Flat Roof Extension

Flat roof home extensions are increasingly popular among homeowners in Montreal and across Quebec. Whether you’re looking to increase your living space, add a bright new room, or create an outdoor living area with a rooftop extension, this type of project offers numerous benefits.

At Les Couvreurs Duro-Toit, we are flat roofing experts and support you through every stage of your extension project, from design to completion.

Why choose a flat roof extension?

A roof extension offers a clean, contemporary, and elegant look. This type of construction is often chosen for:

Its modern design that blends seamlessly with existing homes.
Its versatility (additional bedroom, bathroom, living room, office, etc.).
The possibility of using the roof as a terrace or green roof.
Faster execution compared to a pitched roof extension.

An addition that preserves architectural harmony

One of the key advantages of a house extension is its ability to harmonize with the existing structure. By choosing modern materials like wood, metal, or aluminum, it’s possible to create an extension that is both aesthetic and functional.

Whether your home is old or new, a flat roof provides architectural consistency with a contemporary touch.

What types of flat roof extensions are possible?

1. Side extension

A very popular option, a side extension adds one or more rooms on the same level as the main house. It’s ideal for lots with enough surrounding space.

2. Vertical extension with a flat roof

If your land is limited or you want to preserve your yard, a flat roof vertical extension is a smart alternative. It allows you to add a floor without sacrificing your outdoor space, while giving the building a modern style.

3. L-shaped or cube-shaped extension

Adding an L-shaped or cube-shaped volume at the rear or side of the home is a common solution to maximize space while maintaining privacy. With a flat roof, the structure remains lightweight and easy to integrate.

Rooftop terrace extension

A rooftop terrace extension doesn’t just increase your living area—it transforms your roof into a true living space.

By installing non-slip surfacing and securing access, you can create a relaxation zone, a green terrace, or even an urban vegetable garden. It’s also a great way to boost your property’s value.

Ideas for a rooftop terrace layout:

Lounge terrace with outdoor furniture
Urban garden with aromatic plants
Spa area with jacuzzi
Dining or BBQ corner

How much does a flat roof extension cost?

Extending your home involves varying costs depending on several factors. The price will depend on:

The additional surface area
The materials used
Interior and exterior finishes
The type of extension (inaccessible flat roof, rooftop terrace, green roof)

Generally, the total cost of a home extension starts around $70,000, but most projects range between $100,000 and $250,000.

For a rooftop terrace, expect to invest between $15,000 and $30,000, excluding furnishing and finishes (furniture, surfacing, etc.). Material choices—like treated wood or fiberglass—also impact the final price.

Don’t forget to factor in permit fees, which vary depending on the scope and nature of the project.

Why entrust your project to Les Couvreurs DuRoToit?

Choosing Les Couvreurs DuRoToit means working with a company specializing in flat roofing for over 20 years in Montreal. We understand the technical, aesthetic, and climate-related challenges of every flat roof extension project.

Our guarantees: