How much does a home addition cost in Ontario in 2026?

We price a home addition at $350 to $600 per square foot in 2026, and a single-storey rear addition of 300 to 700 sq ft at $180,000 to $450,000, before HST. Your own price comes after James sees the house, and the first estimate is free. In Durham Region, Ontario, the town's share is small by comparison: a 500 sq ft addition pays a building permit of $661 to $1,039 under the 2026 schedules, and no development charges, as of October 2026.

Key takeaways

• Our 2026 range for additions of all types is $350 to $600 a square foot, and $60,000 to $180,000 for a 100 to 300 sq ft bump-out, before HST.
• An addition that only enlarges your home pays no development charges, because the Development Charges Act carves out "the enlargement of an existing residential unit" (as of October 2026).
• A 1,000 sq ft addition pays a building permit of $1,321 in Ajax and $2,078 in Whitby, calculated from the Town of Whitby's 2026 Schedule N and Ajax's 2026 schedule.
• Our permit drawings for an addition are $6,000 to $12,000. That's drawings only: permit fees, HVAC engineering, truss design, committee of adjustment applications and anything unforeseen are extra.
• Pickering asks for a refundable performance deposit of $2,379 on additions over 60 m², about 646 sq ft, in its 2026 user fee schedule, which also lists a separate $1,000 deposit for additions.
• We don't give a set range for a garage addition, so price one from its parts; the permit is $10.65 per square metre in Whitby under Schedule N's garage line.

What does a home addition cost per square foot in Ontario?

We price a home addition at roughly $350 to $600 per square foot in 2026, before HST. That's our range across all types of addition, and where yours lands depends on its type, size and finish.

Here are our 2026 ranges by type of addition:

Note: these are our ranges before 13% HST, not quotes; your price comes after James sees the house, and the first estimate is free. A row with no set range is priced from the site visit; it doesn't mean the work is cheap.

Small additions cost more per square foot than big ones. Excavation, a foundation, a roof tie-in, drawings and a permit cost roughly the same whether the room is small or large, so they weigh heavier on a small one. That's why a bump-out of 100 to 300 sq ft still starts at $60,000 in our range.

Second storeys get their own guide, because the main floor below changes the math. See what a second-storey addition costs in Ontario.

What does a rear addition cost?

We price a one-storey rear addition of 300 to 700 sq ft at $180,000 to $450,000 before HST in 2026. The low end is a simple box off the back wall on a slab or crawl space. The high end is a kitchen or family room with a full basement under it, a structural opening into the old house and plumbing.

What moves a rear addition up or down that range:

• Foundation type: a full basement means deeper digging and more concrete than a crawl space or slab.
• The opening into the existing house: a wide opening in a bearing wall needs a beam and posts down to footings.
• Plumbing: a kitchen or bathroom in the addition costs more than a bedroom or family room.
• Access: a narrow side yard means hand-digging or smaller machines.
• Conservation authority land: in a CLOCA-regulated area, a minor addition needs a CLOCA Minor Permit B at $535, and a standard permit starts at $1,990 (CLOCA 2026 fee schedule).

What does a side addition cost?

We don't give a set range for side additions. Price a side addition like a rear addition of the same size, then check the side yard first, because it decides whether you can build at all.

In Whitby's older R1 to R3 zones, Zoning By-law 1784 requires an interior side yard of at least 1.5 m, as of October 2026. Since November 2025, an Ontario regulation (O. Reg. 545/06, s.1.1) treats urban residential setbacks as 90% of the by-law figure, except near shorelines, valleys, wetlands, railways and in the Greenbelt, so ask the building department what yard it will actually apply. On a narrow lot that can leave very little room, and a side addition that crowds the line goes to the Committee of Adjustment for a minor variance. Whitby charges $1,526 for a residential variance in 2026, so it's worth knowing before you draw.

What does a garage addition cost in Ontario?

We don't give a set range for a garage addition. A garage's price depends on a handful of choices you can price one at a time:

• Attached or detached. An attached garage ties into the house wall, roof and fire separation; a detached one needs its own footings on all sides.
• Heated and insulated, or not.
• Living space above. A room over the garage is priced like an addition, not like a garage.
• Driveway work, and a curb cut if the driveway widens.
• Whether it's later meant to become a garden suite. That brings in servicing, ADU zoning limits and a separate permit path; see our guide to Bill 23 additional units.

The town's permit fee is the one number we can give you. Durham towns charge garages at a lower rate than living space:

Note: these are building permit fees only, calculated for 46.5 m² from the 2026 schedules; they aren't construction costs, and we didn't confirm Pickering's garage line.

What do Durham towns charge for an addition permit?

Durham towns charge the permit per square metre of new floor area, at $14.22 to $22.37 depending on the town, as of October 2026. To convert, 1 sq ft is 0.0929 m², so 500 sq ft is about 46.5 m².

Here are the 2026 permit fees for three common addition sizes:

Note: calculated from each town's 2026 schedule (Whitby, Oshawa, Ajax, Pickering, Clarington); Pickering prints no addition line, so its row uses the new-house rate, and Ajax doesn't print the unit.

