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Green Roof is the name given to type of roof covering that is made of a natural material such as turf, which is overlaid onto an existing roof covering that has been specially prepared to receive the green roof.

The environmental benefits of green roofs are now becoming more widely recognised, with many Local Authorities looking favourably on such installations. A secondary benefit, particularly in cities, is that roof gardens and roof terraces can provide much-needed outdoor space in urban areas.

Due to the high degree of insulation that they provide, green roofs are known for their ability to provide an extremely constant temperature throughout the year. During the winter they keep the heat in, and in the summer they provide a relatively cool environment. Green roofs also have the ability to soften harsh edges of buildings in sensitive environments, helping them blend in with the surrounding area. Turf and green roofs provide habitat for insects and other wildlife. Where new buildings are built on Greenfield (previously undeveloped) sites, this new habitat can replace the habitat that would otherwise have been lost.

Methods of construction differ between pitched green roofs and flat green roofs. Flat green roofs can be either extensive (having a thin layer of growing material such as sedum matting) or intensive (having a greater soil depth with shrubs and even trees). The weight requirements for intensive green roofs are such that they are normally installed over concrete roof decks.

A further type of green roof is known as a biodiverse or brown roof. These are constructed in a similar way to flat green roofs, but are designed with specific biodiversity objectives in mind - for example maximising biodiversity or providing a habitat for a specific plant, insect or bird species.

It is a common misconception that maintenance of green roofs can be time consuming and costly. For simple extensive (sedum) green roofs, all that is required is an annual inspection is required as with any traditional roof. This is to remove any transplanted seedlings and to ensure the drainage system is free-flowing. A roof garden will clearly require more attention to maintain its appearance, depending upon the precise design of the roof in question.

A correctly-designed green roof does not leak. The key to this is that the underlying roof structure must be waterproofed as for any conventional roof. Once this has been carried out, a root-barrier membrane and drainage layer is used to prevent any roots or aggregate from coming into any direct contact with the waterproofing layer. All reputable suppliers of green roof systems will generally offer a full site survey and design specification service to ensure that the correct methods and materials are used and that the installation is properly planned. Whilst there is often an increased installation cost with a green roof, the whole lifecycle of the roof needs to be considered. A simple green roof build-up frequently costs little more than any alternative roof covering, although a more extensive build up can incur a higher initial outlay.