Exterior Stairways - 2 Stories or Less
Exterior stairways that
are used for buildings that are two stories or less can be built from
building materials no less than 2 inches nominal thickness.
Remember that nominal thickness applies to the width of construction standard building materials. Most 2 x 4's aren't 2 inches thick, even though they're referred to as 2 x 4's. The nominal thickness of a 2 x 4 used in Southern California out of Douglas Fir is 1 1/2 by 3 1/2 inches.
Example: The picture above is a set of exterior stairs built using 2 x 12 stringers and 2 x 12 stair treads. It's not uncommon to find a heavy duty exterior stairway built using 4 x 12 stringers and 3 x 12 treads.
I've seen exterior stairs built using 2 x 12 stair stringers, along with plywood treads and risers, so make sure that you check with your local building department to verify this particular building code.
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 This information could be incorrect or outdated.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 some building departments have different interpretations for certain building codes.
Exterior Stairways - 3 Stories or More