Mould in your home: causes, risks and tips

What is mould and how does it form?

Mould refers to various fungi that live on damp, organic materials such as wood and food. Mould forms as a result of excess moisture that condenses on cold surfaces. This mainly occurs on exterior walls and windows where the air temperature is lower than indoors. One in four or five households suffer from such moisture issues and associated mould.

If structural components have poor heat conduction, then there are colder spots, or what are known as thermal bridges, where condensation can very easily form and mould can grow. The usual reasons for mould are incorrect ventilation, structural damage or these thermal bridges.

Mould is not only a visual problem, but can also lead to health issues. Mould spores can trigger allergies, respiratory disorders or infections, especially in those with a weakened immune system. You should therefore avoid mould in your home whenever you can or remove it as quickly as possible.

How to prevent mould formation

An effective strategy against mould formation is a healthy indoor temperature inside your house or flat. If you ventilate your home several times a day, you can destroy the fungi by allowing damp air to escape. Open all the windows for a few minutes every time you cook, shower, take a bath or do the laundry.

You can measure the indoor humidity using a hygrometer. This is a device that displays the relative humidity in percent. It tells you how much moisture is in the air at a certain temperature. The optimum humidity is between 30% and 50%. If condensation forms on your windows, the air is too humid and you should ventilate your home or use a dehumidifier.

What should I do if I have mould?

It isn’t always easy to detect mould in your home. Sometimes it is visible as coloured spots on walls, ceilings or furniture. Sometimes it is hidden behind cupboards, wallpaper or panelling. A typical sign of mould is a nasty or musty smell that doesn’t go away even after you have ventilated your home. This smell comes from the metabolic compounds in the mould that can also harm your health.

If you discover mould in your home and the affected area is larger than half a square metre, you should take the following steps:

1. Document and photograph the mould. This will help you provide evidence or settle a claim.

2. Contact your landlord immediately and notify them of the damage. This means you cannot be held responsible for any consequential damage.

3. Identify and rectify (if possible) the cause of the mould.

4. Have the mould professionally treated. This not only means removing the mould from surfaces, but also replacing or treating the affected items.

5. Have the treatment inspected and verified in accordance with the Federal Office of Public Health (FOPH) regulations (available in German).

6. Ensure that you prevent mould in future. Ventilate regularly, maintain a constant indoor temperature above 18 degrees (especially in poorly insulated buildings) and pay particular attention to structural defects.

Mould FAQs

How dangerous is mould in my home?

Mould in your home can be extremely harmful to your health. This is because mould produces spores and toxins that are inhaled via the air and can lead to various ailments. These include:

• Irritation of the eyes, skin and respiratory tract
• Allergies and asthma
• Headache, fatigue and exhaustion
• Abdominal pain, nausea and digestive disorders

You should never sleep in a room that has mould, as you will be exposed to a higher concentration of mould spores, which increases the risk of disease. You should remove the mould as soon as possible or engage a specialist company to do this.

The length of time it takes for mould to make you ill depends on various factors, such as the type (black mould, white mould, yellow mould) and amount of mould, how susceptible you are, how long you have been exposed to it and the condition of your immune system. Some people develop symptoms fairly quickly, others only after several months or not at all. In principle, however, it is always advisable to avoid coming into contact with mould.

What should I do if I have mould in my home?

If you have mould in your home, you should remove it as soon as possible, as it may harm your health. It is not sufficient to simply eliminate the mould, however. You must also find and remedy the cause of the humidity.

You should adopt a different approach depending on the size and depth of the affected area. If the mould is smaller than half a square metre and is only growing on the surface, you can remove it yourself. To do this, you will need the following materials:

• Disposal gloves
• Face mask
• Goggles
• Cloth or sponge
• A bucket of water
• Mould remover or a household remedy such as vinegar or hydrogen peroxide

How to proceed:

1. Wipe the affected area with a damp cloth or sponge to remove loose mould.
2. Apply the mould remover or household remedy to the area and allow it to soak in.
3. Then wipe the area with a clean cloth or sponge and leave it to dry.
4. Dispose of or thoroughly clean the materials used.

If the mould is larger than half a square metre or has penetrated deep below the surface, you should engage a specialist to professionally remove it.

Who is liable for mould damage in Switzerland?

Liability for mould in the home depends on whether it has been caused by a structural defect or incorrect ventilation and heating. As a general rule, landlords are responsible for removing mould if it is due to a structural defect. Tenants only need to cover the costs if their actions have caused or exacerbated the mould.

To apportion liability, the landlord must prove the cause of the mould. They can do this using an expert report or witness statements, for example. As a tenant, you should report the mould to your landlord as soon as possible and document it to ensure that you will not be held liable for any consequential damage.

More information about mould and its effects is available in the ‘Mould in the home’ brochure (available in German) published by the FOPH together with HEV Schweiz, the Swiss homeowners’ association, the Swiss Tenants’ Association (MV) and the Swiss Real Estate Association (SVIT).