Safety with Every Step: Stair Tread Depth vs. Stair Riser Height

Rise and Run for Stairs

Following building codes specific to stairs is essential in any new construction or remodeling project to ensure safety for everyone. This article outlines stair code requirements to make it easy for builders to meet relevant regulations and safety standards.

Building Codes for Stair Tread Depth

Compliance	Stair Depth	Riser Height
OSHA	9.5″ (240 mm) Minimum	9.5″ (240 mm) Maximum
IBC	11″ (279 mm) Minimum	4″ (102 mm) – 7″ (178 mm) Minimum – Maximum
IBC Occupancy Exceptions Group R-2, R-3, and U (see chart below)	10″ (254 mm) Minimum	7-3/4″ (197 mm) Maximum

Occupancy Classification	Group
Residential transient – occupancies containing sleeping units where the occupants are primarily transient. Structures like hotels, motels, and boarding houses	R-1
Residential permanent – occupancies containing sleeping units or more than two dwelling units where the occupants are primarily permanent	R-2
Residential group – occupancies where the occupants are primarily permanent and not classified as Group R-1, R-2	R-3
Utility and Miscellaneous – General Buildings and structures of an accessory character and miscellaneous structures not classified in any specific occupancy shall be constructed, equipped, and maintained to conform to the requirements of this code commensurate with the fire and life hazard incidental to their occupancy.	U

Standard Stair Tread Depth

The Industrial Building Code (IBC) and the Occupational Safety and Health Administration (OSHA) have varying tread depth specifications for various stair types. In its 2017 revision to the required walking-working surfaces, OSHA added minimum tread depths. On the other hand, IBC has long mandated a minimum tread depth.

OSHA and IBC use research on stairways with varying tread and riser dimensions to determine the minimum tread depths and maximum riser heights.

According to OSHA, a standard stair refers to any fixed or permanent stairway aside from alternating tread stairs, ship stairs, or spiral stairs. Standard stairs must, at minimum, maintain a tread depth of 9.5 inches, or 24 cm, under OSHA 1910.25(c)(3).

IBC 1011.5.2, on the other hand, stipulates that stair treads must be at least 11 inches (27.94 cm) deep, measured horizontally between the vertical planes of the foremost projection of consecutive treads and perpendicular to the leading edge of the treads.

The minimum tread depth must be 10 inches in all group R-3 occupancies, all dwelling units in R-2 occupancies, and all group U occupancies supplementary to either group R-3 occupancies or individual dwelling units in R-2 occupancies. Most multi-family dwellings intended to get occupied permanently must adhere to the standard of a minimum tread depth of 10 inches (25.4 cm).

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Building Codes for Stair Riser Height

Standard stairs must have a maximum riser height of 9.5 inches (24 cm) following OSHA 1910.25(c)(2). IBC 1011.5.2 stipulates that the minimum and maximum stair riser heights must be 4 inches (10.16 cm) and 7 inches (17.78 cm), respectively.

In groups R-3, R-2, and U auxiliary occupancies, the maximum riser height is 7-3/4 inches.

Conclusion

The purpose of building codes for metal stairs is to ensure the safety of everyone who uses them. Any safety risk will significantly decrease if all steps and stairs have the same tread depth and riser height parameters.

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