The subframe is the structural connection between the building and the cladding. It must transfer wind loads and dead loads back to the structure, accommodate thermal movement in the aluminium panels, absorb construction tolerances in the substrate, and maintain a ventilated cavity for rainscreen performance. Getting the subframe right is not optional - it determines whether the facade performs as designed or spends its life fighting the building it is attached to.
This guide covers the practical considerations that matter most when designing and installing subframe systems for aluminium rainscreen cladding, with specific reference to Valmond & Gibson’s interloQ, element13, and conneQt systems.
What does the subframe actually do?
A subframe serves four functions simultaneously, and the design must satisfy all of them:
Load transfer. Dead load (panel self-weight) acts vertically; wind load acts perpendicular to the facade. Both must be transferred through the brackets and fixings into the building structure without exceeding the capacity of any element in the chain.
Thermal movement. Aluminium expands at 23 um/m/K. On a 4-metre panel, a 40-degree temperature swing produces nearly 4mm of movement. If the subframe constrains that movement, thermal cycling leads to fatigue, loosened fixings, or panel distortion. The subframe must allow panels to move in at least one direction - typically through slotted holes in the brackets or panel fixing points.
Construction tolerance absorption. No building structure is perfectly plumb, flat, or level. Concrete slabs can be out by 10-20mm over a storey height. The subframe is where these differences are reconciled. Adjustable brackets allow the installer to set the cladding plane true and plumb regardless of what the structure behind it is doing.
Cavity formation. The rainscreen principle depends on a ventilated cavity between the cladding and the weather-resistant membrane. The subframe creates and maintains that cavity - typically 20-25mm minimum depth, though actual depth depends on the bracket system, insulation build-up, and wind load requirements.
What types of subframe systems are used?
Three broad categories of subframe are used in Australian aluminium facade installation, each with different characteristics.
Aluminium top hat and channel sections
Continuous aluminium sections - top hats, channels, or purpose-designed profiles - run vertically or horizontally across the facade. The cladding fixes directly to these sections, spreading load continuously rather than concentrating it at discrete bracket points.
Aluminium sections share the same thermal expansion coefficient as the cladding (23 um/m/K), simplifying movement detailing and eliminating dissimilar metal corrosion risk. conneQt serves this role - a purpose-designed aluminium batten and adaptor system in 6060/6063 T5 alloy, the same specification as interloQ. conneQt provides both the subframe and the integration layer for interloQ and element13, keeping the entire assembly within a single material family.
Steel angle brackets
Individual galvanised or stainless steel brackets fixed at discrete points on the structure, with aluminium rails spanning between them to carry the cladding. Common on concrete and masonry substrates. Steel brackets are strong and economical, but they introduce a dissimilar metal interface with aluminium cladding - isolation is essential, covered below.
Proprietary bracket systems
Engineered bracket-and-rail systems designed as complete assemblies, often with built-in three-dimensional adjustment. These typically consist of a wall bracket, an adjustable standoff, and a rail that carries the cladding. Proprietary systems simplify installation by packaging the adjustment mechanism and load path into a tested assembly, but they are product-specific and must be used within their rated load capacity.
How do wind loads determine bracket spacing?
Bracket spacing is not a standard dimension - it is calculated for each project based on wind pressure at the site, derived from AS/NZS 1170.2. The process starts with site wind speed (considering terrain, height, shielding, and topography), then calculates design wind pressure for each facade zone. Corner and edge zones experience higher suction than the central field, so bracket spacing in these areas is typically closer.
The cladding span capacity sets the upper limit on bracket spacing. interloQ profiles have defined maximum spans between fixings based on wind pressure, published in the technical manual. element13 panels (3mm solid aluminium) have structural capacity tested to AS 4040.3, reaching SLS 1875Pa and ULS 5559Pa, but the achievable span depends on the fixing arrangement and panel dimensions.
Each bracket and fixing must carry the combined wind and dead load with appropriate safety factors, and the fixing into the substrate must carry the bracket reaction - often the weakest link in the chain. For interloQ, the pre-punched fixing slots dictate fixing positions along the panel. The subframe must align with these slots so fixings land where the panel expects them.
What role does thermal movement play in detailing?
At 23 um/m/K, aluminium moves meaningfully with temperature. A west-facing facade might see surface temperatures of 70-80 degrees in summer. Against a winter overnight low of 5 degrees, the total range could be 60-75 degrees. Over a 60-degree swing, a 3-metre interloQ panel moves about 4.1mm; a 4-metre element13 panel moves about 5.5mm.
