‘Invisible’ 11-year retrofit of huge Geneva housing estate nears completion

Retrofitting Le Lignon has been a huge task of forensic detail, negotiating a multitude of tight spaces in its original design. Each intervention is surgically fitted, with little wriggle-room, the task made downright epic by the sheer scale of the building. Sitting on a bench with detail drawings on our laps, families rambling past, architect Jean-Paul Jaccaud gestures towards the wall of apartments and describes the challenge: ‘You’re kind of navigating between the millimetre on the detail and the kilometre on the building.’

Le Lignon is one of the largest residential buildings in the world, its jaw-dropping 1.1km extent born out of a housing shortage in Geneva in the 1960s. Architects Georges Addor, Dominique Julliard, Louis Payot and Jacques Bolliger designed a satellite city of dual-aspect apartments in the outskirts of Vernier, a rural setting along the Rhône that saw a behemoth of prefabricated concrete and curtain wall rise between 1963 to 1971. Built on a slope, Le Lignon’s footprint splits into two tower blocks of 26 and 30 storeys at the site’s lower end, appearing level with the snaking bulk of a 12-18 storey ‘wall’ that pivots across the site. Walking it takes 15 minutes, passing grocery stores, kiosks, a brasserie, a hospital, a post office, churches, even a local school, all enclosed by the relentlessly democratic wall of apartments – identical despite varied ownership, including social housing (35 of the 84 parcels). People like it here. It’s not uncommon for apartments to be kept across generations.

Formed at the same time as the building, the Comité Centrale du Lignon, with residents as members, manages all 2,780 dwellings, landscaping and maintenance. In the past 12 years some 7,000 Lignonais have undergone the complex and ongoing retrofit of the entire residential block by Jaccaud Spicher Architectes Associés (JSAA).

In 2009 Le Lignon’s deteriorating aluminium and timber curtain walling system was officially listed by the Geneva Heritage Authorities. Then new thermal building regulations led to an academic study of Le Lignon by the Lausanne Federal Institute of Technology’s  Laboratoire des Techniques et de la Sauvegarde de l’Architecture Moderne (TSAM). The outcome was an extensive report to improve the building’s performance, including a prototype façade. By 2011, both the study and JSAA’s commission was finalised, appointed by Le Lignon’s stakeholders (a consortium of eight, including the Comité, pension funds and housing associations) to take over the retrofit and refurbishment.

The result is a gentle series of interventions, all resolutely quiet and almost indistinguishable when seen from outdoors. ‘We didn’t want to have any trace of demonstrative design, any sign of being overly visible, of even showing any modifications,’ explains Jaccaud, and describes the changes applied throughout Le Lignon as an ‘invisible cloak’. Moving on from the academic study meant addressing practical details, such as fire regulations, while also assessing damage in every unit.

 

 

Reverential towards the original design, the interventions were, in Jaccaud’s words, ‘very surgical, pinpointing where we had to intervene; and the rest was left untouched’. Retrofitting began with a real-life prototype, Bloc N. 49, whose owner selected 24 apartments to trial new materials and have their inner timber façade replaced, incorporating new windows with double glazing. At the same time, the listed aluminium wall was cleaned with a gentle acid solution and the glass polished. The curtain wall is so thin that tolerances to refit new profiles were ‘virtually nil’. Jaccaud describes ‘fighting for millimetres in terms of the frame and then repeating it 10,000 times’. Working inside-out, formica kitchens were replaced with metal ones, new toilets and pipeworks installed and interior glazing separating rooms replaced.

While the completed Bloc N. 49 was being monitored for 12 months to check its energy performance, blanket planning permission was obtained for all units with private ownership. A second layer of permission was needed from each owner to officially sanction construction in every apartment. Flexibility in the arrangements allowed several owners to unite into a large group so that a tender could be prepared for the bulk of Le Lignon as one operation. Later on, one of the two towers let a second contract. Alley by alley, walkways, entrances, inner façades and apartment rooms were methodically consolidated, each space thermally updated for each of the residents, who were able to remain in their apartments throughout the process.

