Set against the silhouette of banal housing developments, the new congress centre has an almost surreal character. This abstract, free-standing sculptural object is visible even from the ring road and is linked to the city as an events centre for the nearby trade-fair grounds. Twelve years were to pass between the competition and the opening of the centre on account of the economic crisis in Spain, numerous budget cuts and planning changes. For four years, the structure stood almost complete without being accessible to the public. Even so, it has lost none of its vitality.
"Today, there are so many applications to view the centre that we have to employ more staff," explains Cristina Cano, who is jointly in charge of the programme and heads operations. "Only recently, we welcomed 5,000 participants over a single weekend to a tourism congress." The curiosity of passers-by, who are attracted particularly in the evening by the illuminated volume, is not disappointed; because what from outside looks like a compact volume reveals itself internally to be a spatial wonder with seven different levels, so that it appears to be much larger and more complex than it really is.
The main attraction is a spiralling promenade architecturale that winds its way round the structure between the translucent outer skin and the halls via ramps and stairs, affording glimpses of the spaces inside and out through bullseye windows and all-glass facades. At the same time, separated from the outside by only the thin Etfe membrane, visitors have the impression of moving in the open air. This route full of surprises begins at the edge of the public pavement, where the site falls away by 17 m and a bridge leads over the depths into the foyer, a 10-metre-high space that penetrates the building volume and emerges at the other end on to a balcony with a view over the landscape.
From here, a shallow ramp leads down to a platform in front of the auditorium. This hall, with seating for 800 persons, is entered at the rear end - the highest point. From here, the eye is drawn down over the steeply inclined rows of seating to the glazed rear wall of the stage 11 metres below and to the rocks at the back. When the stage is illuminated, people outside have a reverse view into the audience. The cost-related low spatial height means that the acoustics of this multipurpose hall are not quite up to the standard of a concert hall. On the other hand, when the auditorium is used as a theatre, the funnel-shaped acoustic reflector over the orchestra can be removed, so that the stage is then open to the 18-metre-high flies. Up to a height of 11 metres visitors have access to other spaces from the foyer, whereby they pass internal seminar rooms and exhibition areas as well as the cafe-foyer and a multipurpose space with ample views out through glazed slits and bullseyes in the ceilings and floors.
In addition to the spatial qualities and the "distorting mirror" between inside and outside, what makes this a tour of discovery is the surprising yet functional use of the simplest of materials. That begins with an orange-coloured artificial lawn on the steel entrance bridge to prevent people slipping. This is also used on the walls of the auditorium as a carpet-like covering and acoustic absorber. Knopped formwork mats to the white-painted concrete walls lend the material a rough yet friendly appearance as well as improving the acoustics in the ambulatory areas and creating a haptic quality. The mechanical services are playfully accommodated. An unclad orange ventilation tube in the foyer, for example, also serves as a long bench on which to sit; the numerous bullseyes were formed with spiralling tubes or incorporated in the concrete as permanent shuttering; and reinforcing steel painted in bright colours was used for handrails and clothes rails.
Surprising built forms, bright colours and unconventional details with simple materials are the trademark of selgascano. At the very latest with their multicoloured Serpentine Pavilion in London in 2015, José Selgas and Lucía Cano have achieved international acclaim.
On seeing your congress centre in Plasencia for the first time, a lot of people ask themselves what this form is. What is the reaction of the local population?
José Selgas: Since the opening, it has been very positive. Now that the people can also experience the internal spaces, many are thrilled to bits. That was quite different during the construction phase. After the structure had stood there for four years - with a finished outer skin - prior to its opening, we were sometimes asked when we were going to remove the outer plastic film so that one could see the building. That wasn't meant polemically either. During the first years of construction, a genuine hostility developed. Just imagine: the whole of Spain is caught up in a crisis, and then people believe money is poured down the drain on a project like this. Our main task, therefore, lay in persuading the politicians and the general public to continue with the scheme.
And how did you manage to do that?
JS: By sinking construction costs by means of optimizations made jointly with the client. At €17 million, this is one of the most reasonably priced structures of its kind.
If you had to swallow so much criticism at the outset, how were you able to win the competition with your design in 2005?
JS: The site is situated in an area of new developments on land that had been artificially levelled - in other words, where the wonderful landscape with its lightly rolling topography had been destroyed. All the other competition participants extended this platform further into the natural environment and designed some monument on top of it. We decided to respond not to the banal surroundings as our context, but to nature. By stacking the spatial programme vertically, we were able to minimize the area given over to a foundation slab and thus restrict the despoilment of the ground. Our concept was far more economical than the platform solution, and so this was recommended for implementation.
With the first scheme we realized, we learned one thing: namely that the only important aspect of architecture is its economic efficiency. If one can work intelligently along these lines, one will be in a position to create architecture in a project with an extremely low budget.
In those days, as a young practice, did you have enough experience to implement such a complex project?
