The building facade is the interface between the external and internal environments of a building. A facade is generally one exterior side of a building, usually, but not always, the front. It comes from the French word facade which literally means ‘frontage’ or ‘face’. Facade systems comprises of structural elements that provide lateral and vertical resistance to wind and other actions, and the building envelope elements that provide the weather resistance and thermal, acoustic and fire resisting properties. The types of facade system that are used depends on the type and scale of the building and on local planning requirements that may affect the building’s appearance in relation to its neighbours. For example, brickwork is often specified as the external facade material, but the modern way of constructing the inner leaf consists of light steel wall elements (called infill walling) that have effectively replaced more traditional block-work. Other types of facade materials may be attached to light steel walling, such as insulated render, large boards, metallic panels and terracotta tiles. A wide variety of facade treatments and shapes may be created using light steel wall including large ribbon windows, curved and inclined walls, and with projections such as solar shading or balconies. Facade materials may be mixed to enhance the aesthetics of the building. It is also possible to pre-fabricate light steel wall panels with their cladding pre-attached. In multi-storey buildings, unitised curtain walling systems have been developed that are attached to the floors or edge beams of the primary steel structure. Due to the multiple important roles – i.e., aesthetics, thermal com-fort, day lighting quality, visual connection to the outdoor environment, acoustic performance, and energy-related performances building facades, especially glazing systems, have received much attention in research and development. This results in a wide range of products and technologies available to achieve high performance systems.
Functions of a Facade
The building facade provides the separation between the inside and the outside environments but is also required to provide acceptable light levels and a visual connection with the outside in the form of views out of the building. The facade may also be required to provide the building user with openable windows for ventilation.
The separating functions include:
– Weather tightness including elimination of water ingress and control of air permeability and resistance to wind actions
– Insulation (both thermal and acoustic)
– Control of solar gain and ultraviolet radiation and the management of views into the building
– The building facade also provides the owner and the architect with a canvas on which to create an image representing the owner’s business, ideals or outlook
Feasibility of Facade Technology and Operational Necessities
Being contextually appropriate is an prerequisite for high performance facade systems, i.e., designing with local climatic conditions, solar orientation, prevailing wind direction, view opportunity, safety consideration, acoustics, nature of occupancy, and so on. Following are the key application requirements:
Wall to Window Ratio
Wall to window ratio is a simple rule for high performance building facade design in response to climatic condition and solar orientation. In temperate climatic regions, it is rational to have a low wall-to-window ratio, as the system will allow daylight to penetrate deep into a building’s internal space and sunlight accessibility during cold winter months. In hot climatic regions, it is less sensible to have a low wall-to-window ratio as sunlight is ample, sky illumination is high, and window/ glazing areas are the weak areas for building heat gain. Following the same principle, a high wall-to-window ratio on a west facing facade offers better thermal performance. This is due to the fact that hot afternoon sunlight and radiation are kept away from building’s interior spaces.
Integration of Sun Shading Devices
Integration of sun shading devices is essential for glazing systems or glazing areas that are exposed to sunlight. Sun shading devices keep direct sunlight from shining on glazing surfaces, enhance the shading co-efficiency of façades, and result in less thermal transmission through the façade system.
Air-tight but Operable
Air tight but operable concern about thermal transmittance through building façades has led to the call for air-tight construction. On the other hand, air-tight construction may be detrimental to other building environmental performances, such as natural ventilation and the building’s ability to continue operating during electricity black-outs or HVAC malfunctions. Furthermore, air-tight construction has recently been criticised as a contributing factor to poor indoor air quality and sick building syndrome. In order to mitigate these issues, it is best to provide operable window/glazed panels as part of an air-tight façade system, giving occupants some level of control.
Night time ventilation can be used in double skin facades due to the additional weather protection of the two skin layers and the cavity. It is applicable in hot climatic regions, in summer months in temperate regions and in commercial buildings, which are pre-cooled during the night using natural ventilation. This way, the indoor temperatures will be lower during the early morning hours, reducing the need for and cooling load of air-conditioning.
