Why Is My Aluminum Window Leaking Water?

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An aluminum window usually leaks because water cannot drain out of the frame or because the seals and gaskets have worn, cracked, or shifted. Blocked drainage holes, poor installation, and wind-driven rain pushing past weak weatherstripping are the most frequent culprits. Finding the exact entry point is the first step to a lasting repair.

The Most Common Reason: Blocked Drainage Holes

Every aluminum window is designed with small drainage channels at the bottom of the frame and sash. Their job is to carry rainwater that gets past the outer seal back outside before it can collect inside the frame. When these weep holes become clogged with dust, dirt, leaves, or construction debris, water pools in the track and eventually spills over the sill and into the room.

Check the bottom corners of the frame after rain. If you see water sitting in the track or the sill looks flooded, the drainage is likely blocked. Clearing the holes gently with a thin, flexible tool often solves the problem quickly, and it costs very little time.

Worn or Cracked Seals and Gaskets

The rubber or foam gaskets around the sash are the window's main defense against rain. Over years of sun, heat, and repeated opening and closing, these materials harden, shrink, and crack. Once the seal loses its flexibility, even light wind can drive water through the gap.

Look for cracks, flattening, or gaps along the gasket
Feel for draughts with a hand or a strip of paper when the window is closed
Replace damaged sections rather than only adding sealant

Installation and Sealant Problems

Water can also enter where the window meets the wall. If the original installation left gaps around the frame, or if old sealant has dried out and separated from the masonry, rain can run behind the frame and appear indoors far from the window itself. This is one of the trickiest leaks to diagnose because the water seems to come from the room, not the glass.

Inspect the joint between the frame and the wall from the outside. Cracked or missing sealant along this line is a strong sign of an entry point that needs proper resealing, ideally with a sealant suited to exterior metal and masonry.

Misaligned Sash and Hardware Wear

Aluminum windows rely on tight alignment between the sash and frame. Worn rollers, loose screws, or a bent corner can cause the sash to sit slightly out of square. When that happens, the gasket no longer presses evenly, and small openings appear at the top or along one side.

Watch whether the window closes with a firm, even contact all the way round. If you need to lift or force it to latch, the hardware may need adjusting or replacing before the seal can work properly again.

How to Pinpoint Where the Water Enters

Finding the true source saves time and prevents repeated repairs. Work from the outside in and try to reproduce the leak during or just after rain:

Note exactly where the water appears inside: sill, wall, ceiling, or corner
Check the frame joints, glass edges, and drainage holes after a storm
Use a garden hose on one section at a time, starting low and moving up, while someone watches inside

Marking the wet area with tape helps you compare observations over several rainy days.

When to Call a Professional

Some leaks are simple to fix, such as clearing a drainage hole or replacing a strip of gasket. Others point to deeper issues like a damaged frame, failed glazing, or water running inside the wall cavity. Persistent staining, soft plaster, or mould is a sign that moisture has already caused damage and should not be ignored.

If you have tried basic checks and the water keeps coming in, a qualified metalwork specialist can measure the opening, assess the frame, and recommend a repair or replacement that matches the original window.

Frequently asked questions

Can an aluminum window leak even when it is closed?

Yes. Water can leak through worn gaskets, misaligned sashes, or blocked drainage even when the window is shut. Wind-driven rain is often what reveals these weak points.

Do I need to replace the whole window if it leaks?

Not always. Many leaks come from gaskets, drainage holes, or sealant, which can be repaired or replaced. A full replacement is usually needed only when the frame itself is damaged.

How often should I check my aluminum window seals?

Inspecting the seals and drainage holes once or twice a year, ideally before the rainy season, helps catch problems early. Clean the tracks at the same time.

Can I use silicone to stop a leak in an aluminum window?

Silicone can help seal exterior joints, but it should not be used to cover blocked drainage or failed gaskets. Fixing the underlying cause gives a more reliable result.

Common mistakes to avoid

Many homeowners seal every visible gap with sealant, which can trap water and block drainage paths the window needs. Ignoring small drips for months also allows moisture to damage the wall and plaster behind the frame.

Our recommendation

Start by clearing the drainage holes and inspecting the gaskets, since these fixes are simple and often solve the problem. If the leak continues, have a metalwork specialist check the frame alignment and the wall joint before the damage spreads.

Summary

Aluminum window leaks are usually caused by blocked drainage, worn seals, poor sealant at the wall joint, or a misaligned sash. Identifying the exact entry point and addressing that cause is the most effective way to stop the water.

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