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Strategies of bioclimatic design used in traditional agrarian buildings of Spain.

Cañas Guerrero, Ignacio; Martín Ocaña, Silvia

Departamento de Construcción y Vías Rurales. Escuela Técnica Superior de Ingenieros Agrónomos. Universidad Politécnica de Madrid. Avda. Complutense s/n. 28040. Madrid.

Tel: 913365767, Fax: 913365625, mail: icanas@cvr.etsia.upm.es Abstract The objective of this study is to establish bioclimatic design strategies using the Spanish agrarian popular architecture as a model. The bioclimatic strategies have different purposes depending on the dominant regional climatic factor. Spain is located within the zone of temperate climate, in particular within the Mediterranean type. Nevertheless and in spite of their small extension, many types of climatic areas with widely varying characteristics exists in Spain. In this article the climatic classification proposed by the Building Technical Code is employed. The agrarian popular architecture has responded to these different climates applying different design strategies. By observing cases of popular constructions, suggestions about the passive design strategies suitable for each climatic zone are made.

Keywords: Spanish agrarian architecture, Mediterranean climate

1. Introduction. The aim of this study is to suggest bioclimatic design strategies for the different areas of Spain. This article is based on the climatic classification proposed by the “Building Technical Code” that is going to take effect at an early date, replacing the current Building Basic Regulation NBE-CT-79. The climatic classification of the Building Technical Code divides Spain into twelve zones made by the combination of the summer and winter conditions. The suggestion of the suitable bioclimatic design strategies for each zone is carried out taking into account cases of popular constructions found in bibliography. Agrarian popular architecture has met the different climatic conditions by the implementation of design strategies. Many years ago when the modern systems of environmental control did not exist, man was able to found the means for the protection against inclement weather as well as for taking advantages of natural energy. In this article the popular construction is presented as the beginning of bioclimatic architecture. The design strategies employed in this type of constructions are passive strategies, it is to say that these strategies do not need the use of additional energy.

2. The climatic zones of Spain based on the Building Technical Code. Spain is a country located in the south – west part of the European continent. It is situated in the temperate area, between latitudes 43º47´24´´ N (Estaca de Bares) and 36º00´3´´ ( Punta de Tarifa), and between longitudes 7º00´29´´ E (Cape of Creus) and 5º36´40´´ O (Cape of Tourinan). The area of Spain is 580.850 km2. It borders on Cantabrian Sea, France and Andorra to the North, on Mediterranean Sea to the East, on Mediterranean Sea and Atlantic Ocean to the South and on Portugal and Atlantic Ocean to the West.

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Due to its situation Spain belongs to the temperate climate area, although it is said that Spain has a Mediterranean climate (this term is applied to the areas surrounding the Mediterranean Sea). Nowadays, there is no climatic classification of Spain focused on the bioclimatic architecture. In this study the climatic classification of the Building Technical Code for the calculation of the required thermal insulation is used. The Building Technical Code is a group of regulations that the buildings should observe for improving the quality. It establishes the minimum requirements related to the acoustic, thermal and structural conditions of the building materials as well as of the installations used in buildings. This study centres on the part of the Building Technical Code related to the requirements for energy savings. Like in the current Building Standard (NBE-CT-79), the upper limit of the thermal transmission coefficient depends on the climatic conditions of the place where the building will be constructed. There are differences between the climatic classification proposed in both Regulations. The NBE-CT-79 establishes 5 climatic zones: A,B,C,D and E1 by using different levels of degree/days during the heating season. In the other hand, the Building Technical Code establishes 12 climatic zones by combining the heating and cooling season conditions of the main Spanish cities (see table 1). The climatic zones are set through the climatic severities2, there is a climatic severity for winter and another for summer (see figure 1)

A4 B4 C4 A3 B3 C3 D3 C2 D2

Summer climatic severity

C1 D1 E1 Winter climatic severity

Figure 1: Climatic areas. Winter climatic severity: A=0.3; B= 0.3 - 0.6; C=0.6 – 0.95; D= 0.95 – 1.3; E > 1.3

Summer climatic severity: zone 1= 0.6; zone 2= 0.6 – 0.9; zone 3= 0.9 – 1.25; zone 4> 1.25 The hottest areas are the ones with lowest winter climatic severity and highest summer climatic severity, while the coldest areas are the ones with highest winter climatic severity and lowest summer climatic severity. The table 1 shows the climatic classification of all the Spanish provincial capitals.

