Introduction. 1-History and Background

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1 Introduction The essay has been organized to explore the availability of earth as a construction material; firstly, it focuses on the history and background of its usage. Then, a few examples of vernacular and contemporary buildings are presented. These examples are followed with a myriad of suggestions and proposals to make various earthen mixtures more compatible to different climates and structural demands, with the preference city of Sheffield as a sample. 1-History and Background One half of the population of world about three billion people reside in earth and similar materials like clay or mud constructed buildings. They can be found on all continents with different climatic conditions in various shapes and sizes from individual shelters to massive ceremonial or religious buildings. More specifically in almost all hot-dry moderate climates of the world, has been the main construction material. It has not been possible to fulfill the demand of shelter in developing countries with industrial materials, like brick, concrete or steel nor with the capacity of industrialized production or even to satisfy this need with the financial resources. Shelter requirements in developing countries can only be fulfilled by the local building material usage and through self help construction techniques. 2- Earth Earth is one of the simplest materials used for construction, and all earth buildings have the same basic components: soil from ground, and water. 2-1-What one should know about earth as a building material: Earth as a building material has usually owned different names. Scientifically referred to as loam, it is a mixture of clay, silt (very fine sand), sand, and sometimes larger aggregates like gravel or stones. Mud bricks or adobes are usually used at the time of speaking of handmade unburnt bricks, when speaking of unburnt bricks the term soil blocks is used and if it is compacted within framework it is named rammed earth. In another word, the techniques of preparing the earth are split into two classes: those in which individual units are made, dried then transported to the building site to form the structure which are called adobe and compressed earth blocks, and those which are produced in situ and are homogeneous monolithic constructions named cob and rammed earth Qualifications In many forms of construction from earth, other materials are included in the mixture called stabilizers. They combined with soil to improve its structural characteristics for instance tensile capacity and shrinkage which leads to cracks and improvement in shear strength. The former can be gained by adding hair, straw and the latter by cement. Accordingly loam has three disadvantages: 1- Loam is not a standardized construction material: 1

2 Different types and amounts of clay, silt, sand and aggregates could be found depending on the site where the loam is dug out. As a result, with alteration in locations of excavation site and the procedure of mixing for a specific application, the characteristic of loam may differ. 2- Loam mixtures shrink when drying out Because of the evaporation of water used for preparation the mixture (which is necessary for binding) shrinkage cracks will occur. The shrinkage can be managed by changing the amount of clay and water. 3- Loam is not water resistant Loam has to be sheltered from rain or frost; this matter can be done by roof overhangs, damp roof courses and appropriate coatings on surface and alike. It is prominent to mention the advantages of loam in comparison to industrialized building materials. 1- Loam balances the air humidity: loam is able to absorb and desorb the humidity faster than other materials and as a result it improves the indoor climate. 2- Loam stores heat In thermal insulation massing is always helpful, since loam is a heavy material it stores heat. In climatic zones where the diurnal temperature differences are high like central zone of Iran -which will be introduced later in this paper- or where it is essential to store solar heat gain by passive means, loam can be effective on indoor climate. 3- Loam saves energy and reduces environmental pollution As the construction of loam is an in situ procedure and it is gained at the time of excavation for foundation; to prepare and transport only about 1% of the energy needed for production, transport and handling of burnt bricks or reinforced concrete is used. Thus, loam is significantly a more environment friendly material. 4- Loam is always reusable Unburnt loam can be recycled any number of times. After absorbing water the dried loam turns to wet clay again and can be reused, so it can never be a harmful material for environment. 5- Loam is ideal for self-help construction Earth construction techniques can usually be performed by nonprofessionals with just one experienced supervisor. The techniques are labor intensive and the tools are very cheap. 6- Loam preserves timber and other organic materials Owing to its low equilibrium moisture content, loam conserves timber elements that are in contact with it, as it keeps the wood dry. The importance of this characteristic is that it blocks the growth of insects and fungus, because they need at least 14% to 20% humidity. 2

