In brief
Often, yes. If the lantern frame is straight, sound and free of corrosion or rot, new glazed units can be made to the size of the existing openings and fitted into it, which saves replacing the whole structure. If the frame has moved, the finish has failed or the kerb beneath it is worn, a new lantern is the better route. A survey tells us which applies.
- A sound, square frame can take new sealed units made to its measured openings
- Reglazing keeps the existing lantern, its shape and its position on the roof
- A distorted frame, failed finish or worn kerb points to a new lantern
- The unit sizes come from measuring the frame, not from the old glass
- Reglazing and replacement have different Building Regulations positions
When reglazing makes sense
A roof lantern is a glazed frame sitting on a kerb, usually aluminium, sometimes timber, with a ridge, hips and bars that carry the glass. The glass is the part that most often gives out. Sealed units cloud when the edge seal lets moist air in, a pane can crack, and older lanterns with single or early double glazing can fall well short of what is available now.
If the bars and ridge are still straight and the finish is sound, there is no reason to throw away a good frame because the glass has failed. A frame that has stayed true can take new units, and the lantern keeps its shape, its position and its look from inside the room. That is often the neater job, with less disruption to the ceiling and the roof covering round the kerb.
What we check on the frame
The survey is about the frame as much as the glass. We look at the following before we say yes to reglazing.
- Whether the ridge and hips are straight along their length and the corners are square
- Whether the bars carry the weight of new, heavier glass without bowing
- The condition of the finish on aluminium, or of the timber if the frame is wood
- Whether the glazing gaskets and drainage channels are intact and clear
- Whether the joint between the lantern and the kerb is sound
Modern double glazing is heavier than the glass in an old lantern. A frame designed for thin single panes may not take the extra weight, and if the bars flex when pressed, a new lantern is a safer choice. We tell you what we found and why in the written quote, not in a sales conversation on the roof.
Measuring for new units
New sealed units are made to order, so the measurements matter. We measure the openings between the bars on site, not the old glass, because old glass is often cut slightly small and may not show the true size of the rebate. Each opening on a lantern can differ by a few millimetres from its neighbour, particularly in an older frame, so every unit is measured and labelled to its position.
The unit is then made by the glass supplier to those sizes. The quote names the glazing build-up, any coating you choose, and the lead time, which the maker sets and the order confirms. Lead time is the main wait on a reglazing job, and we plan the fitting date around it. Our page on how long a rooflight replacement takes covers the wait and the day itself.
When a new lantern is the better choice
Some frames are better replaced. Aluminium that has pitted or lost its finish, timber that has softened, joints that have opened, and bars that have moved out of line all point the same way. Fitting new glass into a tired frame means the new units sit in a structure that will fail before they do.
The kerb is the other consideration. A kerb that is too low, cracked or damp will not suit a new lantern or a reglazed one, and the kerb sits under the roof covering, so putting it right is a job for the roofer as well. If the roof is due to be re-covered, replacing the lantern at the same time is usually sensible, and our page on replacing a rooflight during a re-roof sets out how that is planned.
A new lantern also lets you change the glazing, the frame finish or the size within the existing kerb. Our guide to roof lanterns covers what is available.
Building Regulations for each route
The two routes are treated differently. Replacing only the sealed glass units in a lantern frame you keep is not notifiable. A whole new lantern counts as a controlled fitting, so it must be notified, and under Part L a rooflight in an existing home must achieve 2.2 W/m²K.
We deal with that notification ourselves when a job is notifiable. The page on rooflight replacement and the Building Regulations explains the rule, and it is worth reading before you decide how far to go with the lantern you have.
Getting a reglazing quote
A free survey is the starting point. We measure the frame and the openings, check the kerb, and send a written quote that lists the units, the glazing, how long the maker needs and what your builder or roofer must provide. Where the choice between reglazing and replacing is close, we can price both so you see the difference.
Reglazing a lantern is a replacement job, so it comes under our misted rooflight replacement work. If your lantern has gone cloudy, the page on why a rooflight mists between the panes explains what has happened to the glass. We then agree the fitting day with you, so access, the interior and the roof covering are ready when the new glass arrives.
Related questions
- Can the glass be changed to a different type?
- Yes, within what the frame can carry. Units can be made with a different coating, such as solar control, if you want less heat in a south-facing room. The quote names the glazing, and we confirm the frame can take the weight before the order goes in.
- Will the lantern look the same afterwards?
- Yes, because the frame stays. The bars, ridge and kerb are unchanged, so the outline on the roof and the view from inside the room are the same. Only the glass is new.
