Around half of Kiwi kids may be sleeping in rooms that are too cold, suggests a world-first study that adds extra weight to proposed Building Code changes.
The new research, which compared temperature and humidity reading from the rooms of 2000 children with their own health records, also found more than 60 per cent were living in homes that grew too humid.
"Most New Zealand children spend nearly three quarters of their time indoors and this study gives us a deep insight into the quality of their indoor environments across the day and night," said Professor Susan Morton, of the University of Auckland's longitudinal Growing Up In New Zealand Study.
"Unfortunately, this research confirms that many children who live in poor quality indoor environments, where it's too cold or too humid, do experience poorer overall health as a result."
The project, carried out with industry-run Building Research Association of New Zealand (Branz), also added to evidence showing how the most disadvantaged children were more likely to suffer health effects of cold homes.
But this the first time data recorded by kids themselves had been used to demonstrate the connection.
"This study is the first in the world to gather actual temperature and humidity readings from the homes of thousands of children and then link the data to reported measures of child health and wellbeing."
In 2016 and 2017, the children, then aged 8, were provided with a small digital temperature and humidity gauge to measure their indoor environments.
Among them was Arya Naidu of Auckland, who took the device to school and found herself discussing the research with her classmates.
"Lots of us had never really thought about how the temperature in our homes might affect our health," said Arya, now 12.
"It was really special to be part of this research because we are helping people and contributing to something to improve our houses."
That data was cross-referenced with Niwa's own outdoor temperature records for the same period, and later compared with information about the childrens' health, provided by their mothers.
Together, the data showed that an indoor temperature of between 19C and 25C, with a relative humidity of 50 per cent, measured at the children's bedtime, was associated with the best health and wellbeing outcomes.
Arya's mum, Archana Kumar, said each room in her family's brick-and-tile four bedroom Mt Eden home were kept warm with oil heaters.
"I feel that we are lucky to have a house that is comfortable, warm and dry," she told the Herald.
"New Zealand is a world leader in many aspects - but we are lagging behind drastically with regards to housing and providing the basic needs to our most vulnerable members of society, our children."
Around 60 per cent of children lived in homes where they recorded temperatures and humidity outside of the range, while nearly half slept in bedrooms as cold as 19C or below.
Kids sleeping in these environments had a greater likelihood of reported poorer overall health, as did the 13 per cent who slept in bedrooms that were too warm or humid - or with temperatures greater than 25C, and with higher relative humidity.
In all, nearly one in seven children who recorded bedtime temperatures outside the ideal range had poorer health genre rally - and colder conditions were linked with increased anxiety and depression symptoms.
Branz' general manager of research, Dr Chris Litten, said the link between cold and damp indoor temperatures and poorer health was clear.
Not only did the new work back up official World Health Organisation guidelines with child-specific data, but also supported legislation changes, such as the current energy efficiency revisions to the Building Code.
"Keeping buildings warm is complicated," Litten said, "but changes to insulation and glazing requirements, and reducing energy consumption, all contribute to the health and wellbeing of New Zealanders".
Consultation on the Latest Building Code changes run until the end of this week.