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| Perspectives A Quarterly Information Source from Benchmark, Inc. Volume 32 May 1998 |
Client Profile: The Gap's Green Roofby: Michael Newland The Gap, located in San Bruno, California, was looking for a suitable roof for its new corporate office. After an extensive study performed by Hargreaves and Associates, Ove Arup & Partners, Saranfil Roofing, and William McDonough & Partners, it was determined a Green Roof was a viable and cost-effective roof system. A Green Roof's system components consist of (from bottom to top):
Constructed in 1995, the inclusion of a Green Roof in the design of The Gap's buildings in San Bruno creates a visual extension of the surrounding hills. By imitating the appearance and ecology of the native vegetation, the Green Roof construction will allow the architecture of The Gap campus to integrate with the landscape. The grassland plants chosen for this roof prefer gently sloping, well-drained soils and this aerial prairie should provide a long-term, low input landscape. Increased thermal insulation from the Green Roof will save on heating and cooling costs. Through these energy savings the roof is estimated to pay for itself in 11 years. In addition to the aesthetic and thermal benefits, the Green Roof offers other advantages to the conventional roof, which are explored through the following data compiled by the companies mentioned above. These benefits derived from their research, and do not necessarily reflect the opinions of Benchmark, Inc. Benefits of the Green Roof over Conventional Roof Aesthetic - A Green Roof provides engaging surroundings and visual environments for employees. The selection of native grasses and plants further reflects the natural environment in color, texture and structure, and the blooms of prairie grassland flowers will attract birds and butterflies. This combination of building and landscape will be pleasing when viewed from the surrounding freeways and buildings. Improved Acoustic Insulation - Buildings with Green Roofs are quieter. Due to their mass, Green Roofs can attenuate sound transmission by 50 decibels. Thermal Insulation - A building becomes less susceptible to exterior temperatures when it is covered by a Green Roof. The insulating value of soils lowers the cost of heating and cooling a building. The thermal mass of the 69,000 square foot Green Roof modifies the rate of change of temperature and results in an energy savings three times greater than that of a conventional roof membrane. Extended Durability of Membrane - The insulating membrane will be protected from ultraviolet degradation, mechanical puncture, and temperature extremes because it is completely covered by the Green Roof. The life expectancy of this membrane is well beyond that of a conventional roof. Environmental Impact - Green Roofs modify the local microclimate, affecting temperature, humidity and rainfall runoff. The plant materials of the Green Roof will provide increased oxygen to the air and counteract some of the carbon dioxide produced by the building. Water Retention - The average annual rainfall in San Bruno is approximately 30 inches, which equals 520,550 gallons of water on the69,000 square foot area of the Green Roof. This average rainfall would normally be absorbed by the Green Roof, creating little if any run-off. The run-off that does occur will be recycled onto the roof for irrigation purposes. Potential Disadvantages of the Green Roof Annual Maintenance - Annual maintenance is required in the forms of periodic irrigation and seeding. Though rainwater from the roof will be collected and used, an additional irrigation system is required for the roof. To date, no major problems have been experienced by The Gap with the Green Roof. While this roof system is not appropriate for all roofing situations, it does have viable uses in the correct situations. As of yet, we at Benchmark have not specified a Green Roof. We are looking forward to the opportunity, so if any of our readers have an interest, please contact us. We will be happy to explore the possibilities. |