1 INTRODUCTION

1.1 Framework and scope of the study. Within the Departments of Architectural Construc-tions 1 and 2 of the University of Seville the re-search groups TEP206 and TEP211 are fully in-volved in the characterization and cataloguing of the building heritage. Also linked to Terrand Associa-tion, research work concerning the earthen heritage of this region is recently being carried out. This re-search is the first step for a larger plan which will comprise more towns and villages in the south of Spain.

The geographical location of the study corre-sponds approximately to the current provinces of Huelva and Seville, where various settlements were particularly relevant as strategic commerce centres. As latest studies claim, this area holds outstanding examples of rammed-earth constructions, whether monumental or residential. While monuments have been extensively studied, earthen vernacular archi-tecture remains almost unknown. To begin this study two towns -Carmona and Niebla- has been selected in both provinces since they hold valuable historic centres and special urban planning for heritage pro-tection is available.

This study is only focused on housing within his-toric urban areas, although other samples may be studied afterwards. Therefore vernacular rammed-earth architecture will be studied through the gather-ing of historical, archaeological and architectural in-formation, and supported by some local administra-tions.

1.2 Objectives and aims of the research. By means of diagnostic data forms and a data base it is intended to develop a catalogue of selected rammed-earth traditional houses in order to obtain certain conclusions concerning their typologies, sig-nificance and state of conservation.

It is also meant to analyse rammed-earth typolo-gies in detail and prove whether stated prior classifi-cations suit this kind of buildings or not, since they were devised for previous historical periods. In this case, a more suitable arrangement will be proposed.

Finally, those constructive parameters that would arise from the analysis will be compared with the current knowledge on traditional rammed-earth technique in order to highlight any new significance for this ancient building tradition in this region of Andalusia.

1.3 Prior researches on this field. Studies on typologies and techniques of earthen

construction in the south of Spain are scarce, even more in the case of vernacular architecture. Many authors have extensively treated Spanish popular ar-chitecture from the second half of the 20th century, and the traditional rammed-earth technique from the last centuries has been sufficiently investigated. Dur-ing the last decade, several national or international research projects have focused on the study of tradi-tional construction techniques in Spain (BIA 2004-1092, BIA 2010-18921, and Terra Incognita Pro-ject). Additionally, remarkable catalogues and on-site studies have been carried out in the South of Portugal (Correia 2005) Likewise, some authors as

Comparative analysis of vernacular rammed-earth building typologies in the ancient reign of Seville

J. Canivell, R. Rodríguez García, A. M. González Serrano, A. Romero Girón University of Seville, Spain

ABSTRACT: Rammed-earth technique has been spread all over Europe, mostly in the Mediterranean area. Specifically, the south of the Iberian Peninsula holds an extensive heritage of this kind, along with other tech-niques as adobe walls. Although a number of studies are focused on monumental earthen heritage, there is still a lack of knowledge about the development of this kind of vernacular constructive typologies in this re-gion. This paper presents an analysis of the vernacular rammed-earth architecture of several strategic towns. Through the search, analysis, comparison and cataloguing of constructive parameters, patterns and invariants it is intended to enhance their heritage values and promote a more concerned conservation planning for rammed-earth traditional housing.

Castilla (2005) have obtained valuable information directly from old builders who extensively used this technique for walls’ setting up. So a rough overview of procedures and instrumentation involved in rammed earth in Spain is already available. Never-theless, vernacular earthen architecture in Andalusia remains almost unclassified, even more regarding rammed-earth buildings, which are in fact the most common in villages and towns within rural areas.

2 CATALOGUING METHOD

The methodology used for this paper is based on the research study carried out by Canivell (2011), which aimed the analysis of military buildings. The meth-odology involves the use of a series of parameter re-corded by on site data collection and their subse-quent treatment by database means. In a first stage, the data base is managed as several spreadsheets since they are much easier to manage during on-site work. Once all data is collected and analyzed, it is expected to develop a larger data base that will en-able the future implementation of a spatial database.

