Project DescriptionOne of Sydney’s business ambitions is to attract the best talent and enterprises in the world. Starting with the Sydney Opera House, completed in 1973, locals recognized that world-class architecture could make the city a destination. Today, its planning authority, the Central Sydney Planning Committee (CSCP) requires that developers hold competitions for major buildings, and encourages local architects to partner with the stars. An independent design panel makes a nonbinding recommendation for the best solution for each contest, but the CSPC makes the final decision on approval.
It seems to be working. Sydney’s newest tower, 1 Bligh Street, is the result of a 2006 competition won by the team of Ingenhoven Architects from Düsseldorf, Germany, and local firm Architectus. Within a couple of blocks are buildings by Foster + Partners, Rogers Stirk Harbour + Partners, and Kohn Pederson Fox Associates. These join a few of the best ’60s and ’70s Modernist office towers built anywhere, designed by the late Sydneysider, architect Harry Seidler.
Australia’s Dexus Property Group put on the contest for 1 Bligh Street. “Our competition brief was very prescriptive,” says head of development Tony Gulliver. “Among other things, we spelled out it would be a highly sustainable building, with a high-quality indoor environment, minimum distances to daylight, and very large floor plates.” There were also city requirements for a podium, a conservative floor-to-area ratio, and for preventing the new building from casting a shadow over a nearby square.
“We had a lot of restrictions and we did not stick to any of them,” says Martin Reuter, project architect for Ingenhoven. “Well, we did respect the building setback lines, but otherwise we decided to give something better to the city than a podium and a tower. And then we would explain to the planning board what we did.” Luckily, the planning board agreed with their proposal, and the podium requirement was waived.
The sloping rectangle-shaped site is located on the corner of an awkward three-block parcel, which is cocked at a 45-degree angle from the rest of the downtown’s street grid; a remnant of a failed Colonial-era attempt at city planning. One advantage of the site is its commanding view of the Sydney Bridge and harbor to the north. After considering a number of schemes, the architects adopted an elliptical plan, with its long side facing toward the harbor. The ellipse gives each office space floor-to-ceiling panoramic views. The building’s post-tensioned-concrete structure is composed of beams that cantilever out from the columns on every floor, minimizing the interior structure; for much of the floor plate, the view is interrupted only by narrow curtainwall mullions.
“The problem,” says Ray Brown, a principal at Architectus, “is that in this part of the world the heat load comes from the north. The challenge is preserving the view without resorting to black glass. That meant coming up with a high-performance façade.” Arup’s Sydney office designed a practically clear, double-walled façade with automated blinds that has a net shading coefficient of 0.15.
The architects chose to limit the enclosed area at the ground floor to about 40 percent of the tower’s footprint, with the upper floors cantilevering out to form a protective overhang. This yields covered space for an outdoor café, an outdoor play area for the building’s childcare center, and curving stairs that cascade down to the street. On warm days the steps have become public space, a haven for brown baggers.
Inside, a skylit atrium, trimmed in glass and aluminum, rises the full height of the building. Air flows through the lobby’s entry doors and through open glass louvers in the exterior walls, so that balcony corridors on each floor can be naturally ventilated. The building is equipped with a trigeneration plant that provides heating, cooling, and power. A blackwater harvesting system processes over 20,000 gallons of water daily, sourced from Sydney’s sewer systems for use in flushing the building’s toilets and in the building’s cooling tower.
The building is packed with costly finishes and many sustainable features, but Gulliver explained that law and boutique finance firms are willing to pay for them: The building officially opened in late August and only has nine floors (out of 28) left for leasing. And in contrast to American developers who build and flip, he says, “It’s a different ownership profile … [in Australia]. Dexus will have this building in our portfolio for decades.”
The CSCP was happy too. It decided that the project’s design excellence merited a 10 percent floor-to-area ratio bonus.
As sustainable features go, double-walled façades are frequently discussed, but not always well understood. Kerryn Coker, the façade engineer in charge of the 1 Bligh Street façade for Arup says, “The interior wall of the façade is a double-glazed insulating [glass] unit with a very high-performance low-E coating. It has a visible light transmittance (VLT) of about 60 percent. Most commercial office buildings in Sydney have a VLT of about 35 to 40 percent.”
The outer wall of the façade is composed of a single layer of uncoated, but laminated, low-iron glass. Though double-walled façades in cold climates often have operable louvers that can be closed during the winter months, the skin at 1 Bligh was engineered to allow the louvers to stay open all year long. The double-skin assembly protects the computer-controlled venetian blinds which, despite the elliptical form of the building, are actually standard flat assemblies. The curve of the building is so slight that the blinds do not need to have a radius designed into the individual units.
These blinds can be activated either by the building-management system or by photosensors. “If the building had flat walls,” Coker says, “the blinds would be down all day. But, because it is hemispherical the shades come up on the east side as the sun moves toward the west.”
The curved wall is always ventilated, however, by louvers at the edge of each floor slab. “These openings are important so heat does not build up in the cavity,” Coker continues, and thus into the building itself. Using computational fluid dynamic modeling, the shape of each of the louver’s fins was designed to function as an airfoil. This is so that hot air exiting the top of one cavity is not drawn into the cavity above it, and so that passing breezes cannot easily enter the cavity and disturb the venetian blinds during the course of the day.