The Eco-District reinvented – Heilbronn's BUGA rewrites the rulebook

A garden town development showcase in southwest Germany reworks the idea of the Eco-District for the 21st century, bringing a palette of digital dunescapes, AI driverless deliveries and timber towers to bear.

From above – the BUGA Heilbronn 2019 site – Photo Nikolai Benner

Many a self-respecting European capital and major city feature an eco-district in its built fabric portfolio, demonstration projects and/or fig-leaves to help persuade and to project an image that they’re doing their building bit to draw sustainability into the fabric of urban living. From Stockholm to Helsinki, Hamburg to Paris, Lyon to London, you can find showcase examples of living more lightly on densely designed pockets of city land. In Britain the great ur-example is BedZED, the pioneering Zero Energy Development in Beddington, South London. The South London eco-district example is the UK’s shining illustration, still going strong after 20-plus years.

Down river from these major conurbations, Europe has literally hundreds of smaller cities and towns. They lack the kind of financial clout of the big cities but are still home to literally hundreds of millions of the continent’s urban and urbanising populations. These are places which ought to be uncovering new sustainable modes of living, working, and playing; not least in how homes and housing are organised. There are a few examples, but these are mainly old and from another time. In Britain the tail-end of Labour’s last administration promised a new era of Eco-towns, but with the 2008 financial crash the programme lost ambition, funding, and numbers. Only one of the original 20 proposed Eco-towns, in Bicester, survived serial culls and cutbacks during the subsequent Coalition and Conservative administrations. This picture, while not exactly reflected across continental Europe, hasn’t been all that different. There are a few examples to be found: Hurdal in Norway for instance, or Almere in Holland. However, the focus has shifted to co-housing in big cities. The eco-town, and its smaller cousin, the eco-district, seemed destined to be both, in idea and in practice, a wave that happened during a particular time, yet now has dissipated.

From above – the BUGA Heilbronn 2019 site
– Photo Nikolai Benner

Step forward Heilbronn, and its recently created eco-district in – naturally enough – Germany, which opened its first phase in Spring 2019 of 22 blocks within its experimental BUGA eco housing district for 800 new inhabitants. With two further phases ongoing through 2020 and 2021, and a plan to increase inhabitants to 3500, this would considerably expand the relatively small town population of 124,000 in the south-west state of Baden-Württemberg. The emergence of the Heilbronn BUGA seems to be saying, look again, the eco-district as a concept and reality may be down, but it isn’t dead quite yet.

From above – the BUGA Heilbronn 2019 site – Photo Nikolai Benner

Set close to the main station in the city centre, on old railway and industrial land, and within islands sitting on tributaries of the river Neckar, the BUGA eco-district’s 40 hectares has been remodelled and re-landscaped. It encompasses a strip of 23 buildings, facing on their western side a sizeable, parametrically designed rippling dunescape, and two small lakes – ‘to remind people of the old harbour basins’. It also includes a new upgraded protective flood-control embankment into which 500,000 of the 600,000 tonnes of the site’s groundwork materials have been deposited so that the main, man-made watercourse runs through the city. The other side of the grid shaped housing block is where the main BUGA, or to give its full name Bundesgartenschau Heilbronn 2019, garden festival took place through the late spring and summer, running alongside the main perpendicular street, re-landscaped and closed off to vehicle access. Before the road was rerouted to the far side of the Neckar, 17,000 cars streamed in and out of the city centre every day. Today it is a calm and slow front to the parkland, weeping willows, smaller trees, and grassy landscaping. It sits opposite the eight east-facing buildings, with some of the 900 trees planted to replace 230 older removed trees, landscaped terraces rising up from the channelled Neckar riverfront flowing below.

