The most expensive building defect is usually the one people notice last.
Cracks are visible. Concrete spalling gets attention. Storm damage feels urgent.
Waterproofing failure is different.
It often begins quietly, behind finishes, beneath tiles, under membranes or inside slabs. It may first appear as a minor leak, a ceiling stain or a damp smell after rain. Then, over time, it becomes something much larger: repeated callouts, broader repair scopes, frustrated occupants, rising costs, insurance complications and, in many cases, major rectification works that could have been avoided with earlier intervention. The Australian Building Codes Board has gone so far as to describe water leaks in apartments and commercial buildings as “probably the #1 defect in Australia”, with sub-surface water identified as a major cause of failure.
That is why waterproofing is no longer just a maintenance issue. It is becoming a compliance, governance and asset protection issue.
Why This Matters Now
The timing is significant. The NCC 2025 waterproofing reforms represent one of the most substantial shifts in Australia’s waterproofing expectations in decades. The proposed changes reflect a more holistic approach to water management, with a stronger focus on sub-surface water, structural falls, drainage design, thresholds and durability over time, not just whether a membrane has been installed.
For asset owners, strata committees, facility managers and government stakeholders, the message is clear: reactive repairs are no longer enough.
The data behind the reforms is compelling. According to the ABCB’s impact analysis, waterproofing defects are prevalent in 20 to 40 per cent of apartment buildings and affect more than 1,000 Class 2 to 9 buildings across Australia each year. The same analysis found a projected net societal benefit of $1.02 billion for Class 2 buildings and $2.5 billion for Class 3 to 9 buildings if the proposed waterproofing changes are adopted, with benefit-cost ratios of 4.3 and 4.9 respectively.
This is not a small technical update. It is a response to a widespread and costly national problem.
Waterproofing Failure Is Rarely Just A Surface Issue
One of the most important findings from recent ABCB research is that many waterproofing defects do not begin with the visible surface finish. They originate from sub-surface water ingress, water that penetrates beneath the surface and affects the building over time. That is why “membrane-only” thinking is increasingly risky.
When water reaches the slab, podium, balcony substrate or basement structure, the consequences become more serious. Moisture can track through concrete, compromise finishes, affect adjoining elements and create conditions for mould, corrosion and long-term deterioration. By the time symptoms appear internally, the root cause may already be extensive.
This is also why patch repairs often fail. If the underlying issue is poor drainage, inadequate falls, slab deflection or flawed detailing at joints and thresholds, surface-level repair work may only delay the next failure.
What The Recurring Defect Patterns Show
The same themes appear again and again in waterproofing rectification projects across Australia.
The first is poor falls and ponding. NCC 2025 proposes a minimum 1:80 fall to structural substrates in external areas such as concrete roofs, balconies and podiums. This matters because insufficient falls allow water to sit where it should drain, increasing the likelihood of ingress over time.
The second is long-term slab deflection. Buildings do not remain in an “as new” condition forever. Structural substrates move and deflect over time, which can reduce drainage performance if those movements were not allowed for at design stage. NCC 2025 specifically introduces expected 10-year deflection considerations for structural substrates in Part F1.
The third is poor detailing at joints, thresholds and transitions. The proposed NCC changes include 70 mm step-downs from internal to external areas and expanded requirements around exposed joints and drainage detailing. These are not minor adjustments. They are aimed at eliminating some of the most common water entry paths in Australian buildings.
The fourth is over-reliance on membranes. Membranes remain important, but current reform thinking recognises that waterproofing performance depends on the entire water-management system, including substrates, drainage, falls, joints and interfaces. The ABCB’s own consultation material states that the proposed changes address sub-surface water in addition to surface water.
The True Cost Goes Beyond Repair Invoices
The direct cost of rectification is only part of the story.
The ABCB’s analysis estimates avoided rectification costs of $946 million for Class 2 buildings alone under the proposed changes, with further avoided legal, professional and time costs.
Other research has shown just how financially damaging building defects can become. OCN’s 2019 submission, referencing national defect research, noted that over 90 per cent of residential apartment buildings in the NSW study had defects in at least one construction system affecting multiple areas, with water and fire safety systems comprising the bulk of the defects. It also highlighted that defect rectification commonly brings legal costs, expert costs, increased insurance premiums, additional strata management costs and significant owner stress.
In practical terms, waterproofing failures can lead to:
- repeated investigations and invasive testing
- prolonged disruption for occupants and tenants
- reputational damage for owners and managers
- disputes with contractors, consultants and insurers
- delays to leasing, sale or occupation
- long-term asset value erosion
That is why these issues increasingly sit at board and committee level. They affect risk, reputation, budgeting and compliance, not just maintenance.
Why A Proactive Strategy Matters
For older assets, especially flat-slab buildings, ageing balconies, basements, podiums and legacy waterproofing systems, the risk profile is already elevated. Waiting until water ingress becomes visible usually means the damage is more advanced and the remediation scope is larger.
A stronger approach is to identify high-risk zones early, assess whether drainage and detailing still perform as intended and determine whether the asset aligns with current expectations around falls, joints, thresholds and sub-surface water management.
In other words, this is the time to shift from reactive leak response to compliance-first asset planning.
What Asset Owners And Managers Should Do Now
For commercial, strata, institutional and government assets, the priority actions are straightforward.
Start with a targeted asset health check focused on waterproofing and sub-surface water risk. Review exposed slabs, balconies, rooftops, basements, podiums and transition points. Assess whether drainage gradients, threshold details and joint protection remain fit for purpose. Prioritise older flat-slab or membrane-only assemblies where the likelihood of hidden water migration is higher.
Where full rectification is not immediately feasible, staged upgrades can still reduce risk by addressing the highest-consequence areas first.
Most importantly, work with licensed remedial specialists who understand live-site delivery, compliance requirements and the difference between cosmetic repair and root-cause remediation.
Why WS Remedial
WS Remedial supports clients across commercial, government and strata environments with remedial expertise grounded in real-world building risk.
As an Australian-owned, multi-sector specialist, our team delivers practical remedial solutions for live, occupied assets, including complex environments where disruption must be carefully managed and wet-weather works may be required. WS Remedial Group take a diagnostic, compliance-aligned approach to waterproofing and building remediation, investigating defect pathways and recommending appropriate repair methods based on site conditions and accessibility.
Our work is shaped by best practice, national regulatory compliance and the realities of managing buildings that must continue to operate during remediation. For eligible projects, works are backed by a 10-year workmanship warranty, along with manufacturer warranties of up to 35 years.*
As compliance expectations continue to rise, that matters.
Protect Your Asset Before The Damage Escalates
The costliest waterproofing defect is rarely the first one discovered. It is the one that sits unresolved beneath the surface, quietly compromising the asset until the repair bill, operational impact and legal exposure become impossible to ignore.
NCC 2025 is raising the benchmark. Asset strategies need to rise with it.
For owners and managers responsible for protecting building value, the smartest move is not to wait for the next leak. It is to assess the risk now, understand where sub-surface water may already be at work and act before a maintenance issue becomes a major rectification event.
Book an Asset Health Check or Diagnostic Assessment with us.
Disclaimer
All data is sourced from government and leading industry reports as cited. All compliance and licensure details current as of February 2026. Eligibility and warranty terms apply – contact WS Remedial Group for audit-defensible advice.
