Paris’ Urban Planning Renaissance

I said to the mayor, first you do my tower that is green, invisible, so Parisians will begin to accept it is possible to do a tower. Then you can do a bigger tower.

tower architect Eduoard François

“Paris is a historic city and building a new tower is very challenging,” explains tower architect Eduoard François. “This [Biodiversity Tower] is efficient in the landscape – invisible almost.”

The brief was clear. It had to be such an attractive building that it could win over the most cynical of observers — because it would be the first tower in decades to be exempt from the city’s 37m height restriction.

“I said to the mayor, first you do my tower that is green, invisible, so Parisians will begin to accept it is possible to do a tower,” he says. “Then you can do a bigger tower.”

The tower’s invisibility cloak is in the form of a cascade of plants and trees that, now the building is in use, will continue to vegetate. These become more dense the higher up the tower they go. They are knitted into, and will gradually climb up, a second skin, a mesh curtain surrounding the balconies of the titanium clad structure.

The titanium is treated with electricity and heat to turn it as green as forest moss, while the white plants range from fast growing to give immediate benefits through to oaks that will take 20 years to mature. On the top of the tower is 1.8m of vegetated earth for insects and birds, “because we have to continue the green belt, and only then it becomes the tower of biodiversity”, explains François.

François is passionate about the potential for vertical buildings to contribute to, rather than detract from, their surroundings. This tower not only aims to blend into the landscape, it aims to spread its green credentials as wind gathers seeds from the plants and trees and deposits them around the city.

His commitment to the principle led him to undertake a two year research project to prove the viability of his plan for the trees and plants flanking the building to grow out of 350mm diameter, 3m long tubes. Fifty of these were placed in sunny and shaded conditions and sure enough the roots began to grow and now the expectation is – aided by a digital irrigation monitoring system – these tube trees will reach heights of 2.5m.

This attention to detail spread to the structural cladding. A manufacturer in Japan won the supply contract following a live demonstration in a Kyoto garden, that proved the panels could be heat and electricity treated to turn them the exact shade of green required to make them appear to merge into the moss green backdrop.

Attention to detail does not come that cheap – the 13,830m² building cost €37M (£31.5M), including £8.5M for associated infrastructure. But there was a sense that this could afford to be an exceptionally beautiful social housing residence thanks to the city’s desire to unleash future tall building developments.

“This programme is a governmental project so [to a degree] they can do whatever they want – it’s the power of the State,” says François. “It is an icon,” he adds, before exclaiming that approval for towers such as Herzog & de Meuron’s 180m tall Triangle in central Paris could only go ahead “because I do this building well”.

Despite this, François insists that one eye remained on the budget for client and public housing body Paris Habitat. And the complexity of the building’s location strained the budget further.

Structural engineer Arcadis, along with contractor Bouygues, had to face down a litany of challenges – mitigating high flood risk with a requirement for 10m of clearance should the Seine overtop its banks; the close proximity of the traffic-heavy Périphérique; unfavourable ground conditions; and vibrations from TGV and local trains running beneath, in and out of Gare d’Austerlitz.

Fortunately the consultant was familiar with the area thanks to its work in the 1990s and 2000s carrying out detailed design for the concrete slabs that now cover many of the railway tracks and which enabled the Rive Gauche development to flourish. Spring boxes installed in the tower’s lowest levels isolate the worst vibrations.

“The tower’s main difficulties came from the ground conditions,” Arcadis Biodiversity Tower leader Luc Jeansannetas adds. “There is [competent] limestone in this whole area except beneath the tower. That meant we had to dig deeper to find the right rock. It has all the family of deep foundations.”

Those foundations stretch 25m into the soil and total 35m with the additional 10m flood height allowance. Specialist geotechnical contractor Franki Fondation and its sister company Sefi-Intrafor carried out this medley of works, which included 86 structural piles, as well as a piled retaining wall structure and an 820mm thick, 30m deep diaphragm wall.

That the tower commanded such attention to detail is testament to its high profile – not only because it has paved the way for future high rise living but because of its location next to the Périphérique and neighbouring suburb Ivry-sur-Seine. For its supporters this tower is one of the ways Paris can metaphorically jump over the Périphérique.

