Report 3 (of 5): Earthen Architecture

Introduction

In most countries of the world, it is possible to mould earth with sophisticated or primitive tools to construct buildings. The range of the technical, constructional and architectural possibilities of earth is extremely wide. This wide constructional potential has enabled the construction of modest shelters, village houses, urban blocks and religious edifices, as well as palaces and entire cities.

In countries with no industrialised means, in a wide range of latitudes throughout the world, earth remains the main building material. Processed materials are costly both in foreign currencies and imported energy. Communities remain dependent on the use of locally available solutions, materials and knowledge. These materials and techniques are generally very well used and can ensure true architectural quality which makes the most of the human and material resources available.

Principle Techniques of Building Using Unbaked Earth

The techniques mainly associated with processes using moulds, shuttering and direct shaping are "adobe", "rammed earth", "straw clay", "wattle and daub", "cob" and "compressed blocks".

	©T.Joffroy (1)

Wattle and Daub: a supporting frame which is usually wooden, is filled with a daubed lattice or netting woven from vegetable matter. A very clayey earth is used which is mixed with a straw or other vegetable fibre to prevent shrinkage upon drying.

Straw Clay: the soil used is very clayey and is dispersed in water to form a greasy slip which is then added to the straw. The earth binds the straw together. Straw clay can be easily adapted to the prefabrication of various building components, such as bricks, insulating panels and flooring blocks.

Cob: balls of earth are stacked on top of one another and lightly tapped with hands or feet to form monolithic walls. The earth is reinforced by the addition of fibres, usually straw from various types of cereal or other kinds of vegetable fibre, such as grass and twigs.

Adobe (sun-baked earth brick): the bricks are made using a thick malleable earth which straw is often added to. Traditionally, adobes were shaped by hand, in wood or metal moulds, but nowadays the use of machines is widespread.

Rammed Earth: the earth is compacted in framework. In many countries, wooden forms and rammers are used. It is possible to build monolithic walls with the compacted earth.

Compressed Earth Blocks: nowadays, the process of compressing earth blocks has been mechanised and manual or hydraulic presses, or completely integrated plants can be used. Products range from accurately solid shape, cellular and hollow bricks, to flooring and paving elements.

Adobe, rammed earth and compressed earth blocks are the most widespread earth construction techniques used today. They have reached extremely high scientific and technological levels, and permit the construction of a wide variety of components and construction systems - for example, foundations, floors, pitched and flat roofs, arches, tiles, chimneys, canals, roads, dams and bridges etc.

Clay as a Binder

Clays, in their unfired state, are the main binders of earth. They are deeply embedded in traditional building cultures in many parts of the world. It is estimated that over a third of the world’s population are living in houses of earthen construction. Although they have the limitation that they soften when wet, they are the cheapest binders, with very low energy consumption.

©T.Joffroy (2)

Buildings of unstabilised earth, face the risk of erosion unless special design precautions are taken to reduce exposure to rain and moisture. For durability, earth should only be used where it is not prone to water or damp. Optimum designs will depend a lot on the environment, such as the natural drainage and water table; the climate, for example, rainfall (quantity and intensity) and winds during rains; and on the maintenance practices of the users.

Stabilisers and other additives or methods such as good compaction and grain size optimisation can reduce swelling, shrinkage and cracking, increasing strength and water resistance.

©H.Mathissen (1)

When clay is mixed with water it becomes malleable, plastic or liquid, allowing it to be shaped. When drying, clay sets and recovers its cohesive properties, and so can bind the soil together.

Most soils consist of clay together with proportions of silt, sand and gravel. The larger particles give structure to a soil, while the clay holds it together and to a great extent provides the cohesion.

To obtain a good building material which is strong and easy to use, the proportion of clay in a soil should be about 15 per cent on average. The sand should be 40 to 80 per cent, the gravel 0 to 40 per cent and the silt 10 to 25 per cent. If the clay content in a soil is too high, some minerals, such as, sand and gravels, or fibres, such as, straw or hair, can be added.

Earth is a ready building material which requires little further processing. Generally, a fairly wet mix with higher proportions of clay is used in mouldings and spreading applications, while a mix with less clay is best suited to compaction in a moist or damp state.

Environmental Advantages

• Unbaked earth does not contribute to the deforestation which follows the use of organic resources for firing baked earth materials.

• It does not consume any non-renewable energy, for example, oil and gas, at source for the processing and production of materials or further down the production for their application as does the production of cements, lime and other conventional binding materials.

• By exploiting strata on construction sites, it allows a considerable saving in energy for the transportation of materials.

• It does not contribute to the degradation of the landscape as does the extraction of minerals and ores which hollows out hillsides and open cast sites. A great deal of the earth excavated in the course of large public facilities work, for example, roads, can be recycled and used in building (allowing very easy decentralised distribution).

• It does not contribute to the diminishing of resources of aggregates, such as gravel and sand, excavated either from quarries or from water courses, in insular sites or lagoons, putting into peril the ecological balance of these natural environments.

• It uses very little water, essential for the life of the people.

• It produces no industrial or chemical waste and moreover has the additional advantage of being almost entirely recyclable.

• Unbaked earth is not only non-polluting in its use, it also guarantees the absence of harmful effects in the context of daily life such as the absence of gaseous emissions or other toxic chemical components, radioactive emission etc.

• The surface texture, colour, form and luminosity of unbaked earth makes it an attractive material for buildings without ruining the natural environment.

