The importance of correct flashings around windows – protecting every cladding type

Water is one of the most persistent and destructive forces affecting buildings, and one of the simplest yet most critical defences against it is correct window flashing. Whether a home is clad in brick veneer, lightweight panels, fibre cement, or rendered systems, effective flashing installation remains a fundamental requirement under the National Construction Code (NCC) and AS 2047 – Windows and External Glazed Doors in Buildings.

Why Flashings Matter

Flashings are not decorative; they are engineered barriers designed to redirect water away from vulnerable junctions where materials meet — particularly around windows and doors.
Without properly installed flashings, water can infiltrate sills and cavities, leading to timber rot, corrosion of steel framing, mould growth, and damage to internal finishes. In Canberra’s climate — where homes experience extreme temperature swings, driving rain, and frost — even a small defect in flashing detailing can cause long-term structural damage.

Common Flashing Issues Observed in ACT Builds

Across a range of site inspections, the MBA ACT Advisory Team has identified recurring non-compliances and workmanship issues, including:

• Incorrect sequencing: Flashings installed after cladding or render, breaking the intended drainage path.
• Omitted sill flashings: Particularly in brick veneer construction, where the absence or incorrect rubber flashing allows water to drain directly into the cavity.
• Inadequate head flashings: Missing or improperly sealed drip edges over windows, especially in lightweight cladding systems.
• Over-reliance on sealant: Using silicone as a substitute for proper mechanical flashing — a short-term fix that inevitably fails.

Best Practice for All Cladding Systems

While flashing details vary depending on the cladding type, several principles apply universally:

1. Design with drainage in mind: Every window opening must have a defined path for water to escape — not just rely on sealant.
2. Install in sequence: Sill flashings first, followed by jambs and head flashings — always angled to direct water outwards.
3. Integrate with membranes: In lightweight or rendered systems, ensure flashings lap correctly with sarking or pliable membranes.
4. Inspect before cladding: Flashing compliance should be verified at pre-sheet and pre-cladding hold points to avoid costly rework later.
5. Maintain documentation: Keep manufacturer installation guides and photographs for each flashing type as part of your compliance record — a growing focus for regulators and insurers alike.

Why Builders and Owners Should Care

From a builder’s perspective, correct flashing installation is not just about compliance — it’s a frontline defence against defect claims. Building insurers report that they often see claims arising from water ingress that could have been prevented with correct flashing details at window openings. Rework to install them later is exponentially more costly than doing it right the first time.
For homeowners, the peace of mind that comes from knowing their home’s envelope is sealed correctly and drained cannot be overstated.

Final Word

Flashings may seem minor in cost and visibility, but they form one of the most important layers of a compliant, durable, and weather-tight home. Builders are encouraged to revisit manufacturer details for all cladding systems used, cross-check against NCC and AS 2047, and ensure every window opening is flashed and sealed correctly — the first time.

If you have any questions or need further guidance, please don’t hesitate to contact our Advisory team:

📞 (02) 6175 5900
📧 workplace@mba.org.au