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.

“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.