The Height of Stair Treads

Codes

• Local, state and some federal construction codes take their cues from the International Residential Code, or IRC, developed by the International Code Council. Established in 1994, this nonprofit member organization is “dedicated to developing a single set of comprehensive and coordinated national model construction codes.” It also develops building codes, such as the International Fire Code and International Building Code. An expert carpenter or contractor who learns to build stair treads to code in Boston can use the same expertise in Chicago or Seattle. The organization also provides educational programs, certification, plan reviews and informational videos to assist with home construction.

Basics

• Treads are the flat parts that act as steps on a stairway. The 2012 IRC calls for their minimum depth to be 10 inches. The depth of all the treads in a flight of stairs must not vary by more than 0.375 inches. Risers are the vertical walls that separate treads and must have a maximum height of 7.75 inches. They must also be consistent across the stairway, with a maximum difference of 0.375 inches. Risers can also slope but with a maximum angle of 30 degrees from the vertical. Open risers must not have an opening that allows a 4-inch diameter sphere to pass. This prevents children’s heads from becoming stuck in the spaces.

Nosings

• The nosing is the curved protrusions of a stair tread that extends toward the climber. It is only required on treads that are fewer than 11 inches deep. It must have a radius of 0.5625 inches or less. A stairway with solid risers can have risers between 0.75 to 1.25 inches thick. Nosing projections must not vary by more than 0.375 inches across the steps, floors and landings. They may have bevels of 0.5 inches or less.

Disabilities

• The Americans with Disabilities Act or ADA also defines stair standards based on the IRC. These regulations must be followed by commercial establishments but are optional for residential construction. However, disabled homeowners or those who are interested in selling to that market may find these guidelines helpful. Wheelchair users cannot use stairs, but people with balance issues can. So, while specifications for stair widths, tread depths and riser heights remain the same as the IRC, the ADA demands two handrails, one on either side of the stair, which differs from the one-railing requirement by the IRC.