Q & A: Can We Build A 3rd Floor On Our Existing Home?

Q & A: You Ask. We Answer.


This month we answer a question from a homeowner in North York "Can we build a 3rd floor on our existing home?"

Two key things with a 3rd storey addition are structure and zoning.



The City of Toronto regulates the location and size of a building on a property.

All properties have regulations regarding setback from the front, rear and side property lines.

Many properties have a maximum square footage as a percentage of property size.

And the rule that most greatly impacts a third storey addition is the maximum height of building. This is the overall height from the ground to the peak of the roof.

While the City of Toronto allow a third floor home addition, design may be limited by height restrictions and other regulations that limit the design of the roof.

So how can you check zoning? You can visit the local city building department office, or check online at toronto.ca/zoning. You may also consider hiring a design professional to research zoning regulations.



The second key consideration is the integrity of the existing structure.

Is it strong enough to support a 3rd floor? Is the foundation strong enough to support a 3rd floor? Are the walls able to support an additional floor?

These are questions that are best answered by a professional engineer.   An engineer will assess the structure, and determine if the existing structure will support a 3rd floor.  Often it will, sometimes it doesn't.


What if there are issues with zoning or structure?


You may be able to successfully apply to the committee of adjustment for a minor variance.


Foundation and walls can be upgraded to provide the required support for a third floor house addition.


Want to know more?

There are a lot of things to think about before building a third storey addition, many of which we have discussed in a previous blog post: Third Storey Additions: What You Need To Know and House Addition Cost.


Q&A: You Ask. We Answer. is where we answer your house addition and renovation questions. Email us your questions, we will attempt to respond to all questions, and will post the most interesting ones on our blog.