 50,000 $ to build, you'll recoup a good portion of your investment on resale.

And it makes your home more attractive to buyers. Of two similar homes in the same neighborhood, the one with the attached garage often sells faster and for a better price.

With real estate prices in Montérégie up 9.1 % last year, anything that enhances the appeal and functionality of a home becomes a major asset.

Is it legal to build an attached garage in Longueuil?

Yes, it's legal. But there are strict rules to follow.

Many homeowners think they can just build a garage on their land without asking permission. Big mistake. In Longueuil, as elsewhere in Quebec, any addition to a house requires a building permit.

Building permits required

To build an attached garage in Longueuil, you must obtain a building permit from the city.

By-law VL-2025-839 governs all accessory constructions, including garages. You must submit a complete file with plans, certificate of location and all required technical documents.

It generally takes between 20 and 40 working days to obtain a permit in Longueuil, depending on the complexity of the project and the workload of the Urban Planning Department. Sometimes it's faster, sometimes it takes longer if the file is incomplete or if your lot has special features.

You can submit your application online via the Ville de Longueuil portal, or in person at the urban planning counter. We always recommend a pre-consultation before submitting the official file, to make sure everything is in order.

If you build without a permit, you risk a fine of 1,000 $ to 5,000 $, and the City can force you to demolish the garage or bring it up to standard. It can be very expensive in the end.

Zoning rules to be respected

Zoning is what determines where and how you can build on your land.

In Longueuil, each lot is subject to setback rules (minimum distance between the construction and the lot limits). For an attached garage, the typical rules are :

• Lateral setback : minimum 1 m from the side lot line. In some areas, it's 1.5 metres.
• Front setback : minimum 6 metres from the street line. If your main house is already closer, the garage must be aligned or set back from the house.
• Floor area : the total surface area of all constructions (house + garage + other buildings) must not exceed a certain percentage of the lot. In Longueuil, this is generally 40 % to 50 %, depending on the zoning.
• Maximum height : An attached garage can generally not exceed the height of the main house, and often there is a limit of 4 to 5 meters.

Rules vary by area. In Vieux-Longueuil, lots are often smaller and rules stricter. In Saint-Hubert and newer areas, lots are larger and setbacks more generous.

Before you start drawing plans, check your lot's zoning with Infolot (the city's online tool) or call the Urban Planning Department directly. That way you can avoid wasting time and money on a project that could be rejected.

Want to be sure your project complies with zoning? Request a free verification with Cartago Construction.

Documents required before filing

To obtain a building permit for an attached garage, you must provide several documents:

• Site plan : a plan showing the exact location of the garage on the lot, with distances to the lot lines. This plan must be prepared by a land surveyor or architectural technologist.
• Certificate of location : an official document that confirms the dimensions of the lot, the location of the existing house, and any easements or constraints. If your certificate is more than 10 years old, you'll need to have it updated.
• Architectural plans : garage plans (foundations, structure, elevations, construction details). These plans must be signed by a professional if the garage exceeds certain dimensions or if the project is complex.
• Specifications: a detailed description of the materials used, the construction method, and the standards complied with (Quebec Building Code, RBQ standards).
• Permit application form : completed and signed by the owner.
• Proof of ownership : deed of sale or other official document.

Common errors that cause files to be refused: out-of-date certificate of location, inaccurate site plan, setbacks not respected, ground right-of-way exceeded, missing documents. If your file is refused, you have to start all over again, which adds weeks of delay.

That's why it's best to work with an experienced contractor like Cartago Construction, who knows exactly what the city requires and can prepare a complete file the first time.

Key steps to building an attached garage

Now that we know it's legal and how to get the permit, let's take a look at the concrete construction steps.

Building an attached garage isn't as simple as building a garden shed. The garage must be integrated into the existing structure of the house, and comply with waterproofing, drainage and safety standards. Here's how it's done at Cartago Construction.

Step 1 - Site and foundation analysis

Before digging, the ground must be analyzed.

