Aluminium windows leaking when it rains is almost never a fault in the aluminium itself. Water gets in through one of five places: blocked drainage holes, gaps in the sealant around the frame, worn or loose seals, a sash or sliding panel that is not closing properly, or the wall above the window. Most causes of aluminium windows leaking are quick, cheap fixes. This guide shows you how to find where the water is coming from and how to fix leaking aluminium windows and sliding doors.
First, make sure it is a leak. Water on the inside of the glass on a cold morning, with no rain, is condensation – see aluminium window condensation.
Contents
Step 1: Find where the water is coming in
Watch the window in rain, or run a garden hose over it from the bottom up, a section at a time, while someone watches inside. Where the water appears tells you the cause:
| Where you see water | Most likely cause |
|---|---|
| At the bottom of a sliding window or door | Blocked drainage (weep) holes, or debris in the track |
| Around the edge of the frame, inside | Gaps in the perimeter sealant |
| Between the sash and the frame | Worn seals, or a sash that is not closing evenly |
| At the top of the window, from above | Water entering the wall or lintel above the frame |
| On the glass only, no rain | Condensation, not a leak |
Aluminium windows leaking at the bottom: blocked drainage holes
Every aluminium window and sliding door has small drainage (weep) holes or slots at the bottom of the frame. Water that gets past the outer seals is meant to collect in the bottom of the frame and drain out through them. When the holes block with dust, sand, leaves or insects, the water has nowhere to go and overflows inwards. This is the most common reason for a sliding window leaking.
Fix: clear the holes with a pipe cleaner, a thin wire or a soft brush, then pour a little water into the track to check it drains out. Never seal drainage holes with silicone.
Aluminium windows leaking around the frame: failed sealant
The sealant between the frame and the wall keeps rain out of the joint. It can crack, shrink or pull away over time, especially on walls that take driving rain.
Fix: cut out the failed sealant, clean and dry the joint, then run a new continuous bead of exterior-grade sealant. Keep the drainage holes clear while you work. If the gap is wide, ask your installer to repack and reseal it properly – see how to install aluminium windows.
Aluminium windows leaking between sash and frame: worn seals
Rubber gaskets and brush seals between the sash and frame keep wind and rain out. If they are dirty, flattened, shrunk or pulled out of their channel, water and wind get past.
Fix: clean the seals with mild soapy water and press any loose sections back into the channel. Replace seals that are hard, cracked or missing. Seals and gaskets on Coetz™ windows are covered for 2 years against manufacturing defects – see our warranty.
Aluminium windows leaking because a sash will not close
If a top hung or side hung sash does not close evenly along its whole length, the seal is not compressed and water gets in at the gap. On sliding windows and doors, panels that have dropped on worn rollers no longer meet the seals properly.
Fix: check that the sash closes and locks without forcing. Adjust or replace stays and hinges – see aluminium window hinges and stays and top hung window not closing. For sliding doors and windows, clean the track and adjust or replace the rollers – see aluminium sliding door rollers.
Aluminium windows leaking from the top: water from the wall
If water appears at the top of the window and runs down the frame, it is often coming through the wall, the lintel or the roof above, and only showing up at the window. A new frame will not fix it.
Fix: check for cracked plaster, a missing drip or flashing above the window, and blocked gutters. This is building work – ask your builder or a waterproofing contractor.
Aluminium sliding door leaking
A leaking aluminium sliding door almost always comes down to the bottom track:
- Debris in the track stops water draining – vacuum it and clear the drainage slots.
- A track that is not level lets water pool at one end – your installer can repack it.
- Dropped panels on worn rollers no longer meet the seals – adjust or replace the rollers.
- Open, tilted or wind-driven rain – a threshold that faces the weather may need a canopy or a higher sill.
See aluminium stacking doors for track and threshold planning on new doors.
How to stop aluminium windows leaking for good
- Vacuum tracks and clear drainage holes twice a year, and after dust storms.
- Wash seals with mild soapy water and check the sealant once a year.
- Lubricate rollers, hinges and stays once a year with a silicone spray.
- Fix small sealant gaps before the rainy season.
A full routine is in how to clean aluminium windows.
When to replace instead of repair
Repairing aluminium windows leaking from worn seals or sealant is almost always cheaper than replacing them. Replacing makes sense when old steel or timber frames have rusted or rotted, or when the frame itself is damaged. See replace steel windows with aluminium. Coetz™ makes replacement aluminium windows to order with 6.38 mm clear laminated safety glass, delivered nationwide; price them in the online estimator.
Good installation practice for sealing and drainage is set out in SANS 10137, published by the South African Bureau of Standards.
Aluminium windows leaking: frequently asked questions
Why are my aluminium windows leaking when it rains?
Usually because the drainage holes at the bottom of the frame are blocked, the sealant around the frame has cracked, the seals are worn, or the sash is not closing properly. Find where the water appears to find the cause.
Why is my sliding window leaking at the bottom?
Most often the drainage holes in the bottom track are blocked with dirt, so water overflows inwards. Clear them and check that water drains out.
How do I fix leaking aluminium windows?
Clear the drainage holes, reseal gaps around the frame with exterior-grade sealant, clean or replace worn seals, and adjust sashes or rollers so they close properly.
Why is my window leaking from the top?
Water at the top of a window often comes from the wall, lintel or roof above, not the window. Check for cracks, a missing drip or flashing and blocked gutters.
Is my window leaking or is it condensation?
If water forms on the inside of the glass on cold mornings with no rain, it is condensation. If it appears during rain, at the frame edges or at the bottom track, it is a leak.
Will silicone stop my window leaking?
Only if the leak is a gap in the sealant around the frame. Never seal over drainage holes or between the sash and frame – that traps water and makes leaks worse.
