All About Mould: Effect On Health, Government Requirements, Methods of Control

In September, the UK government published important guidance entitled “Understanding and Addressing the Health Risks of Damp and Mould in the Home”. This report highlights the serious health risks posed by mould and clearly outlines landlords’ responsibilities in this area. We will explore how homes can be updated to meet these new guidelines, discuss the dangers of mould and give practical advice on how to deal with this common problem.
In this article we will talk about:

  • Humidity standards in the UK.
  • Mould and health.
  • The current requirements for humidity levels in private homes in the UK.
  • The fines for landlords due to mould and how to avoid them.
  • Methods of controlling humidity in the property.
  • How to avoid excessive humidity in the home with the Prana Recuperator/ decentralised MVHR.

Humidity standards in the UK

In the United Kingdom, humidity standards for homes and buildings are specified to ensure a healthy and comfortable indoor environment. The recommended relative humidity range is 40-60% in dwellings and air-conditioned buildings, and it can be slightly higher, up to 70%, in other types of buildings. The optimal humidity levels vary slightly with the seasons, with 40-60% recommended for summer and 30-50% for winter in an average home. Most parts of a typical house usually maintain a relative humidity in the 40-50% range.

Mould in Rental Property: Tenants’ Rights and Landlord Responsibilities

The UK government report notes that landlords must comply with a number of regulations relating to the control of indoor humidity. These include:

The rules vary slightly for different types of property, but non-compliance can result in fines and prosecution.

Housing act 2004 damp and mould in UK

The Housing Act 2004 in the UK includes provisions relating to damp and mould in residential properties. One of the key elements of this Act is the Housing Health and Safety Rating System (HHSRS), which is a risk-based assessment tool used to identify and protect against potential health and safety risks arising from defects in housing. This includes risks from dampness and mould growth.
The HHSRS assesses hazards and classifies them into categories. Mould and damp are considered ‘Category 1’ hazards, which are the most serious. Category 1 hazards are those that pose a serious threat to the health or safety of occupants, and local authorities have a duty to take action if they are identified in a property. This could include carrying out inspections and requiring landlords to make the necessary repairs or improvements to remedy the situation.
The Housing Act 2004 therefore places a legal duty on landlords to ensure that their properties are free from serious health hazards, including those caused by damp and mould. Failure to comply with these obligations can result in enforcement action by local authorities, including improvement notices and, in more serious cases, fines.


Causes of high indoor humidity and mould growth

The main causes of rising damp are:

  • Lack of ventilation. Poor ventilation traps moist air inside and prevents it from escaping.
  • Daily activities. Activities such as cooking, showering and drying clothes indoors can release excess moisture into the air.
  • Leaking pipes or water ingress. Plumbing leaks or water infiltration from outside can increase indoor humidity.
  • Overuse of humidifiers. Excessive use of humidifiers can add too much moisture to the air.
  • Poor insulation. Inadequate insulation can lead to cold surfaces that cause condensation and increase indoor humidity.
  • Plants. Large numbers of indoor plants can contribute to higher humidity levels.
  • Weather conditions. Penetrating damp outside especially if windows and doors are frequently opened, can provoke mould growth

What are the health effects of mould?

The government’s clear regulation is quite understandable: high indoor humidity, fungi and mould pose a serious threat to human health. High humidity encourages the growth of mould, which causes allergic reactions, respiratory problems and serious health problems. Certain types of mould produce mycotoxins that can be harmful if ingested, inhaled or in contact with the skin.

Mould and Respiratory Issues: Can Mould Cause a Cough?

Exposure to mould is closely linked to respiratory problems. When people breathe in mould spores, it can irritate their lungs and airways, especially people with allergies or weak immune systems. This can lead to symptoms such as coughing, wheezing and difficulty breathing. Over time, if someone is exposed to a lot of mould, they may develop more serious lung problems.
For people with asthma, particularly allergic asthma, mould spores can act as a trigger, leading to an asthma attack. These attacks can manifest as coughing fits, wheezing and difficulty breathing. Similarly, people with mould allergies may experience allergic reactions that primarily affect the respiratory system, leading to persistent coughing, nasal congestion and sneezing. Also prolonged or heavy exposure to mould can lead to the development of respiratory infections.
You can read more about the impact of mould growth on respiratory problems in a large-scale study: “Respiratory and Allergic Health Effects of Dampness, Mold, and Dampness-Related Agents: A Review of the Epidemiologic Evidence“.

Mould and Cancer: Is There a Connection?

The link between mould and cancer is a topic of interest and concern. So far, there’s no direct evidence that conclusively links exposure to mould in the home to the development of cancer. However, there are certain aspects that should be considered:

  • Mycotoxins. Some types of mould produce toxic substances called mycotoxins. The most well-known of these is aflatoxin, which is produced by certain Aspergillus moulds and is a known carcinogen. However, aflatoxins are primarily a concern in food contamination rather than in residential mould exposure.
  • Respiratory Health. While mould exposure is more commonly associated with respiratory problems and allergic reactions, long-term exposure to some types of mould spores and mycotoxins in occupational settings (like farming or working in damp, mouldy buildings) could potentially contribute to an increased risk of certain lung conditions, some of which might have the potential to lead to cancer.
  • Limited Studies. The studies exploring the link between residential mould exposure and cancer are limited and have not established a direct causal relationship. More research is needed to understand the potential long-term health effects of mould exposure.

