Environmental Engineering Reference
In-Depth Information
Table 2 Maintenance activities and costs associated with cisterns
Months
between
events
Cost per
event
Total cost
per year
Routine maintenance activities
Inspection, reporting and information management
6 $130 $260
Roof washing, cleaning in
ow
filters
6 $240 $480
Corrective and infrequent maintenance activities
(
unplanned and/or
>
3 years between events
)
Intermittent
system maintenance (system
ush,
3
$390
$130
debris/sediment removal from tank)
Pump replacement
5
$989
$198
Source WERF (
2009
)
distribution requirements, storage is usually the most expensive element. A cistern
can cost around $1.50
$3.00 per gallon of storage. The more complex the system,
the higher the capital cost. Filtering, pumping, distribution and treatment systems,
plumbing and drainage connections, excavations, installations and other elements
can have an additional cost of around $2
-
-
$5 per gallon (Table
2
).
5 Green Roofs and Green Walls
5.1 What Are Green Roofs?
A green roof, also known as eco-roof, living or vegetated roof, is a roof of a
building that is entirely or to an extent covered with vegetation planted over a
waterproo
ng membrane. Green roofs can be categorised, depending on the depth
of planting medium and level of maintenance they need, as extensive, semi-
intensive and intensive (Fig.
3
).
A typical green roof is a complex system of several layers of materials to attain
waterproo
ng and to remove water from the roof deck (Tolderlund
2010
; Fig.
4
).
5.2 What Are the Risks and Costs Associated with Green
Roofs?
In case of bad construction or inef
cient maintenance, a green roof may face the
risk of leakage and damage or even collapse, or may fail to deliver the desired
energy ef
ciency levels. The main factors affecting the cost of green roofs include
the type of structure (extensive or intensive), types of vegetation, irrigation systems,
accessibility, retro
t or new development. Generally, an intensive green roof has a
higher capital and maintenance cost
than an extensive green roof, as well as
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