Velux and Skylight Leaks: Repair or Replace?

A leaking roof window almost always comes from one of two places: the flashing kit around the frame, or the unit itself failing internally. Telling them apart matters, since one is a straightforward repair and the other usually means replacement.

Flashing failure is by far the more common cause. The lead or flexible flashing kit fitted around a Velux seals the gap between the window frame and the surrounding roof covering. Over 10–15 years that seal can crack or lift, especially if the original installation wasn’t done to the manufacturer’s exact spec. Because the flashing sits under the roof covering, a repair often means lifting nearby slates or tiles rather than just resealing the visible edge.

Condensation gets mistaken for a leak more often than people expect. If water only appears in cold weather and runs down the inside of the glass rather than the frame, that’s usually condensation from indoor humidity, not a leak at all. Improving ventilation in the room often solves it without any roof work needed.

If the unit itself has failed, a double-glazed skylight is 25–30 years old, replacement is usually the better option. Seals inside an older unit degrade in a way that can’t be repaired, and a modern equivalent brings better thermal performance too. Since access and disruption are similar for a repair or replacement, it’s worth weighing the age of the unit before committing to either.

If your Velux or skylight is leaking, we can tell you honestly which of these it is before quoting anything. Our roof repairs team covers skylight work across Polmont, Denny and the surrounding area, with a free survey first. We also cover Falkirk and the surrounding area.

Related guides: How to spot a roof leak. Conservatory roof replacement. Dormer roof repairs. Lead flashing explained. Cracked or slipped tiles. Autumn/winter maintenance checklist. Flat Roof Ponding. Felt vs EPDM vs GRP Fibreglass Flat Roofs Com. Gutter Cleaning and Repair. Moss on Your Roof. Fascias, Soffits and Guttering Explained. Flat Roof Replacement Cost. Garage Roof Replacement Options and Costs. Slate vs Tile Roofs. Storm Damage and Insurance Claims.