What is a green roof?

29th March 2021

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A green roof is a system that uses vegetation as the finish of the roof covering instead of just the weathering materials. The vegetated layers sit on top of the conventional waterproofing layer of the building. The use of vegetation in construction dates back to early times, however, it is only in recent years that they have become a popular alternative to traditional roof finishes due to their environmental benefits and significant cost savings on heating and cooling.

Whilst green roofs come in many different forms and types, usually, a distinction is made between extensive, intensive and biodiverse (brown) roofs. The main difference between the three main types is the depth and thicknesses of the individual layers. Each type of green/brown roof requires the following components;

  • Protection fleece
  • Drainage/reservoir layer
  • Filter fleece
  • Growing medium or crushed aggregate
  • Planting/vegetation
  • Hard landscaping and other components as necessary

Green roof systems can either be installed on new build projects in conjunction with root proof membranes, alternatively for refurbishment applications a green roof system can be retrofitted to existing roof coverings by first laying a root barrier membrane.

What is an intensive green roof?

Intensive systems usually involve the creation of a garden at roof level, by the planting of shrubs, trees, coppices and grassed areas. As well as planting, intensive green roofs may incorporate hard landscaping, decking and paving, the options are endless. This type of green roof is intensive due to the type of plants and vegetation used, which require a greater depth of substrate to support them and sustain growth. After installation, ongoing maintenance is required and the plants will need regular watering and feeding to ensure full establishment.

What is an extensive green roof?

Extensive green roofs are planted for aesthetic and ecological reasons with vegetation such as sedum (succulents), mosses, herbs and grasses. This type of green roof requires little maintenance making it the most economical system. The plants used are wind, frost and drought resistant, enabling them to survive in the tough, exposed conditions experienced at roof level. The plants provide a colourful and attractive green roof, which changes naturally through the seasons.

What is a biodiverse (brown) roof?

Biodiversity (brown) roofs are designed to replicate the environment lost to development and can involve creating natural habitats for various species of plants and birds. Other debris, soil and items of stone and timber may be incorporated to replicate the desired environment.

What are the benefits of a green roof system?

Green roof systems offer many advantages to both the specifier and the client. Apart from introducing a creative dimension to the flat roof project, a green roof provides financial and environmental benefits. Extended life expectancy –increases the life expectancy of the roof waterproofing and reduces whole life costs.

  • Reduces heating and cooling costs – improves the thermal properties of the building
  • Supported by local authorities – helps obtain planning permission
  • Increases property value Absorb a lot of moisture – eliminating the need for such a complex and capacious drainage system
  • Helps the building blend in with the surroundings
  • Absorbs heat and allows evaporation of water, reducing heat in urban areas
  • Provide alternative planting without using valuable building land
  • Reduces flood risk – green roofs can retain 40-90% of the rainwater they receive
  • Reduces CO2 pollution
  • Provides a natural habitat for displaced flora and fauna
  • Reduce noise pollution both externally and internally
  • Stormwater management

Whatever the specification, Bailey can supply the ‘complete’ system together with expert advice, assistance and recommendations. Bailey Eco-Roof Systems come complete with a whole range of components and accessories and a wide variety of plants.