Why Modern Windows Leak – A Pascoe Vale Case Study

Most people assume that when water appears around a window, the window itself is leaking.

In reality, modern windows are only one component of a much larger water management system. In many cases the actual cause of the leak lies in the surrounding wall construction, flashing details or drainage paths rather than the window itself.

This case study from Pascoe Vale demonstrates how water ingress can occur even when the visible symptoms suggest a faulty window.

How Modern Aluminium Windows Work

Contrary to popular belief, aluminium windows are not designed to be completely waterproof.

Modern aluminium windows are designed as water management systems. Water is expected to enter parts of the frame during heavy weather events. The window relies on internal drainage chambers, subsills and weep holes to collect this water and direct it safely back outside.

Unlike uPVC windows, which are typically manufactured from welded sections, aluminium windows are assembled from multiple extrusions which are mechanically joined together. These joints create additional pathways for water movement and increase the importance of correct flashing and drainage details.

uPVC Windows

• Extrusions are welded together.

• Fewer frame joints.

• Reduced opportunity for water migration through frame corners.

• Good thermal performance.

Aluminium Windows

• Multiple mechanically assembled extrusions.

• Greater reliance on drainage paths and sealants.

• More potential leakage points if installation or flashing details are inadequate.

Neither system is inherently leak-proof. Both depend heavily on correct installation and water management.

Flashings Are Not Waterproofing

One of the biggest misconceptions in construction is that flashings stop water.

They do not.

Flashings are designed to manage water by collecting it and redirecting it back to the exterior of the building.

Modern wall systems assume that some moisture will bypass the external cladding. The role of the building wrap, drainage cavity and flashings is to safely collect this moisture and discharge it externally before it can damage the building.

The Building

This Pascoe Vale townhouse incorporated:

• Lightweight rendered cladding over polystyrene.

• Aluminium windows.

• Upper-floor windows located directly above lower-level windows and doors.

• An alfresco roof beneath some upper windows.

• Internal living areas beneath others.

Previous attempts had been made to stop the leaks by applying sealant around the perimeter of the windows.

Unfortunately, this did not address the underlying issue.

What Should Have Happened?

Where upper-level windows are positioned above roofs, doors or other vulnerable building elements, the building wrap and flashing systems should be designed to direct any water that enters the wall cavity back to the exterior.

In this case there were two critical areas.

Window Above Alfresco Roof

The building wrap should ideally have terminated onto the alfresco roof via an appropriate flashing arrangement.

This would have allowed water travelling down the drainage plane to discharge harmlessly onto the roof surface before reaching the door below.

Window Above Internal Ceiling

Other upper-floor windows were located above the lounge and dining areas.

The wall wrap and flashing systems should have directed any moisture safely onto the flat roof below and then back to the exterior.

Instead, water appeared to be bypassing these drainage pathways and entering the building structure.

Why These Problems Are Difficult To Fix

Once the following have been completed:

• Cladding installation

• Rendering

• Roofing

• Internal plastering

Retrofitting compliant flashing systems can become extremely invasive and expensive.

In many cases rectification may require:

• Removal of windows

• Removal of cladding

• Roofing modifications

• Internal repairs

This can result in significant disruption and cost.

Practical Remedial Solution

A full reconstruction of the wall system was not considered practical.

Instead, a targeted remedial solution was adopted.

The aluminium extrusion junctions were carefully cleaned, dried and sealed. Particular attention was paid to frame joints and interfaces where water migration was most likely occurring.

This process was far more involved than simply applying a bead of sealant around the perimeter of the window. Successful remediation required:

• Clean surfaces

• Dry conditions

• Careful preparation

• Attention to detail

• Identification of likely water pathways

Outcome

Following completion of the works, the windows were monitored through subsequent heavy rainfall events.

No further water ingress was reported.

Most importantly, the client was able to enjoy their home without the ongoing concern of recurring leaks.

Key Lessons

This case highlights several important principles:

• Windows rarely leak in isolation.

• Building wraps and flashings must provide a continuous drainage path to the exterior.

• Water management is more important than sealants.

• Perimeter caulking is often not the solution.

• Design decisions made during construction can have significant long-term consequences.

At Leak Masters we regularly investigate leaks that are ultimately caused by failures in water management rather than the window itself. Understanding how water moves through a building is often the key to finding a practical and lasting solution.

We Don’t Just Find the Leak — We Explain How to Fix It

Many leak-detection services simply reproduce the leak, identify where the water appears and then recommend engaging a waterproofer, window specialist or builder to work out the repair.

