Glass is unarguably the most remarkable material ever discovered by man particularly for transparency and hence, favourite of the architects.
Today, it is difficult to imagine contemporary architecture without glass. The three most significant properties of glass i.e. transparency, translucency and reflectance have made it a dominating material over any other building material since inception of glass. Traditionally glass has been used in windows but now it is favourable for interior as well as exterior applications. Today, use of glass can be found in doors, windows, floors, partitions, walls, staircases and furniture while in exterior applications, it has taken over to complete façade in modern architecture. Today, glass not only fulfils aesthetic requirements but also technical and functional requirements for use in various parts of the building hence glass is no longer just a filler material but an essential component of the buildings. In facade, use of glass started in airconditioned multi-storeyed buildings particularly for IT and BPO sectors. Glass facade in such buildings provided a very hi-tech and modern look. It also brought western style of architecture into the country. Though glass facade has many advantages, it has some disadvantages too like many other building materials. Therefore, use of glass in the facade needs to be optimized considering functional and climatic requirements also.
Use of glass
Due to development in manufacturing and refining technology, glass is now the most modern and sophisticated building material. As it can now fulfil aesthetic as well as almost all the functional requirements, it has become a first choice material for many architects. Due to development of insulated glazing and energy efficient glass, it has become automatic choice for modern architecture particularly in western countries due to its efficiency in western climatic conditions. Today apart from the use of glass in windows, it has become a material for many functions like bringing in natural daylight, protection from rain, wind and cold, transparency or translucency, supply of fresh air, heat, sound and solar protection, personal and fire protection, solar energy, bullet resistance, walling etc. These functions combined with facade system have provided freedom to the architects for planning glass facades with
modern and fascinating appearance. From inside, wall becomes almost transparent while at night with the interior lit, it virtually disappears. Important factors to be considered for glazing include pressure equalized system in system design, barriers against water and air leakages, and thermally efficient system for better performance of the building. Performance needs of a façade include material and system performances. For material performance, a material should meet criteria of design life, mechanical, chemical, acoustical and thermal properties, UV resistance and capable of resisting temperature and weather variations. Under system performance, criteria like weather protection as a whole assembly, seismic movements, thermal expansion, heat transfer through façade/thermal loads, acoustics, safety, occupant’s comforts and performance for designed life cycle are to be considered. Glass facade is provided through a curtain wall, typically a thin wall constructed of glass, metal or stone framed in aluminium, attached to the outside structure of a building. As the structure is exposed, it becomes dominant element of façade design. Frameless glass facades are often used for the same reason. The curtain wall does not carry the load for either the
roof or floor of the building, keeps away air and water, and provides resistance to wind and seismic forces. Connected to the floors or columns of a building, curtain wall transfers horizontal loads induced by wind and gravity to keep the structure stable. Most commonly used glass types in external façade are fully tempered, heat strengthened and laminated.
Advantages of Glass Facade
Some of the advantages of using glass in facade are;
i. It reduces the dead load of the building as facade system is very light thereby reducing the load on foundation. ii. It offers unobstructed view thus connecting interior to exterior. iii. It makes area look spacious, wider and creates a sense of feel good due to brightness, natural light and exterior connection. iv. It helps in bringing natural light inside the building leading to increase in the working efficiency. v. It saves energy due to natural light coming inside. vi. Appropriate glass facade can prevent heat absorption, UV rays and glare thus making the building energy efficient. vii. Curtain glazing makes the building aesthetic, provides modern look, and enhances image of the building as well as occupants.
Disadvantages of Glass Facade
i. It is generally costly and requires careful handling. ii. It requires regular cleaning, skilled and high level of maintenance. iii. It may require extra fire safety provisions making building further costly. iv. It may form light pollution under certain conditions. v. Changing of glass is cumbersome, time taking and costly affair.
