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Code Focus - Stairways

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Code Focus;  Stairways

CBC 2007

SECTION 1009 STAIRWAYS

[DSA-AC] In addition to the requirements of  this section, means of  egress, which provide access to, or egress from, buildings or facilities where accessibility is required for applications listed in Section 109.1 regulated by the Division of  the State Architect—Access Compliance, shall also comply with Chapter 11A or Chapter 11B, Section 1133B.4, as applicable.

1009.1 Stairway width.
The width of stairways shall be determined as specified in Section 1005.1, but such width shall not be less than 44 inches. See Section 1007.3 for accessible means of egress stairways.
Exceptions:
1.   Stairways serving an occupant load of less than 50 shall have a width of not less than 36 inches.
2.   Spiral stairways as provided for in Section 1009.8.
3.   Aisle stairs complying with Section 1025.
4.   Where an incline platform lift or stairway chairlift is installed on stairways serving occupancies in Group R-3, or within dwelling units in occupancies in Group R-2, a clear passage width not less than 20 inches shall be provided. If the seat and platform can be folded when not in use, the distance shall be measured from the folded position.  Means of egress stairs in a Group I-2 occupancy used for the movement of beds and litter patients shall provide a clear width not less than 44 inches.

1009.2 Headroom.
Stairways shall have a minimum headroom clearance of 80 inches measured vertically from a line connecting the edge of the nosings. Such headroom shall be continuous above the stairway to the point where the line intersects the landing below, one tread depth beyond the bottom riser. The minimum clearance shall be maintained the full width of the stairway and landing.
Exception: Spiral stairways complying with Section 1009.8 are permitted a 78-inch headroom clearance.

1009.3 Stair treads and risers.
Stair riser heights shall be 7 inches maximum and 4 inches minimum. Stair tread depths shall be 11 inches minimum. The riser height shall be measured vertically between the leading edges of adjacent treads. 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. Winder treads shall have a minimum tread depth of 11 inches measured at a right angle to the tread’s leading edge at a point 12 inches from the side where the treads are narrower and a minimum tread depth of 10 inches.
Exceptions:
1.   Alternating tread devices in accordance with Section 1009.9.
2.   Spiral stairways in accordance with Section 1009.8.
3.   Aisle stairs in assembly seating areas where the stair pitch or slope is set, for sightline reasons, by the slope of the adjacent seating area in accordance with Section 1025.11.2.
4.   In Group R-3 occupancies; within dwelling units in Group R-2 occupancies; and in Group U occupancies that are accessory to a Group R-3 occupancy or accessory to individual dwelling units in Group R-2 occupancies; the maximum riser height shall be 7.75 inches; the minimum tread depth shall be 10 inches; the minimum winder tread depth at the walk line shall be 10 inches; and the minimum winder tread depth shall be 6 inches. A nosing not less than 0.75 inch, but not more than 1.25 inches shall be provided on stairways with solid risers where the tread depth is less than 11 inches.



1009.3.1 Winder treads.
Winder treads are not permitted in means of egress stairways except within a dwelling unit.
Exceptions:
1.   Curved stairways in accordance with Section 1009.7.
2.   Spiral stairways in accordance with Section 1009.8.

1009.3.2 Dimensional uniformity.
Stair treads and risers shall be of uniform size and shape. The tolerance between the largest and smallest riser height or between the largest and smallest tread depth shall not exceed 0.375 inch in any flight of stairs. The greatest winder tread depth at the 12-inch walk line within any flight of stairs shall not exceed the smallest by more than 0.375 inch measured at a right angle to the tread's leading edge.

Exceptions:
1.   Non-uniform riser dimensions of aisle stairs complying with Section 1025.11.2.
2.   Consistently shaped winders, complying with Section 1009.3, differing from rectangular treads in the same stairway flight.

Where the bottom or top riser adjoins a sloping public way, walkway or driveway having an established grade and serving as a landing, the bottom or top riser is permitted to be reduced along the slope to less than 4 inches in height, with the variation in height of the bottom or top riser not to exceed one unit vertical in 12 units horizontal (8-percent slope) of stairway width. The nosings or leading edges of treads at such non-uniform height risers shall have a distinctive marking stripe, different from any other nosing marking provided on the stair flight. The distinctive marking stripe shall be visible in descent of the stair and shall have a slip-resistant surface. Marking stripes shall have a width of at least 1 inch, but not more than 2 inches.

