Stair Building Codes
The Building Codes (codes) have been created to be safety construction guidelines. The codes regulate the structure of buildings and their component parts and make dwellings conform to standards that are continually updated and revised. The latest (2010) stair codes are the most specific yet. This article represents Stair Building and Handrailing in Sonoma County, Marin County, and Napa County in Northern California (North San Francisco bay area) but is pertinent to all of California and reflects stair building and handrailing safety in general.
Stairs are the most dangerous part of a home. In my 25+ years of stair building I have walked up and down countless staircases. I can usually tell if a stair builder has errored in his layout by varying the rise or run, an inconsistency that creates hazard. Stairway accidents are not only caused by carelessness, but by these layout irregularities.
The codes standardize the rise and run of a stair by giving minimum and maximum dimensions as well as allowing for a very small permissible variance. The codes address a stairs handrail height (34" to 38" vertical from an imaginary line from tread nose to nose). They address the handrail dimensions and shape to make sure that it is graspable while one is on the stair (a balcony level railing is considered only as a guard rail and need not be graspable). The codes address the balcony guard railing height (formerly at 36" off of the finish floor and now at 42"). The codes specify a maximum baluster spacing (4 3/8" on a staircase and 4" on a balcony) making sure no child can fall through, as well as the minimum stair width, headroom and landing placement and size requirements. Spiral stairs (circular with a center pole) have specific code variables that allow for them to be a bit steeper than a normal set of stairs.
Here are the 2010 California Residential Codes that apply to interior staircases. This is the newest version to date. It is fairly easy to understand except for Section R3188.8.131.52 Grip-size. Honestly, I don't know what they were thinking when they put that section together. How does one measure the 'perimeter dimension of at least 4 inches and not greater than 6 1/4 inches' and 'edges shall have a minimum radius of 0.01 inch'. I'm sure most building inspectors couldn't figure this out and if there is ever a question, it might require a mathmatician (geometry) to settle it.
Sections from 2010 California Residential Code Section R311 Means of Egress & Section R112 Guards
Section R311 Means of Egress
R311.1 Means of Egress. All dwellings shall be provided with a means of egress as provided in this section. The means of egress shall provide a continuous and unobstructed path of vertical and horizontal egress travel from all portions of the dwelling to the exterior of the dwelling at the required egress door without requiring travel through a garage.
***Sections 311.2 through 311.6 pertain to egress doors, deck attachment and hallway width which do not pertain to stairs and aren't cited here.
R311.7.1 Width. Stairways shall not be less than 36 inches in clear width at all points above the permitted handrail height and below the required headroom height. Handrails shall not project more than 4.5 inches on either side of the stairway and the minimum clear width of the stairway at and below the handrail height, including treads and landings, shall not be less than 31 1/2 inches where a handrail is installed on one side and 27 inches where handrails are provided on bothe sides. Exception: The width of spiral stairways shall be in accordance with Section R3184.108.40.206
R311.7.2 Headroom. The minimum headroom in all parts of the stairway shall not be less than 6 feet 8 inches measured veritcally from the sloped line adjoingng the tread nosing or from the floor surface of the landing or platform on that portion of the stairway.
Exception: Where the nosings of treads at the side of a flight extend under the edge of a floor opening through which the stair passes, the floor opening shall be allowed to project horizontally into the required headroom a maximum of 4 3/4 inches.
R311.7.3 Walkline. The walkline across winder treads shall be concentric to the curved direction of travel through the turn and located 12 inches from the side where the winders are narrower. The 12-inch dimension shall be measured from the widest point of the clear stair width at the walking surface of the winder. If winders are adjacent within the flight, the point of the widest clear stair width of the adjacent winders shall be used.
R311.7.4 Stair treads and risers. Stair treads and risers shall meet the requirements of this section.
For the puroses of this section all dimensions and dimensioned surfaces shall be exclusive of carpets, rugs or runners.
R3220.127.116.11 Riser Height. The maximum riser height shall be 7 3/4 inches. The riser shall be measured vertically between leading edges of the adjacent treads. The greatest riser height within any flight of stairs shall not exceed the smallest by more than 3/8 inch.
