Cold, damp and mouldy homes are devastating to human heath. But Covid-19 has illuminated the true danger of our national problem.

Is there anything more quintessentially Kiwi than a cold, damp home? The black mould on the windowsills, the musty odour in the wardrobe, the sore throat in the morning: they’ve all become the common features of the classic Aotearoa abode, so normalised and accepted that even landlords don’t take them seriously.

But nothing could be more serious, according to the statistics. Almost 1600 New Zealanders die from respiratory illnesses because of our abysmal housing every year and about 80,000 people end up in hospital including nearly 30,000 children.

Among developed countries, New Zealand also has one of the highest rates of asthma and skin infections, conditions exacerbated by toxic mould exposure in damp houses. Nearly 600,000 New Zealanders are living with asthma and of all ethnicities, Māori and Pasifika are three times more likely to end up hospitalised because of it.

They’re stark stats, and have certainly compelled academics and policy makers to try and address the problem over recent years. However, while many of us still regard our substandard houses as something of a nuisance or a cultural idiosyncrasy, fear of Covid-19 has illuminated just how dangerous the issue is.

While cold and damp homes are terrible environments for human beings in general, they can be particularly harsh for immunocompromised people or those with severe respiratory illnesses. Those with chronic obstructive pulmonary disease (COPD) for instance are at particular risk, with high humidity, dust mites and mould exacerbating symptoms.

The evidence has shown that those with pre-existing respiratory conditions such as COPD will have a harder time fighting off Covid-19 and are at an increased risk of severe illness. New Zealand’s very first person whose death was attributed to Covid-19 also had COPD. According to the Asthma Foundation, 11,842 New Zealanders aged 45 and over were hospitalised due to COPD in 2017 and there could be approximately 200,000 New Zealanders living with COPD undiagnosed.

As for links between Covid-19 and environments themselves, research has suggested the virus survives far longer in cold environments – an idea that has spawned a great deal of interest in New Zealand after it was hypothesised the latest Auckland Covid-19 outbreak was imported in a refrigeration unit. While that theory has been disputed, a European study found that cold temperatures exacerbate the severity of Covid-19. Among the 7000 patients researchers analysed, there was a roughly 15% drop in mortality for every 1% rise in temperature.

However, excessively dry environments are also an issue. A study focused on Greater Sydney during the early stages of the epidemic found an association between lower humidity and an increase in community transmission.

One of the researches, Professor Michael Ward, an epidemiologist in the Sydney School of Veterinary Science at the University of Sydney, said dry air appears to favour the spread of Covid-19.

“When the humidity is lower, the air is drier and it makes the aerosols smaller,” he said. “When you sneeze and cough those smaller infectious aerosols can stay suspended in the air for longer. That increases the exposure for other people. When the air is humid and the aerosols are larger and heavier, they fall and hit surfaces quicker.”

It’s quite the predicament: a cold and damp home renders people more susceptible to the virus – and many other illnesses – while an excessively dry environment means Covid-19 will spread more easily.

So other than a comprehensive health response to treat those living with the range of illnesses caused by substandard homes, how can we change our environments to prevent it?

James Powers, the director of building science company Oculus, says it all comes down to applying better performance requirements when we build or rent houses.

“It’s particularly bad in New Zealand, as evidenced by our housing related health problems,” he says. “Our homes are typically too cold and too damp. Because we don’t heat and ventilate our homes effectively, and the reasons we don’t do this is because the code has been below standard for some time.”

Powers says the building code clause for an interior environment is woefully archaic, only mandating for an internal temperature of 16 degrees in childcare centres and retirement homes. For a long time there has been no requirement to build efficient, sealed homes that maintain internal temperature and adequately ventilate air – the essential components of a warm house with the right humidity.

He says there’s a range of factors people need to consider when building or renting houses that will help keep the occupants healthy and free from illness.

“An internal environment is made up of relative humidity, it’s made up of thermal comfort and it’s made up of internal contaminants like CO2 or mould or dust mites or volatile organic compounds; all of the nasties that we get in our homes. There’s nothing to specify what performance standards should be achieved.”

While some new houses such as those being built by Kāinga Ora are being designed over and above what the building code requires, Powers says the problem is with many existing houses, which are poorly insulated and only have single-glazed windows. While recent changes to the Tenancy Act require landlords to provide ceiling and underfloor insulation where accessible, Powers says it’s terribly inadequate.

“It’s just not robust enough. Even if they put in a heat pump, a lot of that heating is going to escape through single-glazed windows and lack of insulation. It’s going to be very expensive to heat.”

So until better standards are enforced, it’s essentially down to the landlords and builders to go beyond the current requirements. While that won’t always happen, Powers says there are simple ways for occupants to try improve indoor air quality.

“If you’re in Auckland, because the external humidity is so high, what will happen is once you start to heat your home that relative humidity will come down, but then what you have to do is ventilate your home effectively to get rid off all that excess moisture that comes from cooking and cleaning, and then you’ll find your humidity comes down to that goldilocks zone.”

The idea humidity zone for most houses is 40% to 60%. Powers says this range 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.

The first port of call, he says, is for occupants to measure the humidity of their homes with a testing device that can be bought online and in hardware stores for about $25. After that, it’s a case of asking landlords to provide better ventilation and double glazed windows to keep homes sealed. Oculus has published a healthy homes guide with tips for people to create a healthy indoor environment.

While opening windows and using dehumidifiers is the conventional approach, there is typically little evidence to support their effectiveness. Opening windows can sometimes make indoor humidity worse. According to Oculus, the best thing people can do is leave the heat on, leave any extractor fans in the kitchens and bathrooms on so that old air is pulled out, circulate air around the room with a fan, and seal all windows to prevent drafts.