Common spaces underwent careful updates. Jaccaud says the aim was ‛to give the impression that the buildings are well-maintained, that they haven’t been refurbished’. Shared hallways are unfussy – freshly painted, new lino floors, new skirting and fire doors lining up with the original mahogany apartment doors, square handles refitted. A photograph of dolphins straight out of a 1990s waiting room hangs in one, a reminder that the architects chose not to intervene a step further than necessary.

‘The aim was to give the impression that the buildings are well-maintained, that they haven’t been refurbished’

Downstairs, inner porch doors have been added to create a new thermal boundary. Old radiators were removed, reducing shared energy costs. Some salvaged materials have also been repurposed, in particular mahogany, a surprisingly precious timber used in the project’s original design. All panels have been sanded and revarnished, with spare boards shifted to replace damaged ones. Mahogany fragments have quietly made their way into regulatory changes; in a hallway Jaccaud holds open a new proprietary fire door to reveal a lip of mahogany running down its edge so it fits into a frame put in place 50 years ago. 

 

 

Like scientists avoiding contamination, there is among the architects an almost obsessive wish to disappear from the refurbishment. Marble walls in the entryways are cautiously sanded; fresh layers of olive-grey paint chosen after a scratch analysis determined the original colour of existing walls. One of the most painstaking details was the insulation of top corners of apartments under walkways from cold bridging, where, in an effort to keep the balustrade at the same level, NASA-grade aerogel insulation was inserted in the tiny gaps. Jokingly described as ‘forensic fiddling’ by Jaccaud, the buffing of each material surface gently envelops the giant building like a thin blanket of care, only visible if you know where to look. One inevitably thinks of similar post-war buildings in the UK that could have been afforded such chances. Robin Hood Gardens was erected a year after Le Lignon and demolished during the second phase of Le Lignon’s renovations. Poor maintenance, avarice, and neglect by political and market forces capitalising on land paid scant regard to the value of its architecture.

Despite fierce loyalty from its residents, Le Lignon isn’t immune to weaknesses. Its elevated walkways, iconic of the building type, have been divided due to security risks. Fires and vandalism are ongoing concerns; debates about installing a police station were held recently. And the retrofit remains to be applied throughout the entire complex, with the cantonal owners of the social housing portion yet to invest fully in the works. I’m told it’s only a matter of time until this part catches up, as the partial renovation isn’t complying with thermal regulations by only updating minor parts such as the walkways.

Looking up at the varnished mahogany panels on Bloc N.49, it’s hard to call the retrofit anything short of ego-less. ‘The biggest compliment you could give us is to say you don’t have the impression that an architect has come through here,’ says Jaccaud. He is showing the new doors when an older resident bustles past, peering at us gawking at the timber frames. ‘Vous admirez notre belle résidence?’ she asks. Although half her face is masked, she beams before passing along a marble wall, faded but softly shining, and disappearing.
Sabrina Syed is an architectural designer and writer on architecture

 

 

Architect’s view

Built between 1963 and 1971 by the architects Georges Addor, Dominique Julliard, Louis Payot and Jacques Bolliger, Le Lignon is the largest residential complex in Switzerland, a satellite city boasting a total of 2,780 individual dwellings alongside a school, shopping arcade, medical centre, church, recreational space and urban farm with allotments. It is located on a sharply sloping site on the banks of the Rhône on the western edge of the city of Geneva. Built to address a housing shortage in the 1960s and early 70s, it continues to accommodate approximately 7,000 residents (a significant portion of Vernier’s 34,000 population), to this day.

JSAA was commissioned in 2010 by a consortium of eight of Le Lignon’s main stakeholders – including pension funds and housing associations – to rehabilitate large sections of the building, improving its comfort and energy efficiency to meet Switzerland’s new thermal performance building standards. Despite the complexity of ownership, the consortium was driven by a sense of responsibility to maintain the unity and identity of Le Lignon, appointing the practice to oversee a holistic and phased renovation framework to reinforce the unity between the different parts, which had diminished as a result of ad hoc, intermittent maintenance.

