Roof Lantern Glossary

Upstand: The raised frame around a roof opening that a lantern sits on. Also called a kerb.
Kerb: Another word for upstand. Lanterns are sold by the external size of the kerb.
External kerb size: The outside width and length of the upstand, which is the size a lantern is ordered to.
Ridge: The horizontal top bar of a rectangular lantern, running along its length.
Hip: The sloping bar running from the end of the ridge down to each corner of the lantern.
Rafter: A sloping glazing bar between the ridge and the eaves that supports the glass.
Intermediate rafter: An extra structural rafter used on longer lanterns to carry larger glass.
Glazing bar: Any bar in the lantern frame that holds glass on either side.
Eaves beam: The frame member around the base of the lantern that sits on the upstand.
Apex: The top point where the four panes of a pyramid lantern meet.
Pitch: The angle of the glass from horizontal, usually around 20–25° on lanterns.
Pyramid lantern: A square lantern with four triangular panes meeting at an apex.
Double-hipped lantern: A rectangular lantern with a hip at each end and a ridge between.
Gable-ended lantern: A lantern with a vertical glazed end, usually against a wall, instead of a hip.
Cresting: Decorative metalwork along the ridge of a traditional lantern.
Finial: A decorative spike or ball at the end of a ridge.
Sightline: How much frame you see. Slimmer sightlines mean more visible glass.
Thermal break: An insulating barrier inside an aluminium frame that reduces heat flow through the metal.
Powder coating: A baked-on polyester finish used on aluminium frames.
RAL: A standard colour reference system, for example RAL 7016 anthracite grey.
RAL 7016: Anthracite grey, a widely used lantern colour.
RAL 9005: Jet black.
RAL 9016: Traffic white, a common white for frames.
Dual colour: A different frame colour inside and outside.
Double glazed unit: Two panes of glass sealed with a gap between them.
Triple glazed unit: Three panes of glass with two sealed gaps.
Warm-edge spacer: A low-conductivity spacer between panes that keeps the glass edge warmer.
Argon: An inert gas used to fill the gap in glazing units to reduce heat loss.
Low-E coating: A low-emissivity coating that reflects heat back into the room.
Self-cleaning glass: Glass with an outer coating that breaks down dirt in daylight and lets rain wash it away.
Solar-control glass: Glass with a coating that reduces the sun's heat entering the room.
g-value: The share of solar energy that passes through glass. Lower means less heat gain.
U-value: A measure of heat loss in W/m²K. Lower means better insulation.
Light transmission: The share of visible light that passes through glass.
Toughened glass: Glass heat-treated to be stronger, which breaks into small blunt pieces.
Laminated glass: Two panes bonded with an interlayer, which holds together if broken.
Horizontal U-value: A rooflight U-value calculated with the glass horizontal, as rooflight standards use.
Opening vent: A glazed panel that opens, usually on an electric actuator.
Actuator: The motor that opens and closes a lantern vent.
Rain sensor: A sensor that closes an opening vent automatically when it rains.
Purge ventilation: Rapid ventilation to clear heat or fumes, usually by opening windows or vents.
Background ventilation: Continuous low-level ventilation, for example from trickle vents.
Trimmer: A beam or joist that frames the opening in a roof around a lantern.
Flat rooflight: A single, almost flat glazed unit on an upstand.
Walk-on rooflight: A rooflight designed to be walked on, usually set flush in a roof terrace.
Roof window: A window set into the slope of a pitched roof.
Orangery: An extension with a mostly solid roof and a central glazed lantern.
Polycarbonate: A plastic sheet used on older lanterns and conservatories; it discolours with age.
GRP roof: A glass-reinforced plastic flat roof finish, often called fibreglass.
EPDM: A synthetic rubber membrane used on flat roofs.
Single-ply membrane: A flat roof waterproofing sheet such as PVC or TPO.
Fall: A slight slope that lets water drain off a roof or rooflight.
Plaster return: The lined inner face of the opening between the ceiling and the lantern.
Supply only: Buying the lantern without fitting; your own installer fits it.
Made to measure: Manufactured to your exact kerb size rather than a standard size.
Lead time: The time from order to dispatch or delivery.
Competent person scheme: A government-authorised scheme that lets registered installers self-certify certain building work.
Building control: The service that checks building work meets building regulations.
Permitted development: Building work that can be done without applying for planning permission, within set limits.
Listed building consent: Permission needed for works affecting a listed building's character.
Building warrant: Scotland's approval needed before most building work starts.

Know the price before you order.