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House Extension Project: What You Need to Know

Last modified: 2018/03/21 | 4 mins

As time passes, the same house that you bought a few years ago can become too small to fill your needs. While some people choose to move out, others prefer to extend their property. This article explains what you need to know about building a house extension: 

Planning a house extension project:

Adding an extension to your house is a great way to add more space to your property. There are many different ways to create a house extension but most people tend to add extra living space above the garage or at the back of the building. Whatever  you decide, it all depends on what you're looking to achieve. In some cases, preexisting spaces such as a porch can be converted into a house extension.

This type of renovation project is quite major and involves a lot of planning. Before anything else, try to identify your needs. Why do you want to extend your house? Is it because you need new rooms or because you don’t have enough space in the kitchen? Knowing what you want is the most important part of the planning process.

Next, think about how much money you want to invest in this project. Setting a fixed budget will help you find ways to finance your renovations and prevent you from a experiencing a financial crisis. Usually, this type of renovation project costs at least $40 000.

Once you're past the first step, contact an architect or an engineer who will create the plans for your house extension project. You’ll be able to talk about your project with them and see if your ideas are feasible. If not the case, they will give their own point of view and help you find the best alternatives.

The third step is to contact your municipality to obtain a construction permit. Based on the drawings made by the architect or the engineer, they will decide if you can go on with your project and if so, will give out the construction permit. Generally, municipal staff do not accept house extensions that are added to the front of a building. You’ll probably have to create an extension from the sides or from the back.

Another option is to add a new floor. However, this way off adding space will be more expensive since you’ll have to remove the roof and knock down a few walls. Make sure you plan enough space on the first floor for the staircase that will lead to the new floor.

Last but not least, look for a qualified contractor who has knowledge and expertise about the general structure of a house. Meet different contractors and ask them to give you quotes.

An estimate of the costs of a home extension project

  • Installing an interior wall with door opening : $500 - $1000 +
  • Turning a roof into a floor : $125- $250 / sq.ft.
  • Extra floors: $100-$200/sq.ft.
  • Installing collar beams: $30-$50+ each
  • Installing lateral bracing on collar beams : $100 - $200 +
  • Replacing a cover support: $4 - $6/sq.ft.
  • Adding an extra floor: $100 000
  • Adding a floor over a garage: $50 000
  • Adding a room over a ground floor: $60 000
  • Cantilever expansion: $25 000

Building a home extension involves complicated financial calculations. This processus includes fixed fees, which means that a smaller expansion can have a higher price per square foot than a big one. However, the fewer square feet, the lower the full cost of the expansion will be due to the cost of materials. 

Yet, when all is said and done, what is the cost of an extension when compared to the fact of living in a neighborhood that you like and that has a lot of advantages, instead of having to move to a new house due to lack of space. 

Extension de maison

Photo: Fotolia

The different ways to expand your home

It should be noted that in general, municipalities do not allow the building of an extension in the front part of the house. It is best to envision an extension from the side or the back. Adding space towards the top is also an option. If the work touching on the structure is expensive, adding one or several floors is even more expensive. This type of expansion implies removing the roof, demolishing the walls and planning space for a staircase leading to this floor. 

It is often easier to build a home addition over a garage. Depending on your needs and on the municipal rules that are currently in effect, you can increase the size of your home by taking over the backyard. Why not transform your back porch into a sunroom?

This glass-enclosed space will allow you to enjoy your backyard during the cold season, whilst adding more space to your kitchen or living room. Ideally, the extension will be done over the whole length of the house without affecting the architecture. 

There are several other types of home additions: adding a basement, building a garage, building an extension on foundations, home addition on stakes and home addition on a concrete slab.

For more information about home extensions, check out the following articles:

The cost of a home addition project

The average costs to build a home addition

Get 3 renovation quotes for your house extension project can help you get quotes for your house extension project. If you submit your project to us, we’ll put you in contact with contractors that are the most suitable for you. Fill in the form on the homepage ( it only takes a few minutes), and you will receive quotes from companies that are specialized in house extension projects.


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