In Longueuil and throughout the Montérégie region, clay soils are common. Clay is a soil that moves: it swells when it's wet, and contracts when it's dry. This can cause differential settling, cracks in foundations and structural problems.

If your lot has clay soil, you'll need deeper or reinforced foundations. This may add 10 % to the cost of the foundations, but it's essential to avoid problems later on.

We always recommend a geotechnical study before building an attached garage, especially if the land has a slope or if you have doubts about the quality of the soil. It costs between 500 $ and 1,500 $, but it saves you from surprises of 10,000 $ or 20,000 $ later.

You also need to check the drainage. If the garage is built below the house, or if the ground retains water, you're going to have seepage. You need to install a French drain around the garage's foundation, make sure the water runs away from the house, and comply with Building Code standards.

Step 2 - Design and home integration

An attached garage isn't just a building glued to the side of the house. It has to be properly integrated.

This means sharing a wall with the house (or building a party wall if the garage is attached but not fully integrated), ensuring a watertight seal between the garage and the house to prevent moisture and gasoline odors from entering, and complying with firewall standards if the garage is directly connected to the living space.

According to RBQ standards, the wall between the garage and the house must have a fire resistance rating of at least 45 minutes. This means a fire-resistant gypsum wall (type X, 5/8"), well sealed, with no unprotected openings.

The garage must also be adequately ventilated to prevent the build-up of carbon monoxide. If you heat the garage, you'll need a mechanical ventilation system that complies with standards.

The garage roof must be designed to harmonize with the house roof. Ideally, the slope and materials should match so that it looks like a coherent whole, not a haphazard addition.

Traditional garage vs. modular garage

There are two main approaches to building an attached garage: traditional on-site construction, or prefabricated modular garage.

• Traditional garage : built entirely on your site, step by step. More flexible in terms of design, can be totally customized to your needs. But takes longer (4 to 8 weeks, depending on weather and complexity).
• Modular garage : prefabricated in the factory, delivered in sections, and assembled on site in just a few days. This reduces construction times by around 20 %, and sometimes costs too. On the other hand, customization options are more limited.

Both approaches are valid. It depends on your budget, your aesthetic preferences, and your schedule. At Cartago Construction, we can do both, depending on what works best for your project.

Stage 3 - Budget and actual costs in 2025

Let's talk money. It's often the first question we're asked: how much does it cost?

In 2025 in Quebec, the average cost of building an attached garage will be around 240 $ to 300 $ per square foot, all inclusive (excavation, foundations, structure, roof, doors, electricity, finishing).

For a 20' x 20' (400 ft²) single garage, count between 50,000 $ and 70,000 $, depending on finishes and options chosen. If you want a 24' x 24' (576 ft²) double garage, that's 70,000 $ to 90,000 $.

Here is an approximate breakdown of costs:

• Excavation and foundations : 8,000 $ to 12,000 $ (depending on soil quality and depth required)
• Structure (framework, framing, exterior cladding) : 20,000 $ to 30,000 $
• Roofing (shingles, insulation, ventilation) : 5,000 $ to 8,000 $
• Motorized garage door : 1,500 $ to 3,000 $ (depending on size and options)
• Electricity (lighting, sockets, door opener) : 2,000 $ to 4,000 $
• Interior finishes (gypsum, insulation, flooring) : 5,000 $ to 10,000 $ (optional, depending on your needs)
• Permits and professional fees (plans, certificate of location, permits) : 2,000 $ to 4,000 $
• Contingencies (always allow for 10 % of the total budget) : 5,000 $ to 8,000 $

Total: around 50,000 $ to 90,000 $, depending on size and finish.

Costs can vary depending on several factors: access to the lot (if it's hard to get to, it costs more), quality of materials (standard asphalt shingles vs. architectural roofing, vinyl vs. brick siding), level of interior finish (rough vs. finished with gypsum and paint), and complexity of the project (sloping lot, integration into an existing house with complex architecture).

Want to know how much it would cost for your specific plot? Get a free personalized estimate with Cartago Construction.

Stage 4 - Construction and final inspections

Once the permit has been obtained and the budget confirmed, we move on to construction.

