The first proper rain of the season arrives, the balcony is soaked, and the clothes airer makes its annual migration into the living room. It feels like the cheap, sensible option. The water in your washing has to go somewhere, however, and when it dries indoors, that somewhere is your home.
Where the water goes
A single load of washing dried indoors can release around two litres of water into the air, according to researchers at the Mackintosh Environmental Architecture Research Unit at the Glasgow School of Art, who studied 100 homes over three years. They found the air in many homes was too moist, with up to a third of that moisture coming from laundry dried indoors in cold weather. Most households did it, with 87% of those studied drying clothes inside during the colder months. Building scientists put it starkly: it takes surprisingly little extra water to push a small flat from a comfortable 50% relative humidity to around 70%, the level at which mould starts to become a risk.
That moisture does not stay in the air. It settles on the coldest surfaces in the house, which is why the same homes that dry laundry indoors often wake up to streaming windows, a stuffy smell and, eventually, black patches in the corners of ceilings and behind furniture. The Glasgow researchers also linked indoor drying to higher mould spore counts, and doctors have warned that this can pose a real risk for people with severe asthma or weakened immune systems.
How to do it better
You do not have to give up the airer altogether. Pick one room, close the door and keep it ventilated, ideally with a window open or a dehumidifier running, so the moisture stays in one place instead of spreading through the house. Bathrooms with an extractor fan work well. Avoid the bedroom, where humidity builds up overnight and feeds condensation and mould. Placing the airer near a window also helps, as the Glasgow team recommended, and so does giving each item space so that air can circulate around it rather than hanging towels and jeans folded over one another.
A faster spin cycle helps too, since the less water left in your clothes when they come out of the machine, the less ends up in your walls. A cheap hygrometer, which measures relative humidity, is a simple way to see what is actually happening in your home and whether your efforts are working.
Is the tumble dryer really the expensive option?
Not necessarily. Drying indoors is never quite free, because the moisture has to be removed somehow, whether by a dehumidifier, extra heating or opening windows and letting the warmth out. On cold, damp days, a modern heat-pump tumble dryer, which uses far less electricity than older models, can work out cheaper than running a dehumidifier and heating to dry clothes on an airer, while sparing you the mould. And whenever the sun comes back out, the old advice still stands: the best place to dry your washing is outside.
Source: Mackintosh Environmental Architecture Research Unit
