Integrating stormwater performance and architectural design - Living Roofs in Integrated Urban Water Systems - page 129

the same visual quality. Frequent use can result in growing medium compaction,
which could impede permeability, which in turn might cause ponding on the
roof. This is both a structural safety and plant safety issue. To reduce potential
compaction requires appropriately strong aggregate in the growing media and
access to the roof might need “people-free periods” at regular intervals over the
year. This will help the growing medium to recover its structure and the plants to
regrow. In comparison, an inaccessible lat sedum roof on top of a one-storey
building will experience only minimal compaction by maintenance crews. See
Section 4.11 for further design solutions regarding publicly accessible living roofs.
In this case the planning team should decide to what extent the roof is acces-
sible. The planners should make a checklist. Will there be:
1 Frequent access by visitors?
2 Access only by maintenance crew?
3 A limited amount of visitors and a designated gathering space - for example,
a terrace or loating grate?
4 Protection of the vegetation from visitors - for example, a fence?
5 Life-safety equipment/design elements?
6 Comfortable and safe roof access?
4.9.2 Design for general maintenance access
Designing safe access for maintenance is the irst step in creating a feasible main-
tenance regime; understanding maintenance requirements promotes good
design, which prevents risk ( Figure 4.14 ). Research suggests that workers can be
tempted to accept high levels of risk in situations where maintenance access is
relatively infrequent (e.g., on a living roof compared to conventional roofs) and
the time required to complete tasks is relatively short (Behm 2012; Cameron et
al. 2007).
The primary risk to a person accessing a living roof is a fall from height. Elimi-
nation of fall hazards, prevention of falls, safety netting or administrative actions
(e.g., a second person watching over the activity) is suggested in order of prefer-
ence or design priority to promote safety (Ellis 2001). Passive systems are further
preferred over active systems, as the person does not have to consciously engage
in implementing the safety measure - i.e., they don't have to take the time to
clip into a harness and anchor (Health and Safety Executive 2008).
Key items on the design consultants' checklist for maintenance design should
include, but are not limited to, the following:
1 The physical access to the roof needs to be safe. Windows or doors accessible
by stairs, elevator or ladder are possible. Vertical ladders, especially through a
roof hatch or enclosed cages, should be avoided, as maintenance equipment
is dificult to be carried up/out.
2 The living roof needs to be designed so that the roof parapets are accessible
to building/façade maintenance crews, either via pathways or direct access to
the roof parapet.