Selection of Facade
The façade or the building skin or building envelop has become popular in recent times. It is an independent frame made of Aluminium Composite Panel (ACP), double glazed glass, pre-cast stone, natural stones or metal panels mounted and fixed in Galvanized Iron (GI) or on aluminium framed structure. It is fixed with stainless steel components along with rubber gaskets, sealant, silicone gel, metal screws etc. generally on RCC. The building has vision area and spandrel area. The vision area is directly exposed to the sunlight hence the materials used should allow sunlight transmittance to the interior and also act as a weather barrier against air and water infiltration. The spandrel area where horizontal and vertical structure is opaque, selection of the materials should be made based on durability, maintainability, compatibility, health and safety, economy, availability, functional performance, thermal performance, acoustical requirements and sustainability. Therefore, architect needs to co-ordinate with the structural designer and quantity surveyor/engineer for selection of the materials. Glass façade is also adopted based on location and height of the building. Some of the factors affecting the selection of glass facade are discussed briefly as follows: Durability The façade materials should be sufficiently durable so that they are not to be replaced after a short period. Ideal condition is that the materials last for the building life. If it is not feasible, it must last as long as possible. As far as glass is concerned, toughened double glazed glass used for the facade is quite durable. Aesthetic considerations Aesthetic is one of the basic requirements for selection of facade material. Sometimes, adjoining structures are also given weightage in selection of such materials. Due to such consideration, most of the buildings in BKC Mumbai have been designed with glass facade. Glass facade provides beautiful and modern look which may not be feasible in other materials. CBI Building, BKC, Mumbai RTI, CAG Building, BKC, Mumbai Videsh Bhawan, BKC, Mumbai SEBI Building, BKC, Mumbai PNB Building, BKC, Mumbai IDBI, Building, KBC, Mumbai Functional Performance The facade has to perform its function for which it is provided. The functions include client’s requirements, architect’s concept and structural requirements. Quality is another criterion included in the functional requirements. Glass can be used to provide walls, to bring sun inside, to reflect sun, to absorb sun to generate solar power, energy efficiency and as a light weight material. Orientation Centre, NISM, Mumbai Dining Hall, NISM, Mumbai Academic Blocks, NISM, Mumbai Auditorium, NISM, Mumbai Hostel for NITIE, Mumbai Academic Block, NITIE, Mumbai Maintainability The materials for the facade should be such that they require minimum, easy and economic maintenance. The second factor to be considered is about cleaning the façade, particularly in multi-storeyed buildings. Glass facade is easy to be cleaned but cannot be done through traditional ladders and cleaning equipment being a specialized job hence costly. In future when glass facade becomes common, cost may also come down. To maintain the exterior look, it is necessary to keep the façade sparkling clean. Specially trained workers are
required during all weathers. Health and safety Another important selection criterion is the health and safety impact of the materials selected during their initial installation for the workers as well as during their life span for the occupants. Safety from toxicity, wind, humidity, temperature, earthquakes and other disasters, impact and breakage etc are to be ensured. Also use of proper glass provides safety to the occupants. Fire safety is another issue which has to be addressed appropriately in glass facade buildings. Confederation of Construction Products and Services (CCPS) has brought out guidelines on use of glass in buildings – human safety in 2007. Subsequently, IS: 16231 (Pt. 4) 2014 “Code of Practice for Use of Glass in Buildings – Safety related to Human Impact” was brought out by BIS, derived mainly from CCPS Guidelines. Recently, a new section on “Glass and Glazing” Part 6/ Section 8 has been added in the National Building Code (NBC) 2016. This section provides guidance on the selection of appropriate glazing for buildings, energy and light aspects, determination of thickness of glass used in glazing, specialised operations for fixing and with respect to rescue and fire fighting operations, human safety aspects while using glass in buildings. Therefore, glass can now be appropriately selected and used in buildings following CCPS guidelines and NBC provisions to ensure safety and structural stability. Bird hitting to the glass is also to be given due consideration particularly in windows of high rise buildings for safety. Economy Cost is a basic criterion in selection of a material by the ar chitect and engineer but it has to be compatible with durability, quality, safety and aesthetics. Based on client’s requirements, cost has to be given adequate weightage. Glass facade at present is costly but considering the aesthetics and functions, cost