A good aluminium window profile specification states five things: the alloy and temper, the section properties the frame needs to resist wind load, the thermal-break construction that delivers the target U-value, the dimensional tolerance standard and the finish class. This guide works through each one with the calculations, standards and checklists that window fabricators, system companies and project buyers use when they order extruded window profiles.
An aluminium window is a set of extruded profiles (outer frame, sash or vent, mullion, transom, glazing bead, sill and trims) that a fabricator cuts, machines, crimps and glazes into a finished unit. The profiles decide almost everything about how the window performs: its stiffness under wind, its insulation value, how well it drains water, how slim the sightlines can be and how long the finish lasts.
Metline supplies the aluminium for this work: standard and custom-die extruded window profiles, thermal-break profiles, flat bar, angles, tube, sheet and coil for flashings and panels, cut to length or machined to drawing on request. We do not fabricate, assemble or install windows. This page is written for the people who do, and for the architects and project buyers who specify the material they use.
If you are looking for an overview of profile types (frames, sashes, beads, sills, trims and clad-timber profiles), see our aluminium window profiles guide. This page goes one step further: how to turn a window design into a profile specification that a supplier can quote and an inspector can check.
Almost all window profiles are extruded from the 6xxx alloys, which combine easy extrusion of thin, complex shapes with heat-treatable strength and a surface that anodises and coats well. The three grades below cover nearly every window system.
| Alloy and temper | Rm min (MPa) | Rp0.2 min (MPa) | Wall range | Typical window use |
|---|---|---|---|---|
| EN AW-6060-T5 | 160 | 120 | ≤ 5 mm | Residential frames, beads, trims; best surface for anodising |
| EN AW-6060-T6 | 190 | 150 | ≤ 3 mm | Frames and sashes needing a little more strength |
| EN AW-6060-T66 | 215 | 160 | ≤ 3 mm | Higher-strength 6060 for larger vents |
| EN AW-6063-T5 | 175 | 130 | ≤ 10 mm | General window frames and sashes |
| EN AW-6063-T6 | 215 | 170 | ≤ 10 mm | Mullions, transoms, large sliding frames |
| EN AW-6063-T66 | 245 | 200 | ≤ 10 mm | Heavy mullions and large-span frames |
| EN AW-6005A-T6 | 270 | 225 | ≤ 5 mm (open) | Structural mullions, curtain-wall-scale sections |
Minimum values from EN 755-2 for extruded profiles in the thinner wall band; limits fall for thicker walls. For ASTM orders, 6063-T5 to ASTM B221 requires 152 MPa tensile and 110 MPa yield, and 6063-T6 207 MPa and 172 MPa.
The choice is a balance. 6060 extrudes fastest and gives the most uniform anodised finish, so European system houses use it widely. 6063 is the international default and slightly stronger. 6005A is stronger again but costs more to extrude and needs care with anodised appearance; it is usually reserved for structural mullions in large openings. Stiffness does not change between them: every 6xxx alloy has a modulus of about 69–70 GPa, so if deflection governs the design, a stronger alloy does not help. Only a deeper or thicker section does.
Temper matters for fabrication too. T5 (cooled at the press and aged) is normal for thin window sections. T6 and T66 require a controlled quench and give higher strength. Profiles that will be bent into arches are often ordered in T4 and aged after bending, or bent in T5/T6 with a generous radius.
A window is tested and classified as a complete unit, but those classes are won or lost in the profile design: drainage chambers, gasket grooves, overlap between frame and sash, and section stiffness. Know the target classes before you choose or design a profile system.
| Property | European standard | Classes | What it asks of the profile |
|---|---|---|---|
| Air permeability | EN 12207 (test EN 1026) | Class 1 – 4 | Continuous gasket lines, accurate corner joints, tight frame-to-sash overlaps |
| Watertightness | EN 12208 (test EN 1027) | 1A – 9A, then E-classes above 600 Pa | Pressure-equalised drainage chambers, drain slots, sill design |
| Resistance to wind load | EN 12210 (test EN 12211) | Pressure classes 1 – 5 and E; deflection A, B or C | Moment of inertia of frame, mullions and transoms |
| Thermal transmittance | EN ISO 10077-1 / -2 | Declared Uw and Uf | Thermal-break width and design, chamber geometry |
| Product standard | EN 14351-1 | CE / UKCA declaration of performance | All of the above, tested as a system |
Under EN 12210 the deflection classes limit the frontal deflection of the most-stressed member to 1/150 of its span (class A), 1/200 (class B) or 1/300 (class C). Class B is a common project requirement for double-glazed units. In North America the equivalent framework is AAMA/WDMA/CSA 101/I.S.2/A440 (the North American Fenestration Standard), which grades windows into performance classes R, LC, CW and AW with a design pressure, while in India IS 1948 covers aluminium doors, windows and ventilators.
