What rear addition actually costs in Toronto

What actually moves the price

One storey or two. This is the largest single factor and it is close to a doubling, because a second storey brings a heavier foundation, a stair, and structural work where the addition meets the existing house.

Whether you need a minor variance. This is the factor homeowners underestimate most. Toronto zoning constrains how much of your lot you can cover, how close to the rear you can build, and how tall the result can be. If your design exceeds any of it, you go to the Committee of Adjustment. That means an application, a notice period, a hearing, and the real possibility of being refused or asked to redesign. It adds months before a shovel moves, and if a neighbour objects it can add considerably more.

A design that fits inside the zoning envelope is dramatically cheaper and faster than one that does not. It is worth asking a designer to price both before you fall in love with the larger one.

What the addition lands on, and what it connects to. Existing foundation condition, whether the drain has to be rerouted, whether the electrical service can carry the new load, and whether the furnace can heat the extra volume are all discovered late and paid for late.

What the declared value excludes

This job has the widest gap between the permit figure and the cheque you write. The declared value excludes architectural and engineering fees, which on a project this size are a real percentage, not a rounding error. It excludes the survey, the Committee of Adjustment application if you need one, and the permit fee. It also generally excludes interior finishing, so an addition declared at the midpoint above is a weathertight shell, not a room you can move into.

Three questions before you sign

• Does this design need a minor variance? Ask before you pay for drawings. If the answer is yes, ask what the timeline and the risk of refusal look like for your specific street.
• Is finishing included, and to what standard? Get the line between shell and finished space defined explicitly. This is where quotes that look comparable turn out not to be.
• What is the payment schedule tied to? On a job of this length, milestones tied to passed inspections protect you far better than tying them to dates.