An Explanation of how the (NZ) Building Act 2004 came to be:

Up until 1931 the building of houses in New Zealand was relatively unregulated, since most building work from earliest times predominantly used local timber for framing and for cladding following established (British) building methods. It became evident from the widespread damage and loss of life resulting from a major earthquake in Napier in 1931, particularly from buildings built from brick and masonry, that better trade practices requiring new building standards were necessary to protect life and property. As a result the Buildings Regulations Committee and Standards New Zealand were established the following year. These became the forerunners to the development of some dozen or so Bylaws, several Regulations and various Acts, set up for governing the way New Zealanders built houses.

In 1991 the Government of the day took a bold step incorporating a carefully developed concept of using generic ‘performance requirements’ (in place of prescriptive requirements) into legislation to manage the way we build houses. The Building Act 1991, combining many Relegations and Acts into one Act, was born. With the passage of the Building Regulations 1992, came a new concept of how the quality and reliability of building was to be achieved. With these Regulations came the ‘Building Code’ – a set of minimum performance requirements that all new building work had to meet. And since the Building Code did not say how buildings were to be built, it created the need for a set of explanatory documents on how the requirements of the Code could be achieved. A new Building Industry Authority was established to provide these explanatory documents. Territorial Authorities and District Councils were made responsible for ensuring the design for buildings and houses met the performance requirements, and building inspectors became the default authority for building work in their area.

Since the use of performance requirements allowed for the widest possible use of new and potentially cost-saving building materials and methods, the Government, Territorial Authorities, consumers and the building industry itself, felt comfortable that New Zealand was able to enjoy both affordable housing and new materials and methods at the same time.

As history now tells us this comfortable arrangement was to be shocked into a realisation that houses beginning in 1995, were being built to leak, and the use of untreated framing without the use of a 'cavity' behind the exterior cladding, was vulnerable to widespread rotting.

According to the web site ConsumerBuild, the Building Industry Authority commenced their investigations into the causes of “leaky homes” in 2002 and by 2003 as a result of a major inquiry and report, a new Building Act (2004) was proposed. At the same time a new Department of Building and Housing was to be established to manage new standards for design, materials and construction methods. 
The Department of Building and Housing (known as the 'DBH') is now responsible for the management, review and maintenance of the Building Code and issues related to the Building Act 2004. Their web site is www.dbh.govt.nz