Code Requirements for Stairs: Risers, Treads, Stair Width and Headroom

Floating stairs in a modern home
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There should be no guesswork when it comes to building stairs. Stair risers and treads, as well as width and headroom, are dictated by building code, which itself is often dictated by good, common sense. These rules are aimed at making stairways as safe as possible, so they should never be ignored or bypassed. 

Following are suggested specifications for risers, treads, width, and headroom. These specs will help you build a safe, comfortable set of stairs for most houses.

Stair Riser Height: 7 3/4 Inches Maximum

  • Translated: This means that the distance you lift your foot from one stair to an adjacent stair can be no more than 7.75 inches high.
  • Reason: To prevent stairs from being too high if walking upstairs or too low if descending.  Both are safety hazards. Further, the riser measurement of each tread in a stairway should be as close as possible to identical. A stairway in which there is noticeable variation between the risers is a safety hazard. 

Stair Tread (Run) Length: 10 Inches Minimum

  • Translated:  This means that the horizontal distance from the edge of the stair to the back part where it stops (called the riser) should be at least 10 inches long.
  • Reason:  To allow a majority of your foot to have enough room to rest on the stair.  Stair tread length is more of an issue for descending, rather than ascending, stairs. Further, the tread measurement of each tread in a stairway should be as close as possible to identical. A stairway in which there is noticeable variation between the treads is a safety hazard. 

    Stair Width:  36 Inches Minimum (Not Including Handrails)

    • Translated: This means that any stairs must be at least 3 feet wide, measured from side to side as if you are walking up or down the stairs.
    • Reason: Among many reasons, narrow stairs make it more difficult to carry items up and down stairs.  Awkward positioning of these items may lead to falls.

      Stair Headroom:  6 Ft., 8 Inches Minimum

      • Translated: At any point on the staircase, you should have a full 6 feet, 8 inches minimum vertical distance between the stair tread and the ceiling.  See the terminology section below for a more accurate description of how this is calculated.
      • Reason: Anyone walking up or down the stairs should have plenty of clear headroom without having to duck down.

      These do not universally dictate all stair measurements; rather, be sure to check with local agencies about building codes that apply to your structure.

      Many communities adopt the International Building Code wholesale, while others make modifications.

      Common Stairway Terms You Should Know

      • Stringer: The ​stringer is the entire "saw-toothed" member upon which risers and tread rest. You will need two per staircase. Some utility stairways, such as basement stairs or deck stairs, may not use a sawtooth stringer design, but, instead, use solid side stringers which anchor the treads by means of metal connectors. 
      • Riser: A riser is the vertical measurement of each stair. Risers can either be enclosed or left open, as in deck stairs or basement stairs.
      • Tread: The tread is the horizontal section of each stair, sometimes called the run. This is the part you step on.
      • Stair width: When we say width, we are referring to the measurement of risers and treads from side to side, as if you were walking up or down the stairs.
      • Headroom: Headroom is one dimension that often gets ignored. Imagine drawing a sloped line along the noses of each tread.  The vertical measurement above this sloped line is the headroom.