Part 11.2 Stairway and ramp construction
Explanation of terms
- not more than 18 and not less than 2 risers in each flight; and
- goings (G), risers (R) and a slope relationship quantity (2R + G) in accordance with Table 11.2.2a, except as permitted by (2) and (3); and
- constant goings and risers throughout each flight, except as permitted by (3) and (4), and the dimensions of goings (G) and risers (R) in accordance with (1), (2) and (3) are considered constant if the variation between—
- risers which do not have any openings that would allow a 125 mm sphere to pass through between the treads; and
- treads of solid construction (not mesh or other perforated material) if the stairway is more than 10 m high or connects more than 3 storeys.
- a maximum of 3 consecutive winders in lieu of a quarter landing in a flight and a maximum of 6 consecutive winders in lieu of a half landing in a flight; and
- the going (G) of all winders in lieu of a quarter or half landing may vary from the going of the straight treads within the same flight provided that the going (G) of such winders is constant.
- for tapered treads, other than treads in a spiral stairway—
- for treads in spiral stairways, the point seven tenths of the unobstructed width from the face of the centre pole or support towards the handrail side (see Figure 11.2.2d and Figure 11.2.2e).
|Stair type||Riser (R) (see Figure 11.2.2f)||Going (G) (see Figure 11.2.2f)||Slope relationship (2R+G)|
|Stairs (other than spiral)||190||115||355||240||700||550|
|Riser (R)||Going (G)||Slope relationship (2R+G)|
The going (G) must be not more than the tread depth plus a maximum gap of 30 mm between the rear edge of one tread and the nosing of the tread above.
Explanatory information: Not more than 18 and not less than 2 risers
11.2.2(1)(a) states that a stairway must have not more than 18 and not less than 2 risers in each flight. Where there are less than 2 risers in a flight, it does not comprise a stairway for the purpose of the NCC. 18 risers is considered to be the maximum reasonable number that an average person can negotiate before requiring a rest. Winders are counted as part of the maximum number of 18 risers. More than 1 riser is considered necessary for a person to observe and adjust to a change in level.
Explanatory information: Going and riser dimensions
The purpose of 11.2.2 is to achieve constant going and riser dimensions deemed safe for people to walk up and down. This minimises the risk of people overstepping during descent on uneven stairs (due to short goings) and tripping on ascent (due to high risers). Table 11.2.2a and Table 11.2.2b express ratios between going and riser dimensions which are considered safe for use. 11.2.2(1)(c) accounts for conditions such as movement of materials due to atmospheric moisture changes or minor deviations related to variations in materials which affect finished stair dimensions.
Explanatory Figure 11.2.2a illustrates adjacent risers within a flight with minor deviations in the materials affecting the finished stair dimensions. The nominated riser height is exceeded by riser A. As a consequence riser height B is less than the nominated riser height. The difference between riser A and riser B cannot exceed 5 mm.
Explanatory Figure 11.2.2b illustrates an entire flight with minor deviations in the materials affecting the finished riser dimensions. In addition to the 5 mm difference permitted between adjacent goings or risers, the maximum difference between the smallest and largest going or riser within a flight must not exceed 10 mm. Despite the deviations shown in both diagrams, the stairs in the flight are deemed constant. Irrespective of any minor deviations permitted by 11.2.2(1)(c), finished going and riser dimensions must not exceed the limitations stipulated in Table 11.2.2a.
Explanatory information: Solid treads
11.2.2(1)(e) specifies a height where solid treads must be used so that people cannot see through them. This minimises the risk of people being affected by vertigo.
Explanatory information: Stairways with winders
- 11.2.2(3) allows the use of winders in stairways. However, 11.2.2(3) places a restriction on the number of allowable winders in a stairway flight, this restriction would apply equally to not permit a stairway incorporating a consecutive series of winders in a flight.
- This also means the maximum number of consecutive winders in any stairway flight is 6.
An external ramp serving an external doorway or a ramp within a building must—
Notes: Livable housing design
Where an external ramp is provided for the purposes of compliance with the ABCB Standard for Livable Housing Design, the requirements of that Standard apply.
In relation to external ramps, 11.2.3 applies to a ramp serving an external door. For the purpose of 11.2.3 a driveway is not considered to be a ramp.
- a surface with a slip-resistance classification not less than that listed in Table 11.2.4 when tested in accordance with AS 4586, for not less than 190 mm from the stair nosing; or
- a nosing strip with a slip-resistance classification not less than that listed in Table 11.2.4 when tested in accordance with AS 4586.
Table 11.2.4 Slip-resistance classification Application Dry surface conditions Wet surface conditions Ramp not steeper than 1:8 P4 or R10 P5 or R12 Tread surface P3 or R10 P4 or R11 Nosing or landing edge strip P3 P4
- To determine the appropriate surface of a tread or the floor surface of a ramp, it is necessary to determine the likely conditions the tread or ramp will be subject to over the life of the building. This can be either dry, wet or both. A dry surface is one that is not normally wet or likely to be made wet other than by an accidental spill. A wet surface is one that is normally wet or likely to be made wet, including areas exposed to the weather.
- Under 11.2.4(2) stair treads must have a surface or nosing strip which minimises the risk of people slipping and injuring themselves. In each case the surface or nosing must have a slip-resistance classification when tested in accordance with AS 4586. There are two tests (the Wet Pendulum Test or the Oil-Wet Inclining Platform Test) and two conditions (dry or wet) to be considered.
- Under 11.2.4(3) the floor surface of a ramp must be slip-resistant to minimise the risk of people slipping and injuring themselves. The surface must have a slip-resistance classification when tested in accordance with AS 4586.
- be not less than 750 mm long and where this involves a change in direction, the length is measured 500 mm from the inside edge of the landing (see Figure 11.2.5a); and
- have a gradient not steeper than 1:50; and
- be provided where the sill of a threshold of a doorway opens onto a stairway or ramp that provides a change in floor level or floor to ground level greater than 3 risers or 570 mm (see Figure 11.2.5b); and
- extend across the full width of a doorway.
Explanatory information: Purpose of a landing
The purpose of a landing is to provide a rest area for people using the stairway or ramp, and to allow the stairway or ramp to change direction if needed.