Technical Booklet N Drainage·Page 15·2.12
Unventilated branch pipes
Branch ventilating pipes may not be required if the branch pipe length and slope do not exceed the maximum dimensions and gradients specified for the relevant pipe diameters.
A branch ventilating pipe should not be required if the length and slope of a branch pipe does not exceed the maximum dimensions and gradients for the relevant pipe diameters given in Diagram 2.5.
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