R311.7.5.3

Section R311.7.5.3 is titled 'Nosings' and covers the requirements for projections of treads over the tread below. Shape limitations, minimum and maximum projection dimensions, and consistency of projection dimensions within a stairway are established. The purpose of this section is to reduce trip and fall hazards. This section has an exception which allows for no projection when the treads depths are 11 inches or greater. The purpose of this exception is to allow for no projection because the risk of trip and fall with a larger tread depth is reduced.

The model shows 3 tread examples. The bottom tread shows a highlighted projection with a circular radius of 9/16". The middle tread shows a highlighted 1/2" beveled projection. The backside shows the minimum and maximum allowed dimensions for tread projections. The top tread shows the exception allowance for no projection with a tread depth equal to or greater than 11".

Not shown in the model is the requirement for consistent nosing depth within a stairway. An inspector needs to measure every nosing projection in every stairway to assure that in each stairway, the largest nosing doesn't exceed the smallest by more than 3/8". Take note that nosings must be consistent for an entire stairway, whereas riser heights and tread depths only have to be consistent within a flight.