Basic insulated
Thermal break of about 20 – 24 mm, double Low-E IGU, standard spacer, two gasket lines and standard hardware. Typical Uw about 1.8 – 2.2 W/m²K. Suits apartments and homes in mild climates.
Window systems
Insulated Aluminium Windows System
An insulated aluminium window is a complete system in which every heat path is interrupted: a thermally broken frame, an insulating glass unit with a warm-edge spacer, continuous gaskets, compression hardware and a sealed installation joint. Get one link wrong and the window loses heat or forms condensation, however good the rest is. Metline supplies thermal break window profiles and accessories to window fabricators, selected for each project's climate, window schedule and target standards, worldwide.
- Frame
- 6060 / 6063 with PA66 GF25 strips
- Glazing
- Low-E double or triple IGU
- Typical Uw
- About 0.9 – 2.0 W/m²K
- Standards
- EN 14351-1 · EN ISO 10077 · NFRC
What makes an aluminium window "insulated"?
Aluminium conducts heat roughly 700 times better than the polyamide used in thermal breaks. A plain aluminium frame therefore acts as a bridge between the warm room and the cold outside, with a frame U-value (Uf) of around 5.5 – 7 W/m²K. In winter its inner face can drop below the dew point and run with condensation. An insulated system cuts that bridge so the inner and outer aluminium shells are joined only by low-conductivity material.
The thermal break is necessary but not sufficient. Heat also leaves through the glass centre, through the metal spacer at the glass edge, through gaps where the sash meets the frame, and through the joint between frame and wall. A window specification that only says "thermal break frame and double glazing" leaves most of these open, which is why two windows sold under the same description can differ in whole-window U-value (Uw) by a factor of two.
Thinking of the window as a continuous insulation line, running from the wall insulation through the installation joint, the thermal break, the gasket plane and the glazing, is the most useful way to configure an insulated system. The sections below follow that path.
Where heat escapes, and what stops it
| Position | Component that insulates | What to confirm |
|---|---|---|
| Frame and sash | Thermally broken aluminium profiles | Frame and sash depth, strip width, chamber design, profile drawing |
| Thermal break | Glass-fibre reinforced polyamide (PA66 GF25) strips, sometimes with foam inserts | Strip width and shape, alignment with the glass and wall insulation |
| Glass centre | Insulating glass unit (IGU) | Double or triple, Low-E coatings, gas fill (argon or krypton), cavity width |
| Glass edge | Spacer bar | Aluminium versus warm-edge (stainless or polymer) spacer, linear thermal transmittance Ψg |
| Sash to frame | Gaskets | EPDM or TPE, centre gasket, vulcanised or moulded corners, continuity |
| Locking | Hardware compression | Number of locking points, keep positions, adjustability |
| Wall junction | Installation joint | Gap size, insulation fill, inner vapour-tight and outer weatherproof membranes or sealants |
Each of these must be at least as good as its neighbours. A 34 mm thermal break combined with an aluminium spacer and an uninsulated wall gap behaves much like a cheaper system, because heat simply takes the easier route.
Thermal break profiles: strip width, depth and alloy
Most insulated windows use the "crimped strip" method: two aluminium extrusions are knurled and rolled onto polyamide strips that run the full length. The composite profile must transmit shear between the shells, which is tested to EN 14024. The North American alternative is "pour and debridge", where liquid polyurethane fills a channel and the aluminium bridge is cut away; it is common in storefront and commercial windows.
| System class | Strip width (approx.) | Typical Uf (W/m²K) | Typical use |
|---|---|---|---|
| Non-insulated | — | 5.5 – 7.0 | Interior partitions, hot climates without cooling targets |
| Basic thermal break | 14 – 20 mm | 3.0 – 3.8 | Mild climates, budget housing |
| Standard insulated | 24 – 27.5 mm | 2.4 – 3.0 | Most residential and hotel projects |
| Enhanced | 32 – 38 mm | 1.8 – 2.4 | Cold climates, premium residential, offices |
| High performance | 40 mm and up with foam inserts | 1.0 – 1.6 | Very cold regions, low-energy and passive-house buildings |
Uf ranges are indicative, calculated to EN ISO 10077-2; actual values depend on profile geometry and must come from the system calculation or test report.
