Green Roofs - Living Architecture Monitor - Spring 2020 - 22

POLICY

DRIVING GREEN ROOF STORMWATER
MANAGEMENT THROUGH
PERFORMANCE-BASED POLICIES
BY DR. CLAYTON RUGH

Government green roof policies and incentive programs have been an
effective stimulus for community awareness and project development
throughout the United States and Canada over the past decade.

V

ery few North American green roofs were built before 2000,
though several notable flagship projects in the late 1990's and
early 2000's - such as the Chicago and Toronto City Hall
buildings, the MEC buidling and the Ford Motor Company
Dearborn Rouge Plant - helped raise awareness and spur steady
growth over the subsequent two decades. Since these early high visibility installations, more than thirty municipal governments have
offered financial incentives and legislative mandates to encourage
and require green roofs on buildings. Although green roofs provide
many benefits, these policies and incentives have been adopted
primarily to help address flooding and water quality impacts related
to urban stormwater runoff.
Green roofs are a recognized US EPA Agency Best Management Practice (BMP) for management of urban stormwater by
reducing runoff volume, peak flow, and dissolved or particulate
pollutants (https://www.epa.gov/soakuptherain/soak-rain-greenroofs). In highly urbanized areas, stormwater surface runoff from
impermeable surfaces - such as roofs, roadways, parking areas, and
sidewalks - can overwhelm conventional stormwater systems to
cause local flooding and combined sewer overflows (CSOs) from
treatment facilities (in communities without separated storm and
wastewater systems).
Conventional "gray" stormwater infrastructure conveys stormwater through gutters and enclosed pipes of limited capacity to
temporary storage basins of various configurations before being
released through some sort of control structure at a measured rate

LIVING ARCHITECTURE MONITOR / SPRING 2020 / 22

downstream, eventually daylighting to the lowest point in the system, usually a river, lake, ocean or stream. All municipal stormwater
infrastructure and sewerage management systems deploy two basic
strategies to store/manage stormwater runoff:
RETENTION - This generally refers to "retaining" water long-term,
typically in permanent ponds, pools and other natural or constructed areas that have capacity to receive runoff and allow surplus
water to evaporate , transpire and/or infiltrate into the ground over
a longer period of time. At the ground level, retention storage in
ponds and pools can an effective, conventional infrastructural strategy to help manage stormwater and direct overflow to recipient
bodies of water as part of the system.
DETENTION - This often means "detaining" water in areas that
hold runoff temporarily and are otherwise dry, single-use basins
designed for this purpose. These basins can provide a finite amount
of temporary flood storage but tend to be difficult to maintain and
use for other purposes and often become weedy, sediment-laden,
and unattractive elements in the landscape.
Green infrastructure elements, such as public parks, permeable
pavement, bioswales/rain gardens and green roofs, serve as "source
control" and provide elements of both detention and retention
storage while optimizing the use and beauty of these facilities. In
a rain garden, for example, some water (smaller rainfall events) is
evaporated and transpired through the vegetation, never running off
LIVINGARCHITECTUREMONITOR.COM
https://www.epa.gov/soakuptherain/soak-rain-green-roofs http://www.LIVINGARCHITECTUREMONITOR.COM
Green Roofs - Living Architecture Monitor - Spring 2020

Table of Contents for the Digital Edition of Green Roofs - Living Architecture Monitor - Spring 2020
