The argument for green and brown roofs to support urban nature recovery is a powerful one. Biodiverse rooftops can help to stabilise bee and other insect populations.
The city of Utrecht in the Netherlands completed a scheme of greening the roofs of their 316 bus stops in 2019, which captured fine particles of air pollution, stored rainwater and provided cooling during summer. Following this success, the city has introduced a “no roof unused” policy, where every buildings’ roof will also be turned green with plants and mosses, or have solar panels. For aesthetics, the lower rooftops will be mainly green, and the higher ones mainly solar. Where possible, greenery and solar will be combined as the greenery provides cooling for the solar panels.
How does this translate elsewhere?
Thinking about rooftops
The University of Cambridge hit the headlines when securing consent to install almost 500 photovoltaic panels on the lead roof of the 15th century King’s College Chapel. The panels will have minimal visual impact, while meeting the energy needs of the building and reducing the college’s carbon emissions by more than 27 tons each year.
In London, roof gardens now cover an area larger than Hyde Park (142ha).
Nature loss in the UK
Britain has lost more of its natural biodiversity than all the G7 nations, ranking 12th lowest of 240 countries. The United Kingdom’s (UK’s) wildlife, plants and pollinators needed helping hands, and to reduce carbon consumption and emissions to get close to the net-zero targets by 2050.
For English firm, LDA Design Consulting, this meant thinking much harder about the role of new developments, such as asking how they build, demolish or retrofit, who they are building for and if there is social equity.
In King’s Cross, at the primary new office for Meta by Bennetts Associates, LDA Design created a substantial rooftop landscape featuring species typically found alongside rail verges. There are wildflower meadows, brown roofs, log piles, native plant species and plants for pollinators. It is the largest roof garden on the successful King’s Cross estate.
The starting point was to design the landscape and then work out routes for circulation, space for amenity and access to building facilities.
Rethinking roof space is not without its technical challenges – taking close collaboration between architects, structural engineers and landscape architects to create an impactful rooftop landscape. The soil had to be built up sufficiently to ensure the planting could thrive.
Solutions included raising the level of the floor to the centre of the main terraces by designing in ramped areas. Where even greater depth was needed, linear “berms”, mimicking rail-side landforms, allowed suitable depth for trees.
LDA Design believes that the way forward for the built environment must include maximising the potential of every square inch of new development to benefit people and the planet, as well as more historic buildings looking to the roof level for answers.
Full acknowledgement and thanks go to https://www.lda-design.co.uk/ and https://www.theguardian.com/ for the information in this editorial.
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