The cataloguing has been divided into three main sections, in which each record is totally defined ac-cording to its location, typology, constructive pa-rameters and its state of conservation. Since the analysis aims only those dwellings built with rammed earth, a prior filtering has been needed in order to discard other constructive systems. Al-though it is already known, rammed-earth walls is a widespread technique in the south of Spain, it is fre-quently difficult to state whether there is a rammed- earth wall or not, mainly due to the renderings and coatings.

2.1 General data In the first place, in order to identify each record, it is essential to determine a number of parameters that will define the location and the main physical char-acteristics of the building. Each record is given a singular alphanumerical code, related to the city and whether is residential (RE), religious (IG) or military (CAS) building, along with a correlative number. Other parameters such as address and geographical coordinates (latitude and longitude) are used to plot them on a map. Once a minimum number of records is reached, a spatial database will be implemented to a more efficiently management of such amount of information.

Urban location data are treated separately since they are not related to geographical location but re-fer to properties where buildings are set up. As it will be discussed afterwards, most records are de-tached plots in a consolidated urban frame. Never-theless, other settings are taken into account such as isolated dwellings in a building lot, either sur-

rounded by gardens or not. Although, all cases have been selected in historic centres, sometimes happens that the urban area is not consolidated. These cases correspond to rural areas in the countryside (farm houses), but this is out of the frame of the current analysis.

In order to establish categories according to the rate of construction within the plot, the square me-ters of each plot, the free area (backyards, court-yards,…) and the square meter of the build-up area have been recorded. All this data have been taken from the National Land Registry (www.sedecatastro.gob.es). This will allow us to de-termine whether each category is related to a spe-cific physical configuration.

2.2 Typology features Firstly, parameters referred to the use of the building are recorded, mainly stating the difference between multi-family residential unit or single one. Although other uses such as military, educational, religious or industrial are detailed, they are not presented here-under due to the scope of this study. In any case, it is essential to determine whether the building is in use (occupied), which would mean a better rate of con-servation and hence a longer life. Abandoned ones are likely to be crushed down; this probability in-creases when the building is not protected by local regulations. Therefore, vernacular architecture in historic centres is usually under regulations which prevent building from inappropriate restorations. As stated in the Spanish Law of Historic Heritage (1985), all historic sites must be protected under Special Plans for Protection. Furthermore, LOUA (Law 7/2002, Law for Urban Management of Anda-lusia) establish the need to develop catalogues when local regulations identify singular values in urban areas. This study focus on those urban protected ar-eas which harbour outstanding samples of historic architecture. Hence, the level of protection has been addressed from fully protected (site of cultural inter-est) to partial protected buildings, as it is stated in each local regulation.

Typologies have been classified under three points of view regarding the building global con-structive configuration. The parameter “typology I” refers to the study of popular architecture in Spain, carried out by Feduchi (1978), who details six basic typologies for Andalusia [(A) Huts, (B) Caves, (C1) Mountain house, (C2) Valley-house, (D) Earth-ceiling-house, (E). Farm-house] although this study will only consider one of them (type C2) since the geographical distribution of case studies is for the time being limited to Guadalquivir valley. Likewise, Feduchi (1978) defines Andalucian popular build-ings as concavity architecture because all the spaces in a house tend to converge towards the inside of the

lot itself, where it is usually the courtyard that holds the main role in the private living management.

Typology II and III parameters describe respec-tively the physiognomy, complexity and quality of the construction techniques and the spatial distribu-tion of the house. As many authors have proposed (Feduchi (1978), Fernández Ruiz (1991), Carmona (2007)), vernacular buildings may be sorted out ac-cording to their size and number of floors, ranging from one-storey houses (basic, see figure 1), one-storey houses with a garret bellow the roof (ba-sic+garret) or two-storey houses.

