Build a deck
Decks bring together three separate things homeowners tend to miss: a locate before you dig, a building permit that depends on height and size, and zoning setbacks that are a different question from the Building Code. The locate is free, required by law, and the step most often skipped — Ontario One Call exists precisely because people put fence posts and deck footings through buried gas and telecom lines every spring.
What applies when you build a deck in Ontario?
In Ontario, this job can involve two bodies: Ontario One Call — a utility locate before any digging; and your municipal building department — a building permit, depending on height, area, and whether it is attached.
Source: Ontario One Call — homeowners (Ontario Underground Infrastructure Notification System Act, 2012) · Reviewed 2026-09-10 (reviewer placeholder — not credentialed sign-off)
What applies
A utility locate before any digging
Who files Whoever is digging — including you.
Free, and required by law under the Ontario Underground Infrastructure Notification System Act, 2012. Submit the request ahead of your dig date; locates are not instant.
A building permit, depending on height, area, and whether it is attached
Who files The contractor, or you if building it yourself.
Thresholds vary by municipality. Zoning setbacks are a separate question from the Building Code and are also handled locally.
Who has to be certified
| Trade | What they need | Ask them |
|---|---|---|
| General | No province-wide licence; check municipal requirements | “What does this municipality require for this kind of work, and do you carry it?” |
| Electrical | ECRA/ESA licensed contractor if adding lighting or outlets Find a licensed electrical contractor (ESA) |
“Who is doing the electrical for the deck lighting?” |
What a complete quote contains
- Who is calling in the locate, and confirmation it will be done before digging
- Footing depth and type, stated explicitly
- Whether a permit is required and who pulls it
- Guard and railing heights, and stair details
- Ledger attachment method where the deck attaches to the house
- Species and grade of lumber, or the specific composite product
- Grading and drainage where the deck changes how water moves
Questions to ask out loud
Who is calling Ontario One Call, and when?
Good answer Names who is doing it and builds the wait into the schedule.
Worrying answer Has never mentioned it, or says they know where the lines are.
How deep are the footings going?
Good answer A specific depth, with a reason tied to frost.
Worrying answer Whatever's easiest, or deck blocks on grade for a structure that needs more.
Does this need a permit at this height and size?
Good answer Knows the local threshold and offers to confirm with the municipality.
Worrying answer Says decks never need permits.
How is the ledger attached to the house, and how is it flashed?
Good answer Describes the fastening and the flashing that keeps water out of the wall.
Worrying answer Doesn't distinguish attachment from flashing. Ledger failures are a known cause of deck collapse.
Are we within the zoning setbacks for this lot?
Good answer Treats zoning as a separate check from the Building Code.
Worrying answer Conflates the two, or assumes.
Watch for
high Digging starts without a locate.
But before you accuse anyone None. It is free and it is the law. Striking a gas line is a life-safety event.
medium Deck blocks on grade for a large or elevated structure.
But before you accuse anyone Legitimate for small ground-level platforms in some municipalities. Not a universal shortcut — ask what the local requirement is for your height and size.
medium "Permits are only for decks over a certain size, and yours is under."
But before you accuse anyone Often true — thresholds exist. The way to settle it is confirming the threshold with your municipality rather than accepting the claim.
Currency note
Zoning and Building Code are two different approvals from the same building department, and a deck can satisfy one while failing the other. Ask about both by name.
Systems this job touches
Sources and review
Reviewed Reviewed 2026-09-10 Next review 2027-03-09 Tier A · 180-day SLA Reviewer: Trade reviewer (to be appointed) (placeholder)