1009.3.3 Profile.
The radius of curvature at the leading edge of the tread shall be not greater than 0.5 inch. Beveling of nosings shall not exceed 0.5 inch. Risers shall be solid and vertical or sloped from the underside of the leading edge of the tread above at an angle not more than 30 degrees from the vertical. The leading edge (nosings) of treads shall project not more than 1.25 inches beyond the tread below and all projections of the leading edges shall be of uniform size, including the leading edge of the floor at the top of a flight.

Exceptions:
1.   Solid risers are not required for stairways that are not required to comply with Section 1007.3, provided that the opening between treads does not permit the passage of a sphere with a diameter of 4 inches.
2.   Solid risers are not required for occupancies in Group I-3.

1009.4 Stairway landings.

There shall be a floor or landing at the top and bottom of each stairway. The width of landings shall not be less than the width of stairways they serve. Every landing shall have a minimum dimension measured in the direction of travel equal to the width of the stairway. Such dimension need not exceed 48 inches where the stairway has straight run.
Exceptions:
1.   Aisle stairs complying with Section 1025.
2.   Doors opening onto a landing shall not reduce the landing to less than one-half the required width. When fully open, the door shall not project more than 7 inches into a landing.
3.   [HCD 1 & SFM] In Group R-3 occupancies, 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.

1009.5 Stairway construction.
All stairways shall be built of materials consistent with the types permitted for the type of construction of the building, except that wood handrails shall be permitted for all types of construction.

1009.5.1 Stairway walking surface.
The walking surface of treads and landings of a stairway shall not be sloped steeper than one unit vertical in 48 units horizontal (2-percent slope) in any direction. Stairway treads and landings shall have a solid surface. Finish floor surfaces shall be securely attached.
Exception: In Group F, H and S occupancies, other than areas of parking structures accessible to the public, openings in treads and landings shall not be prohibited provided a sphere with a diameter of 1.125 inches cannot pass through the opening.

1009.5.2 Outdoor conditions.
Outdoor stairways and outdoor approaches to stairways shall be designed so that water will not accumulate on walking surfaces.

1009.5.3 Enclosures under stairways.
The walls and soffits within enclosed usable spaces under enclosed and unenclosed stairways shall be protected by 1-hour fire-resistance-rated construction or the fire-resistance rating of the stairway enclosure, whichever is greater. Access to the enclosed space shall not be directly from within the stair enclosure.

Exception: Spaces under stairways serving and contained within a single residential dwelling unit in Group R-2 or R-3 shall be permitted to be protected on the enclosed side with 0.5-inch gypsum board.  There shall be no enclosed usable space under exterior exit stairways unless the space is completely enclosed in 1-hour fire-resistance-rated construction. The open space under exterior stairways shall not be used for any purpose.

1009.6 Vertical rise.
A flight of stairs shall not have a vertical rise greater than 12 feet between floor levels or landings.

Exception: Aisle stairs complying with Section 1025.

1009.7 Curved stairways.
Curved stairways with winder treads shall have treads and risers in accordance with Section 1009.3 and the smallest radius shall not be less than twice the required width of the stairway.
Exception: The radius restriction shall not apply to curved stairways for occupancies in Group R-3 and within individual dwelling units in occupancies in Group R-2.

1009.8 Spiral stairways.
Spiral stairways are permitted to be used as a component in the means of egress only within dwelling units or from a space not more than 250 square feet in area and serving not more than five occupants, or from galleries, catwalks and gridirons in accordance with Section 1015.6.
A spiral stairway shall have a 7.5 inch minimum clear tread depth at a point 12 inches from the narrow edge. The risers shall be sufficient to provide a headroom of 78 inches minimum, but riser height shall not be more than 9.5 inches. The minimum stairway width shall be 26 inches.

1009.9 Alternating tread devices.
Alternating tread devices are limited to an element of a means of egress in buildings of Groups F, H and S from a mezzanine not more than 250 square feet in area and which serves not more than five occupants; in buildings of Group I-3 from a guard tower, observation station or control room not more than 250 square feet in area and for access to unoccupied roofs.

1009.9.1 Handrails of alternating tread devices.
Handrails shall be provided on both sides of alternating tread devices and shall comply with Section 1012.

1009.9.2 Treads of alternating tread devices.
Alternating tread devices shall have a minimum projected tread of 5 inches), a minimum tread depth of 8.5 inches, a minimum tread width of 7 inches and a maximum riser height of 9.5 inches. The initial tread of the device shall begin at the same elevation as the platform, landing or floor surface.
Exception: Alternating tread devices used as an element of a means of egress in buildings from a mezzanine area not more than 250 square feet) in area which serves not more than five occupants shall have a minimum projected tread of 8.5 inches with a minimum tread depth of 10.5 inches. The rise to the next alternating tread surface should not be more than 8 inches.
 

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