The Problem Is Getting Worse
New Zealand’s summers are intensifying. Auckland and Whangarei are already recording double the number of days above 25 degrees Celsius compared to historical baselines, and projections put that figure at 50 days per year by 2050. For anyone living in a recently built terraced house or apartment, the effects are already noticeable.
Research from BRANZ covering summer 2023/24 found that 70 percent of respondents reported their homes were warmer than they wanted. Around 500 children under five are hospitalised annually for heat-related illness. These are not weather events — they are design failures.
Why New Housing Is Particularly Vulnerable
The shift toward medium-density and high-density housing has introduced a set of design conditions that, when combined, create buildings that trap heat aggressively:
- Extensive glazing on north and west facades
- Closely packed buildings with limited cross-ventilation
- Darker roofing materials absorbing radiant heat
- Narrow gaps between units that restrict airflow
- Minimal thermal mass in lightweight timber-framed construction
Christchurch’s townhouse stock now represents 24 percent of its total housing. Auckland’s intensification has produced thousands of units with these characteristics. The Building Code currently has no requirement to assess overheating risk at the design stage — unlike the building codes in Australia and the United Kingdom, which both mandate thermal comfort assessments.
What NZGBC Is Proposing
The New Zealand Green Building Council is calling for mandatory overheating assessments to be incorporated into the H1 energy efficiency framework of the Building Code. The proposal targets terraced housing and apartment buildings — the typologies most susceptible to heat accumulation. NZGBC notes that this would not be expected to increase construction costs materially, as it requires a design assessment rather than additional physical components.
The proposal has attracted support from the New Zealand Institute of Architects, the Architectural Designers New Zealand, BRANZ, the New Zealand Construction Industry Council, and Auckland Council. Minister Chris Penk acknowledged the problem publicly in May 2025, describing the experience of homeowners being “cooked alive” in their own houses.
What Designers and Builders Should Do Now
While the code change moves through the regulatory process, designers and builders can act ahead of any mandate. Simple interventions — carefully considered window orientation, adequate eave overhangs, openable windows that allow cross-ventilation, and specifying reflective roofing — can substantially reduce overheating risk at minimal cost. The time to incorporate these considerations is at the design stage, not after the concrete has been poured.
The industry has been building hotter homes. The regulatory system is catching up. Getting ahead of this issue now will position firms well once compliance becomes a legal requirement.
