Estimate the cost of an extension

For the same floor surface, the building cost of a home extension is much higher in renovation than in new constructions. In renovation, the cost of the construction works per square foot is usually double and sometimes triple the cost of new constructions, because the quantities are smaller so there is less economy of scale. Also, many related works on the existing building must be made. Here are various standard additions and a summary assessment of the related costs.

Basic costs and supplements

Whether it is for a lateral extension, the addition of a floor or to dig a basement, it is necessary to distinguish the basic costs from the supplements. Basic costs are defined for rooms without fixed furniture or without specialized equipment such as kitchen cabinets, fireplaces, staircases, radiant heating, sanitary equipment or abundant windows. All of these supplements will be added to the basic costs.

Adding a lateral extension

The cost of a lateral extension depends of its size, its number of floors, the addition of a basement, the function for this extension, the fenestration and the exterior cladding.

A single floor extension with no basement and about 150 square feet (14 square meters) in size will cost a minimum of $ 315 per square foot of floor space. If we double the size of this extension to 300 square feet, its total cost will not double because it will benefit from an economy of scale and its cost can drop to $ 285 per square foot.

In the case where this extension of 150 square feet would include a complete basement with its interior finish, a decrease of approximately $ 30 per square foot for the complete project can be expected, if it does not include a bathroom.

Adding a floor to an existing house

The addition of a floor is much more complex to achieve than a lateral extension. This involves the demolition of the roof, the addition of an internal staircase, the reinforcement of the structure, the partial restoration of the exterior cladding and sometimes the replacement of the existing floor windows for the arrangement of the ground floor to the new floor.

Some buildings are very suitable for a partial or complete floor addition, but others are much more difficult. For a 600 square foot addition, a base cost would be of $ 250 per square foot for the construction plus a minimum of $ 65 per square foot for the related work for the modifications of the existing building.

Adding a basement

In general, digging a basement to add a bedroom or a living space is very expensive and not really profitable. However, if the foundations have to be redone because they are in bad conditions, digging the basement to create new rooms or even a small housing can be a way to make this necessary work profitable.

In this case, the accessibility around the building is decisive for the excavation costs, which, on their own, can range from $ 30 to $ 60 per square foot.

To add value to the building after the renovation, it is often best to have the building raised to increase the size of the basement windows, to meet the building code safety requirements and to reduce the risk of flooding.

An appropriate design for a good investment

For an extension to be a good investment, the overall design must be pleasing to the eye with a functional layout and all, at an optimal cost.

This requires a good initial planning and execution of work, good experience in cost management and a collaborative approach of the design between the owners and the designers.

We offer you our experienced service of design, estimation and planning for the realization of all your projects in the Montreal area. Contact-us for more information on our house and bungalow expansion services.