cannot be compared with ordinary brickwork/stonework. In case efficiency and per formance of glass becomes ver y high, its use may increase manifolds simultaneously bringing down the cost. Material availability, delivery time and workforce availability This is another important factor to be considered while selecting the façade material for its overall cost and time required in its procurement for completion of building. Material’s availability locally is always economic and environment friendly. In case, materials are to be procured from abroad or from a large distance, it becomes costly and its delivery may get delayed affecting completion time, and lead to cost overrun. Special glass is not common because of its fewer requirements at present. When use of special glasses becomes common, more and more fabricators and skilled workers may be available in the market. Thermal properties of the product India has different weather conditions hence it is important that glass facades are suited to the weather requirements. The façade materials are exposed to different weather conditions and get affected by weather conditions during different weathers and even based on the orientation. They may also affect thermal conditions of the interiors as well. The façade material should be compatible to the weather conditions during various weathers and even daytime requirements. Glass has to be used with proper design and based on the orientation of the building. Like any other energy efficient material, glass also needs to be selected based on site requirements and energy efficiency. Acoustical performance of the product Acoustical or sound proofing performance of the façade product is also critical to the selection process to minimize sound pollution. For acoustic and heat insulation, double glazing is provided filled with an inert gas like Helium. The use of inert gas can also withstand climatic conditions and temperature fluctuations. Acoustic properties can be obtained by using acoustic glass having acoustic interlayers in double glazing. Sustainability criterion Glass is a fully recyclable material that can be recycled in close loop over and over again. Glass recycling also helps in saving energy as cullet melt at a lower temperature than raw materials. Consequently, less energy is required for the melting process. It does not contain VOC, lead, copper, formaldehyde or arsenic, thus contributing to environmental sustainability. In few places where glass is not preferred to be used like in hot and warm climate, special glasses like solar glass or reflective glass can be used. Solar glass has added advantage of producing solar power. Waste glass powder can be used as partial replacement of cement for sustainable concrete practices and in manufacturing other building materials like fibre glass used in cladding, flooring, roofing and glass mosaic tiles which make glass a green material. Recommended Use of Glass Facade Based on the above, the following recommendations are made for the facade in India; 1. Based on functional basis like hotels, airports, large lobbies of institutional buildings to have seamless view and use of natural light, glass facade is recommended. In such structures glass becomes an integral and important part of the construction. 2. Based on aesthetic considerations where aesthetics carry more weightage like convention centers, civic centers, museums, corporate headquarter buildings, IT and BPO buildings and in areas where entry to sunlight is important due to weather conditions. 3. Partly on aesthetic and partly on functional basis to have balance between use of glass and solid walls for efficient performance of envelop and simultaneously keeping the Air conditioning load to minimum like retail and mixed-use centers, office buildings, residential buildings, churches, institutes and other privately funded public buildings, particularly where weather conditions are not completely favourable. Glass has additional advantage of compatibility of using with various materials. Though availability of glass has increased in the country but technical knowhow for special glasses, their testing laboratories and skilled workforce for its use need to be made available at large scale. Use of Solar Control Glass in Glass Facades In glass façade, it becomes essential to use the right type of glass for indoor comfort with respect to heat and light. Depending upon the climate and orientation, glass must be chosen very carefully. Although extensive use of glass is not recommended for Indian climate but sometimes aesthetical appearance and view are to be given priority over functional requirements. Solar control glass is used primarily to control solar heat gain hence is most appropriate to hot climates. It reduces the cooling load on one hand but reduces the visible light transmission inside the building on the other hand resulting into increase the need for electrical lighting. Wide varieties of solar control glasses are now available and one has to select right type of glass making a balance between the reduction in cooling load and VLT (Visible Light Transmission). The three important criteria for selection of solar control glass