Designing with Green Roofs: Maximizing Sustainability and Stormwater Management

New urban roof top gardens lower energy costs and increase environmental benefits
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Celeste Allen Novak, AIA, LEED AP

Standards For Green Roofs

New codes are being developed for green roofs and testing standards by the ASTM International Green Roof Task Group. These standards include standard guides for selecting plants, determining dead loads and live loads, tests for water retention, wind loading, and definitions of components.

Manufacturers typically provide warranties for green roofs, and guarantee that their products will last with proper installation. Green roof suppliers should provide green roofs with the following:

  • All of the components of the entire system, from waterproofing membrane to the growing medium.
  • Proper considerations for wind loading and fire safety
  • Material data proving that the system conforms to FLL and ASTM standards
  • The total weight of the system
  • Stormwater calculations for the site location
  • Plant recommendations, especially for extensive roofs
  • Specifications for all products
  • A single source warranty for all components from the deck up
  • Authorized trained installars ensure good workmanship
  • A portfolio of successful projects

An Environmental Tool

Architects, owners, and contractors who care about the environment, love green roofs. They help the environment by mimicking the natural cycle of rainfall on the earth, while adding new outdoor spaces in dense urban environments. Green roofs lower heating bills by adding insulation, and extend the life of the roof by protecting it from ultraviolet rays. They create visual excitement and new uses for leftover building areas. Green roofs provide many environmental benefits to building owners and communities. Tenants living in mixed-use projects with green roofs have the advantage of a place to get some fresh air and quiet respite in urban environments.

The U.S. Green Building Council's rating system, LEED, grants points that certify a building as green. Green roofs will allow points based on the LEED 2.1 rating system. Points can be given for numerous benefits including stormwater management, since the effect of a green roof is that it decreases the impervious surface of a site. A specific credit addressing reduction of heat islands is available and green roofs qualify as long as they cover at least 50 percent of the roof surface.

In addition, some green roof manufacturers use recycled content in the waterproofing membrane, granting additional points towards certification. Green roofs can provide credits for supplying materials within a 500-mile radius of the site, and also count for the reduction of site disturbance. Innovation credits are often given to projects that incorporate green roofs. Leaders in the environmental movement know that adding a green roof contributes to the environmental qualities of a project.

'To create a garden is to search for a better world."1

Visions of Paradise: Themes and Variations on the Garden. Photographs: Maria Schinz, text: Susan Littlefield. New York: Stewart, Tabori & Chang, 1985

Roof gardens change the nature of the built environment. They also add to biodiversity. Reid R. Coffman, University of Oklahoma assistant professor of landscape architecture who researches green roof fauna and habitats says, "Longstanding living examples in Switzerland have shown green roofs can be viable habitats for threatened and endangered species. The wonderful part about biodiversity is the challenge designers will face with regards to context. This demand for contextualism will perpetuate a flurry of wonderful, innovative projects. These attempts, trying to connect the extremes of rooftops and viable habitats, will subsequently uncover essential knowledge in the mission of ecological design."

By providing sustainable, aesthetic and functional outdoor spaces, design professionals can plan projects with exciting new elements, added value, and significant, tangible benefits, thereby enhancing the built environment, and creating new landscapes for the 21st century.

Celeste Allen Novak, AIA, LEED AP, is an architect, environmentalist and writer in Ann Arbor, Michigan.


  1. Visions of Paradise: Themes and Variations on the Garden.
    Photographs: Maria Schinz, text: Susan Littlefield. New York: Stewart, Tabori & Chang, 1985


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Originally published in Architectural Record.