A wet sill, a stained ceiling corner or a bubbling patch of paint under a window is usually where a leak is noticed, not where it starts. Water moves along framing, slab edges and cavities before it shows itself, sometimes a metre or more from the point where it got in. That is why so many window leaks get “fixed” two or three times without stopping.
This article explains how leaks travel, where they most often start on Melbourne apartment buildings, and how a facade specialist proves the source before anyone spends money on repairs.
Why the wet spot is a poor guide
Water follows the path of least resistance and gravity. Once it is past the outer face of the building, it can run:
- along the top of a window head and drop out at the far end of the frame
- sideways along a slab edge before appearing at a junction with a wall
- down inside a cavity and out at the next floor’s window or ceiling
- through a balcony above and into the unit below.
So a stain under the left corner of a window can be caused by a failed joint at the right-hand corner, a gap in the flashing above, or a balcony on the floor above. Treating the wet spot alone treats the symptom.
The usual entry points
On Melbourne apartment buildings the same handful of culprits come up again and again.
Perimeter sealant around the window frame
The sealant joint between the window frame and the wall is the single most common entry point. Sealant hardens, cracks and loses adhesion with age and sun exposure, and once it lets go along one edge, wind-driven rain is pushed straight in. A joint can look intact from the inside of the unit and still be failing on the outer face.
Glazing seals and frame joints
Inside the window itself, the gaskets and seals that hold the glass, and the corner joints of the aluminium frame, can open up over time. Water then enters the frame and drains out where it was never meant to.
Blocked or missing weep holes
Window frames are designed to let some water in and drain it straight back out through weep holes at the bottom of the frame. When those holes are painted over, sealed shut or blocked with debris, water builds up in the sill and overflows to the inside.
Flashings and head details
Above many windows sits a flashing or head detail that is meant to throw water clear of the opening. Where that detail is missing, poorly lapped or damaged, water runs down behind the cladding or render and into the opening.
Balconies and slab edges above
If the window sits beneath a balcony, the balcony waterproofing, its drainage and the junction where the balcony meets the wall are all suspects. Leaks from a balcony above are often blamed on the window below.
How the source is proven
Guesswork is expensive on a high-rise because every repair visit needs access equipment. A proper investigation narrows the cause down before any repair is scoped.
1. History and pattern. When does it leak? Only in heavy rain from one direction, or in any rain? After the balcony above is washed down? Patterns point to specific entry points.
2. External inspection. A close-up inspection of the outer face, usually from rope access or an elevated work platform, checks sealant, frame joints, weep holes and flashings at the affected window and around it.
3. Controlled water testing. Water is applied to one element at a time, starting low and working up: the sill, then the jambs, then the head, then the wall and balcony above. When water appears inside, the element under test at that moment is the source. Testing one element at a time is the only reliable way to separate a sealant failure from a glazing leak or a balcony leak.
4. Documentation. Every test location, method and result is photographed and recorded, so the repair scope and any insurance or builder conversation rests on evidence rather than opinion.
What it usually costs to get wrong
The cost of a misdiagnosed leak is rarely the repair itself. It is the repeat access, the interior damage that keeps happening in the meantime, and the dispute that follows when one trade blames another. On strata buildings, an unresolved leak can also turn into a disagreement over whether the problem sits with the owners corporation (common property such as the external walls and windows in many plans) or the individual lot owner, which is another reason to establish the actual source first.
When to call a specialist
Book an investigation if:
- the same window has leaked again after a previous repair
- leaks appear on more than one floor or more than one unit
- there is visible staining, rust marks or bubbling render on the outside of the building near the window
- the leak only happens in wind-driven rain, which usually means a facade path rather than a plumbing one.
Summit Facades investigates water ingress as part of our facade inspections, with every finding written up in a photo-referenced facade defect report that can be handed straight to a repairer, insurer or engineer. If the building has a run of ageing joints and seals, a planned maintenance program stops the next leak before it starts.
