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ADU Building Permit
ADU Building Permit designed, permitted and built across the 30 municipalities of the Greater Toronto Area - zoning review, permit drawings and construction handled by one team.
ADU Building Permit - Overview
Key Takeaways
- Key features: Zoning and by-law compliance review, Complete permit application package, Municipal comment responses and resubmissions
Permit and approvals handling - zoning review, by-law compliance, application submission and minor variance representation at the Committee of Adjustment where needed.
Features & Specifications
- Zoning and by-law compliance review
- Complete permit application package
- Municipal comment responses and resubmissions
- Minor variance and Committee of Adjustment support
- Conservation authority and utility clearances
Key takeaways
- An ADU building permit is the municipal approval that makes a second dwelling legal to build, occupy, insure and rent - we carry the file through plan-examiner comments to issuance.
- A complete Ontario package is never one drawing: architectural drawings, site plan, structural calculations, SB-10/SB-12 energy compliance, and plumbing and HVAC layouts.
- Two approvals sit outside the building department and stall GTA files most often - conservation authority sign-off (mandatory since 1 April 2024) and servicing capacity confirmation.
- Mississauga charges about $1,050 for a 600 sq ft unit and refunds it in full after final inspection; review runs four to eight weeks once a complete package is in.
An ADU building permit is the municipal approval that makes a second dwelling legal to build, occupy, insure and rent. We prepare and submit the full application, answer plan-examiner comments, and carry the file to issuance - for owners building with us and for owners who intend to build with someone else.
A complete Ontario permit package for an additional residential unit is not a single drawing. It contains architectural drawings, a site plan showing setbacks and lot coverage, structural calculations, an energy compliance filing under the SB-10 or SB-12 supplementary standard, and plumbing and HVAC layouts. Missing or inconsistent items are the ordinary cause of a rejection, and each round trip with a plan examiner adds weeks.
What this includes
- Complete submission package assembled - architectural drawings, site plan, structural calculations, SB-10/SB-12 energy compliance, plumbing and HVAC layouts
- Plan-examiner comments answered by us through to issuance, not handed back to the owner
- Bill 23 as-of-right zoning check confirming up to three units without a rezoning application
- Conservation authority submission where TRCA or Credit Valley regulates the lot - mandatory since 1 April 2024
- Servicing capacity confirmation for existing water and sanitary connections before submission
- Written against O. Reg. 299/19 (amended November 2024) and O. Reg. 462/24 as currently in force
- Mississauga ARU fee (about $1,050 for 600 sq ft, $18.44/m², $244 minimum) filed for its full post-inspection refund
- Permit-only engagement available - we take the file even if you build with another contractor
Two approvals sit outside the building department and catch owners by surprise. Since 1 April 2024, an amended Conservation Authorities Act requires TRCA or Credit Valley Conservation sign-off for additional residential units inside a regulated area - ravines, valley lands, the Oak Ridges Moraine and the Niagara Escarpment all qualify, and this is the most common cause of a stalled GTA file. Servicing capacity is the other: a municipality can require confirmation that existing water and sanitary connections will carry a second dwelling before it will issue.
Zoning is where Bill 23, the More Homes Built Faster Act (2022), changed the arithmetic. Most serviced lots already holding a detached, semi-detached or townhouse dwelling now permit up to three residential units as-of-right, so no rezoning is required. Before Bill 23 a second unit typically meant a rezoning application of six to twelve months, and Toronto files also faced a three-to-six-month Committee of Adjustment step that as-of-right permission removed. O. Reg. 299/19, amended November 2024, and O. Reg. 462/24, in force November 2024, are the provincial instruments the package is written against.
Review takes four to eight weeks in most GTA municipalities once a complete package is submitted, and fees vary widely. Mississauga charges roughly $1,050 for a 600 sq ft additional residential unit at the 2025 rate - about $18.44 per square metre with a $244 minimum - and refunds that fee in full once construction passes final inspection, which is worth filing correctly for. Toronto's combined permit, development and plan-review fees run materially higher.
