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How to Design and Build a Deck in Ontario: Permits, Footings, Guards, Stairs and the Ledger That Fails
Finishes and upgrades Decks From a builder
How to Design and Build a Deck in Ontario: Permits, Footings, Guards, Stairs and the Ledger That Fails
Decks are where good homeowners become amateur structural engineers. Most of the time it works out. When it does not, it is the ledger pulling off the house with thirty people on it, which is why the Code has opinions about decks and the building department wants to see them.
Short version: In Ontario, a deck attached to the house, or any deck more than 600 mm (24 inches) above grade, needs a building permit; a small freestanding deck close to the ground generally does not, but check your municipality. Footings go below frost (typically 1.2 m, deeper north), the ledger is bolted to the rim joist with flashing behind it (never nailed, never over siding), beams and joists are sized from the Code span tables for a 1.9 kPa live load, guards are required above 600 mm (900 mm high up to 1.8 m above grade, 1,070 mm above that) with openings under 100 mm, and stairs follow the house rules: rise no more than 200 mm, run at least 255 mm. Budget $45 to $90 per square foot for a contractor-built pressure-treated deck in 2026 and more for composite; price it with the deck calculator before you draw it.
Design it for how you will use it
Start with the furniture and the people. A table for eight needs about 12 by 12 feet by itself; a lounge area another 10 by 12; a barbecue corner out of the traffic. Stake it out on the lawn with string at rail height and put the chairs in it before you order lumber; the most common mistake is a deck that is four feet too small, and the second is one so big it dwarfs the house. Size in two-foot increments to match lumber lengths. Put it where the sun and the wind say, not just where the door is: west decks bake in July, north decks are cool, and a privacy screen or a pergola can move the shade. On a sloped lot, step it down in levels rather than building one tall platform. Designing a custom home has the same orientation logic for the house.
When you need a permit
Under the Building Code Act, a deck attached to the house needs a permit, as does a deck that is more than 600 mm above grade. A small freestanding deck that is low to the ground is often exempt, but municipalities vary and many want a permit for anything with a guard. The permit drawings are simple: a site plan showing setbacks, a framing plan with post, beam and joist sizes and spacing, footing details, the ledger detail, guard and stair details. Zoning sets the setbacks and sometimes the lot coverage, and a conservation authority or a shoreline by-law can add rules near water. Do I need a building permit? and how to get one cover the process; call for locates before anyone digs.
The structure, in Code terms
| Element | Ontario rule of thumb | Notes |
|---|---|---|
| Footings | Below frost: 1.2 m in most of southern Ontario, deeper north; on undisturbed soil | Sonotubes with a flared base or poured pads; deck blocks only for low freestanding decks |
| Posts | 6×6 pressure-treated on a saddle, above grade, not buried in concrete | 4×4 is allowed for low decks but twists; 6×6 is the builder standard |
| Beams | Built-up 2×8 to 2×12 from the span tables, bolted or on post caps | Never notched into a 4×4 post; use a cap or a 6×6 notch |
| Joists | 2×8 at 16 inches is typical for 10 to 12 foot spans; from the tables | Joist hangers at the ledger and beam; blocking at mid-span over 8 feet |
| Ledger | Bolted or lag-screwed to the house rim joist at Code spacing, flashed, with the siding cut back | The failure point on most collapsed decks; never nails, never through siding or brick veneer |
| Lateral support | Freestanding decks need bracing; attached decks need lateral ties at the house | Required above about 600 mm; the inspector looks for it |
| Guards | Required over 600 mm above grade; 900 mm high to 1.8 m, 1,070 mm above; openings under 100 mm; built to resist the Code loads | Horizontal rails that can be climbed are restricted; cable rails need engineering in some municipalities |
| Stairs | Rise 125 to 200 mm, run at least 255 mm, treads 235 to 355 mm, width 860 mm minimum; handrail on one side over two risers | Stringers on a footing or a pad, not on the lawn |
Deck railing height and guard rules goes through the guard section line by line, and the deck building calculator sizes and prices it. The snow load calculator matters for a roofed deck.
