This glossary is meant to short-circuit that. We’ve grouped the terms most likely to come up during a project into five themed sections – types of rooflight, glass and glazing, frames and structure, performance, and opening and operation – so you can either read it through or jump to the part you need. Each entry is written in plain English, with links to the product pages or deeper articles where it’s worth knowing more.

If you’re stuck on something not covered here, our team is always happy to talk it through.

Types of rooflight

Despite the catch-all name, “rooflight” describes a family of products with quite different shapes, structures and uses. Here are the main types you’ll come across.

Flat rooflight

A rooflight designed to be installed in or on a flat roof. Despite the name, a “flat” rooflight is actually pitched at a minimum of around five degrees (with help from a builder’s kerb – see below) so that rainwater can run off rather than pool on the glass. Our flat rooflights come in fixed, opening, walk-on and round (O-Lite®) versions. Browse the full range on our Fixed Flat and Hinged Opening Flat pages.

Pitched rooflight

A rooflight designed for a sloped (pitched) roof, sitting flush with the surrounding roof covering. Our Luxlite® range is the pitched family, with double-glazed, triple-glazed, conservation and fully-opening Luxlite® Plus variants.

Roof lantern

A three-dimensional glazed structure that rises above the roof plane, usually shaped like a shallow elongated pyramid. Lanterns add both light and height to a room, catching the sun from multiple angles through the day. See our Slimline® Roof Lantern and Pyramid Slimline® Lantern for the two main styles.

Modular rooflight

A system of individual rooflights joined together with supporting bars between them to cover a much larger area than a single pane could manage. Ideal for big open-plan spaces, awkward layouts, or creative geometric arrangements. See the Modular Rooflights page for examples.

Walk-on rooflight

A glazed unit engineered to be safely walked on – used to bring daylight into a basement or lower floor while doubling as part of a terrace, walkway or patio above. The glass is structurally rated for foot traffic. See Walk-on Rooflights.

Wall abutment rooflight

A rooflight designed to sit against an adjoining wall – typically where an extension meets the main house, or where a flat roof butts up against a taller structure. The rooflight is engineered with a specific detail at the wall edge to weatherproof the junction cleanly, so you can bring daylight right up to the abutment without an awkward flashing strip cutting across the glass. See our Wall Abutment Rooflights page.

Conservation rooflight

A pitched rooflight designed to sit discreetly within a traditional or listed roof, usually with a slimmer, lower profile and a central vertical glazing bar (a “split bar”) to echo the look of older cast-iron rooflights. Our Conservation Luxlite® is built for these situations, where planning conditions in a conservation area or on a listed building may require a more traditional appearance.

Round rooflight

A circular fixed rooflight, frameless from the inside, suited to spaces with rounded geometry or where a more sculptural feature is wanted. Available in 750mm, 1000mm, 1500mm and 1800mm diameters. See the O-Lite® page.

Glass and glazing

The glass is where most of the performance comes from – both in terms of how much heat your rooflight holds in or keeps out, and how much light it lets through. These are the terms you’ll see on a spec sheet.

Double vs triple glazing

A double-glazed unit is two panes of glass with a sealed cavity between them; a triple-glazed unit adds a third pane and a second cavity. More panes mean better insulation and lower heat loss, which is why triple glazing has become the standard for serious thermal performance in UK rooflights. Our Luxlite® is available in both, with the triple-glazed version achieving meaningfully lower Ug-values for cold climates and energy-conscious builds.

Low-E coating

Short for “low emissivity.” A microscopically thin metallic coating, usually based on silver, tin or zinc, applied to one face of a glass pane inside the sealed unit. It reflects radiant heat back into the room in winter (cutting heat loss) and reflects some solar heat away in summer. Low-E is now standard on any glazing meant to meet UK Building Regulations.

Argon gas

An inert gas used to fill the cavity between the panes of glass in a sealed glazing unit. Argon is denser than air and conducts heat more slowly, which improves the unit’s thermal performance noticeably over an air-filled cavity. All Roof Maker glazing units are argon-filled as standard.

Solar control glass

Glass with a coating engineered to let visible light through while reflecting away a large portion of the sun’s heat (infrared radiation). Useful on south- or west-facing rooflights where overheating is a concern, and available as an upgrade across most of our range – including on our Luxlite® Plus. For more on how this works in a real glazed extension, see our guide on stopping a glazed extension overheating in summer.