At Cartago Construction, we follow a structured process:

• Week 1-2: Excavation and foundations. We dig, pour the concrete footings and install the French drain. If the weather cooperates and there are no complications with the soil, it's done quickly.
• Week 3-4: Structure and framework. We erect the wood frame (or steel if the customer chooses), install the roof structure, and lay the exterior cladding (OSB or plywood).
• Week 5: Roof and windows. We install the roof membrane, shingles and garage door. Windows are installed if the project includes them.
• Week 6: Electricity and insulation. The electrician runs the wires, installs outlets, lighting and the motorized door opener. Walls and ceilings are insulated according to building code standards.
• Week 7-8: Finishing touches. If you're finishing the interior, we install the gypsum, paint, and install the flooring (epoxy, tiles, or other). Make the connections with the house, seal and clean.

Throughout the process, there are municipal inspections. In Longueuil, there are generally three inspections: one after the foundation, one after the framing, and a final one before the certificate of compliance is issued.

If everything is done by the book, inspections go smoothly. That's why it's important to work with an RBQ-certified contractor who knows the standards and doesn't cut corners.

Once all inspections have been completed and the certificate of conformity issued, your garage is officially legal and compliant. You can use it without fear.

Important: remember to inform your insurance company of the addition of the garage. It will affect your premium, but it's mandatory if you want to be properly covered. And if you sell your home at a later date, you'll need to provide a declaration from the seller stating that the garage was built with a permit and is compliant.

Common myths about attached garages (and the reality)

As with any construction project, there are myths out there. Let's get to the bottom of them.

«No need for a permit if it's a small garage».»

False. In Longueuil, all attached garages require a building permit, regardless of size.

Even a 10' x 12' garage, even a carport enclosed on three sides, even an addition to an existing garage... all require a permit.

If you build without a permit, you risk a fine of between 1,000 $ and 5,000 $. And if a municipal inspector comes by (which can happen if a neighbor complains), you'll either have to demolish the garage or bring it up to code and pay retroactive fees, which often cost more than if you'd done things right from the start.

There's also a legal risk on resale: if you sell your home and the buyer discovers that the garage was built without a permit, he can sue you or ask for a price reduction.

In short, it's always worth doing things by the book.

«An attached garage is always more expensive than a detached one».»

Not necessarily. In fact, the opposite is often true.

An attached garage shares a wall with the house, reducing material and labor costs. You also save on excavation and foundations, because you don't need to build four complete walls.

According to industry estimates, an attached garage generally costs 10 % to 20 % less than a detached garage of the same size, because there's less structure to build.

On the other hand, there are integration costs: ensuring watertightness, complying with firewall standards, harmonizing the design with the house. But in most cases, it's still more economical than a detached garage.

And there's a big practical advantage: with an attached garage, you can access your car directly from the house, without having to go outside. In the middle of winter at -20°C, that's worth its weight in gold.

«Petrol fumes still enter the house».»

It's a myth based on old, badly-built constructions.

If the garage is built to current RBQ standards, there's no problem with fumes. The wall between the garage and the house must be perfectly sealed, with a vapour barrier and sealant in all joints. The access door must be a fire door with a watertight threshold.

And you need mechanical ventilation in the garage: either natural ventilation (e.g. louvres) or an extractor fan that exhausts stale air to the outside.

If it's done properly, you'll never smell gasoline or carbon monoxide in the house. We've been building attached garages for decades in Quebec, and it's a problem that's long been solved when it's done right.

FAQ - Building an attached garage in Longueuil

Here are the questions we're most often asked.

What is the average cost of building an attached garage in Longueuil in 2025?

Between 50,000 $ and 90,000 $, depending on size and finish. A 20' x 20' single garage costs around 50,000 $ to 70,000 $. A 24' x 24' double garage with interior finishes can cost up to 90,000 $ or more. Cost per square foot hovers around 240 $ to 300 $.

How long does an attached garage project take, from start to finish?

