We often need a good breath of fresh air

The damaging health effects of mould and moisture are dramatic – but simple enough to prevent.

Whether we’re at home or at the workplace, Australians spend up to 90% of our time indoors. This makes the quality of the air we breathe indoors such an important factor in our lives.

Many of today’s buildings are built and decorated with materials loaded with Volatile Organic Compounds (VOCs) creating airborne emissions arising from paints, sealants, carpets and adhesives – all dramatically reducing our indoor air quality.

With modern energy efficiency targets, many buildings also tend to have less uncontrolled leakage of outdoor air. Reducing air leakage certainly improves the overall efficiency of heating and cooling – however, we also need to be mindful of what this does for fresh air supply.

With the combination of improved air tightness and in-door pollutants mixing with increased time indoors, it’s no surprise this is having a significant effect on our collective health.

According to the National Asthma Council, there are 2.3 million people living in Australia with asthma. Asthma sufferers are sensitive to a wide range of airborne pollutants – with the most common triggers for asthma including VOCs and mould.

In recent studies, the World Health Organisation (WHO) have concluded that the most damaging effects of the accumulation of internal moisture and mould in buildings led to a direct increase of respiratory symptoms, allergies and asthma.

Even new buildings can suffer from mould and mildew, especially when internal spaces are not regularly or sufficiently ventilated. In addition, emissions from un-flued gas appliances, pet hair and pollen may also contribute to detrimental air quality.

This is a classic Catch 22 of modern buildings: we want great air quality and well ventilated buildings; however we also need them be well sealed for efficient operation of heating and cooling systems.

Is this an impossible contradiction? Well, not necessarily!

CSR research suggests that many new Australian detached homes allow a natural purge rate of over 24 volumetric air changes per day, that’s one air change per hour (1 ACH). While this may be better than our parents’ and grandparents’ homes, this still lags behind other developed countries in terms of detached building performance.

Australian apartments however are much less leaky with CSR recently measuring a small collection of new apartments at an average of 0.15 ACH. Anecdotal evidence across the industry also suggests that many modern apartments in Australia are suffering from moisture, mould and poor indoor air quality, creating fertile ground for a possible asthma epidemic.

In Europe and North America their building codes require between 0.15 to 0.25 ACH, yet they’re not seeing an increase in respiratory disorders, asthma rates and general ill health of their building occupants. Their building codes have evolved to adopt fresh air supply standards to ensure suitable indoor air quality is maintained.

The development of modern building codes and techniques require research and development of new technologies, systems and products as well as developing awareness of operational strategies to enhance indoor air quality.


Air quality can correspond positively to ventilation and there are simple measures that home buyers, builders and renovators can take to improve indoor air quality and reduce the risk of mould:

  1. Reduce the quantity of pollutants through appropriate selection of furnishings and products (i.e. low or zero VOC products)
  2. Ensure extract ventilation direct to the outside for bathrooms, laundries and kitchens, this removes water vapour and odours at the source
  3. Install low volume continuous ventilation of rooms or spaces to dilute and flush out pollutants and water vapour, that may not be removed by operation of extract ventilation
  4. Utilise purge ventilation, or manually controlled ventilation of rooms and spaces at a high rate to rapidly dilute pollutants and water vapour (i.e. open windows and doors on a daily basis).

Air quality is also now a key focus for independent assessment bodies including the Green Building Council of Australia (GBCA) and Good Environmental Choice Australia (GECA), which help to maintain high construction standards.

Source Control

Ventilation is not always sufficient in improving indoor air quality in dwellings, dilution by ventilation may actually increase indoor pollution problems.

Many powerful contaminants can overpower ventilation systems which should not always be expected to provide good air quality if ill-advised actions are taken.

Such actions may include:

  • Air sealing a home with a damp sub-floor
  • Air sealing a building filled with noxious chemicals from old paint cans, cleaning products, petrol cans and adhesives
  • Living spaces directly linked to garages with potential exhaust fumes.

In general the best approach to manage indoor air quality is source control of pollutants and water vapour, ie. the removal of the contaminant and/or moisture.

When this is not entirely possible smart material selection will aid source control with low VOC paints, sealants, plasterboards, timber composites and flooring all readily available for both commercial and residential buildings. The Green Building Council of Australia (GBCA) and Good Environmental Choice Australia (GECA) both set strict limits on what emission rates are acceptable in occupied spaces.

