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Sustainable School by Lucien Kroll (Caundry, France)

One of the most rigorous programmes ever devised ensured that this French school is environmentally appropriate in multiple ways. It has many lessons to teach.

Originally published in AR January 2002, this piece was republished online in February 2012

The new Lycee at Caudry near Cambrai in north-east France involved the most stringent design and construction ecological competition yet for a school in France. All aspects were considered: running energy, embodied energy, lighting, environmental quality, rainwater, sustainability, toxicity of materials, long and short term pollution, potential re-use and recycling, even waste management on the building site.

A government department called HQE (Haute Qualite Environmentale) prepared a table of 67 performance criteria, and competitors were invited to bid for the minimum environmental load they could achieve. If awarded the contract, they might stray outside the figure for this or that item, but would have to make up the loss elsewhere.

Adding all together they were obliged to meet their chosen figure, with a financial penalty imposed for every point in which they fell short. Performance was to be measured on site after completion, so predictions had to be accurate. Main contractor Caroni-Sogea took, as Kroll put it, ‘mad risks’, but the figure was achieved. An enormous amount of research and technical work had to be done, different aspects of the design being shared between Kroll’s office (A. U. A. I. Brussels), a second architect’s office Quatr’A of Lille, and three offices of technical consultants, Tribu, Sodeg and Alain Bornarel.

Kroll stresses the need for a holistic approach, drawing no hard lines between physical and psychological issues, cultural and technical ones, or between the well-being of the individual and that of the planet. These concerns interact in complex ways, so stringent energy demands were not allowed, for example, suddenly to dictate the whole design of the school as with tile famous glass wall at Wallasey, or with a huge hemispherical form for minimal surface area. Rather,

Kroll went for his usual complexity and differentiation, and it makes the story complicated. The ecological design affects the form, but in ways not obvious at a glance. East-west alignment of both main teaching blocks is perhaps the strongest move, which gives them north and south faces. Southern exposure is needed for maximum solar gain, but is also more manageable with shading devices in summer because the sun is high. It is important too for the ecological concept that the linear blocks have a shallow plan-depthfor daylighting.

Ecological design also profoundly affected landscape treatment, with green roofs, newly made ponds to the east, and a hillside to the west. Roof strategy was to grow vegetation on all low-pitched or flat ones not paved for access. This increases insulation and avoids the need for surface treatment, while the vegetation absorbs rain like a sponge, reducing or at least delaying run-off.

AR 1992 January – Ecological School, Kroll 1

It also increases the biomass, replacing lost ground with more CO2 absorbing plants, though oddly this item was missing from the French bureaucrats’ list, but Kroll did it anyway. The ponds, besides being wildlife habitats, are reservoirs for the rainwater system, supplying water for flushing lavatories and absorbing excessive run-off that could cause flash floods elsewhere.

The low hill, another ecological habitat, shades the building from the west the most difficult side for unwanted solar gain. It also absorbed all foundation soil from the site, so none needed to be carried off (so transporting energy) or dumped elsewhere (generating pollution).

As in earlier projects (see for instance AR March 1987), Kroll considered that the school should be a group of buildings rather than a single monolith, and that the parts should have recognizable identities. The complex shows both that it houses a varied community engaged in many tasks, and that it is in itself a small city. Excessive scale and long labyrinthine corridors were avoided by focusing the whole institution on a single central court, open to the public but using the administrative offices as a gatehouse for symbolic control.

Paved as the main concourse, the court was ordered in the traditional French way (for ‘those who love order’, Kroll says) with a grid of plane trees for summer shade. Glass canopies along the’ edge provide shelter for pupils moving from class to class. North of the court is a linear block for general teaching which ends to the west in the specialized arts tower with its cascading roofs.

Opposite is the largest block, used for teaching technical subjects: Sciences, laboratories, workshops. In the most publicly accessible corner north of the entrance are assembly hall and information centre (library and IT). The pointed building to left of the entrance is the pupils’ common room: In the most protected position centre rear of the court is the vulnerable infirmary, an in the north-west corner the school restaurant and kitchen.

Going against the rules of the original Competition, Kroll persuaded the municipality that Staff accommodation should extend an existing housing street to the south-west, integrating them into the local community. In keeping with the principles of his earlier work, there was user participation as soon as the competition was over when, as Kroll put it, the ‘cold skeleton’ of the competition programme could be ‘fleshed out’ in discussions with teachers. While this resulted in no major changes of layout, there were many developments in detail.

Most classrooms are conventionally rectangular and set in linear ranges conditioned by daylighting. Social spaces for larger groups such as the library, assembly hall and restaurant have more complex polygonal forms with faceted roofs. This differentiates them visually and spatially from the other parts, but they are also more centralized in form. Polygonal shapes allowed development of semi-separate bays - for example in the library- which break down the scale of the whole into sub- appeared for electric constituents being drawn from a spaces ‘owned’ by smaller groups.

Small variations of shape and angle make each corridor and staircase individually recognizable, removing the anaesthetizing effect of repetition, and improving sense of place. This is ecological planning in a psychological sense.Spatial variety is accompanied by a wilful variety in visible construction techniques typical of Kroll, whose aim is to use everything in the catalogue. In this case, though, techniques and materials all had to run the gauntlet of ecological scrutiny, avoiding high embodied energy, journeys to the site of more than 200km, toxicity now or in the future and other harmful effects, but still a range was possible.

The high energy input of the zinc-clad administrative block could be balanced, for example, by larger areas of untreated larch shingles, the most energy-efficient and sustainable cladding used, with a life of 30-50 years. Under such tight scrutiny, materials had to be chosen with care. Plastics were as far as possible avoided, but PVC inevitably appeared for electric cables and some plumbing pipes.

