Glass structures have become a pertinent feature of the urban landscape. The ultra-modern buildings have taken glass to an innovative, dramatic and surprising high. It is now one of the most versatile and cutting-edge building materials available.

Newer production and development techniques have turned construction from glass into an art. Expanses of glass can now be suspended in front of a series of nearly invisible metal trusses and braces. It is not only spectacular to look at and look through; it is also safer, stronger and more energy-efficient.

Heat-strengthened glass and tempered glass are amongst the stronger varieties of glass. Glass must be strengthened for three basic reasons: to handle wind-load, to increase impact-resistance and to combat thermal stress. Architects and designers must consider the force of wind on a building or installation when choosing to use glass. Wind causes glass to deflect, straining not only the glass, but the entire glazing system: the framework, gaskets and sealants. Impact-resistance is closely related to wind-load, because the wind carries hailstones, dust, small stones and other debris.

However, in a tropical country like ours, it becomes more important to beat the heat. Certain types of glass available absorb over 70 per cent of heat that falls on it. The transmission to the inside of a building is about 20 per cent. Energy transmitted through ordinary glass is absorbed by the floor, walls and furnishings and released much later. The heat storage capacity of these objects tends to spread the cooling load over a considerable period of time so that the peak amount of heat felt is reduced. The effectiveness of heat-absorbing glass may be increased by using it as the outer pane of a double-glazed window so that absorbed energy is dissipated outside.

Reflective glass

Reflective glass is clear or tinted glass that has a very thin layer of metal, metallic oxide or a film of dielectric material on the surface. The reflective coating reduces heat gain and glare from the outside while allowing visible light to enter. Sealed double glazed units are now available with a reflective coating on the inner surface of the outer pane. Their reflectivity depends on the angle at which light hits the glass, but it is higher than that of ordinary glass.

Characteristics

• It gives a building a mirror-like appearance

• The coatings are available in silver, copper, gold and earthtone

•It reflects and absorbs the sun's rays; therefore it reduces the amount of solar radiation that enters the building, thus reducing power costs

Low E glass

Low emissivity glass, commonly called low E glass, is a type of reflective glass that is gaining popularity, especially in residential and office applications. Low E coatings are very thin metallic coatings that reduce visible light transmission by about 10 per cent compared to uncoated glass. In northern areas, low E coatings let in the heat from the winter sun while retaining the heat generated from inside the building. In southern areas, low E coatings are usually applied to bronze, green or gray tinted glass. They reduce glare and reflect the sun's heat away from the structure.

Characteristics

•Reduced heat loss through windows

•Re-radiation of the heat absorbed from sunlight inside the room

•Allows sunlight into a room without letting heat outside

•Resists ultraviolet light, which results in less damage to carpets, draperies and other furnishings

•Reduces glare

Insulating glass

Insulating glass units, also known as IG units, are made from two or more sheets of glass separated by a sealed air space. The metal tube around the perimeter of the insulated unit which separates the two sheets of glass is called the spacer. It is filled with a special moisture absorbing material called a dessicant. The perimeter of the entire unit is sealed with a high grade sealant.

Characteristics

•Reduces the tendency of condensation forming on the room side of the glass

•Reduces cold transmittance at windows and helps maintain a uniform temperature. In the winter, IG units reduce heat loss and in the summer they reduce heat gain

• Reduce the level of noise from the outside

Glass glossary

Float glass: The process involves floating molten glass on a bed of molten tin. This gives the glass uniform thickness and makes it very flat. Float glass-making was perfected in 1959 by Pilkington Brothers Ltd of England.

Tinted, or heat absorbing glass: It is made by adding colouring agents to the batch mix. These agents include bronze, grey, green and blue. Tinting glass reduces the amount of light that passes through the glass. As the glass gets thicker, the density of the colour also increases. This causes the glass to transmit less visible light.

Patterned glass: Also called figured glass, obscure glass and decorative glass, patterned glass is made by passing it through rollers that have patterns on them. The pattern is transferred to one or both sides of the glass. Patterned glass also helps control the transmission of light and diffuses the details of objects that would be clearly visible through ordinary glass.

Mirrors: These are made from high-quality annealed float glass designated as either mirror quality or mirror select. Mirrors are made by depositing a layer of silver on the back surface of the glass, because the tin side does not accept silver properly. The reflectivity of the mirror depends on the thickness of the silver layer, glass, and glass colour. High quality mirrors could have a copper backing, which offers the best protection.

Laminated glass: It is used as the inboard sheet in skylights. By varying the thickness and colour of the PVB (polyvinyl butyral), laminated glass can be used to control glare, reduce the transmission of solar energy, and screen out ultraviolet radiation.

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