Environmental Engineering Reference
In-Depth Information
biodiversity it is harder to establish on an extensive roof than on an intensive roof
(Brenneisen
2006
). A variety of substrate thicknesses leads to different microcli-
mates, and provides a wider potential for different species to establish. But in
general can be stated that creating a green roof to foster biodiversity is a difficult
task. Construction method, selection, and storage of local soil to create suitable
substrate is crucial (Brenneisen
2006
). Koster (
2013
) also emphasizes the
importance of the substrate layer for the establishment of bees and in particular
wild bees on green roofs. The composition of the substrate, the amount of nutrients
in the soils, and the humidity of the soil determine which plants can grow there.
For wild bees is the soil also directly important as nesting space, they especially
like to nest in sandy soils (Koster
2013
).
6.5.3 Greening of Outside Walls of Buildings
The same advantages of vegetation on roofs can be described for greening systems
on walls. In recent years, different systems (Fig.
6.1
) have been developed, like
greening direct on the wall, greening systems before the wall, and greening pos-
sibilities incorporated within the construction of the wall (Hendriks
2000
). Despite
the range of possibilities there is still great hesitation in the building sector (from
the originator, designer, architect, to the builder and the user) to increase the
amount of outdoor wall greening. Probably mainly due to the possible disadvan-
tages: the need for extra maintenance, falling of leaves, chance of damaging the
wall structure, increase of the amount of insect and spiders in the house, and the
expected extra costs involved.
By allowing and encouraging plants to grow on walls the natural environment is
being extended into urban areas; the natural habitats of cliff and rock slopes are
simulated by brick and concrete. There is a widespread belief that plants are
harmful to building structures, ripping out mortar and prising apart joints with their
roots (Johnston et al. 2004). The evidence suggests that these problems have been
greatly exaggerated, except where decay has already set in and plants can accel-
erate the process of deterioration by the growing process. Certainly, there is little
evidence that plants damage walls. In most cases the exact of opposite is true, with
plant cover protecting the wall from the elements. Ancient walls still stand, despite
centuries of plant growth (Johnston et al. 2004).
The leaves of climbing plants on walls provide a large surface area, which is
capable of filtering out a lot of dust particles (particulate matter PM
x
) and other
pollutants such as NO
x
and taking up CO
2
in daytime. Hard surfaces of concrete
and glass encourage runoff of rainwater into the sewage system. Many plants hold
water on their leaf surfaces longer than materials and processes of transpiration,
and evaporation can add more water into the air. The result of this is a more
pleasant climate in the urban area. Vegetation provides also nesting places for
birds such as, blackbirds, song thrushes, and house sparrows.
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