AR 1992 January – Ecological School, Kroll 2

Recycled paper (Warmcell) was employed for the main insulation, 150mm thick for roofs and180mm for walls, generally applied outside the main structure. This pushed thermal loss down to 0.25 W/m2/per deg C, but only with ‘fanatical’ attention to continuity at eaves and corners, and with stringent elimination of cold-bridges.

Potentially harmful solvents in paints and glues had to be avoided, both for the health of the construction workers and that of the children and staff. Linoleum turned out to be one of the most desirable flooring materials because it is 86 per cent recyclable, but it is a bit hard acoustically. Structurally, timber was used as much as possible, in laminated beams for large spans, but concrete was needed for fireproof and ground-based parts, and also for thermal mass.

A large part of the embodied energy load, this could at least be reconed a local material, all its constituents being drawn from a short distance. Window frames were of softwood, though with added aluminium trim on the exposed heads and cills to extend its life: again a high-energy material used very sparingly.

Only when environmental costs are highlighted in this way are so many aspects of normal practice made so questionable. Great efforts were made with lighting, heating, and ventilation. An ambitious aim was to make the classrooms fully daylit, but even a complete side wall of glass allows a daylight factor only of 3.5 percent at the back of the room.z

To get satisfactory light levels throughout, further daylight was introduced from the corridor side via clerestoreys, the corridors being given glass roofs. Such a large glazed area threatened excessive heat loss, so high performance double-glazing units were used, with an air-gap of 16mm and heat transmission down to 1.39 watts/m2/deg C.

Inert gases in the cavity had to be avoided because of their embodied energy costs. South-facing classrooms required solar protection and, to maintain daylighting, horizontal visors were designed to act as reflectors, bouncing light up on to the ceiling. As short-stay spaces, the glazed corridors could be allowed more temperature variation, used as solar-collectors, even solar chimneys to aid the ventilation system.

For a typical classroom block, air is drawn from some metres away through pipes buried a couple of metres underground, which cools a few degrees in summer and warms in winter. In the basement, input air exchanges heat with outgoing, then it is admitted to the classroom’s outer side.

From the inner side it passes to the corridor, rising to extract at roof level, and in winter fans return it to the basement heat exchanger. As with other services, performance is controlled electronically, electric fans cutting in when the natural effect is too weak. The artificial lighting too is computer controlled, turning on as daylight fails, but also turning off after a few minutes if no movement is detected in the room - when it comes to saving energy, every little helps.

In the upper corridor of the administration/entrance building a more ambitious solar chimney protrudes from the roof, doubling as a rhetorical entrance tower. Venting itself by convection in the summer, it is fan-assisted in winter.

A modicum of active solar collection was included. Most significant is a large water-based collector on the kitchen roof, which pre-warms water for the kitchens and lavatories. Aided by a heat pump, which raises it to a usable temperature, this device accounts for about half of the hot water energy. There are also 120m2 of photovoltaics on the south roof, which provide around 4100 kilowatt hours of electricity a year, or around 11 units per day.

AR 1992 January – Ecological School, Kroll 3

This would run a one-bar electricfire for half the time, or 25 x 20 watt lightbulbs continuously. With mains electricity at round 5 pence a unit you can see why the payback period is currently so unrealistic. Waste produced on the building site means both energy loss and pollution, so at Caudry it was carefully regulated, all stacked in separate heaps for recycling.

Waste liquids and wash water were also controlled. Entrants to the competition were even expected to produce calculations for the long-term destiny of the site, so not only was the recyclability of the building materials taken into consideration: test designs were made for conversion.Most of the school was tested in a model for conversion into housing. The larger-scale technical teaching areas were conceived as a Lace Museum, celebrating a local craft.

Always political, always outspoken. Kroll has pursued a career of polemical projects that seldom reached as far as he wished. His first great participative scheme, the Meme student housing on the edge of Brussels, involved user participation to produce a complex differentiated form in conscious reaction against the adjacent system-built hospital.

The hospital and other buildings of its kind represented for Kroll a technical or military kind of dictatorship: impersonal, alienating, and unforgivably top-down as opposed to bottom-up.

Appointed as architect in the wake of events In May 1968, he devised a complex interactive design process based on a cumulative physical model, and produced a chaotic building form, which thrilled or shocked the architectural world, depending on one’s point of view. It questioned the ’60s tendency that architecture need express no more than the logic of the assembly process, and so seemed aggressively anti-rational.

Yet ironically, Kroll was a rational operator, using a Habraken-based module to coordinate construction. He remained in his own way systematic, even becoming a pioneer of CAD, and now he has pioneered the most comprehensively researched of ecological buildings: much rationality, much work.

His concern for continuity of landscape - and for the planet as a whole - as opposed to the hateful ‘selfish’ or even ‘autistic’ object, is clear. His latest book is called Tout est Paysage: ‘All is landscape’. Yet a recognizable Kroll style has emerged with its own signature elements, and many readers will recognize a Kroll building before they see an ecological one.

It reflects his bid for complexity: even complexity for complexity’s sake, and it is undoubtedly artificial. His argument has always been that artificially provoked complexity is better than militaristic simplicity, because it plays a catalytic role, standing in for a complexity which in traditional settlements developed naturally over a long time.

As he once observed, to paint your door a different colour in a long row of identical doors takes an act of courage, but to add your colour to an already varied row is natural and straight forward.

Architect: Lucien Kroll
Location: Caudry, France


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