Addition pricing varies more than almost any other construction job, because so much depends on your existing structure. These are realistic 2026 ranges to plan around before you talk to a contractor.

Average Cost by Type

• Single-storey rear addition: roughly $180–$320 per square foot, fully finished.

• Two-storey addition: roughly $150–$280 per square foot, as structure is shared.

• Garage or basement conversion: roughly $90–$180 per square foot.

What Drives the Price

Foundation work, roof tie-ins, and anything that touches structure move the number most. After that it is services — moving a kitchen, a bathroom, or a panel is far more expensive than adding plain floor area. Finish level is the last lever, and usually the one owners control best.

Demolition and Site Prep

Removing an existing structure, excavating, and getting machines onto a tight site can add meaningfully to the total. Restricted access, protected trees, or a sloping lot all add days before any new work begins — and those days are real money.

Size Examples

A modest 200 sq ft single-storey addition typically lands between $36,000 and $64,000 finished. A 600 sq ft two-storey addition usually runs $90,000 to $168,000. A straightforward garage conversion often comes in between $18,000 and $36,000.

How to Get an Accurate Quote

Get at least three written quotes against the same drawings and scope. A quote that skips the structural detail, the services, or the permit allowance is not cheaper — it is incomplete. Ask what is excluded, not just what is included.