2.6 FACADE

The primary purpose of the facade is to protect the building and its occupants from the weather and extremes of climatic conditions. In some parts of the world, this will mean protection from the heat of the sun, and in others, this will mean protection from rain or wind. A thorough review of all of the likely requirements of the facade is recommended before work on the design begins. It should be recognised that not all parts of the facade will need to satisfy the same criteria. Some of the most relevant criteria are listed below.

• Thermal: where the facade also acts as the wall of internal, enclosed accommodation, which is heated or cooled, it will need to be designed to conserve the energy contained within. This is achieved with thermal insulation if the facade is opaque or with double or triple glazing, if it is transparent. Conversely, where the external conditions are likely to be warmer than internal conditions, the facade should be designed to prevent excessive solar gain, which can be problematic for glazed facades. Under such circumstances, external shading devices and/or high-performance glazing is likely to be required. The thermal performance of the facade should be considered alongside other elements, such as roofs and floors, to achieve the required thermal performance within the stadium (see Sub-Section 2.7.1).

• Acoustic: stadiums need public address systems for the safety of spectators, and music is often played for entertainment purposes. This can cause a nuisance to the neighbours of a stadium if the facade is not designed to reduce noise breakout to acceptable levels. This is relatively straightforward to achieve for the enclosed parts of the stadium, such as accommodation, but more challenging for those parts of the facade surrounding the seating tiers, where there is no accommodation behind to block the sound.

• Ventilation/air movement: many stadiums have open concourses, which are not completely sealed to external conditions, and are therefore not heated or cooled. In such situations, the facade could provide protection from the wind, rain and sun, but it would need to be designed to enable sufficient ventilation, providing free air movement through the naturally ventilated areas.

• Waterproofing: where the facade forms the wall for internal, enclosed accommodation, it should be adequately sealed against the ingress of water, with special consideration given to wind-driven rain. Where the facade does not enclose internal accommodation, a lower standard of waterproofing is typically acceptable, but all components should resist corrosion to applicable local standards.

• Daylighting: stadiums often have larger floor plates than those typically found in other types of buildings. Where possible, the facade should incorporate glazing so that natural light can penetrate the building, which not only contributes to the well-being of occupants, but also reduces energy consumption as less artificial lighting is required.

• Fire performance: just like on other types of buildings, stadium facades need to be designed to be of limited combustibility or non-combustible, depending on local building codes. They must also resist the external spread of flame to enable occupants of the building to escape safely, and to prevent exposing neighbouring buildings to fire.

• Robustness: facades should be designed to be sufficiently robust, providing adequate resistance to wind loads appropriate to the stadium location. Where members of the public or stadium staff and equipment come into close contact with the facade, it should be designed to withstand crowd and typical impact loads without damage.

• Security: in most circumstances, the facade should be considered as part of the stadium’s security. Where members of the public come into contact with the facade, it should be designed to withstand burglary, attacks and accidental or malicious damage, and be unclimbable. Where required by the security assessment, the facade can be designed to withstand expected potential blast loading.

The technologies and materials that will likely need to be used to meet these criteria will probably vary in different parts of the world. For example, what may be appropriate in a northern European urban environment may not be suitable in a South American semi-rural environment since the climatic conditions, available materials and labour costs may differ greatly. Some examples of building technologies and their different qualities are listed below.

• Concrete provides robustness and can be attractive if skilled designer and construction labour is available.

• Masonry is a traditional method used to build attractive, solid opaque walls, but it is labour-intensive and time-consuming to build.

• Framed structures can accommodate different kinds of infill panels, which means they are able to respond to local conditions, making this a particularly flexible technology. Infill panels may include transparent materials like glass, ETFE or polycarbonate, translucent materials like PVC or PTFE-coated fabric, or solid opaque materials such as stainless steel, aluminium, glass-reinforced concrete, terracotta or treated timber. Framed structures tend to be relatively fast to erect and lend themselves to pre-fabrication, which can be very efficient in parts of the world where on-site labour is expensive.

Typically, the design of the facade evolves alongside the design of the stadium as a whole. However, the appearance of the stadium often needs to be visualised from an early stage. This is achieved using digitally produced renderings (often called computer-generated images or CGIs) so that the visual images can be presented to the approving authorities, funders, affected neighbours, and for general marketing purposes. Sophisticated motion-graphic animations are also increasingly common, as are virtual and augmented reality representations (see Section 2.1).

It is sometimes necessary to undertake computational fluid dynamics (CFD) or wind tunnel testing to test the behaviour of the building under anticipated wind conditions, and its impact on neighbouring areas. To approve the visual appearance of the facade prior to construction, it may be necessary for samples of the materials to be produced and, in particularly sensitive locations, for prototypes to be prepared to show how the materials are used together. It is common for there to be on-site performance testing of the facade, particularly if the design involves bespoke components.