On this page
- The short answer, and the checks that decide it
- Where the 600 mm number really comes from
- Permit triggers in five Ontario municipalities
- Replacing, repairing or rebuilding an existing deck
- A permit is not the only approval, and it is not the first one
- What the permit process looks like from your side
- What it costs, and what skipping it costs
- Hiring the deck builder, and what to settle before the first payment
- Frequently asked questions
The short answer, and the checks that decide it
The Building Code Act sets the province-wide definition of a building and the permit requirement. Municipal building departments publish the project guidance homeowners use, but those pages do not all line up with one another or with the Act's 10 square metre definition.
One thing first. We're describing published rules, not ruling on your deck. The chief building official in your municipality decides whether it needs a permit, and their answer governs.
Question one, is the deck a building on its own
Section 8(1) carries the whole permit requirement: no person shall construct a building without a permit from the chief building official. What counts as a building comes from section 1(1), which defines one as "a structure occupying an area greater than ten square metres consisting of a wall, roof and floor or any of them".
Any of them. A deck floor over 10 square metres meets that definition. That's about 108 square feet, or a square roughly 3.2 metres a side. Ask the building department how it measures an addition to an existing deck.
Question two, what does your municipality say about attachment
The same section defines "construct" to include the erection, installation, extension or material alteration or repair of a building. Attachment can matter, but the published municipal rules do not treat it as one province-wide yes-or-no test. Hamilton requires a permit for any attached deck. Ottawa applies its 600 mm height test to decks attached or adjacent to the house.
Hamilton's wording is about as plain as municipal guidance gets: a permit is required for "any-sized deck or porch (covered or uncovered) where it is attached to a building."
Where the 600 mm number really comes from
Municipal deck pages often cluster around the same height, but not always at the same boundary: 600 mm, 60 centimetres and 0.61 metres all appear, with 24 inches used as a rounded equivalent. The number also does different work on different pages.
What the Building Code actually says at 600 mm
The current Building Code is O. Reg. 163/24, which adopts the National Building Code of Canada 2020 with Ontario amendments. In Ontario's publicly downloadable compendium updated January 16, 2025, Division B, Article 9.8.8.1 requires a guard where the elevation difference is more than 600 mm between a walking surface and the adjacent surface within 1.2 metres. The ministry directs readers to request the later Ontario Amendment Document by email, so confirm the current text before designing to this boundary.
That's a guard rule. It isn't a permit exemption.
The current Code's Division C permit exemptions include certain tents, farm-building demolitions and qualifying sheds of 15 square metres or less. They do not create a general deck exemption.
Why your municipality still uses it to decide permits
Municipalities administer the permit system and publish plain-language tests so a homeowner doesn't have to read a regulation. Height matters because elevated walking surfaces can trigger guard, stair and structural requirements.
The published height tests differ by municipality. They are guidance for local administration, not amendments to the provincial Act or Code.
Permit triggers in five Ontario municipalities
What five Ontario building departments publish. Read your own row, then the one next door.
| Municipality | Deck attached to the house | Freestanding deck, uncovered | Freestanding deck, covered | Also stated on the page |
|---|---|---|---|---|
| Toronto | The city lists porches and decks as additions, but it also exempts a qualifying uncovered platform up to 60 cm; the page does not expressly reconcile attachment with that exemption | Permit if more than 60 cm (24 in) above adjacent finished grade. No area test is stated for decks | Not separately stated; a covered structure falls outside the uncovered-platform exemption | The exemption also requires that the platform does not form part of a required exit and complies with the Zoning By-law |
| Ottawa | Permit if the walking surface is more than 600 mm (24 in) above adjacent grade, regardless of area | Permit if the walking surface is greater than 10 square metres and more than 600 mm above adjacent grade | Not separately stated | Permit regardless of size if it is an elevated deck providing principal access to a building. First review target 5 business days |
| Hamilton | Permit for any-sized deck or porch, covered or uncovered, attached to a building | Permit if greater than 10 square metres and more than 200 mm above adjacent grade. Permit if 10 square metres or less where it is adjacent to or associated with a door and more than 600 mm above grade | Permit if greater than 10 square metres, regardless of height | Replacement or installation of new guards requires a permit. Where no permit is required, the Zoning By-law and other regulations still apply |
| Mississauga | Not stated separately from the height rule | Permit for a deck greater than 0.61 m (2 ft) high. The same page's no-permit list reads "deck less than 600 mm (2 feet) in height" | A covered porch requires a permit | Any building or structure other than a shed greater than 10 square metres, or any size containing plumbing, requires a permit |
| London | City pages conflict. The common-homeowner page says attached side and rear decks below 600 mm need a permit | The newer before-you-apply page says decks below 600 mm need no permit except at a suite entrance, while the common-homeowner page limits that statement to unattached decks | The newer page says decks over 0.61 m need a permit; balconies, porches and enclosed decks have separate definitions | The common-homeowner page says decks may encroach up to 3 m into required yard setbacks but must stay at least 1.2 m from the property line, or 3 m beside an OS4 or OS5 Open Space zone. Ask London Building which page governs |
Each row reports that municipality's published wording. Toronto leaves attachment and its low-platform exemption unreconciled, Mississauga leaves a 600-to-610 mm gap, and London's two pages conflict. Do not fill those gaps by inference.
