Fixing our woeful Building Code: An NZGBC wishlist

02 April 2020

New Zealand’s Building Code is forever being criticised and complained about, so much so you wonder why nothing has changed. The Building Code[1] and the rest of the Building Act 2004 sets the standards for New Zealand’s buildings. Unfortunately, it has not evolved fast enough, and fails to provide New Zealanders with warm, dry, and sustainable places to live and work. 

In the face of a changing climate and in the interests of providing healthy homes and reducing our emissions, the Building Code must change, fast. Covid-19 has huge ramifications for our construction sector and it will take time to recover. We are continuing to work with industry and Government to build the timeline for change that provides certainty and a clear vision of the future. We must work together to ensure we’re creating homes and buildings New Zealanders deserve.

The Building Code is a vast piece of legislation. We don’t intend to go over all its issues and specifics here, however there are priority areas which we believe need fundamental and meaningful change.

  •  Better insulation requirements
  •  Inclusion of air tightness and thermal bridging standards
  •  Improved ventilation
  •  Requirements to mitigate overheating
  •  Efficiency standards for all energy uses
  •  Energy performance modelling and reporting

Our insulation levels and airtightness

The insulation levels currently required in New Zealand are weak when compared internationally. London and Christchurch have similar heating degree days (a measure of the number and severity of cold days) but the required insulation levels and air tightness are at least double and, in the case of floor insulation, five times higher in the UK.  To give one example, the majority of new homes are built on concrete slabs. They don’t need to be insulated to meet Code, a requirement that’s been in the UK for well over a decade.

As well as being weak, the Building Code is very limited in its scope. Ensuring a healthy, comfortable, energy efficient place relies on more than the amount of insulation. The Building Code does nothing to mitigate gaps and cracks in a home (draughts) or any consideration of thermal bridging (heat lost from areas like window frames or lintels). You can have a home incredibly well insulated, but a lot of heat can still escape through cracks and highly conductive materials bridging the insulation.

In areas like the UK, pressure testing a home is mandatory so see how airtight a place is and there’s a minimum standard they must reach. Air pressure testing should be better incentivised here.

One of the biggest thermal bridges we’ve got now in New Zealand is our window frames. The majority of these are not insulated (thermally broken in the jargon) in new homes, contributing to rooms being cold all winter, and leading to condensation and mould. Thermally-broken window frames that have an insulated space to avoid this heat loss are available and could be mandated.


As homes have become more air-tight for better energy efficiency it has been increasingly recognised in many other jurisdictions throughout the world that relying on occupants to open windows to remove moisture and pollutants is not a successful strategy. Evidence is emerging that this is a problem in New Zealand also, which shouldn’t be a surprise as physics is the same here as anywhere else in the Universe!

To combat the problem, other international building codes have started to incorporate requirements for mechanical ventilation in homes and we would like to see this adopted in New Zealand. The Building Code was changed in 2019 to require mechanical ventilation in kitchens and bathrooms but we would like to see whole-house systems mandated to ensure that all of the home (bedrooms are particularly affected) is property ventilated.

Energy and climate change – the elephant in the room

In a typical New Zealand house, a third of the energy used is for heating the space, a third is used for heating water, and the remaining third powers appliances and lighting. The Building Code is notably silent on space heating, hot water and lighting systems, meaning there is huge potential to encourage energy efficiency to reduce running costs for New Zealanders and lower emissions.

The Building Code does not set standards of efficiency for space heating and hot water, and the type of fuel used is not regulated. Many new homes are still heated with inefficient portable electric heaters rather than heat pumps which would typically use three times less electricity for the same result.

There’s nothing to disincentivise installing fossil fuel heating such as gas heaters or coal boilers for example. As a result, instantaneous gas water heaters are being specified in large numbers and were, according to BRANZ, responsible for an increase in emissions from new consented homes in Christchurch between 2012 and 2016.  The UK Climate Change Committee is calling for gas boilers to be banned in new homes by 2025. We should do the same by a similar date.


As our climate changes the importance of tackling overheating, as well as cold housing, grows. If, as we hope, insulation and airtightness requirements strengthen, there will have to be consideration in the Building Code for homes overheating. We’re already seeing it emerge in our move towards higher density, some apartments lacking cross-ventilation with only one means of getting air in and out.

The Building Code is silent when it comes to overheating and needs to better incentivise cross-ventilation, minimum window openings, window orientation and shade levels. Some countries require full modelling to show the home isn’t going to overheat for more than a certain number of days a year. We would like to see as a minimum requirements to mitigate overheating in new homes.


At the moment there’s no simple way for consumers to transparently understand how energy efficient their new home is likely to be, or differentiate it from other homes available. Homestar does this to a degree but the energy efficiency of the homes is hidden behind other issues such as ventilation, water efficiency, indoor air-quality, healthy materials and the like.

We want to see clear energy performance reporting embedded in the Building Code that ensures better standards and transparency. If somebody wants to build an efficient home, there’s no nationally agreed quantifiable bar to reach for (or ask for from a volume house builder). Many of the OECD countries have mandatory energy ratings (labels) which must be declared at point of sale. The NZGBC has been calling for this for some time. The provision of labels helps the sector to understand, incentivise and reward A-rated buildings, and poorly performing builds are exposed.

The building code needs to embed a holistic energy modelling and rating system that considers a variety of things like the insulation, air tightness, the energy performance of the lighting, heating, and hot water systems. The Building Code should require transparency, and establish benchmarks for better building.

A pathway to change

While we would love to see these changes introduced overnight, we’re conscious of the industry’s ability to adapt. The sector is grappling with a shortage of skills, with its smaller scale, with the COVID19 lockdown, bespoke builder culture, and an attitude of doing things the way they’ve always been done.

The Building Code, despite its aim to be a performance based legislative framework, has become prescriptive among industry and consenting authorities through Acceptable Solutions. As a result, the vast majority of houses are built in the same way, following the same patterns. In some ways that’s good because you can change the pattern and people will follow, but it’s a large ship to steer.

As NZGBC laid out in our Zero Carbon Road Map, we believe the Building Code should be adapted in three steps between now and 2030. We would like to work with the sector and Government to create a clear timetable for what needs to change when. A timetable would be really helpful. This could set out when key changes could take place. For instance, if agreed with the sector, thermal bridging requirements and a ban on gas boilers could be added in 2026.  Signalling this early allows the industry and market to gear up and prepare for what is to come.

There can be no doubt that change is needed. If we’re going to tackle New Zealand’s high rates of respiratory illness and meet our climate emission obligations, we have to build better.



[1] The term “Building Code” is used in this article as short-hand for the suite of documents that set the requirements for new homes. The detailed requirements are mostly contained in separate Acceptable Solutions documents that the general public thinks of these as the “Building Code”.