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11.2

Part 11.2 Stairway and ramp construction

Part 11.2 Stairway and ramp construction

(1) Figure 11.2.1 depicts stairway members and associated terminology used to describe them in the ABCB Housing Provisions.

(2) Some items such as barriers and handrails have been omitted for clarity.

Figure 11.2.1 Stairway terms
image-11-2-1-stairway-terms.svg

Explanatory information: Alpine areas

The requirements of this Part are to be read in conjunction with Part 12.2 where a building is located in an alpine area and contains an external stairway or ramp.

Explanatory information: Room heights

Part 10.3 contains the required height for a ceiling above a stairway, ramp or landing, measured vertically above the nosing line of stairway treads or the floor surface of a ramp or landing.

(1) A stairway must be designed to take loading forces in accordance with AS/NZS 1170.1 and must have—

  1. not more than 18 and not less than 2 risers in each flight; and
  2. 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
  3. 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—
    1. adjacent risers, or between adjacent goings, is not more than 5 mm; and
    2. the largest and smallest riser within a flight, or the largest and smallest going within a flight, is not more than 10 mm; and
  4. risers which do not have any openings that would allow a 125 mm sphere to pass through between the treads; and
  5. 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.

(2) In the case of a stairway serving only non-habitable rooms, such as attics, storerooms and the like that are not used on a regular or daily basis—

  1. the going (G), riser (R) and slope relationship quantity (2R + G) in accordance with Table 11.2.2a may be substituted with those in Table 11.2.2b; and
  2. need not comply with (1)(d).

(3) In the case of a stairway with winders—

  1. 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
  2. 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.

(4) The point of measurement of the going (G) in the slope relationship quantity (2R + G) for tapered treads and treads in spiral stairways as described in Table 11.2.2a (see Figure 11.2.2a, Figure 11.2.2b and Figure 11.2.2c) must be—

  1. for tapered treads, other than treads in a spiral stairway—
    1. not more than 1 m in width, the middle of the unobstructed width of the stairway (see Figure 11.2.2b); and
    2. more than 1 m in width, 400 mm from the unobstructed width of each side of the stairway (see Figure 11.2.2c); and
  2. 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).

(5) Riser and going dimensions must be measured in accordance with Figure 11.2.2f.

Table 11.2.2a Riser and going dimensions (mm)
Stair type Riser (R) (see Figure 11.2.2f) Going (G) (see Figure 11.2.2f) Slope relationship (2R+G)
Max Min Max Min Max Min
Stairs (other than spiral) 190 115 355 240 700 550
Spiral 220 140 370 210 680 590
Table Notes

Riser and going dimensions must be measured in accordance with Figure 11.2.2f

Table 11.2.2b Riser and going dimensions (mm) — stairways serving non-habitable rooms used infrequently
Riser (R) Going (G) Slope relationship (2R+G)
Max Min Max Min Max Min
225 130 355 215 700 540
Table Notes

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.

Figure 11.2.2a Measurement of slope relationship — Plan view — Stair with 2 flights
image-11-2-2a-measurement-of-slope-relationship-plan-view-stair-with-2-flights.svg
Figure 11.2.2b Measurement of slope relationship — Plan view — Tapered treads not more than 1 m wide
image-11-2-2b-measurement-of-slope-relationship-plan-view-tapered-treads-not-more-than-1-m-wide.svg
Figure 11.2.2c Measurement of slope relationship — Plan view —Tapered treads more than 1 m wide
image-11-2-2c-measurement-of-slope-relationship-plan-view-tapered-treads-more-than-1-m-wide.svg
Figure 11.2.2d Spiral stairs — Measurement for slope relationship
image-11-2-2d-spiral-stairs-measurement-for-slope-relationship.svg
Figure 11.2.2e Spiral stairs — Measurement of openings in stairs
image-11-2-2e-spiral-stairs-measurement-of-openings-in-stairs.svg
Figure 11.2.2f Riser and going dimensions — Measurement
image-11-2-2f-riser-and-going-dimensions-measurement.svg

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.

Figure 11.2.2a (explanatory) Minor deviations in a stairway — deviation in adjacent risers
image-11-2-2a-explanatory-minor-deviations-in-a-stairway-deviation-in-adjacent-risers.svg
Figure Notes
  1. A = larger riser of two adjacent risers.
  2. B = smaller riser of two adjacent risers.
  3. This diagram only shows deviations in risers, however the same principle can apply for goings.
Figure 11.2.2b (explanatory) Minor deviations in a stairway – deviations over a flight
image-11-2-2b-explanatory-minor-deviations-in-a-stairway-deviations-over-a-flight.svg
Figure Notes
  1. C = largest riser of the flight.
  2. D = smallest riser of the flight.
  3. This diagram only shows deviations in risers, however the same principle can apply for goings.

Explanatory information: Openings in stair risers

11.2.2(1)(d) allows the use of open riser stairs. However, it limits the openings to 125 mm to minimise the risk of a person (especially a young child) falling through the opening created by the open riser.

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—

  1. be designed to take loading forces in accordance with AS/NZS 1170.1; and
  2. have a gradient not steeper than 1:8; and
  3. be provided with landings complying with 11.2.5 at the top and bottom of the ramp and at intervals not greater than 15 m.

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.

Explanatory information

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.

(1) The requirements for slip-resistance treatment to stair treads, ramps and landings are as set out in (2), (3) and (4).

(2) Treads must have—

  1. a surface with a slip-resistance classification not less than that listed in Table 11.2.4 when tested in accordance with AS 4586; or
  2. 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.

(3) The floor surface of a ramp must have a slip-resistance classification not less than that listed in Table 11.2.4 when tested in accordance with AS 4586.

(4) Landings, where the edge leads to the flight below, must have—

  1. 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
  2. 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

Explanatory information

  • 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.

(1) Landings must—

  1. 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
  2. have a gradient not steeper than 1:50; and
  3. 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
  4. extend across the full width of a doorway.

(2) In the case of a stairway serving only non-habitable rooms, such as attics, storerooms and the like that are not used on a regular or daily basis, the requirements of (1)(a) may be substituted with a minimum length of landing being not less than 600 mm long.

Figure 11.2.5a Landings
image-11-2-5a-landings.svg
Figure 11.2.5b Threshold landing
image-11-2-5b-threshold-landing.svg

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.

Explanatory information: Minimum landing length

The minimum length of a landing allows people using a stairway or ramp to rest, and reduces the risk of people falling more than one flight of stairs.

Explanatory information: Maximum grade of 1:50

The maximum grade of 1 in 50 required under 11.2.5(1)(b) makes sure that the landing is as level as possible, but still allows a slight slope for drainage if necessary.

Where the threshold of a doorway is more than 230 mm above the adjoining surface it must incorporate steps having riser (R) and going (G) dimensions in accordance with 11.2.2.