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EARTH BUILDING UPDATE
Thanks to The Owner Builder for permission to re-print this article.
213 – JUNE/JULY 2019 B E I N S P I R E D – R E A L S TO R I E S A B O U T R E A L OW N E R BU I L D E R S
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The Earth Building Association of Australia (EBAA) promotes the use of unfired earth construction.
PASSIVE SOLAR
u LOW WASTE BUILDING u HEALTHY HOME u STARTING OUT
Earth building is the practice of building using unfired earth material. Earth is used to construct walls, floors, roofs and even furniture, fireplaces and ovens. It is a building technology with an 11,000-year-old history and tradition, which is used worldwide. Today it is estimated that between one third to one half of the world’s population are currently housed in earth homes.
The common feature in all earth building techniques is that the material used is subsoil that is composed of clay, silt and sand, where clay is the binder or ‘cementing’ ingredient, and that the drying process is through the evaporative effect of sun drying. The methods and techniques used are as varied as the people, the resources available and the climates in which they are used.
Earth building techniques
There are at least 12 methods of earth building used and these can be further divided into a total of at least 18 approaches. The following is a summary of what are perhaps the best known of the earth building techniques used in Australia today. This is by no means an exhaustive list, but provides a useful overview and starting point.
Mud brick or adobe
Mud brick is the most popular name used in Australia to describe bricks made from various compositions of soil with water, which is mixed, moulded and dried at air temperature through the evaporative effect of the sun during thebrick production stage.
There are almost as many ways of making mud bricks as there are mud brick makers. With puddled mud bricks, the moisture content is quite high and the texture is that of mud or dough. The material is poured into or moulded in simple bottomless moulds. The mould is often lifted off immediately and the brick left to dry through evaporation.
When dry, mud bricks have a density of around 1750kg/m 3 .
Pressed earth bricks
With pressed earth bricks, moisture content is lower and the consistency is that of damp soil similar to rammed earth. The material is pressed into shape using a hydraulic ram that is released immediately, with the bricks then moved to a drying area.
When dry, pressed earth bricks have adensity of around 2100kg/m 3 .
Rammed earth or pisé
Rammed earth uses damp or moist earth, with or without any additive, which is then rammed (tamped) in place between temporary moveable formwork. It is a solid masonry wall which does not have, and does not need, any cavity.
Since the 1970s, cement has been used as a stabiliser in rammed earth; with
Photo courtesy: Rob Hadden
Left page: Western Australia leads the world in modern cement stabilised rammed earth construction. Above: Cob, sometimes called ‘sculptural adobe’, can be free formed in situ and trimmed to shape later. Below: Mud bricks are made with a variety of methods and consistencies, but all are air dried.
the addition of a waterproofing additive, stabilised rammed earth has proved itself capable of competing with other forms of masonry walling.
When dry, rammed earth has a density of around 2100kg/m 3 .
Cob
Cob is similar to rammed earth in that it produces a monolithic or one piece wall,though it is different to rammed earth in two ways. The earth material used has more clay, and straw is added to reduce the potential for cracking as the wall dries through evaporation. The process requires less water than in mud brick making though more than is used inrammed earth.
The wall can be free formed and trimmed to shape later or built within simple shutters. It isn’t so much tamped but pressed gently or worked into the wall until a lump (or cob) of earth material becomes part of the wall.
When dry, cob has a density of around 1450kg/m 3 .
Wattle and daub
Wattle and daub (above left) is an earth building technique that, like all of the above techniques, was popular in theearly Australian colonies; it is rarely used here today although it is still popular elsewhere.
A timber frame is prepared with timber lattice, often using Acacia sticks woven together, before a mixture of wet clay, dung and straw is daubed (placed byslapping handfuls) onto each side of the lattice. Density will depend on the size, amount and spacing of the lattice and the amount of straw or other fibrous material added to the clay. Light earth/clay straw
Light earth (above right) is a technique that is relatively new to Australia. It was first popular in much colder climates though it has found some popularity in colder parts of Victoria, where it is being used to reduce heating loads and more easily complies with energy regulations.
Light earth is produced through wetting straw with a wet clay slurry that is gently tamped into temporary forms between a timber stud frame. It is often finished with earth render inside and clay or lime render outside, completely covering the timber frame in the process.
When dry, light earth/clay straw has adensity of 600kg/m 3 , which is too weakto be loadbearing and is therefore better used as wall infill between framework and for internal walls.
