Adding a skylight is one of the simplest ways to bring more natural light into a home, but the terminology can be confusing before you’ve even chosen a style. Skylight, rooflight, roof window: you will see all three used to describe similar products, sometimes on the same page, and it’s not always clear whether suppliers mean the same thing or something different.
In this guide, our team sets out what a skylight actually is, where the confusion between these terms comes from, and the one difference that has real, practical consequences for which product suits your roof. We then cover every major type of skylight we supply, what determines the right choice for your home, and the planning and cost questions that come next.
What is a skylight?
A skylight is a glazed unit installed in a roof to bring natural daylight into the room below. That is the core function shared by every product this guide covers, whatever it happens to be called on a given supplier’s website. It is also the definition we use: skylights, rooflights, and roof windows are glazed units installed in a roof to bring natural light, ventilation, and energy efficiency benefits into a space, whichever term a given supplier applies to them.
In UK usage, ‘skylight’ is applied broadly. Some suppliers use it for any roof glazing, flat or pitched, fixed or opening. Others reserve it specifically for units on pitched roofs, using ‘rooflight’ for flat roof installations instead. Both usages are common, and neither is wrong in a technical sense, because there is no single body that legally defines ‘skylight’ as a protected term.
Skylight vs rooflight vs roof window: what’s the real difference?
Most homeowners assume ‘skylight,’ ‘rooflight,’ and ‘roof window’ mean the same thing, and for two of the three, that assumption is broadly correct. The third is genuinely different, and knowing which is which will save you time when you start comparing products.
Skylight and rooflight are, in practice, used interchangeably across the UK glazing industry. Whether a supplier calls their product a skylight or a rooflight generally comes down to house style and regional habit rather than a technical rule. You will see both terms used for the same flat roof glazing, and both used for pitched roof glazing, depending on which company you are reading.
Roof windows are different. A roof window has a formal definition under BS EN 14351-1, the British and European standard covering windows and external pedestrian doorsets. Roof windows must be installed ‘in plane’ with the surrounding roof structure, meaning the glass sits flush with the roof surface, following the same slope as the tiles or covering around it, rather than sitting raised above it. This generally requires a minimum pitch, and the unit must carry CE or UKCA marking against that standard. Rooflights and skylights are typically installed ‘out of plane’ instead, sitting on a raised timber or GRP upstand that protrudes above the roof surface, which is how flat roofs achieve drainage since there is no slope for the glazing to sit flush against. Out-of-plane units are not subject to the same marking requirement.
In practical terms, this comes down to installation method rather than marketing language:
| Term | Typical roof type | Installation | Formal marking required |
|---|---|---|---|
| Rooflight | Flat or low-pitch | Out of plane, on an upstand or kerb | No |
| Skylight | Flat or pitched, usage varies | Out of plane, on an upstand or kerb | No |
| Roof window | Pitched | In plane with the roof surface | Yes, under BS EN 14351-1 |
Roof lanterns sit in a related but distinct category. They are raised, multi-paned glazed structures rather than flush or near-flush units, and they are covered separately below.
Are roof windows more expensive than rooflights and skylights?
Not inherently. Price is driven far more by size, glazing specification, and opening mechanism than by which of these three category names applies. A basic fixed flat rooflight and a basic fixed pitched roof window in a comparable size will often land in a similar price bracket. The bigger cost differences come from glass thickness, self-cleaning coatings, and whether the unit opens manually or electrically, covered in the sections below.
Types of skylights
Between fixed, opening, and specialist products, there are more types worth understanding than most people expect. The detail below reflects the actual products we supply, including real prices, warranties, and lead times, rather than generic categories.
Flat roof skylights
Flat roof skylights are our most popular product, and the type most homeowners searching for ‘what is a skylight’ end up choosing, generally suited to roofs pitched between 0 and 15 degrees on single-storey extensions and loft conversions. Specification and price vary considerably within the range: our entry-level flat rooflight starts from around £259 ex VAT, a framed flat skylight with a 10-year guarantee runs from £420 to £3,558, and a triple-glazed, self-cleaning flat rooflight starts from as little as £163 up to £619 for larger sizes. Lead times on standard sizes are typically 2 to 5 working days. Browse our full flat roof skylight range or read our flat roof skylight buying guide for more detail.
