What is a roof lantern?

What it does that a flat unit does not

It catches light from more directions. Sloped panes facing four ways pick up light through more of the day than a single horizontal pane.

It sheds water and dirt. The pitch means rain runs off rather than sitting, so it stays cleaner and self cleaning coatings actually work.

It gives the room height. The volume above the ceiling line is a real architectural effect that a flat unit cannot produce.

What it costs you

More structure, because it is heavier and taller. More cost, both in the unit and often in a steel beneath it. And more height above the roof, which occasionally matters under permitted development.

Where it belongs

Over a kitchen extension, a dining space or a central living area where the room is the main space in the house. Over a utility or a bathroom, a flat rooflight does the job for a fraction of the money.

Full detail on the roof lantern installation page.

A pitched glazed structure on a flat roof

A roof lantern is a framed structure standing above the plane of a flat roof, glazed on all its sloping faces and usually rectangular in plan with a ridge running along it. It sits on a kerb built up from the roof deck.

It is quite different from a flat rooflight, which lies in the plane of the roof. A lantern adds height and volume to the room below as well as light.

What it gives you that a flat rooflight does not

Light from more than one direction. The sloping faces face different ways, so the room stays bright as the sun moves round rather than having one good hour. On an overcast day it also collects from a wider arc of sky.

Volume. A flat ceilinged room with a lantern gains real height at its centre, which changes the character of the space in a way glazing alone does not.

Architecture. On a larger extension a lantern reads as a designed element rather than as a hole in the roof.

Self cleaning. The pitch, typically 15 to 25 degrees, means rain sheds and carries dirt away. A near flat pane does not, which is why flat rooflights need cleaning more often.

What a lantern demands in return

Structure. A lantern is heavy and the opening has to carry it. On a new extension that is designed in. Retrofitting into an existing flat roof means a structural engineer and frequently steel, and that is usually the largest line on the quotation.

Proportion. On a small extension a lantern can look out of scale, and the honest test is the ceiling: where the room is small or already vaulted, flat rooflights do the same job for less.

Heat. A large glazed structure gains heat readily. Solar control glass is close to essential on any south or west facing lantern, and an opening vent at the highest point lets accumulated heat leave.

Lead time. Manufactured to your dimensions, so several weeks from order and longer for a large or unusual configuration.

The kerb

What makes the installation work. At least 150mm of upstand, the deck falling away from it, rigid insulation on its outer face, and a continuous vapour control layer sealed to the frame.

On a lantern the kerb is doing more work than under a flat rooflight, because it carries the structure as well as weathering the opening.

What to send us if you are considering one

A photograph showing how the flat roof meets the house, a rough measurement of the room below, and if you know it, which way the joists run.

That last point changes the answer more than the size of the lantern does. An opening set within the span of existing joists rather than cutting across them frequently avoids steel entirely.

We will give an indicative range by email from those, free and without an appointment, and we will tell you honestly whether a lantern or two or three flat rooflights suit the room better.

We will not fix a price without a survey, because the fall on the existing roof and the structure below it are the two things that decide the cost and neither is visible in a photograph from the ground.

The form

A glazed structure rising from a flat or shallow roof, with sloping glazed sides meeting at a ridge or an apex, set on a kerb built up from the roof deck.

It is distinguished from a flat rooflight by having pitch and volume. A flat rooflight is a plane in the roof; a lantern is a form standing above it, with a shape that reads from the garden and an interior that opens the ceiling upward.

What it is for

Getting daylight into the middle and back of a deep plan.

A single storey rear extension has a specific problem: it is deep, its only walls are at the edges, and the far end against the original house gets nothing. A lantern puts light exactly where no window can reach.

It also adds perceived height. The ceiling opening up over a table or an island changes how a room feels in a way that a flush rooflight does not.

How they vary

Frame material. Aluminium, timber, or timber inside with aluminium capping outside, which is the common compromise between internal warmth and external durability.

Division. Fewer, larger panes look contemporary and perform better thermally. Many small panes look traditional and have far more frame, which costs more and loses more heat.

Pitch. Steeper sheds water and dirt better and looks traditional. Shallower is more discreet and more contemporary.

Opening vents, which are worth having because hot air collects at the top of the room, which is inside the lantern.

What always applies

Made to measure, with a lead time of weeks. Structural design and usually steel. A kerb built square, level and insulated. And a survey to the finished kerb before ordering.