The practice was asked to devise a strategy in response to a research study into the required repairs undertaken by the TSAM laboratory of the Federal Institute of Technology, Lausanne, under the direction of Franz Graf and Giulia Marino.

The key elements of the renovation include conserving the outer aluminium and glass layers of the curtain wall façades and replacing the inner timber layers of the interior.
Jean-Paul Jaccaud, partner, Jaccaud Spicher Architectes Associés

 

 

Engineers’ view

An initial study by the Laboratoire des Techniques et de la Sauvegarde de l’Architecture Moderne (TSAM) had identified solutions for the thermal improvement of the buildings at Le Lignon that retained the heritage value of the whole.

The aim of the refurbishment was to comply with the Geneva canton’s energy requirements, SIA norm 380/1 2009. The thermal strategy involves increasing the insulation of all vertical façade elements to ensure a strong reduction in heat loss in winter and enhancement of solar protection with thin blinds between the layers of the façade in summer. The insulation had to fit within the existing thickness of the façade elements, reducing the possible thickness to 80mm. Rockwool has been used to achieve an overall thermal transmission U-value for the renovated façade of 0.62 W/m²K. Extract ventilation units have been placed in the bathrooms at the centre of the plan and trickle ventilation slots have been introduced in the timber frames.

The entrance halls were originally heated and the large areas of single glazing were causing very heavy heat loss. To counter this, an additional thermally insulated double-glazed door was introduced to separate the stairs and the lift from the main entrance hall space. Heating was removed from the main entrance areas and the existing large single-glazed units have been preserved.
Alexandre Buclin, Buclin Ingénieurs-conseils, and Mathias Blanc, Effin’Art Sàrl

Working detail

 

The typical façade refurbishment detail takes into account an intervention from the interior of the building to replace the inner timber layer of the façades, leaving the exterior aluminium and glass layers intact. This approach enables a significant thermal performance enhancement of the façades while leaving the exterior appearance virtually unchanged.

The inner timber single-glazed windows are dismantled and replaced with new timber-framed double-glazed units of 4/20/4 glass with a U-value of 1 W/m²K.

The new frames require very accurate fitting onto the openings in the curtain wall and the size of the timber window profiles are custom-made to fit within the very tight section of the existing frames. In the void between the outer aluminium layer and the internal timber one, very thin DVKL aluminium blinds are inserted, matching the dimensions of the original fixtures.

The spandrel panels are also refurbished with the replacement of the original 30mm thermal insulation with 80mm rockwool (λ=0.03 W/mK). The insulation is protected with layers of plasterboard fitted tight onto the subframe. Existing radiators are moved 10cm toward the interior of the apartments to avoid contact with the newly insulated panels.
Jean-Paul Jaccaud, partner, Jaccaud Spicher Architectes Associés

 

Project data

Start on site  December 2009
Completion  2021
Gross internal floor area  10,910m²
Construction cost  £70,850,000 (CHF 94,124,000)
Construction cost per m²  N/A
Architect  Jaccaud Spicher Architectes Associés (refurbishment)
Clients  Anlagestiftung Pensimo, Bellerive Immobilien, Comité Central Du Lignon, Immobilien Anlagestiftung Turidomus, Imoka Immobilien Anlagestiftung, La Fondation HBM Camille Martin, La Rente Immobilière, Marconi Investment
Façade engineering  BCS Façades
Mechanical & thermal engineering  Effin’Art Sàrl, Buclin Ingénieurs-Conseils
Structural engineer  ESM Ingénierie
Main contractor  Losinger Marazzi
CAD software used  ArchiCAD
On-site energy generation  Nil
Overall area-weighted U-value  0.62 W/m²K
Predicted design life  40 years