Quick answer: Leaking aluminium windows are usually caused by blocked drainage paths, failed perimeter sealant, worn gaskets, poor sash alignment, damaged hardware, cracked glazing seals, sill defects or water entering from the wall above. Start by identifying exactly where the water first appears. Clean accessible drainage channels, but leave glass removal, seal replacement and frame repairs to a qualified window contractor.
Water on an internal sill does not always mean the aluminium frame itself has failed. Rain can enter at the glass, sash, frame-to-wall joint or façade, then travel before it becomes visible. This guide helps homeowners, property managers and project teams diagnose leaking aluminium windows without covering up the real cause.
Table of contents
- First checks during rain
- Eight common causes and fixes
- How to test without making the leak worse
- When repair is not enough
- Frequently asked questions
What to check first when an aluminium window leaks
During the next safe rain event, note the first wet point rather than only the final puddle. Photograph the head, jambs, meeting rails and sill from inside. Record whether the sash was fully locked, which direction the wind came from and whether the leak starts immediately or after prolonged rain.
Do not lean outside a high-rise window or dismantle safety components. Singapore’s Building and Construction Authority (BCA) says windows are continually exposed to wind and rain and need regular checking, cleaning and replacement of damaged parts. For regulated installation or retrofitting work, use an approved window contractor.
Eight common causes of leaking aluminium windows
1. Blocked drainage holes or sill channels
Many window systems manage rainwater through channels and drainage outlets. Dust, insects, paint or renovation debris can obstruct the route, allowing water to back up toward the room. Clean only the visible, accessible channel with a soft brush or cloth; never drill new holes because their position and size are system-specific.
2. Failed sealant around the outer frame
Perimeter sealant bridges the frame-to-wall joint. Gaps, separation, brittleness or an incomplete joint can let rain move behind the frame. Smearing new sealant over an old wet joint often hides the path temporarily, so a contractor should remove failed material, prepare a dry substrate and apply a compatible sealant to the correct joint design.
3. Worn or displaced weather gaskets
Rubber or elastomeric gaskets can shrink, flatten, tear or pull away at corners. The sash may then close without applying even pressure. Inspect accessible seals for visible gaps, but use the window system’s correct replacement profile; a gasket that merely looks similar may not fit its groove or provide the intended compression.
4. The sash is not closing squarely
A dropped sash, loose hardware or incorrect adjustment can create a local gap. Check whether the reveal around the sash looks even and whether the handle reaches its normal locked position without excessive force. Do not force a stiff handle: alignment and hardware should be assessed together so that one adjustment does not create another problem.
5. Dirty, loose or damaged hardware
Locks and hinges help draw an operable sash against its seals. Dirt, corrosion, missing screws or worn components can reduce that pressure. BCA’s homeowner guidance uses a practical “check, clean, change” approach and recommends cleaning movable parts and replacing damaged components rather than ignoring deterioration.
6. Failed glazing seals
Water appearing at the edge of the glass may point to a failed glazing gasket, bead or sealant joint. The glass should not be removed as a DIY test. A glazing professional can check whether the seal is continuous, whether setting blocks and beads remain correct, and whether the glass unit itself is damaged.
7. Poor sill support, slope or frame jointing
A sill that cannot direct water outward, an open frame joint or movement at the opening can defeat otherwise sound seals. BCA’s aluminium-window good-practice guide focuses on watertightness and identifies jointing and component damage as important defect areas. Correcting these issues may require more than surface sealant.
8. Water is coming from somewhere above the window
Cracks, façade joints, an upper-floor opening or an external ledge can admit water that later appears beside the window. A clue is staining at the head or jamb even when the window’s own test area stays dry. In this case, coordinate the window inspection with the building owner, management corporation or façade specialist.
How to test a window leak safely
- Document the pattern: mark the first visible wet point and take time-stamped photos.
- Inspect dry: look for debris, open joints, displaced gaskets and damaged hardware.
- Clean accessible parts: clear the interior track and visible drainage outlet with non-metal tools.
- Retest one area at a time: a contractor can use a controlled, low-volume water test, starting low and moving upward.
- Allow observation time: water may travel inside a joint before it becomes visible.
- Record the repair: keep photos, materials used and the retest result for future maintenance.
Diagnostic rule: Fix the entry path, not just the place where water finally appears.
Repair checklist for homeowners and project teams
- Confirm the exact window, panel and wind direction.
- Check that the sash is fully closed and locked.
- Clean tracks and visible drainage paths.
- Photograph gaskets, corners, sealant and surrounding wall.
- Stop using the window if hardware or glass looks unsafe.
- Ask the contractor to explain the diagnosed entry path.
- Request a controlled retest after the repair.
When should you replace a leaking window?
Replacement may be more practical when the frame is distorted, corrosion or damage is widespread, compatible components are unavailable, repeated repairs have failed, or the opening was poorly designed for its exposure. A project specification should consider the complete assembly: frame, glass, seals, hardware, drainage, installation joint and surrounding wall.
If you are comparing a new opening style, review Forge Windows’ casement windows and sliding windows. For a project-specific assessment, share opening sizes, elevation drawings, exposure and performance requirements through the contact page.
Frequently asked questions
Can I seal leaking aluminium windows from the inside?
Interior sealant may hide the symptom without stopping water from entering the outer joint. Trapped moisture can also move elsewhere. First identify whether the entry point is the glazing, sash seal, drainage system, perimeter joint or surrounding wall, then repair from the appropriate side using compatible materials.
Why does my window leak only during heavy, wind-driven rain?
Wind increases pressure on the façade and can drive water through small gaps that do not leak in calm rain. Overflow from blocked drainage may also need time to develop. Record wind direction and the first wet point, then ask a contractor to reproduce the exposure with a controlled test.
Should window drainage holes be sealed?
No—not unless the window system designer confirms they are redundant. Drainage outlets are often intended to release water collected in the sill or glazing pocket. Blocking them can increase leakage. Clean visible outlets gently and consult the product fabricator if their purpose or route is unclear.
Who should repair high-rise aluminium windows in Singapore?
Use an appropriately qualified contractor and follow current BCA requirements. Do not lean outside, remove glass or alter regulated safety components yourself. BCA publishes homeowner maintenance resources and information on approved window contractors for installation and retrofitting work.
Stop the next leak at its source
The right fix for leaking aluminium windows begins with diagnosis: locate the first wet point, inspect drainage and seals, check closure and hardware, and rule out water from the surrounding façade. If a repair or replacement is needed, ask for a system-level solution and a documented water retest.
Sources: BCA, Good Industry Practices: Aluminium Window; BCA, Windows Safety.
