The New Zealand Green Building Council (NZGBC) and Auckland Council are calling for Building and Construction Minister Chris Penk to take steps to address the problem of new homes overheating.
NZGBC Chief Executive Andrew Eagles says many recently built homes are experiencing unacceptably high indoor temperatures during summer – particularly terraced homes and apartments.
The absence of a check at the design stage is a key contributing factor, says Eagles, in the letter to Minister Penk.
“International building codes, including those in Australia and the UK, require checking at design stage and a limit on internal heat gain. Unfortunately, the New Zealand Building Code has no such requirement,” says Eagles.
“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.”
Climate data shows 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. That number is projected to continue to rise in future years.
“We strongly encourage the Ministry to initiate policy development and consultation to incorporate an overheating assessment requirement into the ‘H1 framework’ for terraced and apartment housing,” says Eagles.
Homes designed and built under current standards are not adequately equipped to maintain healthy indoor conditions under these projected climate scenarios.
Auckland Council chief executive, Phil Wilson, has signed the joint letter, supporting the NZGBC’s call for urgent change.
“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. Currently there are tools that can determine how much energy is required to cool a house over summer, providing a better understanding of how susceptible a house is to overheating.”
Solving this problem needn’t add cost to housing, he says, in fact the opposite might be true.
“In any event, it will help ensure houses are more energy efficient and therefore cheaper to live in downstream.
“Unfortunately, this process is currently only optional. It would be good to see this mandated in the Building Code for terraced housing and apartments. “
The Building Act’s primary purpose is to ensure people can use buildings safely and without endangering their health. Current regulatory settings do not adequately address overheating.
Auckland Council research in 2024 identified overheating as a growing problem leading to occupant discomfort, additional energy costs and health risks.
Read the full letter:
Hon. Chris Penk Minister for Building and Construction Parliament
21st November 2025
Overheating homes and the health risks for New Zealand households
Tēnā koe Minister Penk,
We are writing to recommend urgent action to address overheating in new residential buildings, which is emerging as a significant public health and building performance issue.
As we approach the warmer months, there is increasing evidence that many recently built homes are experiencing unacceptably high indoor temperatures during summer. This issue is now being widely reported by homeowners, designers, and the construction sector.
It was encouraging to hear your acknowledgment of this matter at the Housing Summit in May 2025 and your indication that you wish to see practical steps taken to address it.
Auckland Council research in 2024 identified overheating as a growing problem leading to occupant discomfort, additional energy costs and health risks. Media coverage and industry concern are increasing as the issue becomes more visible and widespread.
The Building Act’s primary purpose is to ensure people can use buildings safely and without endangering their health. Current regulatory settings do not adequately address overheating, particularly in modern higher-density housing typologies.
The scale of the issue
Climate data shows that the number of high-temperature days in New Zealand is increasing sharply. Historically, areas such as Auckland and Whangārei experienced around a dozen summer days above 25 °C. That number is projected to rise to around 50 days per year by 2050. Homes designed and built under current standards are not adequately equipped to maintain healthy indoor conditions under these projected climate scenarios.
Occupants are reporting that parts of their homes become excessively hot and that mechanical cooling is often the only way to maintain comfort. These experiences are consistent with international research showing that overheating in energy-efficient dwellings is becoming a leading cause of indoor environmental stress.
A 2024 study estimated that approximately 500 children under five are hospitalised each year in New Zealand for heat-related reasons. If the data were extended to include all age groups, this figure would likely be substantially higher. People with cardiovascular conditions and older adults are particularly at-risk during periods of prolonged heat.
From an economic and environmental perspective, reliance on air conditioning to manage these conditions places additional cost burdens on households and adds to peak electricity demand, creating unnecessary strain on the national energy system and sadly undoing great strides towards being energy efficient in our houses.
Underlying causes
The absence of explicit performance requirements for managing high indoor temperatures is a key contributing factor. While international building codes, including those in Australia and the UK, set out modelling or performance limits for internal heat gain. Unfortunately, the New Zealand Building Code has no equivalent requirement.
Current design practices often prioritise access to sunlight but do not adequately balance this with shading, ventilation or thermal mass considerations. The shift toward higher-density housing has intensified the issue, as terraced and apartment dwellings have fewer external walls and openings, reducing opportunities for natural cross ventilation.
Proposed solution
We propose that New Zealand introduce a requirement for designers of terraced homes and apartments to model overheating risk during the design phase and to demonstrate compliance with a defined cooling-load limit, the maximum allowable level of internal heat energy that a building may accumulate or require to maintain comfortable temperatures.
This approach aligns with recent amendments to the Australian National Construction Code, where similar measures have been introduced and well received by industry.
We recommend separating heating and cooling metrics in the NZ Building Code modelling pathway so that designs must show both reduced heating and cooling energy demand relative to the reference building.
This requirement would initially apply to terraced and apartment buildings, where the risk of overheating is greatest. The necessary assessment tools and expertise already exist within the industry. Software and guidance materials are available from many providers at low cost, ensuring minimal implementation barriers. An 18-month transition period is suggested to allow for industry familiarisation and adjustment.
Benefits
This approach offers multiple policy and public benefits:
• Improved indoor comfort and health outcomes for New Zealand households.
• Reduced demand on the electricity grid during periods of high heat. • Helps meet the objective of the building code to deliver healthy places
• Alignment with international best practice, particularly Australia’s new performance standards.
• Implementation through existing regulatory pathways without legislative amendment or Cabinet approval.
• Focused application to higher-risk housing types, avoiding unnecessary burden on detached dwellings.
This proposal is supported by Te Kāhui Whaihanga New Zealand Institute of Architects (NZIA), Architectural Designers New Zealand (ADNZ), BRANZ, the New Zealand Construction Industry Council (NZCIC) and Auckland Council. Together, these organisations represent the majority of New Zealand’s architecture, design, research, and construction leadership.
We strongly encourage the Ministry to initiate policy development and consultation to incorporate an overheating assessment requirement into the H1 framework for terraced and apartment housing.
We would welcome the opportunity to discuss implementation options and transitional support measures for industry.
Ngā mihi nui,
Phil Wilson Chief Executive Auckland Council
Andrew Eagles Chief Executive New Zealand Green Building Council
NOTES:
- This requirement to model overheating would initially apply to terraced and apartment buildings, where the risk of is greatest. The necessary assessment tools and expertise already exist within the industry. Software and guidance materials are available from many providers at low cost, ensuring minimal implementation barriers.
- This proposal is also supported by Te Kāhui Whaihanga New Zealand Institute of Architects (NZIA), Architectural Designers New Zealand (ADNZ), BRANZ, and the New Zealand Construction Industry Council (NZCIC). Together, these organisations represent most of New Zealand’s architecture, design, research, and construction leadership.
- See also: New Zealand needs better building code to prevent thousands of overheating Kiwi homes – January 2024