Green roofs

Intentionally vegetated roofs, also known as green roofs, bio-diverse roofs, living roofs, sedum roofs, roof gardens and even blue roofs if their primary function is to hold water. In the UK 'green roof' has become accepted as a term to cover all of these different designs which may have particular primary functions.

Green roofs are one of the few engineered sustainable technologies applied to buildings which have very low embedded energy and provide a whole raft of benefits, often beyond the primary reason for their inclusion on a building.

There are a number of prime drivers for green roofs in the UK, they are:

  • Water holding/detention - simply by adding a layer of growing medium, often referred to as 'substrate' to a roof, rain water is detained on the roof for a period of time. This helps to reduce the volume of surface water going directly into sewage systems and highway drainage.
  • Biodiversity - providing areas of plants, particularly pollen rich plants and growing medium is beneficial to insects and birds. If these areas can be added to urban deserts of concrete and steel, the benefit is all the more important.
  • Protection of roofing material - UV radiation and the constant and rapid fluctuation in surface temperature of un-greened roofs causes roofing membranes and finishes to age very quickly, to the point where many roofs only have a life expectancy of 20 years!
  • Reduce the cost and impact of air conditioning - air conditioning has become more common place, particularly in commercial buildings. Un-covered roof heat up and heat the building below, a green provides a cooling effect through a process of evapotranspiration, similar to a person sweating. Thereby preventing the building from warming up so much and reducing the demand on air conditioning and therefore the amount of hot exhaust they produce.
  • Reduce the 'urban heat island effect - this is what has resulted from city buildings being built close together and never having the opportunity to cool down. In a same way as air conditioning is effected, above, green roofs help to cool urban environments.
  • Improve air quality - cool air carries less heavy metals and particulates, green roofs help to cool air and therefore improving air quality. Specific plants can be grown on green roofs to trap carbons or road dust or other defined pollutants.
  • Reduce sound transfer - the mass of a green roof build-up helps to deaden certain sound frequencies.
  • Look great - a great deal of work has been done over recent years on what species can survive and thrive in the incredibly hostile environment on roofs. Therefore over summer months roofs can provide spectacular displays of colour and texture. In winter months many roofs become less aesthetically attractive to humans, but become beautiful landscapes for insects.

This list is not exhaustive, and whichever of these or any other reason is prime driver for your green roof, you will get many of the other benefits as a 'free' bonus.

More information can be found at:

NOTE: Green roofs and green or living walls are not the same thing. Green roofs are a genuine sustainable technology. Living walls are just for design or art, they have virtually no sustainable credentials.