Design Guidelines: Exterior Stairs
By: Brad Priest, Designer at DG2 Design Landscape Architecture
DESIGNING SAFE AND FUNCTIONAL OUTDOOR STAIRS
Exterior stairs require a set of design guidelines that differs from typical interior stairs. They must function in all types of environmental conditions and provide safe routes for users to navigate comfortably in ways that are unique to the outdoors. One of the most important considerations in designing safe, functional exterior stairs is PROPORTION.
Stairs in an outdoor setting should allow for users to move up and down them at a quicker speed than what is required indoors. With this in mind, the proportion of each stair as well as the overall staircase must be planned accordingly.
The overall width of a set of outdoor stairs should be a minimum of 4 feet in a private setting, and 5 feet in a public space. However, wider stairs are typically more inviting and can feel safer for users, particularly in crowded public spaces.
Perhaps more important than overall stair width are the proportions of each individual stair (all stairs within a single staircase should be uniform in dimension, of course). Risers – the vertical faces of each step – should be 6” whenever possible under typical conditions, as this dimension provides the most ergonomic function. In order to eliminate tripping hazards, the dimension of a Riser should always be a minimum of 4” and a maximum of 7”.
Treads – the horizontal faces of each step – should be sized depending on the dimension of the Risers. The standard acceptable range of dimensions for exterior Treads is 11 to 18 inches. In order to provide the most ergonomic flow, Tread length should be determined based on the following formula whenever possible:
- (2x Riser Height) + Tread Length = 24 to 26”
A few other important aspects to planning a safe, functional set of stairs are landing height, landing length and landing frequency. Landings are the flat breaks between stairs that allow users to navigate up and down more easily. Topography plays a major role in the layout of landings within a run of stairs, but a few rules of thumb include:
- Landings should always be separated by ~5 feet vertically at the most, so that users can see each landing as they ascend the stairs.
- Landing length should be 5 feet, or multiples of 5 feet, to allow for smooth user movement.
- Landing frequency should be every 9 to 11 steps if possible, to ease the exertion required to navigate the stairs.