Deflection usually governs window members, not stress, because aluminium is about one third as stiff as steel. A quick check treats a mullion as a simply supported beam carrying a uniform load from the glass on each side.
For thermal-break profiles the two aluminium halves only act fully together if the polyamide strips transfer shear between them. System documentation quotes an effective moment of inertia that is lower than the sum of the halves would suggest; use that value, not the rigid-section value. If a mullion is too flexible, the usual fixes are a deeper section, a steel or aluminium reinforcing insert, or an extra fixing point that shortens the span.
This is a preliminary check for comparing profiles. Final design must follow the applicable structural code (e.g. EN 1999 Eurocode 9 for aluminium structures) and the system supplier’s test data.
Aluminium conducts heat about a thousand times better than the glass-fibre reinforced polyamide used to break the frame, so a profile without a break has a frame U-value (Uf) of roughly 5–7 W/m²K, while thermally broken profiles typically reach 1.0–3.5 W/m²K depending on break depth and insulation inserts. Most building codes in cold and temperate climates now require a thermal break.
Glass-fibre reinforced PA66 strips are rolled into knurled grooves in the inner and outer profiles, which are then crimped together. Strip depth (commonly from around 14 mm to over 40 mm) is the main lever on Uf. Allows different colours inside and outside.
Liquid polyurethane is poured into a channel in a single extrusion, cured, and the aluminium bridge beneath is cut away. Common in North America; break width is narrower than strip systems.
Polyurethane foam or extruded insulating inserts placed in the chambers between strips cut convection and radiation, lowering Uf further for passive-house-level systems.
Lower cost but less stable at high temperature and under creep; not suitable for profiles that will be powder coated after assembly. Specify PA66 GF25 for durability.
The whole-window value Uw combines glass, frame and the edge of the glazing unit, using EN ISO 10077-1:
Uw = (AgUg + AfUf + lgΨg) / (Ag + Af). For a window with 1.30 m² of glass at Ug 1.1, 0.52 m² of frame at Uf 2.0 and 5.0 m of glass edge at Ψg 0.06 W/mK, Uw = (1.43 + 1.04 + 0.30) / 1.82 ≈ 1.52 W/m²K. Reducing Uf to 1.4 with a deeper break brings Uw to about 1.35. Slim frames help too, because they reduce frame area.
Thermal-break profiles must also hold together structurally. EN 14024 tests the shear strength and transverse tensile strength of the composite profile at low, room and elevated temperature, and the profile system should carry this evidence before you use it on a project.
There is no single worldwide minimum wall thickness for window profiles. It follows from structural need, screw retention, extrusion feasibility and local rules: some national standards set minimum walls for main load-bearing members (for example around 1.4 mm for windows and 2.0 mm for doors), and system houses typically design main walls of 1.4–2.0 mm with thicker screw ports and crimp zones. Thin walls under 1.2 mm are hard to extrude consistently and can show print-through marks after finishing.
| Item | Standard | Notes |
|---|---|---|
| Precision profiles in 6060/6063 | EN 12020-2 | Tighter tolerances on dimensions, wall thickness, straightness, twist and angles than general profiles; normal for window systems |
| General extruded profiles | EN 755-9 | Wider tolerances; suitable for trims and non-critical sections |
| ASTM orders | ANSI H35.2 with ASTM B221 | Standard dimensional tolerances for extrusions in the US |
| Chemical composition | EN 573-3 | Alloy limits for EN AW designations |
| Mechanical properties | EN 755-2 / ASTM B221 | Minimum tensile and yield strength by temper and wall |
Weight per metre is simply cross-sectional area times density (2.70 g/cm³). Use the table to estimate weight from the section area shown on a die drawing, or to check that delivered profiles match the design weight within tolerance.
