Why Do VELUX Windows Leak?

Flashing is the metalwork that ties the window into the tiles or slates and leads rain around the frame. Over the years it can lift at an edge, corrode, split at a corner or be disturbed by movement in the roof covering. Water then tracks beneath it and finds its way down the frame.

The signs are a stain that appears on the lining at one side or at the lower corner, usually after heavy or wind-driven rain. Flashing is cut for one window size, so a mismatched or carelessly fitted kit invites water. When a window is replaced, new flashing is part of the job for exactly this reason.

Tiles and slates nearby

The covering above and beside the window matters just as much. A cracked tile or a slipped slate directly above the frame can send water straight at the junction. What looks like a failed window may turn out to be a fault in the covering next to it, which is why the roof is checked as well as the window.

Many reported leaks turn out to be condensation. Roof windows sit in a cold plane of the roof. Warm, moist air from a bathroom, a bedroom or a kitchen meets the cold glass and frame and turns to water, which runs down and can soak the lining. The marks look the same as a leak, but they appear on cold mornings rather than after rain.

Condensation points to a ventilation problem more than a window problem. A window that can be opened a little to a venting position helps clear moist air. Extractor fans in bathrooms and kitchens, and a gap between the window and any blind, also help. If the glass is misted between the panes, though, the sealed unit has failed and the glass cannot be cleared, which is a case for replacement.

Rubber and foam seals harden over time and lose their grip. Frames, especially timber ones, can weather and move. A sash that no longer closes tight lets in air and, in driving rain, water. Older units also suffer from failed sealed glass units, which mist and lose efficiency, although this is a loss of insulation rather than a leak.

If the frame has softened or the seals have given up, the unit is often beyond repair and a replacement is the sensible route. What a swap involves, including new flashing and the lining made good, is set out in the replacement guide.

Installation faults

A window that has leaked since the week it was fitted points to the installation. A frame fixed out of square, flashing laid in the wrong order or a missing tilting fillet can all allow water in. These faults do not improve with time. They argue for an installer who builds the junction carefully and backs it in writing; our workmanship guarantee runs for 10 years.

Start by working out when the water appears. After rain suggests the flashing or covering. On cold mornings suggests condensation. If it follows both, there may be two causes together.

Photograph the stain and the window from inside, and note which edge it is nearest. If you can see the roof safely from the ground or from an upper window, look for slipped tiles or lifted metal near the frame, but do not climb onto the roof. Check the loft timbers beneath the window for dampness, which shows a leak has been running for some time.

Then book a survey. We examine the roof, the window and the loft, and report where water is getting in and whether the unit needs replacing. The quote is written with a fixed figure. Fill in the survey form or send a WhatsApp to 07880 284133. The VELUX section gives the wider picture, and if several windows are tired, a set done together may suit.