Developers Sand Hill Property Company recently acquired an enviable chunk of Silicon Valley real estate in the form of Cupertino's Vallco Shopping Mall. The firm has big plans for the 50 acre (20 hectare) site, and in a US$3 billion development project, aims to turn it into a sustainable mixed-use town center that boasts the world's largest green roof.

Still in the planning stage and thus subject to change, the Hills at Vallco project involves Rafael Viñoly Architects (of the much-maligned Walkie-Talkie) and OLIN Landscape Architects. Located near the new Apple Campus, the existing mall would be radically overhauled to include retail spaces, some 2 million sq ft (185,806 sq m) of office space, and 800 apartments. The real headline-grabber, however, is undoubtedly its green roof.

The green roof is being promoted by those involved as the world's largest, a claim we think likely given its size, and is expected to cost $300 million. Measuring 30 acres (12.1 hectares), it would cover both large swathes of street level and the rooftops of the new buildings.

The expansive green space would be open to the public and include vineyards, orchards, gardens, an amphitheater, and children's play areas. It would also boast a 3.8 mile (6.1 km) jogging and walking trail. The current proposal calls for existing entertainment facilities including AMC Theaters, bowling, and ice skating to be retained.

Sand Hill Property is aiming for LEED Platinum (a top green building certification) approval for the project. Sustainable features include the use of recycled water for irrigation, heating, and cooling, and rainwater collection to further reduce water consumption. The park would be populated with native, drought-tolerant greenery that requires very little water.

To further sweeten the deal for locals, the developers promise to contribute $40 million toward two local school districts. Sand Hill Property will submit preliminary plans to Cupertino officials in a few weeks.

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