Should you replace or repair an old roof lantern?
Leaks, discoloured polycarbonate and condensation: how to tell whether to repair or replace, and what replacing on the existing kerb involves.
Old lanterns, especially white uPVC ones with polycarbonate sheets, fade, leak and lose a lot of heat. Some problems can be repaired; many are cheaper to solve with a new lantern.
Signs it is time to replace
- Yellowed, cloudy or cracked polycarbonate panels.
- Repeated leaks at the glazing bars or ridge after resealing.
- Condensation between the panes of a double glazed unit, meaning the seal has failed.
- A room that is cold in winter and hot in summer under the lantern.
Is it the lantern or the roof?
Many leaks blamed on lanterns come from the upstand or the roof membrane around it. If the kerb is wet or the membrane is cracked at the upstand, a new lantern alone will not fix it. Inspect before deciding.
Can the new lantern use the old kerb?
If the kerb is sound, dry, level, square and to a size a new lantern can match, yes. Measure the outside of the kerb. If the kerb is rotten or too low, rebuild it and re-dress the roof at the same time.
Building regulations
In England and Wales a replacement rooflight in an existing home should meet the energy standard for replacements and is building work, so it is either self-certified by a competent person scheme installer or goes through building control.
Sources
Written by the Buy Roof Lanterns team. Last reviewed 19 October 2026. General guidance only; your designer, building control body or council confirms what applies to your project.