Thermal Bridging in Aluminium Facade Systems: What Specifiers Need to Know
Thermal bridging in aluminium facades is a known design parameter, not a flaw. Aluminium conducts heat roughly 1,500 times faster than still air, so any element that penetrates the insulation layer creates a localised path for heat transfer. The job of the facade system is to limit those paths through deliberate design - continuous insulation planes, discrete fixings, thermal breaks, and ventilated cavities. The question for specifiers is not whether aluminium bridges thermally, but how the system manages it.
This is well-understood territory. Aluminium alloys used in facade systems - principally 6060 and 6063 in T5 temper for rainscreen cladding and battens, and 6060-T6 and 6005A-T6 for curtain wall framing - have a thermal conductivity of approximately 205 W/mK. That is substantially higher than steel (around 50 W/mK) and orders of magnitude above timber or fibre cement. It is also a stable, published property that facade engineers can model with precision, which is exactly what makes it manageable.
Why does thermal bridging matter for the building envelope?
The NCC Volume 1 Section J sets the energy efficiency requirements for commercial buildings. The building envelope - walls, roof, glazing, and all penetrations - must limit heat flow to meet either the deemed-to-satisfy provisions or the verified performance pathway. For external walls, the relevant provisions under J1.5 and J1.6 prescribe minimum total R-values that account for all components in the wall assembly, including fixings, framing, and any elements that bridge the insulation layer.
The critical point for aluminium facades is that compliance is assessed at the whole-of-wall level, not at the cladding panel level. A non-combustible aluminium panel tested to AS 1530.1 - such as interloQ (CSIRO FNC12595) or element13 (CSIRO FNC12545) - satisfies the combustibility requirements independently. But the thermal performance of the overall wall system depends on how the panel is attached, where the insulation sits, and what happens at every fixing point, bracket, and penetration.
Facade engineers model this using methods set out in AS/NZS 4859.2 or through finite element analysis. The thermal bridge at each fixing point is quantified as a point thermal transmittance (chi-value) or linear thermal transmittance (psi-value) and factored into the total U-value for the wall assembly. Getting this right requires accurate system details - fixing type, bracket dimensions, spacing, material, and the presence of any thermal isolation between the bracket and the structure.
How do rainscreen systems manage thermal bridging?
Rainscreen cladding - the approach used by interloQ and element13 - manages thermal bridging through a fundamentally different strategy to curtain wall. The cladding panel is the outer skin. Behind it sits a ventilated cavity, typically 20-50mm deep. Behind that sits the insulation, which is continuous across the wall face, broken only at the discrete fixing points where brackets penetrate through to the structural substrate.
This arrangement has several advantages for thermal performance.
First, the insulation layer is continuous. Unlike framed wall systems where studs or rails interrupt the insulation at regular centres (typically 450-600mm), a rainscreen system places fixings at wider centres dictated by the structural requirements of the cladding - often 600-1,200mm vertically and horizontally. Fewer fixings means fewer thermal bridges.
Second, each fixing is a point penetration, not a continuous rail. An aluminium bracket passing through insulation creates a localised thermal bridge that can be quantified and, where necessary, mitigated with thermal isolation pads or washers at the bracket-to-structure interface. The thermal impact of a point fixing at 900mm centres is significantly less than a continuous aluminium rail at 600mm centres.
Third, the ventilated cavity itself plays a role. While not an insulating layer in the conventional sense, the drained and ventilated cavity behind the cladding reduces the temperature differential across the insulation by allowing solar-heated air to convect away rather than conduct inward. In cooling-dominated climates - most of coastal Australia - this cavity ventilation measurably reduces the cooling load on the building.
For interloQ, the interlocking extrusion profile (6060/6063 T5, 1.8-3.5mm wall thickness) is supported on vertical or horizontal rails, which in turn fix to brackets at discrete points. For element13, the 3mm solid aluminium panels (8.13 kg/m2) are similarly supported on a subframe of conneQt battens or proprietary brackets. In both cases, the cladding system is thermally decoupled from the structure except at those bracket locations.
How does curtain wall approach thermal bridging differently?
Curtain wall systems carry the full weatherproofing and structural responsibility in a single integrated assembly. The framing - mullions and transoms - spans continuously from slab to slab and is directly exposed to both interior and exterior conditions. Without intervention, this continuous aluminium framing would create a substantial thermal bridge across the entire facade.
The 165CW unitised curtain wall system addresses this through thermally broken glazing adaptors. These use a polyamide strip - a low-conductivity engineering polymer - with an aluminium nose cap to create a thermal separation within the frame profile itself. The interior aluminium section and the exterior aluminium section are structurally connected through the polyamide bridge, which has a thermal conductivity of approximately 0.25 W/mK compared to aluminium’s 205 W/mK. This reduces the frame U-value dramatically without compromising structural performance.