R318.104.22.168 Tread Depth. The minimum tread depth shall be 10 inches. The tread depth shall be measured horizontally between the vertical planes of the foremost projection of adjacent treads and at a right angle to the tread's leading edge. The greatest tread depth within anyh flight of stairs sall not exceed the smallest by more than 3/8 inch. Consistently shaped winders at the walkline shall be allowed within the same flight of stairs as rectangular treads and do not have to be within 3/8 inch of the rectangular tread depth.
Winder treads shall have a minimum tread depth of 10 inches measured between the vertical planes of the foremost projection of adjacent treads at the intersections with the walkline. Winder treads shall have a minimum tread depth of 6 inches at any point within the clear width of the stair. Within any flight of stairs, the largest winder tread depth at the walkline shall not exceed the smallest winder tread by more than 3/8 inch.
R322.214.171.124 Profile. The radius of curvature at the nosing shall be no greater than 9/16 inch. A nosing not less than 3/4 inch but not more than 1 1/4 inches shall be provided on stairways with solid risers. The greatest nosing projection shall not exdceed the smallest nosing projection by more than 3/8 inch between two stories, including the nosing at the level of floors and landings. Beveling of nosings shall not exceed 1/2 inch. Risers shall be vertical or sloped under the tread above from the underside of the nosing above at an angle not mroe than 30 degrees from the vertical Open risers are permitted, provided that the opening between treads does not permit the passage of a 4- inch diameter sphere.
1) A nosing is not required where the tread depth is a minimum of 11 inches.
2) The opening between adjacent treads is not limited on stairs with a total rise of 30 inches or less.
R3126.96.36.199 Exterior wood/plastic composite stair treads. Wood/plansic composite stair treads shall com;ly with the provisions of Section R317.4
R311.7.5 Landings for Stairways. There shall be a floor or landing at the top and bottom of each stairway.
Exception: A floor or landing is not required at the top of an interior flight of stairs, including stairs in an enclosed garage, provided a door does not swing over the stairs. A flight of stairs shall not have a vertical rise larger than 12 feet between floor levels or landings. The width of each landing shall not be less than the width of the stairway served. Every landing shall have a minimum dimension of 36 inches measured in the direction of travel.
R311.7.6 Stairway walking surface. The walking surface of treads and landings of stairways shall be sloped no steeper than one unit vertical in 48 inches horizontal (2-percent slope).
R311.7.7 Handrails. Handrails shall be provided on at least on side of each continuous run of treads or flight with four or more risers.
R3188.8.131.52 Height. Handrail height, measured vertically fom the sloped plane adjoining the tread nosing, or finish surface of ramp slope, shall be not less than 34 inches and not mroe than 38 inches.
1) The use of a volute, turnout or starting easing shall be allowed over the lowest tread.
2) When handrail fittings or bendings are used to provide continuous transition between flights, the transition from hnadrail to guradrail, or used at the start of a flight, the handrail height at the fittings or bendings shall be permitted to execeed the maximum height.
R3184.108.40.206 Continuity. Handrails for stairways shall be continuous for the full length of the flight, from a point directly above the top riser of the flight to a point directly above the lowest riser of the flight. Handrail ends shall be returned or shall terminate in newel posts or safety terminals. Handrails adjacent to a wall shall have a space of not less than 1 1/2 inch between the wall and the handrails.
1) Handrails shall be permitted to be interrupted by a newel post at the turn.
2) The use of a volute, turnout, starting easing or starting newel shall be allowed over the lowest tread.
R3220.127.116.11 Grip-size. All required handrails shall be of one of the following types or provide equivalent graspability.
1)Type I. Handrails with a circular cross section shall have and outside diameter of a least 1 1/4 inches and not greater than 2 inches. If the handrail is not circular, it shall have a perimeter dimension of at least 4 inches and not greater than 6 1/4 inches with a maximum cross section of dimension of 2 1/4 inches. Edges shall have a minimum radius of 0.01 inch.
