Residential Stair Code Check: Rise, Run, and Nosing

A simple but helpful summary of what the IRC code says about building stair rise, run, and nosing.

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The International Residential Code (IRC) has specific instructions on the way stairs can be built. Here&#;s a clear summary of what the IRC code says about stair codes for rise, run, and nosing.

(Note: not every municipality adopts every part of every code, and some cities and states add in their own additional rules. Bottom line, check with your local building official before cutting those stringers or forming that stoop.)

IRC Stair Rise Requirements

The IRC code does not allow a distance greater than 7-¾ of an inch from one step/tread to the next.

IRC Stair Run Requirements

The &#;run&#; is the measurement of the tread, which needs to be a minimum of 10 inches if the tread has an overhang on it (see image).  This is a measurement from the nose of the tread to the nose of the tread.  You are not required to have a nosing/overhang on your stair treads. But if your stairs don&#;t have a nosing you are required to have a tread that is at least 11 inches long.

Variances

From the top flight of stairs to the bottom of the stairs, each individual riser cannot exceed a difference of 3/8 of an inch.

IRC Stair Nosing Requirements

The nosing on treads, believe it or not, has a code minimum and maximum of how far the nosing projects over the next stair. Nosings are required to overhang a minimum of ¾-in. to a maximum of 1-¼-in.  Also the maximum nosing radius cannot exceed 9/16 of an inch.

Remember to Include Flooring

All of these measurements include the finished flooring, so don&#;t forget to take those thicknesses into account when planning your stair dimensions.

Here are three reference numbers for the codes pertaining to rise, run, and nosing in a straight run of stairs:

R 311.7.5.1

R 311.7.5.2

R 311.7.5.3

You can view the code in its entirety here.

The International Building Code (IBC) has many requirements for stairways, and you must also meet the required number of means of egress and areas of refuge for wheelchairs.

Width (IBC .2)

The number of occupants on each floor will determine the required width of the stairs. In short, the width is calculated by multiplying the occupant load served by such stairs by a factor of 0.3 inch per occupant. However, the very minimum width between handrails is 44 inches. You must calculate the IBC stair width for multi-story stairways versus single-story stairways.

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Width = 0.3 x floor&#;s occupant load

Weight (live load) Capacity (IBC )

Uniform live loads. (IBC .3) &#; The live loads used in the design of buildings and other structures shall be the maximum loads expected by the intended use or occupancy but shall not be less than the minimum uniformly distributed live loads as listed in the below table.
Concentrated live loads. (OBC .4) &#; Surfaces shall be designed to support the uniformly distributed live loads or the concentrated live loads, whichever produces the greater load effects. Concentrated live loads are uniformly distributed over an area of 2 1/2 feet by 2 1/2 feet (762 mm by 762 mm) and shall be located so as to produce the maximum load effects in the structural members.

UseUniform (PSF)Concentrated (Pounds)CatwalkStairs & Exits*Fire Escapes100&#;Walkways and Elevated Platforms
Other than exitways60&#;* The minimum concentrated load on stair treads are based on an area of 2&#; x 2&#;

Read More: Differences in IBC and OSHA Requirements

Headroom (IBC .3)

Stairways are required to have a headroom clearance of 80 inches from the edge of each stair nosing measured vertically up to the ceiling. The clearance must continue past the last step for at least one stair tread depth.

Riser Height and Tread Depth (IBC .5)

The step height, or the riser height, must be no less than 4 inches and no greater than 7 inches. The minimum tread depth is 11 inches. If the stairs have nosings, you measure from the leading edge of the nosing to the edge of the next step&#;s nosing.

ComplianceStair DepthRiser HeightOSHA9.5&#; (240 mm)
Minimum9.5&#; (240 mm)
MaximumIBC11&#; (279 mm)
Minimum4&#; (102 mm) &#; 7&#; (178 mm)
Minimum &#; Maximum

More on Stair Tread Depth vs. Stair Riser Height

Uniform Dimensions (IBC .5.4)

IBC stairs must have the same riser and tread dimensions throughout the stairway. The difference between the largest and smallest tread depth or riser height cannot exceed 3/8 inch.

Solid Risers (IBC .5.5.3)

Solid risers are required for IBC stairs except for means of egress stairways as long as the opening between treads does not allow a 1/2 inch diameter sphere to pass through.

Landings (IBC .6 & .6.3)

• There must be a floor or landing at the top and bottom of each stairway.
• The width of landings must be as wide as the stairways that they serve.
• Where the stairway has a straight run, the landing does not need to be more than 48 inches deep.
• Doors opening onto a landing cannot reduce the minimum landing width to less than half.
• When the door is fully open, it cannot project more than 7 inches into the minimum dimensions of the landing.
• If a wheelchair space is required for an area of refuge, the wheelchair space cannot be located in the required minimum landing dimensions or door swing.

Stairway Rise (IBC .8)

Every 12 feet of vertical rise, the stairway must have a landing.

Walking Surface (IBC .7.1)

• The slope of the walking surface cannot be greater than 1:48 in any direction.
• You can have walking surfaces with openings, but the openings cannot allow a 1/2-inch diameter sphere pass through.
• If the stairs are outside, the design of the IBC stairs cannot allow water to accumulate on the walking surface.

Guards (IBC .13 & )

Guards are required along all open-sided walking surfaces of the stairway, including landings and stairs. The guard height must be at least 42 inches high, and it is measured vertically from the leading edges of the tread nosings or from the landing surface. Any spacing in the guards must be less than 4 inches. Shown below, the guards are vertical balusters, but guards can also be pieces of glass, wire, etc.

Handrails (IBC .11 & )

Handrails must be on both sides of the IBC stairs, and they must comply with these additional handrail requirements. You could compare all the ADA, OSHA and IBC stair railing height requirements here.

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