The three measurements that decide if you need a permit
Under the Ontario Building Code (OBC) Division B and the City of Toronto Zoning By-law 569-2013 (and equivalent zoning bylaws in Mississauga, Hamilton, Oakville, and the rest of the GTA), a deck triggers a building permit when any of the following are true:
- Deck surface is more than 24 inches (610 mm) above the adjacent grade at any point. Above this height the OBC requires a guard, which means structural attention, which means a permit.
- Deck is attached to the house (via a ledger board, regardless of height). Attachment to the house implies structural load on the building envelope and triggers a permit in almost every GTA municipality.
- Deck is part of a structure subject to the OBC — for example, decks supporting hot tubs, decks integrated into a covered porch, or decks above a habitable space.
Translation: a free-standing 14″-high ground-level deck on the far end of your yard usually does notneed a permit. Almost every other GTA deck does. The honest version most contractors won’t say out loud: a small ground-level deck off the back door attached with a ledger to the house still technically needs a permit if the joists touch the wall, regardless of how low it sits. The ledger is the trigger, not the height.
The OBC sections that matter
For homeowners, four parts of the Ontario Building Code carry most of the deck-relevant rules:
- OBC 9.4.1 (Loads): residential deck live load is 1.9 kPa (about 40 psf). Snow load adds to this for elevated and covered decks. The structural design — joist size and span, beam size, post count — flows from this number.
- OBC 9.8.8 (Guards):guards required where any walking surface is more than 24″ above the surface below. For residential decks below 5.9 ft, minimum guard height is 36″. For decks above 5.9 ft, minimum 42″. Openings in the guard must not allow a 4-inch sphere to pass through (the“4-inch ball rule”).
- OBC 9.8.4 (Stairs):minimum stair width 860 mm (34″). Risers between 125 and 200 mm (5″–7-7/8″). Treads minimum 235 mm (9-1/4″). Handrails are required for stairs with three or more risers, between 865 and 965 mm above the tread nosing.
- OBC 9.15 (Footings and foundations):minimum depth 1.2 m (4 ft) below grade in southern Ontario to clear the frost line. Concrete sonotubes of 250 mm (10″) diameter are the common solution; deeper or wider for tall decks or soft soil.
There’s also a relatively new layer in OBC 9.36 covering energy efficiency, but it largely doesn’t apply to open decks — only to enclosed three-season porches and additions.
Setback rules — the one most homeowners get wrong
Every GTA municipality has setback requirements that limit how close a deck can sit to a property line. Setbacks are zoning rules, not building-code rules, so they vary by city and even by zone within a city.
The general working rule in Toronto and most surrounding municipalities: a deck up to 0.6 m (24″) above grade can usually be built right up to a 0.6 m side-yard setback; a deck above that height needs a 1.2 m setback from side and rear lot lines. But this is wildly variable — Mississauga’s rear-yard setback for elevated decks is 7.5 m from the rear lot line in some zones; Hamilton allows decks up to 1.2 m from the lot line if they’re no more than 0.6 m above grade.
The fastest way to find your actual setbacks: search your municipality’s zoning bylaw for “deck” or “platform” and look for the table for your zoning category (typically RM, RD, R3, or RL). Call your city’s zoning examiner before drawing the plan — they will tell you the answer in five minutes if you have the lot dimensions in hand.
Where the GTA municipalities diverge
Toronto
Toronto’s deck permit is issued through Toronto Building (toronto.ca/services-payments/building-construction). Permit fee in 2026 is $228.41 minimum, scaling to about $13.10 per sq metre of deck area for larger projects. Plan-review turnaround is officially 10 business days; reality is closer to 15–25 days in spring. Toronto also enforces tree-protection zones aggressively — if your deck is within 6 m of a municipal-owned tree (the boulevard tree out front, neighbour’s tree overhanging your lot), expect a tree protection plan to be required.
Mississauga
Mississauga’s permit fee is $215 base + $11.50 per square metre, with a slightly faster review window (10 business days is usually held). Decks above 600 mm in height require an additional Zoning Compliance review which can add a week. The city’s online ePlans portal is genuinely useful and faster than the Toronto equivalent.
Hamilton
Hamilton’s permits are issued through the Planning and Economic Development department. Base fee $194 + $9 per sq metre. Hamilton is unusually strict on lot coverage — total impervious surface (including the deck if elevated) often pushes lots over their coverage maximum, which then requires a Minor Variance application through the Committee of Adjustment, which adds two to four months and a $500–$1,000 fee.
Oakville and Burlington
Both work through Halton’s building services. Oakville’s permit fee is on the high end ($265 base + $14 per sq metre), but review is fast — 7–10 business days is typical. Oakville is also the only GTA municipality I know of that effectively requires engineered glass railings to come with a manufacturer’s engineering letter at permit submission, which limits which suppliers you can use.
Markham, Vaughan, Richmond Hill (York Region)
Permits issued by the local municipality, with review through York Region’s building services. Permit fees similar to Mississauga ($210–$240 base). Vaughan in particular enforces 9.8.8 guard rules carefully — expect the inspector to put a 4-inch ball through the railing at final inspection.
The fastest path through the building department
Same advice applies whichever municipality you’re in:
- Pre-application call to zoning.Five minutes on the phone with the city’s zoning examiner confirms setback and lot-coverage compliance before you spend $1,500 on drawings. Always free.
- Site plan, deck plan, and elevation. Three drawings. Site plan shows lot lines, house, deck, dimensions, setbacks. Deck plan shows beam layout, joist layout, footing locations. Elevation shows guard height, stair geometry, ledger detail.
- Connection details.The ledger-to-house detail and the post-to-beam detail are the two pages of drawings that reviewers focus on. A standard detail from the Canadian Wood Council’s deck guide is acceptable in every GTA municipality if you reference it correctly.
- Submit and follow up. First-round comments arrive in 7–15 business days. Reply within a week or your file moves to the back of the queue.
- Schedule inspections.Footings inspection before pouring concrete, framing inspection before decking goes down, final inspection when guard and stairs are complete. Most municipalities require 48 hours’ notice.
What to do if your deck is already built without a permit
Common GTA situation: the previous owner built a deck in 2014 and never permitted it. You want to renovate, sell, or just feel comfortable about it. Three options, in increasing order of cost:
- Leave it alone. Most GTA municipalities will not retroactively flag an existing deck unless they receive a neighbour complaint, you initiate a renovation that exposes the ledger or framing, or you apply for a permit elsewhere on the property and a plans examiner notices the deck. Risk is real but not high.
- Apply for a building-permit-after-the-fact. All GTA municipalities have a process for this. The deck must comply with current code — which often means retrofitting handrails, adding bracing, or pouring additional footings. Permit fees may be doubled. Total cost typically $1,500–$5,000 in addition to the remediation work.
- Rebuild it. If the existing deck has structural defects (no proper footings, undersized beams), an after-the-fact permit becomes uneconomic. Rebuilding from scratch on proper footings is sometimes the cheaper answer.
Either way, when you reach the permit stage, the permit application checklist walks through every document your local building department will ask for. From there, the next decision is about who’s actually going to build it — covered in Chapter IV.