Permits 101 · 7 min read · Last updated
Most decks in Ontario need a building permit. The main exception is a small, low, detached deck — and even then, zoning rules still apply. Here is how to tell which side of the line your project falls on, and what to prepare if you do need a permit.
The short answer
If your deck is attached to the house, raised more than about 60 cm (24 inches) off the ground, or larger than 10 m² (about 108 sq ft), plan on getting a building permit. If it is a small, low platform sitting on its own in the yard, it may be exempt from a building permit — but it still has to follow your municipality's zoning by-law and the construction standards in the Ontario Building Code.
When a deck may be exempt from a building permit
Ontario's 2024 Building Code (in force since January 1, 2025) added province-wide exemptions for certain small structures. For decks, the exemption is generally limited to platforms that meet all of these conditions:
- no more than 10 m² (about 108 sq ft) in area,
- a walking surface no more than 600 mm (24 in) above the adjacent ground,
- not attached to or supported by a building, and
- not serving a required entrance or exit of the home.
The exact conditions live in Division C of the Building Code, and your municipal building department applies them — some municipalities publish their own guidance sheets that interpret the rules slightly differently. When in doubt, call the building department or ask for a written confirmation before you skip the permit.
Exempt from a permit ≠ exempt from the rules. A permit-exempt deck must still be built to code (footings, guards, spans) and must still respect zoning setbacks, lot coverage and height limits. The exemption only removes the paperwork, not the standards.
When you definitely need a permit
- The deck is attached to the house (ledger-mounted) or supports part of the building.
- The walking surface is higher than 600 mm above grade at any point.
- The deck is larger than 10 m².
- It has a roof, enclosure or privacy wall over it.
- It supports a hot tub or swim spa (significant structural load).
- It serves a door used as an entrance or exit, including walkouts.
- You are replacing the structure of an existing deck (not just re-boarding the surface).
What about Toronto and Mississauga specifically?
Both cities follow the provincial Building Code, so the exemption thresholds above apply. In practice:
- Toronto reviews deck permits as residential building permit applications and publishes information sheets on typical deck requirements. Zoning By-law 569-2013 controls how close the deck can sit to your lot lines and how much of the rear yard it can cover.
- Mississauga accepts deck applications through its online e-Permits portal and similarly checks the design against Zoning By-law 0225-2007 before issuing the permit.
In both cities, the zoning review happens as part of the permit — a deck that meets code but breaks a setback will be refused until you adjust the design or obtain a minor variance.
Safety rules every deck must meet — permit or not
- Guards (railings): once the walking surface is more than 600 mm above the ground, a guard is required — typically at least 900 mm high for lower decks and 1,070 mm for higher ones, with openings that a 100 mm sphere cannot pass through.
- Footings: supports generally must extend below the frost line (commonly about 1.2 m in southern Ontario) so the deck does not heave.
- Structure: joist and beam spans, post sizes and the ledger connection to the house all have prescribed limits.
What you need to apply
| Document | What it shows |
|---|---|
| Site plan | The deck's size and position on the lot, with distances to all property lines and structures |
| Construction drawings | Framing plan, footing sizes and depths, beam/joist spans, guard details, stair details |
| Elevation or section | Height above grade, guard heights, attachment to the house (if any) |
| Application form + fee | Your municipality's building permit application and the applicable fee (see our Toronto permit cost guide) |
What happens if you build without a permit?
Municipal by-law and building officials can issue an order to comply or an order to uncover finished work, charge additional review fees, and in the worst case require the deck to be removed. An unpermitted deck can also complicate an insurance claim or a home sale — buyers' lawyers routinely ask for permit history. If you already built without one, most municipalities let you apply for a permit retroactively; expect to open up parts of the structure for inspection.
How long does a deck permit take?
A complete residential application is legally required to be reviewed within 10 business days in Ontario. Incomplete drawings are the most common reason decks blow past that — see our full guide to Ontario building permit timelines for how the clock actually works.
Skip the paperwork
Describe your project in plain English and Permits2Go finds, fills and assembles the exact municipal forms you need — for Toronto, Mississauga and municipalities across Ontario.
This guide is general information, not legal or professional advice. Permit requirements, by-laws and fees change and vary by municipality — always confirm the current rules with your local building department before you design or build.