Skaio – Photo Kaden + Lager/Bernd Burchardt

During its opening, the flower festival’s entrance sat to its south-eastern edge, via a footbridge across from a small island, around which the Neckar split and ran. Just in front of the ticketing entrance another new attraction, the Experimenta Science Centre is lodged within a helical five-storey tower, designed by out-of-town Berlin big ticket architects, Sauerbrauch Hutton. There are other architectural statements. Probably the most visible of these, underscoring BUGA’s housing and sustainability message, is Skaio, a Cross Laminated Timber (CLT) housing block. At ten floors high, it is at present Germany’s tallest timber tower, designed by another down-from-Berlin practice, Kaden + Lager. Close to Skaio is a new youth hostel – a carefully scaled long, brick block, by Vorarlberg’s Baumschlager Hutter Partners, the studio Carlo Baumschlager founded after the acrimonious split of Austria’s most famous international architects, Baumschlager Eberle Arkitekten. Round on the far side of the buildings and in the algorithmic wave Campus Park, you will find two experimental pavilions of more regional provenance, designed by the University of Stuttgart’s Institutes of Computational Design, (ICD) and Building Structures and Structural Design (ITKE) team. One is comprised of experimentally produced timber, the other of a robotically spun fibre, bringing fantastical - and what’s described in the German speaking world as Bionic Architecture - experimentation to the site. There were other experimental and temporary projects – a Circular Economy upcycled information centre from Karlsruhe’s architecture school, as part of a market-type area to the immediate south of the housing. All this building was new to the BUGA tradition. The garden festivals run every two years across the country; in 2017 the run-down east Berlin dormitory town of Marzahn played host, and four years earlier, in 2013, Hamburg’s giant Hafen City complex. But up until Heilbronn municipal council’s application, there hadn’t been any precedent for a building dimension component to the flower festival.

BUGA Blockscape -  Photo - Bundesgartenschau
Heilbronn 2019/Roland Halbe

Twelve years of planning later, 144 million euros down, the Neckarbogen eco-model quarter has broken with older approaches and provided a new template in the process. The whole project has been bank-rolled by the third-generation billionaire head of Lidl, the super-market empire CEO Dieter Schwarz, who is from and lives close to Heilbronn. Through his Dieter Schwarz Foundation, the famously reclusive businessman – apparently there are only two photos of him ever recorded and he is completely unknown in public - has underwritten a variety of projects in and for his hometown. The best known and most substantial, the Bildungscampus, a large higher educational campus with links to the local HE infrastructure including Munich TU, begins just the other side of the river’s western shoreline. Focused on a mix of business management and administration, hi-tech innovation and start up entrepreneurial skills, it’s not too difficult to see the Neckarbogen as a next stage in this business-minded mix of funding sponsorship and philanthropy. Alongside some proclamations about a focus, the eco-district as ‘a new future for Heilbronn’s inhabitants’ is a stated mix of current tech plus sustainability concerns, biofuel, IT, AI, Biomechanics, and other forms of computer intelligence, woven into the eco-district.

Photo - Bundesgartenschau Heilbronn
2019/Roland Halbe

There are obvious overlaps with the German motor industry; Stuttgart, one of the beating hearts of the industry is only forty minutes away, and an Audi factory can be found five kilometres away, in the town of Neckar itself. There are literally hundreds of small and medium scaled businesses servicing the regional motor industry, so it doesn’t come as a surprise that one of the subsidiary research projects is focused on autonomous vehicles.  While visiting in 2019 a small four-wheeled pick-up buggy scurried around the site, going through tests for delivering packages and parcels.  Bicycles and Bicycle culture, however, seem to only appear in a walk on role.

The Monday before the weekend opening in April that I visited, the site was in the last frantic countdown hours with workmen in high-visibility orange huddled over drains trying to resolve one problem or another, piles of building materials sat on the roads supporting the grid of buildings, and noises clanged out from high above, as another piece of an inner fit-out was knocked into place. Still, there were four hundred people already living in some of the already completed housing, who would be joined by the planned 1500 residents moving in over the next few months.

Skaio – Photo Kaden + Lager/Bernd Burchardt

Skaio, the 34 metre ten-storey hybrid CLT-concrete housing block is partially inhabited but there is still work going on in other parts of the building. Markus Lager, the young architectural partner who walks me round, has already been on site all morning to deal with a list of last-minute issues in Neckarbogen’s tallest building. We climb the stairs negotiating wiring and taped stairwell boards to the top floor.  With almost 1500 m3 of CLT, the majority of the building’s structural body is taken up with timber, although the internal staircase sits within reinforced concrete (for safety reasons, says Lager.) Likewise, the concrete slab, into which an underground car park has been integrated. Fire, a core regulatory concern, means another safety feature are sprinkler systems throughout the sixty apartments and shared flats of various sizes and descriptions. “Regulation in Germany,” says Lager, “is quite hard and it’s a new field. It’s finding its feet in the different land (county) regulation and in public housing, but it can be complicated.”

