What is the minimum diameter for a main drain vent outlined in the New Zealand Building Code?

The minimum diameter for a main drain vent as outlined in the New Zealand Building Code is 80 mm. This size is specified to ensure adequate airflow for venting purposes, which helps prevent the buildup of harmful gases and maintains proper pressure within the drainage system.

Adequate venting is crucial in a plumbing system, as it allows for the equalization of pressure and the removal of sewer gases, protecting the health and safety of occupants. The larger diameter also accommodates the potential need for multiple connections or future expansions of the system, ensuring longevity and efficiency.

The other options, while potentially suitable for smaller venting needs, do not provide the same level of assurance for a main drain vent in compliance with the Building Code. The 80 mm requirement reinforces the balance between functionality and regulatory standards, making it the correct choice.