Space Saving Stairs

space saving stairs

Space-saving staircase terminology

Space-saving Stair
Alternating stair
Thomas Jefferson Stair
Jeffersonian staircase
Ergonomic stair with staggered treads
Zig-zag-style
Boat Paddle-shaped treads
Ship’s Ladder
Alternating-tread devises
Tiny-house stairs

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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:

  1. As primary access to lofts, mezzanines, or observation decks of not more than 250 sq ft. (1011.14.2)

  2. As secondary access to an upper level that already has one code-compliant stair serving as a means of egress. (R311.7.11)

  3. 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):

  1. The clear width at and below the handrails shall be not less than 20 inches.

  2. 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.

  3. 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.

  4. 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.

  5. Handrails shall be provided on both sides of alternating tread devices and shall comply with Sections R311.7.8.2 to R311.7.8.4. Handrail height shall be uniform, not less than 30 inches and not more than 34 inches. (R311.7.11.2)

Similar Requirements for Ships Ladders (R311.7.12)

  1. 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.

  2. 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.

  3. Handrails shall be provided on both sides of ships ladders and shall comply with Sections R311.7.8.2 to R311.7.8.4. Handrail height shall be uniform, not less than 30 inches and not more than 34 inches. (R311.7.12.2)

SBCCI Standard Building Code

The 1994 edition of the Standard Building Code permits alternating tread stairs with a minimum projected tread of 8.5 inches to access 250 square foot mezzanines or less, occupied by no more than 5 people. They may also be used to and between staff locations in penal facilities. (Section 1007.8)

BOCA National Building Code

The 1999 National Building Code permits alternating tread stairs with a minimum projected tread of 5 inches and a minimum tread depth of 8.5 inches as a means of egress from mezzanines, roofs and various areas in penal facilities; exception as a means of egress from a mezzanine area not more than 250 sq. ft. not serving more than 5 occupants, shall have a minimum projected tread of 8.5 inches, minimum tread depth of 10.5 inches. (Section 1014.6.6 and 1027.0)

U.S. Coast Guard

In September 1984, the U.S. Coast Guard issued a letter addressing the use of alternating tread stairs and the authorized locations of inspected vessels. (Document #16711)

 Canadian Ministry of Housing

A November 1988 letter states that alternating tread stairs may serve as a secondary stair for convenience purposes.

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