Key takeaways
- AS 1684 is the Australian Standard for residential timber framing, including deck framing
- It sets joist and bearer sizing and spacing relative to span and load
- It covers footings, connections, bracing and subfloor ventilation for elevated decks
- A BWC-licensed builder designs or certifies the deck frame to AS 1684 - it is not optional
What AS 1684 is
AS 1684 - Residential Timber-Framed Construction - is the Australian Standard that governs how residential timber framing is designed and built. It applies to house framing and, importantly for a deck, to deck framing.
The frame is the structural skeleton of a deck: the bearers, the joists, the posts and the footings that carry the decking boards and everything on them. AS 1684 is the engineering rulebook that decides how that skeleton is put together so it is strong enough, stiff enough and durable enough. The boards on top are the visible part; AS 1684 governs the part underneath that actually holds the deck up.
What AS 1684 covers in a deck
For a deck, AS 1684 covers several things. Joist sizing and spacing relative to span and load - how big the joists are and how far apart they sit, which depends on how far they span and how much weight they carry. Bearer sizing and spacing - the same logic for the larger members the joists rest on. Footing requirements - bored pier, screw pile, or pad-and-post, sized to the load and the soil. Connection design - joist hangers, hold-downs and bracing that tie the structure together and stop it racking. And subfloor ventilation for elevated decks, because still air under a deck rots the frame.
A cheap deck quote often quietly economises here, because none of it shows in the finished deck. Wider joist spacing than AS 1684 allows for the span makes the deck feel bouncy and shortens its life. Undersized bearers, too few footings, or missing bracing all weaken the deck in ways you cannot see until movement appears.
Why AS 1684 matters and who is responsible for it
AS 1684 matters because the frame is what makes a deck safe and durable. A deck framed to the standard carries its load, stays stiff underfoot, and lasts. A deck framed below the standard can flex, sag and ultimately fail - and a deck failure with people on it is a serious safety event.
A BWC-licensed builder is required to design the deck framing to AS 1684, or to have it certified. For any deck over the $20,000 inc GST threshold, plans must be produced, and council may require framing plans for some installations regardless of cost. This is one reason licensing matters - a licensed builder is accountable for framing the deck to the standard.
When you compare deck quotes, the frame is where the real differences hide. Decking Adelaide gets you 3 itemised quotes from BWC-licensed builders, with the frame as a separate line, so you can see whether the builders priced the same structure. See also our guides on BWC licensing and deck permits in South Australia.
AS 1684 Timber Framing - frequently asked questions
AS 1684 - Residential Timber-Framed Construction - is the Australian Standard that governs how residential timber framing is designed and built, including deck framing. It sets the engineering rules for joists, bearers, footings, connections and bracing - the structural skeleton of a deck that carries the boards and everything on them.
Yes. The frame of a residential deck is designed to AS 1684, the standard for residential timber framing. A BWC-licensed builder designs or has the deck framing certified to the standard. For a deck over the $20,000 inc GST threshold, framing plans must be produced, and council may require them for some decks regardless of cost.
AS 1684 covers joist sizing and spacing relative to span and load, bearer sizing and spacing, footing requirements (bored pier, screw pile or pad-and-post), connection design including joist hangers and bracing, and subfloor ventilation for elevated decks. It governs the structural frame - the part of the deck you never see but that holds it up.
Joist spacing is set by AS 1684 based on the span and the load. Joists spaced wider than the standard allows make the finished deck feel bouncy underfoot and shorten its life. A cheap quote sometimes widens joist spacing to save timber, because it does not show in the finished deck. Itemised quotes on the same framing scope reveal it.
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