3. Spanish popular architecture. In order to suggest some passive design strategies for the different climatic areas defined above, we turned to the main references about Spanish popular construction (Flores, 1974; Claret Rubira, 1976; Feduchi, 1984; Benito, 1998; Ponga, J.C; Rodríguez, M.A, 2000). The relationship between different construction typologies and prevailing climatic conditions was analyzed. The way of establishing the sustainable construction is easy: to restore the values from traditional architecture and to make good use of the technologic advances. The features of 1 Zone A <= 400 annual degree/day; Zone B: from 401 to 800 annual degree/day; Zone C: from 801 to 1300 annual degree/day; Zone D: from 1301 to 1800 annual degree/day, and Zone E > 1800 annual degree/day. The degree/days are calculated on the base 15-15 Celsius degree according to the Regulation UNE:24.046. 2 The climatic severity is a meteorological parameter which combines the influence of the air temperature and the solar radiation, so that in two locations whose climatic severity is the same, the same building will have the same energy requirements.

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different world climates have formed the indigenous architectural shapes for each different geographical location.

Table 1: Climatic classification of the Spanish provincial capitals.

Ref

eren

ce h

eigh

t (m

)

Drop between the town and the provincial capital (m)

Prov

inci

al c

apita

l

Province

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Besides the adaptation to the prevailing climatic conditions, there are other parameters influencing the vernacular architectural shapes, as: topography, availability of building materials, customs, familiar organization, and way of living of different people. In Spain, due to its wide climatic variation, lot of traditional architectural typologies appear. The basis of this article is the study of specific popular buildings that make use of certain construction elements for the “protection against” or the “use of” the prevailing climatic factors. The most important references about vernacular architecture have been revised, focusing on the cases where the author mentions clearly the relationship between some concrete constructive element and the climate of the place. From the whole cases found in the bibliography, only the ones with design strategies directly related to the climatic parameters employed in the climatic classification of the Building Technical Code (temperature and solar radiation) were selected. Eighty nine cases of popular construction with graphical information were analyzed and grouped by climatic zones (see table 2).

Table 2: Studied cases in each climatic zone. Climatic zone Number of cases

A4 3 B4 9 C4 4 A3 13 B3 6 C3 2 D3 2 C2 0 D2 10 C1 5 D1 6 E1 29

The constructive elements found in the analyzed cases try to achieve the next objectives:

• Protection against solar radiation: It is needed when the air temperature is higher than 21º C (Olgyay, 1998), although this value varies according to the location of the building and its final use. The constructive elements employed for the protection against solar radiation try to avoid the overheating and the excessive natural lighting inside the building. The solar protectors can be fixed or mobile, horizontal or vertical, and interior or exterior. They are usually placed on the façade openings, but in areas where solar radiation is extremely high the structural parts of the buildings are also in the shadow. The constructive elements most usually employed to provide shadow to the building are: wing walls, portals, window shutters, window blinds, curtains, lattices, trees and other vegetation. In addition, there is another system whose task is to reflect the solar radiation, so it should be considered as a strategy of protection against solar radiation, it is the use of light colors for painting the façade.

• Use of solar radiation: Three stages are required: capture, store and distribution of solar energy. The elements designed for the passive use of solar energy can carry out the three stages or only some of them, in this case another part of the building will develop the rest.

• High thermal inertia: This strategy is used in areas where the oscillation of temperature is high during the day and during the year, as much in cold climates as

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in hot ones. The thermal inertia causes a gap and a softening of the exterior temperature wave. An example of the use of high thermal inertia is the underground construction.

• Protection against cold: This objective is achieved by means of constructive elements that insulate the building from the exterior environment, as window shutters. Although there is other elements that do not protect the building against cold, they are characteristic of cold climates as the steep pitched roofs for avoiding the accumulation of snow.

