Less cold, less mould
When designing homes, we determine whether we’ve done a good job by assessing things like health, comfort, and energy efficiency. But as an industry, there’s one metric we tend not to do well on in New Zealand – that’s mould. The 2015 BRANZ house condition survey found nearly 50% of homes had visible mould.
Growing mould For mould to grow inside our homes, it needs a high enough relative humidity in a reasonable temperature band. A rough rule of thumb when it comes to mould is “cold spots equal mould spots”. If an indoor surface is colder than the room temperature, it cools the air immediately adjacent, raising the local relative humidity. As an example, assume the warm and dry air inside a typical New Zealand home in the winter is 20°C at 60% relative humidity. If the surface is only 15°C, the relative humidity will be over 80%, which is a great breeding ground for mould. So, it’s not just temperature and ventilation – the interrelation between the indoor relative humidity,
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https://sustainableengineering.co.nz/fuel-poverty-impacts-mental-health
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air temperature and local surface temperature is one more dynamic to manage. To prevent the conditions that allow mould growth we need all three of adequate heating, sufficient ventilation, and high enough surface temperatures. Researchers like Professor Philippa HowdenChapman and her colleagues at the University of Otago1 have made it abundantly clear how important it is for us to heat our homes in winter for our health But heating our homes to 20˚C is not sufficient by itself; we also need to ventilate sufficiently and keep surfaces warm enough.
