Velux or Roof Window Leaking? Causes and Fixes
Roof windows went into Irish homes by the thousand during the building years, and those windows are now reaching the age where seals, glazing units and flashing kits start to fail together. The good news is that a leaking roof window is one of the more diagnosable roof problems, because the list of suspects is short.
Velux is the name everyone uses, but most of this applies to Fakro, Keylite and the other roof-window makes fitted in Ireland.
The four places a roof window leaks
1. The flashing kit. The window sits in a manufactured flashing apron that integrates it with the surrounding slates or tiles. Storm-lifted, cracked or wrongly-fitted flashing is the most common genuine leak. From inside, water marks appear at the top or sides of the frame, usually during wind-driven rain.
2. Failed glazing unit seals. If the glass is fogged between the panes, the sealed unit has failed. That is not a leak yet - the water is inside the glazing unit, not your house - but a failed unit loses heat, looks terrible, and is telling you the window is at the age where other seals deserve a look too.
3. The window's own seals. The rubber gaskets around the opening sash perish with age. Drips that appear when the window is closed, especially at the bottom edge of the sash, point here. These seals are replaceable on many models.
4. Condensation around the frame. Sometimes the "leak" is warm, wet room air condensing on the coldest surface in the house - the window frame and glass. If the moisture is on the room side, appears in cold weather regardless of rain, and wipes away, read our leak or condensation guide before calling anyone.
Repair or replace?
A roof window is a manufactured unit with replaceable parts, which changes the usual repair equation:
- Flashing kit problems: repairable, and often the only thing wrong. A roofer re-seats or replaces the flashing without touching the window.
- Failed glazing unit: the glass unit alone can be replaced on many models - a fraction of full replacement.
- Perished sash seals: replacement gasket kits exist for common models.
- Everything at once: where the frame timber is swollen, the glazing has failed and the seals are gone, a like-for-like replacement window is usually the sensible money, and some replacement units are designed around common opening sizes.
When you get quotes, the useful question is the same one as always: which of those four are you pricing? A "new window" quote and a "new flashing kit" quote are not comparable until both say so.
What you can check from inside
- Open the window and look at the sash gaskets: cracked, flattened or missing sections are visible
- Look at the top corners of the frame after rain for fresh water marks
- Note the window's age if you can - the type plate is usually on the sash edge when open - because installers use it to source parts
- Photograph any staining with dates for the roofer
Everything above roof level - the flashing apron and outer frame - is a professional inspection. No ladders, no roof access.
Ready for quotes? Request quotes from roofers in your county
Related questions
The window fogs between the panes. Is it leaking?
No - that is a failed sealed glazing unit. It affects heat loss and appearance, not water entry. The glass unit can often be replaced on its own.
Can I reseal around the frame with silicone myself?
Interior cosmetic sealant hides symptoms without fixing causes, and exterior sealant belongs to whoever is working safely at roof level. A smear of silicone over failed flashing usually makes the eventual repair messier.
Do I need the same brand for replacement?
No. Replacement roof windows come in standard opening sizes, and a competent installer matches the size and the flashing kit to your roof covering regardless of brand.
Sources checked
General manufacturer part and installation guidance. Glazing and flashing claims remain held for named technical review.