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Understanding & Assessing Mould Risks

31 January 2020

Mould is the common name given to a broad range of microscopic filamentous fungi. They are related to other fungi, such as yeasts and larger fungi, commonly recognised as mushrooms. There may be up to 5.1 million fungal species with only 100,000 currently described.

A water impacted building is at risk of fungal growth, with potential risks to occupant health and property value. These risks are amplified when corrective actions are delayed or if the source of the problem remains undiscovered for months or longer. This risk review will outline how mould grows, the health effects of exposure, how mould is assessed in the built environment and what regulations exist.


Where and how does mould grow?

Mould growth predominately occurs on a wide range of organic materials and is often visible as fluffy or downy discolouration on surfaces.

Mould do not require sunlight to grow and can extract nutrients from a wide range of materials including paper, wood, some glues and resins, porous mineral compounds, leather and textiles. Most moulds require high water availability to proliferate and water damage and persistent moisture in building materials or in cavities is a high-risk factor for fungal growth.

Mould reproduce vegetatively by growth on suitable substrates in the form of hyphae, which are fine threadlike structures similar to tree roots. A mass of hyphal threads is called mycelium. Once mould amass sufficient nutrients and water in the mycelium, they will produce a fruiting structure capable of generating spores – small mould particles capable of germinating and becoming new colonies. Spores are microscopic structures, resistant to drying out and able to be easily aerosolised and remain airborne for extended periods of time (for months) and can travel kilometres in distance. Each colony may produce hundreds of thousands of spores, each capable of colonising a new substrate and beginning the cycle again.

In a natural environmental and given favourable environmental conditions, fungi including mould will degrade the variety of organic materials which accumulate over time; fallen tree branches, leaves, animal carcasses and waste. In a building, we use many of these materials to construct and furnish, such as wood, paper and leather. When a building is water impacted by damage to the roof or plumbing, these materials will absorb moisture and mould growth will begin from germination of dormant spores. If allowed to continue, this growth will cover the material, sporulation will occur and spores will be dispersed allowing the impacted area to expand.

How many mould spores are normally in the air?

The air we breathe naturally contains mould spores and fragments, and their concentration changes depending on a wide range of environmental factors including the season, wind, and the surrounding land use. Inhalation of spores or hyphae rarely causes infection, with normal outdoor air containing anywhere from a few hundred to tens of thousands of spores per cubic meter of air, measured in spore counts per cubic meter (Cts/m3).

Although moulds are naturally abundant in the environment, in order to determine if an indoor source of mould growth is present, the extent of the growth, and if persistently elevated moisture has been present in a building, we may compare:

  • The concentration of fungal spores in air
  • The fungal genera present in a location
  • Observations of materials for fungal growth structures
  • Reference samples and accumulated historic data


Is there an "acceptable" level of mould spores in the workplace?

Typically, indoor air should contain fewer airborne spores than external reference samples collected on the same day, although spores present in external air will likely influence the concentration and genera of mould present in indoor air. The 2009 World Health Organisation (WHO) Guidelines for Indoor Air Quality, Dampness and Mould states that:

As the relationship between dampness, microbial growth and health effects cannot be quantified precisely, no health-based guideline values or thresholds can be recommended for acceptable levels of contamination by microorganisms. Instead, it is recommended that dampness and mould-related problems be prevented. When they occur, they should be remediated because they increase the risk of hazardous exposure to microbes and chemicals.

Currently, no guidelines exist which recommend specific allowable levels of spores or hyphal fragments in either the work or home environment. Greencap uses a range of peer reviewed sources to generate appropriate reference concentrations for fungal elements in air for both ‘normal’ and ‘impacted’ buildings.

The genera present and their water requirements for growth are also a useful differentiating factor when determining if spores found in indoor air are indicative of growth within a building or have migrated from an external environment.


Penicillium sp. require very little water to grow and rapidly appear after water damage


Alternaria sp. require intermediate amounts of available water and are frequently found in outdoor air


Chaetomium sp. require materials to be persistently wet for vigorous growth to occur


Stachybotrys sp. require very high available water to germinate and grow in buildings



Is every type of mould dangerous?