Condensation on Double-glazing Systems
There are three common types of condensation on double-glazing systems: in-door, outdoor and in-between. Indoor condensation is often caused by high internal humidity together with a low outdoor temperature, which cools the inside glazing surface to below the dew point. Condensation forms on the outdoor surface of glass when the glass’s temperature drops below the outdoor dew point temperature. The use of low-emissivity glass can restrict heat exchange through the air layer between the two panes of glass, thus the inner glass panel is kept warm, which reduces the chances of indoor condensation forming. At the same time, the outer glass panel is not warmed up due to the heat transmission from the indoor and inner glass panel, which reduces the chances of outdoor condensation forming. Lastly, when condensation is formed on the surfaces facing the air cavity bet-ween the two glass panels, it is an indication of leakage in the air cavity, where damp air penetrates in the cavity area and forms condensation.
Self-cleaning Facade Solution
Self-cleaning facade solution titanium dioxide (TiO2) can be applied on both the solid walls and glazing system. TiO2 is a type of photo-catalyst. When exposed to sunlight, TiO2 activates its oxygen molecules to decompose germs, bacteria and organic matter. Therefore, by applying a TiO2 coating on external facade surfaces i.e., aluminum claddings, wall tiles, glass, etc., the facade can perform a self-cleaning function. This helps reduce maintenance and cleaning requirements.
Different Types of Building Facade Systems
A wide variety of facade systems may be used in modern commercial buildings. Some are summarized and discussed as followings:
1) Steel Facade System
Light steel infill walls have largely replaced the block-work inner leaf in both steel and concrete framed buildings. A variety of facade systems may be attached to the infill walls.
Benefits of Steel Facade Systems
The benefits of steel facade systems may be presented in terms of their functional and aesthetic requirements, as follows:
– A variety of colours and surface textures is possible
– Lightweight facades minimise the loads on the supporting structure
– Light steel infill walls using C sections can be used to support various cladding systems
– Facades can be highly pre-fabricated for speed of installation
– Steel glazing systems can be used for visual effect in tall entrance areas and atria
– Steel is non-combustible and robust to damage in façade panels
– A high level of thermal and acoustic insulation can be provided.
2) Light Steel Infill Walls
Light steel walls in a steel framed building may be of two types:
– Light steel infill walls that span bet-ween the floors or between the floor and edge beam
– Panelised systems that are placed outside the slab edge and are attached at discrete locations.
Light steel infill walls are more widely used because of the simplicity of the installation process and the ability to deliver cut-to-length C sections for the particular as-built dimensions of the project. The development of light steel infill walls has been one of the major innovations in the last 10 years. Light steel infill walls consists of C sections that span 2.4 to 5m between floors, and are designed to resist the wind pressures applied to the building facade and also to support the weight of the particular type of cladding system that is attached to them.
Benefits of light steel infill walls
The benefits of light steel infill walls are:
– Rapid construction system with an installation rate of over 50m2; per day
– Less materials handling on site than for brick and block-work
– Tall walls up to 5m and high wind pressures up to 2kN/m2
– Ability to create large windows without wind posts
– Minimum material use (less than 5kg/m2; of steel in the facade)
– No onsite waste when C sections are delivered cut to length
– Light weight, which reduces the loads on the supporting structure
– Can be used for a wide range of cladding systems
– Can be dismantled in building extensions etc. and re-used
3) Curtain Walling
Curtain walling is the generic name given to metallic lightweight cladding or glazed cladding systems that are directly supported by a structural frame. In some cases, a stone veneer or large tiled fascia may be attached to give the appearance of a more monolithic cladding system. Curtain wall systems are an assembly of factory-made components which are either made up into panels in the factory and the interlocking units brought to site and in-stalled (unitized curtain walling) or brought to site as components and assembled on the building (stick curtain walling).
The size of the unitised panels is dictated by the floor to floor height and a sensible width for transportation and installation and should be compatible with the planning dimensions of the facade (normally a multiple of 300mm). Panels up to 1.5m wide and 4.2m high are typical. The curtain walling system is designed to provide the necessary functions of weather-tightness, natural lighting and shading, and thermal insulation. The joints between the elements of the curtain walling are therefore very important to these functions. In unitised systems, the panels are manufactured so that they are highly sealed and insulated, and the joints between the large panels are made by rubber gaskets and silicone sealants.