On average, between 8 and 12 weeks. This includes preparing the permit file (2 to 4 weeks), obtaining the permit (3 to 6 weeks), and the actual construction (4 to 8 weeks, depending on weather and complexity). If you work with an experienced contractor who prepares a complete file from the outset, things can go faster.

Attached or detached garage: which to choose?

It all depends on your priorities. An attached garage generally costs less, offers direct access from the house, and frees up more yard space. A detached garage offers more flexibility in terms of design and location, and eliminates any risk of fumes or noise. If you have a large lot and want a separate workshop, a detached garage may be a better choice. Otherwise, an attached garage is often more practical and economical.

What subsidies are available for building an attached garage?

There are no specific subsidies for garages in 2025, but if you incorporate energy-efficient features (superior insulation, high-performance insulated garage door, LED lighting, electric vehicle charging station), you may be eligible for tax credits or programs like Rénoclimat. Talk to your contractor or contact Transition énergétique Québec to check your eligibility.

Can an electric vehicle charging point be integrated into the garage?

Yes, and it's becoming increasingly common. In fact, now is the perfect time to do it: during construction, the electrician can install the wiring and paneling required for a Level 2 (240 V) charging station. It costs between 500 $ and 1,500 $ more during construction, whereas adding it after the fact can cost 2,000 $ to 3,000 $ because you have to open up the walls. Make sure your main electrical panel has sufficient capacity, otherwise it will need to be upgraded.

Will my home insurance increase if I add an attached garage?

Yes, probably a little, because the insurable value of your property increases. But it's not a big increase, and it's worth it for the protection you get. Call your insurer before you start the project to confirm that you'll be well covered during and after construction. Some insurers even offer discounts if the garage improves security (for example, if you store your car inside rather than outside).

Why entrust your attached garage to Cartago Construction?

Building an attached garage is a project that requires expertise, experience and rigor.

Cartago Construction has built dozens of attached garages in Longueuil, Saint-Hubert, Vieux-Longueuil, and all over the South Shore. We're familiar with municipal bylaws, RBQ standards and the particularities of Montérégie land.

Local expertise in residential construction

Yassine Troudi, founder of Cartago Construction, has over 10 years' experience in residential construction in Quebec.

We know exactly what the Ville de Longueuil requires for a garage permit. We know about setbacks, ground clearance rules, firewall standards and waterproofing requirements. We've already prepared dozens of permit files, and we know how to get a file through the first time.

We also know the soils of the Montérégie region. We know where clay is a problem, where foundations need to be strengthened, and where drainage needs particular attention. We work with trusted geotechnicians and land surveyors, and make sure that everything is done by the book.

And we're RBQ certified, insured, and up to date with all Quebec Building Code standards. You have the peace of mind of knowing that your project is in good hands.

A turnkey approach with no surprises

At Cartago Construction, we take care of everything.

We start with a free consultation to assess your property, understand your needs, and give you a realistic estimate. We don't make unrealistic promises. We tell you exactly how much it will cost, how long it will take, and what the potential challenges are.

Then we prepare all the documents required for the permit: site plan, architectural plans, specifications. We submit the file to the city and follow the process until the permit is granted.

During construction, we coordinate all subcontractors: excavation, concrete, framing, roofing, electrical and finishing. You have a single point of contact, and we keep you informed every step of the way.

We stay on schedule and on budget. If something unexpected comes up (for example, a soil problem discovered during excavation), we tell you about it right away, explain the options, and work out a solution together. No hidden costs, no unpleasant surprises.

And we're available even after the project is finished. If you have any questions, if you want to make any adjustments, we're here to help.

Ready to add an attached garage to your home? Schedule your free consultation with Cartago Construction today.

Building an attached garage in Longueuil is an excellent investment. It adds space, comfort and value to your home.

But you have to do it right: obtain permits, respect zoning rules, follow construction standards, and work with professionals who know the trade.

At Cartago Construction, we have the expertise, experience and resources to take your project from start to finish, without stress or surprises.

Contact us to discuss your project. Call us at 438-932-4326 or write to [email protected]. Our office is located at 2580 Rue Cartier, Longueuil.

Your attached garage is our next project.