Adding a Second Story to a House

Running out of space but don’t want to leave your neighbourhood or sacrifice your backyard?
Adding a second story to your home is a smart alternative to moving or building outwards. Whether you want extra bedrooms, a home office, a new bathroom, or a bright living area, this type of project offers plenty of advantages.

However, second storey home additions require careful planning, compliance with building codes, and of course, an appropriate budget.

This guide walks you through the steps, benefits, and average costs of a 2nd floor addition in Quebec.

Why consider adding a second story to your home?

Adding a second floor to a house isn’t just about gaining space—it’s a strategic move to improve comfort, increase real estate value, and future-proof your home.

Gain more space without losing yard area

Unlike horizontal home extensions, adding a second story allows you to increase livable space without reducing your backyard or altering the home’s footprint.

This vertical solution is ideal in urban or densely populated areas where every square foot counts. You preserve outdoor space and natural light, while expanding your interior.

Boost your home’s resale value

A 2nd floor addition significantly enhances your home’s resale potential. By creating new bedrooms, another bathroom, or an upstairs living area, you add square footage—often leading to a higher resale price.

Many buyers are ready to pay more for a home already tailored to a modern family’s needs, with a well-designed second floor.

Adapt to changing family or work needs

Family needs evolve. A new baby, a teen needing privacy, or the need for a dedicated home office are common reasons to reconfigure living space.

Adding a second story lets you rethink the layout without disrupting the home’s balance. This flexible solution adapts to your lifestyle, now and in the future.

Second storey home additions: project types

Before you begin, it’s key to understand the different options for adding a second floor to your house.

Full second story

This involves building a full additional floor across the entire house. It’s the most common and comprehensive type of project. You can double your living space, add multiple rooms, and entirely redesign your home layout.

This usually means removing the existing roof, reinforcing foundations and load-bearing walls, and redoing the façade. It’s a major investment, but a transformative one.

Mezzanine or partial second floor

If your ceiling height or internal structure allows, you can build a mezzanine or partial second floor. This is great for expanding an existing room with a raised platform, often open to the floor below—ideal for a home office, guest room, or reading nook.

Less expensive than a full story, it still requires a detailed structural analysis to ensure safety and stability.

Converting a flat or low-pitch roof

Homes with flat or low-slope roofs often have underused potential. You can build an entirely new level without changing the ground footprint.

This may require raising perimeter walls or adjusting the roof structure, but it allows a seamless integration of a new story into the home’s architecture.

Roof replacement or modification

In some cases, adding a second floor involves removing and rebuilding the entire roof to accommodate the new volume. This is common when the existing pitch is too low or the attic is unusable.

You might install a reverse-slope roof, a dormer, or even a mansard roof depending on your style preferences. Careful planning is essential to address insulation, waterproofing, and visual harmony.

Steps to successfully add a second floor

A 2nd floor addition is an ambitious project requiring organization, precision, and professional support. Here are the key steps to follow:

Check municipal zoning and regulations

First, confirm that second storey home additions are permitted in your area. Every municipality has rules about maximum height, setbacks, architectural style, and lot coverage. Visit your local planning department to ensure your project is feasible.

Check also for requirements related to neighbourhood harmony, heritage restrictions, and building distances.

Assess your home’s existing structure

Once zoning is confirmed, have a structural assessment done. An engineer or building technologist will evaluate whether the foundation and walls can bear the added weight.

If the current structure isn’t strong enough, reinforcements or upgrades will be required—critical for ensuring safety and preventing cracks or settling.

Work with an architect or engineer to design plans

You’ll need technical blueprints showing layout, structure, materials, openings, stairs, interior design, and external appearance. The architect ensures aesthetic integration with your existing home.

A structural engineer may be needed to confirm the building’s strength. These plans are required to obtain your building permit.

Apply for a building permit

With your plans ready, submit a permit application to your municipality. Without it, work cannot legally begin.

Processing times vary by location, project complexity, and time of year. A complete, well-prepared application speeds up approval.

Choose a qualified contractor

Hiring a reputable residential contractor is crucial. Look for companies with experience in home extensions and second story builds, and check their references.

Experience with high-level construction, structural load management, and major renovations is key. Compare quotes, verify RBQ licenses and insurance coverage to make a safe choice.

Ensure proper project oversight

Once construction starts, make sure each phase follows the approved plans, inspections are completed on time, and deadlines are met.

Maintain clear communication with the contractor, subcontractors, and professionals involved. You may assign a project manager or have the architect supervise for peace of mind.

Technical and regulatory constraints

Although adding a second floor is appealing, it comes with technical and regulatory challenges that must be addressed early to avoid surprises and extra costs.

Load-bearing capacity of your current structure

Adding 2nd floor to house places significant weight on your existing structure. Foundations, load-bearing walls, and framing must support this new load.

Often, an engineer’s assessment is required. If reinforcements are needed, they can increase costs and timelines.

Modifications to the existing roof

This project usually involves major changes to your roof. In most cases, the original roof must be removed and replaced with a new, properly designed one.

Costs can rise depending on roofing materials, attic configuration, or complex architectural details. Don’t overlook insulation, waterproofing, ventilation, and drainage—all need to be redesigned.

Temporary relocation during construction

Depending on the work involved, you may need to temporarily vacate your home. If the roof is being removed, structures opened, or plumbing and electrical systems modified, staying inside may be unsafe.

Budget for temporary housing if needed. This also allows contractors to work faster and more efficiently.

How much does a second storey home addition cost?

Cost is a major factor for any homeowner considering a second floor addition. It’s a major investment influenced by technical and design choices.

In Quebec, the average cost ranges from $250 to $400 per square foot. This typically includes roof demolition, new construction, electrical, plumbing, and basic finishing. High-end features like luxury bathrooms will increase the price.

Project Type	Estimated Cost
Full second story addition	Over $200,000 (several bedrooms + bathroom)
Mezzanine or partial second floor	Around $100,000 (minimal structural work)
Roof conversion or raising	Mid-range, depending on scope of work