Also known as living roofs, "green roof" is a term used to describe planting vegetation over a roof’s waterproofing membrane, so that it is either partially or completely covered by greenery. The most important component of a green roof is the substrate (the growing media), which generally contains a low level of nutrients so as to ensure the plants are easy to maintain. This layer will hold a certain level of water, yet also be free-draining in order to prevent rotting of the plant roots. A good substrate should support the entire green roof system and sustain the vegetation layer; additional layers of a green roof will include filter and drainage layers, as well as a root barrier, which is used to separate the green roof system from roofing membranes.
Green roofs are considered an important step in creating a green infrastructure that will aid cities in adapting to, and mitigating, the effects of climate change. They present houses as a part of the aesthetic landscape and, particularly in urban environments, can provide an important refuge for wildlife.
There are plenty of benefits to be had in the installation of a green roof system: heating bills can be decreased due to reduced heat loss and energy consumption in the winter months; the roof naturally filters pollutants and carbon dioxide out of the air, helping to reduce diseases such as asthma as well as reducing the amount of sulphur dioxide (which causes acid rain) in the air; the space acts as a natural habitat for rare or endangered species; stormwater run-off management - vegetation roofs have been shown to have an 82% rainfall retention rate on average, compared to a 27% rate on ordinary gravel rooftops; and the green roof helps protect waterproofing from frost, ice and UV rays, with studies proving that this can triple a roof’s lifespan.
As well as the obvious importance in tackling climate change, there are many other benefits to be considered in having a green roof system, ranging from sound insulation to a reduction in air conditioning bills. There is also the increased possibility of homeowners gaining planning permission when a green roof is factored into the equation.