Critical measurements such as standard stairway width, riser height, and tread depth are not a matter of guesswork when you are remodeling or building a home. Staircase measurements are determined by common practice and by building code, which itself is often informed by generally approved practices. These rules are aimed at making staircases as safe as possible, so they should never be ignored or bypassed.
At the same time, staircase code measurements do allow for some flexibility, since most measurements are accompanied by minimums or maximums. A prime example is the standard stair width. Staircase code states that stairs must be 3 feet wide or wider. As long as the 3-foot width standard is met, you can expand the stairs' width as far as you wish.
Watch Now: How to Keep Your Stairs up to Code
Not only do the suggested standards help you build a safe staircase, but they also assist in building a comfortable staircase that you can use day in and day out, for years to come. Not all staircase measurements are universally the same in all parts of the country, though. Be sure to check with your permitting agency about building codes that apply to your locality. Many communities adopt the International Building Code wholesale, while others make modifications. In any case, the local code is what you must follow to pass inspections.
The following staircase code requirements pertain to straight-run stairs. Winding stairs and spiral stairs have several different code requirements.
Staircase Width: 36 Inches, Minimum
Staircase width refers to the side-to-side distance if you were walking up or down the stairs. This distance must be at least 36 inches and does not include handrails.
Stairs that are too narrow are a hazard in many ways. Narrow stairs make it more difficult to carry items up and down the stairs. Awkward positioning of these items may lead to falls. Most importantly, stairs that are not wide enough can be dangerous during a fire, as they might impede escape.
Staircase Riser Height: 7 3/4 Inches, Maximum
A stair riser is the back, vertical part of a step. Staircase riser height translates to the distance you move your foot either up or down from one step to an adjacent step. This should be no more than 7 3/4 inches.
This code specification was developed to prevent stairs from being too high if walking upstairs or too low if descending. Additionally, the riser measurement of all of the treads should be as close as possible to identical. The greatest riser height within a flight of stairs cannot exceed the smallest by more than 3/8 inch. A stairway in which there is a noticeable variation between the risers is a safety hazard.
If the stairs have open risers, the open space between the steps cannot be large enough to allow a 4-inch sphere to pass through. In other words, the space must be slightly less than 4 inches high.
Staircase Tread (Run) Depth: 10 to 11 Inches, Minimum
A step tread is the flat, horizontal surface that you walk on. The tread depth is the distance from the front edge, or nosing (a tread projection that overhangs the riser below), of one step to the front edge or nose of the next step, measured horizontally. This distance must be at least 10 inches. However, if the steps do not have nosings, and the steps have solid risers, not open risers, the minimum tread depth is 11 inches.
Staircase risers should be adequately deep to allow a majority of your foot to have enough room to rest on the stair. Stair tread depth is more of an issue for descending, rather than ascending, stairs. Further, the tread measurement of every tread in a stairway should be as close as possible to identical. The greatest tread depth within a flight of stairs cannot be more than 3/8 inch larger than the smallest tread depth.
Nosings must project at least 3/4 inch and no more than 1 1/4 inches beyond the riser below. The largest nosing projection cannot be more than 3/8 inch greater than the smallest nosing projection.
Staircase Headroom: 6 Feet, 8 Inches, Minimum
At any point on the staircase, a user should have a full 6 feet, 8 inches minimum vertical distance between the top of the stair tread and the bottom of the ceiling.
Anyone walking up or down the stairs should have plenty of clear headroom without having to duck down. Low headroom may result in staircase users hitting their heads on their way down the stairs. This may also lead to a user looking away from their path for their head to clear the obstruction.
Every staircase should have a landing at the top and bottom. The width of the landing, measured perpendicular to the direction of travel, must be no less than the width of the staircase. The minimum depth, measured in the direction of travel, is 36 inches.
The treads and landings of all straight-run staircases should have an artificial light source capable of lighting the treads and landings to no less than 11 lux (approximately 1-foot candle). For any staircase that has six or more risers, there must be a wall switch at each floor level to control the light source.
Common Stairway Terms
- Stringer: The stringer is the entire sawtooth-shaped member upon which risers and tread rest. You will need at least two per staircase. Some utility stairways, such as basement stairs or deck stairs, may not use a sawtooth stringer design. Instead, they may use solid side stringers that anchor the treads using metal connectors.
- Riser: A riser is the vertical measurement of each stair. Risers can either be enclosed or left open, as in deck stairs or basement stairs. The board that encloses the back of the step is also called a riser.
- Tread: The tread is the horizontal section of each stair, sometimes called the run. This is the surface that the user steps on.
- Landing: A landing is a platform between two flights of stairs. It is also the approach space at the top and bottom of the stairs.
- Nosing: The section of the tread that overhangs the riser below.
- Staircase width: Width refers to the length of risers and treads from side to side. For code requirements, the minimum staircase width is the horizontal dimension between the sidewalls of a staircase, measured above the handrail(s).
- Headroom: Headroom is the vertical dimension from the stair treads to the ceiling directly above. It is measured from a sloping imaginary line that connects all of the stair nosings.