B-09 2020-Current: Code Requirements for Residential Stairs

These guidelines apply to residential stair construction Group R-3 or Group U Occupancies under the scope of the California Residential Code.

Version: 04/01/2020

Stairways in dwellings must be a minimum of 36 inches wide. The rise of every residential step shall not exceed 7.75 inches and the tread depth shall not be less than 10 inches. The largest tread width or riser height within any flight of stairs shall not exceed the smallest by more than .375 inch measured at the walk line. Stairways shall have a headroom clearance of 80 inches measured vertically from a line connecting the nosings. Clearance shall extend one tread depth past the bottom riser.

Winders shall have a tread depth of 10 inches at the walk line and a minimum tread depth of 6 inches.

Spiral stairs shall have a minimum tread depth of 7.5 inches at the walk line, a riser height maximum of 9.5 inches, a minimum width of 26 inches, and a headroom clearance of 78 inches.

Note: Dimensions and stair requirements apply only to individual dwelling units in residential occupancies. Handrails not shown for clarity. Details not drawn to scale.

Handrails shall be placed not less than 34 inches nor more than 38 inches above the nosing of the treads. The handgrip portion of handrails shall not be less than 1 1/4 inches nor more than 2 inches in cross- sectional dimension and the handgrip shall be smooth. Ends shall be returned or shall terminate in newel posts or safety terminals. Handrails shall not project more than 4.5 inches on either side of the stairway.

Stairways greater than 30 inches in height must have guards on any open side and all stairways with more than three risers shall have at least one handrail. Open stair railings shall have intermediate rails of an ornamental pattern such that a sphere 4 3/8 inches in diameter cannot pass through.

Where there is enclosed usable space under stairs, the walls and soffits of the enclosed space shall be protected on the enclosed side by 1/2 inch gypsum board.

There shall be a floor or landing at the top and bottom of each stairway. The width and length of the landings shall be not less than the width of the stairway. Interior stairs from the house to the garage need not have a landing provided the door does not swing over the stairs. Doors opening onto a landing shall not reduce the landing to less than one-half the required width. Doors in the fully open position shall not reduce a required dimension by more than 7 inches. There shall not be more than 151 inches vertically between landings.

Stairs are required to withstand a minimum of 300 pounds concentrated load and 100 pounds per square foot uniform load.

Oblique stairs - Oblique stairs are stairs where the angle between the line of the front of the tread and the edge of the stair is not 90 degrees. On a curved stair, this angle is measured from a line tangent to the curve at the point where the stair tread intersects the curved edge of the stair. In general, flights of oblique stairs are prohibited. However, widening the bottom of a stair so that the wall and handrail are not 90 degrees to the tread is acceptable provided that the treads vary from each other in a uniform ratio and are otherwise of uniform size and shape. A configuration where the treads meet at an angle in the approximate center of the stair is acceptable, provided the minimum tread width is provided at either side of the meeting point.

Landscape stairs - Landscape stairs are stairs which do not form part of the means of egress, which is the path of exit travel from any occupied point in a building or structure to a public way. Landscape stairs are not required to comply with the requirements of R311.7 the California Residential Code. All other stairs are required to comply with the code.

The following stairs are landscape stairs when less than 30 inches in height above adjacent grade:

1. Stairs in paths on the property which simply connect parts of the property together.
2. Stairs which are not attached to a structure and go to some feature on the property, such as a garden, field, woods, etc.
3. Stairs which are not attached to a structure and go to another parcel, or to an ocean, park, lake, etc.
4. Stairs which are not attached to a structure and do not form the most direct path from the main exit of the structure to the public way.

The following are not landscape stairs and must comply with the code:

1. Stairs forming the most direct path from the main exit of the structure to the public way.
2. Stairs attached to the structure.
3. Stairs from attached decks to grade.
4. Stairs forming the path from a swimming pool to the public way or to the single family dwelling or pool house on the same parcel.