The first two floors have been designed to be adaptable, with high ceilings, and with the option to double into two floors. There are four flats specifically for a co-housing group, the overall space totalling 230 m2. With modular prefab bathrooms and floor-to-ceiling glulam framed windows, the one, two or three-storey apartments provide a range mid-size homes and accommodation. On the ground floor is a café and a garden piazza, a small terrace garden, and access to a washing machine anti-room and public kitchens. Right at the top of the building is a further green terrace on the roof.  Lager pronounces himself happy with the result, the build time has been quick - within a year - and acoustics, which continue to be a technical headache across the CLT engineering research world, hasn’t been a problem, with the stats and physics worked on by one of Germany’s pre-eminent timber engineers, the Munich based Stefan Winter. Every outer wall is insulated. A certain amount of timber is visible on the inside, walls, floors, and ceilings left exposed, though it’s a surprise when Lager tells me that the building contains the largest amount of visible timber in Germany to-date. He also states that he’s relaxed about the aluminium façade system Skaio is decked out with.

Skaio – Photo Kaden + Lager/Bernd Burchardt

CLT’s vertical advance in Germany has been stymied by the country’s complicated regulatory regime, so arguably contrary to the perception of it as a timber leader, urban CLT and timber at scale remains rare. Unlike Austria, Norway or the Netherlands, there are no imminent super timber towers about to rise up, and only a handful of six through twelve-storey buildings either on site, or in the process of doing so. Lager’s older practice partner, Tom Kaden was one half of Kaden/Klingbell; two (then young and former GDR or East Germany) architects who built the country’s first and only contribution to the early-era timber mid-rises, the E3 in Berlin. The seven-storey central city infill housing block wasn’t even CLT, but a glue-less Brettstapel system, a yet more radical step in the ecology of industrial timber production.

Skaio adds to the German iteration of what is now international, industrial timber design. It has also placed Kaden and Lager at the forefront of what is still a small offshoot in Germany’s urban timber scene: “We’ve entered a new phase. We can say we can cope with larger projects. This though is the largest so far.” There is a timber school in Leipzig, again using CLT, and a 48-unit Berlin co-housing project, and there are yet others on Kaden and Lager’s books. Lager insists they are not ‘dogmatically using CLT’; “After entering this new level” Lager believes, “we will also enter new building types; universities, labs. It’s made timber construction possible for more people, for architects and engineers.  I’m happy with that, but also need to be very careful. The quality of construction has to be high.”

If timber is both an explicit statement and somewhat hidden from view – from the outside, it could be a steel or concrete building - Skaio is Neckarbogen’s highest-profile timber project. There is wood throughout the on-site buildings, though with not quite the same degree of industrial timber purpose. Other showcase themes step forward in the remaining 21 housing blocks - all six-storey, arranged around a set of three relatively dense and gardened courtyard plots, with the last of the three opened up with grassy space and its outer three blocks angled to run outwards, like a protective wall.

Bundesgartenschau Heilbronn 2019/Roland Halbe

Skaio – Photo Kaden + Lager/Bernd Burchardt

The mix of housing is the result of the city council limiting each participating developer to only two plots. There are up-market apartments in two private projects, with half the homes for rent, and 40% social housing (at €7 per m2), including student homes. At the far end of the site a house for single parents and their children sits in a V-shaped corner house, splitting the approach roads into Neckarbogen. Designed by the Stuttgart practice, Finkh Arkitekten with the municipality as client, the ground floor houses a nursery, and day-care centre, while the upper floors provide homes. A spacious foyer area, the day-care centre, staircases, and other public areas, are decked out in wood, white-washed and with a growing tree in the centre. The staggered entrance provides a sense of protective shelter, while externally the brown timber façade continues the woody theme. The day-care centre opens out into a playground within the open courtyard, albeit closed off by fencing to passers-by.

Finkh Arkitekten's single parents housing block - Photo - Bundesgartenschau Heilbronn 2019/Roland Halbe

Inside the single parent's community housing block - Photo - Bundesgartenschau Heilbronn 2019/Roland Halbe

The building styles are conventional, with façades using a spectrum of brick, sheet metal, plaster, and wood in various applications. There are seven hybrid wood-concrete blocks in total. Munich studio’s Fink Jocher Arkitekten which sits on the westward side, is covered completely in shingles, claims high insulation and light qualities as well as flexible floor room principles. Another of the blocks is an Aktivhaus, the alternative light and ventilation approach to Passivhaus, closely linked to the late Manfred Hegger. Recycled white and other novel concrete systems has been part of the mix, and many of the unit’s feature photovoltaics or a terraced garden on their roof-space.

One of the more interesting projects, particularly in terms of social arrangements is the Apollo 19, a Heilbronn co-housing group who had been looking for somewhere to turn their ideas into reality. The BUGA development offered them this opportunity, allowing the co-housing group working with two studios, Wenzel-Wenzel and Motorlab, to deck out the building in solar panels.

