Nonmonetary Benefits of Green Roofs

Local Environment

• Green roofs absorb pollutants and improve local air quality. They also help with reducing the urban heat island effect, an important consideration in hot cities where temperatures can rise to dangerous levels. The plants of green roofs absorb water through their roots and then emit it through their leaves. Water also evaporates from the soil and the plants. Both processes have a cooling effect. Biodiversity is improved because the roofs providing a habitat for local wildlife, such as bees.

Personal Environment

• The combination of plants and soil insulates against sound, with each trapping a different range of frequencies. This is helpful in urban areas with heavy traffic and other sources of noise pollution. Those living under flight paths in particular may find a green roof beneficial. The amount of noise a green roof can absorb depends on the depth and dampness of the soil and the type of vegetation growing there. If noise insulation is important to you, discuss the efficiency properties of various kinds of green roofs with an architect before choosing one.

Aesthetics

• Many people find green spaces aesthetically pleasing in urban areas predominantly composed of concrete. Parks require large amounts of valuable space, but green roofs can be added to existing commercial and residential buildings. Decorative flowering plants such as crocuses do well on green roofs, turning what was a plain expanse of building materials into an attractive garden. Even basic green roofs provide a fresh, green alternative to plain, functional roofing materials.

Agriculture and Leisure

• Some green roofs are strong enough to provide recreation areas. They also provide the opportunity for residents to practice small-scale farming of herbs, fruits and vegetables. Intensive green roofs, those with more than the bare minimum of substrate, can sustain a huge variety of food crops. Intensive green roofs have a soil depth of up to 12 inches, enough to grow most garden vegetables, apart from root crops, and even small fruit trees and shrubs. The main limitation is that the crops have to be able to cope with direct sunlight most of the day, and very possibly high temperatures. However, shade-loving plants such as spinach grow readily if interspersed with taller crops that provide shade.