Fixed skylights
Non-opening units for daylight only. Simplest to seal, lowest cost and the best thermal performance; common on flat roofs, extensions, corridors and stairwells.
Roof glazing systems
Aluminium Skylights & Rooflights
An aluminium skylight (or rooflight) is a glazed opening in a roof, framed in extruded aluminium, that brings daylight deep into a building and, in opening versions, lets out warm air or smoke. Thermally broken 6063 frames carry glass or polycarbonate in fixed, venting, electric, lantern, continuous and smoke vent designs. Metline supplies skylight frame, rafter and glazing-bar profiles, thermal-break sections and accessories to skylight makers for homes, commercial roofs and industrial buildings worldwide.
- Frame alloy
- 6063-T5 / T6
- Types
- Fixed, venting, lantern, smoke vent
- Glazing
- Laminated IGU, polycarbonate
- Standards
- NAFS · EN 12101-2 · EN 14351-1
What aluminium skylights do and why aluminium frames are used
A roof opening admits several times more daylight than a vertical window of the same size, because it faces the brightest part of the sky and is not blocked by neighbouring buildings. That makes skylights the most effective way to light the middle of deep plan rooms, stairwells, corridors, warehouses and atriums.
The price of that daylight is exposure. A skylight faces rain, snow, hail, full sun and wind uplift, sits in the warmest part of the building where condensation forms, and may be walked on during roof maintenance. The frame has to drain water reliably, stay sealed through daily thermal cycling, carry heavy glass and resist uplift, all without becoming a cold bridge.
Extruded aluminium meets these demands better than most frame materials. 6063 profiles can include drainage channels, glazing pockets, thermal-break slots and fixing ports in a single section; they are strong enough for large, heavy glazed units; and they do not rot, rust or become brittle under ultraviolet light. Powder coat or anodising keeps the external face looking new with little maintenance.
Fixed, venting, lantern and smoke vent skylights
Venting skylights
Manually or electrically opened sashes that release warm air at the highest point of the room. Rain sensors close electric units automatically.
Electric and concealed-motor skylights
Chain or spindle actuators, surface-mounted or hidden in the frame, with wall switches, remote control or building-management links.
Roof lanterns and pyramids
Raised hipped or pyramid structures, often on flat-roof extensions and orangeries, which add height and light to the room below.
Smoke vent skylights
Natural smoke and heat exhaust ventilators that open automatically on a fire signal to let smoke out of warehouses, malls, stations and stairwells, and can also open daily for ventilation.
Walk-on rooflights
Heavy laminated glass on a robust frame, set flush with a terrace or floor to light a room below.
Opening skylights are usually top-hung or hinged at one side and open to 30 – 60 degrees for ventilation; smoke vent flaps open much wider, typically 70 – 90 degrees or more, to achieve the aerodynamic free area the smoke design needs. Panoramic and very large sashes use several synchronised actuators so the sash does not twist as it opens.
Skylight shapes and roof glazing structures
| Category | Common shapes | Typical use |
|---|---|---|
| Unit skylights | Rectangular, square, round, octagonal; flat, domed or pyramid glazing | Single roof openings over rooms, corridors, stairwells and sunrooms |
| Continuous skylights | Endless barrel vault, ridge with vertical or hipped ends, arched with end panels | Long daylight strips over warehouses, factories, malls and walkways |
| Structural skylights | Pyramid, polygon, ridge, single slope, barrel vaults (low, half or quarter round, segmented), domes, gable and arched walkways | Atriums, lobbies, villas and feature roofs |
| Roof lanterns | Hipped, pyramid or ridge lantern on an upstand | Flat-roof extensions and orangeries |
Unit skylights arrive as complete framed products. Continuous and structural skylights are framed from rafter, ridge and perimeter extrusions assembled on site to the roof drawing, which allows almost any plan shape but requires careful engineering of the rafter spans, glass divisions and drainage paths. Larger structural systems often use aluminium rafters with internal steel reinforcement where spans are long.
Frame alloy, thermal breaks, sealing and finishes
Typical frame specification
- Alloy
- 6063-T5 or T6 extrusion to EN 755 / ASTM B221
- Wall thickness
- About 2.0 mm on small units; 2.5 – 3.0 mm on large-format and continuous systems
- Thermal break
- Glass-fibre reinforced polyamide (PA66) strips between inner and outer profiles
- Corners
- Welded or mechanically jointed and sealed corners
- Sealing
- Two or three EPDM gasket lines with a drained and ventilated glazing rebate
- Drainage
- Internal gutters formed by the profile assembly lead water to the outside
- Kerb / upstand
- Aluminium or site-built kerb raising the frame above the roof surface
A thermal break is more important on a skylight than on a window. Warm, moist air collects at the ceiling, so an unbroken aluminium frame at the highest point of the room will run with condensation in cold weather. Polyamide strips separate the internal and external profiles; combined with warm-edge glass spacers, they keep the internal frame surface above the dew point in most heated buildings.
