Why Is My Roof Leaking Around a Velux or Skylight?

Where the water is showing

Where the damp appears tells us something useful before anyone goes up. Water at the head of the window often comes from the covering or flashing above it; water at the sides suggests the side flashings or the slates beside the opening; water on the glass and frame, particularly in cold weather and with no rain, points towards condensation.

Signs to note before you call

• Whether the damp appears only during or after rain
• Whether it is worse with wind from a particular direction
• Whether the reveal, plasterboard or timber around the opening is staining
• Whether water sits on the frame or glass on cold, dry mornings
• Any ponding or debris visible on the flat area around a flat-roof skylight

Possible causes

Possible causes include the following. A roof window sits in a hole cut through the covering, so several separate details have to be right at once.

What may be at fault

• The flashing kit or apron around the unit — displaced, damaged, poorly dressed or badly sealed; see lead flashing
• Slates or tiles above or beside the window that have slipped, cracked or been cut short; see slate and tile repairs
• Installation details: underlay not dressed correctly into the opening, or battens and fixings not set out as they should be
• Deterioration of gaskets, seals or trims through age and weather
• Debris collecting at the head of the window and holding water against the detail
• Water tracking down from a defect higher up the slope and emerging at the first obstruction — which is often the window
• Condensation forming on cold glass and frame, running down and staining the reveal

Condensation or a leak?

It is a genuinely common mix-up, particularly in bathrooms, kitchens and attic conversions. Condensation typically shows as water on the glass and frame itself, is worst on cold mornings, and does not correspond with rainfall. A leak usually tracks in from the edges of the opening and follows the weather.

Both can also be present at once, which is why we look at the detail rather than assume. There is more on telling them apart in our guide to condensation versus a roof leak.

Repair or replacement of the window

Plenty of roof-window leaks are resolved without touching the window: reforming the flashing, replacing damaged coverings around the opening, or correcting a detail that was not right when it went in.

Where the unit itself has reached the end of its life — a failed frame, a rotten timber section, seals that cannot be renewed — replacement is the sensible answer, and we fit new roof windows and skylights as well as repairing existing ones. We are not an authorised agent for any manufacturer, and we do not claim to be.