A variety of building products now offer mould-resistant and hypo-allergenic options. Antifungal agents for example are mixed into the core of Gyprock EC08™ Complete and the new Gyprock Sensitive products. These agents penetrate the paper lining and paint coating to eliminate a potential substrate for mould spores. Wax emulsions within the core of some plasterboards also provide high moisture resistance, which is beneficial for ‘wet areas’ such as laundries and bathrooms.

Mould can be avoided through material selection and ventilation strategies

Hybrid – Source Control & Ventilation

The major sources of contamination including water vapour in dwellings are the bathrooms, laundries and kitchens. NCC Volume 2 for class 1 dwellings recognises this but does not specify any minimum flow rates for bathrooms, laundries, sanitary compartments and kitchens. The loose guidelines state ‘mechanical ventilation may be used’, however, no measureable performance benchmark is provided.

In comparison, the UK Part F Regulations state a minimum of 30 litres per second (l/S) for kitchens, 30 l/s for laundries, 15 l/s for bathrooms and 6 l/s for toilets.

Obviously, there is a fundamental difference in flow rates required in the colder UK climate where windows and doors may rarely be opened – so source extract ventilation effectiveness becomes more critical.

Despite our climatic differences Australia’s National Construction Code (NCC Vol 1 & 2) would still greatly benefit if we set minimum benchmarks for adequate performance. AS 1668.2 recommends minimum ventilation rates of 40 l/s in laundries with non-condensing dryers, 20 l/s in laundries with condensing dryers and 25 l/s for bathrooms and toilets. In addition, it sets guidelines around minimum range hood ventilation rates which are largely dependent on range hood size and installation. None of these are referenced in either NCC volume 1 or 2.

Continuous Ventilation

Periodic ventilation is not 100% effective, especially with user operated switches in bathrooms, laundries and range hoods. This means not all contaminants will be captured, additionally contaminants from the building enclosure and the occupants themselves will remain.

Normal practice in Europe and North America use low flow continuous ventilation throughout the whole building to remove dispersed contaminants – which were not otherwise removed by operation of source extract ventilation. This allows a much higher level of control to the indoor air quality.

In Australia, class 1 and class 2 dwellings desperately lack appropriate minimum requirements to prevent sick building syndrome and moisture related issues resulting from the accumulation of internal moisture.

Many parts of the US actually have very low minimum, continuous ventilation flow rates for acceptable indoor air quality in low-rise residential buildings.  There is a minimum ventilation rate of 15 l/s with an additional 0.05 l/s per m² of floor area.

The UK Building Regulations recommend a minimum continuous ventilation rate for whole building based on 0.3 l/s per m².  In Australia, AS 1668.2 recommends a minimum outdoor air flow rate of 0.35 l/s per m² but is not referenced by the NCC.

For normal air quality expectations in Europe 1 l/s per m² is required.  This is significantly higher than the US, UK or Australia but does seem appropriate when it is assumed that windows are rarely opened in cold European climates.

It can also be argued that the minimum US requirements for source extract ventilation is more effective than Australia, UK and Europe.  For example, in the US, clothes dryers must be ducted directly outside completely eliminating pollutants and water vapour from the building; in addition a dedicated exhaust in kitchens and range hoods is required for larger volume kitchens.

In other words: the more effective the source control then the less continuous ventilation required to maintain air quality.

The European approach has the least stringent bathroom, kitchen and toilet extract flow rates so therefore more contaminants enter the general living space.  This explains the higher continuous ventilation rates; they aim for dispersion and purging of contaminants by increasing total volumetric air changes within the dwelling.

Area based minimum fresh air requirements by geography

Purge Ventilation

Purge ventilation is controlled ventilation of rooms/spaces at a relatively high rate to rapidly dilute pollutants and water vapour. Purge ventilation can be provided by natural means such as simply opening windows and doors, or by mechanical means.

Windows and doors are regularly opened to aid ventilation in many parts of Australia. This is reflected in NCC Volume 2, 3.12.4 Air Movement, which stipulates minimum ventilation openings in external walls.

In Australia we continue to place a large emphasis on appropriate purge ventilation to maintain indoor air quality across all our climatic regions. This assumes the occupants are aware of the benefits, understand the repercussions and are physically capable of purging their home at least once per day.

Seasons can affect user behaviour, hence during winter months houses may be more closed up. Whole building ventilation such as Edmonds Odyssey provides effective purge ventilation to rapidly expel built up contaminants and/or moisture.

Appropriate material selection, contaminant source ventilation, continuous background ventilation and purge ventilation measures are all low-cost, simple and effective means to improve the indoor air quality in your home, and can significantly improve occupant health. For a large number of organisations and companies who recognise the importance of reducing air pollutants, the options available are diverse, but also easily accessible.

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