3 3-Vernacular use: To be more familiar with this material analyzing a number of examples would be helpful: Firstly the biggest mud brick building in the world: 3-1- The great mosque of Djenné: the walls depending on their heights are cm thick and are made of sun baked mud bricks coated with a mud plaster, which makes the surfaces smooth and adds a sculpted look to the whole building. According to one of the advantages of loam which is discussed earlier the thickness of walls keep the building cool during the day and release it after a few hours, which keeps the interior quite warm. The façade of the mosque has the same material as a traditional house in Djenné. To preserve the building the local climate which has a severe changes in temperature and humidity, palm branches have been built into structure to condense cracks and provide ready-made scaffolding for future repairs. In addition ceramic pipes stick out from the structure, to guide the water draining from roof to the walls. Image01- Molds for adobes Source: Earth : construction handbook (the building material earth in modern architecture 3-2-Another instance are the central cities in Iran, life in the deserts town in centre of Iran are accompanied with scorching sun and threat of regular sandstorms. In order to overcome these difficulties these conurbations are formed in a unique vernacular style and have an ingenious underground water supply system, known as qanats. 3

4 Image 02- mosque wall and dome Source: Handmade houses and other buildings: The world of vernacular architecture Residential buildings are constructed from adobe, with thick walls made of muddy bricks, which is the only available material. These buildings rise up to 6 meters (20ft) tall, with domes and arched roofs. Surprisingly the domes have positive effects on the indoor climate working as an insulation parameter of the space. The latter is derived from the fact that usually these domes are constructed in two layers so the air between these will act as insulation, needless to say that these characteristics are more beneficial with the adobe material and its heat storing possession. Since the material for construction is coming from the excavation, the house ground floor is a little below the street level, with the first floor living quarters 3-4 meters (10-12ft) above it. As it is discussed earlier the adobe walls store the heat from sun and release it at night, in winters it is quite favorable but in summers it would cause unbearable heat, which led to invention of systems using wind catchers that are linked to a duct and water reservoir (a branch of those qanats) to cool the place. Image 03- a typical house in Yazd Handmade houses and other buildings: The world of vernacular architecture Image 04- a windcatcher in Yazd Handmade houses and other buildings: The world of vernacular architecture 4

5 The foremost example of this desert architecture is the city of Yazd, which is not only one of the largest cities in the world which is made of adobe, but also has the most complex qanats complex which is still being used. Despite its beautiful adobe houses this city owns the tallest wind catcher and a few numbers of double sided ones Yemen tower house: Tower houses are a dominant form unique to southern Arabia; they are originally from pre Islamic times in Yemen where the tribal quarrels was the motivation of creating an impressive defending towers out of local material. They have spread across the country and have become a very popular form of housing for big families due to their capability of extension in the height; i.e., adding more storeys to the tower. They are usually five storeys high and some reach as many as eight or nine. The foundation of the towers is made of stone or earth (sundried clay, mud bricks or fired blocks), in cities the two first floors are made of tufa and the upper levels are from mud bricks. Image 05- a tower house in Yemen Handmade houses and other buildings: The world of vernacular architecture 4-Contemporary examples: Modern houses which are constructed out of loam need not to have any characteristic outward appearance. They can be modern or traditional, complex or simple, exclusive or humble. In cold climatic regions loam is not usually visible from outside, they are coated with specific thermal insulation and weather protection material. Nonetheless, the interior can manifest any kind of earth building techniques and applications Residence, Hörnerkirchen, Germany Image 06-Residence, Hörnerkirchen, Germany Source: Earth: construction handbook (the building material earth in modern architecture Due to the poor soil conditions; the floors are made of concrete slabs on which a lightweight loam layer was applied in order to give sufficient thermal insulation. The walls are constructed of wooden skeleton with infill of lightweight mineral loams and additional insulation layers on the outside; moreover, the wooden boards with air cavity are forming the façade. 5

