What to do if your basement is too humid

Basements tend to hold more humidity than other parts of the home, which could make them damp, smelly, and mold-infested. But what is humidity, why does it matter and what should you do if your basement is too humid?

Humidity is a measure of the amount of water vapor in the air; the more moisture, the higher the humidity. You can usually tell if your basement is too humid as the air can feel thicker and the walls may be damp to the touch.

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Humidity in basements is often the result of poor insulation and poor ventilation, with the conditions outside affecting the interior temperature and humidity. But why does this matter? The World Health Organization estimates that between 10 and 50% of the indoor environments where people live and work are damp. This can encourage the growth of mold, mildew and other bacteria, and cause health problems in the young, the very old and those with existing respiratory conditions like asthma.

So, what to do if your basement is too humid? Investing in a dehumidifier to remove moisture could help as will maintaining good basement hygiene. For more information on air quality, check out our feature on what causes dampness in a house.

Get an accurate humidity reading 

So, you think you have a problem with humidity in your basement but how can you be sure? You could invest in a combined thermometer with a humidity dial, but this only gives an approximate reading. To get accurate readings of humidity levels in your basement, you’ll need a hygrometer, which you can buy from any hardware store, or online.

Hygrometers measure the relative humidity in the air - the air moisture level and air temperature - which determines how comfortable the room is. They give a simple readout of whether humidity levels are within a comfortable range - between 30 and 50% according to the Centers for Disease Control and Prevention (CDC), but this varies throughout the day and depends on the season and where you live.

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It’s important to regularly check and monitor humidity levels; in the summer, the outside air is hotter and more humid, and could increase humidity levels to around 60% while in the winter, the cold air outside can decrease humidity levels to between 25% and 40%. This could have adverse health effects such as dry skin or increased susceptibility to respiratory infection, according to the International Journal of Biometeorology.

Invest in a dehumidifier 

Humidity can affect the health of the home and the people living there; investing in a dehumidifier can reduce air moisture levels in your basement to a comfortable and safe level.

"Humidity in basements can be a potential issue both for the health of the building and occupants within,” Professor Rajat Gupta, Professor of Sustainable Architecture and Climate Change at Oxford Brookes University told Live Science.

“High relative humidity can result from inadequate ventilation which can cause damp and mold which is not good for the building fabric and also for occupants. Dehumidifiers can help in reducing relative humidity but really what is needed is good levels of ventilation - cross ventilation where possible."

There are two main types; refrigerant dehumidifiers or desiccant dehumidifiers. You’ve likely encountered a refrigerant dehumidifier; they use a fan to draw moisture-laden air across cold evaporator coils which condense the moisture. The moisture then runs into an attached tank, or straight into the drain. They’re ideal for home owners as they work well at room temperatures, but they must be regularly emptied.

Desiccant dehumidifiers draw air through a chamber containing water-absorbing gel packs, a bit like the packets you find in shoe boxes or damp traps. These are generally quieter and use less power than refrigerant dehumidifiers, and their gel pack only needs replacing once saturated.

Keep your basement hygienic 

A dehumidifier is only part of the solution; what else can you do if your basement is too humid? High humidity in basements is often the result of poor insulation and insufficient ventilation, so crack open those windows to encourage circulation of fresh air, and to reduce humidity and the chance of mold and mildew developing. And if you do have signs of either mold or mildew in your basement, it’s time for a rigorous clean.

Mold is likely to be the most common problem; the fungus will grow on anything left in a moist environment. It releases small spores into the air which can cause sneezing, coughing, allergic reactions such as itchy eyes or skin, wheezing and respiratory infections, according to the CDC. If you’re exposed to it for long periods, you could develop severe health issues such as asthma and allergies, and a weakened immune system.

Dust mites and bacteria may also present a problem; dust mites can’t survive in low humidity, while bacteria thrive in dank conditions. Spiders, insects, rats and snakes like the damp too, so to prevent unwanted visitors and keep the household infection-free, make sure your basement is hygienic.

If you have a visible mold-infestation you could call in professionals, or tackle the problem yourself. WHO recommends avoiding personal exposure to microscopic mold spores by wearing a protective mask which covers your nose and mouth, goggles and rubber gloves. Chemical disinfectants and biocides should be avoided as they won’t actually solve the problem, and as they are toxic, could cause more harm than good.

So, if you think your basement is too humid, invest in a hygrometer to help monitor moisture levels in the air, and a dehumidifier to reduce humidity. A rigorous clean of your basement and regular upkeep will prevent the rapid growth of mold and to stop unwanted visitors.