Watch an interview with architect Eduoard François on how the Biodiversity Tower will bring nature to the centre of Paris. (Mobile users choose landscape view)

“A city like Paris must be able to reinvent itself at every moment to meet the many challenges facing it”

In the city’s endeavours to knit its industrial, infrastructure side together with public spaces and residential and commercial buildings a tried and tested technique became established.

The city, or an arms length public development organisation, would in the first instance build over railway tracks with concrete slabs, before inviting interest from design, construction and private development parties.

But the appetite to carry on in this outdated, and frankly costly to the public purse, manner waned. And two years ago the city’s mayor Anne Hidalgo issued a call to arms through the Reinventing Paris initiative.

“A city like Paris must be able to reinvent itself at every moment in order to meet the many challenges facing it,” she said at the launch in November 2014. “Particularly in terms of housing and everything relating to density, desegregation, energy and resilience.”

The initiative brings together 23 troublesome sites — most concentrated in areas near or adjacent to the Périphérique — into a single competition to ensure their development for social and environmental benefit. It represents the next bold move in this city’s attempt to make this concrete and blacktop barrier become a tool of reunification to bring together the city centre’s 2.3M population with the 8.5M living in its outer suburbs.

“Paris is facing massive environmental challenges that call for original solutions,” added deputy mayor Jean-Louis Missika. “Buildings demonstrate environmental innovation by revolutionising energy production, consumption and recovery. By interacting intelligently with their block and the whole city, by integrating ecological materials, by experimenting with innovative planting and by achieving the target of ‘zero waste, zero carbon’.

“Innovation also means investing in new spaces: basements, roofs, wasteland, the Périphérique and all the abandoned spaces that sometimes represent the future of our metropolis.”

1973

Year the Périphérique completed

30%

Proportion of Périphérique that is in tunnel

In other words this competition “marks a fundamental departure from the traditional approach to development in France”, according to Arcadis Europe South buildings engineering and design leader Stéphane Kirkland.

He explains that traditionally, public authorities through their programming processes have controlled urban development very strictly. “A public agency gains control of the land, then commissions experts to determine the best use of the land,” Kirkland elaborates. “Private developers only come in at the end of the process, tendering on each site to build them up according to the specifications set by the public authorities.

“Reinventing Paris inverts the approach. The city of Paris simply defined sites and invited multidisciplinary teams to come up with creative ideas for how to use them. Private developers funded this idea generation process on the understanding that they would then be allowed to buy the sites and then developed them.

“The sites were not sold through a rendering process to a fixed set of specifications. They were instead attributed, based on the social and environmental value added of the project, for a fixed price.”

Mille Arbres – or a thousand trees – is one of the winning schemes that encompasses all the ambitions of the competition at a site in the Pershing district. Acting as civil engineer, Arcadis, alongside partners including architects Sou Fujimoto and Oxo, structural consultant Bollinger & Grohmann and contractor Bouygues developed the concept of a mega bridging building crossing a section of the north west part of the Périphérique.

Arcadis has a clear understanding of the scale of the challenge, having spent a decade advising the city’s building and infrastructure division about how best to cover over the vast ring road.

Perhaps that gave it the confidence it needed to go in with its partners on a bold scheme. The proposed development creates housing, offices, shops, hotels and cultural facilities in a structure that looks not dissimilar to the Titanic in both its shape and epic proportions. It also features a roof that accommodates low energy timber housing units and more than 1,000 trees.

Building permits are expected next April, with tenders due to start in 2018 followed by onsite works in March 2019. The scheme could be complete by 2022.

• More details on the competition and all the shortlisted schemes available here
  
  

So Hidalgo wants more, and is banking on around seven upgrades to iconic public spaces for not much more than the around E30M (£25.6M) cost of the original trendsetting scheme back in 2012/2013.

The city has now appointed four teams, which Arcadis is again among, in a £38M programme to upgrade these public interchanges, and in doing so place less emphasis on their usefulness for cars.

Looking to emulate similar successes in New York and Copenhagen, the idea is to undertake light and sober development work, avoiding major road, pavement or utility renovation, for maximum benefit.

“This is the Parisian answer to the double challenge of cost reduction and citizen participation,” says Arcadis Urban Projects activity manager Nicolas Boffi. The idea is to separate “hard” infrastructure, pavements, utilities and lighting from “soft” playgrounds, kiosks and street furniture.