Most deck how-to guides online are written for the United States, where the guard rule and the frost depth are different. This one uses the Ontario Building Code numbers and the span tables our own municipalities publish, in the order you will need them on site. If you would rather hand it off, that is what we do every week.
The Ontario rules on one page
These are the numbers an inspector checks on a typical house deck. Clause numbers follow the Ontario Building Code text published on buildingcode.online. Your building department has the final word, so check your drawings with them.
| Item | Rule | Source |
|---|---|---|
| Building permit | Needed for any deck attached to the house, and for freestanding decks over 10 m2 and more than 61 cm above grade in Oakville. Hamilton and Burlington apply similar triggers, so ask before you build. | Oakville's deck permit page |
| Footing depth | 1.2 m (4 ft) in clay or where soil is unknown, and never less than frost depth | Article 9.12.2.2 |
| Footings on blocks | Allowed only for decks of one storey, 55 m2 or less, 600 mm or less to the underside of the joists, no roof, not attached | Article 9.12.2.2, sentence 7 |
| Guard required | Where the deck is more than 600 mm above the ground next to it | Article 9.8.8.1 |
| Guard height | 900 mm where the deck is no more than 1,800 mm above the ground, 1,070 mm above that | Article 9.8.8.3 |
| Stair rise and run | Rise 125 to 200 mm, run at least 255 mm | Table 9.8.4.1 |
| Handrail | Not required on exterior stairs of a house with 3 risers or fewer; required from 4 risers | Article 9.8.7.1 |
| Joist and beam size | Spans must meet the span tables | Article 9.23.4.2 |
Our deck stairs code guide covers stair layout in detail, and the permit guide for Hamilton, Burlington and Oakville covers fees and timelines.
How to build a deck, step by step
- Check zoning and the permit first. Setbacks from the lot lines and lot coverage limits apply even when no permit is needed. If a permit is needed, the drawings come before the shovel. Oakville publishes deck sample drawings that show exactly what a permit set includes, and they are a good model wherever you live.
- Book locates. Request a locate from Ontario Dig Authority (formerly Ontario One Call) before you dig. It is free, takes up to 5 business days, and does not cover private lines like a gas line to a BBQ, which you arrange separately.
- Lay it out. Mark the corners with batter boards and string. Square the layout with the 3-4-5 method (3 ft along the house, 4 ft out, 5 ft across) or measure both diagonals until they match.
- Dig and pour footings. Go at least 4 ft below grade onto undisturbed soil, with a cardboard form tube (Sonotube) or a belled footing. Oakville's drawings add one rule people miss: any footing within 4 ft of the house must go down to the level of the house footing, because the soil there was dug out and backfilled when the house was built.
- Set posts on metal bases. Anchor a galvanized post base into each pier, then stand 4x4 posts at minimum, or 6x6 for taller decks. Keep wood out of the concrete. Freestanding decks more than 24 in above grade need bracing so they cannot rack.
- Attach the ledger, or skip it. On an attached deck the ledger is bolted through to the rim joist or into the foundation. Oakville's detail shows a double 2x6 ledger lag bolted with 1/2 in bolts at 32 in on centre into solid masonry or concrete. Strip the siding where the ledger goes and flash above it so water cannot reach the house framing. Many builders now make raised decks freestanding with their own beam near the house instead.
- Build the beam. Nail or screw two or three plies together and seat the beam on the posts with a post and beam connector. A beam can overhang its last post by no more than 1 ft in Oakville's tables.
- Hang the joists. Use joist hangers at the ledger, run joists over the beam, and check the span table for size and spacing. Put joist tape on top of every joist before the decking goes down. It keeps water out of the screw holes and adds years to a pressure-treated frame.
- Lay the decking. Leave a gap between boards for drainage, stagger the butt joints, and follow the manufacturer's joist spacing for composite (often 16 in, closer for diagonal patterns).
- Build the guards and stairs. Guards go on wherever the drop is more than 600 mm. Openings must not pass a 100 mm sphere. Oakville requires a stamped engineered detail for any guard that uses a non-wood component or stands higher than 3 ft 6 in, such as a privacy screen that doubles as a guard.
- Book the inspections. A permitted deck is usually inspected at the footing holes before you pour, at framing before the decking covers it, and at the end. Missing the footing inspection is the costly one.
