What is a roof lantern?
A roof lantern is a raised, pitched glazed structure that stands on a flat roof. Glazing bars run from a perimeter frame up to a ridge, glass sits between them, and the whole assembly is bedded onto a kerb built off the roof structure. From the room below it reads as a small glass roof rather than as a window in a ceiling.
That is the definition. What follows is everything the definition leaves out: the parts it is made from, the words a supplier will use for each of them, and the reasons a lantern gets chosen ahead of a flat panel of glass set into the same roof.
A lantern in its parts, from kerb to ridge
Start at the bottom. The base frame, often called the eaves beam or the ring beam, is a continuous aluminium or timber section that sits on the kerb and carries everything above it. Rafter bars rise from that frame at a set pitch and meet a ridge bar at the top. On a hipped lantern, hip bars run diagonally from the corners of the base frame to the ends of the ridge.
Glass is set into each bay between the bars on a gasket, then held by a pressure plate and covered with a snap-on capping that hides the fixings and sheds water off the bar. At the ends of the ridge a finial or an end cap closes the section. The visible aluminium is therefore two layers: the structural bar and the cosmetic capping over it.
What separates a lantern from a flush unit
Height and geometry. A flat rooflight is a single plane of glass more or less parallel with the roof it sits in, so from the garden it reads as a dark rectangle and nothing more. A lantern stands two hundred to six hundred millimetres proud of the roof surface and presents four or two sloping faces to the sky.
The practical difference is how the light behaves. A single horizontal plane gives a fairly constant pool of daylight. Sloping faces on different bearings pick up sun at different times of day, so the room brightens and shifts as the sun moves round. If you want the quieter option, a flat rooflight does that job instead, and the two are compared properly on that question.
The upstand it stands on, and why it is not part of the lantern
Almost every misunderstanding about lantern pricing starts here. What a supplier sells is the aluminium and the glass. What keeps the water out is the kerb underneath, and that is built on site as part of the roof.
The kerb is a timber upstand framed off the joists or off the deck, insulated, decked and then wrapped by the roof covering, which is dressed up its sides and terminated at the top. The industry figure is one hundred and fifty millimetres from the finished roof surface to the top of the kerb. The lantern base frame lands on that top edge, is bedded on a continuous seal and mechanically fixed down.
Hipped, gable and the shapes on offer
Four shapes cover nearly all domestic work. A hipped lantern has four sloping faces meeting a ridge, which is the familiar form and the one that suits a rectangular extension. A gable lantern has two sloping faces and vertical glazed triangles at each end, which throws more light in at low sun angles and reads as more contemporary.
A pyramid is a hipped lantern on a square footprint, so the ridge collapses to a single point. A lean-to slopes one way only, off a higher wall, and is the answer where a lantern has to sit tight against the back of the house.
The frame, and the three constructions
Aluminium is the common choice: thermally broken extrusions, powder coated, with bars slim enough to keep the glass area high. Timber lanterns are built from engineered softwood or hardwood, painted, with visibly chunkier sections. The third option is a hybrid, timber on the inside face and an aluminium capping outside, which gives a painted interior and no external upkeep.
Each has a place, and the choice usually follows the age of the building rather than the budget. The full comparison sits on aluminium and timber lanterns compared.
What the glass in a lantern has to do
Overhead glazing carries obligations that a vertical window does not. The outer pane is toughened so it fails safely under impact and thermal stress. The inner pane is normally laminated, so that if it breaks it stays bonded to its interlayer rather than falling into the room.
Beyond safety, the coating on the glass does the thermal work. A low-emissivity coating cuts heat loss outwards and a solar control coating cuts heat gain inwards, and on a lantern facing anything from south east to west the second one matters more than people expect. The specification detail is set out under lantern glazing and solar control.
Words you will meet on a lantern quote
The vocabulary is not standardised between suppliers, which causes more confusion than it should.
- Eaves beam or ring beam: the base frame that sits on the kerb.
- Rafter or bar: the sloping members between base and ridge.
- Capping: the clip-on cover over each bar. Its width sets how heavy the lantern looks.
- Self-supporting: the lantern needs no internal posts and carries its own loads to the kerb.
- External size: the footprint of the lantern base, which is usually the kerb outer size, not the glass area.
Ask which size a figure refers to before comparing two quotes. The gap between external, kerb and clear aperture on the same lantern can be a hundred millimetres or more each way.
Where lanterns turn up across Essex housing
The pattern is consistent across the county. Victorian brick terraces in Chelmsford, Colchester and Maldon get a flat-roofed rear extension or a side return infill, and a lantern is what stops that space reading as a corridor. Interwar semis in the commuter towns often already carry a flat-roofed rear addition, which is a ready-made platform.
On the newer estates at Beaulieu Park, Great Notley and South Woodham Ferrers, the flat-roofed garden room or the rear extension off a trussed main roof is the usual home for one. On Canvey and around the Blackwater villages, single-storey bungalows and weatherboarded cottages take lanterns well, because the roof is low and the extra height is not fighting anything above it.
How a lantern gets from a decision to a fitted structure
The order is always the same. A survey settles the roof structure, the covering, the fall and the ceiling line below. The opening is formed and the kerb is built. The lantern is delivered as a kit of bars, glass and cappings, then assembled on the kerb in a few hours by two fitters.
Sunspire fits new lanterns and replaces glazed structures that have reached the end of their working life, with the Building Control notification handled as part of the job. The wider process, from first photograph to finished reveal, is set out on roof lantern installation, and the things that move the figure are covered under costs.
Tell us about your roof
We start with the building, the covering and the slope. Then we tell you what will suit it, and what it will cost, as a fixed written number.
- Surveyed before it is priced
- 10-year workmanship guarantee
- Building Control notification handled
- New installations and replacements