Maximum Stair Building Angles And Building Code Reference Numbers
UNDERSTANDING THE STEEPEST STAIRWAY ANGLES FOR YOUR CONSTRUCTION PROJECT
When planning a staircase for a new home, an outdoor deck, or a commercial space, one of the first questions that comes up is exactly how steep you can make it. Building codes dictate the maximum riser height and minimum tread depth to ensure safety, comfort, and accessibility. However, the correct angle heavily depends on the type of building you are constructing.
Let us break down the most common building codes and the maximum stairway angles you can use for various construction projects.
RESIDENTIAL CONSTRUCTION CODES (37.8 DEGREES)
For most residential construction, including homes, decks, and outdoor landscaping projects, you will likely follow the 2021 International Residential Code (IRC). Under this code, the maximum steepness allowed is a 37.8-degree angle. This is achieved by using a minimum tread (or step) depth of 10 inches and a maximum riser height of 7 and 3/4 inches.
Newer building code requirements also emphasize adding a 1-inch nosing, or tread overhang, to this setup. While adding a nosing does not change the 37.8-degree angle of the staircase, it provides a larger surface area for your feet. This makes it much safer and more comfortable when walking up the stairs, though it may feel slightly different on the descent. Keep in mind that you can always reduce the height of the riser and increase the depth of the tread to lower the angle if desired.
COMMERCIAL AND PUBLIC BUILDINGS (32.5 DEGREES)
If you are building stairs for public, commercial, or industrial spaces, or large apartment buildings with more than 50 occupants, you must follow the International Building Code (IBC) rather than the residential code. The IBC requires a much gentler maximum angle of 32.5 degrees. To meet this code, your stairs must have an 11-inch minimum tread depth, a 7-inch maximum riser height, and a 4-inch minimum riser height.
STEEP ALTERNATIVES FOR TIGHT SPACES (41.6 DEGREES)
In some states, you might encounter codes that allow for a steeper 41.6-degree angle. This requires a 9-inch minimum tread depth and an 8-inch maximum riser height. Building a stairway this steep is generally not recommended and should be avoided if possible. It is best reserved for tight spaces with very low traffic, such as access stairs to an attic storage area.
FINDING THE MOST COMFORTABLE STEP
If you live in an area without strict building codes or simply want to build the most comfortable staircase possible, aim for a maximum riser height of 7 inches and a minimum tread depth of 11 inches. This standard provides a safe, comfortable stepping experience for almost everyone. No matter what your plans are, always verify the minimum tread depth and maximum riser height with your local building department before starting construction to ensure your project is safe and legal.
THREE KEY TIPS FOR BUILDING STAIRS
PRIORITIZE COMFORT OVER STEEPNESS: Even if local codes allow for an 8-inch riser, aiming for a 7-inch maximum riser and an 11-inch minimum tread will provide the most comfortable and safest stairway for daily use.
ALWAYS ADD NOSING TO STEEP STAIRS: If you are forced to build a steeper staircase due to space constraints, adding a 1-inch tread overhang (nosing) will give you a wider surface area for your feet without changing the overall angle of the stairs.
VERIFY WITH LOCAL AUTHORITIES: Building codes vary wildly from state to state and even between residential and commercial projects. Never assume a general code applies to your build without confirming with your local building department first.
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