This is due to high Relative Humidity (RH%).

We have all experienced those horrible summer days when your clothes stick to you like a second skin, you struggle to get a full breath and no matter what you do you just can’t seem to cool off.

Relative humidity is measured in percentages, 100% is when the air is so saturated with water vapour that it cannot hold anymore, meaning that sweat won’t evaporate so you can’t cool off. The higher the RH% the stickier and clammier you feel.

In the outdoor environment we have absolutely no control over the RH% as it is subject to the changes in the weather. But in our homes and offices the responsibility falls on us and if not managed can cause damage to the building and health problems for you and your family.

Ideally, the RH% within the home should be between 40% and 60%. If the RH% drops too low and the air becomes dry it can result in a variety of potential health concerns for occupants. But an RH% that is too high can also have a negative impact on your health.

The Impact of High Humidity

When the RH% in a home or office is high the likelihood of condensation forming on surfaces is high. This moisture will not be able to evaporate due to the already high moisture content in the air, the pooled water can then cause damage to building materials.

Prolonged high RH% can result in rusting of nails and joists, staining on walls and ceilings and can even cause wood and carpet to rot. The combination of moisture and rotting materials can attract pests and insects, increasing the potential damage and health risks to occupants.

Humidity of 70% also increases the risk of a population explosion of Dust mites in residential properties. These microscopic pests are present in carpets, soft furnishings, and bedding. They feed on human skin cells and their faeces can cause allergic reactions and exacerbate asthma.

High humidity makes it easier for moulds to grow. With a constant moisture source, mould can grow in a matter of days and in the case of some species, hours. If left unchecked, can result in significant damage to building materials as well as negatively impact occupant health.

Prolonged high humidity can have serious effects on occupant health. High humidity combined with high temperatures can result in overheating/ heatstroke, which can be fatal, especially to the elderly and young children. If you or someone you are with begins to exhibit symptoms of heatstroke, such as dehydration, fatigue, muscle cramps, fainting, headaches, confusion, or vomiting, seek medical attention immediately.

Causes of High Humidity

There are many different activities we perform every day that creates moisture and adds to the RH%. Things such as breathing, cooking, and bathing increase the water vapour in the air, the effects of which are often seen as condensation on windows and fog on the mirror.  This becomes an issue if there are many people in the home and if the home is small i.e. if your sister and her four children come to stay with your family in your 3×1 unit. While that example may be a little excessive it helps paint the picture.

Another cause of high RH% is often leaks. A cracked ceiling tile or window seal can allow unwanted moisture into your home, as can leaky supply or wastewater pipes. Mould and pooling water are not the only risks associated with leaks in the home. The increase in RH% in these instances is due to the water evaporating, but if the moist air has no way of escaping the home, it becomes trapped and can condense on surfaces within the home only to evaporate again. This is the condensation cycle.

Reducing High Humidity


Many homeowners and tenants, when they identify there is a problem with high humidity, will buy a dehumidifier. You can purchase these from the local hardware store, some supermarkets even stock them. These items collect water from the air, you need to empty them frequently, depending on how quickly they fill up. But these are a temporary solution as they do not remove the cause of the moisture build-up in the air.

Air conditioners

Another way to reduce the RH% is to run your air conditioner on the ‘Dry’ cycle as it acts like a dehumidifier and removes excess moisture from the air as it cools. If your home remains humid while the air conditioner is running, then there may be issues with your system. Ensure to clean and replace the filters often as they can become clogged with dust, debris and sometimes mould.


As mentioned earlier we create moisture by doing the most basic of functions, breathing. When we exhale the RH% of our breath is approximately 90%, this is evident if you cup your hands over your mouth and exhale into them, your hands feel damp afterward, but when you open your hands they dry rapidly. They dry because of the fresh air moving across the surface of your skin. The same occurs in a house. Moisture builds up if the space is enclosed, but if you increase the air flow the surfaces will dry. Cracking a window in high moisture areas such as the bathroom or bedrooms with multiple occupants can help prevent this moisture build up and reduce the potential for the RH% to exceed comfortable levels.

Colder showers

Reducing the temperature and duration of your showers can significantly reduce the water vapour and RH%.

Cooking Habits

Get into the habit of using the extraction fan in the kitchen and putting lids on pots while cooking. Using a slow cooker produces less moisture than cooking in the oven or on the stovetop.

Dry clothes outside

Using your clothes dryer adds a surprising amount of water vapour into the air, if you must use a dryer ensure that it ventilates out of the home or that a window is left open in the room when it is in use.


Indoor plants can increase the humidity in the home, evaporation from the exposed soil of pot plants can add to the problem. Move pot plants outdoors, even if temporarily, and avoid overwatering.

These are just a few possible causes and simple solutions to High RH% in the home.

If you would like more information or if you have any questions or queries, please feel free to contact us on (08) 9355 1060 or drop us an e-mail –