Our Adelaide Hills staircase turns with three winders, and the certifier says the going is too narrow on the inside. How are goings measured on winders, and is a winder even allowed in a Class 1 house?

Not quite, but check your numbers before you push back. Winders are allowed in a Class 1 house, and three of them in place of a quarter landing is exactly what the Standard permits. [1] The going of a winder is not tested at the narrow inside edge. It is tested at a set point across the tread, and that is where your drawing needs to show at least 240 mm. [1] [2]

Are winders allowed? Yes. In a stairway with winders there can be a maximum of 3 consecutive winders in lieu of a quarter landing and a maximum of 6 consecutive winders in lieu of a half landing in a flight. [1] The Standard's explanatory information confirms that the most consecutive winders in any flight is 6. [4] Your three-winder turn sits within the quarter landing allowance.

Where the going is measured on a winder. This is the heart of the certifier's point. For tapered treads (other than a spiral stair), the going used in the slope relationship is measured at: [1]

• a stairway not more than 1 m wide: the middle of the unobstructed width of the stairway (Figure 11.2.2b);
• a stairway more than 1 m wide: 400 mm from the unobstructed width of each side of the stairway (Figure 11.2.2c).

The Standard sets no separate minimum going at the narrow end. But note the second branch: on a stair wider than 1 m, the line 400 mm in from the inside edge is a test point in its own right. If the certifier has taken the going on that line, they may be right.

The figures the going has to meet. At that point of measurement, a stair other than a spiral must meet Table 11.2.2a: [2]

• riser (R): 115 mm minimum, 190 mm maximum;
• going (G): 240 mm minimum, 355 mm maximum;
• slope relationship (2R + G): 550 mm minimum, 700 mm maximum.

Risers and goings are measured in accordance with Figure 11.2.2f. [2]

The winders do not have to match the straight treads. The going of winders in lieu of a quarter or half landing may differ from the going of the straight treads in the same flight, provided the going of the winders is constant. [1] All three winders need the same going at the measurement point.

Winders still count as risers. A flight can have no more than 18 risers and no fewer than 2, [3] and the explanatory information confirms winders are counted in the 18. [4]

A side note on livable housing. The voluntary ABCB Standard for Livable Housing Design bans winders on a stairway subject to its clause 7.2. [5] That only matters if you are designing to it; it is not a general ban for Class 1 houses.

Practical next step. Dimension the unobstructed width of the stair at the turn. If it is 1 m or less, mark the centre line; if it is more than 1 m, mark lines 400 mm in from each side. Then dimension the going of each winder on those lines and check it is at least 240 mm, the same for all three winders, and gives a 2R + G between 550 mm and 700 mm. Send that marked-up plan to the certifier and ask them to confirm which line they measured on.

SA edition note. SA building work is on NCC 2022 (Amendment 2) until 30 April 2027, with SA variations in Ministerial Building Standard MBS 007. No MBS 007 modification to these stair clauses was found, so confirm with your certifier before relying on the national figures alone. NCC 2025 applies to SA building work from 1 May 2027 and carries the same winder limits, measurement points and Table 11.2.2a figures, so the answer does not change when the edition moves. [6]