Are roof lanterns better than flat rooflights?

Where a lantern wins

Presence. The volume above the ceiling line is a real architectural effect that a flat pane cannot produce. In the main living space of a house it is the difference between a lit room and a room people remark on.

Light through the day. Sloped panes facing four directions catch light through more of the day than a single horizontal pane.

Staying clean. The pitch sheds water and dirt, and self cleaning coatings work properly on it.

Drainage. Water leaves rather than sitting.

Where a flat rooflight wins

Cost. Substantially cheaper for the same glass area, both in the unit and often in avoiding a steel.

Height. Almost nothing above the roof plane, which matters under permitted development and on a roof already close to a limit.

Discretion. On a modern flat roofed extension a flush pane often looks more considered than a pitched structure.

Flexibility. Two or three flat units distribute light across a long room better than one lantern, and they suit narrow roofs a lantern cannot fit.

The practical rule

Lantern over the main living space, dining area or kitchen island where the room is the heart of the house. Flat rooflights over utility rooms, bathrooms, hallways and anywhere the job is simply to get daylight in.

And in a long kitchen-diner, two flat rooflights frequently beat one lantern for usable light, while one lantern beats both for how the room feels. That is a genuine choice rather than a technical one, and it is worth pricing both.

Different rather than better

They solve different problems, and the honest test is what the room needs rather than which product is superior.

What a lantern gives you

Volume. A flat ceilinged room gains real height at its centre, which changes the character of the space in a way glazing alone 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.

Self cleaning behaviour. A pitch of 15 to 25 degrees sheds water and carries dirt away. A near flat pane does not, which is why flat rooflights need cleaning more often.

Presence. On a larger extension it reads as a designed element rather than a hole in the roof.

What flat rooflights give you

Cost. Considerably less, particularly on a retrofit, because they are lighter and frequently need far less structural work.

Even light in a long room. Two or three units in a row light a narrow space better than one lantern in the middle, which gives a bright centre with the ends darker.

Discretion. They sit in the plane of the roof, which matters where the extension is overlooked from an upper window or where planning is a consideration.

Independent failure. A seal failure in twenty years means replacing one modest unit rather than a large and expensive pane.

The honest test

Look at the ceiling. Where the extension has a flat ceiling and normal head height, a lantern gives you volume you do not otherwise have and it is worth the money.

Where the ceiling is already vaulted, or the room is small, or the room is long and narrow, flat rooflights do the same job for less and frequently do it better.

What is the same

The kerb decides whether either lasts: 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.

Solar control glass belongs on both where they face south or west, and an opening vent at the highest point matters on both.

The combination

On a large extension, a lantern over the main space with separate flat rooflights over a galley or a utility area frequently beats either on its own.

How to decide for your room

Stand under the ceiling. If it is flat, at normal head height, and the room is broad rather than long, a lantern gives you volume you do not otherwise have and it is worth the money.

If the ceiling is already vaulted, or the room is small, or the room is long and narrow, flat rooflights do the same job for less and frequently do it better.

Then look at the roof. On a retrofit, whether the joists run with or across the proposed opening changes the structural cost more than the choice of product does.

Send a photograph of the room, one showing how the flat roof meets the house, and a rough measurement of the floor area. We will tell you honestly which we would recommend and why, and on a long room that is frequently the cheaper option.

They do different jobs

A flat rooflight is a plane set into the roof. It delivers daylight efficiently, sits quietly, and on a contemporary extension it is frequently the more appropriate form.

A lantern is a form standing above the roof, with pitch and volume. It delivers daylight and it changes how the room feels, because the ceiling opens upward.

Where the lantern wins

Perceived height. The ceiling rising over a table or an island is an effect a flush rooflight cannot produce.

Shedding water and dirt. Pitched glass stays clear. A horizontal pane holds water, dulls over the years, and defeats self cleaning coatings.

Ventilation. An opening vent at the apex is at the highest point in the room, which is where hot air collects.

Suiting a traditional building, where a flush contemporary rooflight can look like an implant.

Where the flat rooflight wins

Cost, generally, and particularly at larger sizes.

Thermal performance. A lantern has rafters, hips and a ridge, so a great deal more frame per square metre, and frame is where a lantern loses heat.

Discretion. Where permitted development height is tight, or where the roof should not have a form standing on it, flat is the answer.

Rain noise, marginally, though both benefit from acoustic laminate.

How to choose

Look at the room, not the catalogue. A deep plan with a low ceiling that needs lifting wants a lantern. A generous ceiling that only needs light wants a flat rooflight, probably a larger one, for less money.