Water Leaking Through a Window: Where It's Coming From

Water leaking through a window is almost always coming in around the frame, sill or seals rather than through the glass itself. Tracing exactly where it's entering is the key step before any repair, since patching the wrong spot won't stop it.

The most common entry points

Water rarely comes straight through a pane of glass; sealed units are watertight by design. It's almost always finding a way in around the edges, and there are a handful of usual suspects.

• Perished or gapped sealant (silicone) around the outside frame edge where it meets brickwork
• A failed weather seal or gasket around the sash itself
• A sill that's cracked, sloping the wrong way, or has a damaged drip groove underneath
• A blocked weep hole (the small drainage channels at the base of the frame) that lets water pool instead of draining out
• Damaged pointing or render above the window, letting water track down behind the frame

Tracing where the water is actually getting in

It helps to watch during or just after heavy rain rather than guessing after the fact, since by the time you notice a damp patch the water may have travelled some distance from where it entered. Look closely at the bottom corners of the frame first, as this is where the majority of window leaks originate, then check along the top and sides.

A useful trick is to run a hose gently over different sections of the frame from outside on a dry day (with someone watching inside), working from the bottom up, to isolate roughly which area lets water through. This avoids guesswork and stops you resealing an area that was never the problem.

Weep holes and why they matter

Every uPVC window frame is designed with small drainage weep holes along the bottom of the outer frame, which let any water that gets into the frame's internal drainage channel escape outward rather than sitting and finding its way inside. Over time these can become blocked with dirt, insect nests, paint from a previous redecoration, or general debris.

If weep holes are blocked, water that would normally drain away safely backs up and can eventually overflow inward, which looks exactly like a frame leak but is actually a drainage problem. Clearing blocked weep holes is a simple check worth doing before assuming the frame itself has failed.

When it's the sill or brickwork, not the window

Not every leak near a window is actually coming from the window. A cracked external sill, missing or perished pointing above the frame, or a render crack can all let water track down behind the frame and appear as a window leak indoors. If the leak seems to track down from above the window rather than along the bottom edge, this is worth considering.

This distinction matters because resealing a window frame won't fix a leak that's actually coming from the brickwork above it, so it's worth having both checked if the source isn't obvious.

Temporary steps while you get it looked at

There's a limited but useful amount you can do to protect the property while a proper repair is arranged.

• Place a towel or container under the affected area to catch water and limit damage to flooring or plasterwork
• Clear any visible debris from the outside weep holes with a soft brush if they're easily reached
• Avoid painting over external sealant to disguise a gap, as it won't stop water tracking through underneath
• Note when the leak happens (heavy rain, wind direction) as this helps narrow down the source

What a proper repair involves

Once we've identified the actual entry point, the fix might be as simple as raking out old, perished sealant and reapplying a proper weatherproof bead around the frame, or as involved as replacing a damaged sill or gasket. Where the frame itself has warped or the drainage channel is damaged internally, that's a bigger job, but this is genuinely uncommon compared to a straightforward seal or weep hole issue.

We'll always identify the actual cause first rather than simply re-sealing everything and hoping, since that approach often leaves the real gap untouched.

Getting the leak sorted

If the window itself has other issues alongside the leak, such as a stiff opener or worn seals, our uPVC window repairs service covers the frame and hardware together. Where the leak has led to a misted or damaged sealed unit as a knock-on effect, our misted double glazed units service deals with that separately, and our double glazing repairs page covers the wider range of frame and seal work.

Send us a photo of where the water is appearing, and if you can, when it tends to happen, through the quote page, and we'll help work out the likely source before booking a visit.

Call Mark on 07535 916982 or request a callback.