Thornhill Design Fees: What Architectural and Engineering Work Costs in 2026

A 2,400 square foot house on Yonge Street carries a design fee between $43,000 and $77,000 in 2026, depending on how much of the structure you are changing and which side of the street you live on. That number covers the architectural drawings, the engineer's stamp for structural work, the mechanical and electrical coordination, and the permit submission to either Vaughan or Markham. Most homeowners expect the design cost and forget the engineering, the HST and the municipal fees that come after.

The per-square-foot range tells you less than the scope does. A cosmetic gut with no walls moving sits at the low end. A project that opens the back wall, underpins the basement and adds a second storey climbs toward the top, because the engineering hours multiply and the permit review takes longer. Thornhill straddles two cities with different bylaw details, and a drawing prepared for the wrong jurisdiction is money spent twice.

What design fees include on a Thornhill project

Design fees pay for the measured drawings, the floor plans, the elevations, the sections and the details that satisfy the building department and guide the trades on site. The architect or designer with a Building Code Identification Number prepares the package, coordinates the engineer's structural drawings where load-bearing walls or beams are involved, and files the application with the city. The fee also covers one round of revisions after the examiner's first comments, which happens on most projects.

Structural changes need an engineer's stamp, and that cost sits inside the design fee or gets billed separately depending on how the contract is written. A load-bearing wall removal with a steel beam costs $3,000 to $8,000 in engineering. Underpinning a basement to gain ceiling height adds another $5,000 to $12,000 for the shoring design and the foundation drawings. A second-storey addition with new footings can reach $15,000 in structural fees alone. HVAC and electrical coordination for a whole-home project adds $2,000 to $5,000, because the mechanical designer needs to size the system and lay out the ductwork before the permit examiner will sign off.

What the design fee does not include: the building permit fee itself, which Vaughan and Markham collect at submission; the Electrical Safety Authority inspection fee for the electrical permit; the TSSA fee if you are touching gas lines; and the cost of any zoning variance or heritage review that the project triggers. Those line items come later, but they add up to several thousand dollars on most projects.

Per-square-foot ranges in Thornhill in 2026

Design fees in Thornhill run $18 to $32 per square foot of the area being renovated, with most projects landing between $22 and $28. A straightforward interior with no structural work and no addition sits near $18 to $22. A project that removes walls, adds a rear extension or reconfigures the second floor moves to $24 to $28. Underpinning the basement or adding a storey pushes the number to $28 to $32, because the engineering and the permit coordination take twice as long.

The Markham side of Thornhill, where Royal Orchard and Thornhill Village sit, includes heritage properties near the old village core. A project inside the heritage conservation district adds $4,000 to $12,000 in design time for the heritage submission and the material specifications that satisfy the district guidelines. The Vaughan side, covering Thornhill Woods and Patterson, has fewer heritage constraints but stricter setback and height rules that can force a design revision before filing.

A 1,500 square foot bungalow gut with no structural work costs $27,000 to $33,000 in design fees. A 2,400 square foot two-storey with a rear addition and a basement underpin runs $58,000 to $77,000. A 3,200 square foot whole-home reconstruction with a second-storey addition lands between $90,000 and $115,000. These numbers assume full architectural and engineering services through to permit issuance, not just sketch drawings.

A worked example on a 2,400 square foot house on Yonge Street

Take a 1978 backsplit on the Markham side, 2,400 square feet across three levels, where the homeowner wants to open the main floor, underpin the basement to gain ceiling height, and add a primary ensuite on the second floor. The scope touches structure, foundation and plumbing, so it needs architectural drawings, structural engineering and mechanical coordination.

Design fees: $26 per square foot times 2,400 square feet equals $62,400. That covers the architectural package, the structural drawings for the underpinning and the main-floor beam, the mechanical layout for the new HVAC zones, and the permit filing with Markham. Engineering for the underpinning adds $8,000. Total design and engineering: $70,400 before HST.

Building permit fee: roughly $4,500 for a whole-home interior alteration with structural work and a basement underpin, paid to Markham at submission. Electrical Safety Authority inspection fee: roughly $350. HVAC and plumbing inspections are included in the building permit. HST at 13 per cent on the design and engineering fees adds $9,152. Total soft costs before construction starts: $84,402.

