As New Zealand has no specific legislation relating directly to the cleaning of commercial kitchen extraction systems, the Australian standard AS1886 is followed. This standard is considered to be best practice when it comes to cleaning in this area.
The purpose of a BWoF (Building Warrant of Fitness) is to ensure the building is safe for those inside it. If your building has any form of mechanical ventilation, and it is on your BWoF schedule of compliance, it must be inspected before the BWoF can be signed off by an Independent Qualified Person (IQP). This is usually done annually before the BWoF can be signed off and presented to the local council. It is the landlord’s responsibility to ensure the inspections are carried out and any remedial work performed, and the system re-inspected before the BWoF deadline. Almost always some form or level of cleaning will be required, then documented. You would be wise to budget for this work and to facilitate regular cleaning, as advised, before the BWoF deadline. The landlord may be fined for non-compliance if this deadline is not met.