4) Aluminum Composite Panel
Aluminum Composite Panel Cladding (ACP) is a widely-used term, describing flat panels that consist of thermoplastic core bonded between two aluminum sheets. ACPs are frequently used for external cladding of buildings (building facades). The main advantage of ACP is that, it is very rigid and strong, despite of its light weight. Due to the ability of painting the aluminum in any colour, ACPs are produced in a wide range of metallic and non-metallic colours as well as patterns that imitate other materials, such as wood or marble. Applications of ACPs are not limited to building’s external cladding; they can be used in any cladding application, partitions, false ceilings etc. Aluminum composite panel are available in various thickness and various brands. ACP sheet are excellent in finish and are PVDF coated which is up to 35 micron. It can be bent, cut, drilled, punched and easily shaped into complex shapes. Easy installation and fabrication save cost and time periods of construction.
Advantages of Aluminum Composite Panel
– Ultra-modern look and excellent flatness
– Light weight
– Sound insulation and pollution resistant
– Acid, alkali and salt spray resistant
– Smooth paint finish and stability of flatness
– Excellent UV characteristics.
– Resistant to blow and breakage.
– Minimizes vibration noise.
– Heat insulation
– Ease of installation and fabrication.
– Complex shapes possible.
– Easy maintenance.
– Superior flatness to other cladding products.
5) Double-skin Facade System
Double-skin facades originated in northern Europe and are formed of two glass walls separated by a cavity on south-facing elevations and are used to reduce the energy consumption of a building. Shading devices are usually mounted in the cavity and, depending on its width, walkways for access and cleaning. This type of facade has many variations in arrangement. The variations relate to:
– Width of cavity
– Type of glazing (single/insulating) for the inner or outer skins
– Division of the cavity horizontally and vertically
– Natural or mechanical ventilation of the cavity
– Integration of the cavity ventilation with the building services
– Use of opening windows into the cavity
The two skins form a thermal buffer zone and passive solar gains in the cavity reduce heat losses in winter. If the cavity ventilation is integrated with the building services, air heated by the sun can be introduced into the building, providing good natural ventilation and reducing the heating load. In summer, the heated air in the cavity is ventilated to the outside, conducting heat away from the building and reducing the cooling load.
6) Brick Slip System
Modern brickwork can be manufactured in the form of brick slips that are attached to a supporting steel sheet or composite panel. The advantage of this system is that it is lightweight and can be installed rapidly as mortar is not necessarily required. Brick slips can also be stacked vertically, and ribbon or unusual shaped windows can be created for architectural effect. In this system, the brick slips are not considered to be weather-tight, and so the wind and weather resistance is provided by the backing material. Composite (or sandwich) panels provide both excellent structural and thermal characteristics for use as the backing system.
7) Precast Concrete Panels
Masonry facades are also formed by supporting brick or natural “hand-set” stone panels from storey-height precast concrete panels. Stainless steel support brackets and restraining pins are used. Thicknesses of hand-set stone vary from 20 mm to 70 mm, depending on the wind load, the tensile strength of the stone and the spacing of fixings. Continuous areas of masonry cladding have naturally low air permeability so generally air permeability is controlled by good detailing at interfaces with windows and doors and other penetrations through the wall for building services. Solar gain, light levels and views out are balanced by choosing appropriate window type, size and arrangement with suitable shading.
8) Steel and Glass Facades
Steel and glass are synergistic materials and are often used in facades and roofs of multi-storey buildings. The glass panels are generally supported by separate vertical steel elements to the main structural frame of the building that may be internal or external to the building. Stainless steel and hollow steel sections are often used in combination with glass.
9) Insulated Wall Panels
Insulated wall panels are interlocking, composite metal-faced sandwich panels or concrete panels with insulation bet-ween internal and external concrete elements. Steel-faced insulated panels are frequently used on single storey and low-rise industrial and commercial buildings.
Panels are usually designed to span one-way (either vertically or horizontally) and are made to suit commonly-used frame spacings without intermediate supports. Various insulation materials are available such as expanded polyurethane (PUR), polyisocyanurate (PIR) and mineral fibre with a range of insulating, fire-resisting and other physical properties. Insulating materials should be selected with care, taking into consideration all the performance and functional requirements. Various surface profiles and colours are available. Insulated wall panel systems have interlocking joints which include overlaps and compression gaskets to prevent water ingress. For horizontally-laid panels, vertical joints at supports are butt joints with compression gaskets and sealed or gasketted cover strips.
– Structural use of glass in buildings, Institution of Structural Engineers, 1999.
– http://www.steelconstruction.info/Facades_ and_interfaces
– http://www.alumaxindia.com/aluminum-com posite-panel-cladding.html.