Green Roofs - Living Architecture Monitor - Summer 2011 - (Page 23)

fundamental precepts. Their goals are achieved through a holistic approach to development, utilizing all of the inherent efficiencies of a fully integrated design-build team. By focusing their detailing around energyefficient building envelopes and simplifying rather than intensifying the buildings’ system technology, Onion Flats’ buildings use significantly less energy and provide decidedly healthier indoor environments than what is required by the international building codes. One of Onion Flats’ recent Northern Liberties’ projects, “Thin Flats,” is a nine-unit condominium made up of four duplexes and one singlefamily residence. The project became the first duplex development in the country to achieve LEED Platinum certification under the LEED for Homes program. Thin Flats has also won numerous awards. Most notably, a 2009 AIA Philadelphia “Honor Award”, a 2010 “Global Awards of Excellence” from the Urban Land Institute, bestowed to only five projects in the world, and more recently a 2011 Green GOOD DESIGN™ Award from the European Centre for Architecture Art Design and Urban Studies and The Chicago Athenaeum Museum of Architecture and Design: all recognize the project for its architectural innovation and as a shining example of highly sustainable building practices. Within its practice, Onion Flats appreciates the tremendous value of green roofs, particularly in urban environments where outdoor green space is at a premium and stormwater management has reached a critical tipping point. From a city planning perspective, older cities as Philadelphia grapple with the challenges of old infrastructure, particularly in the area of combination sewer and stormwater systems. Approximately 40 to 60 percent of Philadelphia’s 130-square-miles are managed by these combined sewers. As new development occurs, dramatic increases in impervious surfaces are created from both rooftops and the surrounding pavement. This in turn generates significantly more stormwater runoff that has traditionally been directed into these antiquated and undersized pipes, forcing them to back up and send sewage into the rivers and streams. In Philadelphia, the combined sewer overflow (CSO) discharges approximately 1.7 billion gallons annually. Additionally, sending fresh rainwater into the combined sewers rather than having it recharge into the ground naturally, necessitates significantly greater water treatment which is costly, wasteful and unnecessary. Given the enormity of the stormwater challenge, the green roof on Thin Flats is an integral part of the architecture and sustainable design of the project. It serves as an integral component of the building’s energy envelope by providing a buffering mass on the rooftop which deflects solar heat gain in the summer months and helps diminish rooftop freezing temperatures during the winter months, effectively reducing the energy needed to heat and cool the homes. The green roofs provide outdoor “living rooms” for the upper condominiums while rear yards serve the lower units. These “rooms” offer tremendous views of the Philadelphia skyline and provide a green oasis for the residents. The buildings’ parapet walls are capped with planter extensions, planted with ornamental grasses, and provide privacy screens from the neighboring spaces. Thin Flats incorporated an intensive Savannah® Roofmeadow® green roof system over a two-ply modified bitumen waterproofing and a loose laid EPDM root barrier. The roof utilizes a dual media system made up of two inches of drainage media at its base and 6”-12” of growing media above, and is planted with Sedum, perennials and ornamental grasses. Because green roofs virtually eliminate the freeze-thaw cycles of the roof membrane, protecting it from surface abrasion and ultraviolet degradation, waterproof membranes are expected to last two- to three-times as long as those exposed to the physical elements. THIN FLATS’ CLOSED LOOP WATER SYSTEM CAPTURES RAINWATER TO HELP EASE PHILLY'S STORMWATER CHALLENGES. NATURAL IRRIGATION As with all green roofs, the intention is to capture and mitigate as much rainfall as possible through media absorption, plant watering and evapotranspiration. Once a green roof system is fully saturated, however, the overflow water bypasses the roof, and in the case of Thin Flats, is captured downstream in a sub-grade rainwater harvesting tank. This water provides a source of irrigation for the development’s vegetation. In systems which do not use rainwater capture, the green roof slows the peak attenuation of the stormwater surge on the sewer system, giving it a chance to dissipate before this additional volume enters the public system, reducing the LIVING ARCHITECTURE MONITOR SUMMER 2011 23

Table of Contents for the Digital Edition of Green Roofs - Living Architecture Monitor - Summer 2011

Green Roofs - Living Architecture Monitor - Summer 2011
Contents
Water Worries
Cities Re-Imagined
Design Strategies for Wild Bees
Special Section: Cities Alive 2011 Conference Guide
Thin Flats
Sky Island at the Visionaire
Welcome New Members
New Corporate Members
Professional Calendar
Seven-Year Pitch

Green Roofs - Living Architecture Monitor - Summer 2011