Figure 1. View of a typical one-storey house in Niebla. Quality has also been described with regarding

the construction techniques complexity and the de-velopment of inner spaces, which are normally linked to families’ social and economical level. Hence, three levels have been considered for “Ty-pology III”: Basic-quality, Medium-quality and Wealthy houses. Basic-quality houses correspond to low constructive quality and short space requirement programs as well as low-tech construction tech-niques. They normally consist on one-storey build-ing of one or two bays, parallel to the main façade. The average span between load bearing walls ranges varies from 3.5 meters in basic models up to 4.5 for the most complex one. Spatial requirement programs are extremely rudimentary so the same room could hold several uses. Nevertheless, the kitchen and bathroom might originally be found at the backyard. In any case, as discussed by Pulido (2007) for ver-nacular housing in Seville, it does not exist a spatial hierarchy, because any of them could hold several uses. These buildings have usually been built by lower social classes and are strongly linked to agri-culture production. Medium-quality houses (see fig-ure 2) normally mean the increase in number of sto-reys, or even a more complex arrangement of the space, but constructive techniques and façade orna-

mentation would still be basic. Wealthy houses nor-mally involve two-storey buildings, with better-arranged inner spaces. More expensive construction materials, as stone or fired bricks, are used for load bearing walls and façades. Although certain con-structive solutions are basically the same (founda-tions, basement of walls, beam supports, wooden roof structure), it has been noticed that they are finer and improved due to the higher economic level of the property owners.

Popular architecture in Andalusia stands out due to the use of courtyards as one the house’s key ele-ment. In that sense, it is maintained that Islamic ar-chitecture may be the source of some features in southern vernacular housing (Feduchi (1978), Ang-lada (2007), among others). Courtyards have been classified according to their location within the building lot as front-courtyards, which are not pre-sented in these case studies, central-courtyards and backyards, which are usually related to cooking area, storage or in rural areas with agricultural labours.

The last step of the building process is the decora-tion and ornamentation of a rammed-earth wall by means of cornices, mouldings or textures. To that end, extra elements are required since the compac-tion technique would not easily allow placing many strange components inside the formwork. With ex-ception of certain “fraga” techniques (see chapter 2.3), all rammed-earth surfaces are rendered or sim-ply left plain. Therefore, since decoration is inde-pendent it has been briefly recorded in three level, from rich to scarce or none ornamentation.

Finally, as considered by many authors, construc-tion typologies of vernacular buildings is related to the number of bays and the span between two con-secutive load bearing walls. Although most of the case studies present only one or two parallel bays to the façade, in basic models the span decrease less than 4 meters. Nevertheless, with regards to rammed-earth walls, the total range of recorded span would not imply any adjustment in the support of beams. In fact, it depends more on the available eco-nomic resources or even on the beam cross-section.

Figure 2. View of a medium-quality house in the centre of Carmona

2.3 Constructive characteristics First, those buildings whose load bearing walls may be made of rammed earth have been pointed out from local catalogues. To this end, disrepair build-ings have to be selected since their coating has fallen revealing the rammed earth underneath.

As this research aims to study in detail vernacular rammed-earth housing, the classification of rammed-earth techniques proposed by Graciani & Tabales (2008) has been initially applied. Given this classifi-cation it was designed in relation to military build-ings; the results will confirm whether an adjustment is needed. Seven different types have been selected: (1) Monolithic, (2) Monolithic with brick courses, (3) Monolitic with stone courses, (4) with brick col-umns, (5) with stone columns, (6a) “Fraga” type with brick, (6b) “Fraga” type with stone. The “Fraga” type means using columns and courses in the same wall.

Although foundation has not been possible to check on site, builders of the corresponding towns maintain that stones are normally used, but there is no evidence at the time being. Nevertheless, the base of walls is sometimes exposed due to rendering crumbling, allowing us to check whether stone or brick has been used.

Renderings are usually applied over rammed earth and specifically limewash, lime or earth mor-tars, or even nowadays some repairs are done with cement mortar. All of them all considered as well as its thickness (millimetres). Most parameters are qualitative, based on visual inspection. Due to the difficulties found in getting enough quantity to ob-tain reliable results, no samples have been taken to obtain quantitative parameters from the composition.

The roof type and shape has been checked. The following list was considered: gable roof, shed roof, flat roof or even a mixture of them. The configura-tion of roofs is usually linked to the typology and re-sources of the building.

Qualitative characteristics of the rammed-earth mass has been taking into consideration, but it was recorded for a short list of case studies, only on those with no renderings.

