Technical Booklet N Drainage·Page 16·2.13(a)
Ventilation stack termination - external air
The upper end of a ventilation stack must terminate in external air at least 900 mm above any building opening within 3 m, with a cage or cover that does not restrict air flow.
The upper end of a ventilation stack should terminate 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).
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