Materials
Pressure-treated spruce or pine is the structure under almost every deck and the cheapest surface; it needs a stain every two or three years and will check and twist some. Cedar is softer and prettier and costs about double; only the heartwood resists rot. Composite and PVC decking cost two to three times treated lumber, need no finish, and are the right call for anyone who does not want to stain a deck every second summer; they still sit on a treated frame. Steel framing is an option for low maintenance and long spans. Fasteners and hangers must be hot-dip galvanized or stainless to survive the copper in modern treated lumber; the wrong screws rust out in a few years. The real cost of upgrades covers where the money matters.
What it costs in 2026
| Deck | Ontario range, contractor built |
|---|---|
| Pressure-treated, ground level, no guards | $35 to $55 per sq ft |
| Pressure-treated, raised, guards and stairs | $45 to $90 per sq ft |
| Composite surface and rails on a treated frame | $75 to $140 per sq ft |
| Cedar | $65 to $110 per sq ft |
| Add a roof or pergola | $8,000 to $30,000 |
| Permit and drawings | $300 to $1,500 |
Owner-built, the materials are roughly a third to a half of those numbers, and the building department inspects the footings before you pour, the framing before you deck it, and the finished guards.
The mistakes we get called to fix
- Ledger nailed through the siding with no flashing; the rim joist rots and the deck lets go.
- Footings on the topsoil or above frost; the deck heaves every spring and the door will not open.
- Posts buried in concrete; they rot at the ground line in ten years.
- Guards at 36 inches on a deck 7 feet up, with 5-inch baluster gaps.
- Stairs that land on grass with a 9-inch first step.
- Hot tub on a deck framed for people. Water is heavy: frame for it or set the tub on a slab.
- No permit, and a buyer’s home inspector who asks for one at resale.
Related guides on this site
Sources and further reading
Questions people ask
Do I need a permit to build a deck in Ontario?
Yes if the deck is attached to the house or is more than 600 mm (24 inches) above grade. Small, low, freestanding decks are often exempt, but municipalities vary; check before you build, and check zoning setbacks either way.
How deep do deck footings need to be in Ontario?
Below the frost line on undisturbed soil: about 1.2 metres in most of southern Ontario, deeper farther north. Deck blocks on grade are only for low freestanding decks.
How high does a deck railing have to be in Ontario?
A guard is required where the deck is more than 600 mm above grade: 900 mm high when the deck is up to 1.8 m above grade, 1,070 mm when higher, with openings that will not pass a 100 mm sphere and no climbable horizontal members.
How much does a deck cost in Ontario in 2026?
Roughly $45 to $90 per square foot for a contractor-built raised pressure-treated deck with guards and stairs, $75 to $140 with composite decking and rails. Owner-built materials run a third to a half of that.
Got a code question this page did not answer?
Ask it in plain English and the OBC Code Navigator answers with the Part, Section and Article from the Ontario Building Code. Two questions free. Your municipality and inspector still have the final word.
Reviewed and updated October 2026. Costs are Ontario ranges, not quotes; code references are to the Ontario Building Code in force at that date.
I found it interesting that you state that posts have to be inserted when the deck is more than 48″ off of the ground. My wife and I want to build a deck so we can have family over for barbeques during the summer. I will keep this in mind while we are planning the deck design.
It really helped when you talked about how it’s important to find the perfect spot for your new deck! Recently, my wife and I decided we’d like to renovate our home by installing a deck. We want to throw awesome BBQ parties, so we’ll be sure to look for a professional’s help. Thanks for the tips on deck designs and how to get the most out of ours.
I appreciated it when you shared that it is great to determine how you want the space to be arranged to accommodate conversations between small groups or in one large common area. My mother just mentioned the other day that she is planning to build a deck since she wants to have a proper place to have tea time outdoor. I will suggest to her to hire a reliable service that can help build it for her house.
What part of Ontario will let you put in a railing
on the horizontal as it shows in your first picture?
The distance between rails has to be equal or less than 4 inches.
I found it very interesting. This is very nice. I will keep this in my mind while we are planning the deck installation. Thanks for the sharing, Keep posting.
It was helpful when you said to check zoning ordinances. My brother was at my house last night for dinner, and he was talking about how he wants to build a deck for his house once he gets the lumber for the project. I’ll pass this information along to him as he gets ready to build a deck for his house.
Thanks for the reminder that the materials are also one of the things to consider when planning to build a deck. I want to find a good deck builder soon because I’m thinking about getting one built soon because I’m thinking improving the exterior look of my house. Having a deck in front of it will make it have a more classic look.