Dry stone, a contribution to the sustainable development of the territories

novembre 2019

Le Collectif Paysages de l’Après-Pétrole (PAP)

In order to ensure the energy transition and, more generally, the transition of our societies towards sustainable development, 40 planning professionals have come together in an association to promote the central role that landscape approaches can play in spatial planning policies.

In this article, Claire Cornu, architect and landscape gardener, draws our attention to the role of traditional dry stone structures in the landscape.

This masonry technique, this universal and timeless architecture of gathering, used to build and maintain the terroirs, is now recognised by UNESCO and the European Landscape Convention for its contribution to the environment and the living environment.

Uses, assets and perspectives.

Dry stone, a contribution to the sustainable development of the territories

The uses of dry stone

Dry stone architecture is a technique that requires the control of the choice of stones and their assembly in order to ensure the long-term stability of the structure. Traditional agriculture is skilled at employing all the components of the geographical environment. Thus, for centuries and all over the world, man has satisfied his needs from the natural elements. By spying on his fields, the farmer collects the stones, stores them in stones and reuses them for a multitude of uses. In sloping regions, it develops cultivable terraces supported by walls in order to obtain as many horizontal surfaces. He builds his house and various shelters for his animals. He fences the plots to mark his property, protect his crops and contain his herds. He built huts in the fields, sheepfolds in the mountains, « paper » walls1

To avoid trampling in the mud, he fills the ground and arranges many calades2 around the fountain and the washhouse, the square in front of his farm, the mule tracks and even the street gutters. In many countries around the world, farmers collect rainwater from cisterns, wells or mines3 and transport it to crops by gravity irrigation. In the driest places there are dew sensors4. To protect the fields, man has reinforced the banks of rivers with pearls5 and erected draining reservoirs across the talwegs to combat hillside erosion by slowing storm rainfall or snowmelt damage.

His assets in terms of sustainable development

After empirical adjustments and without agreement or forced transmission between the different areas of its diffusion, builders around the world have developed a constructive system that is interesting in more than one way and that responds to the environmental, economic and social challenges of our time :

  • A microclimate for crops : dry stone walls capture the heat of the sun’s rays and release it at night. Their thermal inertia is appreciable, especially in mountain agriculture.

  • A draining masonry : by crossing the thickness of the wall, composed of about 25% void, the water deposits fine particles that enrich the crops like a kind of silt trap. The wall preserves the soil but also serves as a retention basin by promoting the infiltration of rain on the cultivable bench. In arid and semi-desert areas, terraces at the bottom of talwegs are often the only fertile place to plant crops.

  • A shelter for biodiversity : due to its multiple crevices, a dry stone wall is a strategic habitat for many plant and animal species. It shelters an ecosystem and can naturally be part of the problems of ecological corridors and green and blue frames in urban planning documents.

  • The image of a quality terroir : a beautiful agricultural landscape, well designed and maintained, undeniably contributes to induce a feeling of good agricultural practice. This landscape expresses a total quality, that of the country, the work of men and productions. It embodies the pride of those who have shaped it and means an agriculture that respects the balance of ecosystems, that is adapted to the rhythm of the seasons, and whose productions reveal the quality of soils, trees and water.

  • A local material with no waste: building without mortar requires a sharp eye, hand dexterity and a lot of experience. The stones are sorted at the beginning of the work and each one, according to its shape and size, will find its place in the masonry. At the end of its life, all the stones of a structure can be reused. Thus, a breach in a wall is repaired from previous materials. After diagnosing the origin of the pathology, the wall is dismantled to its healthy part and then rebuilt using the recovered stones6. A supply of new stones of about 30% is sufficient to ensure its olidity. They are obtained from the nearest quarries, which thus value their waste stock. A stone gleaner, duly authorized by the owners to harvest discovery stones on the plots, can also be solicited. Some municipalities are judiciously organizing the storage of demolition stones in order to reuse them.

