Home extension: complete guide

Expanding your home is an increasingly popular solution among homeowners looking to gain more space without moving. Whether it’s to create an extra room, add a floor, or install a bright extension, the possibilities are numerous and adapt to all types of buildings, including traditional houses.

But before getting started, you need to understand the various expansion options, the steps involved, and the cost of extending your home.

This comprehensive guide presents the types of home extensions, their benefits, and the average prices for expanding a house based on the work involved.

Why expand your home?

When needs evolve — the birth of a child, remote work, limited living space — the question arises: should you move or expand your home? In many cases, expansion proves to be the more advantageous solution, economically, emotionally, and practically.

Clear financial benefits

Moving often involves significant expenses that shouldn’t be underestimated. Notary fees, real estate commissions, transfer taxes, moving costs, setting up a new home, and the time spent searching and visiting all add up quickly — not to mention the stress.

On the other hand, extending a home or adding an extension allows you to keep your living environment while managing your budget more effectively. You can plan the work according to your financial capacity, avoid the costs of buying a new property, and spread out expenses over time. It’s a more flexible, often more profitable, long-term solution.

A real increase in property value

Investing in a home extension usually boosts the resale value of the property. A larger, more functional, and modernized house sells more easily and at a better price.

A well-designed home extension adds tangible square footage, a key factor in the real estate market.

What are the main options for home extension?

Depending on your lot configuration, needs, and budget, several home extension options are available. Here are the main ways to expand your home.

1. Side extension (on the ground)

A side extension is ideal for properties with ample yard space. It extends the main floor naturally, allowing for a seamless flow between existing rooms and the new construction. This option is perfect for adding a larger kitchen, a family room, or an extra bedroom.

However, it requires freeing up outdoor space, which can impact landscaping and reduce backyard area. You’ll also need to comply with municipal setback regulations. Finally, full foundation work is required, which can increase both the duration and cost of the project.

Average cost:
$250 to $400/sq. ft.
Or $60,000 to $160,000 for a 400 sq. ft. extension

2. Vertical expansion (adding a floor)

Adding a floor offers several advantages. It significantly increases living space without encroaching on the lot — ideal for urban settings or narrow lots. It’s a great solution for expanding while preserving outdoor space. New bedrooms, a bathroom, an office, or even a secondary suite can be created.

That said, it often requires reinforcing the existing structure and foundations to support the added load. The work is complex and longer due to the partial demolition and reconstruction of the roof. Careful planning and professional guidance are essential.

Average cost:
$300 to $500/sq. ft.
Or $120,000 to $200,000 for a 400 sq. ft. extension

3. Attic or loft conversion

Converting your attic or loft is a great way to maximize space without changing the exterior structure. This option is ideal for bungalows with high rooflines. The space can be used for a bedroom, office, or lounge area, accessible via stairs. Dormer windows or skylights can add natural light, and a roof hatch can even allow for a small balcony.

Check the available headroom under the roof peak to ensure livability. This project requires careful planning, but many resources are available to guide you through every step.

Average cost:
$120 to $160/sq. ft.
Or $60,000 to $80,000 for around 500 sq. ft.

4. Sunroom or glass extension

Sunrooms and glass extensions are popular for their exceptional brightness. With large window surfaces, they flood the interior with natural light while offering a pleasant view of the garden. They create a soft transition between indoor and outdoor living, ideal for a relaxing space or dining area. Another key benefit: they’re often cheaper than traditional extensions, making them attractive for tighter budgets.

However, proper insulation is crucial for year-round comfort. Without thermal protection, the space may become too cold in winter or overheated in summer. It’s also less suitable for technical rooms like bedrooms or bathrooms due to privacy and plumbing needs.

Average cost:
$200 to $350/sq. ft.
Or $40,000 to $140,000 for a 400 sq. ft. sunroom

5. Converted or raised garage

Converting an integrated garage into living space is a clever way to gain square footage without altering the home’s footprint. You can create an office, playroom, or guest space. Another option is to build a roof extension above the garage to add a bedroom or master suite. These projects are generally quicker than traditional extensions and more budget-friendly.

However, garage conversions often require upgrades to insulation, ventilation, and interior access. For raised garages, a structural assessment is necessary to confirm load-bearing capacity.

Average cost:
Garage conversion: $175 to $275/sq. ft.
Above garage addition: $275 to $450/sq. ft.
Or around $30,000 to $110,000 depending on the project and size

What’s the cost of expanding a house?

The cost varies depending on project type, materials, and complexity.

Type of Expansion	Average Cost per Sq. Ft.	Total Price Range
Side extension	$250 to $400	$50,000 to $200,000
Floor addition	$300 to $500	$100,000 to $250,000
Sunroom or solarium	$200 to $350	$30,000 to $80,000
Above garage addition	$275 to $450	$50,000 to $150,000
Garage conversion	$175 to $275	$20,000 to $60,000
Basement or under-structure	$300 to $600	$75,000 to $200,000

These are estimates and may vary by region, contractor, and project requirements.

What steps should you take before starting a home extension?

A home expansion project requires planning. Before hiring a renovation contractor, certain administrative and technical steps are essential to ensure feasibility and compliance. Here are the main steps to take.

Building permits and municipal regulations

First, consult your municipality to verify:

• Zoning regulations (minimum lot size, maximum height, setbacks)
• Architectural restrictions (materials, colors, style)
• New structure standards (distance from neighbors, easements, etc.)

Once the project is defined, a building permit is required. It is typically issued after reviewing plans, the application form, and sometimes an impact study.

Failure to comply may lead to work stoppages, fines, or even demolition orders.

Soil study and feasibility

A soil study is highly recommended, especially if:

• New foundations are needed
• The lot is sloped or in a flood zone
• The soil composition is uncertain (clay, fill, rock, etc.)

This analysis helps confirm soil stability, excavation needs, and the right foundation techniques — limiting long-term risks like settling or cracking.

Plans and professional guidance

Creating compliant and tailored plans is crucial. Two options are available:

• Hire an architect or architectural technologist: Ideal for complex or heritage projects. Architects design custom, functional, and aesthetic expansions. In some areas, their involvement is mandatory.
• Work with a specialized extension company: Some offer turnkey services including plans, permits, and construction — simplifying coordination and saving time. Plans can also be adjusted during the project as needed.

In all cases, professional support is key to ensuring the project meets building standards, stays within budget, and truly adds value.

How to choose the right contractor for your extension?

Choosing the right contractor is critical. A skilled professional ensures a code-compliant, well-managed project that stays on time and on budget. Here’s what to look for.

Licensing, insurance, and experience

• Valid RBQ license (Québec’s building authority)
• Liability insurance
• References for similar projects (extensions, floor additions, garage work)
• Customer reviews and past work
• Ability to explain technical choices and handle unexpected issues

Quotes and comparisons

• Detailed list of included work (foundations, roofing, insulation, etc.)
• Total estimated cost with breakdown
• Timelines for each project stage

What to compare in quotes

• Clear estimates (avoid vague offers)
• Balanced pricing (neither suspiciously low nor unjustified)
• Payment terms
• Provided warranties

Project management and warranties

• Structured work calendar with checkpoints
• Regular site visits
• Presence of a supervisor or project manager
• Labor and material warranties

Trust a professional for your home extension

By choosing Duro-Toit, you’re partnering with an experienced company for all your projects — from waterproofing your roof to expanding your home. Our team supports you every step of the way with durable solutions tailored to your needs and compliant with building standards.

As recognized roofing specialists, we bring our expertise to your home extensions, ensuring seamless integration of your new roof. Entrust us with your project for reliable, aesthetic results without compromising on quality.