For those works that are exempt from the need to obtain a building consent the legislation regards these as being of low risk for non-compliance or a danger to people or property.
This is open to interpretation and you may need to obtain your own legal and/or technical advise in respect to this.
Schedule 1 of the Building Act 2004 sets out the work the building work for which it is not necessary to obtain a building consent. There is an explanation and a copy of the exempt building work in the section Building Work Exempt from Building Consent.
Building work that may require a building consent, is defined in the Building Act 2004, includes work
(a) i) connected with construction, alteration, demolition, or removal of a building: and
(a) ii) on an allotment that that is likely to affect the extent to which an existing building on that allotment complies with the building code; and
(b) includes site work