| Section area (mm²) | Area (cm²) | Weight (kg/m) | 6 m length (kg) |
|---|---|---|---|
| 200 | 2.00 | 0.540 | 3.24 |
| 300 | 3.00 | 0.810 | 4.86 |
| 400 | 4.00 | 1.080 | 6.48 |
| 500 | 5.00 | 1.350 | 8.10 |
| 600 | 6.00 | 1.620 | 9.72 |
| 800 | 8.00 | 2.160 | 12.96 |
| 1000 | 10.00 | 2.700 | 16.20 |
| 1200 | 12.00 | 3.240 | 19.44 |
| 1500 | 15.00 | 4.050 | 24.30 |
Thermal-break profiles also carry the weight of the polyamide strips, typically small compared with the aluminium; system catalogues list the combined weight.
| Finish | Specification to quote | Classes / thickness | Best suited to |
|---|---|---|---|
| Anodising | ISO 7599, QUALANOD, AAMA 611 | AA15 for most exteriors; AA20 – AA25 for coastal, industrial or high-wear sites | Metallic appearance, high abrasion resistance, natural, bronze, black and champagne |
| Polyester powder coating | QUALICOAT, AAMA 2603 / 2604, EN 12206-1 | Typically 60 µm minimum; Qualicoat Class 1, 2 (super-durable) or 3 | Any RAL colour, textures, matt finishes; most window projects |
| PVDF (fluoropolymer) coating | AAMA 2605 | Multi-coat liquid system, typically 70 % PVDF resin | High-rise and premium projects needing long colour and gloss retention |
| Wood-grain effect | Sublimation transfer over powder base | Base coat to coating specification | Timber appearance on aluminium frames |
| Dual colour | Different finish inside and out | Each half to its own spec | Thermal-break profiles, finished before crimping |
Pre-treatment decides how long a coating lasts, especially near the sea. For coastal projects, specify a pre-anodised or enhanced conversion pre-treatment under powder coating (the Qualicoat seaside option), a super-durable powder, and sealed anodising for anodised work. State colour by RAL, gloss level and texture, and approve a set of limit samples so that profiles from different batches match once installed.
Remember that cut ends, drilled holes and machined slots expose bare metal. Good fabricators seal or touch up these areas and use stainless steel or coated fasteners to avoid galvanic contact with carbon steel.
Profiles are cut at 45° for mitred frames or 90° for butt joints. Order lengths that minimise offcuts; standard extrusion lengths are around 6 m, with longer lengths possible for large sliding systems.
Mitred corners are joined by crimping onto aluminium corner cleats or by pinning, with a two-part corner adhesive. Cleat channels in the profile must be held to tight tolerance for the joint to stay square.
Drainage slots, hardware routing, lock and handle cut-outs and end milling for mullion joints are done on copy routers or CNC centres. Profiles can be supplied pre-cut and pre-machined to drawing.
Arched and circular windows are bent on profile-bending machines. Thermal-break profiles need specialist bending to avoid separating the strips.
Request protective film or interleaving for finished profiles, and packing that keeps faces apart, so that visible surfaces arrive unmarked.
Euro-groove and C-groove hardware channels, gasket grooves and bead clips must match the hardware and gasket suppliers you plan to use.
EN AW-6063 in T5 or T6 is the international default; 6060 is preferred where the finest anodised surface matters, and 6005A-T6 is used for heavily loaded structural mullions. All have the same stiffness, so section design matters more than alloy for deflection.
Main load-bearing walls are typically 1.4 – 2.0 mm, with thicker screw ports and crimp zones. Some national standards set minimum walls for windows and doors; the final value comes from the wind-load calculation and the system design.
Calculate the moment of inertia required to keep deflection within the project limit (often span/200 under EN 12210 class B) at the design wind pressure, and compare it with the profile’s effective Ix from the system data.
Typically about 1.0 – 3.5 W/m²K depending on polyamide strip depth and insulating inserts, compared with roughly 5 – 7 W/m²K for profiles without a thermal break.
Anodising to class AA20 or AA25 with good sealing, or super-durable powder or PVDF coating over a seaside-grade pre-treatment. Use stainless steel fasteners and seal cut ends.
No. Metline supplies the aluminium: extruded window and thermal-break profiles, accessories profiles, sheet and coil, cut or machined to drawing, with mill certificates and export packing to fabricators and project buyers worldwide.
Send the die drawings, alloy, temper, finish and quantities. We will confirm tolerances, certification and a delivered price for your fabrication shop.
