Mini forest and ‘green tower’ plans among first to meet London’s new green guidelines

Developers will consider contribution to environment using Urban Greening Factor formula

The first proposals for a spate of developments designed to meet new green measures in London include a biodiverse training complex at the All England Lawn Tennis Club in Wimbledon, a green-walled skyscraper in the City of London and a densely planted mini forest in Chelsea.

Skyscrapers, historic estates and suburban parks across the capital are counting up scores for greenery under new planning metrics set out in Mayor Sadiq Khan’s London Plan, which are intended to enhance developments’ contribution to the environment.

The Urban Greening Factor (UGF) formula, inspired by the Swedish city of Malmö’s “green points” system, scores each part of a development’s plan – including street-level areas, balconies and roofs – from 0 to 1, with trees, planters and green roofs earning high scores, while paving slabs and barren rooftops receive no score. Central government has also set out plans in the Environment Act 2021 to make developments deliver an uplift to biodiversity, which will require a 10% “biodiversity net gain”.

“The Urban Greening Factor is a complete step-change in how much green stuff we’re putting on buildings,” said Craig Robertson, head of sustainability at AHMM architects. Even city centre sites will be tasked with achieving a UGF score of 0.4, equivalent to turning 40% of their footprints over to nature. Biodiversity net gain will mark another big shift, Robertson added, pushing developers to consider vegetation and ecological benefits to their surroundings. “It’s really difficult – in a positive way. It’s a really positive challenge to have.”

Biodiversity net gain, which will be required in planning law from 2023, uses a complex algorithm to account for nature losses and gains – although critics have called for urgent revisions to the current formula.

Although some London boroughs are yet to formally adopt UGF measures, the Greater London Authority (GLA) began requiring it in March, meaning all large developments across the capital must now calculate their score. Draft guidance to help boroughs and developers deliver UGF effectively has been put out for public consultation and will formally be adopted next year.

Residential developments are typically set a target of 0.4 and commercial developments 0.3, giving landscape architects and designers “authority and opportunity” to reach these scores in creative ways, said Peter Massini, an ecologist who helped write the UGF policy at the GLA.

London was already spattered with green roofs, with 700 in central London alone, but the UGF makes them all but essential in dense urban plots with little street-level space. Green walls offer another way of lifting UGF on crowded sites, but Robertson said many designers are doubtful of their benefits amid a rash of high-profile die-offs. The “cascading” green terraces of The Ray, his practice’s redevelopment of the Guardian’s former headquarters in Farringdon, are one indicator of where the city could be heading under UGF, said Robertson, alongside biosolar roofs, which combine plants growing around photovoltaic panels. The City of London approved a 33-storey “green tower” at 70 Gracechurch Street in February, which exceeded a UGF target of 0.3 with a collection of living roofs, planted terraces and a green wall.

Cadogan, the main landlord in Chelsea and Knightsbridge, is targeting a 25% increase in its UGF across its 36-hectare (90-acre) Chelsea estate, including designing a densely planted Miyawaki forest. The UGF incentivises developers to not settle for bland green space, said City Hall. Wild grassland or dense tree planting score more than double typical lawns, meaning lawns can be upgraded to help reach targets in historic areas where buildings are protected.

Plans for an extension to the home of the Wimbledon Championships has reached the near-perfect UGF of 0.97, almost totally green space. The All England Lawn Tennis Club (AELTC) bought a former private golf club in 2018 neighbouring the tournament’s courts, on site that been a parkland estate designed by Capability Brown. By 2030, it will provide 39 tennis courts, designed to sit within a “mosaic of habitats”, with much open to the public, said Andrew Wayro, senior landscape design manager at AELTC. While its UGF was already far above the 0.4 requirement at the outset of the project, it aims to push it higher while achieving a 10% biodiversity increase by switching rolling fairways for “priority habitats for the area, like reedbeds and acid grassland” and specialist habitats for hedgehogs and Daubenton’s bats, said Wayro. But the Wimbledon plan has met with objections by some residents, who argue that the development will “cause substantial harm” to the park.

Vanessa Ross, founder of Arc Landscape Design and Planning, said it remains up to developers, designers and ecologists whether the new metrics will truly make a difference to lives and ecosystems in London, or simply push architects into “designing by numbers”. For example, private gardens can score highly for green space but offer little benefit to people unless accessible, Ross added.

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Matthew Ponsford

Cover photo: The Urban Greening Factor incentivises developers to look at ways to create green spaces, such as this roof garden on the top of the Hachette building overlooking the Thames. Photograph: Diana Jarvis/Alamy