Green Roofs and the Rainwater Crisis

Sourced from Building Enclosure

From Chicago City Hall to Tokyo’s Imperial Hotel, green roofs are growing fast. They’ve been well established in Europe for years, and now have taken hold in the United States, with millions of square-feet of green roofs installed or in process since the early 2000s.

At the same time, growing development in U.S. cities is leading to increased levels of pollution. A main area of concern is the polluting of one of our most valuable resources: water.

Rapid Urbanization and Rainwater Management

In urban areas, there is a considerable amount of hardscape and not much ground to absorb rainwater. Urban rainwater runoff results from rain, snow and sleet that lands on rooftops, parking lots, streets, sidewalks and other surfaces. These impermeable surfaces do not allow water to infiltrate into the ground or be utilized by plants, both of which are key elements of the natural water cycle. Instead, they shed water, which then becomes runoff that eventually enters the city sewer system or is discharged directly to adjacent water bodies.

Most rainwater infrastructure in the U.S. was built 50-75 years ago and is not big enough to handle the amount of water now entering the systems. In response, cities across the U.S. have implemented new water management regulations.

In 2012, New York City’s Department of Environmental Protection (DEP) released a new storm water performance standard. The DEP published guidelines for design and construction experts to assist licensed professionals in the selection, planning, design and construction of onsite source controls that comply with the new rule. The guidelines were developed in consultation with the Department of Buildings, and feature guidance on siting, design and construction considerations for various rainwater control systems, as well as operation and maintenance recommendations. In our nation’s capital, the Department of Energy & Environment (DOEE) released a new guidebook on rainwater management in 2013 to control, prevent and provide remediation for sources of water pollution to District of Columbia waters and the Chesapeake Bay.

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