A pioneering green developer in Philadelphia is pushing the envelope of sustainability with a mixed-use project called The Ridge on the banks of the Schuylkill River, which is expected to become the nation’s largest Passive House, a net-zero energy building. In doing so, design-build development firm Onion Flats aims to redefine mixed-use development by example. “Our work is pretty well known for its sustainability,” said Timothy McDonald, a principal at Onion Flats. “Now we’re taking it to the next level.” On December 5, Onion Flats was selected by the Philadelphia Redevelopment Authority (PRA) to redevelop a vacant site bound by Kelly Drive, Calumet Street, and Ridge Avenue at the terminus of the Fairmount Park jogging and biking trails, forming a gateway for the East Falls neighborhood.

Onion Flats plans a new five-story structure to include 8,700 square feet of retail on the ground floor that will anchor a plaza along the river, and 126 predominantly one- and two-bedroom units above. McDonald said The Ridge’s design is an interpretation of the classic Philly townhome and its sociable stoop. Residences are clustered around a second-floor garden serving as a communal gathering space, reinforced by an open interior circulation system of elevated platforms. Special attention was paid to creating a building that uses a minimum of resources, generating its own power from a 200-kilowatt solar array, and includes a completely permeable, green-roof covered site.

With such sustainable ambitions, Onion Flats hopes to raise the bar on development in Philadelphia. “We think this way because most developers won’t,” McDonald said. “For us, it’s really common sense stuff.” McDonald, who recently became a certified Passive House consultant, explained that, among other requirements, Passive House calls for a super-insulated exterior envelope, which Onion Flats hopes to show can be simplified in a mixed-use building. “What’s going to be important is to demonstrate that it’s easier to meet Passive House standards on large-scale buildings than small buildings,” McDonald said. “We want to show that it’s not only possible but also much easier to take on larger buildings without losing quality design.”

The project will be prefabricated in a facility just outside the city, offering substantial savings on construction time. “Modular construction cuts the building time in half,” McDonald said. “The building is being built while the foundation is being built.” Four years ago, Onion Flats formed a partnership with prefab manufacturer BLOX Sustainable Building Systems, but the recession has limited Onion Flats’ ability to implement their designs. The firm is preparing to break ground on two other smaller, prefab projects containing three and 27 units each that will serve as a testing ground for the Ridge.

Onion Flats will develop The Ridge’s design through 2012 and the project will begin construction in the first quarter of 2013 and be complete in the first quarter of 2014. Developers have until June to enter a full redevelopment agreement with PRA including sale of the site and final design and sustainability features.