Most leaking roof windows are not leaking through the glass. The cause is usually the flashing, the seals, condensation or the covering around the frame. This guide explains how to tell which.
A damp patch beneath a roof window is easy to blame on the window itself. In practice the glass is rarely the problem. VELUX and similar roof windows in Lawrence Hill lofts leak because of what surrounds them: flashing that has worn, seals that have aged, condensation that looks like a leak or a roof covering that has slipped.
Flashing around the frame
The flashing kit is the set of metal pieces that directs water around the window and over the surrounding tiles. If it was the wrong kit for the roof covering, was fitted loosely or has been pushed out of place, rain can slip underneath and track along the rafters. This is the most common cause on windows that were fitted a long time ago, or on ones swapped without changing the flashing.
Seals and fixings
Rubber seals and sealant joints harden and shrink. A sash that no longer closes tightly lets driven rain past the gasket, usually in strong wind. Loose or corroded fixings also allow the frame to shift slightly and open a gap. These problems often appear along one side of the window, and the damp mark will follow the same line.
Condensation that looks like a leak
Warm, damp air from a bedroom or bathroom meets the cold glass and frame and turns to water. It runs down the pane, sits on the sill and drips. People report it as a leak, and the clue is that it appears on cold mornings rather than after rain. Poor insulation around the lining or a missing vapour barrier can make it worse.
- Water on the glass or frame on cold mornings
- No marks on the ceiling after a heavy shower
- Mist between the two panes of glass
- Streaks that start at the top of the frame
Misting between the panes
If the glass looks cloudy or beaded between the two layers, the sealed unit has failed. That is a ventilation and insulation problem rather than a leak, and the fix is a replacement unit or window, not a repair to the roof. We can tell the difference on site by looking at where the moisture sits.
The covering around the window
Sometimes the window is fine and the leak comes from slipped or broken tiles above it, which let water run down onto the head of the frame. Terraced loft rooms with a dormer or a window high on the slope are particularly prone to this. We check the whole area, from the tiles above to the lining inside, before recommending anything.
Frequently Asked Questions
Can a leaking roof window be resealed?
Sometimes a small seal or fixing can be renewed, but if the flashing is wrong or the surrounding covering is worn, resealing only hides the fault. We find the actual cause first and then choose between a repair and a new installation.
How can I tell if it is condensation or a leak?
A leak appears or gets worse after rain and leaves marks around the frame. Condensation shows on cold, still mornings and wets the glass and sill first. Photograph what you see and when, and share it with us.
Does the whole window need replacing when it leaks?
Not usually. Many leaks are fixed by renewing the flashing, the seals or the covering around the frame. If the window is old, the glass has misted or the frame is damaged, a replacement is more sensible, and we say so.
Talk to our team about VELUX and roof window installation in Lawrence Hill
Every roof is different — the fastest way to get an accurate answer is a quick chat with our team.