Standard Stair Dimensions for Indoors

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What You'll Need
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All flights of stairs are not created equal. Some require effort to climb, others give us the feeling we're about to trip. Some get the height balance just right, so you almost feel like you're walking normally as you ascend or descend them.

The difference is all in the planning of the staircase. Given their height, stairs can cause serious safety hazards, so most municipalities have building codes for dimensions and other related specifications. If you're constructing a new staircase, you need to know what these are so you can follow them accurately.

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About the Code

Many communities adopt the IRC code (International Residential Code) with no modifications. Others use it as a base but alter it to create their own local code, which you must follow to pass inspections.

The code establishes a set of standards to help you build a safe staircase, and assists in building a staircase that will provide maximum physical comfort over years of frequent use.

person measuring the height of a stair rise

Stair Width, Run, and Rise

Width

According to the IRC, the width of staircases is limited only by a minimum of three feet, which is the narrowest a stairway can be without causing safety issues for most users. There is no maximum width, except the limits imposed by structural design.

The 36-inches (or more) staircase width refers to the side-to-side width, with the idea being that you should be able to safely move up and down, even while carrying awkward or large items. That width does not include handrails. A staircase narrower than this might be dangerous for routine use, and could potentially impede swift exit during an emergency like a fire.

Tread

The stair tread is the flat horizontal surface you set your foot on to go up or down the stairs. It's measured horizontally from the edge of its nosing up to the nosing of the next tread up. This measurement is the tread depth and should be no less than 10-inches with a proper nosing and an open riser (without a solid riser).

Where the stair tread is flush with its preceding riser or does have a solid riser, the treads require a minimum depth of 11-inches. This is to allow enough room for the majority of a foot to rest on the tread. Every tread on a stairway should be the same depth, with no more than a 3/8-inches difference between the widest tread and the smallest one.

The stair tread nosing should extend between 3/4 inch and 1 1/4 inch beyond the solid riser below.

Rise

Staircase risers (solid or open risers), which are measured vertically from the top of one tread to the top of the adjacent step, can never be more than 7-3/4 inches high. In the case of open risers, however, the opened space should be less than four inches, and should be at least partially covered if any wider. To reduce the safety issues, the maximum difference between the greatest and the smallest riser height is set at 3/8 inches.

clean wood stairs with white riser molding

Tread and Riser Ratio

The floor-to-floor distance measured between the two floors to be linked with the staircase determines the riser and tread dimensions of the staircase. Using seven inches as the riser height to divide with, if you have a total riser height of 109 inches between two floors, dividing 109 by seven equals 15.57. That means you'll need at least 15 full risers for your staircase. To find the width of each riser, divide the floor-to-floor height again by the number of risers—in the case of the example, 109 divided by 15, to get the height of 7.27 inches 7-1/4 inches (or slightly more).

There are several formulas to determine the width of the tread. The most common and preferred formula is the sum of two times the rise plus the run, resulting for this case in a width between 24 and 25 inches.

Two times the rise of 7.25 is 14.5 inches, which subtracted from 25 results in 10-1/2 inches. That's not deep enough by code if you have solid risers. Therefore, in this case, the number of risers should be increased, which would consequently reduce the risers' height to increase the run to 11 + inches when using the formula based on the 24/25 inches. Having 16 instead of 15 risers reduces the riser height to 6.8 inches or 6-13/16 inches, with a resulting tread run between 11 and 11-3/8 inches.

Staircase Complements

Landings

There must always be a landing at the top and bottom of every staircase, and it must be as wide or wider than the staircase's width (measured perpendicular to the direction of travel) with a minimum depth of 36-inches, measured in the direction of travel.

stairway landing with finished wood treads

Handrails

The staircase handrail should never exceed 38-inches in height. This is the vertical length measured from the top of the leading edge of the stair nosing to the railing top. The same measurement applies throughout the staircase at all of the stair nosings, thus resulting in a railing that is parallel to the stairs. For a handrail installed against a wall, the US standard for handrails is between 30 and 38-inches, with a minimum of 1-1/2 inches space from the wall. For an opened staircase, the handrail height, measured between the nosing and the top of the railing, ranges between 34 and 38-inches.

The Canadian Difference

In Canada, however, for railings installed either against a wall or on opened staircases, the code limits the railing's minimum height at 32-inches and the maximum allowable height at 36-inches, instead of 38-inches as in the US. Your regional code may vary, so it's worth looking up.

Spindles

The building codes mandate that handrail spindles be installed with a maximum four-inch gap between them, still allowing for visibility between spindles, but mainly for preventing small children from slipping through or getting stuck in between.

With regard to headroom clearance, there must be a minimum vertical distance of 6 feet 8 inches between any point of the floor (landings, nosings) up to any obstacle at the ceiling. This clearance will prevent anyone's head from hitting the ceiling or any overhead obstructions.

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