Acoustic glass

A glazing build that uses a laminated inner pane (two layers of glass bonded with an acoustic interlayer) to reduce sound transmission. Useful under flight paths, near busy roads, or anywhere rain noise on the roof is a concern. Available as an option on our pitched and flat rooflights.

Toughened vs laminated glass

Two different ways of making glass safer. Toughened glass is heat-treated so that if it breaks, it shatters into small, blunt fragments rather than dangerous shards – it’s standard across our range. Laminated glass is two panes bonded together with a plastic interlayer, so if it breaks the pieces stay stuck to the layer rather than falling – it’s available as an upgrade where the extra safety performance is wanted, such as installations over heavily-used living spaces or where security is a particular concern.

Easy clean glass

A coating applied to the outer face of the rooflight glass that helps it stay cleaner for longer. It uses a hydrophobic action that causes rainwater to sheet off the glass rather than form beads, washing loose dirt away and reducing streaking, together with a durable protective layer (applied as standard during our manufacturing process) that resists dirt and staining. It doesn’t eliminate cleaning – no glass coating does, despite some industry claims – but it makes the job less frequent and less effort, which matters most for rooflights in awkward-to-reach positions. See our piece on why “self-cleaning” glass is a myth for the full picture.

Tint

A subtle colour cast in the glass itself, often a soft blue, green or grey. Tints can be aesthetic (to complement a particular interior or roof colour) or functional (some tints help further reduce solar gain). Tinted glass is available as a custom option on most of our rooflights – speak to our team for current choices.

Frames and structure

This is the part of the rooflight you don’t often think about until something goes wrong – and getting it right is what separates a rooflight that lasts decades from one that doesn’t.

Aperture

The opening cut into the roof for a rooflight to sit in. You’ll sometimes see rooflights described by their aperture size – that’s the dimension of the hole in the roof, not the size of the glass or the finished frame. Worth knowing because some manufacturers quote on external frame size rather than aperture, which can make their products look larger than they really are. We always quote on aperture so you can compare like-for-like. There’s more on this in our piece on internal vs external measurements for rooflights.

Builder’s kerb (or upstand)

A raised box-like structure built up from the roof deck on which a flat rooflight is fixed. It lifts the glass above the level of the finished roof so water runs away from the unit rather than pooling against it, and it provides a stable, level fixing surface. You’ll hear it called a builder’s kerb, an upstand, or sometimes a timber upstand – they all refer to the same thing. UK Building Regulations effectively require a minimum 150mm height above the finished roof surface, which is also the threshold for permitted development.

Flashing

A weatherproof skirt of material – typically lead, aluminium or a flexible composite – fitted around the base of a rooflight to seal the join between the rooflight frame and the surrounding roof covering. Done well, it directs rainwater away from the rooflight and into the roof’s normal drainage path; done badly, it’s the single most common source of leaks.

Flashing apron

A Roof Maker innovation built into our Luxlite® range. Where traditional pitched rooflights need a separate flashing kit cut, dressed and sealed around the frame on site – fiddly, time-consuming, and a common failure point – our flashing apron arrives as a fixed structural part of the rooflight itself. The roof covering simply meets it at the edge, removing a whole stage of the install and one of the most common places water can find its way in. Cleaner install, faster fit, and a more reliable weatherproof seal from day one.

Frameless

On a Roof Maker rooflight, “frameless” describes the view from inside – the glazing bars and frame components are concealed within the kerb and ceiling line so that, looking up from below, you see only glass and sky. Externally, there’s still a slim aluminium frame holding the unit together; “frameless” doesn’t mean the rooflight has no frame at all. The benefit is uninterrupted sky views and more visible glass area for the same aperture. Read more on our piece know the difference: frameless views vs frameless rooflights.

Marine-grade powder coating

A tough, weather-resistant finish applied to the aluminium frame after fabrication. “Marine-grade” means it’s specified to withstand the harshest weather conditions – heavy rain, salt-laden coastal air, prolonged UV exposure – without fading, chalking or corroding. It’s available in virtually any RAL colour so the rooflight can match your window frames, fascias or interior trim.

Thermal break

A strip of low-conductivity material – typically polyamide, resin or silicone – placed between the inner and outer sections of the aluminium frame. Aluminium is structurally excellent for rooflights but it’s also an efficient conductor of heat, so without a break it would simply hand warmth straight from inside to out. The thermal break interrupts that path, keeping the inside face of the frame warmer in winter (which also reduces condensation) and the inside cooler in summer. For more, see our piece on what a thermal break is.

