Innovative Curtain Walling Techniques Shaping Modern Architecture

[edit] Introduction

Curtain walling is a non-load-bearing external wall system that separates the interior of a building from the external environment while transferring its own weight and environmental loads, such as wind loads, back to the primary structure. It is commonly used on multi-storey commercial, institutional and residential buildings, and can accommodate glazed and opaque infill panels.

The development of curtain walling has allowed architects to combine large areas of glazing with lightweight framing and increasingly sophisticated environmental performance. Contemporary systems can be designed to address requirements for daylight, thermal insulation, solar control, weather resistance, acoustic performance, fire safety, durability and architectural appearance.

[edit] Modern curtain walling requirements

Modern façades are required to perform several functions simultaneously. In addition to defining the external appearance of a building, curtain walling must provide resistance to wind and weather, control heat transfer and solar gains, and maintain appropriate levels of airtightness and watertightness.

Glazed curtain walls can provide extensive daylight and views while creating relatively uninterrupted elevations. However, large areas of glazing can also increase heat loss, solar gains and glare if they are not appropriately designed. The selection of glass, frame, coatings, shading and ventilation therefore needs to be considered as part of the building's overall environmental strategy.

Curtain wall systems can accommodate a range of geometries and architectural treatments. Aluminium framing is common because of its relatively low weight, durability and ability to be manufactured into complex profiles, although other materials and hybrid systems can also be used.

[edit] Curtain walling systems and construction techniques

Curtain walling can be constructed using several systems, the most common being stick and unitised systems. A stick system is assembled progressively on site, with mullions, transoms and infill panels installed individually. This approach can provide considerable flexibility where dimensions or site conditions require adjustments during installation.

A unitised system consists of factory-assembled modules that are transported to site and connected to the building structure. Factory production can provide greater control over manufacturing conditions and quality, while reducing the amount of assembly required at height. Unitised systems can be particularly advantageous for large, repetitive façades and high-rise buildings, although they require careful coordination of module dimensions, structural tolerances and transportation.

Semi-unitised systems combine characteristics of stick and unitised construction. The appropriate system depends on the scale and geometry of the building, repetition of the façade, access constraints, programme, manufacturing requirements and project-specific performance criteria.

Modern curtain walls can also incorporate different forms of glazing, including single, double and triple-glazed units, as well as spandrel panels and opaque infill materials. Low-emissivity and solar-control coatings can be used to modify thermal and solar performance.

[edit] Engineering and installation

The performance of a curtain wall depends on the design and execution of the complete system rather than the glazing alone. Structural design needs to establish the loads acting on the façade and ensure that mullions, transoms, brackets, fixings and connections can transfer these loads safely to the primary structure.

Installation generally involves setting out the supporting brackets and anchors, installing the framing or prefabricated units, fitting the glazing and infill panels, and completing seals, gaskets and other weatherproofing components. Interfaces with floors, roofs, columns and adjacent wall systems require particular attention because they can be potential points of air or water leakage.

Accuracy is important because excessive deviations from the designed geometry can affect the operation of joints, the appearance of the façade and the performance of seals and drainage systems. Tall or geometrically complex buildings may require specialist lifting and access equipment to position curtain wall modules safely.

Quality control and testing can include checks of dimensions, alignment, fixings, glazing, seals and drainage, together with project-specific tests for air permeability, watertightness and structural performance where required.

[edit] Environmental and architectural performance

Curtain walling can form an important part of a building's environmental strategy. High-performance glazing, thermally improved framing, insulated spandrel zones and carefully designed interfaces can reduce unwanted heat transfer. Solar-control glazing and external shading can reduce solar gains and glare, particularly on façades exposed to significant levels of direct sunlight.

Double-skin façades provide another approach in which two layers of enclosure are separated by a cavity. Depending on the configuration, the cavity can be naturally or mechanically ventilated and can incorporate shading devices. Such systems can be used to influence thermal and solar performance, although their design is more complex than that of conventional single-skin curtain walling.

Architectural development has also expanded the range of materials and patterns that can be incorporated into curtain walls. In addition to transparent vision glazing, systems can accommodate opaque panels, spandrel glazing, metal panels, stone and other infill materials. Different colours, finishes, frame proportions and panel arrangements can therefore be combined to create varied façade treatments.

[edit] Contemporary developments

One of the significant developments in curtain walling has been the increasing use of prefabrication and factory-controlled production. Unitised systems can allow larger sections of the façade to be manufactured and inspected before delivery to site, potentially improving consistency and reducing installation time.

Digital design and building information modelling can also assist with the coordination of curtain wall geometry, structural interfaces, glazing specifications and building services. For complex façades, detailed digital models can help identify clashes and establish accurate fabrication information before manufacture.

The development of high-performance glazing and framing systems has also expanded the potential for glazed façades in buildings with demanding energy-performance requirements. However, the use of more glass does not automatically improve environmental performance. The balance between daylight, solar gain, thermal insulation, glare, ventilation and shading needs to be assessed for the building's location, orientation and intended use.

Curtain walling remains an important component of contemporary architecture because it combines relatively lightweight construction with considerable freedom in the treatment of external elevations. Advances in prefabrication, glazing, thermal performance, digital coordination and installation methods continue to expand the range of applications, while the fundamental requirement remains the same: the façade must provide a durable and weather-resistant enclosure without forming part of the building's primary structural system.

[edit] Related articles on Designing Buildings

• Curtain wall systems
• Framed-type glass curtain wall
• Cladding for buildings
• Types of cladding
• Brise soleil
• Design information
• Limiting fabric parameters
• Glass mullion system
• The myths of modular construction
• Architectural Technology Studio 3

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