Space Saving Stairs
Space-saving staircase terminology
Thomas Jefferson Stair
Ergonomic stair with staggered treads
Boat Paddle-shaped treads
Space-saving Stairs have been used widely in Europe for many years and now have become quite popular in the US with the rise of the Tiny House movement. A further boost has been given to the Space-saving staircase with several of the major building codes in the US allowing them. Below are a few examples:
International Building Code 2015 (R311.7.10)
The IBC defines an ALTERNATING TREAD DEVICE as a device that has a series of steps between 50 and 70 degrees from horizontal… in an alternating manner so that the user does not have both feet on the same level at the same time.
Alternating Tread Stairs are allowable as a means of egress for the following:
As primary access to lofts, mezzanines, or observation decks of not more than 250 sq ft. (1011.14.2)
As secondary access to an upper level that already has one code-compliant stair serving as a means of egress. (R311.7.11)
As access to unoccupied roofs, unoccupied storage areas (attics) and control rooms (HVAC equipment). (1009.12, 1014.3,4, 1014.6.1)
Alternating Tread Dimensional requirements (R311.7.11):
The clear width at and below the handrails shall be not less than 20 inches.
Alternating tread devices shall have a tread depth of not less than 5 inches, a projected tread depth of not less than 8-1/2 inches, a tread width of not less than 7 inches and a riser height of not more than 9-1/2 inches.
The tread depth shall be measured horizontally between the vertical planes of the foremost projections of adjacent treads. The riser height shall be measured vertically between the leading edges of adjacent treads.
The riser height and tread depth provided shall result in an angle of ascent from the horizontal of between 50 and 70 degrees. The initial tread of the device shall begin at the same elevation as the platform, landing or floor surface.
Handrails shall be provided on both sides of alternating tread devices and shall comply with Sections R3220.127.116.11 to R318.104.22.168. Handrail height shall be uniform, not less than 30 inches and not more than 34 inches. (R322.214.171.124)
Similar Requirements for Ships Ladders (R311.7.12)
Ships ladders shall not be used as an element of a means of egress. Ships ladders shall be permitted provided that a required means of egress stairway or ramp serves the same space at each adjoining level or where a means of egress is not required. The clear width at and below the handrails shall be not less than 20 inches.
7.12.1 Treads of Ships Ladders: Treads shall have a depth of not less than 5 inches. The tread shall be projected such that the total of the tread depth plus the nosing projection is not less than 81/2 inches. The riser height shall be not more than 91/2 inches.
Handrails shall be provided on both sides of ships ladders and shall comply with Sections R3126.96.36.199 to R3188.8.131.52. Handrail height shall be uniform, not less than 30 inches and not more than 34 inches. (R3184.108.40.206)