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The Cost of a Home Addition Project

Last modified: 2022-10-14 | Approximate reading time 5 mins

Léa Plourde-Archer

When your home becomes too small due to the arrival of a new family member, or because the house just doesn’t suit your needs anymore, know that instead of moving, another solution is available: building a home addition!

What are the elements that need to be taken into consideration when constructing a home addition? What is the price of a home extension? When should you expand and when should you move? answers a few questions that often emerge in the process:

Building a home addition, what do you need to know?

Before taking on any sizeable home extension project, several elements need to be taken into consideration when designing the plan. However, even before making any specific plans, it is important to know about the specific zoning laws and restrictions in your area. Don’t hesitate to ask your municipal authorities about the requirements and conditions for building on your land (square meters upon which you can build).

Next, you will have to evaluate the following elements: the structure and the framework; the current architecture; the architectural style that you wish to choose for the home extension; the size of the expansion; access to the land where you will build; the difficulty level of the work to build a home addition; the materials used for the finishing.

Here are the 5 key points to remember:

  • Find out about zoning regulations;
  • Evaluate the structure and the frame of your house;
  • Determine the architecture style and dimensions of the extension;
  • Determine the complexity of the work;
  • Choose the materials.

The costs of a home addition project

A house extension comes at a price. This price varies depending on how exactly the home will be expanded, as well as the complexity of the work to be done. The costs relating to this type of project can be quite elevated; in general, they are two to three times higher than those of a new construction.

That is why it is important to know when to expand and when to move. Don’t hesitate to ask for price estimates to get an idea of the costs associated with your project. According to architect Guy Demers building an annex for a house at less than $48 000 is practically impossible. The labour costs and the heavy machinery will eat up a large part of the budget. Adding a floor to a bungalow will bring the bill up to more than $120 000. It cannot be less than that; we remove the roof, demolish the walls, etc.”

Home addition

Photo: Flickr DesignMilk-

Different types of home extension projects and their costs

Lateral expansion:

A lateral expansion consists in making your house bigger by building directly on one of the exterior façades. “A one-floor expansion with an unfinished, 120 square foot standard quality basement, will cost at least 480$ per square foot of floor surface, explains Yves Perrier, an independent consultant in the field of construction and home renovations. However, this same expansion project for a surface of 300 square feet will cost around $360 per square foot, as the cost per square foot diminishes when the size of the surface increases.”

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Adding a floor:

The costs involved in building a whole new floor on a house can vary depending on the difficulty of the work to be done and the transformations that will affect the house’s façade, structure and mechanical systems. According to M. Perrier, one must “plan at least $200 per square foot, plus a minimum of $12 000 for related work pertaining to modifications on the existing building.”

Digging out your basement

Digging can be an interesting option if your house is fairly old and, for example, your foundations show weaknesses and are not solid enough to support an extra floor. For consultant Yves Perrier excavation is a costly process. It can amount to approximately $30 to $60 per square foot, depending on the size, the desired depth, the type of ground and ease of access to the basement for the machinery. This generally includes cement foundations. Then, you must add the costs for finishing and setting up the basement.”

Adding a room that is supported on spikes:

This type of extension is ideal for zones where the ground is unstable (without being rocky or loamy), risks being flooded or is characterized by a steep incline.

However, its installation requires several caution warnings. First, the floor is harder to insulate than with traditional construction and extra precautions must be taken to ensure that the structure is airtight. Next, any movement in the ground can cause the spikes to move around if the installation is not done properly.

If you are still interested in using this technique, know that it will cost around 160$ to 185$/square foot, excluding fees relating to the installation of a bathroom.

extension maison

Good vs. Bad Home Addition Projects

As you will have understood from reading the previous paragraphs, expanding your home is not always the most economically friendly option to gain space. Below are examples of home addition projects that are cost-effective and others that are not usually worth the investment (source: La Presse (article in French).

Favourable expansions

  • On top of a garage: if your structure is solid enough to support an extra floor, the added space can be advantageous.
  • From behind the house: when the municipal laws allow you to do so, it is possible to gain considerable space for your home’s surface area by encroaching on the backyard. Ideally, this expansion is done on the full length of the house.
  • As a bump-out or cantilever addition: this technique consists of adding up to four feet to a room and requires no excavation. This type of expansion is completed like the addition of a backyard deck.

Unfavourable expansions

  • Transforming a bungalow into a cottage: the cost for removing a roof makes it not worthwhile. Unless you want to keep the current location of your house, it is best to move elsewhere.
  • Adding a room to an apartment: in the city, most apartments are rectangular-shaped. Building a new room often means blocking sunlight.
  • An addition that interferes with the look of the house: the original architecture must be taken into consideration. Home extensions that do not respect the building’s original style will not do it justice.

To help you plan out your home extension project, check out this article: House addition project: what you need to know

To find out about the average prices of different home renovation projects, check out our Home renovation price guide. 

Get 3 renovation quotes for your home addition project can help you get quotes for. By submitting your home addition project to us, we’ll put you in contact with top-rated contractors. Fill in the form on the homepage (it only takes a few minutes), and you will get estimates from trusted professionals.

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