The short answer: If the mist is between the panes, no. That moisture is inside a sealed unit whose seal has failed, and it cannot be wiped away or drained out in any way that lasts. The misting may come back, the insulation is already reduced, and the honest fix is a replacement skylight. If the mist is on the room side or the outside face, it is only surface condensation or dirt, and that can be dealt with.
Start by working out which kind of mist you have. This page is part of our guidance on misted and failed rooflights, and the first job is a simple one: find where the moisture sits.
Surface mist or mist between the panes
There are three places moisture can be, and each means something different.
- On the room side. This is condensation from the air in the room. It wipes off with a cloth and usually shows up on cold mornings, in kitchens and bathrooms, and after cooking or showering.
- On the outside. This is dew or dirt. It clears with the weather or with cleaning.
- Between the panes. This sits inside the sealed gap. You cannot reach it with a cloth, and it does not clear when the room warms up.
Only the last one is a failed unit. The first two are not faults in the glass.
Why mist between the panes will not clear
A sealed unit is made in a factory. The gap is filled with dry gas, a desiccant strip at the edge soaks up any trace of moisture, and a sealant locks the edge. That sealed space is what gives the glass its insulating value.
When the edge seal breaks down, damp air gets in. The desiccant fills up and can take no more. After that, moisture condenses on the cold inner faces of the glass whenever the temperature drops. You see it as a cloudy haze, droplets, or a white film of mineral deposits that dries into streaks.
The seal cannot be put back on a unit that is already glazed into the frame. Drilling holes to let the damp out, or injecting something into the gap, breaks the sealed space further and does not restore the gas or the coating. Those routes tend to leave you with a unit that is still compromised and looks worse. For that reason we treat a misted sealed unit as one that needs replacing. Our page on why rooflights mist between the panes covers the causes.
What the failed seal costs you
A misted unit usually looks worse than it performs, but it is still losing its insulating gas. In winter that can show up as a colder surface under the rooflight and more condensation on the room side. In summer the cloudy glass reduces the clear view of the sky.
The unit no longer matches the thermal values the regulations expect of a new one. Today a pitched-roof window is expected to reach Window Energy Rating band B or 1.4 W/m²K, and a flat-roof unit or lantern 2.2 W/m²K. Whatever replaces the misted one will have to meet the figure for its type, and energy efficient rooflights shows what a good replacement looks like.
Glass only, or the whole rooflight
Replacing the sealed glass unit in a sound frame is sometimes possible. It depends on the condition of the frame, the kerb and the fixings. On older dome rooflights, plastic domes, or timber frames that have rotted, the whole unit is the sensible choice. We look at which applies on your roof, and set it out in replacing the glass or the whole rooflight.
Under the Building Regulations, taking out a complete rooflight or roof window and fitting its equal is building work. Fresh glass fitted into an existing sound frame does not count. If a misted-unit replacement is notifiable, the notice to Building Control comes from us. The Building Regulations guide goes through the detail, and does replacing a rooflight need Building Regulations answers the question directly.
Is it urgent?
A misted unit is not usually an emergency, but it will not improve by waiting. A broken seal does not heal. If the mist is accompanied by drips, stained plaster or a damp ceiling, treat that as a separate problem: the water may be getting in at the kerb or flashing, and the survey should look at that too. Our page is a misted rooflight urgent explains how to judge it.
Why cleaning products and tricks fall short
You will find advice online about drying the unit out, drilling a tiny hole, or using a kit to flush the gap. These approaches treat the symptom. The moisture was a sign that the edge seal had let the outside in, and the outside is still there afterwards.
A drilled unit can look clear for a while. The coating inside the gap is still exposed to damp air, the gas fill has gone, and dirt and mineral marks can settle on the inner faces where nobody can wipe them. The rooflight is also less insulating than it was, and it will not meet the value a new unit must meet.
Anything that opens the sealed space also puts the question of who is responsible for the glass in doubt. A clean replacement unit, made to size and fitted with a new seal, gives you a fresh start and a known specification.
There is one more reason to be cautious. On a flat roof, the glass often sits on a kerb that you cannot see from inside. Moisture marks round the edge may be a sealed unit problem, or they may point to a problem at the upstand. Looking at both in one visit is quicker than guessing.
What happens next
The first step is a free survey, where we examine the unit, the frame, the kerb and the roof around it before quoting a fixed price. The access plan inside every quote sets down the route up, which of us makes any scaffold licence or bay suspension application, and the price. The replacement carries our 10-year workmanship guarantee. For the full sequence, see what replacing a failed rooflight involves.
If your rooflight has misted, request a survey and we will confirm what it needs, or go back to the misted and failed rooflights hub.
