AUST – HENDRY building surveyors advise that an aisle in a theatre or auditorium must either be sloped at 1:8 or less or the floor must be stepped. Stepped floors are common and the maximum angle must not exceed 30 ̊ when a line is drawn over the consecutive nosings of the steps.
The height difference of the stepped floors must not exceed 600mm. Stepped floors therefore introduce a need to have additional steps in aisles that are provided for both escape reasons and functional access reasons.
One intermediate tread is required when the step exceeds 230mm up to a height of 400mm and two treads are required when the height exceed 400mm, noting that the maximum step height is 600mm.
Immediately, for a step height of 600mm, 2 treads are needed which results in a riser height of 200mm. Similarly, if the step height is 400mm, only one tread is needed and the same riser height is the result. The step height configurations in theatres and auditoriums are treated differently to a normal stair flight (or steps) where 190mm is the maximum rise height permitted and the 2R+G calculation is not applied.
Additionally, no handrails are provided to sloped or stepped floors and the tread width in stepped aisles must not be less than 270mm, no opening in the riser can exceed 125mm and aisle lights must illuminate the treads and the full length of the aisles.
A further point of difference is that the treads do not require non-slip nosings or surfaces although it may be good practice to provide a tread nosing to reduce a common law risk. Reference to AS 1428.1 is also good practice when considering the design for theatres and auditoriums.