Agriculture Reference
In-Depth Information
2011; Stovin et al. 2012; Voyde et al. 2010). Modiications to the timing of
runoff compared to a conventional roof surface or direct rainfall is usually
observed (Carter and Rasmussen 2006; DeNardo et al. 2005; Getter et al. 2007;
Liu 2003; VanWoert et al. 2005).
Detailed consideration of performance reveals that the speciic magnitude of
effects varies amongst reports, and even from the same living roof subjected to
different characteristic storms. Comparing performance studies found in the liter-
ature is complicated by the observation that there is very little consistency in
living roof design (Theodosiou 2009). Nonetheless, the evidence overall shows
that living roofs' manipulation of rainfall is likely to reduce the burden on storm
or combined sewers that exceed capacity even in small events. Stormwater miti-
gation beneits increase with the proportion and location of roofs vegetated in a
catchment or sewershed. At a site, city or watershed scale, effective GI is predi-
cated on a system of distributed measures (see Chapter 2 ). Individual component
design, such as a living roof, is a fundamental contributor to the composite
results.
1.2.2 An environmental comfort control
A living roof can operate as a “green” and “living” open space, due to its inher-
ently organic, multi-layered composition. The living roof performs as a useful reg-
ulator of exterior and interior thermal environments (Koehler et al. 2002). Interior
temperature regulation is contributed by the number and insulative properties of
a living roof's layers (Koehler et al. 2002). The living roof can help cool a building
in warmer climates and decrease heat loss through the top of the building in
colder climates. The vegetation and growing medium of a living roof can signii-
cantly improve the microclimate in the immediate area of the living roof itself (up
to 1°C), during both day and night (Banting et al. 2005; Umweltbundesamt
2012), as solar energy absorption and water storage in the growing media
increases humidity and cooling through evapotranspiration (US EPA 2008).
In both cases, living roofs can help save energy that would otherwise be used
for thermo-regulating units to achieve desirable interior thermal conditions
(Berghage et al. 2010; Kumar and Kaushik 2004; Tanner and Scholz-Barth 2004).
If peak energy demands (from air-conditioning systems, for example) are reduced
in times of temperature extremes, power outages may be avoided. Prevention of
power outages can in turn reduce the occurrence of heat stroke-related mortali-
ties in over-heated buildings. This was a signiicant driver behind Chicago's living
roof policy.
Reducing the urban heat island effect through the use of living roofs has
strong health implications for city dwellers, especially in the prevention of unprec-
edented and recurring increases in elderly and adult mortalities that was seen in
Europe and the United States from high urban temperatures in the last few years
(Corburn 2009; Kovats and Kristie 2006; Than 2012). A study in New York City
found a reduction of the mid-day heat of about 0.4°C, if 75 percent of New
York's lat roofs were converted into living roofs (Rosenzweig et al. 2006). While
 
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