  • Local and non-relocatable employment: the construction method of dry stone will never be industrialisable. It simply requires time, patience and the know-how of the wall7 with its few tools8. In mountainous areas, dry stone installations are often located in uneven sites, inaccessible to vehicles or earthmoving machinery. In terms of life cycle analysis and overall cost, dry stone support has real economic relevance compared to concrete or gabion support9. To set up these modern construction systems, an external company must be called in and will leave once the work is completed. On the other hand, making the artisan who lives and consumes in the village work, training the municipal agent in charge of the maintenance of the space in dry stone, making the farmer aware so that he can maintain his terraces and enclosures, means caring for and maintaining a living environment, instead of importing construction techniques whose intrusion will be visible.

  • Walling, a profession that makes sense: the walling uses a natural material, it repairs without transgressing the heritage of previous generations, without risk to its health or the environment. He builds useful, modest and environmentally friendly structures for decades to come. In this fresco from the past, his imprint will be identifiable by the choices of assembly he will make to compose his wall.

Inspire tomorrow from yesterday’s good practices

Every time a landscape closes in by overlapping, walls built along the roads collapse and disappear to be replaced by other constructive systems, this transformation can evoke a feeling of nostalgia and the observation of an absurdity. Why use cement block where earth or stone architecture had its place ? Why, now that we are aware of our values, concrete terroirs where the earth or dry stone heritage is present ? Views on the cultural heritage of past generations are evolving in the fields of construction, development and agriculture. The right of everyone to live in a coherent environment and the imperative need to adapt to climate change are claimed in all parts of the world. In developed countries, a need for traceability, authenticity and a growing concern for sustainability and deconsumption invite us to question the old techniques that have proven their worth and have been abandoned without trial. In developing countries, the disappearance of traditional techniques means an often ruinous deculturation. Today, organic and geosourced materials are studied, tested and valorized as green building materials10. The contribution of new scientific knowledge validates and reinforces the reappropriation of these techniques.

Unlike globalization, which erases cultural singularities and destroys social belonging, the renewal of dry stone techniques can ensure the autonomy, economy and resilience of local cultures in sometimes difficult environments whose abandonment would entail considerable risks. It can be a sign of renewal and inventive modernity to ensure adaptation to the resources and constraints of the geographical environment.

Renaissance of a practice, creation of a professional path

The recognition of the dry stone technique originates from the initiative of actors in Vaucluse. Drawing on the knowledge acquired by various voluntary associations, these activists intended to perpetuate this vernacular and landscape heritage of Provence’s identity, with the ambition of creating a collective dynamic. A beautiful human adventure marked in 1983 by the survey11 of extraordinary dry-stone sheepfolds in the Lure mountain12, the publication in 1984 of Paysages et paysans des terrasses de l’Ardèche by Jean-François Blanc, then in 1989 of Paysages de terrasses13.

In 1995, the conference Pierres qui rouent à Gordes en Luberon questioned the survival of dry stone road structures. In 1999, a political decision14 laid down the conditions for the creation of a vocational stream. Dusting off an outdated image, the ambition is to recognize the innovative image that suits dry stone, a material and techniques that can become sources of inspiration to build and develop space from local resources, maintain a landscape and enhance people.

For the relay to be effective throughout the decision-making chain, the association of the technical services of local authorities and administrations, partners and residents is essential. One of the specific features of the rural environment is the small size of the technical teams that will ensure the daily monitoring of the project in collaboration with citizens and elected officials. This dimension can be a brake on the implementation and monitoring of projects, but also an asset when it comes to reinventing working methods to move away from an administrative management logic and engage in collaboration around the project. The small number of staff becomes a positive factor when these teams are voluntary and stable over time, and when they have the opportunity to be in close and regular contact with the actors in the field, which promotes mutual knowledge and builds trust. Industrial processes reduce the implementation to simplified techniques of laying and applying materials. On the other hand, a craftsman develops specific skills by studying the possibilities of materials and adapting to them in order to renew dialogue with the architect and work collectively. The approach aimed to bring together skills and territories from the Vaucluse to create an economic sector with a view to the emergence of a market that several programmes or studies were anticipating, in particular :

1. The European Reppis programme15 (1996-1999) presented the first reflections of engineers on dry stone road supports in the Luberon. It showed how the restoration of terraces, paths and ice houses on Mallorca had rebalanced the island’s economy by ensuring professional integration. Faced with the consequences of heliotropism, a lever for sustainable tourism and social development had emerged.