are its U-value, SHGC and VLT. For further details, ECBC code and NBC should be referred. Now low – e coating glass is also gaining importance as in contrast to the solar control glass, low-e coatings have lower reflection and greater light transmission. According to the US Department of Energy’s EERE (Energy Efficiency and Renewably Energy), low-e coatings may add 10-15% to the cost of glass products, but reduce energy loss by as much as 30-50%. Fire Safety of Glass Façade Fire safety becomes of prime importance when there are no or limited escape routes in a building. Due to non-availability of stringent norms of fire protection, fire fighting and escape for the occupants as well for evacuating them by fire personnel, and their implementation particularly when glass façade is used, fire accidents have occurred in the country. Due to such incidents in glass buildings, new fire provisions have been added for glass façade buildings such as; 1. Refuge areas should be clearly identifiable and the path leading to these spaces should be easy to trace and free from obstructions. 2. Refuge areas should have 2 or 3 sides with fire resistant materials. A minimum of 2 hour rating is desirable considering the average rescue times in our country. The remaining side should face the building exterior facade from where escape is possible. 3. These glass walls should have openable panels (either manual or automatic) that can be operated from inside by the occupants and outside by the fire-fighters. Such openings should be of size not less than 1000 mm X 1000 mm or as prescribed by fire authorities. 4. The emergency panels should be clearly labelled with an ‘Emergency Exit’ sign along with a large red triangle on the external facade so that the fire authorities can easily identify the exit panels. 5. The openable windows have glass which is non-laminated. Fully tempered glass (monolithic or insulated) should be used in these panels so that it can be easily broken with a sharp object if needed. 6. The distance between the building’s main structure and the glass facade should not exceed 300 mm. This is to ensure that people exiting through the openable panels are not subjected to risk of falling through the building void. 7. Smoke seals made of noncombustible material must be laid between the building structure and the glass façade. 8. To restrict the spread of fire, automatic water sprinkler systems should be installed on every floor. 9. Ceilings should have a pop-up vent which can be easily accessed from the floor and should be integrated to the central smoke detection system. 10. The aluminium sections and the fixing materials should not have any coating of combustible materials. 11. Staircase areas on all floors should have direct access to the ground level. At all levels, fire rated doors that can resist fire for up to 2 hours should be installed at the staircase entry points. These doors should have a 2 hour fire rated glass vision panel of size minimum 200mm by 300mm to facilitate viewing of the hazard side in the event of fire. Glass Façade Testing Glass façade is to be tested for its designed performance for structural stability and leakage against air and water infiltration. It also ensures quality and provides chance to correct design deficiencies in the system including fabrication and installation, provides certificate of stability, peoples safety and is mandatory as per International Standards. Also façade design has to be customized for every building due to wind pressure, floor spanning, building movements including seismic movements, glass panel sizing and configuration, bracketing arrangement, variation in structural requirements and
workmanship. Testing is essential as building materials of façade are exposed to climatic changes and severe wear and tear that may become potential safety hazards. Therefore such materials should be tested to ensure weatherproofing, safety, stability and durability. Such tests are to be done on every building as two projects are not similar. The tests ensure performance requirements, air and water leakages, and structural adequacy against design and seismic failure. ASTM codes are available for the tests. Concluding Remarks i. Façade is the most important component of building responsible for its performance and aesthetics hence should be considered specialized subject for important buildings. Use of glass enhances not only aesthetics but also performance though glass needs to be chosen based on the climatic conditions of the area and orientation of the building. ii. Specifying glass is challenging because of the large number of available options and it is essential to choose the right type of glass for maintaining balance between heat and light transmission hence glass should be included as a specialized subject in architecture and engineering. The property of solar control glass helps in reducing the heat transmission inside the building thereby reducing AC load and sufficient daylight. iii. Remarkable property of glass of unobstructed view and connecting indoor to outdoor is beyond comparison with any other building material. iv. Glass is a fully recyclable and sustainable material.