The Mold Problem: How to get rid of excess humidity at home

Portugal in winter. High humidity or excess moisture can damage materials or cause health problems. Learn how to keep humidity at the right level in your home. See the best solutions for the most common humidity problems.

In cold, rainy weather, homes tend to show problems caused by dampness that is not at optimum levels. In excess, humidity is uncomfortable, as well as promoting corrosion and other damage to materials, not to mention the unpleasant musty smell.

On top of all this, humidity can lead to the development of fungi and dust mites, which can be harmful to health by causing respiratory infections, allergies and asthma in sensitive individuals. Very low levels of humidity can also lead to material damage, for example to wood, and discomfort in the respiratory tract, nasal mucous membranes and eyes.

Damp in the walls can have external causes, often associated with problems in the building. When this is the case, ask for the opinion of a validated professional.

Maintaining optimum humidity indoors

Bathrooms and kitchens are the most critical areas in a home. The steam produced by baths and hot pots is the main culprit in these rooms, but it’s not the only one. In the other rooms of the house, human breathing, the presence of animals and plants and the use of household appliances such as the tumble dryer and iron also contribute to raising the humidity in the air.

According to various studies, most fungi only grow above 60% humidity. And below 50%, dust mites stop proliferating. At an even lower humidity level, dust mites become inactive, which explains why they are almost non-existent in regions with a dry climate. Viruses, on the other hand, have a higher survival rate when humidity drops below 40 percent. So, what is the ideal humidity inside a house?

To find out, you need to calculate the relative humidity, i.e. the maximum amount of water vapor that the air can hold at a given time, at a given temperature and atmospheric pressure. Simply put, relative humidity is the ratio between the amount of water in the air (absolute humidity) and the maximum amount that could be there at the same temperature (saturation point). For example, if the air only holds half of its maximum capacity, then the relative humidity is 50 percent.

Thus, if the relative humidity is below 40%, the air is considered to be too dry. If the relative humidity is above 60 percent, the air is considered to be too humid. Ideally, the relative humidity should be between 40% and 60%. In order to accurately calculate humidity levels and avoid the consequences of too much or too little humidity in your home, it can be useful to buy a hygrometer, a device on sale in household appliance stores from 10 euros.

Consequences of excess humidity

Mold and deterioration of goods

Mold and mildew are one of the main consequences of excessive humidity inside a home. They develop in humid environments with high relative humidity, leading to damage to buildings and organic materials (paper, fabrics, paintings, wood, leather, etc.).

Mold is the name given to a cluster of fungi. The most common types of mold that form inside houses are Cladosporium, Penicillium and Aspergillus. Mold growth, which often takes the form of stains, can have many different colors and smell musty. Color is not an indicator of the danger of mold.

Furniture and objects made of wood, in particular, are very sensitive to the relative humidity of their environment. Wood is a hygroscopic material with the ability to absorb water. Therefore, high percentages of relative humidity lead to an increase in the water content of the wood, which in turn can lead to its deterioration.

There is also a risk to the health of people who frequent environments affected by mold. If the relative humidity exceeds 70% very continuously, the risk of fungi appearing and growing is significant. This risk is greater if we are talking about cold surfaces or surfaces in contact with the outside world. As cold air has a lower water retention capacity, as the temperature drops, the water vapor in the air condenses on colder surfaces – on cold surfaces, with a temperature below 12.6°C, the risk of mold formation is very significant.

How does mold get into the indoor environment and how does it develop?

Mold can enter the home through doors and windows or through heating and air conditioning systems. It can also be transported from outside on clothing, shoes or through pets. Mold develops when spores fall into places with excess moisture, such as leaks in the ceiling, pipes or walls. There are some materials that are favorable to the growth of certain types of mold. Examples include damp cellulose materials, cardboard, wood, dust, paint, wallpaper, carpets, fabric or upholstery.

Condensation

The appearance and formation of condensation is another consequence. This phenomenon occurs when humid air is cooled to a temperature below the dew point. The moisture contained in the air (water vapor) condenses (turns to liquid) on the cold surface (which is below the dew point temperature).

The result is water running down windows, walls, pipes and so on. This contributes significantly to the degradation of indoor air quality and also to the degradation of materials and objects (from the oxidation of metals to the growth of fungi) – on cold surfaces with a temperature below 9.6°C, the risk of condensation is very significant.

Health problems

Exposure to damp and moldy environments can have a number of health effects. Continued and prolonged exposure to mold can cause respiratory problems, coughs or asthma, and reactions in people with allergies. These problems can affect healthy people, but represent an increased risk for those who already have this type of pathology. People with immunodepression or underlying lung disease are more susceptible to fungal infections. Moisture in walls, for example, is the perfect habitat for fungi and bacteria responsible for causing illness and allergies.

According to the World Health Organization (WHO), dampness and the presence of mold are closely related to poor respiratory health. Occupants of damp or moldy buildings, both homes and public buildings, are at increased risk of respiratory symptoms, respiratory infections and exacerbation of asthma. Some evidence suggests increased risks of allergic rhinitis and asthma.

Tips to stop humidity

When cooking, cover the pans and turn on the extractor fan.

Avoid drying clothes indoors. If you can't avoid it, ventilate or air the room to prevent foggy windows, water droplets on the walls and the consequent formation of fungus.