Rammed earth may be classified according to the components that fill each formwork. Depending on the tradition and available construction materials, there is a wide range of possibilities. The most fre-quent traditional materials are earth, lime, gypsum, aggregate, stone and ceramic rubble. Therefore, the considered types are as follows: (1) earthen when only earth and aggregate are used; (2) stabilized earth if lime or gypsum is mixed with earth and ag-gregate (lime is usually perceived as little white dots); (3) Stone and lime type when a mixture of stones and lime mortar is used instead of earth (4) “calicastrado”, which is a earthen type with a crust

of lime mortar on the surface made during the com-paction process.

Maximum particle size is checked in order to as-sess the quality of the rammed earth. Various au-thors claim that particle size distribution should re-main within certain values, so the particles have to be uniformly ranged. In addition, stones larger than 30 millimetres will be recorded.

Graciani & Tabales (2008) discussed that ceramic rubble in rammed earth may be a procedure of cer-tain historic types. In fact these authors argued that its use was wide-spread during Islamic (XII-XIII C.) and Mudejar (XIII-XV C.) periods. Therefore, the existence of ceramic is registered when its mass proportion is high.

The measurements of rammed-earth parts may reveal some clues of how the wall was built and which instruments were involved in the process. Height, length and width (centimetres) of a rammed-earth building unit provide an evidence of the size of the original formwork, since any mark on them is usually left on the wall surface. Nevertheless, origi-nal formworks were a bit larger as overlapping be-tween consecutive rammed-earth units area needed. Some authors as Cuchi (1996) and Font & Hidalgo (2009) argued that the 75-80 cm height and 200 cm long are the traditional dimensions of formworks. Measuring the gap between the putlocks give us a rough measure, considering that three putlocks are normally used to support the formwork. Finally, the shape of the cross-section of the putlock has been recorded because it may range from circular to square or flat, depending on the technique, region or historic period.

2.4 Study of conservation Damages have been sorted into three groups as structural, material and superficial, according to their nature or location. First, a rough assessment of the state of conservation is carried out according to three qualitative levels of deterioration. Each group comprises several types of damages whose presence is simply checked.

Structural failure includes frequent concerns in rammed earth as fissures, crack or leans, and other unusual as wall buckling. Material failure refers to deterioration of the mass due to whether external or own factors. Erosion due to weathering and loss of mass, which would require restitution, are simply checked as material failures. Loss of cohesion has been graded from strong hardness –similar to stone- to soft matter, which would easily lead to disintegra-tion of rammed earth. Finally, surface damage con-cerns the deterioration of the external layers and renderings. Therefore, efflorescence, dirtiness, crust and deterioration of the corresponding coating are assessed.

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Failures. It is noteworthy that within the case studies, structural failure is rare and there is a low percentage of material failure. On the other hand, as is shown in table 1, surface damage is far more fre-quent in all cases. Table 1. Percentage of case studies failures. ___________________________________________

Structural failures (%) ______________________________________ Grade of failures Carmona Niebla ______________________________________ High 0 0 Moderate 0 8 Low 27 17 No failures 73 76 ______________________________________

Material failures (%) ______________________________________ High 0 0 Moderate 0 11 Low 15 17 No failures 85 72 ______________________________________

Surface failures (%) ______________________________________ High 15 0 Moderate 30 8 Low 46 58 No failures 9 34 ______________________________________

4 CONCLUSION

Given the discussed results, a specific typology for rammed-earth buildings within the studied context can be suggested, which consists of a single-family house in detached plots, with gable roof mainly on monolithic rammed-earth walls, which are covered by limewash.

According to the analysis of parameters Typology II and III, it is confirmed that earthen construction might not be exclusively linked to low-cost dwell-ing. Therefore, it must be considered as valuable heritage regardless the scale of this kind of vernacu-lar architecture.

With regard to the structural stability and the ma-terial deterioration, the state of conservation of the case studies is good, and allows us to conclude that as for any other construction system involved in vernacular architecture, when materials and building processes are suitable, raw earth shows a similar du-

rability and aging under similar maintenance cir-cumstances.

5 AKNONWLEGDEMENTS

Thanks to the City Council of Niebla for making possible the research on site and providing useful documentation, local regulations and catalogues that actually have made this research more valuable. Thanks to all selfless people, citizens and builders whose testimonies have been crucial to clear up some matters related to rammed-earth traditional techniques in these towns.

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