A roof lantern is a glazed structure that stands above the plane of a flat roof, built from a frame of rafters rising from a perimeter to a ridge, with glass in each of the sloping faces. It sits on a kerb built into the roof. Where a flat rooflight is a pane laid into the surface, a lantern is a small pitched roof made of glass.
The shape
A ridge, two slopes and two hipped ends on the usual arrangement.
Glazing bars run from an eaves beam at the perimeter up to a ridge beam, and the ends are hipped in, so the whole thing reads as a miniature pitched roof standing proud of the flat one.
Square plans give a pyramid instead, with four faces meeting at a point.
The frame
Aluminium on almost everything current.
Thermally broken aluminium sections carry the glass, resist the loads and hold their finish, and the slimness of the bars is what separates a good lantern from a clumsy one.
Timber and steel lanterns exist, usually on period or bespoke work.
The kerb
Not part of the lantern, and this catches people out.
A lantern is designed to sit on an upstand built by the roofer or the builder, and the height, insulation and weathering of that upstand are a separate piece of construction.
How it is built is on how high should a rooflight kerb be.
The glass
Sealed units, usually with something specified into them.
Because a lantern faces several directions at once and takes a great deal of sky, solar control is normal rather than optional, and toughened or laminated panes are used according to position.
What to ask for is on what is the best glass for a south facing rooflight.
Why the shape gives more light
Because it collects from several directions.
A flat pane sees the sky directly above it. A lantern has faces looking east, west, north and south as well, so it gathers light through the whole day rather than at midday.
That is what people are describing when they say a lantern feels different.
What it does to the ceiling
Opens it upward.
Because the structure rises, the ceiling of the room continues up into the lantern rather than stopping at a pane, and the room reads as taller as well as brighter.
It is the reason a lantern suits a kitchen extension.
Where it is used
Almost always over a single storey rear extension.
A kitchen or a kitchen diner with a flat roof is the classic position, and the lantern goes roughly over the middle of the room or over the island.
Standard against bespoke
Both are ordinary and they suit different jobs.
Standard sizes are made to a set of common dimensions and are quick and economical. Bespoke lanterns are made to the opening, which matters where a room dimension is awkward or a proportion has to be right.
Hipped against gabled ends
A choice worth making deliberately.
A hipped end slopes in like the rest of the roof. A gable end is vertical glass, which lets in more light at low sun angles and gives a different, more architectural line.
The ridge
Where the proportion is decided.
A long low ridge reads quietly against a house. A steep one reads as a feature, and a very steep one on a small plan looks top heavy from the garden.
What pitch suits is on what pitch should a roof lantern be.
Opening versions
Available, usually as one or two opening panes within the structure.
An opening face gives ventilation at the highest point of the room, which pulls cooking heat and steam out efficiently.
What that involves is on can a roof lantern be opened.
How it is fixed down
Through the eaves beam into the kerb.
The perimeter frame is bedded and mechanically fixed to the top of the upstand, and the covering is dressed up the kerb and under the frame so water never reaches the fixing line.
Where the water goes
Down the glass, into channels in the bars, and out at the eaves.
Glazing bars carry drainage channels that take any water passing the outer seal down to the perimeter and out over the kerb.
It is a drained system rather than a sealed one, and that distinction matters.
Against a flat rooflight
A different product for a different intention.
A flat rooflight is quiet and modern and sits in the plane. A lantern is a feature and stands above it, and one is not a better version of the other.
The comparison is on what is the difference between a roof lantern and a skylight.
Against a roof window
Not comparable at all.
A roof window goes into a pitched slope between rafters. A lantern stands on a flat roof. They solve different problems on different roofs.
What it weighs
Enough that the roof structure is part of the conversation.
A glazed structure of any size is a substantial load, and the deck, the joists and the trimming around the opening are designed for it rather than assumed.
What it costs in heat
More than the same area of insulated roof, inevitably.
Glass is a worse insulator than a roof build up, and a lantern has more glass area than its plan area because of the slopes.
The figures are on how much heat do you lose through a roof lantern.
Where the name comes from
From the buildings that had them first.
Victorian and Edwardian houses used glazed lanterns over stairwells and back additions to get daylight into the middle of deep plans, and the modern product is a descendant of those.
What it does to the sound of a room
Something, and it is worth knowing before rather than after.
A large area of glass overhead reflects sound rather than absorbing it, so a kitchen with a lantern and hard floors can feel livelier than the same room without one.
Soft furnishing elsewhere in the room is the usual answer.
Rain on the glass
Audible, and most people like it.
Glass over a room carries the sound of heavy rain into it in a way an insulated roof does not, and it is one of the reasons people give for wanting one.
How we treat it on a lantern
We treat the kerb as part of the job rather than as somebody else’s problem, because a well made lantern on a poorly built upstand is where the complaints come from.
The whole picture is on the roof lantern installation page.
Thinking about this job? We survey across Worthing, West Sussex and the South Downs and give you a fixed price before any work starts, with a 10-year workmanship guarantee.