A leaking window is one of the most common complaints strata managers and building managers hear from residents. Water shows up on the sill, stains the plasterboard under the frame or runs down the inside of the glass in a storm. Most window leaks in apartment buildings can be fixed without replacing the window, but only once you know where the water is actually getting in.
This guide explains the usual causes, how a leaking window repair is done on a multi-storey building, and what to ask for in a quote.
Why windows leak in apartment buildings
Water rarely comes through the glass itself. It finds its way in through the joints around and under the window. The most common causes we see on Sydney buildings are:
- Failed perimeter sealant. The sealant between the frame and the wall hardens, cracks or pulls away on one side, leaving a gap that wind-driven rain is pushed through.
- Blocked or missing weep holes. Window frames are designed to drain water that gets into the sill track. If the weep holes are blocked with dirt or paint, the track fills and overflows inside.
- Sill and flashing defects. A sill without enough fall, or a flashing that is damaged or missing, can direct water back towards the building instead of away from it.
- Cracked render or concrete around the frame. Cracks next to the window let water into the wall, and it then appears at the frame on the inside.
- Worn glazing seals and frame joints. The rubber seals that hold the glass, and the corner joints of the frame, can also shrink or open up as the window ages.
More than one of these is often involved, which is why replacing sealant on its own does not always stop the leak. We cover the role of wind in more detail in why buildings leak in wind-driven rain.
Step 1: find where the water gets in
A reliable window leak repair starts with an investigation, not a tube of silicone. On a high-rise building that usually means getting to the outside of the window by rope access and checking it up close: the sealant, the sill, the weep holes, the render around the frame and any flashings above it.
Where the cause is not obvious, a controlled water test helps. Water is applied to one part of the window at a time from outside while someone watches from inside the unit, so the leak can be traced to a specific joint. A thermal camera can also show where moisture is sitting in the wall around the frame.
Read more about the method in our guides to façade water testing and high-rise leak detection in Sydney.
Step 2: repair the cause
Once the source is confirmed, the repair matches the defect:
- Sealant replacement. The old sealant is cut out completely, the joint is cleaned and prepared, backing rod and primer are used where the joint needs them, and new sealant suited to the movement and exposure is applied and tooled.
- Weep holes cleared and sill tracks cleaned so the frame can drain as designed.
- Crack repairs to the render or concrete around the frame, before any repainting.
- Sill, flashing or glazing defects identified and reported, so the right trade can be engaged if the fix is outside sealant and façade repair work.
Our caulking and sealant replacement page explains the resealing process in more detail, and signs your window sealant needs replacing shows what failed sealant looks like.
Step 3: test again and record the result
After the repair, the same area should be tested again where possible, so you know the leak has stopped before the inside of the unit is repaired and repainted. Photos of each repaired window give the strata committee a record for the building file and make it easy to track the same window if a complaint comes back.
Why rope access suits window leak repairs
On a multi-storey building, most leaking windows can only be reached properly from the outside. Rope access lets technicians go straight to the affected windows without scaffolding, which keeps the cost in proportion when only a few units are affected. If several windows on the same elevation are failing, the work can be planned drop by drop and combined with crack repairs or a repaint in the same setup. See rope access services in Sydney for the other work that can be done at the same time.
Who pays for a leaking window in a strata building?
In many NSW strata schemes, the windows and their frames are common property, which usually makes the repair the responsibility of the owners corporation. This depends on the strata plan and the by-laws, so check with your strata manager before work is approved. If the leak has damaged the inside of a unit, it is worth recording that damage with photos before any repair starts.
What to ask for in a window leak repair quote
- How the cause will be confirmed (inspection, water test or both).
- Which windows and joints are included, by unit or elevation.
- Whether old sealant will be fully removed, and which sealant will be used.
- The access method and how residents and the footpath will be protected.
- Before and after photos, and whether the area will be retested.
- The contractor’s licence and insurance details.
FAQs
Can a leaking window be fixed without replacing it?
Usually, yes. Most leaks come from the sealant, the drainage or the wall around the frame, and these can be repaired with the window left in place. Replacement is only needed when the frame itself has failed.
Why does my window only leak in some storms?
Leaks that appear only in strong wind and rain are often caused by water being pushed sideways into joints that stay dry in normal rain. They are a common sign of failed sealant or blocked drainage on exposed elevations.
Is silicone over the gap enough?
Running a new bead over old sealant is a common shortcut, but it rarely lasts, because the new sealant bonds to material that is already failing. A durable repair removes the old sealant first.
How long does a window leak repair take?
It depends on how many windows are affected, how easy they are to reach and the weather, because sealant has to go onto dry, clean joints. We confirm the timing in the written quote.
Get a leaking window checked
Ace Abseiling finds and repairs window leaks on strata and commercial buildings across Sydney, Wollongong and the Central Coast by rope access. We hold NSW Contractor Licence 465770C (Decorator, Painter), work under IRATA Level 3 supervision and carry $20M public liability cover. Request a leak inspection or call 1300 926 176.
