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If your roof is leaking near a chimney, a skylight, a vent or where the roof meets a wall, there’s a strong chance the culprit is flashing rather than the tiles or sheeting themselves. Flashing is the quiet workhorse of a roof, you rarely notice it until it fails, and it fails often enough that it’s the most common leak sources roofers deal with across Sydney.
This guide covers what flashing is, why the joins it protects are so vulnerable, how flashing fails in Sydney’s climate, and what a proper repair involves.
What flashing actually is
Flashing is the thin sheet material, usually metal installed to seal and waterproof the joins where a flat run of roof meets something else. Every roof has these junctions, and each one is a potential entry point for water. Flashing is fitted around chimneys, skylights, vent pipes, the base of walls that rise through the roof, and along the edges and valleys. Its job is to direct water away from the seam and back onto the main roof surface, so it never gets the chance to seep into the gap underneath.
Because these junctions are where water naturally concentrates and where two different materials or planes meet, they’re inherently the weakest points on a roof. Flashing is what makes them watertight, and when it fails, those weak points do precisely what they’re prone to do.
Why the joins are so vulnerable
Junctions leak more than open roof for a few reasons. Water runs toward them and pools or channels through them in volume, in valleys and around chimneys. They involve joins between different materials that expand and contract at different rates in the heat, working the seal loose over time. And they’re complex shapes, around a chimney or skylight, that are fiddly to seal perfectly, so any weakness in the original workmanship shows up here first. Add Sydney’s heat-then-storm cycle and you have joints that are constantly stressed.
How flashing fails
Flashing lets water in through a handful of common failures:
- Rust and corrosion – Metal flashing corrodes over the years, and much faster in coastal areas where salt air is aggressive. Rusted flashing develops holes and thin spots that leak.
- Lifting and movement – As the building and roof move with temperature changes, flashing can pull away, lift at the edges or come loose from its fixings, opening a gap.
- Perished sealant – Where flashing relies on sealant, Sydney’s UV dries and cracks it, breaking the waterproof line.
- Poor original installation – Flashing that was fitted badly, with gaps or the wrong detailing, may leak from early in its life or fail well before it should.
A leak that appears near a chimney breast, around a skylight, along an internal wall or partway down a valley is flashing rather than the surrounding roof. which is why tracing the true source matters, as we cover in how to find the source of a roof leak [add link once published].
Signs of a flashing problem
From a safe vantage point or inside the home, watch for:
- Water stains on ceilings or walls near a chimney, skylight or where the roof meets a wall.
- Visible rust, lifting or gaps in metal flashing when you look up at those junctions.
- Damp or staining around a skylight frame inside the house.
- Leaks that show up in wind-driven rain, when water is forced into a compromised seal.
How flashing is repaired
The right repair depends on the failure. Minor issues, a length of perished sealant or a small lift, can sometimes be resealed or re-secured. Corroded or damaged flashing is replaced entirely, because sealing over rusted metal is a short-lived fix. In coastal Sydney suburbs, it’s frequently worth upgrading to a corrosion-resistant flashing material during the repair, so the same problem doesn’t return within a few years. The key is that the repair addresses the actual junction properly rather than smearing sealant over the symptom, a common shortcut that fails fast.
Flashing repair and replacement is a standard part of our roof repairs, and on a roof where flashing failure sits alongside broader wear, it’s addressed within a full roof restoration.
Why flashing shouldn’t be a DIY job
Flashing sits at the trickiest parts of a roof, around chimneys, on valleys, at height, and getting the detailing right is genuinely skilled work. A poorly executed flashing repair leaks as surely as the failure it replaced, and getting to these junctions safely means working at height on a surface that cracks underfoot. It’s a repair that rewards doing properly the first time, which is why it belongs to a professional.
Get flashing checked and fixed
If you’ve got a leak near a chimney, skylight or wall, flashing is a prime suspect, and one that a proper inspection can confirm quickly. Fixing it correctly stops a leak that sealant alone won’t. To have your roof’s junctions checked and any failed flashing repaired, request an inspection and quote.
A leaking roof doesn’t always mean damaged tiles or sheets. Failed flashing around chimneys, skylights and wall joins can let water in quickly. Aabacus Roofing Solutions can inspect the problem, identify the cause and carry out the right repair. Call 0404 397 198 to arrange an inspection and quote.
FAQs
What is roof flashing?
Flashing is thin sheet material, usually metal, fitted to seal the joins where a roof meets a chimney, skylight, vent or wall. It directs water away from these seams so it can’t seep into the gaps underneath, making it critical to keeping the most vulnerable parts of a roof watertight.
Why do roofs leak around chimneys and skylights?
Because those junctions are where water concentrates and where different materials meet and move against each other. The flashing that seals them can rust, lift, or lose its sealant over time, and once it fails, water gets straight into the seam. Leaks near these features are very often flashing rather than the roof itself.
Can flashing be repaired or does it need replacing?
Minor issues like perished sealant or a small lift can sometimes be resealed or re-secured. Corroded or damaged flashing is replaced, since sealing over rusted metal is short-lived. In coastal areas, upgrading to a corrosion-resistant material during the repair helps prevent a repeat.
Is a flashing leak serious?
Any leak that lets water into the roof cavity can cause hidden damage to timber, insulation and ceilings over time, so it’s worth fixing promptly. Flashing leaks near skylights and chimneys can also track into walls, so they shouldn’t be left.