Construction value for this scope runs $420,000 to $540,000, so the design and engineering total lands at about 13 to 17 per cent of construction cost when you include the permit fees and HST. That ratio holds across most design and build services in the GTA. Clients who budget only the base design fee and forget the engineering and the tax are short by $15,000 to $20,000 before the first trade arrives.

What moves the design fee up or down in this area

Structural complexity is the first driver. A cosmetic project with no walls moving and no new openings needs only architectural drawings and sits at the low end of the range. Adding a rear bump-out or removing a load-bearing wall brings in an engineer and pushes the fee up by $5,000 to $10,000. Underpinning a basement or adding a second storey doubles the engineering time, because the foundation and the framing both need stamped drawings and the permit review takes longer.

The age of the house changes the contingency and sometimes the design approach. Post-war houses from the 1950s to 1980s are straightforward to document and rarely hold surprises. Older homes in Thornhill Village, built before 1950, often have knob and tube wiring replacement needs, plaster walls that complicate the structural assessment, and foundation details that require more investigation before the engineer can sign off. The design fee does not usually change, but the engineering hours do.

Jurisdiction matters less for the design fee than for the approval timeline. Vaughan and Markham charge similar permit fees and review applications under the same Ontario Building Code, but Markham's heritage district on the east side of Yonge adds review time and design iterations that cost money. A project near the village core that needs heritage approval can add two months to the schedule and $8,000 to $12,000 in design revisions and submission fees.

Custom details drive the fee up when the homeowner wants something the trades cannot build from a standard drawing. A curved staircase, a cantilevered balcony, a vaulted ceiling with exposed beams, or a wine cellar like the one we built in Royal Orchard all need extra sections, details and coordination time. Each custom element adds $1,500 to $4,000 in design hours, and the fee climbs accordingly.

Line items people forget: permits, engineering and HST

The building permit fee in Vaughan or Markham for a whole-home interior alteration with structural work runs $2,500 to $6,000 depending on the construction value and the scope. The fee schedule is public but changes annually, so confirm the current rate with the building department before you finalize the budget. Electrical work needs a separate permit from the Electrical Safety Authority, roughly $300 to $500 for a whole-home rewire. Gas work needs a TSSA inspection if you are relocating the furnace or the water heater, another $200 to $400.

Engineering is billed separately by some firms and rolled into the design fee by others. Ask which model the contract uses before you sign. Structural engineering for a project with one or two beam installations runs $3,000 to $8,000. Underpinning design adds $5,000 to $12,000. A second-storey addition with new footings and framing can reach $15,000 to $25,000 in engineering fees, because the calculations take longer and the liability is higher.

HST at 13 per cent applies to all design, engineering and construction contracts in Ontario. On a $70,000 design and engineering package, HST adds $9,100. On a $500,000 construction contract, it adds $65,000. The GST/HST New Housing Rebate can return part of the tax if the project qualifies as a substantial renovation, meaning you gut at least 90 per cent of the interior, but most projects do not meet that threshold and the rebate does not apply. Confirm the rules with your accountant before you count on the money.

Contingency is not a line item you pay to the designer, but it belongs in the budget from the start. Plan on 10 per cent of construction value for post-war houses and 12 to 15 per cent for older homes. On a $500,000 project, that is $50,000 to $75,000 set aside for the things you find when the walls come down. Clients who skip the contingency line end up stopping work halfway through or making finish compromises they regret.

When you pay the design fee during the project

Design fees are billed in three or four stages, not as one lump sum at the start. The first payment, usually 25 to 35 per cent of the total design fee, comes due when you sign the design contract and the team begins the measured drawings and the feasibility review. The second payment, another 30 to 40 per cent, is invoiced when you approve the schematic design and the floor plans. The third payment, the remaining 25 to 35 per cent, comes when the permit drawings are complete and filed with the city.

Some contracts add a fourth payment tied to permit issuance, covering the final revisions after the examiner's comments and the stamped approval set. That structure protects both sides: you pay for work completed, and the designer does not carry months of unpaid hours waiting for a permit to clear. The permit fee itself is paid directly to the municipality at submission, separate from the design contract.

Engineering fees follow a similar schedule, with the structural engineer billing half at the start of calculations and half when the stamped drawings are delivered. HVAC and electrical coordination are usually billed at completion, after the mechanical drawings are submitted with the permit package. In a design and build in Thornhill contract, the design and engineering fees are often rolled into the total project cost and billed as part of the construction draws, which simplifies the payment schedule but does not change the total amount.