Unlike steel and concrete, glass is a relatively new material in the construction sector. Romans began using glass for architectural purposes by casting windows in around AD100, but it wasn't until the latter part of the Industrial Revolution that scientific research started to reveal the exciting functions and properties of glass.
For a long time, glass was cast in buildings for the sole purpose of letting light in and keeping the weather out. It was widely believed - and is still to an extent - that too much of the transparent material wouldn't be strong enough to guard a property from vandalism and destruction; it wouldn't be sturdy enough to withstand a hurricane; and is too transparent to protect a building from heat gain.
Fortunately for the industry and consumers, designers, engineers and scientists are quickly discovering new technologies that are proving the skeptics wrong.
One of the most obvious functions of glass is its ability to open up views and welcome natural light into a building.
For this reason, buildings with greater visual transparency than ever before are beginning to rise, with some curtain walls made almost entirely out of glass. The spherical headquarters of construction giant Aldar in Abu Dhabi, UAE, for example, has an envelope made up of 25,000m³ of glass.
But one major problem with implementing so much glass in warm countries is the amount of heat that builds up inside buildings as a result, and the ultimate rise in air-conditioning costs.
The easiest solution is to reduce the amount of glass used in construction, which is exactly what the city of Abu Dhabi, UAE is doing.
The capital's Department of Municipal Affairs plans to issue new building regulations next year, which would mean that glass will make up just 30% of a building's façade. But this proposed code has caused controversy among architects.
Stride Treglown's Abu Dhabi general manager Nathan Hones says that the plans discourage creative ideas. "What we should be looking at is a performance-based approach which still requires the designer to address the sustainability issues at hand, but also allows and encourages innovative thinking and solutions to meet these requirements."
So how can we build sustainably without hindering designers' work? "Solutions include sun-shade devices, light wells, high performance low-e glass, and double or triple glazing," says Hones.
US-based RTKL principal and architect Douglas Palladino agrees. "High performance coatings are being increasingly used for glass so we can have the benefit of daylight without the negative effect of unwanted solar radiation."
One project that has incorporated both an attractive and energy efficient glass façade is China's Hong Kong Science Park. This development incorporates a double-glazing curtain wall system and sunshades, as well as window units integrated with power-generating photovoltaic panels.
Robert Stephens, Middle East regional director of Inhabit Group, which worked as an engineering consultant on the Science Park project, believes that architects need to understand where the limitations lie when it comes to designing with glass. "It's kind of a balancing act. Obviously, the more light you let into a building, inherently the more heat is associated with that, but there are coatings available with high thermal insulation properties which don't detriment visual performance."
It's a scientific fact that the molecules that come together to form glass are arranged randomly, which explains why the material is so fragile.
Because of this, the health and safety risks associated with using glass in construction are much higher than when steel or brick is used, explains Stephens. "Steel is a homogenous material and before it snaps it bends. If you take glass, it doesn't deform before it breaks. There will not be any signs of failure when it comes to glass; it will suddenly just give."
Despite its fragility, the use of glass in construction is becoming increasingly popular. Nowadays it is even being used as a structural material.
The Willis Tower in Chicago, the tallest building in the US, has an observation deck made entirely out of glass and sits 412m above the city.
In theory, the glass should break when a person steps onto it, but Ross Wimer, design partner for Skidmore, Owings and Merrill (SOM), the firm which designed the deck, explains why this is not the case.
"Three layers of glass, bonded together, make up the walls and floor of the observation deck platform. The laminated glass can support the weight of an elephant, which is reassuring since this glass floor is 1300ft in the air," says Wimer.
Another project where glass has been used as a structural material is the Apple Store on 5th Avenue, New York. Designed by Bohlin Cywinski Jackson and structural engineers Eckersly O'Callahan, the 9m structural glass cube houses a transparent glass elevator wrapped by a circular glass stair. The store occupies the underground retail concourse, with entry from the plaza level above.
A challenge faced by many designers, however, is using inner layers to create strength without distorting the glass.
Wimer explains that it's all about sizing the thickness of the glass to minimise deflection. "Deflection causes distortion or 'pillowing' that is particularly apparent if the glass has a reflective coating."
"One needs to pay particular attention to the jointing and supporting structures to ensure that these do not detract from the transparent character of the glass surface. Thankfully there have been some amazing advancements in jointing material and mullion supports, not to mention the use of glass structurally itself which have overcome any detrimental effects of the limit on the glass panel sizes," adds Hones.
Low iron-glass also minimises green tint, which appears when layers of glass are made thicker, as Palladino explains. "We use this for visual appeal in lower portions of buildings where there is retail space. There are also low reflection coatings in glass that you use in retail so you can achieve even greater visual transparency."
Glass in buildings isn't always transparent, however. Some designers are using technology to create visual interest in what would otherwise be a repetitive curtain wall, according to Palladino. "The desire for nothingness in glass from a design perspective is only one way we approach the use of glass. Often we use it for its physical presence and its material quality. We have designed the Changsha Xin He Delta, a 45-storey building in China that uses different colours of glass to create visual patterns."
Despite its lucid appearance, the future of glass in construction is not so clear, says Stephens. "Even the codes we are working with at the moment are contradictory, depending on whether you follow an American code or an Australian code. With steel, the codes are all consistent. A lot of the time, with glass, we are not even following the codes 100% because they are trying to catch up with the industry."
"Glass is being researched today and there are conflicting views surrounding it. It is not fully understood even today," he adds. But the fact that there are still undiscovered glass techniques is a sign of exciting times ahead for architects and contractors alike.
As Palladino says, "It's a timeless material and people are using it more because of the way it's evolving."
Hones adds, "The industry has developed some very talented facade engineers and glass material supplier specialists who are always at hand to assist the design team with challenging projects. Working with glass is always interesting and one quickly realises how much one doesn't know when trying to push the boundaries."