Stairbuilders and Manufacturers Association
Stair Design Basics
The following links provide valuable information related to the design of stairways that can be of assistance to both the novice and the professional in understanding and incorporating basic elements.
SMA Glossary of Stair Terms
Riser Height Chart
Tread Depth or Unit Run
Stair Gradient & Angle Chart
Individuals can also download the SMA’s Stair Code Visual Interpretation guides which simplify complex technical concepts relating to stair codes
through clear illustrations. These visual representations make it easier to understand important regulations that you should be aware of when having stairs installed in your property. SMA professionals in your area may already have a copy of the latest edition of this publication as many stairbuilding professionals consider it a vital resource. Created by trade experts, the depictions are designed for easy interpretation by stairbuilders and property owners alike. Download the latest edition of this resource to stay informed on any changes to industry standards. Other SMA code publications include technical guides and research studies.
The First Step
When choosing the Riser height and Tread depth you are essentially designing the geometry of a single interval, stair or step of your stairway.Optimally each step should be the same interval of the total rise and run so that the stairway users gait is the same at all the steps in the stairway minimizing the need to adjust their gait and balance.
The angle of ascent should be between 20 and 38 degrees
In choosing the riser height and tread depth it should always be proportioned to the human stride to assure a comfortable gradient in ascent and descent, eliminating stretching or baby stepping. The rule of proportion frequently used is:
The sum of two riser heights plus the depth of one tread should equal between 23-5/8 inches and 25-5/8 inches or 600- 650 mm
Once you have determined the possible riser height and tread depth combination from the charts check them in this simple formula and look up the angle in the angle table to make sure it is between 20 and 38 degrees.
Determining the geometry should always be done as part of the design process prior to construction. Your designer should be able to give you this information in advance for you to do comparative walking tests on any number of existing stairways to decide what is most comfortable and meets the design criteria for your home. An SMA professional
will be able to accommodate you in this process.
In existing buildings however the designer is limited to the space that can be made available for the stairway. Again SMA stair professionals can provide valuable input recommending possible options that are feasible.In either case the geometry of stairs is regulated by the building codes. The new model code developed and published by the International Code Council recognizes 7-3/4” as the maximum riser height and 10” as the minimum tread depth. Consult with your local building official prior to construction to find out what codes are applicable to your project and jurisdiction and download the "SMA Visual Interpretation of the Stair Codes"
. This pictorial guide shows exactly how the riser height, tread depth and the many other requirements for stairways, handrails and Guards are enforced.