Façade Systems

Rains Screens

Rain screens are a key strategy in building envelope design, offering robust protection against moisture and air infiltration. These systems typically rely on two lines of defence:

• Primary barrier (outer façade): Deflects most rain and wind-driven water

• Secondary barrier (inner layer): Stops residual moisture and vapour that bypass the outer layer

Standard Rain Screen Design

Rather than being fully airtight or waterproof, the outer cladding layer of a rain screen resists direct rain but allows ventilation and drainage through a ventilated cavity between the outer and inner layers. This air space equalises pressure and provides a drainage path, significantly reducing the risk of moisture penetration.

Cladding materials are selected for their aesthetic appeal—common choices include stone, precast concrete, terra cotta, metal panels, and glazing. The inner layer, although hidden, plays a structural role, supporting wind and seismic loads, providing insulation, and forming the primary air and moisture barrier.

Pressure-Equalised Rain Screens (PER)

PER systems improve rain screen performance by equalising the air pressure within the cavity and at the building’s exterior. This minimises the pressure-driven entry of water. Achieving this requires carefully designed ventilation openings in the outer cladding. When executed effectively, PER systems rely on a combination of gravity drainage and pressure balance to manage water ingress.

Curtain Wall Systems

Curtain walls are non-loadbearing, exterior façade systems, typically composed of an aluminium frame infilled with glazing or other cladding materials. The framing is anchored to the structure but does not support floor or roof loads—these are transferred back to the building structure, typically at the slab edges.

Curtain wall systems vary from standard modular products to fully custom designs, often delivered by façade specialists.

Stick Systems

Stick-built curtain walls are assembled piece by piece on-site:

• Perimeter anchorages are installed

• Vertical mullions are fixed to slab edges (often spanning multiple floors)

• Horizontal transoms are attached to create a grid

• Glazing, insulation, and back pans are added

While cost-effective, stick systems are considered lower quality due to reduced control over on-site assembly and sealing.

Semi-Unitised Systems

Semi-unitised systems combine site-assembled framing (mullions and transoms) with factory-glazed cassettes that are fixed onto the frame:

• 2-sided cassettes are structurally glazed on vertical edges; horizontal joints are sealed on-site

• 4-sided cassettes are fully factory-glazed, then attached on-site

• Sealing is typically achieved with gaskets or sealants—gaskets are preferred for durability and flexibility

These systems improve quality compared to stick systems but still face site-related quality control challenges.

Unitised Systems

Fully factory-assembled and glazed, unitised curtain walls are shipped as large prefabricated units and installed on-site. Their design allows for:

• Split mullions and transoms that interlock

• Compressed gaskets that ensure air and moisture tightness

• Flexibility to accommodate building movement without stressing components

These systems offer the highest quality control and are ideal for large-scale commercial façades.

Spandrel Systems

Spandrel curtain walls feature a continuous horizontal frame at each floor, covering the zone between the floor slab and the window sill above. Vision glazing and short mullions are installed between these frames.

• Suitable for designs with horizontal banding

• Can be either fully site-assembled or partially preassembled

• Offers excellent movement accommodation, though thermal resistance may be reduced due to increased frame surface area