Curtain Wall Systems for Australian Commercial Buildings: A Specification and Procurement Guide

The curtain wall is the defining architectural element of the modern commercial building. From the glass towers of the Sydney CBD to the mixed-use developments of Melbourne’s Fishermans Bend, from Brisbane’s Queen’s Wharf precinct to Perth’s Elizabeth Quay, the non-structural outer wall—transparent, weathertight, and engineered for decades of service—defines both the aesthetic and the performance of the contemporary Australian commercial building.

Specifying a curtain wall system is one of the most consequential procurement decisions in a commercial building project. It represents 15–25% of total construction cost, sets the energy performance of the building for its operational life, and—if poorly specified or installed—can generate cascading defects that are extraordinarily expensive to remediate. This guide from MC Windows & Doors (Meichen International Windows & Doors) provides architects, façade consultants, and procurement managers with a structured framework for specifying aluminium curtain wall systems that meet Australian Standards, deliver performance, and provide long-term value.

Curtain Wall Types: Unitised vs. Stick Systems

Stick Systems

In a stick curtain wall, the mullions (vertical members) and transoms (horizontal members) are installed piece-by-piece on site, with the glazing panels inserted into the framing grid afterwards. This approach:

• Lower factory investment required: Stick systems are fabricated in a workshop and assembled on site, so the manufacturer does not need the same level of capital equipment as a unitised line
• More flexible on site: Minor dimensional variations in the concrete slab edge can be accommodated by adjusting the stick positions
• Slower installation: Each mullion and transom must be individually installed, sealed, and glazed
• More site labour: The proportion of on-site work is higher, which is a cost and risk factor
• Quality control challenges: Sealant joints are formed on site, where temperature, humidity, and contamination can affect performance

Stick systems are appropriate for low-rise commercial buildings (up to 4–5 storeys), buildings with complex or irregular geometry, and projects where local labour rates are favourable.

Unitised Systems

In a unitised curtain wall, complete panels—mullions, transoms, glazing, and internal seals—are assembled in a factory, shipped to site, and hung on the building frame as modular units. The units interlock at the joints, with the weather seals formed by the interlock geometry rather than by site-applied sealant. This approach:

• Faster installation: A single unit can be installed in 15–30 minutes using a crane or building maintenance unit, compared to several hours for an equivalent area of stick system
• Factory-quality control: All critical joints are assembled in a controlled environment with consistent temperature, humidity, and cleanliness
• Reduced site labour: The on-site workforce is smaller, and the work is primarily lifting and connecting rather than cutting and sealing
• Higher factory investment required: Unitised assembly requires dedicated jigs, lifting equipment, and production line layout
• Higher transport costs: Units are bulky and must be transported flat or on specialised racks

MC Windows & Doors’ BA150 curtain wall system is available in both unitised and stick configurations, allowing the specification to be matched to the project’s scale, timeline, and site access constraints.

AS 4284: The Governing Standard for Australian Façades

While AS 2047 covers windows and external glazed doors, curtain walls are tested and certified under AS 4284: Simulation of wind loads on structures and the parallel standard AS/NZS 4284: Testing of building façades. AS/NZS 4284 defines the test procedures for:

1. Air Infiltration

The completed curtain wall mock-up is pressurised and the air leakage rate is measured. The maximum permissible leakage for a commercial façade is typically 1.0 m³/h·m² at a reference pressure of 75 Pa (positive) and 75 Pa (negative). Higher rates indicate poor seal performance, which leads to energy waste and occupant discomfort.

2. Water Penetration

Two water tests are performed:

• Static water test: Water is sprayed at the facade at a rate of 3 litres/m²/minute while a positive pressure of 300 Pa is applied. No water penetration to the interior is permitted
• Dynamic water test: Water is sprayed while a fluctuating pressure (simulating wind gusts) is applied. This test is more aggressive because the pressure cycling pumps water through gaps that a static test would not detect

3. Structural Performance

The curtain wall is pressurised to the design wind load (positive and negative) and the deflection of mullions and transoms is measured. Deflection limits are typically:

• Span/180 for mullions (maximum deflection = span / 180)
• Span/250 for transoms
• Span/360 for elements supporting stone or other brittle cladding

Residual deflection (measured after the load is removed) must be less than 0.2% of the span.

4. Seismic Drift

In addition to wind loads, curtain walls must accommodate inter-storey drift caused by seismic events. AS 4284 requires the façade to maintain weathertightness after being subjected to a specified displacement (typically ±15mm for low-rise, ±25mm for mid-rise) without seal failure or glass edge contact.