| Finish | Typical specification | Notes |
|---|---|---|
| Polyester powder coat | AAMA 2603/2604 or Qualicoat Class 1 | Most residential and commercial units |
| Super-durable powder / PVDF | AAMA 2604/2605 or Qualicoat Class 2 | Roofs see the strongest UV of any façade surface |
| Anodising | EN ISO 7599, class 20 – 25 µm | Metallic finish; approve samples to control shade variation across batches |
| Dual colour | Different colours inside and outside | Possible with thermally broken frames |
Glass, polycarbonate and thermal performance
Overhead glazing must stay in place if it breaks, so codes restrict what can be used. In the US, the International Building Code (Section 2405) and International Residential Code (R308.6) allow laminated glass, wired glass, heat-strengthened or fully tempered glass and approved rigid plastics, and require screens under some tempered or heat-strengthened glass. In practice, the inner pane of an overhead insulated unit is almost always laminated.
| Glazing | Benefits | Limitations | Typical use |
|---|---|---|---|
| Laminated inner + toughened outer IGU, Low-E, argon | Clear view, safe if broken, good insulation | Heavy (around 30 – 40 kg/m²) | Homes, lanterns, commercial roofs |
| Triple laminated IGU | Lowest heat loss | Heaviest; needs stronger frames | Cold climates |
| Solar control glass | Cuts solar heat gain and glare | Slightly lower light transmission | Hot climates, south-facing roofs |
| Multiwall polycarbonate | Very light, impact resistant, low cost | Translucent, not clear; can yellow without UV protection | Industrial and continuous rooflights |
| Solid polycarbonate domes | Impact resistant, formable | Scratches; limited insulation | Unit skylights and smoke vents |
| Walk-on laminated glass | Carries foot traffic | Thick and heavy; needs engineering | Terraces and floors |
Glass loses more heat when laid flat than when vertical, because convection inside the cavity is stronger. A double-glazed unit rated at about 1.1 W/m²·K in a vertical window can perform several tenths of a W/m²·K worse in a horizontal skylight, which is why roof glazing is rated at its installed slope. Solar heat gain matters even more: too much clear roof glazing over a room causes overheating, so solar control coatings, internal blinds or external shading are often worth specifying.
Smoke vent skylights and EN 12101-2
In a fire, most deaths and much of the property damage are caused by smoke, not flames. Smoke vent skylights open automatically on a signal from the fire alarm, letting hot smoke rise out of the roof so escape routes stay clear and firefighters can see. In Europe these units are natural smoke and heat exhaust ventilators (NSHEVs) and must be CE marked to EN 12101-2.
| EN 12101-2 property | What it means | Typical declared class |
|---|---|---|
| Aerodynamic free area (Aa) | The effective opening for smoke flow, smaller than the geometric opening | Declared in m² for each size |
| Reliability | Number of test cycles to the smoke position (plus ventilation cycles for dual-purpose units) | Re 1000 for dual-purpose vents |
| Opening under load | Opens against a snow load | SL classes, depending on size and flap weight |
| Low ambient temperature | Opens at sub-zero temperatures | T(-05), T(-15) or T(-25) |
| Wind load | Stays closed and undamaged under suction | WL classes such as WL 1500 |
| Heat exposure | Keeps working at high temperature | B300 (300 °C) |
Smoke vents come in several forms: triangular units with a flap opening to 70 – 90 degrees, low-profile flat vents for roofs where wind resistance must be low, arched units for good water run-off, and arched units with side-wall flaps for large industrial roofs. Actuators can be chain, spindle or articulated-arm, electric or pneumatic. The vent size, number and position come from the fire engineer's smoke design under the local fire code, not from the skylight supplier.
Smoke vent configuration and compliance must be confirmed against the local fire code and the fire strategy for the building. Outside Europe, local listings or approvals may apply instead of, or in addition to, EN 12101-2.
Design, installation and roof safety
Kerbs and upstands
Raise the frame above the roof so standing water cannot reach the seals. US residential codes generally require curbs at least 4 in above low-slope roofs; UK flat-roof practice uses upstands of about 150 mm.
Drainage and fall
Flat rooflights are built with a few degrees of fall in the glass or kerb. Level glass holds water, dirt and staining.
Structural loads
Frames and glass must be designed for snow, wind uplift and maintenance loads under the local loading code, and for impact where hail or hurricanes are expected.
