R311.7.5.1

Section R311.7.5.1 is titled 'Risers' and covers the requirements for the vertical component of steps in a stairway. A maximum height, method of making height measurement, consistency of height, maximum slope (from vertical), and maximum openness of risers are established. The purpose of this section is to reduce trip and fall hazards. This section has two exceptions which both deal with spiral stairways; the first allowing for unlimited open area risers and the second cross-referencing another section of the code for riser height. The purpose of these exceptions are to allow for the use of and practical application of spiral stairways.

The model shows a partial stairway with the maximum allowed riser height depicted, risers adjusting from a zero to 30° slope, 4" spheres in front of the open risers, and a partial spiral stairway. Notice that the riser height is different for the top group of steps than the bottom group. Separate flights within the same stairway are allowed. (See the definitions of 'flight' and 'stairway' in chapter 2). The top flight, of which all risers are greater than 30" above the floor below, shows that the 4" spheres will not pass through them, making this part of the model compliant with its related code section. The spiral stairway also has open risers, that a 4" sphere would pass through, which is allowed per the exception.

Not shown in the model is the requirement for consistent riser heights within a flight. An inspector needs to measure every riser in every flight to assure that in each flight, the largest riser height doesn't exceed the smallest by more than 3/8".