Ventilation of drains and branch drains

The system should be ventilated at or near the head of a main drain, and a branch drain longer than 10 m. A ventilation stack (see paragraph 2.13) or, a ventilated discharge stack (see paragraph 2.15) or a separate ventilation pipe should be used. Where a separate ventilation pipe is used it should terminate either – (a) in the external air at least 900 mm above any opening into a building within 3 m, with a cage or cover which does not restrict the air flow (see Diagram 2.3); or (b) with an air admittance valve which complies with BS EN 12056: Part 2 and BS EN 12380.