Wellington bedrooms are reaching carbon dioxide concentrations up to 10 times higher than safe levels during the night, according to research published in the New Zealand Medical Journal.
A team from the University of Otago and Earth Sciences NZ monitored 20 Wellington houses during winter and spring, finding many exceeded the 800ppm target for CO2. Half the bedrooms studied recorded peak concentrations above 2000ppm, with one bedroom exceeding 8000ppm.
The research found that insufficient airflow reduces sleep quality and efficiency, with effects on productivity and awareness the following day. The authors said "increasing ventilation through window or door opening are associated with small but measurable improvements in sleep quality and efficiency, as well as next-day performance".
The study found that newer houses showed worse ventilation problems than older homes, as modern buildings are more airtight and allow less natural airflow. According to the research, inadequate ventilation can increase mould, bacteria and dust in stale air, which may worsen respiratory conditions like asthma.
The study recommends opening windows or doors and keeping vents unobstructed to reduce overnight CO2 levels, but notes this alone cannot adequately control humidity or maintain temperatures suitable for healthy sleep. Current building codes contain no frameworks addressing ventilation requirements.
The researchers said limited nighttime ventilation in New Zealand homes may represent an under-recognised public health issue and called for further research into solutions that could improve bedroom airflow.