The 165CW system uses 6060-T6 primary framing and 6005A-T6 structural members, with a 165mm frame depth that provides space for the thermal break zone and accommodates insulated glazing units from 24mm to 40mm. The thermal break is not an add-on - it is integral to the frame design.
For the spandrel zones of a curtain wall - the opaque areas at slab edge and column locations - insulation is placed within the frame depth, and a vapour barrier prevents condensation on the interior face of the aluminium framing. The spandrel areas are often the most thermally sensitive part of a curtain wall, because the framing-to-slab junction creates both a thermal bridge and a potential condensation risk if not properly detailed.
What role do conneQt battens play in thermal performance?
conneQt aluminium battens and adaptors (6060/6063 T5) serve as the subframe for both interloQ and element13 installations. They also function as standalone architectural elements - screening, fins, and facade features.
From a thermal perspective, the batten subframe is the component that physically bridges the insulation layer. The thermal performance of the overall wall system is therefore sensitive to batten profile, spacing, and how the batten is connected to the structural substrate.
Where thermal modelling shows that the batten fixings create unacceptable thermal bridging, several strategies are available. Thermal isolation pads - typically nylon, HDPE, or proprietary thermal break materials - can be placed between the bracket and the structure. These reduce heat flow through the bracket without affecting structural capacity, provided they are specified to carry the required loads. Some bracket systems incorporate stainless steel fasteners rather than aluminium, reducing the conductivity of the fastener itself - though this is secondary to the bracket-to-structure interface.
What practical strategies reduce thermal bridging?
For specifiers working through the thermal modelling process with their facade engineer, these are the parameters that have the most impact on the overall wall U-value:
Continuous insulation plane. The single most effective strategy. Insulation that runs unbroken behind the cladding, penetrated only at bracket locations, will always outperform systems where the insulation is interrupted by continuous rails or framing.
Bracket design and spacing. Fewer brackets at wider centres means fewer thermal bridges. Bracket cross-section matters too - a narrow bracket presents less conductive area than a wide one. Selecting bracket geometry is a balance between structural adequacy (wind load resistance, dead load of the cladding) and thermal performance.
Thermal isolation pads. A 3-6mm thermal break pad at each bracket-to-structure interface can reduce the point thermal transmittance by 40-60%, depending on the pad material and bracket geometry. This is a straightforward, cost-effective measure for rainscreen systems.
Material selection at fixings. Stainless steel fixings (thermal conductivity around 15 W/mK) conduct less heat than aluminium fixings (205 W/mK). Where every fraction of a watt matters in the thermal model, this is worth considering.
Ventilated cavity depth. A deeper cavity provides more effective ventilation and a greater buffer against solar gain. For cooling-dominated climates, the cavity contribution to thermal performance is not trivial.
What about thermal expansion?
This is related but distinct from thermal bridging - and worth addressing because it affects detailing at the same connections.
Aluminium has a thermal expansion coefficient of 23 um/m/K. A 6-metre length of aluminium exposed to a 60-degree temperature swing (not unusual for a dark-coloured facade in Australian summer) will expand and contract by approximately 8.3mm. At 2,680 kg/m3 density, the material is light but it moves.
Every fixing detail needs to accommodate this movement without imposing load on the structure or the insulation layer. Slotted holes, sliding brackets, and expansion joints are standard practice. For thermal modelling purposes, it is worth noting that the fixings must allow movement - they cannot be fully rigid connections - which in turn affects the area of metal-to-metal contact and the thermal bridge calculation.
How does Valmond & Gibson support thermal modelling?
V&G supplies system details - bracket types, fixing configurations, subframe options, and material specifications - to support facade engineers in their thermal modelling. This includes CAD details, point fixing locations, and material data sheets for all components in the interloQ, element13, 165CW, and conneQt systems.
The thermal modelling itself sits with the facade engineer or energy consultant. V&G does not certify thermal performance or provide U-value calculations for wall assemblies - that is project-specific work that depends on the full build-up, climate zone, and NCC compliance pathway. What V&G does provide is the accurate, detailed system information that makes that modelling reliable.
For specifiers writing facade specifications, it is worth including a requirement for the cladding supplier to provide thermal bridge details for the proposed fixing system. This ensures the facade engineer has the data they need at the right stage, rather than discovering gaps during the energy modelling process.
Aluminium’s thermal conductivity is a material property. It is fixed, published, and well understood. The design response is to manage it through system design - and that is what well-engineered facade systems do.
Related Reading
- NCC Section J: Thermal Performance Requirements for Facades
- Ventilated Facade Design: Principles and Performance
- Subframe Design for Aluminium Rainscreen Cladding
- Green Star and Aluminium Facade Systems
Last updated: 4 April 2026