To stop water leaking from aluminium windows, first clear the drainage slots along the bottom of the outer frame, then replace any cracked sealant around the outside of the frame and renew worn gaskets or weatherstrips. If water still gets in, test with a hose to find the exact entry point, as the leak may be coming through the wall above rather than the window.
High-quality windows and proper installation can help to prevent window leaks, and the material of your window frames will also play a big part in how long they should last and how often they must be maintained.
This article will explore the main causes of a leaky window and give you the hints and tips necessary to resolve the issue.
What Causes Aluminium Windows to Leak?
Most leaks come from blocked drainage slots, cracked or failed perimeter sealant, worn gaskets around the glass or sash, poor installation such as missing cavity trays or sill seals, or water entering through the wall above rather than the window itself. Pinpoint the source before you repair anything.
There are multiple benefits to installing an aluminium window frame. As well as offering excellent security, thermal efficiency, and a range of aesthetically pleasing styles and colours, aluminium window frames can withstand heavy rain and wet conditions when properly installed.
Aluminium is a versatile material that can be extruded to meet functional and structural needs. Unlike wood frames, you don't need to worry about aluminium frames rotting.
Unfortunately, there can still be instances where windows leak. Being able to source the cause and, if possible, repair the cause of the leaky window can help to save you the cost and inconvenience of having to replace them.
The following examples can lead to leaky windows and the problems that a leak can bring.
Could Poor Installation Be the Cause?
New windows should last a significant amount of time before you should have any concerns about performance. If your new windows start leaking, you should look into your warranty. You should also check if it is not the window that is leaking too as it may be the poor building standards
Using reputable installers is important, and you should only consider carrying out an installation project if you have the relevant experience.
Can an Older Property Cause Window Leaks?
Older homes can settle and shift slightly, and this can cause alignment issues which can lead to small gaps around the window frame.
Sometimes the design of the house or other exterior issues can be the cause of a leak, with water getting in through the wall rather than the window itself. Problems with the roof, cladding, render, a poor overhang, or structural damage can be bigger issues that you will need professional help to resolve.
Is Failed Sealant Letting Water In?
Damaged flashing or cavity trays, as well as failed sealant or sealing along the edges of the glass and frame, can result in the seal being broken. This can allow moisture to get in and compromise the surrounding area.
Cracked glazing or damaged panes can also let water in.
Some seal wear is expected over time, so regular maintenance helps keep it effective.
Are Blocked Drainage Slots Causing the Leak?
Blocked drainage slots are the most common cause of leaks in aluminium windows and doors. Water that gets past the outer seal is meant to collect in the frame and drain out through small slots or weep holes along the bottom; if dirt, leaves or insects block them, water backs up and overflows inside. Open the window and check the slots in the bottom of the frame, clear them gently with a plastic tool or pipe cleaner, then pour a little water into the frame to make sure it drains away outside. Do this every few months, and never seal over the drainage slots with silicone.
How Do You Find Where a Window Is Leaking?
Note when it leaks (during any rain, only wind-driven rain, or only on cold mornings, which suggests condensation), look for stains and bubbling plaster around the frame, then run a hose over the window from the bottom up, section by section, while someone watches inside. The point where water first appears shows the leak.
Locating the cause of a leaky window often takes a closer look to identify the source of the leak. Carrying out regular checks can also help to diagnose and fix issues early on, helping to stop them before they develop into big issues.
Inspect inside around the window frame for any visible sign of damage.
Check for water stains above the window frame, along with bubbling plaster or peeling paint around the window.
Inspect the window board and surrounding plaster for damp or soft spots to assess whether damage has occurred.
One of the best ways to detect where a window leak is coming from is by trying to detect where the air is coming through, as these checks can help identify where leaks occur.
This can be done more easily on windy days, where you can feel the wind coming through.
Alternatively, using a thermal imaging camera to alert you to the leak or gap can be an easy way to determine where water can get in.
How Do You Fix a Leaking Aluminium Window?
Clear the drainage slots in the outer frame first, then replace any cracked external sealant around the frame and renew worn gaskets or weatherstrips. If water is coming through the wall or the window was badly installed, contact the installer or a specialist, especially if the window is still under guarantee.
