Mid-landing offset on switchback stairs: why the handrail goes vertical (AS 1428.1)

On a switchback or 90 degree stair, the two flights at the mid landing must be offset by one tread width. That offset is required so the handrail can extend one tread length past the riser at the bottom of a flight and the inner rail can continue parallel to the pitch. If the risers are drawn in line, the rail has to go vertical, which fails the Standard's handrail geometry and can get in the way in an evacuation. NSW applies NCC 2022 Amendment 2 (in effect since 29 July 2025). D4D4(a)(ii) calls up clause 8 of AS 1428.1:2021 for a stairway that is not fire-isolated. A vertical inner rail on a fire-isolated required exit is also a failure under clause 9 / D3D22(1)(f). NCC 2025 applies in NSW from 1 May 2027.

Call (02) 9586 3111. The free initial consultation covers a review of the floor plans only. A site inspection of a built stair is chargeable. Call for a fee.

The regular error: flights lined up at the mid landing

The same one-tread offset is required on both a U-return / switchback (180 degree) stair and a 90 degree (L-shaped) stair with an intermediate landing.

The usual drawing mistake is to align the last riser of the lower flight with the first riser of the upper flight. That gives a rectangular landing and looks tidy on plan. That alignment leaves a full riser of height to make up in a very short run of inner rail, so the fabricator is forced into a vertical or near-vertical crank. It also leaves no room for the handrail to extend one tread length past the riser at the bottom of the flight.

With the offset, the upper flight's first riser is set back one tread width, so the inner rail can protrude one tread length beyond the lowest riser, then turn while staying on the same pitch and at a consistent height.

Why the offset is mandatory, not optional

The handrail must extend one tread length past the riser at the bottom of a flight. That one-tread extension is the reason the flights have to be offset. Some published material suggests a deeper landing as an alternative (the rail runs one going, then turns 180 degrees) if the flights are not offset. Sydney Access Consultants does not accept a deeper landing as a substitute, because it does not provide the required one-tread extension at the bottom of the flight in the way the Standard's mid-landing geometry requires.

What Figure 28 is asking for

AS 1428.1:2021 Figure 28, "Handrails to stairs with intermediate landings", shows the geometry. The figure itself is not reproduced here. The confirmed points are:

• The two flights at the mid landing are offset by one tread width, so the handrail can extend one tread length past the riser at the bottom of a flight.
• The inner handrail continues parallel to the pitch through the turn.
• At the top and bottom of the stair, the handrail extends at least 300 mm, parallel to the surface, and is turned through 180 degrees or returned fully to an end post or wall face. At the bottom of a flight the rail must also extend one tread length past the riser. Do not collapse that one-tread extension into the 300 mm end return, or treat the 300 mm as a substitute for it.
• The plan shows two internal-handrail options at mid landings. Both depend on the offset.
• The plan marks a 1000 mm minimum at the mid landings, on both sides. That 1000 mm is clear of any obstruction, including handrails.

Figure 28 itself is a 180 degree switchback. The same one-tread offset is required at a 90 degree mid landing, so the handrail can protrude one tread length beyond the lowest riser in the flight.

Related handrail rules the reader will expect, without turning this page into a full catalogue: height 865 mm to 1000 mm, consistent along the flight and landings; rails on both sides of an accessible stair; no obstruction to the passage of a hand. See handrails at stairs and accessible stairways.

Why a vertical section fails

It does not follow the nosing line, it breaks a continuous grasp, and the height of the rail is no longer consistent through the landing. In a crowd or an evacuation, a vertical crank is something to hit, catch on, or lose hold of.

Which NCC clauses apply in NSW now

• D3D22 is the general handrail clause (location, height, continuity along a flight).
• D3D22(1)(e) requires a continuous handrail between stair-flight landings. The ABCB Guide says that requirement does not apply around a landing. Do not blur this with the stricter AS 1428.1 mid-landing rules.
• D3D22(1)(f), as amended by Amendment 2, requires a handrail in a required exit serving an area required to be accessible to comply with clause 9 of AS 1428.1:2021 (with the stated exception for clause 9(d) on a primary-school lower rail).
• D3D22(4) points the reader to Part D4 for disability-access handrails.
• D4D4(a)(ii) calls up clause 8 (including 8.2, stairway handrails, and Figure 28) for every stairway except a fire-isolated stairway and except stairs in areas exempted by D4D5.
• D4D4(a)(iii) limits a fire-isolated stairway, under Part D4, to clause 8.1(f) and (g) (the nosing-strip provisions). That is not the end of the story. A vertical inner handrail on a fire-isolated required exit serving an area required to be accessible is also a failure under clause 9 / D3D22(1)(f). The offset and the one-tread extension at the bottom of the flight still matter on a fire-isolated required exit.

D4D7 is braille and tactile signage. It is not a stair clause. NSW stays on NCC 2022 Amendment 2 until 1 May 2027, when NCC 2025 is adopted.

2009 versus 2021 numbering

Older pages and many search results still say clause 11.2 and clause 12. In AS 1428.1:2021 those are clause 8.2 (stairway handrails) and clause 9 (handrails). Figure 28 kept its number. This page cites 2021.

Fix it on the plan, before the pour or the fabrication

The architect's plan must leave a mid landing that can take the one-tread offset and still provide the 1000 mm minimum, measured clear of any obstruction, including handrails. This applies to both 180 degree switchbacks and 90 degree mid landings.

This is a set-out decision, not a handrail-catalogue decision. Once the concrete mid landing is poured, or the steel stair is fabricated with the flights in line, moving a flight by one tread is a structural change.

At DA, the report should flag whether the mid-landing geometry is capable of compliance. At CC, the sections and shop drawings should show the offset, the inner-rail path, and the 300 mm extensions at the top and bottom. See what certifiers want in an access report and DA, CC and CDC access reports.

What is checked at the occupation-certificate inspection

• The built inner rail is compared with the approved detail: does it follow the pitch through the turn, or has a vertical or steep crank appeared?
• Extensions of at least 300 mm at the top and bottom, with ends turned or returned.
• Height in the 865 mm to 1000 mm range, and consistent through the landing.
• Clear width, and no obstruction to the passage of a hand.

A vertical inner rail is the kind of late defect that holds up an Occupation Certificate.

Frequently asked questions

Why must the two flights at a mid landing be offset by one tread width?

Because the handrail must extend one tread length past the riser at the bottom of a flight. That extension is what lets the inner rail stay continuous and parallel to the pitch through the turn.

What happens to the inner handrail if the flights are lined up?

The rail has to drop through a vertical or near-vertical section. That breaks a proper grasp and can impede people in a crowd or an evacuation.

Does the rule apply to fire-isolated stairs?

Yes. A vertical inner rail on a fire-isolated required exit serving an accessible area is also a failure under clause 9 / D3D22(1)(f), not only under clause 8.

Does the same one-tread offset apply at a 90 degree mid landing?

Yes, so the handrail can protrude one tread length beyond the lowest riser in the flight.

What does the 1000 mm minimum at mid landings measure?

It is clear of any obstruction, including handrails.

Is a deeper mid landing an acceptable alternative to the offset?

No. Sydney Access Consultants does not accept a deeper landing as a substitute for the one-tread offset.

Call (02) 9586 3111 for a fee.