• Shape and location of the building: The compact shapes reduce the contact with the exterior environment, so they are found in areas of extreme climates. On the contrary, with extended shapes the exposed surface is higher so the contact with the exterior environment is higher and the possibility of ventilation is increased. On the other hand, the selection of the location of settlements has been an important task since ancient times, the best places are the ones protected from the inclemency of the weather and rich in natural resources.

4. Results.

The analysis carried out in this article shows that taking the vernacular architecture as the model of bioclimatic architecture, it is only possible to make suggestions for areas wider than the ones proposed by the Building Technical Code (CTE). The results are showed in the next tables:

Table 3: Results Bioclimatic area

CTE areas

NBE-CT-79 areas

Recommended Design Strategies

A4 B4

A

A3

Hot zone B3

B

Protection against solar radiation: small openings, facades of light colors, courtyards, underground dwellings, lengthening of the wing walls, lattices and other mechanisms of solar protection. Elements for the capture of rain water for domestic use and as a cooling mechanism.

D2 D1

Cold zone E1

E

Compact shapes and close to the ground for the reduction of the contact with the exterior environment. Location of settlements on protected places as the end of a valley. Predominance of the wall opposite the openings. When there is suntraps, they are protected by wood boards or other elements. Pitched roofs encouraging the loss of the snow.

Transitional zone 1

C1 D In this zone some elements found in the cold zone are kept. Predominance of suntraps for the capture of solar radiation in winter.

Transitional zone 2

C4 This zone is very similar to the hot zone but some elements for the heating of the building are present.

C3 Transitional zone 3 D3

C This zone is characterized by its temperate climate. Elements for achieving opposite purposes could be found in this zone.

Table 4: Bioclimatic zones based on the classification of the Building Technical Code.

Transitional zone 2

Hot climate

Transitional zone 3 No data

Summer climatic severity

Transitional zone 1

Cold climate

Winter climatic severity

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In the following figures it is showed a specific vernacular building for each bioclimatic area.

Alcaracejos (Cordoba), hot climate Lucillo (Leon), cold climate

Rada (Santander), transitional zone 1 Garrovillas (Caceres), transitional zone 2

Illana (Guadalajara), transitional zone 3

5. Conclusions. The proposal of bioclimatic design strategies taking the vernacular architecture as a model only allows to make a distinction between wide areas where there are important changes in the constructive typologies. Naturally, the majority of cases of popular buildings in which there is a clear relationship between some particular constructive element and the climate

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match with areas where the weather is hard. Popular architecture give answer to social, cultural and economic situation of the location, as well as to the dominant climate and to the suitability of building materials. In areas where the climate is harsh (cold or hot), the climatic parameter is more important than the rest so the relationship between climate and construction is more clear. In the transitional zones generalizations can not be made, however the observation of the prevailing constructive typology in the area will help in the establishment of some design elements for the integration of the construction on the environment. Acknowledgements The authors wish to express their appreciation to the Ministry of Science and Technology of Spain within the Project of Investigation PB8-0720 “Aproximación a una metodología de reutilización de construcciones rurales” for their financial support. References 1. Benito, F. La arquitectura tradicional de Castilla y León. Volúmenes 1 y 2. Junta de Castilla y León. Consejería de Medio Ambiente y Ordenación del Territorio. 1998. 2. Claret Rubira, J. Detalles de Arquitectura Popular Española. Editorial Gustavo Gili, S.A. 1976. 3. Feduchi, L. Itinerarios por la Arquitectura Popular. Barcelona: Blume. 1984. 4. Flores, C. (1974). Arquitectura popular española. Editorial Aguilar S.A. Madrid. 5. Olgyay, V. (1998). Arquitectura y clima. Manual de diseño bioclimático para arquitectos y urbanistas. Editorial Gustavo Gili, SA. Barcelona, España. 6. Ponga Mayo, J.C; Rodríguez Rodríguez, M.A. (2000). Arquitectura popular en las comarcas de Castilla y León. Junta de Castilla y León, Consejería de Educación y Cultura.