Lanterns versus flat rooflights, sizing rules of thumb and what matters in the frame and glass.
Short answer: a roof lantern is a raised, pitched glazed structure that sits on an upstand in a flat roof, bringing daylight into the room from every angle. It is the usual choice for kitchen extensions, orangeries and flat-roofed rooms that feel dark, and a slim, thermally broken aluminium frame keeps heat loss and condensation down.
Before choosing a size, it is worth confirming the flat roof itself is sound, because a lantern is only as watertight as the roof it sits in.
A flat rooflight is a single pane laid almost level with the roof. A lantern rises above it with pitched sides, which gives more glass area, sheds rain better and creates a focal point from inside. Lanterns also make a room feel taller.
There is no single rule, but most designers size a lantern relative to the room below rather than the roof. Too small and it looks like an afterthought; too large and the room can overheat on sunny days. As a general guide, a lantern that leaves a comfortable border of solid ceiling around it tends to look balanced.
Our lanterns use slim aluminium profiles to maximise glass area, with a thermal break to limit heat loss and condensation. Glass options typically include solar control and self-cleaning coatings, which help on south-facing roofs and on lanterns that are hard to reach.
A lantern sits on a raised kerb, called an upstand, which is built into the flat roof and waterproofed with it. If the roof covering is near the end of its life, it makes sense to renew it at the same time rather than cutting into a membrane that will soon need replacing.
Lanterns can be added to an existing flat roof if the joists can be trimmed to form the opening. That is a structural change, so it should be checked before a size is fixed.
Heat rises, so a lantern at the highest point of a room is a natural place to let warm air out. Many lanterns can be specified with opening vents, operated manually or electrically, which help keep a kitchen extension or orangery comfortable on warm days. Where a lantern cannot open, trickle vents or opening windows and doors elsewhere in the room do the same job.
Rain sensors that close electric vents automatically are worth considering if the lantern is out of reach.
Send us your room size and roof details and we will quote for a lantern to suit. We beat any like-for-like quote.
A skylight or flat rooflight is a single pane close to the roof line; a lantern is a raised, pitched structure with more glass that lets light in from all sides.
Often yes, if the joists can be trimmed to form the opening. The roof covering around it should be in good condition.
A thermally broken aluminium frame and modern double glazing keep condensation to a minimum. Good room ventilation helps too.
It can on south-facing roofs if it is oversized. Solar control glass and sensible sizing help.