Pitched roof skylights (roof windows)
For pitched roofs, our pitched roof window range includes products from Fakro and RoofLITE+. A Fakro centre pivot roof window is priced from £252.33 to £574.05 ex VAT, with a 2 to 3 working day lead time, and rotates on a central hinge so both sides of the glass can be cleaned from inside the room. A Fakro top hung roof window opens from the top rather than pivoting centrally, priced from £374.79 to £689.17, with the same 2 to 3 day lead time. Our RoofLITE+ pitched roof window runs from £194.57 to £736.82 ex VAT, offering a lower entry price point within the same category. Whether a specific model meets the formal in-plane roof window definition covered above depends on its individual installation method and certification, which is worth confirming on the product page or with our team before ordering.
Fixed skylights
Fixed, or non-opening, skylights have no hinge mechanism, which means the frame carries no extra hardware and the unit can use a larger pane of glass for the same overall size as an equivalent opening skylight. This also means fixed skylights generally cost less and cause less disruption to install, since no additional rafters are needed either side to support an opening casement. The flat rooflight range above is available in fixed configurations as standard, and our dedicated fixed rooflight range also covers pitched and dome options. Fixed units suit rooms where light is the priority and ventilation is already handled elsewhere, such as hallways, stairwells, and living rooms. Read more in our opening vs non-opening skylights guide.
Opening skylights (manual and electric)
Opening skylights add ventilation to the light they provide. Manual versions are operated with a pole or winding rod and need no wiring, making them the simpler installation. Electric versions connect to the mains and can be operated by wall switch, remote control, or remote with a rain sensor that closes the unit automatically, with a manual override available if there is a power cut.
Specification varies more than most buyers expect. Our electric and manual opening rooflights, priced from £618.81 to £9,999 ex VAT depending on size and finish, use a 6.4mm laminated inner pane as standard, against the 6mm often used elsewhere in the market, rising to 8.8mm, 9.5mm or 11.5mm on larger sizes. They carry a centre-pane U-value of 1.1 W/m²K, a minimum working pitch of 4 degrees and a maximum of 15, and are backed by a 10-year guarantee with an expected 20-year service life. Actuators on electric units are separately guaranteed for 1 year and rated to over 10,000 open/close cycles.
Electric rooflights are not generally recommended for bathrooms or kitchens with limited ventilation, since sustained high humidity around the mechanism can affect the manufacturer’s warranty terms. A manual unit is the safer choice in those rooms. See our electric vs manual opening skylights guide for a full comparison.
Roof lanterns
Roof lanterns are raised, multi-paned glazed structures that sit above the roofline rather than flush with it, typically used to make a stronger architectural statement over kitchens, dining areas, and open-plan extensions. Because they project above the roof, lanterns are installed at a fixed internal pitch regardless of how flat the surrounding roof is, and that pitch varies meaningfully by manufacturer.
A Korniche roof lantern runs a fixed 25 degree internal pitch, achieves U-values from 1.0 to 1.2 W/m²K, and comes with self-cleaning glass as standard. Sizes range from 1000mm x 1000mm up to 6000mm x 2500mm, priced from £694.56 to £4,247.01 ex VAT, with a 10-year warranty and a 15 to 25 year expected lifespan. Larger frames use a spar tensioning system to maintain weathertightness under load; a 6m x 4m Korniche lantern is rated to support over 8 tonnes.
A Wendland roof lantern uses a lower 20 degree fixed pitch, achieves a 1.2 U-value as standard (1.0 available on request), and uses a RidgeLOCK fixing system designed to minimise the number of visible glazing bars. It is priced from £449.45 to £2,009.28 ex VAT, with a faster 5 to 10 working day lead time against roughly 2 to 3 weeks for Korniche. Wendland’s optional Celsius Blue Tint glass reflects around 78% of solar heat, over three times standard glass, and retains roughly 50% more heat than neutral glass, making it a stronger choice for south-facing installations, while neutral glass suits north-facing rooms where maximising light matters more than solar control.