When it comes to window leaks, prevention is better than repair, so routine maintenance and taking the time to regularly check and clean can make a significant difference.
Clearing the window and guttering from dirt, and cleaning drainage channels to avoid water accumulation, can minimise the risk of clogging or further issues. If you do find a leaky window, the following process should help you to fix it. Fixing leaks early is generally easier than waiting for more serious damage;
How Do You Replace Failed Window Sealant?
Step 1 - Remove Existing Sealant
You will be able to remove old sealant from the space between the window and the frames using a knife or spatula. A plastic spatula will minimise the risk of scratching your aluminium frame or the glass. Start the process by removing any loose or cracked sealant completely before applying new material.
Step 2 - Prepare the Sealant for Application
Choose a low-modulus, neutral-cure silicone or MS polymer sealant, which bonds well to aluminium, masonry and render and stays flexible as the frame expands and contracts.
You should also invest in a sealant gun for a smooth and level application on your window. Before using it, you may need to create a small hole in the nozzle.
Step 3 - Evenly Apply the Sealant
Move at a steady pace applying a steady level of pressure to the sealant gun trigger.
Ensure you completely seal any leaks and apply the sealant evenly along the frame edges. This will help to minimise the risk of further damage or leaks.
You will be able to smooth the sealant using a spatula to ensure you get a good finish that blends in well with the surrounding area and looks good. If the old seal cannot be restored, it should be replaced and the area properly fixed.
How Do You Replace Worn Weatherstripping?
Weatherstripping is used to seal the sash area and other window openings, minimising the risk of water getting through gaps.
If your weather stripping is damaged or worn out, it can lead to leaks.
Identify worn weather stripping early, because leaks can still occur around moving parts.
Follow these steps on how to seal aluminium windows with weather stripping;
Step 1 - Remove the Damaged or Worn Out Weather Stripping
You should be able to cut out the existing weather stripping so you can pull it out completely.
Step 2 - Clean and Dry the Area
Fully cleaning and drying the area before applying your fresh weather stripping is essential. This will allow you to get a flush seal and start from a good position.
Step 3 - Measure the Area
Measuring the area so you can cut the perfect length is essential. Too short, and you will have to start over or risk a gap between stripping.
If your stripping is too long, that is easier to deal with as you can trim it down. However, you should never try to just cram it in. This can cause it to bunch and will break the seal.
Step 4 - Apply the New Weather Stripping
Applying the new weather stripping properly will help you enjoy a leak-free, draught-free, and energy-efficient home, and it can often be fixed with replacement rather than requiring entirely new windows.
When Should You Replace a Leaking Aluminium Window?
Replace the window if the frame is bent or corroded, the corner joints have opened up, the glazing units keep failing, or repeated repairs have not stopped the leak. Older aluminium windows without a thermal break are often worth replacing anyway for the energy savings. Our guide to how much aluminium windows cost explains what to budget, and if a leaking patio or garden door is the problem, take a look at our weatherproof aluminium bifold doors and sliding doors.
Leaking Aluminium Window FAQs
How do I stop rainwater coming in through my window?
Check your window for any leaks, and fix them using the methods explained above. As a temporary measure, a bead of exterior-grade silicone can seal small gaps, but always find and fix the real cause.
Why is water coming in through my window?
A leaky window is most commonly a result of the sealant breaking down, allowing water to enter your home.
Who should I call for a leaking window?
Contact the original installer first if the window is under guarantee, as most installations are covered for several years. Otherwise, a local window repair specialist can reseal frames, replace gaskets and clear drainage. If water is coming through the wall above, a roofer or builder is more likely to be needed.
Why does my window only leak in heavy rain?
A leak that only appears in heavy or wind-driven rain usually points to blocked drainage slots overwhelmed by volume, a gap in the external sealant on the exposed side, or worn gaskets that let water past under wind pressure. Test with a hose while the window is closed to recreate the conditions.
Is it a leak or condensation?
If water appears on cold mornings without rain, it is almost certainly condensation rather than a leak. Our guide to preventing condensation on aluminium window frames explains how to tell the difference and stop it, and if it has led to mould, see how to clean mould off aluminium window frames.
