The Northern Virginia Regional Commission has launched a web app that depicts the green roof potential for buildings within the region’s urban core (Arlington County, Fairfax County, Cities of Alexandria, Fairfax and Falls Church).
The map shows the following elements of a green roof:
- Event volume capture capacity
- Annual volume capture capacity
- Annual stormwater interception value
- Annual energy savings
- Annual CO2 offset
- Annual Air Pollutants Removed
In the five jurisdictions there are 541,248,585 square feet of potential usable green roof. That square footage of green roof has the potential on an annual basis to capture 8.7 billion gallons of rainwater, offset 119,345 tons of CO2 and provide energy savings of $146.1 million dollars.
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Jurisdiction | Select Usable Green Roof (ft2) | Annual Volume Capture Capacity (MG) | Annual CO2 Offset (t) | Annual Energy Savings |
Alexandria | 56,751,017 | 921 | 12,514 | $15,322,856 |
Arlington | 58,899,246 | 956 | 12,987 | $15,902,833 |
Fairfax City | 15,455,102 | 251 | 3,408 | $4,172,887 |
Fairfax County | 404,116,592 | 6,559 | 89,108 | $109,111,751 |
Falls Church | 6,026,627 | 98 | 1,329 | $1,627,200 |
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Total | 541,248,585 | 8,784 | 119,345 | $146,137,527 |
Potential green roof area was determined using the degree of building roof slope which was calculated from a digital surface model (DSM) and building footprint data. The Center for Neighborhood Technology Green Values Calculator was utilized to determine the green roof effect on stormwater runoff. Pollution reduction values were calculated based on findings from green roof reports from the Center for Neighborhood Technology and U.S. General Services Administration.
Stormwater is a major source of pollution in local streams, rivers, and the Chesapeake Bay. Green roofs are just one element that can help reduce stormwater runoff in communities. Efforts to reduce stormwater runoff are critical to the region achieving its required pollution reduction to the Chesapeake Bay.
What is a Green Roof?
Green roofs are partially or completely covered with a growing medium and vegetation planted over a waterproofing membrane. They may include additional layers, such as a root barrier, and drainage and irrigation systems. Extensive green roofs typically have a depth that ranges between 4-6 inches. In addition to providing onsite stormwater management, green roofs mitigate urban heat island impacts, reduce building energy costs, decrease noise pollution, and improve air quality and mental wellbeing.
Buildings with roof slopes between 0-9 degrees are ideal for green roofs and the least expensive roof to construct and maintain. Roof slopes 9-30 degrees are suitable for green roofs. They may require additional erosion control which can increase construction costs. Roofs with slopes greater than 30 degrees are not considered suitable for green roofs.
Additional information regarding green roofs can be found on the Commission's website: https://www.novaregion.org/1548/Green-Roofs