Go to BPC Homepage Go to BPC Homepage

Log in

Improving building envelope resilience to moisture damage

What we did and why

The Building and Plumbing Commission (BPC) supported research conducted by The University of Sydney’s School of Architecture, Design and Planning to investigate how residential building envelopes can be made more resilient to moisture ingress and water-related damage.

Moisture damage is a significant issue in buildings and can result from inadequate design, construction defects, poor detailing, and occupant behaviour including insufficient maintenance. Water ingress and moisture accumulation can lead to condensation, mould growth and structural deterioration, affecting occupant health, safety and amenity, while reducing the durability and performance of buildings.

The research examined how heat and moisture move through typical Victorian residential wall and roof construction systems. Using advanced computer modelling (hygrothermal simulations), researchers assessed the moisture resilience of common wall and roof systems under a range of environmental conditions including increased rainfall and indoor humidity. The research also investigated how factors such as increased rainfall, higher indoor humidity and ventilation affect building performance, and examined critical construction details and building junctions where moisture-related problems are more likely to occur.

The research was undertaken in three phases. It assessed common wall and roof assemblies that complied with National Construction Code (NCC) 2022, examined how they performed under increased moisture loads, and investigated building junctions and construction details that can be vulnerable to moisture ingress.

The research analysed a range of common Victorian construction systems, including lightweight timber-framed walls, brick veneer systems, cavity brick construction, externally insulated masonry walls and a range of insulated roof assemblies.

By identifying vulnerabilities in building envelopes and testing how construction systems perform under different conditions, the research highlighted opportunities to improve moisture resilience and reduce the risk of water damage, condensation and mould growth. The findings provide an evidence base to support more resilient building design and construction practices, to improve the durability, quality and performance of future Victorian homes.

The research was led by Associate Professor Arianna Brambilla and was supported by the BPC through a research grant awarded in 2022. The research also received in-kind support from Mott MacDonald, an engineering consultancy. The project was completed in 2025.

What we found

The research found that moisture resilience is influenced by climate conditions, material selection, construction detailing, ventilation and building design.

Granular climate zoning supports better assessment of moisture-related risk

Victoria's climate is more diverse than is reflected by the broad climate zones used in the National Construction Code (NCC).

The research found that a more accurate assessment of moisture-related risks could be determined using the more detailed climate classifications provided by the Nationwide House Energy Rating Scheme (NatHERS). This approach better captures local climatic conditions and supports more reliable assessments of building resilience and construction practices to reduce moisture-related risks.

Porous materials are more susceptible to moisture-related risk

Masonry assemblies, including brick veneer and cavity brick systems, are particularly susceptible to moisture accumulation and mould growth across most climate zones.

Porous construction materials can absorb and retain moisture, especially when exposed to rain, humidity and temperature fluctuations. The arrangement of construction layers, membrane performance and ventilation all play an important role in managing moisture within these systems.

The research found that masonry wall systems and tiled roof assemblies require particular attention during design and construction to minimise moisture-related risks.

Climate change is likely to increase mould growth risk

Increased rainfall, higher indoor humidity and warmer temperatures can significantly increase the risk of moisture-related damage and mould growth.

As climatic conditions change over time, buildings may be exposed to more intense rainfall and higher moisture loads. The findings highlight the importance of considering future climate conditions when designing and constructing residential buildings to reduce the risk of water ingress, condensation and mould growth.

Attention to detail during construction is critical to reduce mould growth risk

Moisture-related problems are often concentrated in specific construction details and junctions, even when the broader wall or roof system performs well. Proper flashing, sealing, and moisture management are essential to maintaining a building's structural integrity and preventing water ingress.

Particular areas of concern included:

  • wall bases, where moisture can accumulate if water is not effectively diverted
  • window heads and windowsills, which can trap moisture and are vulnerable to water ingress
  • window-wall interfaces, where inadequate sealing and flashing can result in air leakage and condensation
  • vapour-permeable membranes, where installation failures such as perforations or discontinuities can allow moisture to penetrate building layers
  • roof penetrations and skylight junctions, which require careful sealing and flashing, and
  • corner junctions, which can be vulnerable to moisture accumulation and condensation.

The research found that these construction details can be more vulnerable to moisture-related damage than the surrounding wall or roof systems. This highlights the importance of careful design, quality workmanship and attention to detail during construction to reduce the risk of water ingress, condensation and mould growth.

Ventilated cavities can significantly reduce mould growth risk

Ventilation is one of the most effective ways to improve moisture resilience across a wide range of residential wall and roof systems.

Ventilated cavities help remove moisture from building assemblies by improving airflow and supporting drying when moisture is present. The research found that well-ventilated wall and roof cavities can significantly reduce the risk of mould growth, particularly in construction systems that are more susceptible to moisture accumulation.

The study also found that cavity design plays an important role in moisture management. Adequate cavity thickness is necessary to allow effective airflow, while higher levels of ventilation generally improved drying performance and reduced mould growth risk.

To better understand the role of ventilation, researchers tested a range of ventilation scenarios and found that improved airflow consistently reduced moisture-related risks in many wall and roof systems.

The findings highlight the importance of considering ventilation, cavity design, sealing, flashing and material selection together as part of an integrated approach to moisture management.

What difference this made

This research provides a comprehensive assessment of moisture resilience in Victorian residential construction systems and strengthens the evidence base for reducing moisture-related harm in buildings.

The research demonstrated that a building’s moisture resilience can vary significantly depending on climate conditions, material selection, ventilation and construction quality. By examining how common Victorian construction systems respond to a range of conditions, the research provides a stronger evidence base for improving moisture resilience and reducing the risk of water-related damage, condensation and mould growth in residential buildings.

  • For the BPC, it provides evidence to inform policy development, regulatory reform, guidance materials and education initiatives focused on moisture management and building resilience. See the consumer safety guide on Condensation, moisture damage and mould.
  • For practitioners (including designers, builders, plumbers, building surveyors and building inspectors), it identifies practical opportunities to improve building performance through better material selection, ventilation design, moisture management and construction detailing.
  • For consumers, it contributes to improved building quality by supporting more durable homes that are better protected against moisture damage, condensation and mould growth.

The research contributed to the evidence base that informed improvements to condensation and moisture management requirements in the National Construction Code. Since the project commenced, NCC 2025 has strengthened provisions relating to moisture management, including requirements for drained and ventilated cavities, roof ventilation, vapour permeable membranes and condensation mitigation measures. Many of these areas were investigated as part of this research project.

The findings also contribute to a better understanding of how future climate conditions may affect building performance and highlight opportunities to continuously improve the resilience of Victorian homes over time.

Download the report

Read the full report: Increasing the Building Envelope Resilience to Moisture Damage

Related research

This research complements other BPC-supported research that aims to reduce harms associated with moisture ingress, water damage and other risks that affect the safety, performance and durability of buildings, including:

  • Print this page

Was this page helpful?
Your rating will help us improve our website.