Most single-storey flat-roofed extensions need some form of rooflight simply because the depth of the room makes side windows alone insufficient for daylight in the middle of the space.
The choice between flat rooflights and a lantern isn't really about which lets in more light in total — both can be sized to bring in plenty. It's about how that light is distributed and what the roof looks like from outside.
How the light lands in the room
A flat rooflight throws a fairly direct column of light straight down, which works well positioned over a kitchen island or dining table where a defined pool of light is wanted.
A lantern, because of its pitched sides, brings light in from multiple angles through the day as the sun moves, giving a softer and more even spread across a larger area of ceiling and room below it.
Appearance, inside and out
From inside, a lantern reads as an architectural feature — the upstand and glazed pyramid are visible and draw the eye upward, which suits a traditional or period-influenced extension design.
A flat rooflight all but disappears into the ceiling from below, which suits a deliberately minimal, contemporary design where the roof shouldn't compete with anything else in the room.
Cost and roof detailing
A lantern is a heavier, more complex structure with more junctions, more glazing bars and generally a bigger footprint, so it costs more to supply and fit than a flat rooflight of a similar glazed area, and the upstand and flashing detail take longer to get weathertight.
Flat rooflights are simpler single units that drop onto an upstand, with fewer junctions to seal, which is part of why they've become the default choice on contemporary flat-roof extensions.
Practical considerations
Both need an upstand built to the correct height above the finished roof covering to avoid ponding and water ingress at the frame — this is a detail that gets skipped on poor-quality jobs and causes leaks within a few years.
Opening vents can be specified in either type for ventilation, but the mechanism and cost to add powered opening vents is usually higher on a lantern because of its size and the number of glazed faces involved.
Common questions
Which is better for a very deep extension?+
A lantern's wider spread of light generally serves a large, deep open-plan space better than several smaller flat rooflights, though a run of well-placed flat rooflights can achieve a similar overall effect at lower cost.
Do lanterns overheat a room more than flat rooflights?+
A lantern has more glazed surface area for the same footprint, so solar gain can be higher unless the glass specification includes solar control coating. This should be specified deliberately on a south-facing roof regardless of which type is chosen.
Can I add a lantern to an existing flat rooflight opening later?+
Usually not without altering the upstand and roof structure around it, since a lantern typically needs a different upstand height and additional support for its heavier frame. It's worth deciding at design stage rather than retrofitting.
Ask us to spec the rooflight for your extension
We'll size and position either option correctly for your room and give you a written quote showing the roof detailing involved.