See our full roof lantern range, or read more on how rooflights differ from roof lanterns.
Pyramid skylights
Pyramid skylights use a four-sided sloped design that draws in light from every direction rather than a single overhead angle, making them a common choice where a striking interior feature matters as much as the light itself. Our pyramid skylight range is priced from £436.51 to £4,453.77 ex VAT and carries a 10-year warranty. Because all four faces catch the sun at different points in the day, orientation has a more noticeable effect on a pyramid skylight than on a flat unit: a west-facing installation gains more heat in the afternoon, while a south-facing one gains more passive warmth through winter.
Walk-on rooflights
Basement conversions, roof terraces, and decking all share a problem standard rooflights cannot solve: something has to be able to stand on top of the glass. Our walk-on rooflight range is structurally reinforced to be trafficable for exactly this reason, priced from £869 to £3,575 ex VAT, with a longer 15 to 20 working day lead time reflecting the specialist glazing involved. Standard units use a 33mm toughened top pane built to BS EN 12150 and BS EN 1279, an 18mm argon-filled cavity, and a Low-E coating, achieving a centre pane U-value of 1.1 W/m²K, with triple and quad glazed options available for higher performance.
The laminated construction means that if the surface is chipped or cracked, it holds together rather than failing outright. Given the reinforced glass, walk-on units are considerably heavier than standard rooflights, typically around 90 kg per square metre, which affects both delivery and installation planning.
Circular rooflights
Circular rooflights bring a distinct, contemporary look often specified by architects for museums, galleries, and modern residential extensions where a conventional rectangular unit would feel out of place. Our circular rooflight range is fixed rather than opening, available in 600mm, 900mm, 1200mm and 1500mm diameters, priced from £977.13 to £3,230.39 ex VAT with a 10-year warranty. Glazing achieves a U-value as low as 1.16 W/m²K, and installation is generally recommended at a minimum pitch of around 5 degrees purely for drainage, since a completely flat circular unit risks water sitting on the glass surface after rain. Lead times run longer than most other types, typically 15 to 30 working days.
Quick specification comparison
| Type | Price range (ex VAT) | Typical U-value | Warranty | Lead time |
|---|---|---|---|---|
| Fixed flat rooflight | £259 to £2,800 | 1.1 to 1.2 W/m²K | 10 years | 2 to 5 days |
| Triple-glazed self-clean flat rooflight | £163 to £619 | Improved on double glazing | 10 years | 2 to 5 days |
| Pitched roof window (Fakro/RoofLITE+) | £194.57 to £736.82 | Manufacturer-specific, check product page | Manufacturer’s warranty | 2 to 3 days |
| Electric/manual opening rooflight | £618.81 to £9,999 | 1.1 W/m²K | 10-year guarantee, | 3 to 5 days |
| Korniche roof lantern | £694.56 to £4,247.01 | 1.0 to 1.2 W/m²K | 10 years | 2 to 3 weeks |
| Wendland roof lantern | £449.45 to £2,009.28 | 1.0 to 1.2 W/m²K | 10 years | 5 to 10 days |
| Pyramid skylight | £436.51 to £4,453.77 | Varies by glazing | 10 years | Varies |
| Walk-on rooflight | £869 to £3,575 | 1.1 W/m²K | Manufacturer’s warranty | 15 to 20 days |
| Circular rooflight | £977.13 to £3,230.39 | As low as 1.16 W/m²K | 10 years | 15 to 30 days |
Prices and lead times are indicative and vary by size, glazing specification, and finish. Check individual product pages for current figures before ordering.
Materials and glazing options
Once the type is decided, the glass and frame specification determines most of the performance, and this is where competitor guides tend to stay generic rather than naming actual products or figures.
