When a roof window drips, the glass is rarely to blame. Flashing, sealing, condensation and the tiles around the frame are the usual suspects, and each needs a different fix.
A drip beside a loft window in a Brentry semi or bungalow can come from several places, and the cure depends on which. VELUX and similar roof windows are built to be watertight, so a leak usually points to what surrounds the window, or to moisture forming inside the room, rather than to a faulty pane.
First, is it really a leak?
Condensation can look exactly like a leak. Warm, damp air meets cold glass or frame and runs down as droplets. If it appears on cold mornings, is spread evenly and goes when the room is aired, it is moisture rather than rain. A leak, by contrast, appears after rain and usually follows the same path each time.
Flashing that has failed
Each roof window is matched to a flashing kit for the roof covering. The flashing channels water around the frame and onto the tiles. If the kit is the wrong type, has lifted, split or been disturbed by a later repair, water gets under it. This is the commonest cause of a leak, and it is invisible from inside.
A replacement flashing should be fitted properly with the tiles around it rather than sealed over with a bead of mastic. Sealant alone may stop a drip for a few weeks, but if the kit is wrong or worn, the leak returns with the next heavy rain.
- Drips only during or after heavy rain
- Staining on the lining or plasterboard
- Water tracking down the frame corners
- Wet insulation around the opening
Seals, glass and the surrounding roof
Seals around the sash can perish. A misted pane means the sealed unit has failed, which is a separate fault from a leak. Slipped or cracked tiles above the window, or a blocked channel beside the frame, can also send water into the opening. We check the covering around the window as well as the window itself.
If the window is old, the seal and the frame may have reached the end of the road together, in which case replacing the whole window with a new flashing kit is more sensible than a string of small repairs on a tired unit.
Inside the opening
The lining, insulation and vapour control around the frame also matter. If they are poorly fitted, warm moist air gets into the gaps and condenses on cold surfaces, then drips. We check these from the room side, along with the rafters around the opening, and put right whatever is out of order.
What to do now
Place a towel or tray under the drip, note when it happens and tell us. Do not go out onto the roof or sit on it to inspect from above. We carry out the checks safely. If any work may need planning or Building Regulations checks, we advise before work starts.
Frequently Asked Questions
Can a roof window leak even if it is fitted correctly?
Yes, if the tiles around it are damaged, or a later repair has disturbed the flashing. Condensation inside can also look like a leak. We check both the window and the roof around it before suggesting a cure.
Does a misted pane mean it leaks?
No. Misting means the sealed glazing unit has failed and moisture has got between the panes. It is a different fault from a leak. The unit, or the whole window, has to be replaced rather than repaired.
How do I tell condensation from a leak?
Condensation tends to appear on cold mornings, over the whole glass or frame, and clears with ventilation. A leak follows rain and shows in one place. Noting when it happens helps us work out which it is.
Talk to our team about VELUX and roof window installation in Brentry
Every roof is different — the fastest way to get an accurate answer is a quick chat with our team.