General Rise and Run Rules for Stairs

Earlier this year I built a dog step for My Helper and had to figure out maximum rise, and run dimensions when designing the stairs for her. So I thought I might as well make her steps to building code :). Here are some notes about the International Residential Code (IRC) for building stairs. All the dimensions listed below could be different depending on local code. There is a link at the end of the post that will help find local building codes.

Anatomy of a Step

Riser – The vertical elements in a set of stairs.
Tread – The horizontal part of a stair, also known as a the step.
Nosing – The horizontally projecting edge of a stair tread.

Riser Height

The finished riser height is measured from the top of the starting tread to the top of the next tread up the stairs.

• The finished riser height can be no more than 7 3/4 inches.
• The International Residential Code (IRC) does not mandate a minimum finished riser height.
• Keep in mind that there might be a height difference if different floor coverings are used. This usually occurs at the top and bottom landings.

Tread Depth

• Finished tread depth should be at least 10 inches.
• If treads have no nosing the tread depth should be at least 11 inches
• It is measured horizontally from the leading edge of the adjacent treads.
• There shouldn’t be more than a 3/8 inch variance between any two treads in the flight of stairs. This doesn’t apply to consistently shaped winding treads in the same flight of stairs.

Tread Nosing

• There must be a finished tread nosing of at least 3/4 inch and not more than 1 1/4 inches for stairs with a solid wood riser.
• Tread nosing is not necessary if the tread is at least 11 inches deep.
• There shouldn’t be more than a 3/8 inch depth difference between any two treads for all the treads between two stories. This includes floors and landings.
• For the finish detail on the tread nosing, the curvature radius should not exceed 9/16 inch and 1/2 inch for a bevel edge.

Notes

In researching this article I’ve come across some variations that people have posted about local building codes. I believe it was Alabama that allowed a finished riser height of 8 inches. Here are some links that might help.

• Local Building Code Reference – There are links, if available, by state for local building codes.
• Codes for Homeowners: Electrical Codes, Mechanical Codes, Plumbing Codes, Building Codes – A really well put together basic code reference with a lot of good pictures and easy to understand language. If you don’t buy it, at least check it out at the library.
• Residential Building Codes Illustrated – An easy-to-use illustrated guide to the building code requirements for construction of residential structures.
• Stairway Manufacturer’s Association – This has some useful charts on riser heights, tread depth and stair gradients.