Glass versus polycarbonate
Glass is the more common choice for domestic installations, offering better clarity, a wider choice of coatings, and a longer expected lifespan. Our Coxdome and Mardome ranges use polycarbonate domes, which are lighter and less expensive than glass and offer strong impact resistance, making them a practical option for larger commercial spans or budget-conscious projects, though they do not match glass for optical clarity or long-term appearance.
Double versus triple glazing
A standard double-glazed unit typically pairs a 6mm toughened outer pane with an 18 to 20mm argon-filled cavity and a Low-E (low-emissivity) inner pane, a coating that reflects heat back into the room rather than letting it escape through the glass, achieving centre-pane U-values around 1.1 to 1.2 W/m²K, as seen across our opening rooflight and walk-on rooflight ranges. Triple glazing adds a further pane and cavity, improving thermal performance and reducing external noise, with our triple-glazed self-clean flat rooflight range achieving figures closer to 0.9 W/m²K on some sizes.
Laminated glass
Building regulations require laminated glass in specific scenarios: installations more than 5 metres above floor level, and rooflights positioned above swimming pools, since toughened glass alone can shatter into small fragments that fall into the space below. Laminated panes hold together on impact instead, which is why they are standard on walk-on rooflights and on the inner pane of our opening rooflights.
Self-cleaning and solar control coatings
A self-cleaning coating, such as Pilkington Activ, breaks down organic dirt using UV light and rinses it away with rainfall, reducing (though not eliminating) manual cleaning, and only works effectively above a minimum pitch, usually around 10 degrees. Solar control coatings and tints, such as the Celsius Blue Tint used on Wendland roof lanterns, reduce glare and limit heat gain, which matters more on south and west-facing installations than north-facing ones. Read our glazing options guide for more detail on choosing between them.
| Attribute | Glass | Polycarbonate |
|---|---|---|
| Optical clarity | High, minimal distortion | Lower, can appear slightly hazy |
| Weight | Heavier, affects handling and frame design | Significantly lighter |
| Impact resistance | Good when toughened or laminated | Very high |
| Typical lifespan | Longer, resists UV yellowing | Shorter, can yellow or degrade over time |
| Typical cost | Higher | Lower |
| Common TGS ranges | Flat rooflights, roof lanterns, walk-on rooflights | Coxdome, Mardome dome rooflights |
Choosing the right skylight for your home
Roof type and pitch
This is the single factor that narrows down the product options fastest. Flat and low-pitch roofs (0 to 15 degrees) suit flat rooflights, roof lanterns, and circular units. Pitched roofs suit our pitched roof window range, which can be installed at pitches up to 90 degrees. Some products, including opening rooflights, have a defined minimum and maximum working pitch, typically 4 to 15 degrees, outside of which performance and drainage are affected. Our rooflight size guide covers how pitch interacts with sizing in more detail.
Room and use case
Each room has different priorities, and the right product varies accordingly.
| Room | What matters most | Suggested option |
|---|---|---|
| Kitchen | Clearing steam and cooking odours | Opening rooflight, positioned over worktops or dining areas |
| Bathroom | Ventilation and privacy | Obscured or satin glass with a manual opening mechanism (avoid electric, given the humidity caveat above) |
| Bedroom or loft conversion | Softer light, quieter operation | Fixed flat rooflight or a Wendland roof lantern with solar control glazing |
| Hallway or stairwell | Brightening a whole circulation space with one unit | Circular rooflight or a well-placed fixed unit |
Orientation
The direction a skylight faces changes both the amount and quality of light it lets in.
| Orientation | Effect | Best suited to |
|---|---|---|
| North-facing | Consistent, even light, minimal heat gain | Rooms prone to overheating, spaces used for detailed work |
| South-facing | Most passive winter warmth, most summer heat | Living spaces wanting winter light; pair with solar control glazing |
| East-facing | Stronger morning light | Kitchens, breakfast rooms |
| West-facing | More heat in the afternoon | Living rooms used mainly in the evening |
Fixed or opening
Fixed units cost less, let in more glass for the same overall size, and involve less structural work to install. Opening units add ventilation control at the expense of a higher price point and a small increase in long-term maintenance, since moving parts (particularly electric actuators) are the most likely component to need servicing over the product’s lifespan.