The same deck, three published answers and one legal conflict
Run one ordinary backyard deck through three of those rows.
Worked example: a freestanding, uncovered deck, 12 square metres, 250 mm above grade. Hamilton's page says permit required. The deck is over 10 square metres and over Hamilton's 200 mm detached trigger. Ottawa's page does not trigger a permit. It requires an independent deck to be both over 10 square metres and over 600 mm. Because the Act separately defines a structure over 10 square metres as a building, get that answer in writing before building without a permit. Toronto's page does not trigger a permit if its other conditions are met. The platform is uncovered and below 60 cm, but it cannot form part of a required exit and must comply with zoning. The same statutory caution applies.
Hamilton's 200 mm line is one-third of the 600 mm figure used on several other pages.
If your municipality is not in the table
This table has five of Ontario's hundreds of municipalities. Search your own municipality's building or permits page for the word "deck". If it is silent, internally inconsistent, or conflicts with the Act's 10 square metre definition, phone the building department and ask for the answer in writing. Our Ontario pros by city pages will tell you which municipality you're in.
The five facts to have in front of you before you call
- Your municipality, and whether the property is inside its urban or rural service area
- The walking surface area of the deck in square metres, and in square feet
- The height from the finished deck surface to the adjacent grade, in millimetres, measured at the highest point
- Whether any part of the structure fastens to the house, including a ledger board
- Whether it will be covered, roofed or later enclosed, and whether it will be the main way into the house
That fifth one matters: Ottawa requires a permit regardless of size for an elevated deck providing principal access to a building.
Replacing, repairing or rebuilding an existing deck
Replacing deck boards on sound framing is generally maintenance. Confirm the scope with the building department before opening structural framing or replacing a guard.
Replacing what's underneath is a different job in the same clothes. New beams, posts or footings, a changed footprint or height, and you're constructing again, back at the permit checks. Hamilton also requires a permit for the replacement or installation of new guards, at any size or height.
"It was there when I bought the house" does not retroactively authorize the work. A registered order can also bind a later owner, so check the permit and property records before relying on the deck's age.
A permit is not the only approval, and it is not the first one
You can design a perfectly Code-compliant deck and still be told no. Section 8(2)(a) requires the chief building official to refuse a permit if the work would contravene "any other applicable law", which pulls in zoning and everything else that applies to your lot.
Zoning setbacks, lot coverage and encroachment
Zoning applies whether or not a permit does. Toronto, Hamilton, Mississauga and London each say so on their own pages, which tells you how often people assume the opposite.
London publishes its numbers: a deck may encroach up to 3 metres into a required yard setback, but must stay 1.2 metres from the property line, rising to 3 metres beside an OS4 or OS5 Open Space zone. Coverage is the one people miss. On a small lot, a deck adds more of it than anyone expects.
Land you may not be able to build on at all
Some back yards carry a second regulator. Where a property sits in a conservation authority's regulated area, which can include river and stream valleys, wetlands, land within 30 metres of a wetland, shorelines and hazardous land, section 28 of the Conservation Authorities Act prohibits specified development activities. Section 28.1 provides the permit route, and O. Reg. 41/24 defines development activity to include placing a structure of any kind.
There's a deck-shaped exception. The prohibition doesn't apply to "an unenclosed detached deck or patio that is 15 square metres or less", provided it isn't placed in a watercourse or wetland and doesn't use any method of cantilevering. Note the number: 15 square metres here, 10 for the building permit.
Two more to raise before you design. Easements and drainage rights-of-way cross plenty of back yards with nothing on the surface to show it. And on a septic system, the Building Code requires a leaching bed to shed water and be protected from compaction that could damage the pipes, so the bed decides where the deck can't go.
What the permit process looks like from your side
This is the small-projects stream: a form, a fee, a drawing set and a few staged inspections.
What goes in the application
You file an Application for a Permit to Construct or Demolish, pay the fee, and submit drawings. Toronto's published requirements are a fair guide to what any Ontario municipality wants: footing size, spacing, depth, height above grade and frost protection; the sizes and spans of every column and beam; stair details; guard details covering openings and climbability; and a site plan showing property lines, easements and setbacks.
The ten day decision clock
Division C, Article 1.3.1.3 puts the chief building official on a clock: issue the permit, or refuse it in writing with all of the reasons, within the period set out in Table 1.3.1.3. For a house or a detached structure serving it with a building area up to 55 square metres, the period is 10 days. Saturdays, holidays and days the office is closed are excluded.
The clock starts only once the application is complete, and complete has a legal definition rather than a friendly one. Missing drawings or structural information can keep it from starting.
