Buildings with specified intended lives
Section 113 of the Building Act 2004 applies if a building is intended to have a life of less than 50 years.
Where a building with a specified intended life is issued with a building consent that is subject to the condition that the building be altered, removed, or demolished before the end of its life, an 'extension of life' can be obtained.
An owner of a building must give written notice to the council if it proposes extending the life of a building, or they could be fined.
Change of use, alterations and extension of life (MBIE website)