Budget and maintenance
Entry-level flat rooflights start from under £300, while premium roof lanterns and larger opening units can run into several thousand pounds depending on size and specification. As a general rule, fixed units cost less to buy and maintain than opening units, and glass costs more upfront than polycarbonate but holds its appearance and performance for longer. Our rooflight and skylight cost guide breaks pricing down by product type.
Planning permission and building regulations
Most rooflight, skylight, and roof window installations in England and Wales fall under permitted development, meaning formal planning permission is not required, provided the installation meets specific conditions. Broadly, alterations must not project more than 150mm from the existing roof plane, must not exceed the height of the existing roof, and side-facing windows must be obscure-glazed if within a set distance of a boundary. Permitted development rights do not automatically apply to listed buildings, conservation areas, or properties where an Article 4 direction has removed them, so it is always worth checking with your local planning authority before ordering. Full technical detail is available in the government’s permitted development guidance, and our own planning permission and building regulations guide sets out the detail specific to rooflights.
Separately from planning permission, every installation still needs to meet Building Regulations, covering structural safety, thermal performance, and glazing safety requirements regardless of whether planning permission was needed in the first place.
Benefits of skylights
The core benefits are consistent across every type covered in this guide: more natural daylight, reduced reliance on artificial lighting during the day, and (for opening units) improved ventilation and reduced condensation risk in humid rooms. Increased natural light is also linked to improvements in mood, sleep quality and general wellbeing, and a well-specified skylight can add measurable value to a property at resale. Our dedicated benefits guide covers this in full.
Contact Toughened Glass Systems
At Toughened Glass Systems, we supply flat rooflights, roof lanterns, pyramid skylights, walk-on rooflights, and pitched roof windows across the UK, with detailed specifications available on every product page. If you are still deciding which type suits your project, browse our full range of rooflights and skylights or get in touch for advice on your specific roof.
See what customers have said about our range in our reviews and trade history.
Frequently asked questions
Is a rooflight the same as a skylight?
In practice, yes. Both terms are used across the UK glazing industry to describe the same kind of product: a glazed unit installed out of plane on a roof, sitting on an upstand or kerb rather than flush with the roofing material. Which word a given supplier uses tends to reflect house style rather than a technical distinction. The one related term that does carry a formal, different definition is roof window, covered above.
What is the difference between a skylight and a Velux window?
Velux is a brand name, not a product category. A Velux window is a specific manufacturer’s roof window, built to the same BS EN 14351-1 standard as other roof windows on the market. Several UK suppliers, including TGS, offer alternatives that meet comparable specifications, often at a lower price. See our Velux alternatives guide for a direct comparison.
Do skylights leak?
A correctly measured and installed skylight, fitted onto a properly weathered upstand of at least 150mm, should not leak. Most leaks that do occur trace back to installation error, a degraded seal, or a unit installed below its recommended minimum pitch rather than a fault with the glass itself.
Is a roof lantern the same as a skylight?
No. A roof lantern is a raised, multi-paned structure that sits above the roofline, while a rooflight or skylight typically sits flush or close to flush with the roof surface. The practical difference is profile: a lantern is a more visible architectural feature, while a rooflight has a lower profile.
Do I need planning permission for a skylight?
Usually not, provided the installation meets permitted development conditions covered above. Listed buildings, conservation areas, and properties with an Article 4 direction are the main exceptions, and it is worth confirming with your local planning authority before ordering if any of these apply to your property.
What is a laylight?
A laylight is an internal fixture, often a diffusing panel set into a ceiling below a skylight, that spreads light more evenly through a room. It is a separate interior feature rather than a type of roof glazing, and is more common in commercial or larger residential buildings than standard homes.
Is a dormer a skylight?
No. A dormer is a structural extension projecting from the roof with a vertical window, adding headroom as well as light. A skylight sits within the plane or profile of the existing roof and does not extend the roofline itself.