Green Roofs in Washington, DC are Expanding

The District of Columbia (District) is a national leader in the use of green roofs, with over 2 million square feet installed on more than 200 buildings. The exciting growth in the use of green roof technology has been led by the District Department of the Environment (DDOE), private companies, and several non-profits over the past 10 years. Many of these roofs can be seen by browsing the Washington, DC Green Roofs collection in GBIG.

Green roofs are being installed in the District for a variety of reasons – one of the primary reasons is that they are excellent at managing stormwater. With an average of 42 inches of rainfall every year, property owners in the District use green roofs to manage approximately 12,826,247 gallons of stormwater every year. As a whole, these property owners are expected to save $127,388; 1,194,370 kWh; and 10,000 Therms of natural gas every year.¹ The District benefits from cooler temperatures in warm months, reduced heat island effect, additional habitat, increased property value, and cleaner air.

For those interested in LEED, green roofs can contribute to 11 credits for both new construction and renovations, including:

SS CREDIT: SITE DEVELOPMENT – PROTECT OR RESTORE HABITAT
SS CREDIT: OPEN SPACE
SS CREDIT: RAINWATER MANAGEMENT
SS CREDIT: HEAT ISLAND REDUCTION
SS CREDIT: PLACES OF RESPITE
EA CREDIT: RENEWABLE ENERGY PRODUCTION
MR CREDIT: BUILDING PRODUCT DISCLOSURE AND OPTIMIZATION – ENVIRONMENTAL PRODUCT DECLARATIONS
MR CREDIT: BUILDING PRODUCT DISCLOSURE AND OPTIMIZATION – SOURCING OF RAW MATERIALS
MR CREDIT: BUILDING PRODUCT DISCLOSURE AND OPTIMIZATION – MATERIAL INGREDIENTS
MR CREDIT: CONSTRUCTION AND DEMOLITION WASTE MANAGEMENT
IEQ CREDIT: LOW-EMITTING MATERIALS

DDOE is using several strategies to encourage the installation of new green roofs in the District. New development projects and additions over 5,000 square feet are required to manage the first 1.2 inches of rainfall so many green roofs are used to meet this requirement. DDOE also provides a reduced stormwater fee for green roofs and other stormwater management systems that meet basic criteria through their RiverSmart Rewards Program. There is also a green roof rebate program administered by the Anacostia Watershed Society that provides $7-15 for any property owner that voluntarily installs a new green roof. Last, but not least, DDOE has launched a Stormwater Retention Credit trading system where property owners can have their stormwater management facilities certified by DDOE to buy and sell credits. More information about all of these programs can be found at: green.dc.gov.

The RiverSmart Rooftops – Green Roof Rebate Program is designed to help businesses and residents plan and finance green roofs of any size in the District. The amount of green roofs funded through this rebate program for the two most recently completed grant periods are shown below:

More information about the District’s Green Roof Rebate Program and case studies on the most recent projects can be found here.

Cost and energy savings from Green Roofs for Healthy Cities Calculator using the following assumptions: green roof has 4 inches of growing media, covers 100% of the roof, has a leaf index value of 2 and is not irrigated.

Note: this article was co-authored by Stephen Reiling, Environmental Protection Specialist, DDOE.