Thermally broken aluminium windows now sit at the centre of every serious Australian energy compliance conversation. Specifically, from May 2025, every new home and major renovation must meet a minimum 7-star NatHERS rating. Notably, this is a substantial step up from the previous 6-star benchmark. Consequently, builders, architects and homeowners face an immediate question. Namely, how do you hit 7 stars without compromising design or budget?
The answer for most Australian projects is the use of thermally broken aluminium window glazing. This single component is the most effective lever for whole-of-home energy performance. Furthermore, it delivers the result without resorting to bulky imported window systems.
The Thermal Performance Problem That Thermally Broken Aluminium Windows Solve
Aluminium is an excellent thermal conductor. This makes it superb for cookware. However, it is problematic for windows. Specifically, heat moves through a continuous aluminium frame the way water moves through a pipe — easily, in either direction. In summer, an unbroken frame absorbs solar heat and conducts it inside. Conversely, in winter, it draws conditioned heat outward to the cold exterior. As a result, the frame itself becomes a thermal bridge. This bypasses every other piece of insulation in the wall.
Consequently, a standard aluminium frame carries a generic U-value of around 12.7 W/m²K. By comparison, a typical brick veneer wall sits at roughly 0.5 W/m²K. Furthermore, industry data shows up to 40% of a home’s heating energy escapes through windows. Equally, up to 87% of unwanted heat enters the same way.
How Thermally Broken Aluminium Windows Transform Performance
A thermally broken aluminium window addresses this conduction problem at its source. Specifically, manufacturers mechanically join two aluminium profiles with a structural insulating polymer. Typically, this polymer uses reinforced polyamide. As a result, it carries the structural load while interrupting the heat path. Notably, modern high-performance systems use breaks of 24mm or wider.
Done correctly, the result is dramatic. Specifically, a quality thermally broken frame brings the frame U-value down to the 2–4 W/m²K range. Furthermore, paired with a high-performance IGU, whole-window U-values of 1.8–2.5 W/m²K become routinely achievable. This matches mid-range uPVC systems. However, aluminium retains all the structural, design and durability advantages of metal.
The Three Levers: Frame, Glass and SHGC
Maximum energy performance is never a single-component problem. Specifically, three variables interact. These are the frame, the insulated glazing unit (IGU), and the solar heat gain coefficient (SHGC).
The polyamide thermal break is the foundation. Furthermore, glazing performance compounds it. For instance, standard double glazing sits at 2.5–3.0 W/m²K. Adding a Low-E coating brings it to 1.5–2.0 W/m²K. Additionally, argon gas fill and warm-edge spacers add further refinement. SHGC, meanwhile, describes how much solar radiation passes through. North-facing glazing in Melbourne typically benefits from high SHGC for free winter warmth. By contrast, west-facing glazing usually wants lower SHGC to manage summer afternoon heat. Therefore, a skilled energy assessor models orientation-by-orientation.
Why WERS-Rated Products Matter – Thermally Broken Included
Manufacturer claims are only as good as their independent verification. Specifically, the Australian Glass and Window Association administers the Window Energy Rating Scheme (WERS). It rates window products against generic baselines using accredited simulation tools. Furthermore, each rated product receives a whole-of-window U-value, SHGC, air infiltration value and visible light transmittance figure. Notably, NatHERS, BASIX, AccuRate, FirstRate and BERS Pro all accept these figures as modelling inputs.
Without WERS data, energy assessors must use generic default values. However, these defaults are deliberately conservative. As a result, a non-rated window may force the rest of the house to compensate. For example, more wall insulation, smaller glazing, or reduced design ambition. By contrast, a WERS-rated equivalent simply does its job.
For independent product verification, the Window Energy Rating Scheme (WERS) database lists every accredited thermally broken aluminium window alongside its certified U-value, SHGC and air infiltration figures.
City Aluminium’s Thermally Broken Aluminium Windows Capability
- Forty years of Melbourne fabrication — we have operated since 1986. Furthermore, we bring the process precision that thermal break work demands.
- Architectural and Commercial ranges configured for thermal performance — double glazing as standard across the Architectural Range (Ultra Low-Profile Series, Designer Door Range). Furthermore, the same thermal capability is available at scale across the Commercial Range.
- Local manufacture, local control — we manufacture every product in our Melbourne facility. Consequently, we tune products to Victorian conditions rather than imported defaults.
- Comprehensive glazing options — single, double, laminated and tinted glazing. Additionally, this allows precise specification of U-value and SHGC by orientation.
- End-to-end service — manufacture, delivery, installation, retrofit and replacement. Furthermore, supply-only is available for builders managing their own install.
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Frequently Asked Questions
A thermally broken aluminium window has its inner and outer frames separated by a structural polyamide polymer barrier. Specifically, this polymer carries the structural load. At the same time, it interrupts the heat path. As a result, the frame’s thermal conduction drops dramatically.
For 7-star compliance in Victoria, whole-window U-values typically need to sit between 2.0 and 4.0 W/m²K. However, the exact figure depends on orientation, glazing area and other building elements. Notably, thermally broken aluminium with Low-E double glazing routinely delivers 1.8–2.2 W/m²K. Therefore, it provides margin to spare.
Usually not, if the frame is standard aluminium. Specifically, the frame’s high U-value undermines the glazing. After all, the whole-window figure is what counts. Consequently, double glazing in a thermally broken frame is the practical 7-star pathway in most Victorian projects.
SHGC is the solar heat gain coefficient. It measures how much solar radiation passes through the window, on a scale of 0 to 1. Specifically, high SHGC (~0.6+) is desirable on north-facing winter glazing. Conversely, low SHGC (~0.3 or below) is desirable on west-facing summer glazing. Therefore, specifying by orientation — rather than uniformly — optimises whole-house performance.
Rarely, in Victorian climate zones. Specifically, thermally broken aluminium with Low-E argon-filled double glazing typically delivers 7 stars with margin. Indeed, 8 stars is achievable in many configurations. However, triple glazing adds cost and weight without proportional benefit outside Passive House territory.
Yes, significantly. For example, air infiltration around the frame can negate gains entirely. Likewise, thermal bridging through the reveal and poor flashing both undermine performance. Therefore, the window must seal to the building’s air barrier. Furthermore, insulation around the rough opening must run continuously so rated performance translates to delivered performance.
