What is the New Zealand Building Code – a minimum or maximum rulebook?

Opinion: Recent stories about Gib shortages and delays in new home insulation standards have given the New Zealand Building Code more limelight than it’s had for a while. 

At the risk of stating the obvious, a building code plays a major role in determining the quality of new builds, including houses. There’s plenty of information about the Code on the Building Performance website, run by the Ministry of Business, Innovation and Employment.

But 30 years after it was introduced, it seems many people do not know why we have the Building Code or what it is.

How did we get here? 

Major New Zealand cities have had building controls since the 1840s and smaller centres since the 1870s. While building bylaws varied between the various cities, towns and boroughs, they typically covered fire, basic structure, sanitation and nuisance.

The 1931 Napier earthquake brought home the need for national building controls in our shaky isles. In the aftermath of the quake, a government-appointed review committee recommended a ‘Uniform Building Code’ and the newly established Standards Institute appointed committees to make this possible.

In 1935, the first model building bylaw came into being, known by its standards number NZSS 95. Major revisions to the model building bylaw took place in the 1960s, leading to the new NZSS 1900. 

These bylaws were prepared through the standards process: representative committees prepared the base documents; public comments were sort; and the final version represented a broad consensus. 

Both bylaws were adopted by most councils, although many added their own variations to the rules. These variations eventually led to complaints about a lack of consistency between councils, as well as complaints about the growing cost of excessive requirements. 

In 1984, a government-appointed review team recommended shifting from the prescriptive NZSS 1900 to a code with performance objectives. This new code would leave to the “market, professional and technical competence, the provision of good technical information, and pride in doing a good job”. 

For the first time, New Zealand was to have a building code concerned with minimum, not good, performance.

The job of developing the new regime was given to the Building Industry Commission. Its report led to the Building Act 1991 and the associated Building Regulations 1992. The first schedule in these regulations is the “New Zealand Building Code”, mandatory for all local authorities, and in a major change, also for central government. 

A new agency, the Building Industry Authority, was initially given responsibility for the code. Authority decisions, coupled with industry behaviour, led to the weathertightness or “leaky buildings” disaster of the 1990s and early 2000s.  

It was subsequently decided the Authority should become part of the Department of Internal Affairs. But this didn’t last long: it soon became the Department of Building and Housing, and then the Building Performance branch within the Ministry of Business, where it still resides.

The Building Act itself was revised in 2004, with an added focus on “designing and building it right the first time”. The Act has not proved to be technically or politically robust. From 2004 to 2021, it has been amended about once a year – a high rate of change for any legislation.

Decoding the Building Code 

The building code’s regulatory framework is illustrated in the figure below.

Source: Ministry of Business, Innovation and Employment

 The code provides high level statements or “objectives” about how various aspects of a building should perform at worst. The code designers expected the market would call for higher performance where appropriate e.g., for prestige buildings.

Each objective is contained in one of 40 separate clauses – for example, “Clause H1 Energy Efficiency”. The objective is supported by a hierarchy of “functional requirements” and then “performance criteria”.

Compliance with the code is achieved through three possible paths: 

  • using an “Acceptable Solution” (AS) – do this exactly and you have complied; 
  • using a “Verification Method” (VM) – use this method to show you have complied; or 
  • creating an “alternative solution”, which complies with the performance criteria.

Clause H1 Energy Efficiency now has five separate ASs and VMs for houses and larger non-residential buildings. Not all 40 clauses in the code have both an AS and a VM, but all have at least one of them. The ministry updates these on a regular basis, following public consultation.

Just to make life more complicated, not all issues in the Building Act are covered by the code. 

For example, one of the stated purposes of the Act is to set performance standards ensuring “buildings are designed, constructed, and able to be used in ways that promote sustainable development”. Apart from the energy efficiency requirements in clause H1, there are no code provisions to support this. 

Clause B2 Durability does set minimum lifetimes for different parts of a building – 50, 15 or 5 years depending on factors such as ease of replacement and relative importance, and assuming “normal maintenance”. The Act’s principles also put on onus on builders – as well as others involved in building design and construction – to take into account “the need to ensure that maintenance requirements of household units are reasonable”. But the code has nothing to say on how this might be done. 

Despite these gaps, the Building Code’s minimum performance approach has already resulted in a huge amount of documentation relating to building controls. 

Building Code by the numbers

Since the advent of building controls in New Zealand, the rulebook has increased significantly. 

The 1854 Auckland City Building Act ran to just eight pages (see Table).

Today, the code, and its acceptable solutions and verification methods, comprise 47 documents totalling 1,500 pages. According to Google, a further 9,900 web pages providing guidance on the code are available on the ministry’s Building Performance website. 

The ministry’s Building Code Hub provides another 11,000 supporting documents and webpages. These include legally binding determinations about the interpretation of building rules. There are currently 1,775 determinations, of which 925 relate to housing. 

Why such an increase in size? Codes have increased in coverage, administrative requirements and enforcement provisions. Buildings have become more complex, as they now meet wider owner and societal expectations. There are now many more building systems and materials, often with tighter requirements on their use and maintenance. 

There has also been a shift in knowledge, education and training away from the people building on-site to those working off-site.

Although not all these documents will be relevant for every building, the ones specific to the building type must be followed – not to create a high performing building, but merely to ensure the legal minimum requirements are met.

Doing things better is another story.

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