2. In 1998, the report Runoff and Major Hazards16 concluded that dry stone terraces and enclosures were an effective means of slowing down rapid runoff and partially compensated for the dangerous soil sealing caused by urbanization. Maintaining them upstream of the sites would have contained the deadly effects of the deadly floods in Nîmes (1988, 9 deaths) and Vaison-la-Romaine (1992, 47 deaths and 34 missing).

3. In 1998, the Road Directorate listed the stone structures. In 2004, EDF demonstrated its desire to optimize the operation of small high-altitude hydroelectric dams built on perreous slopes. During this period, our strategy was to prospect on a large scale to collect experiences, studies, expectations, assess sensitivities by department, identify and federate resource persons likely to contribute to pooling to fight prejudice. Indeed, the trade had disappeared because of the disregard that weighed on this dry stone technique considered as a poor man’s technique unlike industrial processes. This dynamic launched by our collective of professionals, coming from different disciplines and several departments, has borne fruit: the Vaucluse core has been joined by actors from the Cévennes and Gard, practitioners and researchers from the major public engineering schools. Since 2010, the peasant art of the murailler has been recognized as a rare craft17 at the Ministry of Culture, in 2015 it is inscribed as a specific know-how of «  maçon du patrimoine  » in the National List of Crafts18 and in 2018 it is distinguished by Unesco. The promotion of dry stone technology and know-how has opened up a market.

It is now a niche market, but these niches are numerous and could expand significantly. In this emerging market, it is necessary to be able to guarantee good practices. Due to lack of knowledge, some old structures that have collapsed due to lack of maintenance are rebuilt in imitation. Although effective from a functional point of view, these processes cause our beautiful tourist routes to lose their personality. A small winding road, with its dry-stone road support structures, embodies a tradition of ingenuity that makes these landscapes so charming. This is why acculturation remains essential for professionals and the general public.

Practitioner professionals19 and prescribers20

The lack of knowledge of the material and its techniques considerably hinders their use in France. It is imperative that natural stone can be rethought and used as a material of the future in building formations21 and that the values of dry stone structures are also studied in the worlds of agriculture, forestry, water, landscape and environment. Scientific tests carried out as part of engineering doctoral theses22 have shown that it is the rigour with which these masonries are implemented that guarantees their reliability and durability. In this respect, several scale test walls (1/1) have been built to be pushed to the breaking point and only one technique is effective : the double facing. A visible and neat exterior facing, an interior facing, then a drain. The equipment must be tightened and crossed in all three dimensions. Experiments show that, for supports higher than one metre in height, the technique of single-sided peasant walls is less resistant to bad weather. They were able to resist over time because there was a large workforce to monitor and repair them without delay. On the other hand, many Mediterranean sites have ancient examples of double-sided walls, particularly in olive groves in Mallorca where heavy rainfall can occur after periods of drought. In order for this transmission to be effective, the knowledge and skills of teachers and trainers must be validated to ensure the transmission of good practice23.

Ordering parties

It is necessary to make decision-makers fully understand the different advantages of dry stone in the balance of the site. Comparison with other masonries will help them in their choice of management for the natural and agricultural areas of the municipalities, their urbanized areas, their paths, roads, forests and rivers, and also in the preparation of urban planning documents. Until the 1960s, there was a roadmasters’ service in France. They closely monitored structures, gullies, canals, roads and their verges, to anticipate disorders and avoid emergency interventions. Training municipal employees in this way would be beneficial because nothing is done in a hurry, especially when it comes to heritage.

Citizens

We often notice that the habit of a daily landscape makes us forget or ignore the value it can take for a new look that is filled with wonder at its beauty. Once they have disappeared, regrets are expressed. Whether it is a question of monumental or vernacular heritage, wisdom is to know how to preserve the character of places by maintaining their components through careful care.