2) Type II. Handrails with a perimeter greater than 6 1/4 inches shall have a graspable finger recess area on both sides of the profile. The finger recess shall begin within a distance of 3/4 inch measured vertically from the tallest portion of the profile and achieve a depth of at least 5/16 inch within 7/8 inch below the widest portion of the profile. This required depth shall continue for at least 3/8 inch to a level that is not less than 1 3/4 inches below the tallest protion of the profile. The minimum width of the handrail above the recess shall be 1 1/4 inches to a maimum of 2 3/4 inches. Edges shall have a minimum radius of 0.01 inch.
R318.104.22.168 Exterior wood/plastic composite hadrails. Wood/;pastic somposite handrails shall comply with the provisions of Section R317.4.
R311.7.8 Illumination. All stairs shall be provided with illumination in accordance with Section R303.6
R311.7.9 Special stairways. Spiral stairways and bulkbead enclosure stairways shall comply with all requirements of Section R311.7 except as specified below.
R322.214.171.124 Spiral stairways. Spiral stairways are permitted, provided the minimum clear width at and below the handrail shall be 26 inches with each tread having a 7 1/2" minimum tread depth at 12 inches from the narrower edge. All treads shall be identical, and the rise shall be no more than 9 1/2 inches. A minimum headroom of 6 feet 6 inches shal be provided.
R3126.96.36.199 Bulkhead enclosure stairways. Stairways serving bulkhead enclosures, not part of the required building egress, providing access from the outside grade level to the basement shall be exempt from the requirements of Sections R311.3 and R311.7 where the maximum height from the basement finished floor level to grade adjacent to the stairway does not exceed 8 feet and the grade level opening to the stairway is covered by a bulkhead enclosure with hinged doors or other approved means.
R311.8.1 Maximum slope. Ramps shall have a maximum slope of 1 unit vertical in 12 units horizontal (8.3 percent slope).
Exception: Where it is technically infeasible to comply because of site constraints, ramps may have a maximum slope of one unit vertical in eight horizontal (12.5 percent slope).
R311.8.2 Landings required. A minimum 3-foot-by-3-foot landing shall be provided:
1) At the top and bottom of ramps.
2) Where doors open onto ramps.
3) Where ramps change direction.
R311.8.3 Handrails required. Handrails shall be provided on at least one side of all ramps exceeding a slope of one unit vertical in 12 units horizontal (8.33 percent slope).
R3188.8.131.52 Height. Handrail height, measured above the finsihed surface of the ramp slope, shall be not less than 34 inches and not more than 38 inches.
R3184.108.40.206 Grip size. Handrails on ramps shall comply with Section R3220.127.116.11
R318.104.22.168 Continuity. Handrails where required on ramps shall be continuous for the full lenght of the ramp. Handrail ends shall be returned or shall terminate in newel posts or safety terminals. Handrails adjacent to a wall shall have a space of not less than 1 1/2 inches between the wall and the handrails.
Section R312 Guards
R312.1 Where required. Guards shall be located along open-sided walking surfaces, including stairs, ramps and landings, that are located more than 30 inches measured vertically to the floor or grade below at any point within 36 inches horizontally to the edge of the open side. Insect screening shall not be considered as a guard.
R312.2 Height. Required guards at open-sided walking surfaces, including stairs, proches, balconies or landings, shall be not less than 42 inches high measured vertically above the adjacent walking surface, adjacent fixed seating or the line connecting the leading edges of the treads.
1) The triangular openings at the open side of a stair, formed by ther riser, tread and bottom rail of a guard, shall not allow passage of a sphere 6 inches in diameter.
2) Where the top of the guard also serves as a handrail on the open sides of stairs, the top of the guard shall not be less than 34 inches and not more than 38 inches measured vertically from a line connection the leading edges of the treads.
R312.3 Opening limitations. Required guards shall not have openings from the walking surface to the required guard height which allow passage of a sphere 4 inches in diameter.
1) The triangular openings at the open side of a stair, formed by the riser, tread and bottom rail of a guard, shall not allow passage of a sphere 6 inches in diameter.
2) Guards on the open sides of stairs shall not have openings which allow passage of a sphere 4 3/8 inches in diameter.
R312.4 Exterior woodplastic composite guards. Wood plastic composit guards shall comply with the provisions of Section R317.4