The answer
Choose a flat rooflight when the extension is small, the ceiling is low and you want a clean roof. Choose a roof lantern when you have height to gain and enough roof around the opening. Both bring daylight from straight above, so the decision rests on the shape of the room, not on whether the light is good.
What each one does for a small room
A flat rooflight is a pane of glass on a low upstand. It brings light down into the room and keeps the roofline quiet. A roof lantern is a glazed structure that rises from a flat roof, with sloping sides. It brings light in from several angles and lifts the ceiling into the space above.
In a small extension, both solve the same problem. Doors and side windows look out on fences, walls and the people next door. Straight up is clear, so a skylight gives the room the one view nothing blocks.
The difference is how they do it. A flat pane is a window onto the sky. A lantern is closer to a small glass room that sits on top of the real one, and that changes how the space feels as well as how bright it is.
Think of the garden too. A lantern gives a view of treetops and passing clouds from an angle, while a flat pane gives a view straight up. At night a lantern can glow gently from outside if the room is lit, and a flat pane reads as a quiet dark square.
Where the ceiling is low
A small extension can have a low flat roof with limited space between the ceiling and the covering. A lantern needs room for its upstand and for the frame to sit properly. If that space is tight, a flat rooflight is easier to fit and calmer on the roof.
Where the structure allows, a lantern adds height to the room, because the ceiling opens up into the glass. That can make a small kitchen feel larger than its footprint. We check what the structure can carry at the survey and tell you plainly which option works.
Neighbours matter as well, and so does the view from the upstairs landing. A lantern rises above the roof, so it is worth looking at how it will sit against the boundary and the windows above. A flat rooflight barely changes the outline of the extension, which is why it is the lighter-touch choice on a tight plot.
The table compares the two on the questions that decide it for a small extension.
| Question | Flat rooflight | Roof lantern |
|---|---|---|
| Roof space needed | Little | More around the opening |
| Effect on ceiling | Stays flat | Lifts into the glass |
| Seen from above | Low and quiet | More of a feature |
| Opening vent | Available | Available |
Light across the room
A flat pane drops a clear block of light straight down. Put it over a worktop and that area is bright. A lantern spreads the light around its sloping sides, so it reaches the middle and back of the room more gently.
If the room is long and narrow, two flat rooflights can light it evenly. If it is nearly square, a single lantern in the centre can suit. A skylight over a dining table, a reading corner or a sink each does a slightly different job, so think about where you stand and sit before you think about glass.
Size matters too. A small extension rarely has room for a large lantern, and an oversized one can overpower a small roof. A well-judged flat pane, or a pair, can give better balance than a lantern squeezed into too little space.
Our guide to roof lantern or flat rooflight compares the two for larger rooms, and the lantern size guide shows how size is worked out.
Heat, glare and fresh air
Both types come with insulated sealed units, and both can have solar-control glass if the roof faces south. Approved Document L sets a heat-loss ceiling of 2.2 W/m²K for rooflights in existing homes, and the glass we fit is chosen to meet it.
A small room warms quickly in summer, so ventilation is worth thinking about early. Either type can have an opening vent, through which warm air escapes from the top of the room. A lantern has more glass area, so it benefits more from solar-control glazing and a blind.
Look, planning and cost
Seen from upstairs windows or next door, a lantern is a visible feature, while a flat rooflight is hardly noticed. Neither choice is wrong. It is a question of what you want the roof to say.
Planning depends on your house and street, so begin with our planning guide. A lantern also needs more glass and more build than a flat pane, which moves the cost. The guide to flat rooflight costs sets out what changes a quote.
Make the choice at the survey
The quickest route is a free survey. The roof is measured, the room below is looked at and you are told which option fits. A written quote follows with a figure that stays put on the day.
Fitting is a short job and the inside is left finished. A ten-year workmanship guarantee comes in writing, and the Building Control notification is dealt with where it is needed. Send photos by WhatsApp on 07880 284133, or read more on the flat roof rooflights hub.
Small extension questions
Can a small extension take a lantern?
Only if there is enough roof around the opening. The structure and the space for the upstand decide it, and we check both at the survey.
Is a flat rooflight cheaper than a lantern?
A flat pane is a simpler build, so it tends to cost less. The quote is fixed in writing after the survey.
Will a lantern make a small room too bright?
Not if the glass suits the roof. Solar-control glass and a blind keep a south-facing room comfortable, while an opening vent releases warm air.
