Passive homes and mould: How to prevent mould in your home

by | May 22, 2022 | Designs, Performance

One of the principles of passive house design is creating an airtight home to control the internal environment. This creates a comfortable and stable inside temperature – but has many people worried about mould potentially creeping into their new home.

But while mould is a very serious problem, especially in Australian buildings, the passive house focus on high air quality paired with ventilation and insulation make these types of houses almost immune against mould.

Let’s have a closer look at what mould actually is, how it can affect your health, and how passive homes prevent mould build up by using a well-curated system to create the best possible air quality.

  • What is mould?
  • How does mould affect your health?
  • The sick building syndrome in Australia
  • How mould is prevented in passive homes
  • Ventilation
  • Condensation
  • Conclusion: Air quality is everything



Mould is a type of fungi that naturally occurs in many places in nature. It thrives in damp and moist areas with low ventilation and limited to no exposure to sunlight.

It can grow in many different materials both indoors and outdoors, which is why we often see mould occur in low ventilated bathrooms, with frequent high humidity from showering, or in other building materials that are often exposed to moisture, such as wood or carpet.

There are many ways to get rid of mould, but if you want to live mould-free, you need to remove the water source that is enabling the mould growth. After you have done that, you can choose to try out some natural remedies against the mould, or speak to a professional mould removalist.


While mould organisms are an important part of our ecosystem, there is a good reason for not wanting them inside our homes other than the unappealing looks of a fungi growing on your wall.

As any fungi, mould reproduces by making spores. During this process, spores, cells and other organic compounds can enter the air and are then broken down due to the dampness in the room. This then increases the volume of particles in the air – or to be more clear, the amount of dust in a room.

Increased particles can cause allergic reactions or irritations of lungs, nose and throat, especially affecting people with pre-existing respiratory conditions like asthma.

And if you are suffering from hayfever or other allergies, chances are your body will react similarly to the increased amount of particles and compounds in the air.

If you want to learn more about the health risks of mould exposure, the World Health Organisation (WHO) has written an extensive guide on indoor air quality with a focus on dampness and mould and its effects.


Mould 03

There is a proper term that describes buildings with poor indoor air quality which literally makes people sick: Sick building syndrome, or SBS for short. It refers to any type of building, residential or commercial, in which more than 20% of the frequent occupants experience symptoms such as headaches, throat irritation, or fatigue. 

Most cases of sick buildings are due to air pollution caused by bacteria or fungi, but complaints due to overly hot or cold conditions are also common. 

More often than not, the cause for the aforementioned symptoms is poor air quality. According to the Australian Department of Agriculture, Water and Environment, Australians spend 90% of their time indoors, so it only makes sense to focus on having the highest possible air quality in your house to keep you and everyone living with you healthy and comfortable.


We already touched on the principles of passive house design, including the airtight building envelope aiming to reduce all air flow to an absolute minimum. But that doesn’t mean that there is no air in passive homes. In fact, having an airtight layer allows us to control the air we let into the home through regulated ventilation systems.

Mould 04 bigger 980x734

This is especially beneficial for some of Australia’s humid coastal regions. Not only will a passive house in such climates keep the house nice and cool during intense summer days without the excessive need for cooling with an AC unit, but the ventilation system also extracts the moisture out of the air, thereby reducing any chance of discomfort or mould build up.


One of the main factors of passive house design is the integration of a ventilation system. The Heat Recovery Ventilation (HRV) unit draws filtered outdoor air into living spaces and bedrooms, while exhausting the stale air from bathrooms and kitchens. This removes  not only moisture from cooking or showering, but also bad odours, dust and pollutants.

mould Heat recovery infographic

Depending on the setting of the HRV system, the air in your home will change between 8 to 12 times a day. That ensures excellent air quality at all times, and also helps indoor plants thrive!


Mould does not only just grow from humidity. Condensation is another factor that can enable moist air in buildings, which then becomes a growing ground for fungi.

Condensation is basically what happens when moist air comes into contact with colder surfaces. This could be a wall, but also windows, doors, or mirrors. It therefore most commonly occurs in winter, when external temperatures are low, but also relates to the activities of people living in a home, such as showering, cooking, or even breathing.

In fact, a family of four will generate up to 0.2 litres of water vapour per hour, which adds up to 5 litres a day when inside a home simply through breathing.

Fortunately, in passive house design, we use high-performing windows and doors that not only help maintain a stable indoor temperature, but also regulate their own surface temperature, reducing the risk of condensation.


Mould Plant

Mould is a health risk that should be avoided at all costs when building a house. One of the main factors in avoiding the growth of fungi is eliminating water sources. This includes high levels of humidity within a home, and condensation.

The airtight building envelope of passive homes allows you to fully control the air quality within your home. By using an HRV system, you can determine the amount of air changes to draw in filtered fresh air from outside, and exhaust stale or moist air from inside.

Paired with high-performing windows and doors without any condensation, you will have the perfect living conditions for you and your family – and can keep the fungi growing to your backyard.

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