Flat rooflight vs roof lantern: which is right for your extension?

A flat roof extension showing both a roof lantern and a flat rooflight, highlighting two different approaches to roof glazing.

When planning a flat roof extension, one of the biggest design decisions is how to bring natural light into the space below. For most homeowners and builders, the choice usually comes down to a roof lantern vs flat rooflight.

Both do the same basic job, but they behave very differently once installed. Understanding those differences early can save time, cost, and disappointment later on.

This guide explains how to choose between the two based on real-world use — not brochure claims.

Flat rooflight vs roof lantern: the fundamental difference

The simplest way to think about it is this:

• A roof lantern adds height and architectural presence above the roof

• A flat rooflight sits flush or near-flush within the roof surface

Neither is “better” by default. The right choice depends on the roof, the room below, and what you want the space to feel like day to day.

When a roof lantern makes sense

Roof lanterns are often chosen where light needs to travel further into the room, or where the lantern itself is part of the design.

They tend to work best when:

• The room below is large or open-plan

• There’s enough roof area to accommodate the lantern comfortably

• Ceiling height allows the lantern to be visually appreciated

• The extension is intended to feel architectural rather than minimal

Because lanterns introduce vertical glazing, they can help pull light deeper into the space, especially in kitchen-diner extensions.

Systems like Korniche roof lanterns are purpose-designed for flat roofs, which helps keep internal sightlines slim without relying on heavy framing.

Internal view of a roof lantern showing how light spreads into an open-plan extension.

When a flat rooflight is the better option

Flat rooflights are often chosen for cleaner lines and a more understated finish.

They’re usually the better choice when:

• The extension has a lower ceiling height

• Planning restrictions limit roof features

• You want light without visual dominance

• The design prioritises simplicity and minimalism

Flat rooflights also work well in narrower rooms or spaces where the light opening needs to be carefully controlled.

Internal view of a flat rooflight showing a clean ceiling line and controlled natural light.

Performance isn’t just about the glass

It’s easy to compare lanterns and rooflights purely on glass specification, but that only tells part of the story.

What really matters is:

• How the frame is thermally broken

• How the unit interfaces with the roof build-up

• How loads are transferred into the structure

• How seals perform after years of movement

Both lanterns and flat rooflights are systems, not just pieces of glass dropped into a hole. Poor detailing at this stage is where most long-term issues begin.

Installation considerations that often get overlooked

From an installation point of view:

• Roof lanterns require more structural planning but offer visual impact

• Flat rooflights are simpler to integrate but demand precise detailing

Neither option should rely on excessive sealant or on-site modification. Well-designed systems are engineered to install predictably, regardless of who fits them.

External view of a flat rooflight installed flush to the roof surface, showing how it integrates with the roof build-up.

Which should you choose?

As a general rule:

• Choose a roof lantern if architectural presence and light spread are priorities

• Choose a flat rooflight if clean lines and restraint matter more

The right answer often becomes clear once ceiling height, roof structure, and room layout are properly considered.

Final thought

Most problems with roof glazing don’t come from the product itself — they come from choosing the wrong solution for the space.

That’s why getting advice before committing matters. At The Plastics Shed, roof lanterns and flat rooflights are supplied with guidance based on real installations, not assumptions.

If you’re still weighing up the options, understanding the difference now is far easier than correcting it later.