Photo - Buga Heilbronn 2019/Gaby Höss.

Consisting of 12 apartments looking westwards towards the artificial lakes and rippling grass dunes, all the living arrangements were arrived at in dialogue with the architect. The resulting design intended to respond to specific needs and ideas about how the members envisaged their lives, from a secondary annexe to age-sensitive design, each with flexible floor plans. There are community areas, such as a roof garden and at ground level, catering facilities, a kitchen, toilets, storage rooms, bicycle parking, and rubbish bin spaces, along with a café. Another timber-concrete hybrid, where both the stairwell’s core and foundations are made up of concrete, around which the units have been constructed from timber. Yet its most novel technical feature is a vertical solar energy array, in the sun’s golden colour, running up the side of the building’s façade and optimising its insulation potential, partially through its design, providing external shading. To complete the solar vision, photovoltaics have been deployed on Apollo 19’s roof.

There are other experiments and ecological design provision on Neckarbogen such as autonomous buggies and a Makerspace,  designed by Studio Inges, providing facilities to draw the Co-housing and other residents into their own make-and-re-use projects. The extent to which these have become central elements, rather than small-scale promotional devices in the larger promotion wasn’t at all clear. They did however pale by comparison to the whole festival project that drew the eye in, and directed you, if one turned from facing Apollo 19 and its blocky neighbours to look west, towards the railway liens and BUGA’s rippling parkscape.

LOMA's digital dunescape – Photo Buga Heilbronn 2019
- Photo Nickolai Benner

That park area looked, when I visited, easily the most futuristic part of the eco-district, sitting between the near and far-side lakes.  This was the clear intention with the two ICD pavilions placed within its undulating folds. By comparison, whatever their eco-credentials, their social sustainability, and their various living experiments, when you turned back to look at the housing blocks, they felt comparatively mundane, almost staid. The brainchild of Kassel studio, LOMA, a digital landscape design team led by Wolfgang Schück, with colleagues Ilja Vukorep and Wigbert Riehl, the summer island was a temporary piece of landscaping, which, understandably caught the general public’s imagination, aided by some out-there drone photography. Though distantly reminiscent of some of the late Charles Jencks’s landscape designs, there is – to my knowledge – nothing comparable currently being realised in Britain. LOMA’s BUGA dunescape, being the aberrant lovechild of digital tech cross-bred with construction machinery in the service of the kind of horticulture you’d possibly imagine practicing on Mars, that is if you were figuring out how to entertain space tourists wanting a biodome horticultural attraction. Welcome, as Schück, said in an interview, to the 21st century.

The Hafenberg climbing wall – Photo
Buga Heilbronn 2019/Nikolai Benner

With the aim of arriving at a dune and moraine-scape across the four hectares available to the LOMA team, and with clayey, sandy alluvial soil to contend with, flowering plants were always going to be challenging. A Grasshopper programme assisted 3D Rhino software, providing a digital interface with the GPS controlled excavators, guided the excavator drivers in exact centimeter by centimeter choreography of where exactly, and how much sandy earth was to be placed where. In the midst of these the two ICD pavilions fitted right in. With rivulets of sand between the waves of grassy dunes, LOMA worked with horticulturalists to create a garden landscape which was fully experimental yet appealing to garden festival audience. Play and scenography are artful parts of their practice, uber-evident from the results, which were the big hit among the visiting public through the summer.

Experimenta Science Centre seen from upstream in the Buga
eco-district – Photo SauerbrauchHutton/Jan Bitter

Beyond the alien nature of LOMA’s Summer Island, and the more easily recognisable outer lake reedbeds, are the re-engineered walls rising up to make an edge boundary to the whole site bordering the main rail line which runs deep in a man-made cutting on its far side. Here, an elaborate adventure climbing wall has been constructed partially out of the gritty recycled substrates of the main site. 15 metres tall, the Hafenberg, as it is called, provides a sound barrier for the park and housing, from the industrial area and railway lines beyond. Picnic areas and specialist habitats peaceably vie with climbing frames in the vertical playground. My press guide for the visit, Doris Kircher, noted just how little rainfall there had been in her part of Southern Germany over the last few summers – this is a continental climate after all - and that temperatures regularly hit 40 degrees. The lakes are there to act as water reservoirs as well as for their cooling capacity. In the couple of years since, drought and flooding have only increased, bringing natural disasters and worldwide attention.

