This study looked at 88 homes across New Zealand and measured temperature and relative humidity during the winter months at locations in Auckland, Wellington, the upper South Island and Dunedin in 2016 and again in Wellington in 2017.

Key findings:

The median temperature inside bedrooms was 16.4°C, and relative humidity levels were above 65% for 46% percent of the time. The bedrooms were found to be below 18°C for 84% of the night and morning time period (23:00–09:00). The mould index at each home was determined, indicating that many homes show mould growth in bedrooms and/or bathrooms. These results indicate a lack of heating and/or ventilation in these dwellings causing mould growth with its potential adverse health effects. Air and dust samples were also taken to determine the fungal spore count in the air and the presence of mycotoxins in the dust. Very high spore counts were observed in several homes, which were subsequently remeasured to confirm the findings.