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Second Storey House Addition Cost

Etobicoke House Addition Before and After | Etobicoke, Toronto, ON | Inspire Homes

In one of our first blog posts, we wrote about the 7 Things That Affect House Addition Cost. To summarize, the key considerations in determining the cost of a house addition project were:

1. Size – Larger additions are obviously more expensive, but cost less per square foot

2. Purpose – a kitchen addition will be more expensive than a bedroom addition

3. Complexity of Design – complex roof lines, vaulted ceilings and other architectural features add to the cost of a home addition project.

4. Quality of Finishes – hardwood costs more than carpet, stone costs more than brick etc.

5. Site Conditions – a house addition on a narrow property in Toronto will cost more to build on than a project on a large suburban lot in Etobicoke or Mississauga.

6. The Rest of the House – what else do you want to renovate while you’re building the addition?

7) Other – how is the addition connected to the house, do you need a larger furnace, upgraded electrical panel, etc.


With a second storey house addition, there are specific costs that are not found with other house addition projects:

1. Demolition – Our process is to remove the roof and the ceiling of the home, along with the attic insulation, and any electrical wiring that may be running through the ceiling. With a second storey addition, bedrooms are being moved to the upper floor, so demolition usually includes removing walls and existing finishes on the main floor.

2. Structural Considerations – A common request is to create an open concept main floor, which means the house will not have any load bearing wall in the middle of the house. We achieve this through the use of clear span floor joists, which are supported only by the outside walls. These are often 14 inches or 16 inches deep, twice as deep as a standard floor joist.

3. Heating system – Most older homes have mid-efficiency furnaces that are vented through the chimney. Extending a chimney through the new roof is costly, and generally unnecessary. It is usually less expensive to replace the furnace with a high efficiency model which can be vented through a pipe in the wall. Same goes for the hot water tank. On the other hand, if you want to keep that wood burning stove you have in the basement, add in the cost of extending the chimney.

4. Exterior – Most older homes are made of brick, often a brick that is difficult to match. The least expensive option is to install siding or stucco on the new second floor. But the old brick on the bottom, new stucco on the top is not a look that most homeowners want for their home, so redoing the existing exterior of the main floor is often part of the project – sometimes just the front wall, sometimes the entire house.

5. Main Floor Renovations – A second floor addition without a main floor renovation is rare. Most second storey additions we have worked on have involved a complete tear out and rebuild of the main floor – including all new insulation, plumbing, electrical, drywall, and interior finishes.

So when we’re asked to give cost per square foot for a second storey house addition project in Toronto, we need to have a full understanding of the extent of the project before discussing costs. The cost of building the second storey addition is often only half the cost, with the other half of the cost being main floor renovations, exterior façade improvements, and mechanical improvements to the home.