Open the windows and let fresh air into the house. And by the way, do it every day. As well as combating excess humidity, it helps to reduce pollutants in the indoor air.

If these measures aren't enough, don't give up. A dehumidifier can help.

When to use a dehumidifier

A dehumidifier is a device whose main function is to reduce the relative humidity of an enclosed space. Using a fan, this device removes excess water vapor from the surrounding air and draws it inside. Inside, in contact with a cold surface (coil), there is a thermal shock that leads to condensation of the water vapor, which changes from a gas to a liquid. The water is then stored in a reservoir, which must be emptied when it reaches maximum capacity.

By removing excess water vapor, dehumidifiers substantially improve air quality. In addition to providing a greater sense of comfort by reducing unpleasant stains on walls and odors, these devices can help preserve furniture and clothing, which tend to deteriorate with excessive humidity.

How to use the water from the dehumidifier

The water extracted by the dehumidifier is stored in a reservoir. Don’t waste it. There are several ways to use it.

Water pots or garden areas.
Wash clothes.
Use it for small flushes.

Refuel the iron. However, do this in a balanced way: half with water from the dehumidifier and half with tap water. The water taken from the dehumidifier is distilled water and has very low levels of salts, which can increase the corrosion of the iron, so make up for this deficit. We also recommend that you always consult the manufacturer's instructions.

Washing outside areas such as balconies or patios.

Use the dehumidifier correctly

To use your dehumidifier effectively, close the doors and windows in the room you want to dehumidify. This will speed up extraction, as it reduces the entry of new air, whose humidity levels may even be higher. It is also important that the appliance is placed on a flat surface, with no objects blocking the passage of air. Some dehumidifiers have a cover in the fan area, where the air passes through, which should be left open whenever the appliance is in operation.

Also pay attention to the time and place you choose to install the appliance while it is working. The operation of the fan makes some dehumidifiers noisy, which can be annoying, even for neighbors.

When to ventilate the house

Opening the doors and windows and letting the air in is an important step towards proper ventilation in the home. This ventilation can be natural (through doors and windows) or forced (fans, extractors and exhaust fans). In spaces where there is a greater release of water vapor into the air, such as the bathroom and kitchen, ventilation should be reinforced in order to extract most of the water vapor produced.

Ideally, homes should be properly ventilated using a mechanical cross ventilation system with energy recovery. These systems promote adequate renewal of indoor air, removing air from areas of intensive use (kitchen and bathroom) and blowing new air from outside into useful areas such as bedrooms and social areas. In this way, a balance is achieved between the new air blown in from outside and that which is removed from inside the home, while at the same time recovering energy (heat or cold) from the extracted air for the blown-in air. These systems take on greater importance when homes have higher levels of air tightness.

There are also some indoor ventilation and air renewal procedures, combined with the use of air conditioning systems and a dehumidifier, which can bring significant improvements to air quality in both winter and summer.

In winter and in a small house with two people

From 8 a.m. to 11 a.m.: open the windows of the house (preferably opposite each other and with just a small crack).

From 11:00 a.m. to 4:00 p.m.: close the windows and turn on the dehumidifier to adjust the relative humidity in the room and promote gentle heating. During this period, make the most of the solar gain from the windows.

From 4 p.m. to 10 p.m.: switch off the dehumidifier if it reaches the right relative humidity and correct the indoor temperature with another climate control system (air conditioning, pellet stove, etc.). 

In winter and in a large house with four or more people

From 8:00 a.m. to 11:00 a.m.: open the windows (preferably opposite each other and with just a small crack).

From 11:00 a.m. to 2:00 p.m.: close the windows and turn on the dehumidifier to adjust the relative humidity in the room and promote gentle heating. During this period, make the most of the solar gain from the windows.
From 2 p.m. to 5 p.m.: open the windows (preferably opposite each other and with just a small crack).

From 5 p.m. to 10 p.m.: close the windows and turn on the dehumidifier to adjust the relative humidity in the room and promote gentle heating. You can also use the dehumidifier in parallel with other climate control systems, such as air conditioning or pellet stoves, whose heating of the rooms leads to a reduction in relative humidity. 

In both cases, you should always turn on the bathroom exhaust fans when you shower (or open windows) and the kitchen exhaust fans when you cook (or open windows). Don’t use catalytic heaters (gas bottle heaters) or other heaters without a chimney (e.g. paraffin or bio-alcohol heaters). Burning these fuels emits significant amounts of water vapor into the room, among other more harmful gases, thus increasing the relative humidity levels in the room. In addition, an adult can emit around 15 kilos of water vapor a day, so if there are a lot of people in a room for long periods of time, it is always advisable to ventilate the room.

In summer and in a small or large house with two or four people

From 8 a.m. to 11 a.m.: keep the windows slightly open, but start to control solar gains by adjusting blinds, shutters and shutters, if they are facades with sun exposure.

From 11 a.m. to 8 p.m.: on facades with a lot of sun exposure, close the windows and all the blinds, shutters or shutters. On very hot days, reduce the number of windows open on facades without sun exposure: even if they are not exposed to the sun, the air is very hot outside and will heat up the house.

From 8 p.m. to 8 a.m.: open the windows to take advantage of the fresh night air: this promotes the renewal of indoor air while lowering the temperature in the house.