Waterproofing is crucial to maintaining the integrity of buildings over their service life, minimising post-completion problems or defects primarily caused by water damage.
The primary factors that lead to effective and comprehensive waterproofing include product selection, membrane detail, drainage design, substrate preparation, design, installation, quality assurance, and maintenance.
The implementation of adequate project, installation, inspection, and maintenance techniques can significantly reduce the waterproofing failure rate and repair costs.
The choice of materials, as well as the skill of workers, is also fundamental in guaranteeing the adequate performance of these materials in buildings.
A study by researchers from Victoria University examined domestic building claims data from the Victorian Managed Insurance Agency (VMIA) and found that at least 92 per cent of the 2,187 claims analysed involved one water-related defect.
VBA State Building Surveyor Andrew Cialini explained that waterproofing and drainage had been among the top risks highlighted in VBA’s quarterly reports.
Cialini said: “We are sharing these findings with practitioners to better educate the wider industry on how to improve the quality of building and plumbing work in high-risk areas.”
Water intrusion is by far the most commonly cited building defect in Australia, and mitigating the risk of defective waterproofing requires early building design consideration of several factors.
WATER INGRESS A NATIONAL PROBLEM THAT NEEDS THE RIGHT POLICY SETTINGS
A deeper analysis of a representative sample (54) of the claims examined factors likely to lead to mould, noting complex design work as a potential root cause of questionable construction efforts that could infringe on a building’s waterproof capabilities.
The review of inspection and building reports identified repeated patterns of ‘problematic building and plumbing work’ that were likely to result in moisture damage and indoor mould.
The study also raised the possibility of a general misunderstanding of roofing and waterproof requirements in the designing, building, and plumbing industries.
WATERPROOFING’S WHAT, WHY AND HOW
The two main sources of water and/or water vapour in a structure are condensation and a leaking external wall.
A relative humidity of 60 per cent or more will generate the conditions for condensation to occur, and so can be mitigated through control of the interior space’s humidity level and/or the temperature at the internal face of an external wall.
A leaking external wall – whether a basement wall or façade – typically results in far greater water presence than condensation alone, particularly in below-ground structures. Leaking basement walls commonly stem from poorly installed or damaged membranes, often compromised over the building’s lifecycle from structural movement.
Other contributing factors include air voids caused by inadequate concrete mixes, as well as congested reinforcement or tight construction spaces that prevent proper compaction and coverage.
There are several types of waterproofing materials used in varying applications, including liquid-applied and sheet-based membranes, as well as cementitious, bituminous, and other materials such as polyurethane membranes.
Selecting a proper waterproofing membrane system is crucial, as both the membrane and primer determine their adhesion to the substrate.
Liquid membranes, for example, are used across a range of applications, forming a continuous, flexible barrier.
Their versatility makes them ideal for irregular surfaces and intricate detailing, delivering a continuous finish across complex junctions – particularly where planes shift from floors to walls or into tight, hard-to-reach areas.
They are usually applied by brush or roller and typically require at least two coats to eliminate air pockets.
Sheet membrane systems have long been used for their consistent thickness and high durability. However, they are labour-intensive, requiring extensive handling, cutting, positioning, and detailing during installation.
Spray-on membrane systems are increasingly replacing traditional roll-on, brush-on, and sheet-applied methods. By forming a seamless barrier, they reduce labour demands and simplify the application of waterproofing.
Cementitious waterproofing is used in internal wet areas such as bathrooms, laundries, and kitchens and is a rigid material comprising a cement-based compound that adheres to concrete or masonry surfaces.
Bituminous systems – using materials such as asphalt and tar – are widely applied on low-sloped roofs, specified for their durability and long service life in protecting against weather and external conditions.
The waterproofing industry has also developed membrane systems with little or no volatile organic compound content, without affecting performance.
Despite continued advancements of waterproofing products, however, the sector continues to contend with longstanding issues that contribute to costly building failures.
WATER-RELATED DEFECTS AND THEIR IMPACTS
Recent research has shown 40 per cent of work rectification orders for stand-alone homes in NSW were not being complied with within the mandated period, with defects being found in nearly 25 per cent of apartment complexes across the state.
Defective buildings across Sydney are costing homeowners and taxpayers an estimated $700 million each year. And while Building Commission NSW has ramped up investigations and prosecutions, there is still little industry data to show whether building quality is actually improving.
According to the Building Commission, water ingress is the single biggest problem in construction across the state.
The urgency is reflected in the data – 53 per cent of NSW strata buildings surveyed in 2023 had serious defects, up from 39 per cent in 2021, while 97 per cent of NSW apartment buildings, 74 per cent in Victoria, and 71 per cent in Queensland suffered from at least one defect.
Waterproofing failures alone impacted 42 per cent of defective NSW buildings.
Another major 2024 study found 20 to 40 per cent of all apartment buildings nationally faced problems with water ingress, costing between $235 and $610 million a year to fix.
Along with water ingress, defects such as structural failures and flammable cladding were undermining confidence in strata living, according to the Strata Community Association (SCA), leading to its call for federal intervention as widespread and costly building defects across Australia were left in the hands of owners.
The SCA is advocating for a national framework to shift accountability onto developers and builders, with three pillars central to their campaign: mandatory developer bonds, extended warranty protections, and stricter accountability measures.