The profiles themselves are extruded in 6060-T6/T66 (common in Europe) or 6063-T5/T6 (common in North America and Asia). These alloys give the clean surface needed for anodising and powder coating and enough stiffness for normal sash sizes. Typical wall thickness is 1.4 – 2.0 mm, increasing for large sashes, high wind loads and heavy triple glazing.
Choosing the insulating glass unit and spacer
Glass is usually 70 – 85 % of the window area, so the IGU sets most of the result. Low-emissivity coatings reflect long-wave heat back into the room; argon in the cavity reduces conduction; a third pane adds a second insulating cavity at the cost of weight and some light.
| Glass unit | Example build-up | Typical Ug (W/m²K) | Weight (kg/m²) |
|---|---|---|---|
| Double, clear, air | 4 / 16 / 4 | 2.7 – 2.9 | About 20 |
| Double, Low-E, argon | 4 / 16 Ar / 4 Low-E | 1.0 – 1.1 | About 20 |
| Double, Low-E, laminated | 4 / 16 Ar / 6.4 laminated | 1.0 – 1.1 | About 26 |
| Triple, two Low-E, argon | 4 / 14 Ar / 4 / 14 Ar / 4 | 0.5 – 0.7 | About 30 |
The spacer is the strip that separates the panes at the edge. A traditional aluminium spacer adds a significant linear heat loss (Ψ around 0.08 – 0.11 W/m·K in an aluminium frame), while warm-edge spacers of stainless steel or reinforced polymer typically achieve 0.03 – 0.05 W/m·K. On a normal residential window, switching to warm edge lowers Uw by roughly 0.1 – 0.2 W/m²K and, just as important, raises the glass-edge temperature to prevent condensation along the bottom of the pane.
In hot climates the priority shifts from U-value to solar control. A solar-control Low-E coating with a low g-value (solar heat gain coefficient) keeps cooling loads down while maintaining daylight.
Basic, enhanced and high-performance configurations
Enhanced insulated
Thermal break of about 28 – 34 mm, double Low-E argon IGU with warm-edge spacer, centre gasket and multi-point locking. Typical Uw about 1.3 – 1.6 W/m²K. Suits hotels, villas and urban residential towers.
High performance
Wide thermal break with foam-filled chambers, triple IGU, warm-edge spacer, three gasket lines and high-compression hardware. Typical Uw about 0.8 – 1.1 W/m²K. Suits cold regions and low-energy buildings.
Uw values above are indicative for a standard reference window of about 1.23 × 1.48 m; large fixed lights achieve better figures and small, frame-heavy windows worse ones. Ask for the Uw calculated for your actual sizes.
Standards for insulated aluminium windows
| Property | Europe and international | North America |
|---|---|---|
| Product standard | EN 14351-1 (CE marking of windows and external doors) | AAMA/WDMA/CSA 101/I.S.2/A440 (NAFS) |
| Thermal transmittance | EN ISO 10077-1 and -2 (Uw, Uf), EN 673 (Ug) | NFRC 100 (U-factor), NFRC 200 (SHGC) |
| Air permeability | EN 1026 test, EN 12207 classes 1 – 4 | ASTM E283 |
| Watertightness | EN 1027 test, EN 12208 classes 1A – 9A and E | ASTM E331 / E547 |
| Wind resistance | EN 12211 test, EN 12210 classes 1 – 5 (A, B, C) | ASTM E330 |
| Condensation | Temperature factor fRsi to EN ISO 10211 / 13788 | NFRC 500, AAMA 1503 |
| Thermal break strips | EN 14024 (composite profile shear and tensile strength) | AAMA 505 / AAMA TIR-A8 |
Energy codes then set the targets: for example, national building regulations across Europe set maximum Uw values for new and replacement windows, while in the United States the IECC and ENERGY STAR use NFRC-rated U-factors by climate zone. Note that 1 Btu/h·ft²·°F equals 5.678 W/m²K, so a U-factor of 0.30 is about 1.7 W/m²K.
