Sustainable exterior site design, or green exterior landscaping, adds to the holistic character of a landscape. The interaction of a site’s climate, resources, and attributes creates patterns and processes to which the building and its inhabitants are undeniably linked.
In an effort to define and achieve sustainability, the Washington, D.C.-based U.S. Green Building Council (USGBC) (www.usgbc.org) is pushing for a new generation of buildings that deliver efficiency inside and out through its Leadership in Energy and Environmental Design (LEED)™ rating system. This highly regarded rating system offers credit points for green considerations of a site’s exterior.
Building exteriors present abundant opportunities for utilizing primary renewable energy resources; producing food; and returning water, nutrients, and other materials to the natural environment. Sustainable exterior site designs use ecologically based strategies to create projects that work in harmony with nature while supporting the needs of the property, including the following fundamental principles:
Recognition of Context and Reduced Site Disturbance. The USGBC’s rating system offers credit points for site exteriors that make the least possible environmental impact while preserving ecological integrity, enhancing biodiversity, and protecting local wildlife. The USGBC suggests using exterior plants that serve as wildlife food; provide water sources for wildlife drinking/bathing; and require minimal chemicals, fertilizers, and pest management. Land usage and the connection of residual fragments of natural features should strengthen what remains after construction takes place. Promoting the idea that landscapes are interdependent and interconnected, the USGBC offers credit points if 50 percent or more of the site exterior’s open areas are vegetated (with native or adaptive vegetation), or if green space covers 25 percent of the horizontal roof of the building.
Reduction of Heat Islands. The USGBC offers credit points for exterior landscapes with a minimum of 30 percent of non-roof impervious surfaces that are shaded (high-albedo materials can be applied to non-roof impervious surfaces to accentuate the reflectance of installed materials).
Water-efficient Landscaping, Captured Rain Systems, and Recycled Site Water Systems. According to the USGBC, green exteriors should incorporate landscaping designs that dramatically limit or eliminate the use of potable water for landscape irrigation. The USGBC provides credit points for the use of high-efficiency irrigation equipment demonstrating that potable water consumption for irrigation/watering is reduced by 50 percent, compared to conventional technology. Capturing rainwater from the impervious areas of the building to recharge groundwater and limiting the disruption of natural water flows by minimizing rainwater run-off are two methods the USGBC suggests for reducing water consumption. In addition, LEED credit points are offered for landscape designs that do not require a permanent landscape irrigation system and can demonstrate that annual water usage does not exceed the baseline of 100-percent reduction.
Based on estimated values determined by the Conservation Design Forum Inc., Elmhurst, IL, sustainable and native landscape installation and maintenance is, over the long run, less expensive than the traditional idiom. The organization constructed a detailed comparison of costs for both the sustainable and traditional landscape features required for a 10-acre corporate landscape (www.cdfinc.com).
MJ Gilhooley (mj@plantsatwork.org) is director of media relations for Focal Point Communications, Los Angeles, and has shaped numerous green industry media campaigns, such as the Interior Plant Industry Initiative, Plants at Work.