We hold the file through examiner comments rather than handing it back to the owner. Where a design element blocks issuance, we tell you which element and what change clears it.
ADU Building Permit - Permits and Approvals by Municipality
What approval typically costs, and what the lots look like, in the GTA municipalities we build in most.
| Municipality | Typical approval fees | Lot typology |
|---|---|---|
| Toronto | $8,000-$14,000 in permit, development and plan-review fees | Narrow downtown lots with rear public laneways - Toronto has over 300 km of them, more laneway frontage than any other Canadian city. |
| Brampton | $5,500-$10,000 including Brampton registration and Peel charges | Deep newer-subdivision lots, many with an existing unregistered basement apartment that must be brought to Ontario Building Code fire-separation standard. |
| Mississauga | $6,500-$11,000 in City of Mississauga and Region of Peel charges | Large 1970s-90s subdivision lots with attached garages; garage conversions and rear coach houses are both common outcomes. |
| York | $8,000-$14,000 under the City of Toronto fee schedule | Older narrow semi-detached lots on a laneway grid, with frequent shared-driveway conditions that must be resolved before permit. |
| Etobicoke | $8,000-$14,000 under the City of Toronto fee schedule | Split personality - laneway-served lakeshore grid in Mimico and New Toronto, versus large treed lots in The Kingsway where garden suites dominate. |
| Ajax | $7,000-$12,000 including Durham Region charges | Compact 1990s-2000s subdivision lots where the required 1.2 m side-yard construction access sets the maximum module width we can crane in. |
| King | $9,000-$16,500 including York Region and septic charges | Estate and agricultural parcels, many over an acre, on private well and septic with moraine core-area restrictions. |
| North York | $8,000-$14,000 under the City of Toronto fee schedule | Deep post-war bungalow lots, commonly 50 ft × 120 ft, with rear yards large enough for a detached garden suite plus the required 1.5 m separation. |
Fee bands are indicative, drawn from project experience - confirm current tariffs with the municipality before budgeting.
Related Unit Types
Frequently Asked Questions
Everything you need to know about our services.
Permit and approvals handling - zoning review, by-law compliance, application submission and minor variance representation at the Committee of Adjustment where needed. Concretely that means: zoning and by-law compliance review; complete permit application package; municipal comment responses and resubmissions; minor variance and committee of adjustment support. One contract covers design, permit and construction, so there is no handoff between a designer and a builder halfway through.
Related service: Accessory Dwelling Units
On a 700 sq ft reference unit our estimate band runs $16,000-$32,500 in King up to $17,000-$34,000 in East York - roughly $385 to $402 per square foot. The spread is not a markup: this work involves drawings, calculations and the permit submission rather than construction, and the per-municipality difference comes from approval fees, frost depth and snow load. Final pricing follows a site visit.
Related service: Accessory Dwelling Units
Yes - a building permit is required in every GTA municipality. Bill 23 (More Homes Built Faster Act, 2022) and O. Reg. 299/19 permit up to three residential units as-of-right on most serviced lots, so a rezoning application is usually not needed.
Municipal approval costs range from $5,500-$10,000 including Brampton registration and Peel charges in Brampton to $9,000-$16,000 including Peel Region and septic permit charges in Caledon, quoted separately from construction. Plan review typically takes four to eight weeks.
Related service: Our ADU services
All 30 municipalities of the Greater Toronto Area, from Toronto out to Clarington. Each one has its own by-law, fee schedule and review stream, and we file into the local one - the municipal page for your address carries that city's approval band, frost depth and building season.
Related service: Accessory Dwelling Units
Eight to fourteen months is the honest end-to-end range: design and drawings, four to eight weeks of plan review, then construction. Because this work is drawings, calculations and the permit submission rather than construction, the build phase is the part that moves most between projects. Excavation is scheduled inside the local building season, and interior work carries on through winter.
Related service: Accessory Dwelling Units
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Ready to start your adu building permit project? Send us your address and we will tell you what your lot allows, what it costs and how long the permits take.