An aluminium casement window is a hinged sash that closes against compressed gaskets, which is why it outperforms sliding windows on air tightness, water tightness and sound reduction. Performance depends on the system depth, the thermal break, the glazing and the hardware working together. Metline supplies casement window profiles in 6063 and 6060, thermal break sections, sheet and accessories, to window fabricators, system companies and project buyers worldwide.
A casement sash swings on hinges at its side (or, for a tilt-turn, on a combined hinge and stay). When the handle is turned, locking cams pull the sash tight against one or more continuous gaskets. That compression seal is the reason casements are the default choice where a building must meet strict energy, acoustic or weather targets.
A sliding window relies on brush seals that must let the sash move, so some air always passes. A casement has no moving seal in the closed position: the gasket is squeezed, not wiped. In laboratory tests to EN 12207, well-built aluminium casements routinely reach air permeability class 4, the highest class, while most sliders sit in classes 2 or 3. The same principle helps watertightness and acoustic insulation, because sound and wind-driven rain both follow air paths.
Aluminium suits the casement format because extruded profiles are stiff, dimensionally stable and can carry large insulated glass units on narrow sightlines. With a polyamide thermal break between the inner and outer shells, a modern aluminium casement can reach whole-window U-values that meet current European, UK and Australian energy rules, while needing far less maintenance than timber and staying rigid in sizes where uPVC needs steel reinforcement.
The traditional format in the UK, Australia, India and much of Asia. Wind pressure pushes the sash onto its seals, which helps weather performance, and the sash never intrudes into the room. Friction stays or restrictors control the opening.
Common in continental Europe and high-rise housing, because the glass can be cleaned from inside and the sash is not exposed to wind when open. Needs a well-drained sill, since rain on the closed sash is driven towards the inner seal.
One handle gives two actions: tilt for secure, draught-free ventilation, turn for full opening and cleaning. Standard in Germany and widely specified for apartments, schools and hotels where safe night ventilation matters.
The sash sits in the same plane as the frame rather than lipping over it. Popular for UK refurbishment and contemporary villas because it echoes traditional timber casements.
Narrow face widths that maximise glass area. Strength comes from deeper sections and thicker walls instead of wider ones, so check glass weight and sash size limits.
A fixed light with one or more opening sashes, joined by mullions and transoms. Gives daylight and views with a controlled opening ratio, common on offices and apartment facades.
Once the opening type is fixed, the frame depth decides how much insulation, how heavy a glass unit and what wind load the window can take. Deeper systems allow wider thermal break strips, triple glazing and stiffer profiles. The ranges below are typical of the market, not a single manufacturer; every system has its own tested limits.
| System class | Typical frame depth | Thermal break strip | Typical glazing | Typical use |
|---|---|---|---|---|
| Non-insulated | 45 – 55 mm | None | Single or 5-12-5 double | Warm climates, internal screens, budget housing |
| Standard thermal break | 55 – 65 mm | About 14 – 24 mm | 24 – 28 mm double glazing | Mainstream housing and light commercial |
| High insulation | 70 – 80 mm | About 24 – 35 mm | Low-E double or slim triple | Energy-efficient homes, UK, EU and Australian projects |
| High performance | 80 – 90 mm | About 34 – 45 mm | Triple glazing up to about 50 mm | High-rise, coastal, acoustic and commercial work |
| Passive-house direction | 90 – 100 mm+ | Wide strips plus foam inserts | Triple Low-E, warm-edge spacers | Cold climates and very low-energy buildings |
Profile wall thickness in casement systems is typically 1.4 – 2.0 mm. Many specifications ask for at least 1.4 mm on main frame walls; heavier sashes and high wind loads may call for 1.8 – 2.0 mm. The governing values are those in the system test report.
Almost all window profiles are extruded from 6xxx-series alloys, which flow well through complex dies, harden by ageing and take an even anodised or powder-coated finish. The choice between them is mostly about surface quality versus strength.
| Alloy and temper | Typical tensile / yield (MPa) | Standard | Why it is used |
|---|---|---|---|
| 6063-T5 | about 150 – 175 / 110 – 130 (by standard and wall) | ASTM B221, EN 755-2 | The standard window alloy: good surface, easy extrusion, adequate strength for most frames and sashes |
| 6063-T6 | ≥ 205 / ≥ 170 (ASTM); 215 / 170 thin walls (EN) | ASTM B221, EN 755-2 | Higher strength for mullions, large sashes and high wind loads |
| 6060-T66 | ≥ 215 / ≥ 160 thin walls; 195 / 150 thicker | EN 755-2 | The usual European window alloy; very close to 6063 with a slightly leaner chemistry |
| 6005A-T6 | about 260 – 270 / 215 – 225 (by wall) | EN 755-2 | Reinforcing mullions and transoms where 6063 is not stiff or strong enough |
Values are specified minimums from the extrusion standards and fall into wall-thickness bands; the extruder's certificate shows the bands that apply. For precision architectural sections, EN 12020-2 sets tighter dimensional tolerances than EN 755-9, which matters for how well corner joints and gasket grooves fit. More on the alloy itself is in our 6063 aluminium guide and on 6063 extrusions.
Glass-fibre-reinforced polyamide strips (typically PA66 GF25) are rolled into the profile to join the inner and outer aluminium shells. The strip interrupts heat flow; foam or extra cavities inside it reduce radiation and convection. Its shear strength is tested to EN 14024 so the composite profile still acts structurally.
