Agriculture Reference
In-Depth Information
recommend careful use of desert annuals on living roofs, primarily to populate
the roof with some vegetation cover (more for the public's than for the roof's
sake) in the irst year while perennials are establishing. Annuals, like geophyte
bulbs, avoid drought through dormancy, and provide intense bursts of spring and
early-summer color.
EROSION CONTROL THROuGH PLANTS AND FABRICATED MATERIALS
Wind and surface water lowing across a living roof can cause erosion that
suppresses plant growth, decreases moisture storage, exposes irrigation pipes,
and provides sites for weed invasion. Plants that bind to the living roof surface by
rooting from nodes or rhizomes help prevent erosion. An expansive horizontal
root system also stabilizes the growing medium against surface stormwater low
(Dunnett and Kingsbury 2008).
Areas susceptible to erosion should be mapped by the structural and
stormwater engineer in the planning phase. Wind turbulence and concentration
can be reduced by many design solutions, including edge orientations, parapet
designs and other strategies. A properly designed growing medium should
entirely prevent surface low, with the exception of steep roofs. Drainage of large
roofs and areas with complex slopes usually include surface drains within the
roof, such as on the Vancouver Convention Centre (British Columbia, Canada) or
the California Academy of Sciences (San Francisco, California) living roofs. Steeply
sloping roofs usually use additional anchoring of the growing medium, either
Erosion control mats (often coir, but can be made from permanent materials)
can increase the resistance of surfaces to erosion. This has the beneit of main-
taining undisrupted stormwater low and also prevents birds from pulling out
plugs. Permanent materials such as stone mulches can also be used, and in areas
of greatest concern (at corners, for example), pavers may be used. However,
where used extensively, stone mulches and pavers may compromise overall
stormwater runoff retention. As an alternative to conventional pavers,
interlocking punctuated concrete pavers can be illed with substrate and planted
with cuttings or plugs. Of course, the loads generated by these areas have to be
integrated into the structural calculations of the roof.
3.4.2.3 Aesthetic appearance throughout the seasons
The year-round appearance of vegetation needs to be considered for viewed
areas of living roofs, as plants have a continuously changing lifecycle. The
different states of “aesthetic” appearance (i.e., color of lowers, fruits, leaves and
stems, plant growth), over the course of the changing seasons and years have to
be considered by the landscape architect and/or horticulturalist when selecting
plants. Even a healthy roof may appear brown and “dead” from a distance if the
overall foliage colors are browns, reds and yellow. This effect can be exacerbated
by the color of any mulch used, particularly during plant establishment. Sedum
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