Facades and building envelopes, which are the external skin of a building, project the image and creative intent. They can also become important environmental moderators and key influencers in project risk and commercial success. A well designed façade allows a new building to work more effectively for its owners, occupants and the environment. The façade plays a crucial role in heat and light exchange as it is the interface between the exterior environment and interior space. Comfort, productivity, energy use and running costs can all be improved.
Double skin facades are often used in Europe to resist the cold climate however double-skin systems in Australia are relatively new. One example where the double façade system is demonstrated in Australia is Sydney’s 1 Bligh Street high rise. The façade provides great solar control while maintaining clear views of the Sydney Harbour.
1 Bligh Street is a premium grade high-rise building offering 27 levels of office accommodation and features a double-skin, glass facade with a naturally ventilated full height atrium. Amenities include a cafe, childcare centre, shower facilities, bicycle racks and parking for 92 cars. The building’s 6 Star, Green Star rating achievement is the highest awarded in NSW and includes the maximum allowable five points for innovation in categories such as environmental design initiative and exceeding Green Star standards. The building was designed with a focus on maintaining views while providing sufficient daylight levels and solar control. Ray Brown, director of Architectus, stated that the geographic and climatic conditions at 1 Bligh Street were major influences on specification of the double skin façade.
Owners – Co-owned by DEXUS Property Group, DEXUS Wholesale Property Fund (DWPF) and Cbus Property.
Architects – Australian Architectus and Germany’s Ingenhoven who came together in 2006 for a design competition.
Builders – Grocon : Australia’s largest privately owned development and construction company.
Facade Contractor – Arup.
Facade Consultant – Enstrust.
Awards – 1 Bligh has received a number of awards and has been highly commended for its sustainable design, development and architecture.
– Awarded Best Retail/Commercial Development – Urban Development Institute of Australia
– NSW Highly commended Office Development – Australia category, Asia Pacific Property Awards (May 2011)
– Highly commended Office Architecture – Australia category, Asia Pacific Property Awards
– Voted Best Tall Building 2012 for Asia and Australis by the CTBUH (Council for tall Building and Urban and Urban Habitat, IL, USA)
2012 NSW Architecture Awards
– Urban Design Award
– Sir Arthur G. Stephenson Award for commercial architecture 2012
– Milo Dunphy Award for sustainable architecture
Ingenhoven produced a design allowing workers and the public to see and feel the whole of the community of the building. 1 Bligh Street’s elliptical geometry effectively resolves the site’s urban condition at the meeting of two city grids. The ellipse is rotated on the site to encompass views to the harbour, thus resolving the urban condition and maximising the building’s commercial value (). The disadvantage is that it is more costly to construct an elliptical building than a square building. However, this is made worthwhile by a magnificent curved atrium at the building’s core providing a sanctuary to its inhabitants.
A naturally ventilated glass atrium climbs the full height of the building, providing a circulation of fresh air and a sense of openness on all floors. The glass provides dynamic views through the building making the atrium an arrival point for every floor, enhancing communication, connection and community.
The building’s scale is broken in the centre by a large outdoor terrace cut into the floor plate at the lift transfer level. This space has been reserved as its reception floor, making it one of the most spectacular and unique reception of any legal firm in the city. The terrace also cleverly conceals the air intake for the air handling plant above, which is covered in a glass skin making it fully visible within the building.
At the top of the building, the inner glass layer peels away, creating a large outdoor timber terrace incorporating banksia trees. This creates the building’s fifth elevation which is observed by taller surrounding buildings.
ENVIRONMENTAL & THERMAL STRATEGIES
Cost effective and sustainable buildings have been a key focus in building design for years. Double skin façade systems are becoming increasingly common in high profile buildings and are being enthused as an exemplary green building strategy. The system consists generally of exterior skins which respond dynamically to varying ambient conditions, which can incorporate a range of shading, natural ventilation, and thermal insulation strategies.