Earth render
Earth render is a covering layer composed of clay, sand and silt, often with the addition of dung and sometimes lime. It can be used to coat some forms of earth wall, especially the lightweight (light earth) methods, as well as other natural building techniques such as straw bale construction.
Stabilised vs. unstabilised
When clay is the only binder then the earth building technique may be called unstabilised; this is the most natural form of earth building. Stabilisation refers to the process of putting additives into the mix, which otherwise is just earth (with clay) and water, with the water content varied to suit the constructiontechnique. Stabilising additives can include cement, lime, bitumen, plant based products and sometimes even modern chemicals.
Unstabilised mud bricks and rammed earth are by far the most common worldwide building techniques, of all building techniques. In Australia, stabilised and unstabilised mixes are used in many different earth building techniques.
Thermal performance
All earth wall material can be optimised for thermal performance by reducing the silt, sand, gravel components of the earth wall material mix and replacing some of it with fibre orlightweight aggregates like pumice, plant material, sawdust, grains or expanded/aerated glass.
Mud brick and cob can have their thermal mass reduced to as low as
1000kg/m 3 in order to reduce thermal conductivity. However, this also reduces heat capacity which is a valuable attribute for energy efficiency, especially if designing to negate the need for cooling in hot weather. Good thermal mass design, construction and operation can negate the need for air conditioning. In traditional vernacular architecture it was common for lightweight techniques to be used in cooler climates and heavier techniques to be used in hotter climates. The good sense of ancient design is confirmed by modern modelling of passive low energy architecture.
Rammed earth can have a density of 2350 kg/m 3 to 1700 kg/m 3 . Rammed limestone typically has a density above 1750 kg/m 3 and, being white, is quite reflective. Generally for rammed earth, 2100kg/m 3 is a common ‘mid range’ figure. This is with ‘regular’ earthen materials; specialised materials such as scoria and pumice can give lower densities and better insulative properties.
Generally speaking the denser the material the more ‘thermal mass’ it has, which is fundamentally its ability to store heat (or cold) energy; the less the density the more insulative a material is, providing a better barrier to the passage of heat or cold. One secret to good design is the strategic placement of high thermal mass (dense) and insulative (lightweight) structures to achieve optimal or designed temperature management conditions, which require minimal – or ideally no – artificial or external heating or cooling energy. The easiest way to introduce thermal mass is by having more walls, by including internal earth walls or increasing the thickness of the walls.
Insulation rating
With passive low energy architecture and high thermal mass, well ventilated free running unfired earth buildings can and do provide good comfort conditions with near zero energy input. Built with local materials and local labour, full thermal comfort is achievable.Achieving a nil air conditioning load in summer is common. Achieving a low winter heating load is possible, with a small source of warmth from a fire, solar or otherresulting in low energy living.
The Australian National Construction Code (NCC), administered by the Australian Building Codes Board, currently unfairly favours insulation rather than thermal mass. It defines and tabulates and sets minimum insulation levels in parts of buildings in the NCC, but does not mention the words thermal mass once. The scientific truth is that the ideal thermal home – or even a fair thermal performing home – needs a combination of insulation and thermal mass, and that the combination requireddepends on the location, orientation, design, etc.
With the NCC so skewed toward insulation, the insulative properties of earth walls have been investigated by earth wall builders. Lower density earth walls generally give better insulation butlower thermal mass, while higher density walls generally give better thermal mass. To achieve a better insulation rating, modern rammed earth walls can be built with a layer of insulation (typically foam) within the wall, providing both high insulation andhigh thermal mass, all in one wall.
Appropriate technology
Earth building is appropriate technology because it is simple and available to everyone – poor or rich alike. The material is durable (100-400 years plus proven in Australia, Europe, England, Middle East) offering longevity rivalling modern western housing (25-50 years in Australia).
Earth building is adaptable, able to beused for footings, floors, walls and roofs by using different techniques. It is flexible because it can be moulded and shaped when wet, rammed and pressed when moist, and then hardens in the sun so that it becomes durable. It can becarved, shaved and sawn when dry. The surface (if unstabilised) can be wet and reworked to a polished finish if required. It can be used to create buildings of any shape or style.
Earth building is raw and natural, has low embodied energy and can be used to achieve thermal mass and insulation by adjusting its density and thickness. The material is non-toxic, non-allergenic, controls humidity, is fire, rot and termite proof and therefore earth can be used to create safe and healthy buildings. Earth offers great sound isolation and is effective in screening (reducing) high frequency electromagnetic radiation (Building with Earth, Minke, p.33).