Leak Masters is different.

Our assessments are undertaken by an experienced builder using a proven, controlled testing process. We not only identify how and where water is entering—we understand how the building was constructed, why the component has failed and what is required to repair it.

Anyone can spray water at a window until it leaks. The real value is correctly diagnosing the underlying defect and providing a practical repair solution.

Our reports clearly explain:

• Where the water is entering

• Why the leak is occurring

• Which building component has failed

• The repair work required

• How the completed repair should be tested

With Leak Masters, you receive more than leak detection. You receive a practical pathway to fixing the problem.

Leaking Window Repair – Wyndham Vale

The Problem

The owner of a two-storey brick-veneer home in Wyndham Vale had ongoing water ingress associated with an upstairs aluminium window.

During heavy rain, water entered around the window installation and caused damage to the ceiling of the lounge room below. Previous movement to the house and cracking in the surrounding brickwork made it important to determine whether the water was entering through the window, the wall construction or another nearby defect.

The Investigation

Leak Masters undertook a visual inspection followed by controlled water testing.

Water was applied progressively to the surrounding wall, window and drainage points to identify the path of entry without unnecessarily wetting the entire area.

The testing confirmed that water was passing through the window installation and into the building rather than being safely collected and discharged outside.

What We Found

The property had a single-glazed aluminium sliding bay window installed within a brick-veneer wall. The cavity flashing and sarking/building wrap did not drain externally but into the ceiling directly below.

The problem was not something that could be reliably resolved by simply applying additional silicone around the outside of the frame. The window needed to be removed so the concealed opening, flashing and drainage details could be accessed and repaired.

The Repair

The affected window was carefully removed from the brick-veneer opening.

Once the window was out, the concealed installation details were inspected and rectified. The opening was prepared to manage any water entering around the window and direct it back to the exterior.

The existing window was then reinstalled, sealed. The damaged internal plaster was also repaired once the source of the leak had been addressed.

The Result

Following completion of the repairs, the window and repaired plaster area remained dry through several subsequent storms.

Why Proper Diagnosis Matters

Applying more sealant may temporarily reduce a leak, but it does not correct defective concealed flashing or installation details.

Because Leak Masters combines controlled water testing with practical building experience, we can identify not only where water is entering but also how the building needs to be repaired.

Leak Masters — we don’t just find leaks. We provide a practical pathway to fixing them.

Sliding-Door Leak Investigation – Hawthorn

The Problem

Water was entering a recently renovated Hawthorn home below an upper-level balcony containing an aluminium sliding door and adjacent window.

A previous balcony flood test had not reproduced the leak.

Controlled Testing

Leak Masters tested each component separately:

• The balcony was flooded for approximately 30 minutes — no leakage.

• The adjacent window was sprayed progressively — no leakage.

• Water was applied to the sliding-door bottom rail — water entered between the sub-sill and wall construction within approximately two minutes.

The leak was isolated to the sliding-door sill area.

The Defect

The door incorporated an integrated sub-sill and drainage system. However, water escaping from the sub-sill was able to enter the building instead of being collected and discharged outside.

This is a commonly misunderstood part of window and door installation.

A sub-sill does not replace the requirement to flash the surrounding external wall opening.

The National Construction Code (NCC) requires exposed external wall openings to be flashed at the sill, jambs and head. Importantly, it is the external wall opening that requires flashing—not merely the window or door product.

These flashings provide a secondary line of protection. If the window or door is damaged, its drainage becomes obstructed, or a sub-sill end dam begins leaking, the opening flashings should still prevent water entering the building.

The testing indicated that the concealed sill flashing was absent, incomplete or ineffective.

(Note: Features like upper-level balconies over habitable rooms consistently rank as high-risk structures on the Leak Masters Building Durability Index due to the precision required during construction.)

Recommended Repair

The sliding door should be removed so the concealed sill and surrounding wall opening can be inspected.

Compliant sill and jamb flashings should then be installed, connected to the adjoining wall wrap and arranged to drain externally. The door can then be reinstalled and controlled-water-tested.

Retrofitting flashings is considerably more difficult and expensive than installing them correctly during construction—but it is often the only reliable way to correct the underlying defect.

How Leak Masters Can Help

Leak Masters assists builders, homeowners and window manufacturers at every stage—from construction through to occupancy.

We use controlled testing and practical building experience to identify:

• Where the water is entering

• Why the building is not managing it

• Which construction detail has failed

• How the defect should be repaired

We don’t just reproduce leaks. We understand how buildings are constructed and provide a practical pathway to fixing them.