Examining indoor mould and moisture damage in Victorian residential buildings

What we did and why

Mould in buildings is an indicator of the presence of an underlying moisture problem, which can occur because of water ingress through defective cladding, a plumbing failure or due to a lack of management of water vapour. Mould is linked to negative impacts on human health and amenity, as well as building structural integrity.

Water damage routinely tops the list of defects encountered in buildings and in complaints to the BPC. Learn how to make a claim or find out more about the dispute resolution process. Wet areas and water proofing and drainage issues are commonly occurring areas of compliance risk we identify through the BPC’s Proactive Inspections Program.

To help understand the scope and causes of this problem and to identify opportunities for improvement or reform, we undertook a scoping study to obtain baseline data on indoor mould and moisture damage in residential buildings in Victoria.

We partnered with the VMIA and Victoria University to undertake this research. The research examines VMIA’s accepted claims against domestic building insurance, overlaid with information from the BPC.

Dr Tim Law was the lead researcher for this work at Victoria University. Dr Law is an architectural scientist, and at the time of undertaking the research was a lecturer and course chair of building surveying at Victoria University. In 2016, Dr Law co-authored a Scoping Study of Condensation in Residential Buildings for the Australian Building Codes Board, which became the basis for the condensation management provisions in the National Construction Code 2019. Dr Law gave public testimony at the federal Inquiry into Biotoxin-related Illnesses in Australia and his submission to the inquiry, together with his public testimony were featured in the 2018 Inquiry report.

What we found

The scoping study was based on VMIA accepted domestic building insurance claims data between July 2018 and November 2020, overlaid with BPC data about building permits sourced from the BPC’s Building Activity Management System (BAMS) and the earlier Permit Levy System. Of the 2,178 claims analysed, 92 per cent (1,995 claims) had at least one water-related defect.[1] A series of key observations and emerging patterns was derived from a metadata analysis of this data set.

A representative sample of 54 claims was selected for more thorough analysis, aimed at identifying relevant factors that are likely to result in indoor mould, and which are indicative of a common root cause. A desktop review of insurance inspection reports (including photographs) and building permit documentation for these claims identified patterns and clusters of problematic building and plumbing work that are likely to result in moisture damage and indoor mould. From this, likely causes, and opportunities to reduce the likelihood of this problematic work occurring were identified.

There were limitations to this scoping study, and caution should be taken in extrapolation of results:

• The study was limited to residential buildings up to three storeys in height.
• This was a study of buildings with accepted defects against domestic building insurance policies issued by the VMIA, and which represent a small proportion of all policies issued by the VMIA[2].
• Determining the extent to which the observations are representative of the broader built environment was beyond the scope of the study.
• Desktop reviews of documentation for case studies were limited to insurance reports and building permit documentation held by the VMIA. Building permit documentation was not available for all claims, and the documentation reviewed (such as drawings and plans) may have been incomplete.

The scoping study identified two broad factors that were likely to result in moisture accumulation and indoor mould:

• Poor or incomplete design documentation.
• Non-compliant design and construction of balconies and internal wet areas.

The research identified the root cause of problematic work was likely attributed to one or more of the following factors:

• Design decisions (such as the selection of articulated forms and the inclusion of balconies as part of the design) make it more complicated to effectively weatherproof a building and can have extensive repercussions.
• Design aspirations that involve geometric complexities at the external walls may be exceeding designers’ and builders’ understanding and technical abilities to design and construct water-tight buildings.
• Poor design documentation which does not incorporate construction detail that meets relevant standards and guidance documents for waterproofing resulted in non-compliant and poor-quality work that has compromised the water-tightness of buildings.
• There may be a misunderstanding or lack of awareness of requirements in mandatory and guidance documentation for roofing and waterproofing requirements among designers, building surveyors, builders and plumbers.

What difference this made

The research identified improvement opportunities for building design, certification, construction, inspection and improved guidance for waterproofing including:

• Improving practitioner education and awareness around high-risk areas such as balcony design and construction and watertightness of external building envelopes, and the consequences of poor weatherproofing and waterproofing practice.
• Prescribing critical details for inclusion in drawings/building plans.
• Increased supervision of the design and construction of balconies and other high-risk building elements such as roofing and waterproofing through mandatory inspections.
• Use of technology to support safe roofing inspections, such as through drones and reality capture images, and
• Developing guidance and education on protection of construction materials from exposure to weather.

The research also identified the importance of interdisciplinary conversations between the health and building professions to support achievement of healthy buildings.

We are using these research insights to inform our Proactive Inspections Program and its continuing focus on areas of compliance risk that could cause water ingress and moisture damage. A Practitioner Education Series webinar was held in February 2023 to provide practitioners with valuable learnings from subject matter experts and to increase awareness of the causes and impacts of indoor mould in Victorian buildings.

The research insights informed a decision by the BPC to focus the 2022 Research Grant Program on research that will assist in reducing moisture ingress and water damage in Victorian buildings. The BPC is also supporting research by the University of Tasmania, through a research grant awarded in 2021, to assess the risk of mould growth in external wall systems used in the construction of new housing in Victoria and identify opportunities to improve the way external walls are constructed to reduce the risk of indoor mould.

In August 2023 we hosted the fifth annual Building Surveyors Conference. The Improving Building Health panel showcased research supported by the BPC on issues impacting the health and safety of building occupants. Facilitated by Bronwyn Weir (co-author of the 2018 Building Confidence Report), the panel comprised Dr Tim Law discussing insights from this research, as well as Dr Nicole Johnston discussing insights from the Investigating passive fire protection defects in residential multi-owned properties research, Professor Rebecca Bentley discussing research into healthy housing and Dan O’Brien of Cladding Safety Victoria discussing balcony defects and water ingress issues identified through the Victorian Government’s Cladding Rectification Program. A video recording of the panel discussion is available for viewing.

[1] Almost 93 percent of the 1,995 accepted water-related domestic building insurance claims analysed were triggered by builder insolvency. No link should be drawn from this research between builder insolvency and building defects.

[2] In Victoria, the VMIA is the main provider of domestic building insurance. Over the three years to 30 June 2020, the annual number of claims settled by the VMIA was less than three per cent in comparison to the number of domestic building insurance certificates issued annually (for example, in 2019-20 the VMIA issued 71,500 domestic building insurance certificates, and settled 1,945 claims).