Our deck on a sloping Brisbane block sits 800 mm above ground at the house and about 1.3 m at the far corner. The certifier wants a barrier the whole way round. Where exactly does the 1 m trigger bite?

The trigger is a height test taken at each point along the edge, not a single test applied to the whole deck. A barrier is required along the sections where the fall reaches 1 m, which on your block means the far end, and not at the house end where the drop is 800 mm. [1]

The provision is worded as a per-point test. A continuous barrier must be provided along the side of a trafficable surface, a deck included, where it is possible to fall 1 m or more measured from the level of the trafficable surface to the surface beneath. [1] Figure 11.3.3a puts the same test in a diagram: the vertical drop H below 1 m needs no barrier, and H of 1 m or more does. [1]

Applied to a sloping block, that gives you two different answers along one continuous edge:

• House end, 800 mm drop: below the trigger, so no barrier is required by this provision. [1]
• Far corner, about 1.3 m drop: at or above the trigger, so a barrier is required. [1]

The obligation starts at the point where the drop reaches 1 m and continues around the perimeter for every section where the fall is 1 m or more.

Where a barrier is required, it must be not less than 1 m above the deck floor. [2]

The margin is the thing to check before you argue the point. At 800 mm you have only 200 mm of clearance, and on a sloping site that number moves with the finished ground level, not the level on the drawings. Have the drop confirmed as-built from the finished deck surface down to the finished surface beneath at the critical points, particularly anywhere landscaping or a cut-and-fill batter may change the ground line after handover. If the fall reaches 1 m anywhere you had assumed it would not, the barrier follows.

On the certifier's whole-of-perimeter position: the provision as written does not support a blanket barrier based on the deck's highest drop. Clause 11.3.3 states the test strictly as a 1 m fall at the point in question. That does not make the certifier wrong, but it does mean the requirement has to come from somewhere other than this clause. Ask them to identify the specific provision they are relying on for the sub-1 m sections before you price the extra work.

Queensland is on NCC 2022 Amendment 2 and moves to NCC 2025 on 1 May 2027. The equivalent NCC 2025 provision carries the same 1 m fall trigger, adding an exemption for barriers complying with AS 1657 serving fixed platforms and walkways, which does not reach a domestic deck. [3] The Queensland Development Code continues to apply alongside whichever NCC edition is in force, so check whether anything in the QDC or a local planning condition touches your deck as well.