Needle of a hygrometer indicating the relative humidity

What is the ideal humidity level in a house?

Whatever the time of year, we think about heating or cooling our homes. But have you ever thought about the ideal humidity level in your home? A poorly managed humidity level can have a significant impact on your health. For example, air that is too dry will tend to dehydrate your mucous membranes, while moist air will encourage the onset of respiratory diseases such as asthma.

What is humidity?

Moisture is the mass of water suspended in the air and can be referred to in two ways:

  • Absolute humidity measures the amount of water vapour in the air. It is calculated from the concentration of water in the atmosphere divided by the existing air mass in a given space. This is expressed in grams of moisture per cubic metre of air (g/m³)
  • Relative humidity It measures the percentage of current humidity in the air. This is the measurement you are probably most familiar with. It is also the one we will use to determine the optimum humidity level in your home.

What is the ideal humidity level?

You have probably already felt uncomfortable in a very humid place. This is because your skin cannot get rid of the moisture on your body, i.e. sweat. In order to get rid of the moisture, your skin uses the air around it, but if the humidity index is close to 100 %, the air around you can no longer absorb it, which creates a feeling of disgust, stickiness and discomfort.

The ideal indoor humidity level for your home depends on many factors such as the time of year and where your family lives. Research shows that the optimum relative humidity for your home is between 40 and 60 %. However, to prevent the growth and spread of mould, this percentage must be kept below 50 %. Another factor you will need to consider is the absolute outdoor humidity level.

Woman fanning herself with a fan in the heat

As you probably know, absolute humidity levels change with temperature and season. In summer, the air contains more moisture, and in winter, it contains much less. To give you a better idea, the table below shows a scale of the ideal humidity level in your home. However, this can be adjusted to suit your own subjective well-being.

Outside air temperature in ° CelsiusIdeal indoor humidity level at 20 °C
10 or morenot more than 50 %
between 6 and 10not more than 40 %
between -12 and 6not more than 35 %
-12 or lessnot more than 30 %

As you can see, you need to adjust your humidity level over the seasons. But what happens when it doesn't reach its ideal level?

Problems with low humidity

It is advisable to maintain a humidity level of at least 30 % in your home if you wish to avoid the following health problems: allergies, asthma, dry skin, chapped lips, eczema, migraines and dehydration. In addition to health, an atmosphere that is too dry will also consequences for your home. As the air dries out, it draws moisture from wherever it is found, such as your wooden furniture or even your plants: your possessions are likely to crack, while your indoor garden will see its foliage damaged.

Problems with high indoor humidity

It is recommended that you do not exceed 50 % of humidity in your home. Beyond this, there is an increased risk of mould appearing on your walls and ceilings. You will also be exposed to a proliferation of dust mites in your room, as they like warm, moist places. So don't turn on your humidifier too much.

Too much humidity can have consequences for your health If you have allergies, asthma or other respiratory problems, they can get worse and prevent you from sleeping well.

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How to regulate humidity in your home?

Once you have determined your indoor humidity with a hygrometer, you may need a quality device to help you regulate your humidity level.

If the air in your home is too dry, we suggest that you install a humidifier for plants or for babies. On the other hand, if your house is too damp, in addition to purchasing a professional dehumidifier or a moisture absorber, you can also apply the following tips:

  • Air out your home at least 10 minutes a day, even in winter.
  • Ventilate your bathroom after taking a bath or shower to remove condensation.
  • Do not block the ventilation ducts of your CMV and remember to clean them regularly.
  • Use an extractor fan when cooking and cover your pots and pans if you are boiling water.
  • Dry your laundry outside the residence or in a room with an efficient ventilation system.
  • Install a VMC if possible. It will allow you to renew the internal air and to evacuate humidity and pollutants present in the atmosphere of your house.
  • Maintain an adequate level of heating in your home (an ideal temperature of 20°C in your main rooms and 18°C in your bedroom).
  • Check the insulation of your windows and call in a professional if necessary. You can then deduct the work from your taxes.

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How to measure the humidity level?

There are two types of moisture meters: the moisture meter and the hygrometer. The former is used to determine the moisture content of materials, while the latter quantifies the moisture in the air. The two products use different techniques.

What is a hygrometer?

If you want to know the air humidity index, you will need a hygrometer. This product is designed to sense and analyse the air in the room and tell you the relative humidity of the room. Often combined with a thermometer, this product calculates the dew point, the temperature at which water vapour condenses.

What is a moisture meter?

A moisture meter will benefit you if you want to check the condition of the materials in your home. This device quantifies the moisture content of solid materials such as wood, concrete, plaster, etc. It can be used as a preventive (or curative) measure if you have any doubts about the humidity level in your bathroom, cellar or laundry room. Used early, it will allow you to intervene quickly to prevent the appearance of mould, saltpetre, etc.

Hygrometer for high humidity in the kitchen

There are two types of moisture meters:

The spike moisture meter It uses a resistive measurement system to obtain qualitative readings on materials such as wood, concrete, bricks, etc. The idea is to measure the point to be tested and compare it to another dry point. This will make the interpretation of your readings potentially less biased. It is important to note that the presence of mineral salts on the surface of the wall favours conductivity, which affects the results.

Radio frequency moisture meter It quantifies the moisture content of materials 20-40mm deep, by simply touching a flat surface. If you use it, you should first calibrate it on a dry wall and then place it on a potentially wet area. The result displayed will increase if the wall is watery.

Both devices have a margin of error: the smaller the margin of error, the more accurate the readings.

What are the sources of moisture in a house?

There can be many sources of humidity. If the humidity level in your home is not between 30 % and 60 %, then we advise you to check the following sources of humidity:

Impact of a raindrop on a river at the microscopic scale

Water ingress

Water ingress is also a cause that can explain the presence of moisture in your house. If your house has construction defects or poor quality materials, it is possible for rainwater to penetrate in different places: in the sub-roof, in cracks in the outside walls, in the window insulation and through the tiles.

Rising damp (by capillary rise)

If you live in an old building, capillary rise can be one of the main causes of damp in your home. Buildings that are not watertight can have water rising up the walls by capillary action. This is known as rising damp up to a height of 1.5 m.

Human activity

The number of inhabitants can affect your home humidity level. When you breathe or sweat, you produce moisture. You can add to this the humidity generated by your household activities such as cooking, bathing, washing, showering or drying clothes in your bedroom.

The humidity generated by all these activities can lead to a condensation problem if your home is not properly ventilated. Indeed, you should know thata family of four produces an average of 12 litres of water vapour per day. Without effective heating and ventilation, your home will not be able to absorb or remove all the water and stale air from your human activities.