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The overall purpose of the double skin differs from the conventional system used in European buildings where the intention is to trap the heat by incorporating an extra thermal layer of air. The thermal skin of 1 Bligh is designed to keep the building cool. It does this by stopping direct sunlight from hitting the internal glass. Between the inner and outer glass layers, motorised venetian blinds track the sun and automatically adjust to suit. The outer glass skin incorporates fixed horizontal ventilation slots at each level of the building to encourage upward airflow within the cavity which helps to expel unwelcome hot air. This flow is driven by natural wind since Sydney rarely experiences a completely still day. This result is that the internal skin will never be exposed to air temperatures that are vastly higher than the outside ambient air temperature. The outer glass layer also acts as a weather shield to protect the blinds from severe winds. The inner layer which is double glazed for world class thermal efficiency acts as a barrier against heat gain in summer and heat loss in winter, thus complimenting the benefits derived from the venetian blinds. http://www.architectus.com.au/sites/default/files/06_0.jpg
One of the major benefits of the double skin façade is that operable external blinds can be introduced which normally can’t be installed on a high-rise, thus producing a shading coefficient of 0.15 with the blinds down and uninterrupted views when up. Reduced heat and optimised light is obtained as a result, underpinning high performance sustainability and unprecedented environmental innovation.
It can be foreseen that double-skin façade systems require more cleaning than a single-skin glass façade, however the outer skin which is the only surface exposed to the elements, will only require six-monthly cleaning with minimal cleaning required on other surfaces. The cavity between the skins is less vulnerable to environmental grime, and the gantry set up will significantly improve the speed and safety of the cleaning task.
Overall, the key sustainability innovations which have been encompassed along with the double glass façade include, natural ventilation to the atrium, 40% recycled concrete, 90% recycled steel, FSC certified timber, recycled timber, solar cooling, tri-generation, black water treatment, rainwater harvesting, sewer mining.
94% of the demolished buildings’ materials were recycled including steel and concrete (Horiso). An advanced hybrid of VAV and chilled beam air conditioning systems are run off a series of curved solar thermal collectors. The tri-generation system uses gas and solar energy to generate cooling, heating and electricity. The black water recycling method, which is the first to be used in an office tower, reduces the overall water consumption throughout the building with some of the recycled water being used for irrigation. Recycled rain water is also used for irrigation.
The sustainability features of 1 Bligh Street result in the lowest operating costs of a premium grade building in Sydney, equating to estimated savings of approximately $2 million per annum (Horiso).
The inner skin was constructed of high-quality, double-glazed windows, while the outer skin was constructed of single-sheet laminated glass. A 600mm cavity between the two skins provides the required space to accommodate the automated venetian blind system, as well as walkway gantries at each level of the building for access by cleaners and maintenance personnel. 1780 blinds were used in total http://www.architectus.com.au/sites/default/files/05_0.jpg
The construction process took ten years to complete. Where normally one subcontractor works the building perimeter, Grocon had three to coordinate the façade contractor, the waterproofers and the blinds contractor.
Office buildings typically incorporate some form of tinted or reflective glazing in order to minimise the amount of direct sunlight and heat entering the building. The trade-off is a darkened or pearlescent finish that can visually isolate the occupants of the building from the natural environment and create unwanted reflectivity, particularly at night, when the inner glass can resemble a mirror.
The Bligh Street glass, supplied by G. James, has a 62% Visual Light Transmission (VLT), compared to normal office glazing specifications of approximately 25 – 40%. In other words, onlookers will be struck by the crystal clear views into the building; meantime, the occupants will experience ‘true-to-life’ panoramic views of the harbour and the city’s genuine colours. This is because the sun protection is very efficient, and therefore non-tinted glass could be used on the outer skin. This makes the building extremely transparent and offers the user a different experience.
In conclusion, it can be seen that building strategies such as the double façade system, can be adapted to suit a specific climate while maintaining sufficient sustainability and economic properties. Similarly, glass as a building material can be used in many applications not only for aesthetic purposes but also for a thermal and sustainable strategy. 1 Bligh Street may be the beginning of an effective double glass façade system which will be implemented on high-rise buildings throughout Australia.
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