A damp patch beneath a window after heavy rain is rarely something to ignore. To stop water leaking through windows, you need to find out whether rain is getting past the frame, the sealed unit, the surrounding wall or a fault above the opening. Acting early can prevent damaged plaster, mould, rotten timber and disruption to a home, rental property or business premises.
A window leak does not always mean the whole window needs replacing. In many cases, a failed seal, blocked drainage channel or worn section of external sealant can be repaired. The right solution depends on where the water appears, when it happens and the condition of the frame and glass.
First, make the area safe and limit the damage
Move furniture, stock and electrical items away from the affected area. Put down towels or a waterproof container to catch drips, but avoid covering vents or drainage slots in the window frame. Take clear photographs of the water marks, visible gaps and the outside of the window if it is safe to do so. This is useful for a landlord, managing agent, insurer or repair professional.
If water is running near sockets, light fittings or electrical equipment, switch off the relevant circuit only if you can do so safely. Do not touch wet electrical fittings. A broken pane, loose frame or damaged shopfront alongside a leak needs urgent attention, particularly where the property cannot be secured overnight.
Work out where the water is entering
The location of the dampness tells you a great deal. Water collecting on the inside sill during rainfall may point to a problem around the frame, external sealant or drainage system. Moisture sitting between the panes of double glazing is different: it usually indicates a failed sealed unit, which causes misting but does not normally allow rainwater into the room.
Check whether the leak occurs only in wind-driven rain. Windows can perform adequately in light showers but reveal gaps when strong winds force water against the frame. If a leak continues after the rain has stopped, look higher up the wall as well. Overflowing gutters, damaged roof flashing, cracked brickwork and leaking pipes can all send water down behind or around a window.
Check drainage holes and window tracks
Most modern uPVC and aluminium windows have small drainage holes, often called weep holes, at the bottom of the outer frame. They allow rainwater that enters the outer channel to drain away safely. Dirt, moss, dead insects and paint can block them, leaving water with nowhere to go except indoors.
Open the window and inspect the track carefully. Clear loose debris with a soft brush, then use a small plastic tool or gentle air flow to remove a blockage. Avoid forcing sharp metal objects into the holes, as this can damage the drainage path. Test the window afterwards with a small amount of water in the external channel, not by soaking the entire frame.
Inspect seals, hinges and frame joints
Rubber gaskets around an opening sash should sit evenly and feel flexible. If they are flattened, split, missing or pulling away at corners, rain can bypass them. A window that does not close tightly because of worn hinges, a faulty handle or an alignment issue may also let in water during bad weather.
From outside, look for cracked, shrinking or detached sealant where the frame meets the brickwork or render. Small gaps can become a route for water, especially on exposed elevations. Timber frames need a closer inspection for flaking paint, open joints, soft wood or decay around the sill. These issues should be repaired properly rather than simply covered with sealant.
How to stop water leaking windows without making it worse
It is tempting to run silicone around every visible edge, but this can trap water inside the frame or hide a more serious fault. Internal sealant is rarely the answer to rain penetration from outside. Water should be stopped at the external point of entry and allowed to drain through the frame as designed.
For a minor gap in sound external sealant, carefully remove loose material, clean and dry the surface, and apply a suitable exterior-grade sealant. This works only where the frame is stable and the gap is clearly the cause. Sealant will not correct a warped frame, failed hinges, damaged sill, loose glazing bead or water entering from the wall above.
Keep external sills and drainage paths clear. Do not block weep holes with paint, filler, tape or sealant. If you have recently had external wall insulation, rendering or decorating work completed, check that it has not bridged the window drainage system or left gaps around the frame.
For commercial premises, avoid temporary fixes that obstruct entrances, fire exits or shopfront visibility. A leaking glass door or front window can quickly create a slip risk for staff and customers. It may also signal that the door closer, hinges or frame needs adjustment.
When a repair is the sensible option
A professional window repair is often enough when the glass is intact and the frame remains structurally sound. Replacing worn gaskets, realigning an opening sash, renewing external perimeter sealant or clearing and repairing drainage channels can restore weather resistance without the cost of a full replacement.
A misted double-glazed unit may need replacing if the seal between the panes has failed. This improves insulation and appearance, but it is worth checking for a separate rainwater route at the same time. Replacing a sealed unit alone will not fix water coming through gaps around the frame.
Timber windows can frequently be repaired where decay is localised. The affected timber may be cut back, treated and rebuilt before repainting. However, widespread rot, severe distortion or repeated leaks may make replacement better value over time. The same principle applies to older uPVC frames that have cracked, warped or lost their ability to close securely.
Signs you need urgent glazing help
Some leaks can wait for a planned repair, but others need prompt attendance. Arrange urgent help if water is entering through broken glass, a window has become loose in its opening, a frame is visibly damaged after an attempted break-in, or rain is reaching electrical fittings. A boarded-up opening can protect the property while replacement glass or parts are arranged.
Landlords and facilities managers should act quickly where a leak affects a tenant’s living space, shared hallway, office, retail unit or stored goods. Delaying repairs can turn a straightforward window fault into damaged finishes, mould growth and a larger maintenance issue. Keep a record of the report, photographs and any steps taken to make the area safe.
Prevent future window leaks
A quick seasonal check is usually enough to catch early problems. After autumn leaf fall and before periods of heavy rain, clear window tracks, inspect external sealant and look for debris around sills. Open and close each window to make sure handles, hinges and locks pull the sash firmly into the seals.
If water marks keep returning in the same place, do not assume the window is at fault. Ask for the surrounding wall, guttering and roofline to be assessed as well. A good repair addresses the true route of the water, not just the point where it finally appears indoors.
For London homes, flats, shops and managed properties, fast action makes a real difference when rain gets in. Glazing Squad can assess damaged windows, failed seals, broken glass and insecure openings, then carry out the repair needed to keep your property dry, secure and ready for the next spell of bad weather.