• Unbaked earth is often comparable in cost with, or indeed more economical than, competing technologies. It requires no major financial transport costs because its generally light production infrastructure.

• Unbaked earth requires only simple production and application tools (moulds, presses, light shuttering and masonry tools etc.) which are accessible to a wide population of masons and self-help builders.

• Unbaked earth follows on in the heritage of the traditional architecture of numerous countries using local materials. It allows local populations to take charge of the production of their built environment and thus control their living environment.

For further information, please contact:
 

Intermediate Technology would like to thank CRATerre - in particular, Hugo Houben - for providing the original material and photographs on earthen architecture.

Photographs

T.Joffroy (1): Mayotte, Tsangamouji, 1993. Low cost CEB housing, Lagavie II housing estate. Architects from SIM (the Mayotte Housing Company).

T.Joffroy (2): Saudi Arabia, Janadryah, 1988. CEB exhibition building built for the Royal Commission for Jubail and Ynabu. Architects from CRATerre.

H.Mathissen (1): Mali, Segou, 1987. Gabriel Cisse Centre built with CEBs. Architects: N.Widmer and A.Klien.
 

Further reading available from ITDG Development Bookshop

Adobe and Rammed Earth Buildings: Design and construction
Paul Graham McHenry
£19.95, (University of Arizona Press), 1989, ISBN 0 81651 124 1

Building with Earth: A handbook (Second Edition)
John Norton
This handbook provides practical help in choosing whether and how to build with earth, from soil selection through to construction and maintenance. The techniques described in the second edition - revised and updated - of this book have a focus on achieving good quality results with accessible methods, that can go on being used by rich and poor, and for simple buildings as well as the more sophisticated.
£9.95, (ITP), 1997, ISBN 1 85339 337 1

Buildings of Earth and Straw
Bruce King
In this book, Bruce King explores the details and methods for building durable and safe earth and straw houses. While many technical books can be dry, uninteresting and difficult to read, Bruce has managed to provide technical information in an accessible and entertaining manner. Although parts of this book will admittedly require engineering training to understand, even the uninitiated builder will find a wealth of usable material here.
£15.95, (Chelsea Green), 1996, ISBN 0 96447 187 6

The Cob Builders Handbook: You can hand-sculpt your own home
Becky Bee
A handbook aimed at encouraging the rebirth of natural building. It is written for people with or without building experience and is full of easy to follow diagrams and instructions. Becky Bee has built natural structures in the United States, Australia, New Zealand, Central America, and Samoa. Her company, Groundworks, has been at the forefront of the cob revival: building, teaching workshops, and hosting natural building symposiums.
£17.95, (Chelsea Green), 1997, ISBN 0 96590 820 8

Compressed Earth Blocks Volume 1: Manual of production
Vincent Rigassi
Volume 1 deals with the production of compressed earth blocks (CEB), both technically and economically, and is particularly suited for producers considering to make such blocks commercially. The book considers a range of production technologies, from a manual press - 600 blocks per day - to an automated press producing ten times as much.
£16.95, (Vieweg), 1995, ISBN 3 5280 2079 2

Compressed Earth Blocks Volume 2: Manual of design and construction
H.Guillaud, T.Joffroy and P.Odul
Volume 2 deals with the use of CEBs and must interest both designers and builders. Its introduction links the use of CEBs with often age-old traditions, and shows what has been achieved more recently, both in the South and the North, using CEBs for various types of building.
£18.95, (Vieweg), 1995, ISBN 3 5280 2080 6

Earth Construction: A comprehensive guide
Hugo Houben and Hubert Guillaud
A comprehensive and illustrated handbook which will be essential reading for anyone involved in construction. Earth is extremely versatile and cheap but users must have a proper knowledge of its real potential in order to use it to its best effect.
£25.00, (ITP), 1994, ISBN 1 85339 193 X

The Rammed Earth House: Rediscovering the most ancient building material
David Easton
This book is an eye-opening example of how the most dramatic innovations in home design and construction frequently have their origins in the distant past. By rediscovering the most ancient of all building materials - earth - forward-thinking home builders can now create structures that set new standards for beauty, durability, and efficient use of natural resources.

Rammed earth construction is a step forward into a sustainable future, when homes will combine pleasing aesthetics and intense practicality with a powerful sense of place. Rammed earth homes are built entirely on site, using basic elements - earth, water, and a little cement. The solid masonry walls permit design flexibility while providing year-round comfort and minimal use of energy.

In this book, David Easton shares the gift of his hard-won secrets for making this age-old technology viable today.
£25.00, (Chelsea Green), 1996, ISBN 0 93003 179 2

Rammed Earth Structures: A code of practice
Julian Keable
Ramming earth has been a method of construction for centuries in various parts of the world. This technique can produce buildings that are strong, durable safe and desirable, and because earth is an abundant and cheap resources, rammed earth buildings are often very economical.

To achieve the best results the right techniques for selection and testing of soils must be used to protect walls from water damage and shrinkage. This book aims to show how high standards can be achieved and the criteria on which rammed earth structures and building techniques can be judged.
£12.95, (ITP), 1996, ISBN 1 85339 350 9
 

TVE/ Practical Action gratefully acknowledge support for the HANDS ON programmes from the UK's Department for International Development (DFID), the European Commission (EC), the UN Foundation and UNDP/The Equator Initiative in collaboration with the Government of Canada, IDRC, IUCN, BrasilConnects and the Nature Conservancy.