Integrating stormwater performance and architectural design - Living Roofs in Integrated Urban Water Systems - page 132

4.11 DESIGN FOR SOCIAL FUNCTION WITHOUT COMPROMISING
STORMWATER CONTROL

Various design solutions for an extensive living roof can be created to achieve
public access without comprising stormwater control. The most important design
consideration to allow for public accessibility of an extensive living roof is the
additional loading. Any supplemental weight on the roof such as people (live
load) and pavers for a patio area (dead load), or raised above the living roof such
as a shade pergola, have to be calculated into the overall structural design of the
building. Structures or architectural elements (e.g., patio, cistern, and large struc-
ture footings, including those for beehives) should not impede free drainage from
the living roof, and drainage of any structure (e.g., a patio) itself must be
considered.

4.11.1 Patio with barrier
A paved patio with a barrier is advantageous in that the paved area clearly
deines the vegetation zone from publicly accessible space. The barrier prevents
damage to the vegetation from trampling and ensures the safety of the public.
Visitors are allowed to view the living roof from one or more sides, although
access for maintenance and monitoring may still need to be provided. The place-
ment of a guardrail or balustrade around a paved patio in the interior of the
living roof allows greater viewing possibilities from the ground because the roof
edge is not blocked (see Section 4.6.2 ).
Pavers should have wide gaps for surface drainage, or be made of pervious
materials themselves (e.g., permeable concrete or pervious/porous resin-bound
aggregates) ( Figure 4.15 ). Impermeable paving materials could discharge runoff
to the living roof. In this case, a short transitional zone of large diameter light-
weight aggregates or rocks may be needed to protect the surface of the living
roof from erosion in the vicinity where runoff lows onto the vegetation.

Figure 4.15
Patio paving

Perforated aluminium
angle with strutting

Permeable
pavers

Wide gap for drainage

Plants

Structurally strong,
lightweight material
to support pavers

Growing medium

Geotextile

Drainage layer

Waterproo ng
membrane integrated
root barrier

Insulation
Moisture barrier

Roof slab/deck