MC Windows & Doors’ BA150 curtain wall system has been tested in full mock-up to AS/NZS 4284 and meets the following performance:

• Air infiltration: 0.4 m³/h·m² at 75 Pa (well below the 1.0 maximum)
• Water penetration: No penetration at 600 Pa static and 300 Pa dynamic
• Structural: N4 wind classification (1.65 kPa) with deflection within span/180
• Seismic drift: ±25mm with no seal failure

Design Wind Loads for Australian Commercial Buildings

The design wind load is determined in accordance with AS/NZS 1170.2: Structural Design Actions – Wind Actions. Key factors include:

Regional Wind Speed

Australia is divided into four wind regions (A, B, C, D):

• Region A: Most of the continent, including all capital city CBDs except Darwin and Brisbane. Basic wind speed (V500) = 45 m/s
• Region B: Coastal areas exposed to non-cyclonic winds (Sydney coastal, Perth coastal). V500 = 45 m/s with terrain factors
• Region C: Cyclonic coastal regions (Queensland north of Bundaberg, Western Australia north of Carnarvon). V500 = 50 m/s
• Region D: Severe cyclonic regions (Darwin, Broome). V500 = 55 m/s

Terrain Category

The terrain roughness affects wind speed at building height:

• Terrain Category 2: Open terrain with scattered obstructions (airports, coastal fringe). Most exposure
• Terrain Category 3: Suburban and urban terrain with numerous closely-spaced obstructions
• Terrain Category 4: City centres with very dense urban fabric

Building Height and Shape

Wind pressure increases with height. For a 100m tower in Region A, Terrain Category 3, the design wind pressure at the top of the building can reach 2.5–3.5 kPa, compared to 0.8–1.2 kPa at ground level. The curtain wall must be engineered to resist the maximum pressure, which means mullion sections typically increase in depth or wall thickness at higher levels.

Corner and Edge Effects

Wind pressures are not uniform across a facade. Corners and edges experience local pressure concentrations that can be 1.5–2.0 times the field pressure. The mullions at building corners must be designed for these enhanced loads, or the glass thickness must be increased.

Glazing Options for Commercial Curtain Walls

Insulating Glass Units (IGUs)

Commercial curtain walls almost universally use double-glazed IGUs with:

• Outer pane: 6mm or 8mm toughened or heat-strengthened glass
• Air gap: 12mm or 16mm argon-filled
• Inner pane: 6mm toughened or laminated glass

The Low-E coating is typically on the #2 surface (inner face of outer pane) for solar control applications or the #3 surface (inner face of inner pane) for cold-climate applications.

Solar Control Glass

For Australian commercial buildings, solar control is critical. Options include:

• Soft Low-E coatings: High-performance coatings with SHGC of 0.25–0.35 and visible light transmittance of 50–70%. These are the most common choice for Australian office buildings
• Body-tinted glass: Grey, green, blue, or bronze tints that absorb solar radiation. Often used in combination with Low-E coatings
• Ceramic frit: Pattern of ceramic ink fused to the glass surface. Commonly applied as a gradient or full coverage to the spandrel zone (non-vision area)

Spandrel Glass

The spandrel zone (the opaque band between floor levels, concealing slabs and services) is typically glazed with ceramic-fritted or opacified glass to match the vision area. The spandrel glass must be heat-strengthened or toughened because the frit creates thermal stress differentials.

Thermal Performance for Commercial Buildings

Section J Compliance

Under the National Construction Code Section J, commercial buildings must meet specific energy efficiency requirements. For the building envelope, this includes:

• Maximum wall-glazing U-value (varies by climate zone, typically 2.2–3.4 W/m²·K for curtain walls)
• Maximum SHGC (varies by orientation and climate zone, typically 0.20–0.35 for full glazing)
• Minimum visible light transmittance for occupied spaces

MC Windows & Doors’ BA150 system with Low-E double-glazed IGUs achieves:

• Whole-system U-value: 1.8–2.2 W/m²·K (meets all climate zone requirements)
• SHGC: 0.22–0.35 (tunable based on orientation)
• Visible light transmittance: 50–70%

Thermal Break in Curtain Wall Mullions

Just as in windows, aluminium mullions in curtain walls create thermal bridges. MC Windows & Doors’ BA150 system incorporates polyamide thermal break strips in the mullion and transom profiles, reducing the frame U-value from approximately 5.8 (non-thermal-break) to 2.5 W/m²·K (thermal break). This improvement:

• Reduces building heating and cooling loads by 10–15%
• Eliminates condensation on interior mullion surfaces in air-conditioned buildings
• Improves thermal comfort for occupants seated near the facade

Procurement Strategy: Specifying Curtain Wall for Your Project

Step 1: Define Performance Requirements

Before approaching suppliers, develop a performance specification that defines:

• Wind classification (AS 4055 or AS/NZS 1170.2)
• Air infiltration limit (target: 0.5 m³/h·m² at 75 Pa)
• Water penetration test pressure (target: 600 Pa static, 300 Pa dynamic)
• Maximum deflection limits (span/180 for mullions)
• U-value and SHGC targets (per Section J)
• Acoustic requirements (Rw, typically 32–40 for commercial)
• Fire performance (fire-rated spandrels where required)

Step 2: Design Development and Mock-Up Testing

Before bulk procurement, a full-size mock-up of the curtain wall (typically 3m × 6m, representing two bays and two storeys) should be fabricated and tested to AS/NZS 4284. The mock-up:

• Validates the design before committing to production
• Identifies any water leakage paths or structural weaknesses
• Establishes the quality standard for production
• Provides a reference for dispute resolution if production units differ

MC Windows & Doors can arrange mock-up fabrication and testing at an accredited NATA facility as part of the procurement package.

