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Stair Tread Minimum
The minimum stair tread is 11 inches, but there are some
exceptions.
The minimum stair tread for private stairways is 9 inches.
Again, this is where we could run into problems as architects,
contractors and building department officials. Just exactly how do you
interpret a private stairway. My interpretation of this particular
building code is that a private stairway would be a stairway used in a
single-family residence with less than 10 occupants.
The 2000 International Building Code states that a 10
inch minimum tread width is acceptable as long as you have a 1 inch
nosing. Getting confused yet. This was for R-2 and R-3 building types.
The 2010 California Building Code Book has a 10 inch
minimum tread for Residential 2 and Residential 3. I couldn't find
anything on Residential 1 building types, suggesting a 9 inch minimum
stair tread depth.
Attention: Don't forget to check with your local
building department to verify any building codes on this website. This
information could be incorrect or outdated. Building codes are updated
regularly and to some building departments have different
interpretations for certain building codes.
Other building code books use different verbiage to describe this
particular building code, but the end result is basically this. The
minimum stair tread for almost anything used by the public is 11 inches,
with the exception of a single-family private residence, where the
minimum stair tread can be 9 inches in depth.
How Do We Measure the Stair Tread Width? If you look at the picture
above, the actual stair tread width is measured from the upper stair
tread nosing, to the lower stair tread nosing. These measurements will
be horizontal or right to left, not vertical up and down.
Maximum Rise
Maximum Total Stairway Rise
Maximum Angle of the Stair Risers
Closed Stairway Riser Options
Maximum Variation in Stair Risers
Stair
Tread Nosing Requirements
Floor and
Landing Overhang
Closed Treads and Open Risers
What's an Open Riser
Staircase?
Problems with Open Risers Stairways
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