JS: We were already 40. Our first building, the congress centre in Badajoz, was nearing completion. There, the auditorium is integrated in the former bullfighting arena in the bastion of a fortress. That's why it has a round shape. Our client, by the way, was also the same as in Plasencia. A year before Plasencia, we had won the competition for the congress centre in the harbour of Cartagena. There, the row of rectilinear blocks echoes the typology of the surrounding harbour buildings, and internally, we designed a kind of beach in place of the former sandy beach that had existed there earlier. We were intimately acquainted with the construction task, therefore.
Did you wish to find a new architectural form for your third congress centre that would differ from the previous ones?
JS: One of the principles we have stuck to over the years is to approach our projects without any predetermined design intentions. We are completely detached when we start and let the various influences work on us - through the site, the budget, or the construction process and materials. For Plasencia, the design came about almost on its own. Every auditorium has more or less the same section: this is predetermined by optimal sight lines. In this case, the hall is narrower and the rows of seating are somewhat steeper in order to reduce the overall volume. We stacked the other functions on top of the auditorium - and so the main parameters were defined.
What is so special about the structure in Plasencia?
JS: The open quality that is able to accommodate all kinds of functions. Congresses can be held here as well, of course. That is guaranteed by the financial framework. But in view of the great competition between congress centres in Spain, we wanted to create something unique: a versatile spatial ambience that would tolerate a much broader range of activities, such as one is not familiar with today. In fact, only now are the operators in the process of finding out what programme they should best plan for their new building. It might be art exhibitions, performances or even a discotheque.
Your architecture is highly individual. What are the sources of your inspiration? Not only that, but how do you manage to implement all the unconventional details on site?
JS: We draw inspiration from many sources that lie outside architecture. After all, we are not building for architects, but for the people out there, and they can often judge a building better than certain experts. What people don't understand, however, are the flat grey concrete walls so beloved of architects, and that is why we don't construct them. We accept commissions only where we have full control over the building, from the concept to the details and above all over the entire construction process. Often we pick up interesting ideas from firms, and we work these into the design. We devote special attention to the load-bearing structure, because we leave the structures of our buildings visible - either directly or through the skin. In order to retain these qualities, we don't want to get much bigger as an architectural practice. Instead, we have our own people on every site, as in London, Lisbon and Los Angeles at present.
How may one visualize the division of labour between you and your partner, Lucía Cano?
JS: Our office is so small that everyone does everything. Often assistants change projects when their own ones don't move forward at a particular point. As a result, we always have a lively exchange and question our own decisions.
A quite different question to end with: what happened to your Serpentine Pavilion in London, dating from 2015?
JS: It really is being built up again, this time for the Los Angeles County Museum of Art. We would have liked to be able to keep the original structure, of course, but the transport costs would have been more than those for a new building. We were, therefore, able to use a much better membrane material than in London.
" "I don't think we would ever have invented anything. We don't even try to invent things. Much more important is that we allow ourselves the greatest possible design freedom."
The demands made by the architects of the structure and the skin seemed simple at first. The building was to be in contact with the rocky ground over as small an area as possible. Just two parallel reinforced concrete walls rise to a height of 26 m from the foundation slab. Intermediate floors, ramps suspended on the outside and the broad cantilevered area beneath the auditorium are constructed with steel sections. The skin was meant to veil the inner structure, yet leave it recognizable. The skin acts as a means of weather protection, as shading and to scatter the lighting after dark. A single-layer Etfe membrane 0.25 mm thick was chosen. As thermal insulation to the air-conditioned circulation areas, this outer membrane was complemented with single-layer glazing over the intermediate storeys to form a double-skin facade. To retain the desired properties, the membrane is white and coloured green in the lower areas, with a light transmittance of 29 percent. With an average temperature of 25 °C in July, Plasencia is not as hot as the provincial capital, Cáceres. The architects wanted large membrane bays of up to 12 × 8 m. Normally with such dimensions, diagonal steel cables would be welded into the membranes, so that in the event of great wind loads and temperature changes, these do not sag as a result of stretching. But for design reasons, selgascano rejected ideas of laying diagonal cables over the facade construction as well as in the plane of the membrane. A different solution had to be found that would keep the skin taut: despite the great temperature differences between day and night, summer and winter, the material was prestressed to its technical limits. In addition, the firm responsible for the construction suggested executing the large bays not flat but with a slight double curvature. This resulted in a geometric pretensioning that - together with specially developed edge sections - creates greater stability.
The surfaces are, therefore, concave in form, which lends the skin an attractive distorting-mirror effect and softens the angular severity of the volume. In some bays, the membrane was omitted, so that an unfiltered view out through the panes of glass is left free. On the viewing balcony and in the plinth zone, one emerges into the open air. Playful elements like the green plastic net over the stage window or the round toilet mirrors that shimmer through in the darkness are additional attractions in the building skin.
