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WAC 296-307-26033

What requirements apply to alternating tread-type stairs?

"Alternating tread-type stairs" means stairs with a series of steps between 50 and 70 degrees from horizontal, attached to a center support rail in an alternating manner so that a user of the stairs never has both feet at the same level at the same time.
(1) Alternating tread-type stairs must be designed, installed, used, and maintained according to the manufacturer's specifications, and must have the following:
(a) Stair rails on all open sides;
(b) Handrails on both sides of enclosed stairs;
(c) Stair rails and handrails that provide an adequate handhold for a user grasping it to avoid a fall;
(d) A minimum of 17 inches between handrails;
(e) A minimum width of 22 inches overall;
(f) A minimum tread depth of 8 inches;
(g) A minimum tread width of 7 inches; and
(h) A maximum rise of 9 1/2 inches to the tread surface of the next alternating tread.
(2) Alternating tread-type stairs must have a maximum 20-foot continuous rise. Where more than a 20-foot rise is necessary to reach the top of a required stair, one or more intermediate platforms must be provided according to WAC 296-307-26027.
(3) Stairs and platforms must be installed so the top landing of the alternating tread stair is flush with the top of the landing platform.
(4) Stair design and construction must sustain a load of at least five times the normal live load, and be at least strong enough to carry safely a moving concentrated load of 1,000 pounds.
(5) Treads must have slip-resistant surfaces.
(6) Where a platform or landing is used, the width must be at least as wide as the stair and at least 30-inches deep in the direction of travel. Stairs must be flush with the top of the landing platform.
[Statutory Authority: RCW 49.17.040. WSR 98-24-096, § 296-307-26033, filed 12/1/98, effective 3/1/99. WSR 97-09-013, recodified as § 296-307-26033, filed 4/7/97, effective 4/7/97. Statutory Authority: RCW 49.17.040, [49.17.]050 and [49.17.]060. WSR 96-22-048, § 296-306A-26033, filed 10/31/96, effective 12/1/96.]
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