Leaking Velux

Why is my Velux window leaking?

Drips round a roof window come from the flashing, the seals, the frame or the covering around it, or they may be condensation. Here is how to tell.

The short answer

A Velux window leaks when rain gets past the flashing or the seals around it, or through a worn part of the window itself, and the cause is only found by looking at the roof. A leak shows during or after rain, while droplets on the glass on a cold dry morning are usually condensation. Catch the water, photograph the damage and book a survey, and stay off the roof yourself.

4 min read · Part of Roof windows & skylights

A hipped red-tile roof on a white-rendered bungalow — Water marks on the lining below a roof window

Where the rain gets in

A roof window is an opening in the slope with a frame fixed into it. The covering round the frame is dressed up to it with flashing, the strips of metal that lead rain away from the joint. Each of those parts is a place where rain can get past, and the list below runs from the outside in.

The flashing at the sides, head or sill, if it has lifted, split or been dressed badly
The roof covering round the opening, if tiles or slates have slipped or cracked
The seals and gaskets on the sash, if they have hardened or pulled away
The frame, if the timber has gone soft or the joints have opened
The lining and fixings, if rain is tracking in from higher up the slope

Rain can run along a rafter or the underlay before it drips, so the stain inside the room may sit well away from the entry point. That is why a survey looks above and beside the window as well as at it.

Leak, condensation or failed seal

Three different faults leave a roof window wet, and the cure for each is different. Reading the pattern saves a wasted visit, so note when the wet appears before you call anyone.

Three wet-window faults and how they differ
What you see	When it happens	Likely cause
Drips or a damp patch	During or after rain	A leak
Droplets on the room side	Cold mornings	Damp air in the room
Mist between the panes	Any time	A failed glazing seal

Our pages on condensation on Velux windows and Velux reglazing cover the second and third in full. A drip that appears only in a strong wind, or after several days of rain, is still a leak even if it comes and goes.

Keep a short diary for a week: the date, the weather, the time you noticed the wet and where it showed. A pattern that follows the rain points to the roof, one that follows cold nights points to the room, and one that never changes points to the glass. A week of notes tells a surveyor more than a single photograph, and it costs nothing to keep.

Steps to take tonight

You can limit the damage safely from inside the house. Move furniture and anything else that could be spoiled, lay a towel on the floor and set a bucket under the drip. Take photographs of the stain, the window and the sky outside, and note the date and the time. If the stain spreads, mark its edge in pencil and date that too, because the growth rate is a useful clue. Do not poke at a bulging ceiling or lining, which can bring the water down in one go.

If you may want to claim, tell your insurer first. The Financial Ombudsman Service, when a dispute reaches it, says it will usually look at expert reports and photos, so keep your dated pictures and the receipt for any temporary repair as well.

Please do not climb onto the roof, or lean out of the window to look at it. Slopes are slippery in the wet, and a fall costs far more than a leak. A roofer with proper access can look in dry conditions, and we arrange the scaffold when a job needs one. If the opening is letting in a steady stream, say so on the phone, because that changes how we plan the visit.

How the survey traces the cause

We start inside, with the stain, the lining and the sill, then go outside to the flashing, the covering and the frame. Where the cause is not obvious, the roof above the window is checked as well, since rain can enter higher up than the mark shows. We also look at the gutter and valley above the window, in case the water is being thrown onto the frame instead of draining away from it, and at the underlay edge where it meets the frame, if that can be reached.

The result is a plain account of what we found. It may be a refixed flashing, a few replaced slates or tiles, a new gasket, or a window that has run its course, and we tell you which, and why. Our page on how long Velux windows last helps you judge the age of yours, and we begin with a repair whenever the window can sensibly be kept.

You then receive a single written price for the work, with any scaffold included in it. The roof windows and skylights page describes the rest of what we do with them.