The short answer
A misted roof lantern can often take new glass panels in its existing frame, provided the bars, seals and kerb are sound and the panel thickness fits the bars. Where the frame is worn, leaking or poorly insulated, replacing the lantern as a whole is the better route.
Why a lantern mists
A roof lantern is glazed with several sealed double-glazed panels held in an aluminium, timber or uPVC frame of bars. Each panel is its own sealed unit, with a spacer and edge sealant like any other double-glazed unit, and each can fail separately. That is why one panel can mist while its neighbours stay clear.
The mist forms in the gap between the two sheets of glass when the edge seal lets damp air in, and it cannot be wiped away from inside or outside. Our answer on why a rooflight mists between the panes goes through the cause, and it applies to a lantern in the same way as to a flat rooflight, and equally to a roof window.
Reglazing against replacing the lantern
Reglazing means taking out the glass panels, usually from the outside, and fitting new sealed units into the same frame. The frame, the kerb and the roof covering stay as they are.
Two ways to deal with a misted lantern
Reglaze the panels
- Frame and bars
- Kept
- Cost
- Usually lower
- Disruption inside
- Usually less
- Best when
- The frame is sound and the panel size is standard for it
A glass-only swap is not notifiable work.
Replace the lantern
- Frame and bars
- Replaced
- Cost
- Usually higher
- Disruption inside
- Usually more
- Best when
- The frame is worn, leaking or has outdated glazing
A replacement of frame and glass has to be notified, and we send in the notification to Building Control.
Our guide to replacing a rooflight and the Building Regulations explains why the two jobs are treated differently. The hub on misted rooflight replacement covers the same choice for other kinds of rooflight.
What we check before reglazing
Not every lantern is a good candidate, and the survey is where that is decided. A reglazing quote depends on what is found in the frame and on the roof round it.
- The bars. They need to be straight, sound and free of corrosion or rot, and they must have a groove deep enough to hold a modern unit.
- The glazing seals and gaskets. Old perished seals are replaced with the new panels, and where the profile has hardened or shrunk the matching profile is not always available.
- The panel sizes. Each panel is measured on site, because the panels in a lantern are often different shapes, and a unit made to the wrong size will not seal.
- The kerb and the flashing. Staining on the plaster inside points to a leak at the base, which new glass will not cure.
- The ridge and the hips. These are the joints most likely to have opened with age.
If the lantern is an older one with single-thickness glass or narrow bars, the new panels may be thicker than the bars were made to hold. In that case a replacement lantern is likely to suit better than forcing new glass into the old frame.
How a reglaze is carried out
The work is done from the roof. The caps or glazing beads that hold each panel are taken off, the old unit is lifted out and the rebate in the bar is cleaned back. New gaskets go in where the old ones have hardened, and each new unit sits on small setting blocks, so its weight rests on the bar rather than on its own edge seal. The caps then go back on, and the ridge and hip covers are checked as they are refitted.
While a panel is out the room below is open to the sky, so we plan the job for a dry day and cover the floor and worktops underneath. Access is from a tower or from crawl boards laid on the flat roof, never by leaning on the glass, and the quote says which we will use.
The glass you can choose
Reglazing is a chance to improve the glass, not only to restore it. The options are the same as for a new lantern, and they can change how the room feels as much as how the lantern looks.
| Item | Standard double glazed | Solar control coated | Self-cleaning outer pane |
|---|---|---|---|
| Heat in summer | Warms a south or west room | Reduced | Similar to standard |
| Winter warmth | Good | Good | Good |
| Looks | Clear | Slight tint or reflection, depending on the coating | Clear |
| Cost | Lowest | Middle | Middle |
Our answer on solar control rooflight glass explains how the coatings work, and the quote shows each choice against each option, which lets you weigh them up.
What happens next
Book the free survey and we will inspect the lantern from the roof and from inside. After that the written quote puts reglazing and replacement next to each other, with several makers on offer when the roof permits, so you see what each route costs and what it leaves in place.
Where a whole replacement is the better choice, the quote covers the Building Control notification, the kerb and the finish inside. Book a free survey and we will say plainly which route we think suits the frame you have.
Related questions
Can only one misted panel be replaced?
Yes, a single panel can be swapped if the rest of the lantern is sound. The survey will show whether the other panels look as though they will follow, so you can decide whether to do them together.
Will new panels match the old ones?
The panels are made to the size of each opening, and the outer face can be matched closely in clear glass. A coating on only some panels would show, so we advise doing the whole lantern in one specification.
Does reglazing need Building Control?
A glass-only job is not notifiable. If the frame comes out too, the work is notifiable, and sending that notification is down to us.
Is the maker's warranty still valid on an old lantern frame?
That depends on the maker and the age of the frame, so we check it on site. New panels come with the maker's own warranty for the unit itself, and our workmanship comes with a 10-year guarantee of its own.