R311.7.11

Section R311.7.11 is titled 'Alternating tread devices' and covers the requirements for a stairway which ascends at an angle of 50 to 70 degrees with steps at different elevations for each foot. These stairways are not allowed as part of the means of egress system, but may supplement access to a level that is also served by a stairway allowed as part of a means of egress system. The clear width of the stairway at and below the handrails is also established. The purpose of this section is to allow for a space saving stairway to a different level within a dwelling, while maintaining a primary stairway which provides an efficient route between such different levels. This section has one exception which allows for an alternating tread device to be used as part of the means of egress system, where it accesses areas with a maximum size and use limitation. The purpose of this exception is to allow for small areas of a dwelling to be utilized instead of being concealed (and wasted), and is not considered to diminish a user's ability to exit the area in an efficient manner.

The model shows an alternating tread device leading to a space which is greater than 200 sq. ft. in floor area, which is also accessed by a stairway allowed to be used in a means of egress system. The alternating tread device has the clear width at and below the handrails highlighted and labeled. The model also switches to the design allowed by the exception with a space that is less than or equal to 200 sq. ft. in floor area, which does not contain fixtures or appliances that would classify the area as a prohibited use, and which is only accessible via the alternating tread device. Both versions are compliant with this section of the code.