Open Access Te Herenga Waka-Victoria University of Wellington
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Design and Construction Features that Cause New Houses in New Zealand to Overheat

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posted on 2021-11-08, 23:02 authored by French, Lisa

Analysis of indoor temperature measurements taken in 397 randomly selected houses has revealed that New Zealand houses are becoming warmer in summer. Houses built at the end of the 20th century are during the daytime (9 am to 5 pm), on average, 2.5 degrees C warmer during summer months (December to February) than houses built at the start. For example, in houses built during the 1990s, temperatures above 25 degrees C are found 40% of the time during the summer early evening (4 pm to 6 pm) - temperatures that could be considered as uncomfortably warm in a temperate climate. Since 2006 there has been a rapid uptake of heat pumps in New Zealand, and a survey provides evidence of a growing number of households actively cooling, when traditionally very little cooling has been done. The ability for occupants to cool during the warm summer early evening has the potential to create an additional peak load on the electricity network. The trend towards increasing indoor summer temperatures could be due to a range of features, including house design, construction and operation. These have been explored through analysis of the temperature data and thermal modelling using SUNREL with validated models of five houses. Although the monitored sample was sizable, the variation in occupant behaviour means it was not possible to explore all potential drivers or eliminate other influences. The use of thermal modelling permitted parametric investigation of the role of different features to be explored. The analysis of monitoring data and the thermal modelling showed that the main causes of increasing temperatures are: increasing glazing area; lower ventilation rates; reduction of external shading through reduced eave size; and to a lesser extent increased levels of thermal insulation. These findings have been used to provide guidance for new house designers as well as suggestions for modifications of existing houses.


Copyright Date


Date of Award



Te Herenga Waka—Victoria University of Wellington

Rights License

Author Retains Copyright

Degree Discipline

Building Science

Degree Grantor

Te Herenga Waka—Victoria University of Wellington

Degree Level


Degree Name

Master of Building Science

Victoria University of Wellington Item Type

Awarded Research Masters Thesis



Victoria University of Wellington School

School of Architecture


Donn, Michael; Isaacs, Nigel