Worked example: a 12 x 16 ft deck
Say the deck runs 16 ft along the back of the house, projects 12 ft into the yard, is attached with a ledger and sits about 30 in above grade. Here is how it sizes out with Oakville's published tables. Treat it as a planning example, not an engineered design: your permit drawings decide.
| Part | Choice | Why it works |
|---|---|---|
| Joists | 2x8 at 16 in on centre | 2x8 at 16 in may span 11 ft 9 in. The beam sits 10 ft 8 in from the house, leaving a 16 in cantilever, within the limit of 16 in or 1/7 of the joist length. A deck that needs a guard needs at least 2x8 joists anyway. |
| Beam | Two-ply 2x10, three posts | Posts at 1 ft, 8 ft and 15 ft along the beam give 7 ft spans and 1 ft overhangs. A two-ply 2x10 may span 8 ft 10 in when it carries 8 ft of joist length. |
| Middle footing | 14 in round, 4 ft deep | About 7 ft of beam x 6.7 ft of joist x 40 lb/sqft is roughly 1,870 lb. A 14 in round footing is rated 2,233 lb on Oakville's table. |
| End footings | 12 in round, 4 ft deep | About 4.5 ft of beam x 6.7 ft x 40 lb/sqft is roughly 1,200 lb, under the 1,640 lb rating of a 12 in footing. |
| Ledger | Double 2x6, 1/2 in bolts at 32 in on centre | Oakville's standard detail for a ledger on a concrete or solid masonry foundation, flashed above. |
| Guard | 900 mm (about 36 in) minimum | The deck is more than 600 mm above grade but less than 1,800 mm, so the lower guard height applies. |
| Stairs | 4 risers of about 190 mm, 3 treads of 280 mm, one handrail | 762 mm of rise divided by 4 is 190 mm, inside the 200 mm limit. Four risers means a handrail is required. |
Add a hot tub, a roof or a privacy wall and the numbers change. Footings under a roof or hot tub have to carry that weight too, which usually means engineered drawings.
What a deck costs, built for you or by you
| Material | Installed, per sqft | 12 x 16 ft deck (192 sqft) |
|---|---|---|
| Pressure-treated | $30 - $55 | $5,800 - $10,600 |
| Cedar | $45 - $75 | $8,600 - $14,400 |
| Composite | $60 - $110 | $11,500 - $21,100 |
Each footing adds $250 to $650 to a contractor's quote, and the permit itself is usually $200 to $700. Building it yourself saves the labour, but not the permit, the footings or the inspections. Our deck cost guide breaks the price down further, and the deck cost calculator gives a number for your size. Building low and freestanding? A floating deck on deck blocks skips the footing line entirely if it meets the code conditions.
Mistakes inspectors catch
- Shallow footings. Anything above 4 ft heaves in our clay, and the deck drifts out of level within a few winters.
- Ledger on the siding. A ledger has to bear on the rim joist or foundation, with flashing. Screws through vinyl siding into sheathing do not count.
- Footings near the house too shallow. Within 4 ft of the foundation, the soil is backfill. Oakville wants those footings down to the house footing.
- Short guards. The guard height is measured from the deck surface, so measure after the boards are on.
- Uneven stairs. Risers must match within a few millimetres, and the bottom step must land on a solid pad, not soil.
- Posts buried in concrete. Wood set in concrete holds water and rots at the top of the footing. Use a metal post base.
Frequently asked questions
Do I need a permit to build a deck in Ontario?
Usually, if the deck is attached to the house or more than about 600 mm (24 in) above grade. Oakville, for example, requires a permit for any attached deck and for freestanding decks over 10 m2 and higher than 61 cm. Check with your own building department before you start.
How deep do deck footings need to be in Ontario?
At least 1.2 m (4 ft) below grade in clay or where the soil is unknown, under Building Code Article 9.12.2.2, and never less than the local frost depth. Low freestanding decks that meet the conditions in sentence 7 can sit on deck blocks instead.
What size joists do I need for a deck?
That depends on the span. Oakville's table allows 2x6 to 9 ft 4 in, 2x8 to 11 ft 9 in, 2x10 to 13 ft 9 in and 2x12 to 15 ft 5 in at 16 in on centre. Any deck that needs a guard needs at least 2x8 joists.
When does a deck need a railing in Ontario?
When the deck surface is more than 600 mm above the ground next to it. The guard must be at least 900 mm high if the deck is no more than 1,800 mm above the ground, and 1,070 mm if it is higher.
Can I attach a deck to my house?
Yes, with a properly bolted and flashed ledger on the rim joist or foundation, and a permit. Many builders now prefer a freestanding deck with its own beam near the house, which avoids opening up the wall.
How long does it take to build a deck?
A crew usually needs 5 to 12 working days on site for a typical house deck. Add 3 to 6 weeks for permit approval before work starts.
How much does it cost to build a 12 x 16 deck?
About $5,800 to $10,600 installed in pressure-treated wood in 2026 Ontario, $8,600 to $14,400 in cedar and $11,500 to $21,100 in composite, before permit fees.