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Tetrarc's collective housing scheme in Nantes, France


Gabled roofs, green allotments and glazed winter gardens give this social housing in Nantes a welcome and liveable atmosphere

Where social housing is concerned, the city of Nantes is probably best known for its unité d’habitation, Le Corbusier’s second, built in the suburb of Rezé in 1955. But this was just one small element in a vast building programme launched in response to the post-war housing crisis. New estates appeared all around Nantes, including Les Dervallières, a giant ensemble of 2,500dwellings built by the architect Michel Favreau in 1956-65.

Located in former parkland, its slabs and bars suffered the classic fate: initial enthusiasm followed by slow decline, an ever-worsening reputation, and finally, in 1996, designation under the official euphemism of Zone Urbaine Sensible (sensitive urban zone).

Improvement programmes have been ongoing since then, of which the latest, launched in 2008 under the direction of architect and urbanist Jean-François Revert, involves the demolition of four of Favreau’s bars and their replacement with smaller, more densely distributed apartment blocks.

CF012108__photo_S.Chalmeau_non_libre_de_droits_smallRaised walkways contribute to a playful tree house atmosphere and create purposeful public meeting spaces

Tetrarc’s Boréal building is one of these. Boréal’s programme was intended to promote what the French call mixité sociale − social diversity, which in this particular instance could be interpreted as de-ghettoisation of the poorest inhabitants − through the dual provision of 21 social-sector rental dwellings and 18 flats reserved for first-time buyers at below-market prices.

Since the private homes were intended to operate as an independent commonhold, the brief called for their complete separation from the rental dwellings in order to simplify management of the ensemble. In its principal dispositions, Boréal is the daughter of an earlier Tetrarc project, completed on the Île de Nantes in 2007 and nicknamed ‘Playtime’ by its designers (a reference to that staple of architecture schools, Jacques Tati’s 1967 film).


Assorted plots come at an extra cost but provide a unique oppportunity for residence to maintain an aspect of self sufficiency

Perched on the street-side summit of this mixed-use complex is a row of eight private-sector ‘houses’ (in reality duplex apartments), whose semi autonomy is signalled by that archetype of houseness, the gable. On their street facade, the duplexes are fronted by galvanised-steel greenhouses, which, as well as providing winter gardens, offer energy savings in terms of insulation and solar gain. Access to the duplexes is at the rear, in what is supposed to read as the complex’s garden.

Initially the architects imagined a walkway hanging off the facade, but in the interests of privacy this was detached from the building to become a covered footbridge. The result, realised in larch in deference to its ‘garden’ setting, takes the form of a monster bird’s nest-cum-treehouse.With Boréal, Tetrarc aimed to scale up the Playtime duplexes into an entire housing block, and we consequently find the same basic disposition of gable ends, bird’s-nest footbridges and greenhouses.

Ground Plan
Abscence of dwellings on the ground floor provides an unobtrusive space for parking

The building’s concrete structure is raised on pilotis to form a parking undercroft, which is closed only with metal netting − this, the architects say, is to allow plant seeds to waft uninhibited across the parkland site. As per the brief, Boréal is divided in two, with commonhold flats at one end and social housing at the other. Where they join, the facades diverge at an angle of 21 degrees, essentially in the interests of formal diversity, but also to create a more ‘embracing’ space on the entrance side.

Since hallways are often dingy problem spaces in collective housing, the architects chose to externalise them: on the ground floor they are entirely absent, the lifts and staircases opening directly onto the outside, while above they take the form of hanging walkways as well as the treehouse footbridges. The Boréal development also includes 25 mini allotments, laid out in strips in front of the greenhouse facades.

Walkway (02)
An open walkway, shaded by timber slats, permeates a potentially dingy communal space with light and air

While the private dwellings were sold with their own allotment strips, social-sector residents must apply to rent these at extra cost.Inside, the building is divided up into six two-room flats, 17 three-room apartments and 16 four-room duplexes. While the private dwellings sold out within 24 hours, a few of the social-sector flats are still empty, rejected by prospective tenants who opted not to leave the more generously dimensioned apartments that were formerly the norm in French social housing.

And this despite the Boréal flats’ enjoying ‘extra’ space in the form of the greenhouses − 25sqm in the duplexes (only 7sqm of which is counted in the rent calculation) and 10-12sqm in the others. So far the development’s success can only really be assessed from the point of view of the private-sector residents, whose flats were completed in July 2011 (the public-sector apartments were finished in January 2012).

Light quality is unimpeeded as all walkways are located adjacant to the North-West elevation. The single-leaf organisation of units innately provides all dwellings with an even distribution of light

Most of them have made good use of their greenhouse terraces − the larger ones serving as dining rooms or cocktail lounges − and their feedback on the building’s thermal performance is highly encouraging, many reporting that they hardly needed heating at all this winter. Even on cold sunny days the greenhouses’ solar gain can be considerable, so it remains to be seen quite how they will perform in a heat wave.

031E1672__photo_S.Chalmeau_non_libre_de_droits_smallThe south east-facing facade is entirely glazed, creating a wall of winter gardens that insulate the apartments and encourage solar gain

The vertical surfaces between each greenhouse and the apartment proper form an insulating barrier, and residents are taught how to use the natural-ventilation systems. Energy-consumption figures are currently unavailable, but Boréal’s performance will be monitored over a period of five years. One thing is sure, the greenhouses pushed up the construction cost (at €1,400 per habitable square metre it was €200 above the norm for social housing), as did the footbridges and the extra facade length necessary to achieve dual-aspect front-back apartment plans, meaning that the cheapest solutions had to be sought for all the rest.

In French there is an old expression, avoir pignon sur rue (literally, ‘to have a gable on the street’), which today means having a (good) public reputation, but which originally referred to successful merchants who could afford an individual house in the dense medieval town.

The equilibrium of light and space throughout the design provides each apartment with unique properties

In the very urban context of the Île de Nantes, Playtime’s gables signify just that, while the greenhouses stand in for the missing gardens. But transferred to an entire apartment building in suburban parkland, this vocabulary becomes more ambiguous. Coupled with the allotment strips, Boréal’s greenhouse facade reads like a jazzed-up agricultural facility; but on its entrance side, painted Portmeirion style, the building appears like a row of tall medieval houses in some Disney pirate village, an impression reinforced by the garden-folly footbridges (which also distract from the cheapness of the facade detailing).

On the one hand Boréal’s gables provide a visual cue that helps residents identify their own flat from among the mass − something that can encourage the appropriation of a home one did not necessarily choose − while on the other they represent the aspiration to, although no longer necessarily the fact of, individual home ownership, evoking the little-house-with-a-garden dream that has seduced a majority of France’s population if opinion polls are to be believed.

Behind the glazed greenhouse facade are spaced filled with warmth and sunlight, which some of the private tenants use as cocktail lounges

But this individualist drive need not entirely quash the collective spirit: Playtime’s residents spontaneously got together for al fresco dinners on their treehouse footbridge, and Tetrarc hopes that, once warmer weather arrives, Boréal’s will do the same.

Fact File

Architect: Tetrarc
Greenhouse Roof: Danpalon
Wire Facade: Arval
Rubber Flooring: Mondo Sportflex
PVC Flooringt: Forbo Novibat
Photographs: Stephane Chalmeau

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