What is a roof lantern?

The short answer

A roof lantern is a glazed pitched structure that stands up off a flat roof: several planes of glass rising from a horizontal base frame to a ridge or an apex, carried on aluminium or timber rafters, and bedded on a timber kerb built above the roof surface. It is the only member of the rooflight family that adds volume to the room as well as daylight, because the glass leaves the plane of the roof and climbs. That is the whole definition. Everything else about it, the pitch, the shape, the frame material, the glass, follows from the fact that it is a small pitched roof made of glass sitting on top of a larger flat one. The full technical treatment is on the roof lantern installation page.

Three planes of glass and a ridge: the geometry that defines it

Take a rectangular opening in a flat roof, build a kerb round it, and stand a horizontal frame on the kerb top. From that frame, sloping rafters run up to a ridge extrusion along the long axis. At each end, diagonal hip rafters run from the ridge ends down to the corners, with shorter jack rafters between them. Glass fills every triangle and every trapezium.

That geometry is what makes a lantern a lantern rather than an angled window. There is no single plane and no single pitch you look through. Standing under it, you see sky in four directions at once, which is why a lantern lights the corners of a room that a flat unit of the same footprint leaves dim.

How it differs from the other glass that goes in a roof

Four products get called skylights in conversation and they are four different things on a survey sheet. A roof window sits in the plane of a pitched roof, in line with the tiles or slates, and comes in manufactured sizes with a matching flashing kit. A flat roof rooflight is one plane of glass at a shallow angle in a slim frame, made to your dimension, sitting on the same sort of kerb a lantern uses. A conservation rooflight is a slim steel frame designed to sit almost flush in a thick slate roof. A lantern is the only one of the four with a ridge.

What each glazed roof unit is for, side by side

Unit	Roof it goes into	Glass arrangement	What it gives the room
Roof lantern	Flat roof, on a kerb	Several sloping planes to a ridge or apex, typically at 20 to 30 degrees	Daylight from four directions plus 300 to 500mm of extra ceiling height
Flat roof rooflight	Flat roof, on a kerb	One plane, 5 degrees or so, or a low profile dome	Daylight with almost no change to the ceiling line, and a slimmer object on the roof
Roof window	Pitched slope, in the plane of the covering	One sash, opening on a centre pivot or top hinge	Daylight and a view out, plus purge ventilation and escape where required
Conservation rooflight	Pitched slope, set nearly flush	One pane with a central bar, cast or pressed steel frame	Daylight on a heritage roof without a modern object on the slope
Sun tunnel	Any roof, dome plus a reflective tube	No visible frame in the ceiling, only a diffuser	Daylight in a windowless room with no structural opening

Where a lantern and a slim flat unit are both possible, the choice comes down to whether the extra height is worth the extra object on the roof, and that comparison is set out on are roof lanterns better than flat rooflights.

Orangery roof, lantern and glazed link: what installers mean by each

The words drift in sales literature, so it is worth pinning them down. A lantern is a discrete glazed pitched structure on a flat roof, usually surrounded by a margin of that roof on all sides. An orangery roof is the same object used at a larger scale, often sitting within a deep insulated perimeter band with a plastered soffit, so the glass reads as a large lantern held inside a picture frame of ceiling. A glazed link is a run of glass joining two buildings, which may be a lantern shape or a simple pitched glazed roof landing on both walls.

A conservatory roof is a different animal again: glass or polycarbonate carried on lightweight bars down to a low eaves on three sides, with no flat roof underneath. Swapping one of those for a lantern on a proper insulated warm deck is a common piece of work and it is closer to building a new roof than to fitting a unit.

Why a lantern is always described with the kerb it stands on

The lantern does not weather the roof. The kerb does. It is a treated timber upstand standing at least 150mm above the finished surface of the waterproofing, measured at the high point of the fall, insulated on its outer face with rigid board so it is not a cold ring around the base of the glass, with the roof membrane dressed up the face and over the top.

That is why a lantern is quoted against a kerb dimension rather than an opening size, and why the kerb goes up, gets weathered and gets checked square and level before the frame is ordered. A base ring is manufactured square and will not sit down onto a kerb that is 8mm out on the diagonal.

What you notice from the room below

Two things surprise people. The first is the grid. A lantern is a framed object seen from directly underneath every evening, so the internal frame colour matters more than the external one, and a dark internal face reads as a strong lattice across a white ceiling. The second is the light after four o’clock in winter. Because the glass faces four ways, low December sun comes through one slope even when the sun is nowhere near overhead, and the room stays usable later than a single horizontal pane manages.

Where lanterns actually go in Gloucestershire

Almost never into an old roof. Cotswold stone slate is laid in diminishing courses on torched battens at 45 to 55 degrees, and a pitched glass structure has no business in a roof like that: the answer there is a flush conservation rooflight. Lanterns go on new and newer flat roofs.

In practice that means the flat roofed kitchen extension across the back of a Gloucester or Tewkesbury terrace, the single storey rear extension on the interwar semis at Longlevens and Hucclecote, the garden rooms and orangeries behind stone parapets in the wolds villages, the rear additions in the Cheltenham conservation areas where consent usually points at a dark painted timber frame, and the garage roofs turned into rooms on the Quedgeley and Bishops Cleeve estates.

What to send if you think a lantern is the right product

Email info@severnskylightsgloucester.co.uk with a photograph of the flat roof taken from an upstairs window looking down, a photograph of the room from inside with the ceiling in frame, the rough size of that flat roof from gutter to house wall, and the address. The postcode already says a good deal about the roof and the conservation position in this county. From there it is an indicative range by email, then a survey, then a fixed price and a date. Individual questions are answered under guides, and coverage town by town is on the areas pages.