Mist on a roof window is either on the inside, which is usually condensation, or between the panes, which means the sealed unit has failed. Here is how to tell and what to do.
Where the mist sits tells you most of what you need to know. Mist on the room side of the glass is nearly always condensation from the air in the room. Mist trapped between the two panes is a failed sealed unit that will not clear. Loft rooms in Bishopston make both common, because the space is small and warm.
Between the panes
If you can see mist or a film between the glass layers, and wiping inside and out does nothing, the seal has failed and moist air has got in. That cannot be cleaned away. The sealed glass unit needs replacing. It is often possible to fit a new unit or a new window without disturbing the room more than necessary.
On the room side
Mist that wipes away from the inside is condensation. Warm air in the room carries moisture, and the glass is the coldest surface it meets. Cooking, showering, drying washing and sleeping all add moisture. A small bedroom in a converted loft collects it fast, especially when the window is closed all day and the room has little air movement.
- Mist that wipes off from inside is condensation.
- Drying laundry in the room makes it worse.
- A closed room with no airflow holds more moisture.
- Cold glass in a warm room shows it first.
Other causes worth ruling out
Sometimes the problem is not the glass. Droplets on the lining or damp around the frame can point to a poor seal, a flashing fault or insulation that has slipped. We look at the surround, the lining and the roof covering near the window, because a leak and condensation can look alike from inside. Staining that grows after rain points to a leak.
- Damp patches on the lining or plaster.
- Staining that grows after rain.
- Drips at the bottom of the frame.
- Mould in the corners of the opening.
What you can do from inside
Open the window for a short while each day, use the trickle vent if there is one, and run extractor fans in bathrooms and kitchens. Keep the room warm enough that surfaces do not turn cold. Wipe the glass in the morning. Do not go outside onto the roof to look at it. If the mist persists, call us for a proper check.
Repair or replace
A failed sealed unit means replacing the glass or the window. An old window with several faults may be best replaced as a whole, with a new flashing kit matched to the roof covering and fresh insulation and lining around it. We explain which makes sense, based on the condition of the frame, the seals and the roof around it.
Frequently Asked Questions
Can misted double glazing be repaired?
Not by cleaning. Once moisture is between the panes the seal has failed. The sealed unit is replaced, and sometimes the whole window if it is old or worn. We check the frame and flashing at the same time.
Is condensation a sign of a leak?
Not usually. Condensation forms on the inside of the glass from room moisture. A leak shows as drips, staining or damp that gets worse after rain. If you are unsure, we can check both.
Will a new window stop condensation?
A new window helps, as the glass will be better insulated, but room moisture still needs somewhere to go. Ventilation and warmth matter as much. We advise on both when we look at the window.
Talk to our team about VELUX and roof window installation in Bishopston
Every roof is different — the fastest way to get an accurate answer is a quick chat with our team.