Misting between the panes and condensation on the room side look similar but have different causes. This guide helps you tell them apart in your Hotwells home and shows what we do.
A roof window that fogs up can be a nuisance and a worry. Sometimes it is only condensation caused by a damp, warm room. Sometimes the sealed glass unit has failed. In Hotwells, with older terraces converted to loft rooms, modern flats and exposed slopes, both happen. Here is how to work out which you have.
Which side is the mist on?
Wipe the inside surface of the glass when it is misted. If the mist wipes off, it is condensation on the room side. If it stays and you can see it between the panes, the sealed unit has failed and moisture has got in. Wiping the outside, from a window you can safely reach, is a way to confirm. Do not lean out or go onto the roof to do it.
Condensation: damp air meeting cold glass
Warm, moist air in a room condenses on the coldest surface it touches, and glass is often that surface. Cooking, bathing, drying washing indoors and sleeping in a closed room all add moisture. Roof windows can show it first because they sit overhead where warm air rises. Ventilating the room, using extractors and opening the window can reduce it. If it is constant, there may be a cold bridge or poor lining around the opening.
- Cooking and bathing without extraction
- Washing dried indoors in the roof space
- Closed bedrooms overnight in the roof space
- Poor insulation or lining around the opening
Failed sealed unit: mist between panes
The glazing is two layers sealed at the edge. Once that seal fails, moist air gets in and condenses between the panes, leaving permanent misting or streaks. It cannot be wiped away. Over time the mist gets worse. The usual cure is replacing the glazed unit or the window, depending on its age and whether parts are still available.
When it is not the glass
Sometimes what looks like misting is a sign of a leak. Water getting past flashings or seals can run down the lining and appear as damp, staining or drips around the frame. Water can also reach the glass from a poor seal at the edges. On older Hotwells roofs, the covering around the window and the lead or flashing kit may be the cause, so we check these as well as the glass.
What we do
We identify whether it is condensation, a failed unit or a leak, then advise. If the unit has failed, we replace the glass or window and re-seal with a flashing kit matched to the covering. If condensation is the issue, we look at the lining and insulation round the opening. Access on steep streets needs planning, and we arrange it before the visit. Replacement may need planning or Building Regulations checks — we advise before work starts.
If the window is older, we also look at whether parts are still available and whether replacing the whole unit makes more sense than one pane. We explain the options in plain terms and leave the choice with you. There is no pressure to decide on the spot.
Frequently Asked Questions
Can I clear misting between the panes?
Not properly. Once moisture is inside the sealed unit, it cannot be dried out in a lasting way. The unit needs replacing. We confirm the cause first so you are not replacing a window that only has condensation.
Does misting mean the window leaks?
Not always. Misting between panes is a failed seal, which is separate from a leak. But if you see damp around the frame or lining, water may be getting past the flashings, and we look at that too.
Will opening the window stop the condensation?
It helps, because it lets moist air out. Regular ventilation, extraction in kitchens and bathrooms and keeping the room warm all reduce condensation, though they will not cure a failed sealed unit. We explain this on site.
Talk to our team about VELUX and roof window installation in Hotwells
Every roof is different — the fastest way to get an accurate answer is a quick chat with our team.