There is a growing trend in the integration of vegetative roof systems in building designs. Green roofs can reduce the overall energy cost of a building by providing insulation, and play a part in storm water management by reducing runoff and protecting against erosion. From intensive roofs such as roof gardens to extensive green roofs with mosses, the vegetation of these eco-roofs can provide cooling through evapotranspiration, shade and reduce the overall temperature of the roof surface.
The EPA notes increasing vegetative roofs in cities are ways in which municipalities can combat urban heat islands. Studies have shown that urban temperatures could be reduced by as much as 12 degrees if the majority of a city’s roofs were comprised of green roofs.
Municipalities are becoming much more involved with energy efficiency and climate change initiatives at a local level with the reduced level of action from the federal government. The Denver Green Roof Initiative, also known as Initiative 300, requires that all new buildings over 25,000 square feet must allocate 20% - 60% of the roof to solar or a vegetative rooftop usage. Cities such as Toronto, Chicago and Washington D.C. already have bylaws and practices in place regarding green roofs.
There are several grades of vegetation with a variety of root systems which can include moss, shrubs, even fully grown trees. Water is collected within the vegetative roof system and released back into the atmosphere via condensation, evaporation and transpiration. Green roofs also filter pollutants and carbon dioxide out of the air.
Proper drainage within the roof system is crucial to avoid green roofs being damaged by water retention. Use of drainage channel boards reduces pooling and the channels allow a clear path for water to move through the insulation layers to continue on to the pre-determined drains or a drainage mat layer.
Although the initial costs of green roofs are higher than that of traditional roofs, the reduced energy costs and potentially longer lifespan can help offset the investment. In addition, green roofs improve quality of life by decreasing temperature and greenhouse gas emissions. They are aesthetically pleasing and provide sustainable solutions for urban areas.