Living roofs and walls — Sustainability article from NBS

Living roofs and walls - Sustainability article from NBS

In this exclusive extract from Biodiversity for Low and Zero Carbon Buildings: A Technical Guide for New Buildby Dr Carol Williams, we take a look at the benefits and practicalities of living roofs and walls.

Living roofs and walls are common in Switzerland and Germany, and there is a growing number now found in London and in other major cities in the UK.

Benefits of living roofs

The area of roofs in an urban environment are considerable and tend to be sterile environments, largely uninviting for biodiversity and not pleasant to look at from upstairs windows. Living roofs can support a whole range of invertebrates, depending on the type of roof grown. There will be generalist insects, such as ladybird species, bees and grasshoppers, but there is also a possibility of supporting more uncommon species, including moth and butterfly species not normally found in the conditions present in gardens. The array of insects and the seeds produced by the flowering plants all provide good feeding opportunities to a range of birds, from common garden birds, such as greenfinch, blackbirds and wrens, to goldfinch, linnets and even the rare black redstarts in certain parts of the country. This proliferation of insects is also likely to be a feature that will be of benefit to foraging bats, as all the UK bats are insectivorous. A bird particularly associated with living roofs is the black redstart. This has a limited distribution in the UK, predominantly being found in London, Birmingham and the Black Country. In these urban areas it can be very beneficial for the populations of black redstart if living roofs, which meet the needs of this species, are incorporated. Details of these needs can be found on the specialist website .

In addition to these benefits for biodiversity, living roofs have other positive benefits such as moderating the temperature of the rooms beneath, helping to keep them cool in warm weather and insulating them against cold. In heavy or prolonged rainfall, living roofs reduce the likelihood of floods by acting as a sponge that absorbs water before allowing it to evaporate back into the atmosphere. Living roofs also protect the roof material from the effects of ultra-violet light and frost that could be damaging.

Types of living roof

Mosses and lichens naturally colonise roofs and establish themselves in the harshest of environments without substrate or support. Roofs that have moss and lichen will host a whole range of associated invertebrates and microscopic creatures, which are, in turn, a valuable food source for birds. It is possible to obtain pre-grown moss mats, but more often it is a case of not being over tidy with what will naturally colonise a roof. Besides these naturally occurring colonists, it is possible to create a living roof on a new or existing building.

There are a range of living roofs available, but they fall under the broad categories of: shallow, which imitates the harsh environments such as cliffs and mountains; and deep roofs, which, due to the deeper growing substrate, allow a greater range of plants to be grown that, in turn, can support a greater range of biodiversity, but they do require more maintenance. Very deep roofs have a depth of substrate sufficient to allow shrubs and even trees to grow, and are less often likely to be a viable option.

A living roof comprises a number of layers, generally a waterproof layer, a root barrier, a filter layer, moisture blanket, drainage layer, the soil mixture and the planting layer.

Where can they be used?

A flat roof is ideal, although other types of roof may be possible to utilise as long as the slope is not too severe.

Benefits of living walls

Whereas roofs are often not a visible feature from the ground level, we are more aware of walls in our towns and cities. Living walls utilise plants in order to derive benefits, not only in visual terms, but also in regard to biodiversity, thermal efficiency and the reduction of pollutants. By providing shading from the sun, living walls can significantly reduce the external temperature of a building. Living walls can also provide a certain amount of insulation, although the effectiveness of this will depend on the type and structure of the living wall and the overall energy performance of the building itself. Living walls can also help reduce the urban heat island effect by intercepting heat which would otherwise be largely absorbed and radiated by the building surfaces back into the surroundings. They also help to shield the surface from ultra-violet light, which could be an important consideration for some modern cladding materials.

Plants on buildings can potentially provide a food source for invertebrates on which, in turn, other invertebrates, bats and birds may feed. They also provide a breeding and nesting habitat for invertebrates and birds, and are ideal for including ready-made nest boxes.

Types of living wall

As with living roofs, there is nothing new in the concept of using plants to green buildings, but in recent years a variety of modern designs and techniques have been developed. Living walls can be separated into a number of categories that include:

Living roofs and walls - Sustainability article from NBS
  • Supported by a wall self-supporting climbers
  • Supported by a structure on a wall trellis, etc.
  • Supported by a self-standing structure away from a wall frameworks, etc.
  • Hanging walls allowing plants to hang from a height
  • Walls with plants growing within them.
Considerations in the use of living walls

The use of planted climbers, either self-supporting or in some way trained against a wall or similar structure, is not a new idea and, as long as the choice of plant is wise for the position and soil type, then it is a tried and tested way of greening a wall. The techniques used where the planted material is supported within the wall structure is not so well understood and some of the earlier designs of planted walls have declined over time, with the occasional outright failure. This is not to say that green walls are high risk, but it is prudent to ensure that an experienced practitioner is consulted and that an understanding of any need for ongoing maintenance is acknowledged if the plants are not rooted in the ground.

A great deal more information can be found on the following websites:

Find out more

The built environment has the potential to have a major impact on biodiversity, not least with the increasingly demanding requirements to design more energy efficient and airtight buildings, leaving less space for species to inhabit. Up until the publication of this book, there was no one place where architects, developers, consultant ecologists, and all those involved in low and zero carbon buildings could find out about how to incorporate provision for biodiversity within their developments.

In this groundbreaking book, author Dr Carol Williams has specially commissioned architects to produce some much needed model designs and practical guidance for the industry. The book also provides a useful summary of all the legislation and regulations relating to biodiversity and sustainable construction in the UK.

To order a copy of this book, please visit RIBA Bookshops .

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