In alternating tread devices, what should the angle of ascent from the horizontal be?

The angle of ascent for alternating tread devices is typically required to be between 50° and 70° from the horizontal. This range is specified because it ensures that the device can be used safely and effectively while still facilitating access between different levels in a building. The design of alternating tread devices aims to provide a compromise between the steepness of stair treads and the requirements for angle accessibility, thus ensuring that users can ascend and descend with relative ease while maintaining a secure footing.

Using angles below 50° may not provide the necessary elevation gain within a limited horizontal space, which can affect the overall functionality. Conversely, using angles greater than 70° can lead to an increased risk of falls and may not comply with safety codes designed to protect individuals using the device. By adhering to the specified range, building codes ensure both safety and functional utility.