Five ways to vent plumbing
G13/AS1's own system and AS/NZS 3500.2's four, compared.
- G13/AS12nd Edition Amendment 102 Nov 2023
- AS/NZS 3500.2:2025
Five systems, one job: keep every trap's water.
G13/AS1 vents nearly every pipe. AS/NZS 3500.2 offers four systems, from venting every trap to venting only the stack, each with its own limits on how far fixtures sit from the stack and how high it goes.
Fewer vents mean fixtures closer to the stack.
Every venting system answers the same problem, keeping each trap's water in place, with more or fewer vent pipes. The fewer the vents, the closer and fewer the fixtures have to be.
Same places, a different mix.
Every system keeps the stack vent at the top. They differ on how many vents sit down by the traps and whether a relief vent runs beside the stack. With fewer vents, fixtures have to sit closer to the stack.
G13/AS1 5.6.2, Table 5 · AS/NZS 3500.2 8.2.2, 8.2.3, 8.5.3.1, 9.2.1, 9.2.3
Every trap vented means a lot of vent pipe.
Our reading: each trap vent has to rise above its fixture before it joins another vent or reaches open air, so check early that the walls and ceilings have room for them. All that pipe adds material and labour, so choose fully vented where the fixtures or the layout need it, not by default.
AS/NZS 3500.2 8.2.2(a), 8.5.1.4
Try it on your own plans.
Put your fixtures on your own floor plans and see what it sizes, vents and draws. The tool is still young, so treat it as a second pair of eyes and check what it gives you. Or start with the three-storey house: plumb it in 3D and watch the rules at work.
Key takeaways
- Every system keeps a stack vent at the top. They differ on how many vents sit lower down.
- More vents free up the layout, but take room, material and labour.
- Fewer vents keep fixtures close to the stack: own pipes ≤ 2.5 m, DN 100 ≤ 6 m.