The primary health risk from mould in buildings is exposure by inhalation of airborne spores, spores containing toxins (mycotoxins) or fragments of hyphae.  Exposure to spores and fragments can cause a range of illnesses including allergy like effects, inflammation of the airways, itchy eyes, and rhinitis.  Exposure to elevated levels of spores or hyphal fragments can cause sensitisation of the immune system and allergy like effects in many people, resulting in general skin and respiratory discomfort. Whilst rare, prolonged or heavy exposure of sensitive individuals to mould particles has been associated with more serious acute and chronic health effects.

The current understanding of environmental mould related illnesses, particularly exposure to the toxins they produce, comes primarily from studies on ingestion of mould food or animal feed and high exposures in occupational settings. Research into domestic or prolonged low/medium level exposures is not of sufficient strength to draw causal relationships between exposure and the development of specific health outcomes, although associations exist between residing in mouldy buildings and asthma, allergies and respiratory illness (Fisk, Eliseeva, and Mendell 2010). 

Not all species or genera of mould produce mycotoxins, with the most common effects of mould growth indoors only causing cosmetic damage to materials or unpleasant and musty odours. Some species of mould which have been confirmed to produce mycotoxins do grow in indoor environments, although they do not produce mycotoxins all the time and need specific nutrition, and moisture conditions to do so. 

Exposure to mycotoxins produced by some mould has been shown to cause a range of health effects and is specific to the species present. Mycotoxins are not volatile - they don’t become a gas - and exposure is by inhalation of fungal particles or ingestion of mould contaminated dusts or food (Viegas et al. 2015). Whilst there are limits set on the allowable concentration of mycotoxins in food, there are no such limits set for mycotoxins in air, or gross limits on the airborne spores.

The musty odours caused by microbes growing indoors is due to the production of compounds known as microbial volatile organic compounds (MVOC), a class of over 1000 chemicals which easily become a gas and are often detectable by smell in indoor environments. MVOC are produced by actively growing microbes (both bacteria and fungi) and due to the volatile nature of these chemicals they tend to act as irritants, affecting mucous membranes such as sinuses, eyes and airways.

In occupational settings mould and specialist remediators are at heightened risk of exposure to fungal particulate and compounds. Other industries identified as being at risk of elevated exposure to spores and mycotoxins includes piggeries and poultry farms, sawmills, composting facilities, solid waste handling and grain and cereal processing. 


How do you assess moisture and mould impacts in the built environment?

In order to determine the level of mould and moisture impacts in a building, Greencap undertakes a detailed inspection which includes the following:

Interview property occupant(s) to establish context around the water intrusion event/moisture issues of the building as well as any known health effects/concerns.


A detailed visual inspection of the exterior and interior of the building, highlighting building construction and visible signs of water damage and/or mould growth.


Airborne and building material moisture assessment in order to establish the level and areas of impact, noting the types of building material impacted or likely impacted.


Development and implementation of a mould sampling plan (air and surface samples) in order to assess the level, extent and type of mould present within the building. These samples are delivered to Greencap’s laboratory where they are analysed.


Where appropriate, recommendations are made on any make safe works required to the building to mitigate losses and limit future growth and possible cross contamination.


A summary of inspection findings and interpretation of sample results are sent via email to the client soon after receipt of laboratory results to guide stakeholders, particularly where time and rapid response is a consideration.


A detailed report presenting the inspection findings, moisture measurements and sample results is provided. If required a Scope of Remedial Works can be prepared in-line with industry best practice guidelines as outlined in the Institute of Inspection, Cleaning and Restoration Certification (IICRC) Standard and Reference Guide for Professional Mould Remediation (S520-2015) and Water Damage Restoration (S500-2015)




Download Greencap’s Guide to Professional Mould Assessment and Remediation to learn about the general process of how water damage and mould remediation projects should be managed.


How are mould samples analysed?

