How to Choose the Best Glass for Your Roof Lantern

Size and orientation 

The larger the glazed area, the greater its influence on the light and temperature within the room.

A large roof lantern can transform an extension by bringing daylight deep into the space, but its position and orientation are important. A lantern exposed to strong direct sunlight may benefit from solar-control glazing, while a more shaded location may benefit from glass that prioritises maximum light transmission.

South- and west-facing rooms can experience stronger solar gain at certain times of day, whereas north-facing or heavily shaded extensions may receive considerably less direct sunlight. The surrounding property, trees and neighbouring buildings can also make a significant difference.

Clear or solar-control glass?

Clear glass is a good option where maximising natural light is the priority, particularly in rooms that receive limited direct sunlight.

Solar-control glass is designed to reduce the amount of solar energy passing through the glazing. This can help moderate heat build-up and glare while still allowing plenty of daylight into the room.

The appearance of solar-control glass should also be considered. Neutral solar glass provides a more understated appearance, while blue solar glass creates a more noticeable tint.

Glazing specifications vary between our roof-lantern collections. Our current timber ranges use high-performance self-cleaning double glazing with a Ug-value of 1.2 W/m²K as standard. Current Atlas aluminium stock lanterns are available with Solar Neutral or Solar Blue self-cleaning low-e glazing at 1.2 Ug, with a 1.0 Ug EcoPlus option also available on selected ranges. 

How the room will be used

The way you use the space should influence the glazing specification as much as the size of the lantern itself.

In a kitchen, dining room or family room that is occupied throughout the day, controlling excessive solar gain and glare may be particularly important. In a hallway, stairwell or other area where the main objective is simply to introduce more daylight, maximising light transmission may be the greater priority.

There is therefore no single glass specification that is right for every roof lantern. The glazing should be considered as part of the room as a whole.

Thermal performance and U-values

The U-value of a glazing unit describes how readily heat passes through it. The lower the U-value, the better the insulating performance of the glazing.

High-performance double glazing is now standard across our principal roof-lantern ranges. Our timber collections currently use glazing with a Ug-value of approximately 1.2 W/m²K, while selected aluminium systems can be specified with glazing down to 1.0 W/m²K. 

It is worth remembering that the quoted Ug-value relates to the glass unit itself. The overall thermal performance of the completed roof lantern also depends on the frame, glazing bars, thermal breaks and installation.

Triple glazing can also be considered on some bespoke designs where enhanced thermal performance is required, but it should not automatically be assumed to be the best solution for every project. Our made-to-measure ranges can accommodate both double- and triple-glazing options depending on the design. 

Toughened or laminated glass?

Thermal performance and solar control are not the only considerations when choosing roof-lantern glass. Because the glazing is overhead, the way a pane behaves if it breaks is also important.

Toughened glass is heat-treated to increase its strength. If it breaks, it shatters into relatively small fragments.

Laminated glass consists of glass bonded with an interlayer. If the pane breaks, that interlayer helps hold the glass together and reduces the risk of pieces falling into the room below.

Guidance for overhead glazing requires laminated inner panes in certain higher-risk situations, including some installations more than 5 metres above floor level and glazing over areas such as swimming pools. At lower heights, toughened inner panes may be suitable depending on the application and specification. See NARM’s guidance on glass rooflights and overhead glazing for further information.

NARM also recommends laminated inner panes more generally for glass rooflights because the interlayer helps retain the glass after breakage. Depending on the roof-lantern system and application, a double-glazed unit may therefore use a toughened outer pane with a laminated inner pane.

It is also worth noting that laminated glass does not automatically make a roof lantern “non-fragile”. Where protection for people working on or around the roof is required, the performance of the complete glazing and framing system needs to be considered.

For further information on regulatory considerations, see our Building Regulations and glazed extensions guide.

Self-cleaning glass and maintenance

Roof glazing can be more difficult to access than conventional windows, so a self-cleaning coating can be particularly useful.

Self-cleaning glass uses a specialist external coating that helps break down organic dirt and allows rainwater to spread across the surface more evenly, helping to reduce deposits and streaking. It can reduce the amount of cleaning required, although the glass and surrounding roof should still be maintained periodically.

Self-cleaning glazing is included within the current specification of our principal timber ranges and Atlas stock aluminium lantern glazing. 

Ventilation and comfort

Glazing is only one part of creating a comfortable extension.

Glazing is only one part of creating a comfortable extension.

Opening roof vents can help warm air escape and improve air movement within the room, particularly during warmer weather. Solar-control glass and ventilation perform different functions: solar-control glazing helps manage solar gain and glare, while ventilation helps release warm air from the space.

If ventilation is important to your project, read our roof lantern ventilation guide for more information about manual and electric opening vents.

Which glass should you choose?

The best roof-lantern glass depends on the property rather than simply choosing the specification with the lowest U-value or strongest solar control.

For a shaded or north-facing room, maximising natural light may be the priority. For a large lantern in a sunny position, solar-control glazing may make the room more comfortable. Where thermal performance is particularly important, a lower Ug-value may be worth considering.

The size of the lantern, its orientation, the amount of surrounding glazing and the way the room will be used should all be considered together.

You can browse our full range of roof lanterns to compare the available designs and glazing options, or contact us if you would like help choosing an appropriate specification for your project.