Thermally broken fully insulated aluminium windows sit at the top of the high-performance glazing market. Most Australian projects targeting 7-star NatHERS get there with thermally broken aluminium framing and double glazing. However, some projects aim higher. For instance, Passive House certifications, 8-star and 9-star NatHERS targets, and all-electric homes designed for net-zero operation. Furthermore, commercial buildings pursuing NABERS or Green Star ratings all require glazing that goes beyond the conventional thermal break.
Fully insulated aluminium window systems answer this brief. Specifically, the frame, glazing unit, sash, and reveal interface all engineer together as a continuous insulated whole. Notably, the difference between a thermally broken window and a fully insulated one matters significantly. Consequently, for projects with serious performance ambitions, it sits as the deciding factor.
Where Standard Systems Reach Their Limit Before Thermally Broken Fully Insulated Windows Take Over
A standard thermally broken aluminium window with Low-E double glazing typically delivers whole-window U-values of 1.8–2.2 W/m²K. Notably, that figure meets 7-star NatHERS compliance with margin in most Victorian projects. However, it falls short for Passive House. Specifically, Passive House whole-window U-values typically need to sit at or below 0.8 W/m²K. As a result, the project requires roughly twice the performance of a standard thermally broken assembly.
The gap has multiple sources. Firstly, the polyamide thermal break still allows some heat transfer. Secondly, the IGU spacer at the glass perimeter creates a localised thermal bridge. This proves particularly true with an aluminium spacer. Thirdly, air infiltration around the sash and through hardware penetrations adds further loss. Furthermore, heat flows around the entire window assembly through the surrounding wall structure. Specifically, this happens if the reveal lacks proper detailing. Notably, each of these counts as a small loss. Collectively, however, they can total a third of the total energy moving through the opening.
What Thermally Broken Fully Insulated Windows Deliver in Practice
Fully insulated systems address each loss path. Firstly, the polyamide break widens. Specifically, high-performance systems use 30mm or wider breaks. Notably, some fill them with insulating foam. Secondly, the IGU uses warm-edge spacers. For example, composite or stainless steel rather than aluminium. As a result, the perimeter thermal bridge disappears. Thirdly, triple glazing replaces double glazing. Furthermore, two Low-E coatings and krypton or argon fills bring centre-of-glass U-values below 0.7 W/m²K.
The sash gains additional gaskets, multi-point compression locking, and air-tightness detailing. Additionally, the reveal insulates and air-seals continuously with the building’s primary insulation layer. Specifically, the reveal forms the timber or steel framing of the rough opening. Consequently, thermal bridging around the window disappears. As a result, every component contributes to thermal performance. Notably, this goes beyond just the centre of the glazing unit.
Whole-window U-values for fully insulated assemblies typically sit between 0.7 and 1.4 W/m²K. Notably, this halves the heat loss of a standard thermally broken window. In a Passive House, this performance becomes non-negotiable. Furthermore, in a high-performance home targeting 8-star or 9-star NatHERS, it provides margin. Specifically, the design ambition holds. For instance, large glazing, north-facing aspects, and slim profiles.
For technical guidance on certified Passive House outcomes, Passive House Australia maintains the local resources covering thermally broken fully insulated windows, building envelope detailing, and certification pathways.
When Fully Insulated Systems Make Sense
Fully insulated systems do not suit every project. Specifically, they cost more, weigh more, and operate heavier. For a typical 7-star Melbourne home, standard thermally broken aluminium with double glazing remains the right answer. However, fully insulated systems start to make sense in specific cases. For instance, Passive House certification, 8-star or 9-star NatHERS targets, all-electric net-zero operation, or severe acoustic exposure. Furthermore, heavily glazed facades where reducing the glazing fraction would hurt the design also qualify. Additionally, commercial buildings pursuing aggressive NABERS or Green Star ratings benefit.
Climate context matters too. Specifically, Melbourne sits in NatHERS climate zone 60 (and 62 for parts). Furthermore, this means cold winter overnight lows and hot summer afternoons. As a result, fully insulated systems pay back fastest in this climate. Notably, both heating and cooling loads benefit. Additionally, cooler regions of Victoria see even stronger payback through winter heating reductions. For example, the Yarra Ranges, Macedon, and the Otways.
Why City Aluminium for High-Performance Glazing
- Forty years of Melbourne fabrication — operating since 1986. Notably, high-performance work demands process precision. Furthermore, four decades of fabrication experience embed it.
- Architectural Range configured for thermal performance — double glazing as standard across the Ultra Low-Profile Series and Designer Door Range. Additionally, thermal break and high-spec glazing options sit available for projects pushing past 7-star.
- Commercial Range delivers the same capability at scale — for NABERS- and Green Star-rated multi-storey developments, schools and hospitals.
- Local manufacture, local control — we make every product in our Melbourne facility. Consequently, we handle project-specific glazing, hardware and finishing in-house.
- Project-specific performance data — we work with energy assessors and architects to provide configuration-specific U-value and SHGC data. As a result, modelling accuracy on Passive House and high-performance briefs improves.
- End-to-end One Stop service — manufacture, delivery, installation, retrofit and replacement. Furthermore, supply-only sits available for builders managing their own install. Notably, installation detailing matters critically for fully insulated systems to perform as rated.
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Frequently Asked Questions
A thermally broken window has a polyamide barrier separating the inner and outer aluminium frame. Typically, it delivers whole-window U-values of 1.8–2.5 W/m²K. By contrast, a fully insulated system goes further. Specifically, wider thermal breaks, warm-edge spacers, triple glazing, additional gasketing, and continuous insulation through the reveal. As a result, it typically delivers 0.7–1.4 W/m²K.
Generally, no. Specifically, standard thermally broken aluminium with Low-E double glazing achieves 7-star compliance with margin in most Victorian projects. However, fully insulated systems become relevant for higher targets. For instance, 8-star and 9-star certification, Passive House, or projects with very heavy glazing fractions.
Passive House forms an international high-performance building standard. Specifically, it emphasises airtightness, continuous insulation and minimal energy use. Notably, whole-window U-values for Passive House typically need to sit at or below 0.8 W/m²K. Furthermore, airtightness around the assembly matters equally.
In most cases, yes. Specifically, triple glazing with dual Low-E coatings and inert gas fill forms the standard glazing for Passive House. Furthermore, it suits other very-low-U-value targets. However, some warmer-climate Passive Houses use high-spec double glazing. Notably, Victorian climates almost always specify triple glazing for full insulation outcomes.
Significantly more than standard thermally broken systems. Specifically, the premium often runs 40–80%. However, the exact figure depends on configuration, glazing specification and finishes. Notably, the cost justifies itself for projects where certification or operational targets require this level of performance. Furthermore, the City Aluminium estimator captures the variables for tailored figures.
Yes, critically. Specifically, a fully insulated window installed without continuous insulation through the reveal loses much of its rated performance. Furthermore, the same applies without a tight air seal to the building’s air barrier and proper flashing. Consequently, installation detailing forms part of the specification. Notably, it sits beyond an afterthought.
