Integrating stormwater performance and architectural design - Living Roofs in Integrated Urban Water Systems - page 128

or ladder; through a door or window; and in the form of visual access through a
window or façade opening ( Figure 4.13 ). The accessibility will dictate the use of the
roof by the general public and/or building occupants. Currently, many extensive
living roofs are constructed on top of lat roofs, at least one storey above ground
level, and are inaccessible to the public. Recently, architectural trends like the sloped
roof at Hypar Pavilion Lincoln Centre, New York, have endorsed the design of exten-
sive living roofs that are accessible from public spaces. One of the irst examples
built was the university library in Delft, the Netherlands (International Ecological
Engineering Society 2007). This roof is used as a sloped lawn for outdoor reading.
In most cases, access to extensive living roofs determines their usage possibilities
and inluences other functions. In addition to determining program and potential
social functions, planning for a publicly accessible extensive living roof requires a
balance of the following considerations: the type of plants used (e.g., “lawn”, dec-
orative plants for visual interest), hardscape for social gatherings, and potentially a
steeper slope, which facilitates visibility from the street but also accelerates drain-
age through the substrate. If accessible to the public, frequent foot trafic might
cause damage to the plants, as the thinness of the growing medium provides little
loading buffer and the roots and plants are more likely to get crushed.
For sloped grass “carpet”-like designs, groundcovers (i.e., wear-and-tear
resistant vegetation) should be used, as they are hardier than grasses and have

Figure 4.13
Ideal roof

Pervious edge

Extensive
living roof

Maintenance
access

Maintenance
path with pervious
edging (e.g., gravel)

Patio

Protrusions with
pervious edge
(e.g., air conditioner)

Roof parapet

Railing

Extensive
green roof Pervious

edge

Perforations with
pervious edge
(e.g., drainage
point)