6 4-2-Two semi-detached houses, Kassel, Germany All interior walls expose the timber frame and display the loam surfaces; meanwhile unburned loam is the dominant material for shelves and even bathroom sink. Image 07- Two semi-detached houses, Kassel, Germany Source: Earth: construction handbook (the building material earth in modern architecture 4-3-Low-cost housing project, Mount Abu, Rajasthan, India This residence is a prototype for low cost housing project for staff and students in university. It is covered by two crossing vaults built of unstabilised soil blocks produced in a manually operated block press from the local soil and also they were constructed with the Nubian technology. Image 08- Low-cost housing project, Mount Abu, Rajasthan, India Source: Earth: construction handbook (the building material earth in modern architecture 4-4- Farmhouse at Wazirpur, India The single-storied house with the structural frame consists of load bearing stone columns, which support beams and stone slabs to form slightly domical enclosure over all rooms, and the only part which is from adobe is the infill walls and the rest of the house is made of various materials like stone for shading or steel for security grills. Image09- Farmhouse at Wazirpur, India Source: Earth: construction handbook (the building material earth in modern architecture 6

7 4-5-Nubian vault building: the presented image is a cross-section of a building made of earth, the wall on the right side illustrates the underlying construction of mud or brick; on the left the wall is coated with a render made of mud or cement. The roof is waterproofed by plastic sheets covering the surface and the final render of enriched mud mortar on top. Image10- Nubian vault building Source: Handmade houses and other buildings: The world of vernacular architecture 5-Appropriateness One question that needs to be asked, however, is whether this material suitable for any kind of climatic conditions? Until this part of the paper and passing through the examples it is depicted that earthen buildings were and still are the most inhibited spaces. Moreover they were the first building material all over the world with some additives to overcome weather severity. In the instance of tower houses in Yemen it is derived that the buildings can bear the nine storey height only with mud bricks. On the other hand; the examples of contemporary mud houses made it clear that in order to have a strong structure the mud bricks can be used with timber or stone columns Region For analysing the appropriateness of the material for cold and humid climate the selected region is in Northern England like Sheffield. By researches in the climatic conditions in Sheffield it is derived that approximately 170 days of year it rains and the percentage of humidity is about 60% in average. In order to design a building with earth or more specifically with adobe there are a number of considerations like water proofing the façade, or damp resistant foundation. In presented examples from earlier times and contemporary, it is depicted that surface coatings and pipes for rain drainage are essential parts of design. 6-Suggestions Respecting the following facts can improve the designed buildings: 1-Trench for foundation: minimum depth of 0.8 meters and minimum width equal to the wall thickness but not less than 0.4 meters. The trench can be filled with stones infield and layers of cement grout to form strip foundations underneath walls. If the pedestal course is constructed of concrete, a formwork can be rose for the pedestal course, and can be made alongside with the foundations. The vertical wall reinforcement must be erected in place and be set in the base. The 7

8 canes must be linked with nylon threads or similar ways to the formwork to guarantee right position which is illustrated in image below. Image 11- Foundation construction (Dowling,2002) Source: yadobe/improvedadobe.html Field stone- max size 250mm Grout- cement based mixed in proportion 1:4 (cement: sand) by volume Vertical reinforcement- bamboo or canes sticks with diameter around 20mm. The length should be determined as follows: H=400 + wall height +bond beam depth(but min 200),[mm] 2-Plinth/Pedestal course: the first few courses of wall on foundation should be built out of mud brick or stone. The height of pedestal should be above the flood water line or 350mm above the ground level in minimum. Vertical cane reinforcement will guarantee the connection with the foundation; furthermore, the plinth course can be made of concrete and after completion of plinth masonry a multiple layered of damp roof should be installed. 3-Different bonds for adobe walls are possible for the wall construction with masonry materials. In the two below images English and Flemish bonds with 1 brick/block thickness for wall is recommended. To build a more technical construction horizontal reinforcement should be installed every fourth layers of adobe. Image 12- Flemish bond for one brick thick wall Source: asonryadobe/improvedadobe.html 8