Step 3: Factory Audit and Production Quality Plan

For projects sourcing curtain wall from MC Windows & Doors’ Zhaoqing manufacturing facility, a factory audit is recommended before production commences. The audit should verify:

• CNC machining centre calibration and tolerance records
• Welding/sealing process parameters (for thermally broken profiles)
• IGU production line (gas fill rate, sealant application, desiccant quantity)
• Quality control testing records (air/water/structural testing of production samples)
• Material certificates for aluminium extrusions, glass, sealants, and gaskets

Step 4: Installation Planning

Curtain wall installation requires:

• Access equipment: BMU (building maintenance unit), scaffold, or crane access
• Storage and staging: A lay-down area for units, protected from weather
• Sequencing: Curtain wall installation typically follows floor slab completion by 1–2 floors
• Interface details: The curtain wall must interface with the slab edge (fire stopping, waterproofing), adjacent walls, and roof. These details must be resolved in the design phase, not on site

Step 5: Commissioning and Handover

After installation, the following checks should be performed:

• Visual inspection: Check for glass damage, sealant continuity, frame alignment
• Water hose test: Spray a representative sample of installed units to verify site-installed joints are weathertight
• Air leakage test: Perform a depressurisation test on a representative room to verify the facade does not leak excessively
• Documentation: Collect all test reports, material certificates, and warrantee documentation

The BA150 Curtain Wall System: Technical Overview

MC Windows & Doors’ BA150 curtain wall system is engineered for Australian commercial applications:

Structural:
– 150mm mullion depth (standard), with 180mm and 200mm options for taller buildings
– 6063-T5 aluminium alloy, wall thicknesses from 2.0mm to 3.5mm
– Span capability: up to 4.5m between slab connections (with engineering assessment)
– Wind classification: N4 standard (C2 available with reinforced sections)

Glazing:
– 28mm to 40mm IGU capacity
– Internal or external glazing options
– Low-E double glazing standard, triple glazing available

Weather performance:
– Air: 0.4 m³/h·m² at 75 Pa
– Water: 600 Pa static, 300 Pa dynamic
– Seismic drift: ±25mm

Thermal:
– Polyamide thermal break in mullions and transoms
– Frame U-value: 2.5 W/m²·K
– Whole-system U-value: 1.8–2.2 W/m²·K (with Low-E IGU)

Finishes:
– Powder coating to AS/NZS 4506 (60–80 micron, super-durable polyester)
– Anodised finishes (15–25 micron)
– Custom RAL colours and metallic finishes

Configurations:
– Fixed vision panels
– Operable awning windows integrated into the curtain wall (BA150 CW Operable Awning)
– Spandrel panels with ceramic frit or aluminium composite
– Louvre panels for ventilation and plant room screening

Long-Term Performance and Maintenance

A well-specified curtain wall should deliver 30–50 years of service. To achieve this, a maintenance regime should be established from handover:

Annually:
– Clean all external glass and frame surfaces
– Inspect sealant joints for cracks, adhesion loss, or weathering
– Check weep holes and drainage channels for blockages
– Inspect operable elements (awning sashes, louvres) for smooth operation

Every 5 years:
– Conduct a detailed sealant inspection, including probing representative joints for adhesion
– Re-seal any degraded joints
– Replace any weathered gaskets in operable elements
– Inspect thermal break strips for any signs of separation (rare, but important)

Every 10 years:
– Engage a facade specialist to conduct a comprehensive condition assessment
– Consider re-coating or re-finishing if powder coating shows chalking or fading
– Review the building’s energy performance data to assess whether the facade is meeting its design performance

Conclusion

The curtain wall is the most complex and most consequential building element in a commercial project. It protects the building from wind and water, manages solar heat gain, provides acoustic isolation from the street, and creates the architectural identity that defines the building in the cityscape. Getting it right requires rigorous standards compliance, precise engineering, and a procurement process that values long-term performance over short-term price.

MC Windows & Doors brings together the manufacturing capability, the engineering depth, and the Australian Standards compliance to deliver curtain wall systems that perform. From the Zhaoqing production facility—equipped with CNC machining centres, NATA-accredited testing capabilities, and a lean production management system—MC Windows & Doors supplies unitised and stick curtain wall systems to commercial projects across Australia. For developers, architects, and façade consultants seeking a supplier that combines engineering rigour with competitive pricing and reliable delivery, the BA150 system represents a proven choice.

For curtain wall specifications, mock-up testing proposals, and commercial project enquiries, contact MC Windows & Doors at Annly@mcwindow.com.au or +61 490 141 931. Technical drawings, performance data sheets, and AS/NZS 4284 test reports are available on request.