Fall protection
Unprotected skylights are a serious roof-work hazard. US rules treat them as holes that must be guarded or screened, and UK practice is to test rooflights for non-fragility.
Condensation
Use thermally broken frames, warm-edge spacers and adequate room ventilation, especially over kitchens, bathrooms and pools.
Flashing and integration
Coordinate the skylight with the roof membrane, insulation and vapour control layer; most leaks occur at the junction, not in the skylight.
Size the daylight carefully. Too little glazing leaves rooms dim; too much causes glare and overheating. Industrial and retail roofs commonly use a rooflight area in the order of 10 – 20 % of the floor area as a starting point, adjusted by daylight modelling; homes generally need far less, placed where light is most useful.
Maintenance is light but should be planned. Clean the glass and clear gutters and drainage slots once or twice a year, check gaskets and sealant joints for cracking, and test actuators, rain sensors and smoke vent controls on the schedule set by the fire strategy. Provide safe access for this work from the start, so cleaners and inspectors never have to lean on the glazing.
Profile supply, inspection and delivery options
| Supply option | Description | Best for |
|---|---|---|
| Mill-length profiles | Frame, rafter, ridge and glazing-bar extrusions in stock or ordered lengths | Skylight makers with their own cutting and assembly |
| Cut and machined profiles | Profiles cut, drilled and machined to the approved drawing, labelled by part | Fabricators who want less shop work |
| Profiles with accessories | Profiles packed with matching gaskets, cleats and fixings | Continuous and structural systems, container shipping |
- Drawing approval and shop-drawing support before production
- Frame and component dimension checks against the approved drawings
- Finish inspection, including coating thickness and shade consistency for anodised batches
- Gasket and accessory fit checked against the profile sections
- Packing list and accessory inventory by part number
- Mill certificates to EN 10204 3.1 for the aluminium extrusions on request
Profiles are film-protected and bundled or crated with edge protection, and shipped on EXW, FOB, CIF or DAP terms; the skylight maker glazes and assembles the units.
How to specify and order skylight profiles
- Describe the roofRoof type and pitch, build-up, opening sizes and positions, and drawings or photos.
- Choose the functionFixed, venting, electric, lantern, continuous, structural or smoke vent; control and fire-alarm interfaces.
- Set performance targetsU-value, solar control, loads, smoke vent classes and the standards that apply locally.
- Select glazing and finishGlass or polycarbonate build-up, frame colour and coating standard.
- Approve and deliverShop drawings, profile list, packing and delivery schedule.
References and standards
- EN 12101-2 – Smoke and heat control systems: natural smoke and heat exhaust ventilators
- AAMA/WDMA/CSA 101/I.S.2/A440 – North American Fenestration Standard, including unit skylights
- International Code Council – IBC Section 2405 and IRC R308.6: Sloped glazing and skylights
- EN 14963 – Roof coverings: continuous rooflights of plastics with or without upstands
- EN 755-2 – Aluminium and aluminium alloys: extruded profiles, mechanical properties
- OSHA 29 CFR 1910.28 – Duty to have fall protection (holes, including skylights)
Aluminium (aluminum) skylights and rooflights: FAQ
What is the difference between a skylight and a rooflight?
Nothing, in practice. "Skylight" is the usual term in North America and "rooflight" in the UK and Europe; both mean a glazed opening in a roof.
What glass should a skylight use?
An insulated unit with a toughened outer pane and a laminated inner pane, so broken glass stays in place, plus a Low-E coating and argon fill. Add solar control glass in hot climates.
Do aluminium skylights cause condensation?
Unbroken aluminium frames can. Thermally broken frames with polyamide strips and warm-edge spacers keep the internal surface warm enough to avoid condensation in most heated buildings, provided the room is ventilated.
What is a smoke vent skylight?
An automatic opening rooflight that releases smoke and heat during a fire. In Europe it is a natural smoke and heat exhaust ventilator tested and CE marked to EN 12101-2, with declared free area, reliability, snow, wind, temperature and heat classes.
Can a skylight be installed on a flat roof?
Yes. Flat-roof skylights sit on a kerb or upstand at least about 100 – 150 mm above the roof, and the glass or kerb is built with a slight fall so water drains off.
Glass or polycarbonate for a skylight?
Glass gives a clear view, better acoustic performance and long life; polycarbonate is lighter, more impact resistant and cheaper, and suits industrial roofs where translucent light is acceptable.
Can skylights be opened electrically?
Yes. Chain or spindle actuators, surface-mounted or concealed, can be wired to switches, remote controls, rain sensors and building-management systems. Large sashes use several synchronised motors.
Planning a skylight or rooflight project?
Send the roof drawings, opening sizes, skylight type, glazing and destination. We will reply with a profile proposal and a delivered price.