9 4-Adobe bricks/blocks Adobe bricks are made of clayey earth including 30-40% clay and 60-70% earth which are mixed together with water. To strengthen the tensile capacity straw can be added to the mentioned mixture and the proportion would be 7-10 kg per m³ of dry earth. Then the mud mixture should rest for couple of days for the optimum water penetration through the mixture to activate the binding characteristics of the clay, noticeably it should be done before the making of the mortar or the brick itself. Image 13- English bond for one brick thick wall Source: onryadobe/improvedadobe.html 5-Mortar The properties of mortar are very prominent because of its direct contact with the blocks which already absorb moisture and also will limit the dying shrinkage. The joint mud (mortar) should be from the same or similar mixture which is used for making the blocks. Some coarse sand can be added to the mixture to make it smoother and also sand will fill the cavities between the earth particles which leads to a more integrated mixture. 6-Roof construction Ideally the roof should be light that the adobe walls can bear its load; in addition, it would reduce the risk of casualties in the events of roof collapse or earthquakes. Earthquake resistant roof type is the low-pitch pyramidal roof, with four planes, sitting on a horizontal beam on top of adobe walls. Single slopped timber roofs are also recommended, but it should be considered that in all types of roofs the structure should not transfer the thrust to the walls. Moreover, timber plate or timber wedges are recommended to uniform load distribution onto bond beam. To avoid water leaks, different approaches can be considered basically it depends on the climatic conditions, but generally 500mm of overhang is preferred in all of forms. Accordingly, the material for roof covers a wide range like board wood sheathing or plywood, ridged sheets, engineered wood, plastic coats and so forth. Needless to say that clay tiles are not proper for this form because of their high mass. 9

10 7-Plastering For protection of adobe walls plastering is essential, preferably hydraulic lime or mud-lime based plasters are suggested; also, they can be improved by adding straw as reinforcement. One of the facts that should not be neglected is not using cement in the plaster mixture, because the adobe wall needs to breathe. 7-Consideration In following some initial points are mentioned which worth considering at the time of design: Build one storey houses Provide foundations Provide buttresses at all corners and junctions of walls Roughly squared rooms Provide at least 4 courses of plinth masonry above foundations Build light low pitched couple roof, four sloped roof or single sloped roof The roof should transfer only vertical loads to the walls. Include a collar beam when constructing pitched roofs. The height of wall should not be greater than 8 times its thickness. The length of a wall, between two consecutive walls at right angles to it, should not be greater than 10 times the wall thickness t nor greater than 64t2/h where h is the height of wall. When a longer wall is required, it should be strengthened by an intermediate vertical buttress. The width of an opening should not be greater than 1.20 m. The distance between an outside corner and the opening should not be less than 1.20 m. The sum of the widths of openings in a wall should not exceed 1/3 of the total wall length. The bearing length (embedment) of lintels on each side of an opening should not be less than 0.5 m. An adequate configuration is shown on the Figure below. Image14- construction proposal Source: onryadobe/improvedadobe.html 10

11 8- Supportive material According to the earlier discussion, earth is the first material that human has used for construction in every climate and geographical situation, it is proven that this material is applicable everywhere. More significantly for a climate like Sheffield and with respect to the fact that it is situated in peak district, the initial adobe constructions can be supported with the abundant stone and wood available from Peak District. Researches on contemporary adobe architecture in Germany which is presented earlier had shown that having stone columns and timber particles as a part of structural design would be a technical support for the whole construction. Needless to say that having pitched roofs which are water proofed with special coatings or even engineered clayey claddings are some of the main design points. 9- Conclusion: The present study was designed to study on one of the low impact materials in architecture production and its history, vernacular use and contemporary samples. Adobe which is made of earth, water and some additives like straw was the focused point. Returning to question posed at the beginning of this study, it is now possible to state that adobe is a good material for construction in different parts of the world, however to overcome some of the bad effects of climatic conditions like humidity a few number of notes should be considered. It is also recommended to consider some supportive elements both in structure design and clay mixture; moreover, examples are provided to make the context wider for future research. 11

12 Bibliography: Jaquin, P, Augarde, G, 2012, Earth building: history, science and conservation, HIS BRE press May, J, 2010, Handmade houses and other buildings: The world of vernacular architecture - Thames & Hudson Minke, G, 2000, Earth : construction handbook (the building material earth in modern architecture, WIT press Mumovic, D and Santamouris M, 2008, A hand book of sustainable building design & engineering: an integrated approach to energy, health and operational performance, London ; Sterling, VA : Earthscan Williams- Ellis, C, 1999, Building in cob, pisé and stabilized earth,, Donhead, 12