What is the minimum size for a vent pipe?
Summary (TL;DR)
Under AS/NZS 3500.2, the absolute minimum size for any vent pipe is DN 50. However, the main upstream vent on a drainage system must be sized based on the main drain it serves (typically DN 50 for a DN 100 drain).
Vent Pipe Sizing Rules (AS/NZS 3500.2)
Venting is essential to allow air into the drainage system, preventing trap seals from being siphoned out when water flows down the pipes.
The DN 50 Minimum
No vent pipe in a sanitary plumbing or drainage system can be smaller than DN 50. This applies to branch vents, relief vents, and trap vents.
Sizing the Main Upstream Vent
Every main drain must have at least one open vent to the atmosphere, usually located at the highest (most upstream) point of the drain. The size of this main vent depends on the size of the drain:
- For a DN 100 main drain, the main vent must be at least DN 50.
- For a DN 150 main drain, the main vent must be at least DN 80.
A good rule of thumb is that the main vent must be at least half the cross-sectional area of the main drain it serves.
Vent Terminations
Remember that vent pipes must terminate in the open air, at least 600mm above any window or door, and at least 150mm above the roof covering.
Design Drainage Systems Faster
Stop second-guessing your vent sizing. TradeDesk.now features a built-in AI Standards Reference tool that knows AS/NZS 3500.2 inside out. Ask it any venting question and get the exact pipe size and clause number instantly.