Balustrades are one of the most commonly failed items on deck inspections. The rules are not complicated, but they are precise, and a few millimetres can decide whether a balustrade passes. This guide walks through what the building code requires for decks on houses.
When a deck needs a balustrade
The building code calls a balustrade a barrier. Part 11.3 of the ABCB Housing Provisions requires a continuous barrier along the edge of a deck, balcony, landing or stair wherever a person might drop 1 m or more. That drop is measured from the deck surface down to the surface beneath.
That means a deck only 800 mm high at the house can still need a balustrade further out if the ground drops away. Measure the fall at every edge, not just one. Retaining walls are generally excluded from these barrier rules.
How high the balustrade must be
- Decks, balconies, landings and verandahs: at least 1 m above the floor.
- Stairs and ramps: at least 865 mm above the stair nosings or ramp floor.
A landing barrier can be 865 mm only along the inside edge of a stair landing for a short length. Where the height changes from the stair to the deck, the code allows a transition.
Think about fixed seats or planter boxes placed hard against the balustrade. They can give a child a foothold, so keep them clear of the edge where possible.
The gap rule
Openings in a balustrade must not let a 125 mm sphere pass through. This applies between balusters, under the bottom rail, and anywhere else in the barrier. Where a balustrade is fixed to the side face of a deck, the gap between them must be no more than 40 mm.
Timber shrinks and moves, so build to a smaller gap than 125 mm to allow for it. Gaps that pass on the day of the inspection can open up over time.
Climbable elements on high decks
If the drop exceeds 4 m, any horizontal elements in the balustrade between 150 mm and 760 mm above the floor must not make it easier to climb. Horizontal rails, wires, decorative infill, and even some framing members can act as a ladder for a small child.
This is why horizontal wire and slat designs are common on low decks but often unsuitable on upper level balconies and high decks on sloping blocks. For lower decks, the climbing rule doesn't apply, though the 125 mm gap test still does.
Wire, glass, strength and pools
Wire balustrades are acceptable if they meet the code's wire rules. Horizontal wires need the right tension or limited deflection, and vertical wire systems have limits on wire size and support spacing. Wires sag over time, so retensioning is part of maintenance.
Glass balustrades must also meet the glazing provisions of the code, including safety glass requirements.
Strength. Barriers must be designed to resist loads set by AS/NZS 1170.1. Posts fixed only to the deck edge joist, without proper blocking or brackets, are a common weakness.
Pools. If a deck doubles as a section of pool fencing, or sits near one, the pool barrier standard AS 1926.1 applies. That standard sets separate rules for barrier height and non-climbable zones, which differ from the deck balustrade rules. Get the pool barrier design checked separately. Our pool and spa certification service covers this.
Getting it right at inspection
Many balustrades fail because they were treated as a finishing detail. Show balustrade height, infill type and fixing on the plans, and confirm product details with your supplier. If the deck is exempt, it still has to comply. See our guide to Deck height and size limits for exempt development.
CertifiBuild certifies decks, pergolas and patios across NSW. Book an inspection at least 48 hours ahead, or request a quote for certification.
Local help across NSW
CertifiBuild certifies Class 1 and Class 10 work in 39 council areas. Local rules on these council pages are a good place to start: Northern Beaches Council, Fairfield City Council, Sutherland Shire Council, Randwick City Council, Blacktown City Council, Blue Mountains City Council.
Suburb pages with local planning notes: Brookvale, Canley Vale, Engadine, Freshwater, Gymea, Kensington, Kings Langley, Leura, Lidcombe, Manly. You can also browse every service area.
Sources
- Housing Provisions, barriers and handrails (Part 11.3), ABCB
- Safe movement and access provisions (Part H5), NCC 2022 Volume Two, ABCB