Glossary - Living Roofs in Integrated Urban Water Systems - page 170

through the gaps between the insulation layer boards, and then runs above
the waterproof membrane to drain locations.
Living roof, warm assembly : the living roof assembly type in which the
insulation layer is below the waterprooing membrane. Water drains through
the growing medium and runs along the drainage layer that sits on the
waterprooing membrane to the roof drain locations.
Living wall/living façade : a vertical surface on an architectural structure clad with
plants. The structure holding the planting is often a modular system complete
with a growing medium and membrane layers (always including a waterprooing
membrane) to protect the supporting wall structure behind (concrete or framed
assembly). The plant “cladding” can be either interior or exterior to the building.
Loading, structural : the force applied to a surface or structure by an object, and
is characterized as either live (imposed, variable) or dead (permanent, constant).
On a roof, live loads are typically a result of people (stationary or in motion) or
by luctuating masses of precipitation. Dead loads generally include the roof
deck itself, mechanical services, and the dry weight of the living roof assembly.
Structural loading is a crucial consideration in living roof design as it determines
the viability of an existing structure or new structure to accommodate a living
roof assembly and will determine what and where living roof elements can be
built. Structural capacity must be assessed by a licensed structural engineer.
Low impact development (LID) : a land (re-)development approach that works
with nature to minimize impacts on or improve receiving environments by
managing stormwater as close to the source as possible. LID incorporates a
combination of land use planning and engineered SCMs, with a preference
for green infrastructure over grey infrastructure. Technically and quantitatively,
LID (and GSI) seeks to maintain or restore the pre-development hydrologic
cycle and minimize pollutant discharges.
Peak low : the maximum stormwater runoff low rate for a given storm event.
Permanent wilting point : the moisture content below which plants cannot
recover viability.
Permeability : the rate at which water moves through a porous medium. For
living roofs, high permeability ensures that water never ponds on its surface
(i.e., no standing water).
Permeable surface : a constructed or natural surface which allows water to inil-
trate through it. At-grade, permeability promotes return of precipitation and/or
surface low to the subsurface. The construction and preservation of permeable
surfaces is an integral GI practice, as they help to recharge deep groundwater
supplies, or enable low through shallow soil layers toward streams to recharge
base (dry weather) low. This helps balance the hydrological cycle, reduce
surface runoff and prevent or diminish excess stormwater discharge and associ-
ated contaminants to receiving waters and potential CSOs.
Plant available water ( PAW ) : the amount of moisture stored in a growing
medium between the ield capacity and the permanent wilting point. PAW is
typically lost to the atmosphere by ET.