FAQs

We hope you will find the answers to your questions below, but if not please get in touch and we'll be happy to help.

What is a green roof?

A roof that is purposely designed to support plant life. Green roofs are typically categorised as extensive, biodiverse or intensive, depending upon their function and maintenance requirement.

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What is an extensive green roof?

An Extensive Green or Living Roof is a low maintenance, lightweight planted roof system that is typically composed of a drainage layer, substrate and a visually attractive plant system that offers solutions to many environmental and building performance challenges.

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What is a 'Biodiverse' Roof?

A biodiverse roof recreates or enhances a habitat designed to attract particularly desirable flora and fauna, whether for environmental benefit (e.g. attracting wildlife) or for building designs that are sympathetic to the local landscape. The planting strategy will therefore involve species that are indigenous to the particular location of the building.

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So, is a 'brown' roof the same as a 'biodiverse' roof?

Actually, a brown roof is a particular, non-vegetated version of a biodiverse roof. Brown roofs are designed to self-colonise with native plants over time, using locally-relevant substrates, and may incorporate additional features to attract wildlife.

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What is an intensive roof?

Also known as a roof garden, an intensive roof provides benefits akin to a domestic garden or small urban park through a combination of soft and hard landscaping. With planting options including lawns, shrubs and even small trees, substrates tend to be greater in depth (i.e. 150 up to 1500 mm), heavier and have a higher organic content. Regular maintenance and irrigation can be expected.

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Why would I want a green roof?

Apart from the aesthetic value and the strong positive statement associated with sustainable design principles, green roofs are typically specified for any one, or combination, of:

  • Ecological or environmental benefits
  • Building performance enhancements
  • Financial incentives
  • Planning Requirements 
The nature and extent of these benefits will vary with the specific green roof construction. Extensive green roofs can be designed to provide a multitude of benefits, such as SUDS or thermal insulation; biodiverse roofs provide environmental benefits through the conservation of the natural environment and enhancement of biodiversity; intensive roofs typically serve recreation or amenity purpose.

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Really? Green roofs can be a planning requirement?

Yes, green roofs are increasingly stipulated as being mandatory if planning consent is to be granted. The need for sustainable drainage has led the Environment Agency to specify that runoff from many new sites must mimic behaviour of a green field site as closely as possible. Climate change forecasts suggest that the number of such mandates will only increase in the years to come.

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How much does a green roof cost?

Any guideline figures would be inaccurate at best. To ascertain prices for your project's specific green roof requirement, please contact our Contracts Department.

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Why not use the roof space for solar panels instead of a green roof?

The two are actually mutually beneficial. The cooling effect of green roofs can improve the efficiency of solar panels (also known as photovoltaics [PV]). The shade provided by the PV units can also enhance the biodiversity potential of the green roof. Plant species must be carefully selected to suit the partially-shaded conditions, enabling the full benefit of a green roof installation to be realised.

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Won't rainwater from a green roof leak into my roof?

No, a range of different roof coverings can be used to provide the requisite weather-tightness, including single ply or bitumen membranes, liquid applied waterproofing or aluminium standing seam systems.

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Could I install a green roof on to my pitched tiled roof?

No. Tiled roofs are not recommended as a waterproof covering beneath green roofs.

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Does a green roof adversely affect performance of the waterproofing?

No, quite the reverse. Provided that the specification is appropriately formulated and detailed, green roofs can significantly extend the lifespan of the waterproofing beneath. This is due to blocking out ultra violet light, reducing thermal fluctuations, wind scour and climatic stress.

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Are green roofs tried & tested?

Yes. It is believed that the first green roof was built at Babylon, where it is considered to be one of the seven wonders of the Ancient World. Modern green roof systems have been in existence in Europe for over 50 years and are commonplace in Germany and other western European countries.

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Can a green roof's performance be covered by a guarantee?

Yes, but as the plant layer is living and developing, its performance can only be guaranteed if a maintenance contract is taken out with Blackdown Contracting.

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