Research into the link between mould in the home and serious illness is outlined in an article from the National Institute of Health: “The Effects of Fungal Volatile Organic Compounds on Bone Marrow Stromal Cells.”

Mould in Residential Environments: Homes and New Builds

Mould in rented home, particularly in bedrooms, poses a significant health risk due to prolonged exposure during sleep. In new buildings, mould can arise from lingering moisture during construction. Common causes in existing homes include poor ventilation, leaking pipes, condensation (often in bathrooms and kitchens), and damp basements or cellars.
Building Standards and Regulations: Adherence to building codes and standards is crucial in new constructions to ensure adequate ventilation and moisture control, which are vital in preventing mould growth.
Ensuring proper ventilation and addressing any water leaks promptly are crucial steps in preventing underlying problem — mould growth.

Mould in Schools: A Public Health Concern

Mould growth in schools is an increasingly recognised public health concern. It can negatively affect the health of students and staff, especially those with allergies, asthma, or weakened immune systems. Common causes in school buildings include inadequate ventilation, leaking roofs or pipes, and high indoor humidity. Addressing this issue requires regular maintenance, proper ventilation, and prompt action to fix moisture problems. Ensuring a mould-free environment in schools is vital for safeguarding the health and well-being of students and staff.

How to prevent mould with Prana?

The presence of mould in any property can have legal implications. Tenants may have the right to withhold rent or pursue legal action if mould issues are not adequately addressed. Similarly, schools and workplaces have a legal obligation to provide a safe environment, free from health hazards like mould.
The Prana Recuperator/ decentralised MVHR is a modern solution designed to combat excessive humidity in homes, which is a common cause of the growth of fungus and mould. Its functioning and features make it an effective tool in controlling indoor climate and maintaining a healthy living environment. Here’s how the Prana Recuperator/ decentralised MVHR helps:

  • Ventilation and Air Exchange. The Prana Recuperator/ decentralised MVHR works by facilitating continuous air exchange. It expels stale, moist indoor air and brings in fresh outdoor air. This process is crucial in reducing indoor humidity levels, as it replaces humid air with drier air from outside, thereby preventing the conditions that mould and fungus thrive in.
  • Heat Recovery Feature. One of the key features of the Prana Recuperator/ decentralised MVHR is its heat recovery system. This system captures heat from the outgoing air and transfers it to the incoming air. This means that while the device is controlling humidity by bringing in fresh air, it doesn’t lead to significant heat loss, making it energy efficient.
  • Humidity Control. By continuously replacing damp indoor air with drier outside air, the Prana Recuperator/ decentralised MVHR helps maintain optimal humidity levels inside the home. This is vital because high levels of indoor humidity can lead to condensation, which is a primary factor in mould and mildew growth.
  • Preventing Condensation and Mould Growth. The device’s ability to maintain a balanced humidity level is crucial in preventing condensation on walls and windows, which is a common cause of mould. By keeping the indoor air drier, the Prana Recuperator/ decentralised MVHR minimises the risk of damp surfaces where mould spores can germinate and grow.
  • Improving Indoor Air Quality. Besides reducing humidity, the continuous air exchange facilitated by the Prana Recuperator/ decentralised MVHR also improves overall indoor air quality. It reduces the concentration of indoor pollutants, allergens, and potentially harmful airborne particles, creating a healthier living environment.
  • User Control and Customisation. The Prana Recuperator/ decentralised MVHR typically comes with user-friendly controls that allow homeowners to adjust settings according to their specific needs. This customisation is crucial in managing indoor climates effectively, as different homes might have different requirements based on size, location, and occupancy.
  • Energy Efficiency. Despite its powerful ventilation capabilities, the Prana Recuperator/ decentralised MVHR is designed to be energy efficient. This is important because maintaining indoor climate control should not come at the expense of excessive energy consumption.

The Prana Recuperator/ decentralised MVHR addresses the problem of excessive humidity by ensuring adequate ventilation, controlling humidity levels, preventing condensation and mould growth, and improving overall air quality, all while being energy efficient. This makes it an effective tool in creating a healthier and more comfortable indoor environment.


Mould is not just an aesthetic problem, it is a significant health issue. Its presence in indoor environments such as homes, schools and rental properties requires immediate attention to prevent respiratory problems, potential long-term health risks and legal complications. Consider installing a decentralised ventilation system. This will not only help to maintain a comfortable indoor climate, but will also help to prevent health problems caused by excessive humidity and mould growth.
Prana is your reliable partner when it comes to ventilation in homes, rental properties, schools and public buildings. We choose the right solution for your comfort.

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