Hot homes issue unacceptable: NZGBC
New Zealand’s Green Building Council (NZGBC) is calling for the Government to address the problem of new builds overheating. The issue means restless nights and rising indoor temperatures as we approach summer.
BRANZ data from summer 2023/2024 showed 70% of people reported their homes were warmer than they wanted at least some of the time.
Wellington residents reported higher discomfort than Aucklanders despite having lower measured indoor temperatures, suggesting that design, layout, and ventilation have a major impact on comfort.
NZGBC chief executive Andrew Eagles says many recently built homes, particularly terraced homes and apartments, continue to experience unacceptably high indoor temperatures during summer.
Townhouses are increasingly popular, particularly in Christchurch, where they now make up about 24% of the housing stock.
Several design factors contribute to overheating: extensive window glazing, harsh sun on north- or west-facing buildings, limited cross-ventilation due to less exterior wall space, fewer windows and reduced airflow in high-density layouts, and smaller outdoor areas, darker roofs, and buildings packed closely together, which reflect heat.
In a letter to the Building and Construction Minister, Chris Penk, Andrew Eagles said international building codes, such as those in Australia and the United Kingdom, require checks for overheating at the design stage and limit internal heat gain. “Unfortunately, the New Zealand Building Code has no such requirement,” the NZGBC chief executive wrote.
“Minister Penk acknowledged this issue for Kiwi families in May 2025 and indicated that he wants to see practical steps taken to address it. Now is the time.”
NZGBC strongly encouraged the Government to develop policies that require an overheating assessment for terraced and apartment housing under the ‘H1 framework’.
They cited climate data showing that the number of high-temperature days in New Zealand is increasing sharply. Areas such as Auckland and Whangārei have seen a doubling in the number of days above 25°C, and this number is projected to rise to around 50 days per year by 2050.
Industry leaders agree
Auckland Council chief executive, Phil Wilson, signed the joint letter in support of the NZGBC’s call for urgent change. NZIA, ADNZ, BRANZ and the NZCIC also support the letter.
“We recognise there is an emerging issue with overheating of new terraced homes, especially as they are being built with more glazing and less shading.
“Auckland Council supports changes to the building code to address high internal temperatures, which good design can mitigate.”
The letter says solving the problem needn’t add to housing costs, and that the opposite might actually be true. Processes to ensure houses are more energy-efficient, so they’re cheaper to live in, are now only optional.
“It would be good to see this mandated in the Building Code for terraced housing and apartments.”
The leaders say the Building Act is clear about its purpose: ensuring people can use buildings safely and without endangering their health. “But our current settings don’t adequately address overheating.”
Many modern homes now become so hot that mechanical cooling is the only way to stay comfortable. Greater reliance on air-conditioning lifts household power bills and places extra strain on the national grid during peak heat periods, undermining progress towards more energy-efficient housing.
Auckland Council research last year identified overheating as a growing cause of discomfort. International studies echo this, pointing to overheating in energy-efficient homes as one of the fastest-rising contributors to indoor environmental stress.
The health impacts are already measurable. A 2024 study estimated that around 500 children under five are hospitalised for heat-related reasons each year in New Zealand. The figure would be far higher if extended to adults, particularly older people and those with cardiovascular conditions, who face heightened risk during sustained heat.
Supporters of the proposal say the benefits are wide-ranging: healthier indoor environments, reduced pressure on the electricity grid during peak summer heat, alignment with international best practice, and a straightforward implementation path that avoids the need for legislative change.
And because the requirements would target dense housing rather than detached homes, the burden on the wider sector would be low.
NZGBC joins EECA on the road
NZGBC, in partnership with EECA, will run a nationwide roadshow in 2026 to share practical knowledge and lift industry competence in residential energy modelling.
“Better technology means that impressive tools now exist which allow designers to properly model how a home will perform once built – the better understood and more widely adopted these tools are, the healthier, energy efficient and comfortable New Zealand’s homes will become,” Andrew Eagles says.
“We are seeing an increasing number of building firms use modelling, and they’re gaining real advantages. This roadshow is about ensuring all builders – no matter what their size or location can gain an understanding of what modelling is and how it can help meet customer needs and assist business.”
The roadshow aims to ensure builders of all sizes and regions can understand how modelling supports customer needs and business success.
The hands-on Residential Energy Modelling Masterclasses will train builders, designers and developers to use ECCHO — the Energy and Carbon Calculator for Homes — to make faster, better design decisions.
ECCHO, a New Zealand-made tool, lets designers test real-world variables such as window placement, insulation, heating systems and home orientation based on local climate. It helps avoid design surprises, accelerates compliance, and supports cost-optimal design choices.
The “Better by Design: residential energy modelling masterclasses” will run throughout 2026 in Auckland, Hamilton, Wellington, Hawke’s Bay, Queenstown, Christchurch and Tauranga.
