Finished one-storey rear home addition with large windows and patio doors on a Toronto brick house

See What Your Toronto Home Addition Costs Before You Draw Plans

A 400 sq ft one-storey rear addition in Toronto costs about $160,000 to $240,000 CAD before HST at 2026 prices. The low end adds open living space under its own roof, and the high end adds a bathroom, joins the existing roof, and upgrades the finishes.

An addition makes room for a larger kitchen, a family room, or more bedrooms. Start with the kind of space you need, and you can price it before you have drawings.

Prices updated October 2026

Price Your Addition

Your Addition

Addition LocationSelect where the addition attaches to your home.
sq ft
Enter the total floor area you want to add, across every storey, in square feet.

StoreysSelect how many storeys the addition has.
Rooms Inside the AdditionSelect the kitchen or bathroom the addition holds.

Roof, House, and Finishes

RoofSelect whether the new roof joins the existing roof.
Changes to the Existing HouseSelect how much of the existing house changes to connect the addition.
Finish LevelSelect the quality level of the flooring, windows, trim, and fixtures.

Upgrades

Tick when the soil needs a deeper foundation or helical piles.
Tick to replace the electrical panel with a larger one.
Tick when equipment and materials reach the yard through a narrow side yard.
Tick to have True Frame Builders prepare the drawings and apply for the building permit.
Tick when the design needs a minor variance from the zoning rules.

Location

Enter the first 3 characters of your postal code to apply location-based pricing.

Fill in the fields above to see your price
Pick a time for True Frame Builders to visit, measure, and prepare your quote.Book a home visit

What Changes the Cost

  • Foundation and soil: Poor soil or a high water table needs a deeper foundation or piles.
  • Roof connection: Joining the new roof to the old one adds framing, flashing, and roofing work.
  • Heating, electrical, and plumbing: The larger home often needs more heating, a bigger panel, and new plumbing lines.
  • Site access: A narrow side yard slows equipment and material delivery.
  • Design, permits, and zoning: Drawings, the building permit, and any minor variance add to the cost before work starts.
Crew installing helical piles for a rear home addition foundation in a Toronto backyard
Helical piles carry the addition when the soil is soft or the water table is high.
Carpenters framing an addition roof where it joins the existing roof of a Toronto semi-detached house
Flashing seals the joint where the new roof meets the old one, so water stays out.
Worker carrying lumber through a narrow side yard to a home addition site behind a Toronto house
A narrow side yard means materials move in by hand, which adds labour time.

What Your Estimate Includes

Your estimate covers the foundation, framing, roof, windows, insulation, interior finishes, and the kitchen or bathroom you select inside the addition. Drawings, permits, and a variance are in the price when you tick them.

Before

Back of a Toronto bungalow with an aging wooden deck before a rear home addition
The back of the house and the yard the addition sits on.

After

The same Toronto bungalow with a finished one-storey rear addition and patio doors to the yard
A one-storey rear addition adds a family room with doors out to the yard.

What True Frame Builders Checks Before Your Quote

Contractor measuring the back wall of a Toronto house with homeowners during a home addition site visit
True Frame Builders measures the house and checks the site with you before sending your quote.

Zoning, soil conditions, and the strength of the existing walls depend on your property. True Frame Builders checks them on site and brings in a designer or engineer when the work needs one. Your final price depends on site conditions, measurements, chosen materials, and the full work plan. True Frame Builders visits, measures, and then sends your quote.

Common Questions

How much does a home addition cost in Toronto?

A 400 sq ft one-storey rear addition costs about $160,000 to $240,000 CAD before HST at 2026 prices. The low end adds open living space under its own roof, and the high end adds a bathroom, joins the existing roof, and upgrades the finishes. Your own cost depends on your answers in the estimate and the condition of your property.

Do I need a permit for a home addition?

Yes. An addition needs a building permit in Toronto, and it has to meet the zoning rules for your lot. A design outside those rules needs a minor variance from the Committee of Adjustment.

Can I put a kitchen or bathroom in my addition?

Yes. Select the kitchen or bathroom in this estimate when it sits inside the addition. For a room in the existing house, use the kitchen or bathroom estimate.

Plan the Next Part of Your Project

Many addition projects also include a second-storey addition, a kitchen renovation, or load-bearing wall removal to open the house into the new space. Each one has its own estimate, and your saved estimates add up to one project total.

For City of Toronto permit rules, see the Toronto guide to small residential additions.