1) Providing a vegetated layer with minimum maintenance and additional infrastructure while maximizing the environmental services delivered to
a. the specific building and
b. the local neighborhood and city environs.
The building enjoy increased roof membrane life; sound and thermal insulation, hence reducing energy expended on heating and cooling;. The local neighborhood and city effects includes improved airquality; stormwater retention, reducing and delaying runoff (and NY this can reduce the combine Sewarge overflow events and the associated environmental cost); reduced heat-island effect; particulate capture; hyper-accumulation of heavy metals; reducing external building temperature and associated public health benefits. 80-90% of the insulation can be achieved with a 3-4” of soil and a selection or monoculture of sedum. This provides minimal hardy vegetation is popular because it requires no irrigation in the dessicated context of a roof, is usually with the structural constraints without having to sister beam or reinforce, yet provides the same CO2 fixing and particulate capture as other vegetation that require more soil.
2) Providing habitat and nutritional resources for diverse organisms and plants; enhancing and maximizing urban biodiversity. This is the most understudied of the greenroof functions, and requires a complex model of interdependent organisms, challenging design that can exploit the uneven structural capacity of roof space (i.e. dense shrubby habitat for birds can be built around the edges while grassy plains and browsing territory cover the span to create a differentiated set of habitats. It also requires a ecosystems approach, rather than the imagistic work of landscape architects, or the popular planting strategies of most gardeners. There is little formal literature to draw on in the vo vocabulary of most green roof enthusiasts.