Inspections, and why the footing one matters
Inspections happen in stages, and the permit drawings have to be on site when the inspector arrives. Work covered up before it's inspected may have to be uncovered, which on a deck means digging out footings a crew has already poured and framed over.
London's rule for an attached deck under permit is an excavation and footing inspection on top of the final one. Ottawa asks for 48 hours' notice to book. Scheduling is your builder's job. Confirming they did it is yours.
What it costs, and what skipping it costs
Two numbers, worth holding side by side.
Permit fees
There's no provincial deck permit fee and nobody can honestly quote you one. Clause 7(1)(c) of the Act lets each municipality set its fees by by-law. Toronto charges a flat $214.79 for residential decks, porches and carports in 2026, and your own municipality's fee schedule will carry its equivalent.
The deck itself is the real spend. Our deck-builder cost page puts the typical range at $4,322 to $11,059, from $1,787 at the low end to $20,486 at the high, based on 657 cost profiles. That is our own data, not a survey limited to Ontario deck projects, so treat it as context rather than a local quote.
The penalties in the Building Code Act
The ceilings in section 36 aren't decoration. An individual convicted of a first offence faces a fine of up to $50,000, and up to $100,000 for a subsequent one. A corporation faces up to $500,000 and $1,500,000. Section 36(6) adds up to $10,000 a day for continuing to ignore an order.
Those are maximums a court may impose. The more immediate enforcement tool is a compliance order. A stop-work order can follow non-compliance, and an order to uncover is available in the circumstances set out in the Act. The exposure still isn't a rounding error, and the alternative is a form and a fee.
Hiring the deck builder, and what to settle before the first payment
Settle who pulls the permit before money moves. The application has to come from the owner or the owner's authorized agent, so a builder who applies is doing it as your agent, against your property. Name the drawing set in the contract as a deliverable. Ask for permit-ready footing and guard details, and confirm who will answer correction requests from the building department.
For a small freestanding deck, a carpenter is often the right hire rather than a full deck company. If the deck is part of a walkout, a pool or a rear addition, a general contractor can sequence the approvals. Once deposits start moving, it's worth knowing what a contractor can do if the money is disputed.
Four things worth a second question A quote saying permits are "not needed for this size" without naming your municipality's rule. Ask which page that came from, and read it yourself. An offer to leave the deck lower "so we can skip the paperwork". Height, area, attachment, access and zoning can all matter, and the published tests differ by municipality. Being asked to pull the permit in your own name for a job you aren't building. Ask why, and understand what you're certifying. No drawing set. The application needs footing, beam, stair and guard details, so a builder with nothing to submit hasn't costed the permit in.
Pro tip: the 10-day clock starts only when the application is complete, and Division C, Article 1.3.1.3(5) says what that means: the right form, the right applicant, every field and schedule filled in and attached, the fee paid, and a signed declaration that it's all true.
If the deck was sold to you on your own front step, read up on your cancellation rights for work sold at your door before the deposit clears.
Frequently asked questions
Do I need a permit for a floating deck in Ontario?
Often not, but "floating" isn't a legal test. It usually means the deck isn't attached, so you still need to check area, height, access and zoning. Hamilton requires a permit for a detached deck over 10 square metres and more than 200 mm up. Toronto exempts a qualifying uncovered platform up to 60 cm.
How much does a deck permit cost in Ontario?
There's no provincial fee. Clause 7(1)(c) of the Building Code Act hands that to each municipality's own by-law, so the number is local to you. Toronto charges a flat $214.79 for residential decks, porches and carports in 2026. Look up your municipality's building permit fee schedule and find the deck line.
What happens if I build a deck without a permit?
The chief building official can issue a compliance order. A stop-work order can follow non-compliance, and the Act also allows an order to uncover work in specified circumstances. The court fine ceiling remains up to $50,000 for an individual on a first conviction.
Do I need a permit to replace the boards on an existing deck?
Replacing deck boards on sound framing is generally maintenance. Replacing the structure underneath is construction and puts you back at the permit checks. Confirm the scope locally before work starts. Guards are their own case: Hamilton requires a permit for replacement or installation of new guards, at any size or height.
Does a deck count towards my lot coverage even when no permit is required?
Usually yes. Zoning applies whether or not a permit does, which Toronto, Hamilton, Mississauga and London each state on their own pages. Coverage, setbacks and encroachment are measured against the Zoning By-law, not the permit. A deck you're free to build can still sit somewhere the by-law won't allow.
How long does it take to get a deck permit?
For a house or a detached structure serving it up to 55 square metres, Division C sets a 10-day period to issue the permit or refuse it in writing. The count excludes Saturdays, holidays and closed days and starts only with a complete application. Ottawa targets a first review in five business days.
What happens if I sell my house with an unpermitted deck?
It can come up during a sale, especially if an open permit or registered order appears in the records. Toronto sells a $92.46 inspection status report for an existing permit, showing which mandatory inspection stages passed or remain outstanding. Because it requires a permit number, it does not establish that unknown deck work was approved.