Can a misted rooflight be fixed without replacing it?

A rooflight that mists on the room side is a different problem from one that mists between its two panes. Condensation on the room side comes from damp air meeting cold glass, and it clears when the air dries or warms. Mist trapped between the panes is a failure of the sealed unit, and it stays.

That second kind is what people mean when they ask whether a misted rooflight can be fixed. It shows as a cloud or a film that cleaning cannot reach, because it is inside the unit. It can start at an edge or a corner and spread, or it can sit in the middle of the pane.

So the first job is telling the two apart. Wipe the inner face of the glass. If the mist wipes away, it was condensation in the room, and better ventilation is the answer. If it does not, it is inside the unit. Night-time condensation on the room side is common on cold glass, and it is a separate matter from a failed seal.

It is a new sealed glass unit fitted into the frame already in the roof, and it depends on a sound frame and on the old unit coming out cleanly. The frame, the upstand or kerb and the finishes round the opening stay where they are, which is why people look at this route before pricing a new rooflight.

The new glass carries the glazing you choose rather than the glazing you had. The decision between this route and a whole new rooflight turns on the frame, the upstand or kerb and the way the glass is held, and the guide to sealed unit or whole rooflight takes that choice step by step.

Neither route is a rush job, and the survey gives you the time to compare what each would leave in place and what each would change.

A whole new rooflight is the sounder job if the frame is damaged or the upstand around it needs attention anyway, and the guide above sets out the rest of that choice. A tired frame holding new glass can mean paying for the same access twice.

It is also the answer when you want something different. Electric opening, a different size, a blackout blind for a loft bedroom or better glazing all come with a new unit. Since the glass reads black at night and mirrors the lamp, a blind can be easier to plan in at this stage than to add to a rooflight already in the roof.

See what replacing the whole rooflight involves, and the misted rooflight cost answer sets out what moves the price of each route.

Approved Document L (Wales) is guidance. It says a replacement rooflight should meet 2.2 W/m²K, and a replacement roof window 1.4 W/m²K or Window Energy Rating band B. In Wales, a rooflight that is new to the roof will generally need approval from building control. A glass-only swap that leaves the old frame in place falls outside building work for the purposes of the energy rules, which is the reason the two routes are treated differently.

Where the work is notifiable, the Building Regulations notification is ours to make, through local authority building control or a registered building control approver. Our page on misted rooflights and Building Regulations in Wales sets out the detail, and the general guide to skylights and Building Regulations in Wales takes in the rest.

At the survey we look at the rooflight from the room and from the roof, check the frame and the way the glass is held, and say which of the routes it allows. A fixed written quote follows, and no price is given before the survey.

Pictures of the misted unit taken in daylight, and sent on WhatsApp at 07880 284133, show us how far the cloud has spread. The survey form arranges the visit, and the survey costs nothing. Email also works, at info@supremeskylightsnewport.co.uk, if you would rather write at length about the roof and the room, the age of the rooflight and how long the mist has been there. Any of that helps us judge which route to look at first.