What to prioritise by climate and building type
- Cold climates: wide thermal break, triple or high-grade double Low-E glazing, warm-edge spacer and an insulated, airtight installation joint. Check the frame temperature factor to rule out condensation.
- Hot climates: solar-control glass with a low g-value, good air tightness to keep humid air out, and a standard thermal break to stop the frame heating the room.
- Coastal sites: marine-grade pretreatment and Qualicoat Class 2 or anodising to at least 20 µm, A4 stainless or coated hardware and drained, ventilated glazing rebates.
- High-rise buildings: wind resistance and watertightness classes rise with height; deeper frames, more locking points and tested pressure equalisation matter as much as U-value.
- Hotels, schools and roadside housing: combine thermal and acoustic needs; laminated acoustic glass in asymmetric build-ups adds sound reduction without hurting Ug.
- Replacement projects: survey the existing opening, wall build-up and insulation position so the new frame sits in line with the insulation rather than in front of it.
Project supply, quality control and packing
- Schedule reviewWe check window types, sizes, opening directions, glass, colour, hardware and performance targets against the chosen system.
- Thermal checkFrame depth, thermal break, IGU, spacer, gasket lines and locking are matched to the target Uw and climate.
- ProcessingOn request, profiles are cut and machined to drawing; gaskets, thermal-break strips and hardware are supplied to match, for your fabricator to assemble and glaze.
- InspectionProfile dimensions, wall thickness, coating thickness and gasket fit are checked before packing.
- Export packingProfiles are labelled by window number and floor, protected with film and edge guards, and bundled or crated with a packing list.
References and standards
- EN 14351-1 – Windows and doors: product standard, performance characteristics
- EN ISO 10077-1 and 10077-2 – Thermal performance of windows, doors and shutters: calculation of thermal transmittance
- EN 14024 – Metal profiles with thermal barrier: mechanical performance
- NFRC 100 – Procedure for Determining Fenestration Product U-factors
- AAMA/WDMA/CSA 101/I.S.2/A440 – North American Fenestration Standard
Insulated aluminium (aluminum) windows: FAQ
If a specification only says "insulated aluminium windows", what must be confirmed?
At least the target Uw or U-factor, the thermal break width or system, the glass build-up (double or triple, Low-E, gas), the spacer type, gasket and locking arrangement, and the air, water and wind classes. Without these, quotations from different suppliers cannot be compared.
Is a thermal break frame with double glazing enough?
Often not. A narrow thermal break with clear double glazing and an aluminium spacer gives a Uw of around 2.5 – 3 W/m²K, which fails many current energy codes. Low-E coatings, argon, warm-edge spacers and a wider break typically bring Uw down to 1.3 – 1.6 W/m²K.
Does triple glazing need different frames and hardware?
Yes. Triple IGUs are thicker (typically 36 – 48 mm) and about 50 % heavier than double units, so the sash needs a deeper glazing rebate and the hinges or rollers must be rated for the extra weight. Check maximum sash weight before choosing triple glazing for large opening windows.
Can aluminium windows reach passive-house levels?
Yes. High-performance systems with wide thermal breaks, foam-filled chambers and triple glazing achieve Uw values below 0.8 – 1.0 W/m²K, and several aluminium systems hold component certification from the Passive House Institute.
Will insulated aluminium windows stop condensation?
They greatly reduce it by keeping inner frame and glass-edge surfaces warmer. Indoor humidity still matters: in very humid rooms or very cold weather, some condensation on glass can occur with any window. Warm-edge spacers specifically help the bottom edge of the glass.
Are insulated aluminium windows also soundproof?
Thermal insulation and sound insulation depend on different things. For noise, use laminated acoustic glass, panes of different thickness, wider cavities and continuous seals. Both can be combined in one window when the requirements are set together.
Need insulated windows for a project?
Send your window schedule, drawings, climate and performance targets to sales@metline.in for a profile proposal and quotation.
