Stairs are among the most inspected parts of any job, and among the most dangerous when they're wrong. Small inconsistencies trip people, because we stop looking at our feet after the first step or two. These are the core rules for stairs within a house under Part 9 of the National Building Code of Canada 2020 (NBC). Always confirm with your municipality’s building department, since each province adopts the NBC with its own changes, and Ontario, BC, Alberta and Quebec publish their own codes.
The key dimensions
| Item | Rule |
|---|---|
| Rise | 125–200 mm (about 5" to 7⅞") |
| Run | 255–355 mm (10" to 14") |
| Tread depth | At least the run, and no more than 25 mm (1") deeper |
| Width | 860 mm (2′10″) minimum |
| Headroom | 1950 mm (6′5″) minimum |
| Height of one flight | 3.7 m (12′1″) maximum |
| Handrail height | 865–1070 mm (34" to 42") |
| Guards | Where the drop is over 600 mm (2 ft); at least 900 mm (35½") high inside a house |
| Guard openings | 100 mm (4") sphere must not pass |
Laying out a flight
- Measure the total rise from finished floor to finished floor. Allow for floor finishes at both ends: carpet, tile and underlayment all change it.
- Divide by the maximum riser and round up to get the number of risers.
- Divide the total rise by that number for the exact riser height.
- Treads = risers − 1. Total run = treads × tread depth.
- Check the total run fits the space, and check headroom along the whole flight against the floor or ceiling above.
- Work out the stringer length and the angle, then mark out a pattern stringer.
A comfortable stair often lands around a 7–7½" (180–190 mm) rise with a 10½–11" (265–280 mm) run. The steeper the stair, the more it saves space but the harder it is to use, especially for children and older people.
Winders and landings
Winders (tapered treads that turn a corner) save space but need care. Under the NBC, each winder must turn through exactly 30° or 45°, and one set of winders can turn no more than 90°. Landings must be at least as wide as the stair and long enough to meet the code, and clear of door swings.
Handrails and guards
Inside a house, a stair needs a handrail on at least one side, 865–1070 mm (34" to 42") high, unless it has only one or two risers; exterior stairs serving a house need one once they have more than three risers. Guards are required on open sides where the drop is more than 600 mm (2 ft): at least 900 mm (35½") high inside a house, with no opening a 100 mm (4") sphere can pass. Guards must resist a set load, so fix posts and balusters properly, not just with nails into the trim.
Common failures
- The top or bottom riser is a different height because the floor finish wasn't allowed for.
- Headroom too low under a beam or at the edge of the stair opening.
- Balusters spaced just over the 100 mm (4") limit.
- A missing handrail where one is required, or handrails that stop short of the last riser.
- Nosings missing or inconsistent, which changes the effective tread depth.
- Gaps under open risers that a child could slip through.
External steps and decks
The same principles apply outside, and consistency matters even more on wet, uneven ground. Make every step the same, give treads a slight fall so water runs off, and add lighting for steps used after dark.
Pricing stairs
Stairs take far longer per material dollar than most carpentry. Allow time for setting out, cutting a pattern stringer, test fits, and the finish work on treads, nosings and handrails. A stair that's "nearly right" has to be rebuilt, so price enough time to get it right first.
The stair calculator runs these checks as you type, the baluster calculator spaces guards to the limit, and the ramp calculator covers access ramps.
A worked example
A floor-to-floor height of 108" (2743 mm). 108 ÷ 7⅞ = 13.7, so 14 risers at 7.71" (196 mm). That gives 13 treads; with a 10½" (267 mm) run, the total run is 136½" (11 ft 4½ in). The angle is about 36°, comfortably within the rules. A 36" wide stair takes three stringers.
Common questions
Can I build a steeper stair to save space?
Only within the limits above. The code relaxes the rules only for a few special cases, such as stairs to unfinished spaces, so check with your building department before planning anything steeper.
Do deck and porch stairs follow the same rules?
Yes. Exterior stairs serving a house use the same rise and run limits, need a handrail once they have more than three risers, and need guards where the drop is more than 600 mm (2 ft). Footings for deck stairs must go below frost depth, like the deck itself.
Are open risers allowed?
Yes, as long as the gap between treads doesn’t let a 100 mm (4") sphere through. A riser board or a horizontal bar closes the gap.
How high must a handrail be?
Between 865 and 1070 mm (34" and 42") above the line of the nosings under NBC 2020, continuous for the length of the flight. Some provinces still use the older 965 mm (38") maximum, so check yours.
How deep can a tread be compared with the run?
The tread, including the nosing, must be at least as deep as the run and no more than 25 mm (1") deeper. That keeps nosings short, so people don’t catch their heels on the way down.
Before you build
Mark out the stair at full size on the floor or a wall, including the floor finishes, to check headroom and landing space. Confirm the design with the inspector before cutting, especially for winders, open risers and attic conversions.
This guide is general information for estimating. It is not engineering, legal or tax advice. Check local codes and your inspector for your project.