Performance and measurement

This is where the spec sheets start using letters and numbers, and where it pays to know which one actually matters for what.

U-value

A measure of how easily heat passes through a building element – a wall, a window, a rooflight – expressed in watts per square metre per degree of temperature difference (W/m²K). The lower the number, the better the insulation. A U-value covers the whole assembly: glass, frame, seals and edge details together. Because frame and edge effects matter more on small units than large ones, the overall U-value of a rooflight changes with its size – which is why it’s not always the most useful figure for comparing one product to another.

Ug-value

The U-value of the glass alone, measured at the centre of the pane – the “g” stands for glazing. Because it doesn’t include the frame or edge effects, it stays consistent regardless of how big the rooflight is, which makes it a fairer way to compare the glazing performance of different products. Our Luxlite® Plus, for example, achieves Ug-values as low as 0.6 W/m²K. When you see a Ug-value quoted, that’s the glass spec; when you see a U-value, that’s the unit as a whole.

Solar gain

The warmth that builds up inside when sunlight passes through glass, is absorbed by the surfaces and furnishings of a room, and is re-radiated as heat that can’t easily escape back out. In winter it’s a free source of heating; in summer it’s the reason a south-facing glazed extension can become uncomfortable by mid-afternoon. Managing solar gain is the job of solar control glass, ventilation and shading working together – covered in our piece on stopping a glazed extension overheating in summer.

Aspect

The compass direction a rooflight faces – south, north, east or west. Aspect affects both how much daylight a rooflight receives through the day and how much solar gain comes with it. South- and west-facing rooflights catch the strongest, most direct sun and benefit most from solar control glazing; north-facing rooflights give softer, more even light with much less heat. Knowing the aspect early helps you match the specification to the way the room will actually be used. (Note: on our product pages, “orientation” refers to whether a rooflight is installed portrait or landscape – a separate thing.)

Opening and operation

Whether you want fresh air as well as light shapes a lot of the rest of your spec, and there are more choices here than people often realise.

Fixed vs opening

A fixed rooflight is a sealed, non-opening unit – the most thermally efficient option, with the largest possible glass area for the aperture, and the lowest long-term maintenance. An opening rooflight introduces a mechanism that lets the unit hinge open for ventilation, which means a slightly thicker frame and a few more moving parts, in exchange for the ability to let hot air escape and fresh air in. The right choice depends on the room: kitchens and bathrooms usually benefit from opening for moisture and cooking smells; living rooms and hallways are often better served by fixed for maximum light and minimum fuss.

Hinged opening

A rooflight that opens on a hinge along one edge, much like a door tipping back, rather than sliding or pivoting in the middle. It’s the most common opening mechanism in the UK and gives a large, unobstructed opening when fully extended. Our Hinged Opening Flat range uses this mechanism, as does the Hinged Opening Slimline® Roof Lantern (which opens 300mm to vent hot air) and the Luxlite® Plus, where the entire lid hinges fully open at the press of a wall-mounted switch.

Rain sensor

A small sensor that detects falling rain and automatically closes an opening rooflight when it does – so you can leave a rooflight open on a warm morning without watching the sky all day. It comes fitted as standard on our Hinged Opening Slimline® Roof Lantern, and is available as an optional upgrade on our standard hinged opening flat rooflights.

Blinds

Blinds fitted to a rooflight give you on-demand control over light and solar heat. Two broad types are common: pleated blinds, which diffuse light and reduce glare while still letting some daylight through; and blackout blinds, which cut light out entirely – useful in bedrooms, home offices, media rooms or any space where full light control matters. The most discreet finish comes from blinds fitted into the rooflight itself rather than added afterwards, since the mechanism stays out of sight and there’s no separate fixture cluttering the ceiling. See our Sky-Blind® range for our take on this.

Where to from here

That’s the working vocabulary of a rooflight project, more or less – enough to read a spec sheet, compare two products fairly, and tell what’s a real performance claim from a clever bit of marketing. The terms above show up in our product pages, our guides and our quotes, and we’ve linked through to the deeper articles where any of them are worth understanding more fully.

If you’ve come across a term that isn’t on this list, or you’d like a hand interpreting a spec for a project you’re planning, our team is always happy to talk it through. Take a look at our full range of rooflights, or give us a call on 0116 269 6297.