Spores collected from the air and from surfaces do not need to be grown in order to be analysed. This type of sampling is called ‘non-viable’ or ‘total’ sampling and allows the analyst to count and identify all the spores present in a sample using a microscope. This type of analysis cannot tell the difference between alive and dead spores. When carrying out a full inspection including air samples, textbook and scientific references and suitable outdoor air samples are used to determine if any elevation in spores exists.

Surface samples are able to be categorised depending on the amount and type of fungal spores and growth structures present using the criteria laid out in the Institute of Inspection, Cleaning and Restoration Certification (IICRC) Standard and Reference Guide for Professional Mould Remediation (S520).

Condition 1

(normal fungal ecology)
An indoor environment that may have settled spores, fungal fragments or traces of actual growth whose identity, location and quantity are reflective of normal fungal ecology for a similar indoor environment. The aim of remediation is to return areas impacted by the event to Condition 1.

Condition 2

​​​​​​(settled spores)
An indoor environment which is primarily contaminated with settled spores that were dispersed directly or indirectly from a Condition 3 area (mould growth area), and which may have traces of actual growth.

Condition 3

​​​​​​(actual growth)
An indoor environment contaminated with the presence of actual mould growth and associated spores. Actual growth includes growth that is active, dormant or visible.


Australian Mould Regulation/Legislation 

Currently there are no national Australian mould regulations or legislation which prescribes the allowable concentration of fungal spores in air. However, there is a duty of care required to be upheld by employers, landlords and persons carrying out a business undertaking to ensure employees, tenants and patrons are not adversely affected by preventable conditions which would include exposure to biohazards and potential biohazards such as elevated mould spores.

The current understanding and response to fungal growth or contamination of buildings has been recognised to be insufficient to provide conclusive advice in many circumstances, and to remedy this the federal government requested an inquiry into biotoxin-related illnesses in Australia, which was completed at the end of 2018. This report highlighted several knowledge gaps and provided recommendations to improve outcomes when remediating mould affected buildings.

The recommendations summarised are:

  • For the Department of Health to produce a fact sheet and conduct further investigations on the potential health effects, prevalence in buildings [of mould] and advise on prevention of mould.
  • Further research should be facilitated by the Australian Government to establish agreed standards and/or accreditation requirements for the mould testing and remediation industries
  • To Improve disclosure and rectification of mould and water damage in properties for tenants in rental properties, aged care facilities, community, social and public housing
  • To carry out further research into the adequacy of existing building codes and
    building standards with regard to the prevention of dampness and mould.
  • To review treatment of complex mould related illnesses

Greencap agrees with the recommendations made in this report and is working to develop solutions to the complex problem of dampness and mould growth in buildings. 


Contact Greencap For Assistance



Fisk, W. J., E. A. Eliseeva, and M. J. Mendell. 2010. "Association of residential dampness and mold with respiratory tract infections and bronchitis: a meta-analysis."  Environ Health 9:72. doi: 10.1186/1476-069X-9-72.

Viegas, Carla, Ana Catarina Pinheiro, Raquel Sabino, Susana Viegas, João Brandão, and Cristina Veríssimo. 2015. Environmental mycology in public health: fungi and mycotoxins risk assessment and management: Academic Press.


The information in this material is not intended to provide, and should not be relied upon, for legal or professional advice and is subject to change.
This material provides general information only and does not take into account your particular circumstances. Before making any decisions, you should assess whether this material is appropriate for you and obtain legal advice tailored to you having regard to your particular needs and circumstances.
Greencap Pty Ltd (Greencap), its officers, employees and agents believe that the information in this material and the sources on which the information is based (which may be sourced from third parties) are correct as at the date of publication. While every care has been taken in the preparation of this material, no warranty is given for its reliability or accuracy and no responsibility is accepted by Greencap, its officers, employees or agents. If this material contains links to third party websites, Greencap does not control and is not responsible for the information contained within these websites. None of these links imply Greencap’s support, endorsement or recommendation of any other company, product or service.



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