EPDM gaskets in the frame and sash form two or three sealing lines. The centre (or "middle") gasket divides a drained outer chamber from a dry inner chamber, the core of the rain-screen principle used in good casements.
Espagnolette or gear-driven locks engage several keeps around the sash. More points give even gasket compression, better resistance to wind suction and better security. Larger sashes need more points.
Water that passes the outer seal collects in the frame chamber and leaves through slotted drainage holes, often with baffled covers to stop wind blowing it back. Pressure-equalised chambers make drainage work under storm conditions.
Mitred corners are joined with crimped or pinned aluminium cleats and structural adhesive, then sealed. Joint quality decides long-term squareness and whether the gasket line stays continuous at the corners.
Glass sits on setting blocks, held by snap-in beads with inner and outer gaskets. Correct toe-and-heel packing transfers glass weight to the hinges so the sash does not drop over time.
Casements are tested as complete windows, not as profiles. Ask for the system test report that matches the size, glazing and hardware you intend to use; a report for a small sample does not cover a sash twice the size.
| Market | Product standard | What is classified |
|---|---|---|
| Europe (CE / UKCA) | EN 14351-1 | Air permeability (EN 12207, classes 1 – 4), watertightness (EN 12208, 1A – 9A and E-classes), wind resistance (EN 12210, classes 1 – 5 with deflection A/B/C), thermal transmittance (EN ISO 10077), acoustic (EN ISO 717-1) |
| United Kingdom | BS 6375-1/-2, PAS 24, Approved Document L and Q | Weather and operation classes, enhanced security, energy limits for new and replacement windows |
| North America | AAMA/WDMA/CSA 101/I.S.2/A440 (NAFS); NFRC 100 / 200 | Performance class (R, LC, CW, AW) and grade (design pressure); U-factor and SHGC |
| Australia | AS 2047, AS 1288, AS 2208 | Wind and water ratings by site class, glass selection, safety glazing |
| Profiles and finishes | EN 755, EN 12020, Qualicoat, Qualanod, AAMA 2603/2604/2605 | Alloy properties, tolerances, coating and anodising quality |
| Component | Options | Selection advice |
|---|---|---|
| Glazing | Double IGU (e.g. 4-16-4 to 6-20-6), Low-E, argon fill, triple glazing, laminated, acoustic laminated, toughened | Match glass thickness to the system's glazing range and the hinge load. Use laminated glass at low level, on balconies and where codes require safety glazing. |
| Hinges and stays | Butt hinges, friction stays, concealed hinges, tilt-turn gear | Check the rated sash weight; concealed hinges look cleaner but often carry less load. |
| Locks | Single-point, multi-point espagnolette, keyed handles, secured-by-design hardware | Use multi-point locking on any sash over about 1 m tall or in exposed locations. |
| Restrictors | Opening limiters, child-safety catches, cleaning hinges | Required on upper floors of schools, care homes and many residential towers. |
| Gaskets | EPDM single, double or triple sealing; foam-filled; silicone for special cases | Triple sealing for acoustic and passive-house targets; check corner vulcanising or moulded corners. |
| Surface finish | Polyester powder coating, super-durable powder, PVDF, anodising, wood-grain transfer, dual colour | Use super-durable powder, PVDF or class 20 anodising near the coast; dual colour lets the interior differ from the facade. |
For finishing choices, see our guides to anodised aluminium extrusions and powder-coated aluminium windows.
A typical apartment block specification might call for 70 mm thermally broken tilt-turn sashes, 6-16-6 Low-E argon glazing, air permeability class 4, watertightness class 7A or better and wind class C4 or C5, powder coated in a super-durable grey. Each of those numbers then has to be shown in a test report for the chosen system.
Buyers can order bare profile lengths for their own fabrication shop, or profiles cut and machined to size with matching accessories. Every profile shipment carries a mill test certificate for the alloy, and the finish is documented against the agreed specification.
Choose a casement when air tightness, water tightness, acoustic insulation or a low U-value is a priority, because the sash closes onto compressed gaskets. Choose a slider where the opening must not project, for very wide openings, or where cost is the main driver and performance targets are modest.
The glass unit has the largest effect, followed by the thermal break width and design, the frame face width and the spacer bar. The whole-window value is calculated to EN ISO 10077 or NFRC 100 for a stated size, so compare values for the same reference size.
Yes, if the system has a tested wind class to suit the design pressure, the profiles and mullions are sized for the load, and the finish and hardware are specified for marine exposure: super-durable powder, PVDF or thick anodising with stainless or coated fittings.
Usually 6063-T5 or T6 (aluminum 6063 in US terms) or the European 6060-T66. Heavily loaded mullions may use 6063-T6 or 6005A-T6. These alloys extrude into complex sections and give a smooth surface for coating.
Apartments, schools, hotels and high-rise housing: the tilt position gives secure ventilation without a large opening, and the turn position lets occupants clean the outside glass from inside.
The window schedule or drawings with opening sizes and quantities, opening type, performance targets (U-value, wind load, air and water classes, acoustics), glass and hardware preferences, colour and finish, and the delivery destination.
No. Metline supplies casement profiles in mill finish, anodised or powder coated, in stock lengths or cut to size, with accessories; your fabricator assembles and glazes the windows. Export packing and mill certificates are included.
Send the window schedule, performance targets, finish and destination. Our team will propose a profile series and quote profiles and accessories.
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