Many designs and methods of using earth have been developed around the world to suit various climates and cultures. Earth is a very attractive building material, in harmony with the local environment from which the material was sourced, especially when used with other locally available, natural building materials. The aesthetic beauty and comfort can be further enhanced if local vernacular building styles are used. Local indigenous or traditional building styles often use climate responsive designs and are appropriate in relation toother environmental factors, like weather and natural hazards.
Renewable and sustainable
Having a minimal carbon footprint, earth building is renewable technology. The material is often simply ‘borrowed’ from the earth for the life of the building and (unstabilised) can be reused and recycled indefinitely as a building material or returned to the earth. The energy used to dry the earth into bricks or monolithic walls, floors or roofs is ‘free’ solar energy, as the earth is sun dried through evaporation. The thermal mass of earth can be used to store both warmth and coolth, balancing diurnal fluctuations in temperature in all seasons.
Earth building is sustainable technology. The use of raw unfired earth as a building material dates back to 9000BC and today it still houses one third to one half of the world’s people. The material is abundant and widespread, uses very little energy in the entire process from raw earth to building, is durable, and its properties make it an excellent choice for climate responsive buildings. These buildings achieve thermal comfort and a degree of ‘free’ running through consideration and selection of the appropriate design method for the location.
The sustainability credentials of earth building outshines any modern material in any life cycle analysis; from the embodied energy in creating the building through the reduced energy used in its long life, in maintenance, heating and cooling, to demolition and reuse.
Green building
Earth is possibly the ultimate green building material. • Meeting the challenges of comfortable safe buildings while reducing the energy used in construction, heating and cooling of buildings, improving indoor air quality and longevity of buildings and reducing toxic waste tolandfill. • Raising the living standards of poorer people and maintaining our own without depleting resources, increasing environmental degradation and loss of biodiversity. • Future proofing our buildings against spiralling energy costs and shortages. • Building homes that allow us to enjoy our existing lifestyle and reduce our need for fossil fuelled energy and greenhouse gas emissions.
EBAA believe it is exactly what the world needs today to provide safe, durable, comfortable and desirable homes. Those who have owned or lived in an earth home would know and appreciate this. It is a technology that is ancient yet still most relevant.
Build of earth for the Earth. u
For a more comprehensive picture, read any of the natural construction books by Gernot Minke, in particular ‘Building With Earth: Design and Technology of a Sustainable Architecture’, Birkhäuser (3rdrev. ed. 2012, ISBN 9783034608220). This article first appeared in BuildIT Builders & Renovators Resource Guide March 2019. The 2019 EBAA Conference is being held at the Bamarang Bush Retreat in Nowra NSW, from 27-29 September 2019. The theme is ‘Achieving high thermal performance, comfort and sustainability with unfired earth products.’ Friday will include lectures from experts and discussions with all. Saturday is reserved for workshops and demonstrations, to learn how to build earth walls, to make and lay mud bricks, to build rammed earth walls plus other earth building techniques. Sunday will involve visits to nearby earth built projects in mud brick and rammed earth. All welcome.
Links & resources
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Earth Building Association of Australia
0429 321 104, www.ebaa.asn.au
EBAA
EBAA (Earth Building Association of Australia) is a broad based organisation which has members that include builders, specialist contractors, tradespeople and owner builders, specialist manufacturers and suppliers, architects and designers, consultants, enthusiasts, educators and students, with a common interest in the use of unfired earth.
The formation of EBAA commenced in 1990 at a gathering held in Maldon, Victoria. A subsequent meeting took place in Mildura, Victoria in 1991 which elected the first Committee of EBAA. Since then the primary focus of the Association has been communicating constructively with all levels of Government concerned with the regulation of building practice in Australia as well as educating and informing our members and the public.
Our association has a strong national focus and is the peak body for earth building practitioners, both private and commercial, in Australia. Membership is open to all with an interest in earth building.
Aims and Objectives
• To represent the interests of members in the advancement of unfired earth technology . • To promote the informed use of unfired earth as a building material within Australia. • To establish an information and referral network for those wishing to use earth within the building industry. • To uphold the interests of earth building in public or private forums. • To act as an information source in any process to establish rules, regulations or code of practice which effect the use of unfired earth as a construction material. • To promote earth building technologies which are environmentally benign. • To liaise with other groups or individuals, both in Australia and internationally, who have interests in promoting earth building.
