Integrating stormwater performance and architectural design - Living Roofs in Integrated Urban Water Systems - page 126

plants that require minimal supplemental water inputs, they may still need irri-
gation to ensure survival in long hot, dry periods without precipitation
common to continental climate zones - e.g., Southeastern USA summers.
Here the primary concern is maintaining healthy-looking plant cover for visible
roof areas, and/or preventing wide-scale plant death that may invite adventive
(weedy) species' invasion and establishment. A long-term irrigation system
should be installed below the growing medium (but above the geotextile sep-
aration layer) and aided by a basal moisture-wicking or capillary mat, which
enhances moisture availability directly to plant roots.

Further, the design team needs to consider:

1 The production and operation of these systems will need a provision for water
storage (i.e., cisterns, water accumulation systems, capillary mats, drip irriga-
tion, sprinklers). Their load and space requirements must be accounted for in
the structural design.
2 That the irrigation needs regular monitoring and maintenance, the ongoing
cost after construction should be determined by the planning team.
3 When using non-potable water, the irrigation system design may need to
incorporate treatment to prevent particulates from prematurely clogging
pipes, valves or nozzles.
4 In colder climates, the irrigation system needs to be ventilated with air pres-
sure to remove the standing water in the pipes during frost periods.
5 The method for how water is harvested from an adjacent conventional roof or
as part of the living roof should be planned before the living roof is installed.
6 Above-ground irrigation equipment is exposed to UV light and useful mainly
for temporary irrigation. Surface irrigation may not be as effective, as it may
directly evaporate before percolating to a depth accessible by roots; however,
one study indicated overhead irrigation provides the advantage of good
surface area coverage in application (Rowe et al. 2014).

Figure 4.11
Hybrid system

Rain Rain

Plants

Growing medium

Geotextile

Drainage layer

Waterprooing
membrane and
root barrier

Roof slab/deck

Paver/lightweight
aggregate/mulch
Polystyrene block
Edge drainage
aggregate