Signs a Rooflight Has Failed and What to Do Next

This is the sign that tends to catch the eye first, and the one that is most clearly the glass. When mist or tiny beads sit between the two panes and cannot be wiped away from either side, the edge seal of the unit has let go and damp air sits inside the gap.

The cloud often begins at one edge and spreads. It may come and go with the weather in the early stages, which can make it look as though the glass is recovering. It is not. A sealed unit cannot dry out once the edge seal has opened.

On its own, a misted pane is a fault in the glass and is not a threat to the roof. It does cost you the view and some of the insulation. The full story of that fogging is in our misted rooflight glass guide, and the choice between glass only and the whole unit is set out in rooflight sealed unit replacement.

A brown or yellow mark on the lining round a rooflight is a different story. It means water has been getting past the unit, over the frame or round the flashing, and soaking into the plaster or board. A tide-line ring is typical: the stain dries, then the next rain adds another ring outside the first.

Not every mark means the same thing. A stain at the very top of a roof window lining can mean the upper flashing is letting water in. A stain at the base of the frame, with water collecting on the sill, may mean condensation running down the room side of the glass and onto the lining. The second is a ventilation matter, and the first a roofing one.

Press the lining gently with a finger. If it is soft, flaking or cold and damp to the touch, the water has been arriving for a while. Take a photograph and a note of the date so we can compare it at the survey. A stain that grows after rain is more telling than one that has stayed the same for years.

Some signs show only when the weather turns. A drip in heavy rain is the obvious one. A whistle in wind is another. A cold draught that falls from the frame on a still evening is a third.

All three point to the same area: the seals between the sash and the frame, or the fixings between the frame and the roof. The rubber or foam seal in a sash hardens with age and loses its spring, so it no longer presses firmly all the way round. The frame itself may have shifted slightly in its opening.

This is why it pays to be careful about the word "failed". The glass can be fine while the unit as a whole is not. A new set of sash seals can help in some cases. But where the frame is also soft, or the flashing is tired, we would rather tell you plainly that the neat answer is a new unit. The road to that answer starts at the survey, and Is a misted rooflight worth replacing shows how we weigh up the choice.

On an opening rooflight, the sash is worth testing on a dry day. Open it fully, then close it slowly and watch the line where it meets the frame. It should shut with a gentle push and sit flush all the way round.

A sash that drags on one side suggests the frame has gone out of square, often because the surround has moved or the hinge has worn. One that will not stay open suggests a tired stay or a slipping friction hinge. One that closes but shows a gap at a corner means the seal no longer meets the frame evenly.

For an electric or solar unit, the signs are different. A motor that hesitates, a unit that opens only part of the way, or a rain sensor that no longer reacts can point to the control rather than the window. A rain sensor that stops working matters more than it sounds, because the point of the sensor is to close the unit while you are out.

An opening that cannot be relied on to shut is a reason to act, since the room is then open to weather. It is also a good moment to think about what you want from the new unit, and the fresh air rooflights guide compares manual, electric and solar openers.

The frame is the quietest part to fail, and the most important to inspect. It is easy to look at fresh glass and miss that the timber beneath it has begun to give way.

On a timber frame, check the corners and the lowest edge. Dark staining, flaking paint or timber that gives under a thumbnail are signs of moisture. On a metal frame, look for bubbling in the coating, chalky areas or white salts, which tell you the metal has begun to corrode. On a plastic frame, check for warping, yellowing and cracks at the corners.

1. Run a finger round the lower frame and feel for softness.
2. Look along the joints for gaps or lifting paint.
3. Check the fixings and the flashing for slipped, lifted or cracked sections.
4. Close the sash and look for an even gap all round.

A frame that fails any of these checks is a candidate for replacement as a whole, with new glass, a new frame and new flashing. The new unit then has to meet the Part L 2021 limits, which differ for a roof window and a rooflight. The Building Control side is notifiable, and we deal with it for you. The misted and failed rooflights hub shows how that sits with the rest of our work.

Some signs are about how the room feels rather than what the unit looks like. A bedroom that has become colder under the window. A landing that rings with rain. A bathroom where the steam seems to stay put longer than it used to.

A cold area under the unit often tracks a loss of insulation in the glass, which is what happens when a sealed unit has taken in damp air. It also follows from a worn frame seal, or from the lining insulation having slumped. The rain noise is more about the type of glass than failure, though a loosely seated unit can rattle in the wind.

The steam point is about air. A rooflight that opens helps a room clear steam and stale air, and one that is stuck shut cannot. If a unit used to open and now will not, the room will feel the difference even though the glass looks fine.

These are softer signs, but they matter. They are the way a failing unit tells you about itself before anything shows on the lining, and they are why a quiet look at a rooflight once a year makes sense. For what to expect as a unit ages, read about rooflight sealed unit lifespan.

Once you have worked out which signs you can see, the next move follows fairly plainly.

• A cloud in the glass and nothing else: a new sealed unit may be enough.
• Marks on the lining or a drip: a survey of the flashing and frame, and probably a whole new unit.
• A sticking or open sash: a new sash mechanism or a new unit, depending on the age.
• Several signs together: plan to replace the whole rooflight.

None of this needs to be rushed, and none of it should be guessed at from the ground. A surveyor visits, studies the unit from inside and out, and says what is there. The quote is written and itemised, shows the choices where there is more than one, and carries no obligation. The costs page gives broad UK market ranges and the things that raise or lower a price.

Any unit we fit is backed by a 10-year workmanship guarantee, spelled out on the guarantee page. The hub for all of this is misted and failed rooflights replaced, and our VELUX glass page is the quickest route if the unit is that make.