A few rules change the bill. Pickering's schedule lists a $2,379 performance deposit for additions over 60 m² and a newer $1,000 deposit line that also names additions; both are refundable, so ask the City which one applies to your permit. Clarington's fees rise 3% every 1 January under By-law 2024-006, so a permit applied for in 2027 costs more. And starting early costs extra everywhere: Whitby charges the greater of $100 or 25% of the fee if work starts before you apply, while Oshawa and Clarington add 25% if work began after applying and 50% with no application at all.

Do home additions pay development charges in Durham?

No. An addition that only enlarges your existing home doesn't trigger development charges, under section 2(3) of the Development Charges Act, as of October 2026. That's a big number to avoid: a new single detached house in Durham pays the Region alone $76,227 from 1 July 2026, per Durham Region's development charge sheet, before the town and school board charges.

The answer changes if the addition holds a separate dwelling unit. A second or third unit inside the 3-unit provincial limits is also exempt, but in Whitby education development charges still apply to detached ADUs, per the Town of Whitby's ADU page. Tell the building department what the space is for before you apply.

What does a full addition budget look like?

Add the pieces in this order: construction from a real quote, then permit drawings, then the town's permit from the table above, then any variance or conservation authority fee, then 13% HST. Our permit drawings for an addition are $6,000 to $12,000. That's drawings only: permit fees, HVAC engineering, truss design, committee of adjustment applications and anything unforeseen are on top, so keep a reserve for the unforeseen.

For a 500 sq ft rear addition in Whitby, the costs outside construction are the drawings and the $1,039 permit, before a variance or a CLOCA permit. Construction is the part that swings, from $180,000 to $450,000 across our rear-addition range, which is why the scope matters more than the town.

If the addition is part of a bigger question about staying or selling, our guide on whether to add on or move puts land transfer tax and selling costs next to these numbers. If you're torn between a rear addition and going up, read is it cheaper to build up or out.

How we price additions at Jarvis

We're a family design-build firm in Ajax. Ceara Jarvis leads design through her studio, Juliette Interiors, and James Jarvis runs the build. Our contracts are fixed price. James prices the whole job and the contract is signed, with a 10% deposit, before design begins. Then we draw the permit set ourselves, so the foundation, the opening into the house and the finish level are drawn to that price. Any change goes through a change order you sign. The ranges on this page are ours for 2026; your price comes after James sees the house, and the first estimate is free.

The nearest finished addition we can show is Greenwood, in east Toronto, roughly 40 km west of Whitby: a rear extension plus a new top storey, with the basement enlarged by removing a brick wall and full interior design, done in 10 months including design, permits and construction. For Durham projects, start at our home additions page.

Questions

How much does a home addition cost in Ontario in 2026?

We price a home addition in Ontario at $350 to $600 per square foot in 2026, before HST. A single-storey rear addition of 300 to 700 sq ft runs $180,000 to $450,000 in our range. These are ranges, not quotes: your price comes after James sees the house, and the first estimate is free.

Do I pay development charges on a home addition in Durham Region?

No development charges apply to a home addition in Durham Region if it only enlarges your existing home, under section 2(3) of the Development Charges Act as of October 2026. If the addition creates a separate dwelling unit, different rules apply, and Whitby still charges education development charges on detached ADUs.

How much is a building permit for a home addition in Whitby?

A building permit for a home addition in Whitby costs $22.37 per square metre of new floor area in 2026, with a $305 minimum. That works out to $1,039 for 500 sq ft and $2,078 for 1,000 sq ft, calculated from Schedule N to By-law 7220-17.

How much does a garage addition cost in Ontario?

We don't give a set range for a garage addition in Ontario, because the cost depends on whether it's attached, heated, or has a room above it. The permit is small: in Whitby, garages are $10.65 per square metre in 2026, about $495 for 500 sq ft.

Is a small addition cheaper per square foot than a big one?

No, a small addition usually costs more per square foot than a big one, because the foundation, roof tie-in, drawings and permit cost about the same either way. That's why our 2026 range for a 100 to 300 sq ft bump-out still starts at $60,000 before HST.

Do I need a minor variance for an addition in Durham?

You need a minor variance for an addition in Durham only if the plan breaks a zoning rule, such as a side yard, rear yard, height or lot coverage limit. Variance fees in 2026 run from $856 per lot in Oshawa to $2,500 in Pickering, and the building permit usually waits until the variance decision is final.

Sources

1. Development Charges Act ontario.ca
2. Town of Whitby's 2026 Schedule N media-003-ca.cdn.govstack.com
3. 2026 user fee schedule corporate.pickering.ca
4. CLOCA 2026 fee schedule cloca.com
5. Zoning By-law 1784 media-003-ca.cdn.govstack.com
6. Ontario regulation ontario.ca
7. By-law 33-2009, item 33 media-002-ca.cdn.govstack.com
8. Schedule A, item B11 ajax.ca
9. By-law 2024-006 weblink.clarington.net
10. Durham Region's development charge sheet media-003-ca.cdn.govstack.com
11. Town of Whitby's ADU page whitby.ca