Green Roofs
Green roofs are an innovative approach to help manage stormwater runoff and provide habitat for plants and wildlife in the otherwise unused and barren space of a building roof. They are made up of a special waterproof and root repellant membrane, a drainage system, filter cloth, a lightweight soil mix and plants. Green roof systems can be installed as small movable modules or as a single large unit on both new and existing structures, even those with sloped roofs.
Plant communities on green roofs can be designed to mimic a variety of habitats including prairies and rock outcroppings. Habitats where minimal maintenance is required can protect and become home to plants and animals easily disturbed by human activity, such as ground nesting birds. Green roofs can also provide opportunities for urban agriculture as well.
In summer, depending on the plants and soil mix, a green roof can retain up to 80% of the precipitation that falls on them. Plants take up rainwater stored by the substrate, where it is returned to the atmosphere through transpiration and evaporation. This not only decreases the stress on our storm sewers and the waterbodies into which they empty, but also naturally filters and moderates the temperature of any water that runs off during a large rainfall.
Plants generally reflect little solar radiation as heat, unlike most hard surfaces. This can greatly reduce the roof temperature and help mitigate the urban heat island effect. On an average summer day, the temperature of a gravel roof can increase by as much as 75 °F. Covered with plants, the temperature of that roof may not rise more than 10-25 °F. This high insulation value helps reduce heating and cooling costs up to 25% in the summer.
While green roofs are more expensive than a conventional roof, their life span is up to twice that of other roofs, saving money on repairs and replacement.
Other Resources:
Green Roofs for Healthy Cities
