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Are we seeing the wood for the trees? The importance of balancing risks when greening our cities

A need for sustainability is driving future cityscapes that are significantly more ‘green’. Architects are increasingly incorporating trees into their conceptual representations of our future living and working environments and the Bosco Verticale in Italy (pictured) is a dramatic visual example. RiskSTOP's David Reynolds, examines the greening of urban areas and looks at how changes that are good for the environment should always be looked at in the context of other risks…

THE CONCEPT of “Green Cities” is not entirely new. In the UK, the planning of Letchworth Garden City began in 1904, followed by Welwyn Garden City in 1920. At the time, garden cities were defined as “designed for healthy living and industry”.

From these early beginnings, we have recently seen greater emphasis on the importance of developing a sustainable future and protecting our environment. City greening is about delivering environmental, as well as economic and social benefits, by increasing the amount of foliage, trees and soft landscaping in urban environments. The specific benefits of green cities include enhanced biodiversity, improved ecosystem services, stormwater management, pollution reduction, urban heat island mitigation and food production.

Approaches vary widely, comprising roof gardens for the growth of herbs and vegetables, dense planting of trees and shrubs in spaces between buildings and the planting of “vertical forests” which scale the façades of high-rise buildings, of which the Bosco Verticale is a striking example.

Towers of trees

Officially opened in October 2014, the Bosco Verticale (Vertical Forest) is a pair of award-winning residential towers in the Porta Nuova district of Milan. The towers have heights of

110 metres and 76 metres respectively and host 900 trees and over 2,000 plants. Similar projects are in the pipeline in other European countries, including France, Switzerland and the Netherlands.

There is an increasing focus on air quality in cities, and green walls or vertical forests are one way of combating pollution within the microclimate of a particular building.

In Paris, an ambitious programme is underway to increase plantation in the city in an effort to improve climate conditions, in which one million square meters of roof and façade greening are to be installed, around 30 hectares of new green areas created and

20,000 new trees planted.

In the UK, an example of such a scheme, albeit on a smaller scale, can be found at the Athenaeum Hotel in London’s Mayfair. There are also more widespread proposals in the UK’s capital to increase green infrastructure such as street trees, green roofs, green walls and rain gardens, together with a framework to assist local authorities and developers.

Associated risks

However, while such measures ought to be lauded from an environmental perspective, inevitably there are a range of associated risks which need to be counter-balanced.

Take, for example, an increased likelihood of arson, particularly during hot, dry summers, similar to that experienced in more rural forested areas. It is obvious just looking at some of the design features that there is greater exposure to fire and serious external fire spread potential, both horizontally and vertically. Conventional sprinkler protection will have little effect on a fire which originates externally and spreads up a building façade. Access for firefighters may also be impeded.

Another possibility is adverse subsidence risk from tree planting schemes in close proximity to buildings, particularly where clay subsoils are involved, as well as potential direct physical damage to building foundations from the roots of trees planted adjacent to structures. It is also important that roof and wall planting schemes are carried out in a way to avoid adverse loads on the building structure, when in a fully-saturated state.

Even water damage becomes a concern. Increased burst pipes risk and consequent escape of water damage arising from extensive irrigation systems, including frost damage to external pipework, may also feature.

In addition, there could be liability exposures arising from falling trees and debris from wall and roof planting schemes caused by windstorm, general decay, insecure planting, or from and to persons conducting routine maintenance, working at considerable height.

Green is good! Don’t get me wrong! Greener is better. Our future existence as a species now appears to depend on us all dramatically changing our approach to environmental matters, before it becomes far too late.

However, the associated risks cannot simply be ignored. Green city buildings are likely to demand careful underwriting and detailed presentation by brokers. Of fundamental importance is the need to ensure that green city projects are fully appraised at the planning stage in liaison with insurers.

Our aim must be to not get in the way of environmental progress, but also to ensure that the hazards posed by these projects are identified, risks are comprehensively assessed and appropriate mitigation and resilience measures agreed and incorporated into project design.

What are your thoughts? What do you see as some of the emerging risks associated with tackling climate change? Comment below or on our Linkedin page here.



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