Code Check: Stair Codes for Rise, Run, and Nosing  

A simple but helpful summary of what the IRC code says about building stair rise, run, and nosing.

A diagram showing multiple stair codes | Construction Pro Tips
Construction Pro Tips

The International Residential Code (IRC) has specific instructions the way stairs can be built. Here’s a clear summary of what the IRC code says about stair rise, run and nosing.

(Note: not every municipality adopts every part of every code, and some cities and states add in their own additional rules. Bottom line, check with your local building official before cutting those stringers or forming that stoop.)

Rise

The IRC code does not allow a distance greater than 7-¾ of an inch  from one step/tread to the next.

Run

The “run” is the measurement of the tread, which needs to be a minimum of 10 inches if the tread has and overhang on it (see image).  This is a measurement from the nose of the tread to nose of the tread.  You are not required to have an nosing/overhang on your stair treads. If your stairs don’t have a nosing you are required to have a tread that is at least 11 inches long.

Variances

From the top flight of stairs to the bottom of the stairs, each individual riser cannot exceed a difference of 3/8 of an inch.

Nosing

The nosing on treads, believe it or not, has a code minimum and maximum of how far the nosing projects over the next stair. Nosings are required to overhang a minimum of ¾-in. to a maximum of 1-¼-in.  Also the maximum nosing radius cannot exceed 9/16 of an inch.

Think flooring

All of these measurements include the finished flooring, so don’t forget to take those thicknesses into account when planning your stair dimensions.

Here are three reference numbers for the codes pertaining to rise, run, and nosing in a straight run of stairs:

R 311.7.5.1

R 311.7.5.2

R 311.7.5.3

You can view the code in its entirety here.