Living roofs are topping the list of real green for buildings

Green roofs for Pasadena

Atop the Art Center College of Design's downtown campus, this roof is covered in 6 inches of soil bearing native grasses and shrubs. More than a garden, it is an ecologically designed green space that cools the building in summer by absorbing heat - much like an urban park does - and insulates it from cold in winter.

Living roofs have a long history. The Vikings grew sod on their homes for insulation. The hanging gardens of Babylon were planted rooftops. Europeans have cultivated green roofs for decades. After World War II, Germany made them mandatory in all major cities to prevent rainwater from washing into aging sewer systems.

Experts say such roofs retain storm water, decrease the cost of greenhouse gas reduction and lessen the need for interior building insulation. They also help to bring fauna back to inner city areas by attracting insects and birds, just as a backyard would.

In April, the city of Pasadena made green roofs mandatory on all new city buildings of 5,000 square feet or larger, on commercial buildings and residential tenant improvement construction of 25,000 square feet or more, and on all mixed-use or residential buildings of four stories or more.

Alice Sterling, Pasadena's green building coordinator, said there are 800,000 square feet of new building construction on the books in Pasadena that, if completed, will all have green roofs.

Green roofs start with a waterproof roof cover called a membrane. Then comes a root barrier, a drainage layer, and finally the growing medium and plants. Many plants native to California are drought-tolerant and need little maintenance

Depending on how the roof is designed, architects say the additional weight, which can equal that of a load of snow, is not unsafe even for older buildings. Greenery can be rooted on roofs that slope up to 60 degrees.

Nancy Goslee Powers, the Santa Monica landscaper who designed the roof at the Pasadena Art Center building, is working on similar projects in Beverly Hills and Century City, where a living roof is being installed on a public parking structure to keep it cool. It will be three-quarters the size of a football field.