Now that most large-scale building projects at least consider a vegetated roof, we feel it would be worthwhile for all of us to think more comprehensively about their uses. They have been advocated primarily for their role in improving the physical environment of cities: reduction of stormwater loads, reduction of the heat-island effect, provision of habitat for beneficial insects, etc. There are, however, a range of other benefits that to our mind are also very important and have implications about the design of vegetated roofs:
•You will not be surprised to know that we consider a green roof’s visual quality to be of critical importance. If done well and not applied in the purely utilitarian manner of other roofing systems, they can enrich our sensory experiences by engaging in pattern-making in the same ways that well-designed building facades can. This is especially important where they are installed on rooftops that can be seen from surrounding buildings. This creates benefits not just for the building’s immediate users but also for the community at large.
•They can be used for active recreation since some of the environmental benefits, particularly their water-storage and purification capacities, can be gained if they are “green” but not vegetated.
•They can be cultivated for food. This is a promising but so far rare use of rooftop space. Rooftop “farms” can provide all of the above benefits, environmental, sensory, and recreational, plus the added one of providing locally-grown food to the city.
There are some wonderful examples of vegetated roofs that serve as “parkland” for the building’s users, some of these are heavy and intensive, but not all. With open space at a premium in every city, it seems wasteful and short-sighted not to occupy them in a meaningful way.