What is the steepest stairs allowed by code?
What is the Steepest Allowable Staircase Slope According to Building Codes?
While building codes don’t usually express staircase steepness in terms of slope degrees, they do regulate riser height and tread depth, which indirectly control the slope. Generally, the steepest allowable staircase translates to a riser height of approximately 7 ¾ inches and a tread depth of about 10 inches.
Understanding Staircase Steepness and Building Code Regulations
Staircase steepness is a crucial factor influencing both safety and comfort. It is primarily determined by the relationship between the riser height (vertical distance between steps) and the tread depth (horizontal distance of each step). Building codes in the US establish guidelines to ensure staircases remain within safe and usable limits.
Maximum Riser Height and Minimum Tread Depth
- Riser Height: Most building codes set a maximum riser height of around 7 ¾ inches. This limit ensures that steps aren’t excessively tall, making them easier to climb, particularly for individuals with limited mobility.
- Tread Depth: A minimum tread depth of about 10 inches is typically mandated. This provides sufficient foot space for safe and comfortable stepping, reducing the risk of slips and falls.
Calculating the Steepest Allowable Slope
While codes don’t directly specify a maximum slope in degrees, we can calculate an approximate value based on the maximum riser height and minimum tread depth. Using basic trigonometry, we find:
- Slope (in degrees) = arctan(riser height / tread depth)
Assuming a 7 ¾ inch riser and a 10 inch tread:
- Slope = arctan(7.75 / 10) ≈ 37.87 degrees
Therefore, the steepest allowable staircase slope is generally around 38 degrees.
Other Factors Influencing Staircase Steepness
While riser height and tread depth are the primary determinants of steepness, other factors can also play a role:
- Nosing: The presence of a nosing (a protruding edge on the tread) can effectively increase the tread depth, thereby reducing the slope slightly.
- Building Type: Some codes may allow for slightly steeper stairs in specific building types, such as attics or basements, where space constraints might be a concern.
- Local Regulations: It’s important to note that specific building codes can vary slightly between jurisdictions. Always consult your local building department to confirm the exact requirements in your area.
Prioritizing Safety and Comfort
While adhering to building codes is essential, it’s equally important to prioritize user safety and comfort. Even within the allowable limits, excessively steep staircases can be challenging to navigate, particularly for children, the elderly, or individuals with mobility impairments. Consider opting for a slightly shallower slope whenever possible to enhance usability and minimize the risk of accidents.