Compared to the LOMA landscape at the edge of the BUGA site, the Experimenta Science Centre felt positively 20th century. Perhaps due to the organic nature, the wispy willows and flowing water on the one hand, and organic machinery of ICD and the parametric landscape on the other, but I couldn’t help feeling that Sauerbrauch Hutton’s helical spiral building, technically complex though it might be, was from a different time, and by a number of metrics. The well-heeled Science Centre had originally opened in 2009 in an old concrete mill building, the conversion by another smaller Berlin firm architects, Studio Inges. The competition for a standalone reboot of the centre was then won by their Berlin counterparts in 2013.

Experimenta's Interior
- Photo SauerbrauchHutton/Jan Bitter

The building’s helical structure involves making each floor rotate a notch, up to the fifth-floor roof, where there’s an observatory and auditorium.  The building’s first layer includes a long spacious arrival foyer and a ground floor restaurant, organised around a steel frame central shaft. There’s a focus on lightness and transparency, the pale external glazed façade transforming colour into a glowing night-time light art spectacle, likely at the single flick of a computer switch. Inside the complexity of the structure is such that the inner core is comprised of huge steel I-beams and other structural girders, holding box-like bays that float in the building’s central void, inside of which are much of the various exhibitions, linked and joined together by aerial corridors. The complexity of the geometry, using parametrics to optimise the form, helped rework the mathematically complicated volumes to optimise and lower the number of mathematically complex columns. Hidden trusswork in the rods holding the bay platforms enabled the Sauerbrauch Hutton architects and their engineers, Schlaich Bergermann Partners,  to reduce the cantilever’s structures potential volumes down to a total of seven columns.

Photo SauerbrauchHutton/Jan Bitter

Designed with a local audience in mind, for the first eight months of its public life, the relaunched Experimenta acted as a gateway for the garden show, close to BUGA’s main ticketing entrance. Though missing the Sauerbrauch Hutton’s signature colour ribbon façade-work, the studio’s obvious interest in light, colour and technology is present in the (relatively) small town-wide helical spiral landmark. Yet, almost by dint of proximity the showcase feels out of time and out of kilter with where contemporary architecture, in Germany and elsewhere, has been heading since the 2008/9 economic crash. A member of what was once called Germany’s SuperGreen architectural movement, alongside the likes of Christoph Ingenhoven and Thomas Herzog, Sauerbrauch Hutton are part of the German architectural Vorsprung durch Technik establishment. Their starting point is that technology is the answer to the environmental crisis. Aside from asking whether such interpretations are looking through a narrow lens, there’s also the question of which technologies? There are multiple versions. Once across the bridge and in the Neckarbogen housing blocks, you see a much less involved, increasingly mainstream, yet equally technical architecture, much of it based on industrial timber-concrete hybrids. The extent to which the last fifteen years of influence towards simpler, more immediate, and lower tech approaches (through practices of ZRS-Arkitekten, the Vorarlberg school, and in the background the likes of Peter Zumthor) may not have had a major influence on much of the DACH countries building sector. However, it has underlined how the likes of Sauerbrauch Hutton and their SuperGreen confreres, increasingly feel bound by a particular, and now past, moment. And then also, beyond the Neckarbogen housing there are the further edges of the high-tech world’s collisions with different aspects of what in Germany is known as the Organic Architecture tradition; ICD is considered the CAD heirs of Frei Otto, and LOMA are fusing horticulture with digital precision and algorithmically-driven design. Yes, all these are technological expressions of built form, but they also feel worlds apart.

This said, Heilbronn is a town that owes its prosperity to the high-tech world of the Baden- Württemberg industry, not least it’s car industry. It is impossible to disentangle the two. And compared to other German eco-districts, particularly regional examples like the Tubingen Sudstadt or the ur-example, Vauban in Freiburg, Neckarbogen is a distinct and sizeable move away from these older models of sustainable urban living, as much as building on them. As it is, though wholly conventional in many respects, coming away from my whistle-stop visit it felt as if different aspects of the recent 21st century threaded through the BUGA experiment. I couldn’t help wondering if what I’d experienced in Heilbronn was opening a page onto the first stages of very different types of possible eco-districts and ecological living. One which is as informed by the last twenty years of digital experiment as it is by the social experiments of the last fifty - the husk of the old school eco-district containing the seeds of the new, so far untried and untested, but with horizons wide open. 


Travel and accommodation for the visit to the project was supported by Buga Heilbronn 2019

Photo Buga Heilbronn 2019/Photo Nickolai Benner