In 2022, continuous and elevated levels of wet weather stretching from mid New South Wales to Southeast Queensland resulted in tens of thousands of houses experiencing mould growth on surfaces and contents at an unprecedented scale. Much of this proliferation was resultant from prolonged periods of high humidity within properties, which was directly caused by the high humidity levels outdoors.

Within the property restoration and mould remediation industry, this specific type of growth is defined as Environmental. This terminology indicates that the growth was a direct result of the environment being conducive to fungal activity. This stands in contrast to most other instances of mould growth, which are typically resultant from materials becoming wet or having excess moisture content as a direct result of being impacted by water.

Regional Perspectives and Misinformation

For tropical and subtropical climates, managing environmental mould growth within buildings is not a new challenge. In regions such as far North Queensland and Darwin, residents are often accustomed to mould growth and expect it to occur during the wet season. However, the 2022 event triggered significant media coverage and online discussion because many people in the affected regions had never experienced this phenomenon before.

The resulting concern led to instances of public hysteria, exacerbated by thousands of websites providing unqualified advice and a myriad of warnings regarding the dangers of mould in the home. This environment allowed various mould experts to emerge through media outlets. It became obvious during this period that many of these discovered experts were not reputable sources of technical information.

The Mechanics of Environmental Growth

To address the misinformation disseminated during such events, it is necessary to understand the scientific drivers of environmental mould growth:

• Humidity Thresholds: The primary driver is high humidity within the property for a prolonged period. Growth generally occurs when relative humidity levels exceed 70%.
• Ubiquity of Spores: Mould spores are ubiquitous, meaning they are present everywhere. When combined with the abundant nutrients found on indoor surfaces, they only require sufficient moisture to thrive.
• Infrastructure Mismatch: A significant exacerbating factor is the use of air conditioning in houses not designed for it. Cooling indoor surfaces while allowing warm, humid air in via natural ventilation or a leaky building envelope creates a high risk of condensation and subsequent growth.

Technical Risks: What to Avoid

Analysis of the 2022 event identified several common practices that inadvertently worsened microbial conditions. Professional investigators and property owners should be aware of the following technical risks:

• Avoid disturbing visible fungal growth without controlled methods, as this causes microscopic spores to be easily aerosolised and spread onto previously unaffected surfaces.
• Avoid amateur cleaning attempts that simply smear microscopic spores across a surface. If humidity levels remain ideal, this can cause the mould growth to return even more aggressively than the initial occurrence.
• Avoid relying on natural ventilation by opening doors and windows during periods of high outdoor humidity, which allows moisture-laden air to enter and equalise within the building envelope.
• Avoid the use of oversized air conditioning systems that cool a space too rapidly. These units often reach the desired temperature and cycle off before they can remove adequate moisture from the air, leaving indoor humidity levels high.

Practical Solutions for Environmental Control

To mitigate the risk of environmental mould growth and ensure a defensible restoration outcome, RIC Solutions recommends the following practical steps based on established building science:

• Maintain indoor humidity levels consistently below 65% relative humidity to inhibit the metabolic activity of mould spores.
• Perform a thorough removal of excess mould spores to establish a stable and healthy indoor environment.
• Ensure all cleaning is performed methodically to prevent the cross-contamination of unaffected zones within the property.
• Engage only qualified independent environmental professionals who provide science-based evidence and assessments that align with recognised industry standards.
• Identify and address any moisture-related defects in building design or construction, such as non-compliant wet areas or poor waterproofing, to prevent long-term environmental issues.

By adhering to these evidence-based protocols, stakeholders can move beyond the hysteria often associated with regional mould events and focus on pragmatic, scientifically sound remediation.