When a window leaks, the instinct is to blame the seal around the glass. More often the culprit is the flashing — the concealed layers of sheet and membrane at the head and sill that are supposed to catch any water that gets past the frame and direct it back out. When a head flashing is missing, poorly lapped or corroded, or a sill has lost its fall and its end dams, the opening stops shedding water and starts collecting it.
Our sill, head and flashing repair service rebuilds those details so the window works the way it was designed to — as a managed water path, not a trap. This is remedial work that lives mostly out of sight, which is exactly why it gets missed and why leaks recur after cosmetic reseals.
We approach every flashing repair on the principle that water will always find the low point, so the detail has to send it outward and downward at every junction, with no reverse falls, unsealed laps or dead ends where water can pool and back up into the structure.
How We Repair Sills, Heads & Flashings
- Expose and assess. We open up the affected head or sill enough to see the existing flashing, confirm how water is bypassing it, and check the condition of the substrate and any concealed corrosion.
- Establish the water path. We work out where water needs to go — the required falls, laps and termination points — so the rebuilt detail sheds outward in line with good waterproofing practice under AS 4654.2.
- Remove failed material. Corroded, torn or incorrectly lapped flashings and perished sealant are stripped back to sound substrate.
- Reinstate flashings. New head flashings, sill trays and end dams are formed and lapped correctly, with membrane or sheet material selected for the exposure and dressed to direct water clear of the opening.
- Seal and integrate. Junctions with the frame, wall and adjacent flashings are sealed with backer rod and elastomeric sealant so the new detail ties cleanly into the surrounding envelope.
- Test and reinstate finishes. The repair is water-tested to confirm it sheds correctly, then reveals and finishes are made good, with the works documented for your records.
Frequently Asked Questions
How can flashing be the problem when the leak looks like it's coming from the glass?
Because flashings sit above and below the visible frame and are hidden by finishes. Water that gets past or around a frame is meant to be caught by the head flashing and carried out over the sill tray. If those are defective, the water is instead funnelled into the wall and reappears lower down — often looking as though it came straight through the glass. Exposing and testing the flashing is the only reliable way to confirm it, and it is a very common root cause.
Do you have to remove the whole window to repair a sill or head flashing?
Not usually. In many cases we can access and rebuild the flashing by opening up the head or sill detail and adjacent finishes without removing the frame. Where the frame itself is corroded or the flashing can only be reinstated correctly with the unit out, we'll say so — but full removal is the exception, not the default.
What standard governs this kind of waterproofing detail?
External above-ground waterproofing, including the falls, laps and terminations that make a flashing work, is guided by AS 4654.2. Correct upstands, drainage falls and lapped junctions all come from that discipline. We detail flashing repairs to shed water positively rather than simply sealing over the top of a failure.
Is flashing repair the owners corporation's responsibility in a strata building?
Typically yes. Head and sill flashings are part of the external building envelope and common property, so their repair generally falls to the owners corporation under the NSW Strata Schemes Management Act 2015, even when the resulting damage is inside one lot. We document the defect and the repair so the committee has a clear basis to authorise and fund the works.
How long should a rebuilt flashing detail last?
A correctly formed and lapped flashing in sound material should perform for the long term — it is the incorrect falls, poor laps and reliance on sealant alone that cause early failure. By reinstating the water path properly rather than patching, we're targeting a durable fix, and the verification test at completion confirms it sheds water before we close the detail up.
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