This acculturation goes through the inventory stage. The inventory provides knowledge of the functions and uses of each type of structure and thus makes it possible to respect the choice of those who built them with the ingenuity invested in the development of their construction methods. The easiest way is to consult the specialists in the associative world who have identified and studied these books and sites. It is then important to protect this heritage in urban planning documents, Park Charters and other means of communication to make it known and respected by citizens. This inscription is a decisive step in ensuring that the contribution of dry stone to heritage, the environment and local development is achieved.

For several decades, on several continents and in several disciplines, specialists have met at biennials24 where they have exchanged inventories, methods and knowledge to help safeguard this vernacular heritage. These exciting meetings demonstrate that professionals, elected officials and researchers are mobilizing everywhere. Their ambition is that dry stone should be used not only in the protection of outstanding heritage works but also in the creation of contemporary projects. Returning to this technique, a commission emerges that replaces standardized processes and encourages this alternative choice for those masonries that have been tried and tested by centuries of use all over the world. The distinctions of UNESCO and the European Landscape Convention represent fine symbolic guarantees that encourage us to pursue and intensify this dynamic in favour of sustainable territorial development.

1 The « paper » walls include niches for hives, well exposed to the sun and sheltered from the wind.

2 A calade is a draining soil composed of stones or pebbles, laid vertically tightly on a bed of sand and covered with sand to fill in the voids.

3 Horizontal well to collect groundwater.

4 Pierrier under which a small central canal is discovered that flows to an external basin, cf. the works of Danièle Larcena, geographer.

5 Retaining wall that protects a slope.

6 On the other hand, a stone coated with cement is irrecoverable.

7 Murailler, speciality of heritage mason in the National List of Crafts (OJ 31 January 2016).

8 Stubborn, hunting, sledgehammer.

9 Parallelepipedic iron cage in which stones are poured or placed.

10 The Ministry of Ecology, Sustainable Development and Energy integrated dry stone into these green sectors in 2011.

11Didier Respaud-Bouny and Claire Cornu, architecture students with Nadine Orloff, ethnologist and Philippe Alexandre, stonecutter, lauzier, caladeur and murailler, for the APARE (Association pour la participation et l’action régionale) based in Vaucluse.

12 Around Banon and Forcalquier, in the Pays de Jean Giono, Alpes de Haute Provence (04).

13 Régis Ambroise, agricultural engineer, Sébastien Giorgis, architect and Pierre Frapa, entomologist, at Edisud.

14 Led by two elected bakers from Vaucluse: Roger Bouvier, Mayor of Beaucet in the Monts de Vaucluse and President of the Environment Commission at the Provence Alpes Côte d’Azur Region and Paul Gilles, President of the Chamber of Trade and Crafts of Vaucluse.

15 European network of dry stone countries, co-led by the Luberon Regional Nature Park and APARE with the Epirus regions in Greece, Majorca in Spain and Apulia in Italy, coordination with the Avignon Landscapes Agency.

16 Written by Martine Guiton, engineer and ecologist at the Laboratoire Central des Ponts & Chaussées (LCPC).

17 Intangible cultural heritage of France.

18 OJ of 31 January 2016.

19 Masons, stonemasons, gardeners, foresters, natural area maintenance officers, community maintenance officers, farmers, olive growers, winegrowers, livestock breeders…

20 Engineers, technicians, architects, landscape designers, community technical managers.

21 Engineering schools, schools of architecture, Centre de Formation d’Apprentis (CFA) and professional high schools in the construction industry.

22 ENTPE and Ecole Centrale de Lyon, Ecole des Ponts-Paris-Tech: Boris Villemus in 2004, Anne-Sophie Colas in 2009, Hong Hanh Le in 2013, Benjamin Terrade in 2017, Nathanaël Savalle in 2019.

23 Guide to Good Practice for the Construction of Dry Stone Retaining Walls, 2008, with profile dimensioning calculation charts - Professional Rules 2016.

24 International congresses of the International Scientific Society for the Multidisciplinary Study of Dry Stone (SPS).

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