Most residential building codes rely on the standards developed by the International Code Council (ICC) and International Building Code (IBC). Note that when looking for commercial stair standards, one must look at the International Building Code (IBC). In this post we will be looking at the code standards related to residential stairs in accordance with the International Residential Code (IRC).
Stair Width – The base width for flights of stairs shall not be less than 36 inches clear. Maximum 4-1/2 inch handrail projection into stair width, on either side. Presently the clear width of the stairs shall not be less than 31 ½ inches and when handrails are provided on both sides, the clear width shall not be less than 27 inches.
Headroom for Stairs – The headroom for stairways measured vertically from the sloped line adjoining the tread nosing or the floor surface of the landing should be no less than 6 feet 8 inches
Vertical Rise for Stairs – The code establishes a maximum vertical height of 147 inches (12 feet 3 inches) between landings or floor levels for a flight of stairs. If the distance between floor levels exceed 147 inches, the flight of stairs would require a level landing somewhere in-between to break up the flight of stairs.
Stair Riser Height – The code specifies that risers should not be more than 7 ¾ inches in height and that any variation of risers within a flight of stairs should not be more than ⅜ inch. Note that dimensions here should be taken excluding carpets, rugs, or runners.
Stair Tread Depth – As for stair treads the depth should not be less than 10 inches however this will require nosing projections. To avoid having to install nosing the code requires the depth of the tread to be no less than 11 inches. Nosing that is beveled should not exceed ½ inch or the radius of curvature not more than 9/16 inch. The projection of nosing shall not be more than 1 ¼ inches and no less than ¾ inch. Again the tolerance of treads or nosing should be no more than ⅜ inch