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Studies Show Home Humidity Levels Link To Viral Transmission And Respiratory Illness - Oculus

Research on the health effects of relative humidity inside houses shows it has a major impact on respiratory illness, allergies and the spread of viral particles such as COVID-19.

Relative humidity - the amount of water vapour in the air compared to the maximum amount it can actually hold - is often at unhealthy levels in many Kiwi homes, with little done to measure or counter this in building legislation, says Oculus co-founder and architectural engineer James Powers.

Powers says these levels can be problematic if they are too high, causing conditions where respiratory illness-causing mould and dust mites thrive, or too low, which makes respiratory infections more severe. The humidity “sweet spot” for most homes should be around 40 to 60 percent. In this range, the transmission of viral particles in the air, including colds, influenza and COVID-19, is slowed too.

This “sweet spot” is beneficial in three ways, Powers says. It allows proper function of the respiratory and immune systems, has an evaporating effect on airborne viruses slowing their transmission, and also prompts the inactivation of viruses.

Factors like inadequate heating and ventilation can contribute to humidity problems in Kiwi homes and workplaces, as can their geographical location. For example, the relative humidity of outside air in Auckland and Wellington is typically between 75 and 80 percent, Powers says.

He says Oculus finds it astounding there is no performance requirement for relative humidity in New Zealand’s building code, even for places with vulnerable occupants, such as schools and hospitals.

“Relative humidity isn’t measured,” he said.

“Heating and ventilation is often poor in Kiwi homes and buildings, so internal moisture sources increase it even more, which is backed up by the extent of housing that has visible mould in New Zealand”.

Powers says the statistics on respiratory illness linked to unhealthy homes in New Zealand are appalling.

“1600 people die and 80,000 are hospitalised per year, with research showing a causal link back to the houses they live in,” he said.

“We have the second highest rate of asthma in the world, 700,000 people have some form of respiratory problem and we also have the highest rate of skin infections.”

He recommends people check their home’s humidity - something that can be done easily with a hygrometer costing as little as $25.

“Humidity is a critical part of the indoor environment quality,” he said.

“Indoor air quality is a function of temperature, relative humidity and indoor contaminants. Get it wrong and it impacts negatively on your health, but get it right and it improves lung function, cognition, productivity, sleep and recovery”.

Powers says Oculus designs buildings to be “built tight and ventilated right”, meaning the inside and outside are effectively separated by the building “envelope”, making the interior environment much easier to manage.

The Auckland-based company, which has also recently opened offices in Queenstown, offers a wide range of free advice and resources, including a recently published Healthy Home Guide. For more information visit

About Oculus: 

Oculus are a team of building scientists who use science to design better buildings. They have expertise in the building “envelope” and in making sure the outside stays out and the inside stays in. The team works closely with architects to deliver weather-tight, cost-effective, energy-efficient, warm, dry buildings. Oculus is working with organisations such as Asthma NZ to give advice to those most affected with respiratory illness because of the quality of their home. They are also helping to develop ESCAPE - an energy step code with a network of New Zealand's built environment professionals providing guidance to support the government to transition the country’s built environment to be warm, dry and net zero carbon.

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