Why glass remains the top choice for today’s skyscrapers
Glass towers are one of the great symbols of the modern age — and their glazed facades, not to mention the technology behind them, are evolving in response to climate change and modern tastes.
The facades on eight of the top ten skyscrapers in the world are substantially or predominantly composed of glass.
This is the finish that particularly appeals to major corporations. “Glass is what everyone is looking for,” says JLL’s Katie Krelle, Associate Director — Project Management. “You can see that in iconic buildings in London such as the Shard and the Gherkin. The look and feel are important – that’s all to do with branding. Corporates want a building to match their reputation.”
Companies also want a building that maximizes daylight, to help achieve the best BREEAM rating for the building (which assesses and certifies its sustainability) and enhance their employees’ working environment. “Daylight is really important in terms of occupants’ wellbeing and this has a direct impact on productivity,” says Krelle.
Research has shown that higher levels of natural light have benefits for employees working inside including reducing eye strain and headaches and helping to boost productivity.
Yet glass-fronted buildings also come with their own challenges. “Glass facades have to be balanced with energy-efficient, mechanical ventilation,” Krelle explains. “Energy reduction requirements under the UK Building Regulations and ambitious BREEAM targets mean that you cannot have a highly glazed façade if you then have maximum mechanical ventilation running 24/7 to avoid overheating. The performance of the facade is critical in terms of protecting the building occupants against the heat of the sun and cold air during the winter months, coupled with reducing energy consumption.”
Clearer and stronger glazing
Advances in technology means the facades of many of today’s high-rise towers are more complex in design, performing their primary task as a barrier between the controlled internal space and global warming taking place outside.
In its simplest form, glass can contribute to increased internal temperatures as solar radiation passes through it. In the past, tinted glass units were used to mitigate the effects; however, with developers aiming to deliver greater levels of daylight to the floor space, along with increasingly stringent energy targets under the Building Regulations, glass technology has evolved and is working harder than ever. So-called ‘solar control glass’ incorporates high technology coatings, which let in daylight while rejecting more than 70 percent of solar radiation.
New techniques and technologies are being used on many modern skyscrapers. London’s tallest building, the Shard, is a stand-out example in a city full of glass buildings, according to Steve Mudie, Facade Specialist at alinea consulting. “The Shard has a dynamic, double-skin facade,” he explains. “The outer glass is single-glazed, creating a ventilated cavity to the inner double-glazing, all set within a façade depth no greater than a conventional double glazed curtain wall. Automated blinds then react to the sun’s path to maximize daylight and views while minimizing solar radiation for the building’s occupants.”
The Shard is not alone; many of the City’s iconic glass towers utilize double skin façade technology. There are many examples in the City, including Heron Tower (now Salesforce Tower) and The Willis Building on Lime Street. The Gherkin and Leadenhall Building (aka the Cheesegrater).
Elsewhere, innovative glass designs are helping to manage buildings’ emissions – a key consideration, given that 40 percent of global carbon emissions come from real estate. The world’s second highest building, the Shanghai Tower, also has a dynamic double-skin facade. Its triangular, curved structure means it uses less glass than a square building would, and the space between the two skins acts as a thermal buffer zone. When conditions warrant, warm air from inside can be released into this zone where it is cooled down before being expelled outside.
Furthermore, new designs ensure that buildings are fit for purpose. Acoustic laminated glass, for example, offers improved noise insulation, protecting occupants primarily from external sounds. In addition, it’s helping make buildings themselves more resilient. The new US Embassy in London, for example, is a pioneer in the use of bomb-resistant glazing.
The creation of cooler offices
For all its positive attributes, there can be downsides if glass and its technologies are not thought through, as was the case with London’s Walkie Talkie building. Local authorities shut some parking bays on Fenchurch Street after reflected sunshine caused damage to property, including the well-publicized melted side panel of a Jaguar car beneath the 37-story building. The issue was subsequently remedied by introducing a black finish solar shading veil to the entire south facing elevation.
“The most common faults are performance related failures, examples including water leaks, air tightness leaks, and in cases, glass breakage, exacerbated where you have a complex façade,” says Krelle. “Remedial works are very costly after the event, as the Walkie Talkie example demonstrates. Fully integrated design coordination early on and quality control procedures throughout are therefore key.”
Wear and tear must also be taken into consideration, says Steve Mudie: “The façade systems can last as long as the building, typically 60 years. However, the glass units have a service life of between 25 to 30 years. After this time, the edge seals could deteriorate, requiring glass units to be replaced, likewise gaskets and other seals, which might require replacing earlier.”
Despite new alternative materials coming on to the market and the higher construction costs of glass facades, Krelle believes corporate demand for such buildings will ensure that it’s a price developers and landlords will be willing to pay.
Yet the growing focus on sustainability will also influence the choices available to building owners and occupiers. “The future will be driven by legislation and by climate change,” says Krelle. “In the UK, the regulations are becoming much more stringent on emissions – so the use of glass must always be in balance with the sustainability requirements. And businesses are becoming more willing to pay for buildings which protect their staff and sustain the environment.”