A metropolis of superlatives, London is a leading global city with strengths in the arts, commerce, education, entertainment, fashion, finance, healthcare, media, professional services, research and development, tourism and transport all contributing to its prominence. It is one of the world's leading financial centers and has the fifth or sixth-largest metropolitan area GDP in the world depending on measurement. London is a world cultural capital and is the world's most-visited city as measured by international arrival.

Skyscrapers in London?

It is not skyscrapers that define London's skyline, but a mix of architectural landmarks that have, over the centuries, come to define a city with a remarkable past. Chief among these are St. Paul's Cathedral, the Palace of Westminster, Tower Bridge and the Tower of London, but these are accompanied by hundreds of church spires and monuments.

Present-day London is home to some of the tallest and most exciting skyscrapers in Europe such as The Pinnacle, The Shard, One Blackfriars Residential Tower and Salesforce Tower London. Some amazing architectural work is still going on, and in the near future two newcomers will be joining their ranks.

The “Walkie-Talkie” in 20 Fenchurch Street

The first is 20 Fenchurch Street, a commercial skyscraper just finalized in London. It takes its name from its address on Fenchurch Street in the City of London financial district and it has been nicknamed The Walkie-Talkie because of its distinctive shape. Finished in spring 2014, the 37-storey building is 160 m tall, making it the fifth-tallest completed building in the City of London.

Weather sealing for durability

The façade was delivered by Permasteelisa UK and Permasteelisa Italy, and the roof was constructed by Josef Gartner. The insulating glass was supplied by Vetrodomus, Italy. For structural glazing, Sika recommended Sikasil® SG-500 and SG-550. The high-performance waterproofing sealant Sikasil® WS-605 S was used for weather sealing as sealant durability under severe weather conditions on the outside of the glass was required.

Furthermore, Sikasil IG-25 HM Plus was used as an insulating glass secondary sealant and SikaGlaze IG-5 PIB as insulating glass primary seal, both in grey to match the aluminum profiles. The most complex challenges arose when the cold bent glass and outwards-sloped façade put the adhesive under permanent stress.

That is why very comprehensive planning and joint size calculations were necessary beforehand. Some corners required complicated installation and application of 2-part adhesive on site. In a number of areas with high load concentrations, the only solution was the new high-strength adhesive Sikasil SG-550 to keep the joint dimension as small as the specifications allow.

The “Cheesegrater” in 122 Leadenhall Street

The second newcomer is to be found at 122 Leadenhall Street. When completed in 1969, the building was 54 m tall with 14 stories above and three stories below ground. It was originally designed as a pair with the Commercial Union headquarters. The two buildings have a central compressional concrete core and have suspended floors which hang using the steel 'chords' visible on the exterior of the building. These chords are hung from power trusses at the top of the building.

It is an example of a tension structure; at the time, it was considered one of the most complex glass-fronted buildings in the United Kingdom. The architect acknowledged the influence of Mies van der Rohe.

Designed by Richard Rogers and developed by British Land and Oxford Properties, the new Leadenhall Building will be 225 m tall, with 48 floors, when it is completed in 2014. With its distinctive wedge-shaped profile it has been nicknamed the Cheesegrater, a name originally given to it by the City of London Corporation's chief planning officer, Peter Rees, who upon seeing a model of the concept told Richard Rogers he could imagine his wife using it to grate Parmesan. The name stuck.

The new tower features a tapered glass façade on one side which reveals steel bracing, along with a ladder frame to emphasize the vertical appearance of the building. It also gives the impression of anchoring the tower to the ground, giving a sense of strength.

Unlike other tall buildings, which typically use a concrete core to provide stability, the steel mega frame, engineered by Arup, provides stability to the entire structure and is the world's tallest of its kind. The base features a 30 m high atrium. This will be open to the public and will extend the adjacent plaza. Exterior glass lifts will be used on the building, similar to the neighboring Lloyd's building designed by the same architect.

Small in floor space - high in height

The main drawback of this unusual design is the building's relatively small floor space of 84,424 m² for a building of its height. The façade was created by Shenyang YuanDa and YuanDa Europe and the insulating glass was delivered by two Chinese producers, SYP and North Glass. Sikasil SG-500 was used for structural glazing and Sikasil WS-605 S for weather sealing in order to guarantee long-term durability. Sikasil IG-25 HM Plus was ideal as a secondary edge seal for air and gas-filled insulating glass in the structural glazing applications.

The elevator control boxes were bonded using the fast-curing adhesive system SikaFast-5000. The triangular glass geometry of the corners and the huge variety of glass dimensions called for intensive planning and joint size calculations.