The standard approach is to fix the panel at one point and allow it to slide at all other fixings via slotted holes. interloQ’s pre-punched fixing slots are designed for this: one fixing is installed tight as the fixed point, and the remaining fixings use the slot to allow longitudinal movement.
If the subframe is aluminium (such as conneQt), it expands at the same rate as the cladding, reducing relative movement. If the subframe is steel (expansion coefficient around 12 um/m/K), the differential movement is roughly half the total panel movement - still enough to require slotted fixings, but less severe.
How do you handle different substrates?
The substrate determines the fixing type, the pull-out capacity, and often the bracket design. Getting the fixing wrong is one of the most common causes of facade problems.
Concrete. Mechanical anchors (expansion or undercut) are standard. Pull-out capacity depends on concrete strength, anchor depth, edge distance, and spacing. Post-installed anchors should comply with AS 5216. Hollow-core or precast panels with thin flanges need particular care - test pull-outs on site if there is any doubt about the concrete quality.
Steel. Self-drilling screws or bolted connections. The critical check is steel thickness - thin gauge steel (less than 3mm) limits pull-through capacity. Connections to structural steel are straightforward; light gauge steel framing requires more careful analysis.
Masonry. Solid masonry takes expansion or chemical anchors. Hollow masonry typically requires cavity-spanning anchors or resin-bonded fixings. Unreinforced masonry has low tensile capacity, so fixing spacings may need to be closer.
Timber frame. Coach screws or structural screws into studs - the screw must engage the stud, not just the sheathing. Stud spacing (typically 450 or 600mm) directly influences bracket layout. Timber also moves with moisture changes, so the subframe needs to accommodate substrate movement in addition to thermal movement in the cladding.
Why does dissimilar metal corrosion matter?
Aluminium and mild steel sit apart on the galvanic series. In direct contact with moisture present, the aluminium corrodes preferentially. This is not a theoretical risk - unpainted mild steel brackets against aluminium cladding will cause visible corrosion, particularly in coastal or industrial environments. The solutions are well established:
- Use aluminium brackets where possible. conneQt eliminates the dissimilar metal issue entirely by keeping the full assembly in the same alloy family.
- Use stainless steel. 304 or 316 grade stainless is much closer to aluminium on the galvanic series. 316 is preferred in coastal locations.
- Isolate the contact. Where galvanised steel brackets are used, nylon or EPDM washers, isolation pads, or barrier coatings between the steel and the aluminium prevent direct metal-to-metal contact.
- Use appropriate fixings. Stainless steel rivets and screws are the standard for fixing aluminium cladding, regardless of the bracket material. Zinc-plated fixings should be avoided in exposed locations.
What about insulation and cavity depth?
In most rainscreen applications, continuous insulation sits between the structure and the ventilated cavity. The subframe penetrates through or sits outboard of the insulation, which means each bracket creates a thermal bridge. Proprietary systems sometimes include thermal break pads at the wall connection to reduce conductive heat flow.
The ventilated cavity must remain clear of insulation. Insulation that sags into the cavity blocks airflow and defeats the rainscreen principle. Rigid insulation boards or mechanically retained batts are preferred over friction-fit products that may shift over time. Minimum cavity depth is typically 20-25mm, but deeper cavities improve ventilation and drainage performance at the cost of increased facade build-up and bracket lever arm.
What standards apply?
The subframe sits at the intersection of several Australian standards:
- AS/NZS 1170.0 and 1170.2 - structural design actions and wind actions
- AS/NZS 1664 - aluminium structures
- AS 4100 - steel structures (for steel brackets)
- AS 5216 - post-installed fastenings in concrete
- AS/NZS 4284 - testing of building facades
The facade engineer is responsible for subframe design on most commercial projects. On smaller projects, it may fall to the installer or the cladding supplier’s technical team. Either way, the design must be documented and fixings specified - not left to site discretion.
Getting it right from the start
The subframe is not the visible part of the facade, but it is arguably the most consequential. A well-designed subframe makes installation straightforward and allows the cladding to perform as intended for the life of the building. A poorly designed one creates problems that no amount of good cladding can overcome.
Valmond & Gibson provides system documentation for interloQ, element13, and conneQt that includes subframe requirements, fixing specifications, and typical bracket details. If you are designing or installing a subframe for a V&G cladding system and need technical guidance, contact us. We will help you work through the specifics for your project.
Related Reading
- Ventilated Facade Design: Principles and Performance
- Thermal Bridging in Aluminium Facade Systems: What Specifiers Need to Know
- Wind Load Design for Aluminium Facade Systems
- Dissimilar Metal Corrosion in Facade Assemblies
Last updated: 4 April 2026