Question answered
Why is my Velux window leaking?
The short answer
A leaking Velux window is most often a flashing problem: the metal or lead collar round the frame has lifted, split or been fitted as the wrong kit for the covering. Perished seals, a slipped tile or debris above the frame can also let water in, and condensation is sometimes taken for a leak. Tracing which one it is must come before any repair.
A roof window that drips is usually let down by what surrounds it, not by the glass. The flashing, the seals, the roof above and the air in the room each have to be ruled in or out.
Flashing is the first suspect
Where a roof window meets the tiles or slates, a flashing kit closes the gap. It is a set of aluminium or lead pieces that overlap one another and the covering, so water runs over every joint and never into it. If the kit does not suit the covering, if a piece has lifted in a gale, or if sealant added by someone else has dried and cracked, water can creep beneath the edge.
The bottom edge and the lower corners are most at risk, because the flow of the whole slope above arrives there. A stain at the lower corners of the lining, or a streak down the wall beside the opening, points to this area. The proper repair is to dress the pieces back into their correct overlap, or renew the kit. Smearing mastic over the joint only sits on top of the problem, and it often traps water behind it, leaving a hidden wet patch for the next person to find.
The roof above the window
Water does not always start at the window. A cracked or slipped tile, a lifted slate, or a build-up of moss and leaves above the frame can drop water onto the head of the window, and it then looks as though the frame is at fault. The head is the top edge of the opening, where the flashing should send water away to both sides.
Debris and broken tile can also hold water against the head so that it spills over the lip and in. The cure is to clear and mend the covering above, then check that the head flashing carries water sideways and does not let it pool. A window set low in a long slope receives the run-off of everything above it, which explains why a small fault high up can show itself as a drip at the window. When we investigate we follow the stain upward from inside, then compare it with what the outside shows.
Seals, gaskets and the frame itself
A roof window depends on rubber or foam seals between the sash and the frame. With age they flatten, harden or tear, particularly where the window is opened often or catches the sun. Water then blows past them in a gale, usually as a drip at the foot of the sash or as damp along the lower side of the lining.
Fresh seals are a modest job, provided the frame is sound. A frame that has swollen, split or rotted calls for a more serious repair, and at that stage replacing the whole unit can be the sensible course, since the flashing is renewed at the same time. A pane that has gone cloudy is a different matter, covered in misted roof window glass, and cloudy glass alone does not mean the window leaks. If the window is on a side slope there may be limits on what can be swapped; see side roof windows and obscure glass.
Telling a drip from damp air
Many reports of a leaking roof window turn out to be condensation. Warm, damp air from the room meets cold glass and the frame, then runs down as water. The clue is timing. Condensation appears on cold mornings and after showers or cooking, and it eases as the room warms and is aired. A true leak follows rain, often heavy rain with wind behind it, and appears even when the room is dry and well ventilated.
Look at where the water sits. Beads on the room side of the glass and a damp sill point to condensation. Staining that runs from the frame into the plaster, or a drip that only appears after a storm, points to a leak. The full explanation is on condensation on a roof window. Keep a note of the dates and the weather each time water appears, because a pattern usually gives the answer quicker than guessing.
What to do first, and what we check
Put a bowl under the drip, move belongings out of the way, and keep off the roof. If water is running near a light fitting, switch the circuit off. We put a live leak ahead of routine work, and the first job is to stop water entering. After that we hunt for the way in: flashing, the roof above, the seals and the frame, with photographs of each finding taken on your slope.
Once the survey is done we send a single total in writing, and it covers the smallest job that properly stops the leak. When the window is old and failing in several ways, we explain why replacement may serve you better than another patch. If the leak is on a glazed lantern or a similar kerb-mounted unit, the page on roof lanterns explains how those differ. The whole range sits under skylights and roof windows.
Roof window leaks: two common worries
Will silicone around the frame stop my Velux window leaking?
Rarely for long. Silicone applied over the flashing or around the frame can hold for a while, but it hides the joint and can trap water behind it. If the cause is a lifted flashing or a perished seal, the fix is to restore the overlap or renew the part, not to add a layer on top.
My roof window only leaks in strong wind. Why?
Wind drives rain sideways and uphill, past joints that cope in ordinary rain. That points to a weakness at the edges: a tired seal, a lifted piece of flashing, or a gap beside the frame. Note which wall the damp appears on and the date of the storm, and tell us when you book.
Tell us about your roof
Describe what is happening and we will call you back to arrange a visit.
- Photographs of what we find
- A written quote with one total price
- Or call 01903 299063
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