Natural Building - Light straw-clay
For most of our existence on Earth, we have lived without architects, engineers, designers and manufactured building materials. In many societies, almost everyone knew how to make their own tools and homes. They learned from observation, experiments and practice. In Europe, light straw-clay houses are examples of culture development. This technique, also known as a light clay or a light loam, evolved from a heavier clay method called wattle and daub, which has been used in construction for at least 6.000 years (now mostly in use in the preservation of historic buildings)
Due to the lack of building materials after World War II, interest in clay building was intensified and a standard clay building code was introduced. In Europe during the 1970s and 1980s clay products were tested, improved and used with renewed vigor. As a further result, "straw/clay" was developed.
Due to its simplicity, affordability and creative possibilities, we believe there is rising opportunity and fertile grounds to apply light straw clay technique nowadays.
Post and beam (also called timber frame) is ideal for building light straw clay walls. Structural frame and the weight of the roof are carried by a wood and it is important to be designed in accordance with the International Building Code. Because the timber frame structure is completely surrounded by the clay and fiber enclosure the frame has timeless protection from environmental factors. Timber structures can be deconstructed and then re-used for many following years.
For building our houses we use Greek pine wood. 10x10 cm beams are placed vertically and horizontally on the stone foundation. The space between columns is 15 cm, which makes exterior walls 35 cm thick. The internal walls are 10 cm thick.
Materials for making light straw clay
The tools and experience necessary to build light clay straw walls are minimal.
Straw - Straw can be wheat, rye, oats, rice or barley, and should be free of visible decay and insects. Availability of straw can fluctuate with the season so it is important to have some knowledge of the local agricultural cycles to access the best selection of material. For our constructions we have chosen wheat straw as it was the most locally available type.
Clay soil - Soil should have a minimum clay content of 50% by volume. Making a clay slip is pretty easy: we place soil in the cement mixer (as it’s easier for bigger quantities) and by slowly adding water, it reaches the right consistency, which is that of a heavy cream.
Light straw clay mixture - We place all straw stems in a big table and pour evenly of clay slurry onto the straw. Everything needs to be mixed well by hands until they are thoroughly and evenly coated so as to avoid pockets of dry straw.
Straw bricks - Light straw clay mixture can be replaced by straw bricks. Our straw bricks are made in a special mold, which allows us to adjust the dimensions by movable partitions.The slip-coated straw is placed into the forms and compacted.
Building the walls
Timber battens - should be fitted horizontally to the structure, in order to "lock in" the straw-clay mass. First we nail battens along the one site of a wall. The next step is to fill the wall with light straw clay mixture. Once each layer is complete we nail horizontal batten, to prevent loss of material from the wall, then we tamp next layer of infill until the wall is complete. The material should be pressed good to fill all corners of the wall. Once the wall has dried for a week, we may need to add more mixture in gaps that appear.
Wall drying time depends on the season and climate (wind and relative humidity). Depending on the straw, there are some of missed seeds sprouting, when they shrivel and die, the wall may be dry enough.
The wall can be checked also by moisture meter, the moisture content of the wallsneeds to go below 18%.
- One Straw Revolution: Light Clay Straw Construction. Jacob Schmidt
- Building without borders. Joseph F. Kennedy
- Natural Building Colloquium.An Introduction to Traditional and Modern German Clay Building. Frank Andresen
- Research Report. Initial Material Characterization of Straw Light Clay. JoshuaThornton 2004
Natural Building - Straw bales
Strawbale buildings were first constructed in the USA in the late 1800s, when baling machines were invented. The settlers on the plains of Nebraska were growing grain crops in an area without stone or timber which could be used for building. They built houses with the bales as if they were giant building blocks, where the bales themselves formed the load bearing structure. The settlers discovered that these bale houses kept them warm throughout the very cold winter yet cool during the hot summer, with the additional sound-proofing benefits of protection from the winds.
This early building method flourished until about 1940, when a combination of war and the rise in the popularity using cement, led to its virtual extinction. In the late 1970s, Judy Knox and Matt Myrhman among other pioneers of the strawbale revival rediscovered some of those early houses and set about refining the building method and passing on this knowledge to environmental enthusiasts.
The first straw building in the UK was built in 1994, and today approximately 1000 new structures are being built annually all over the world.
There are two basic styles of strawbale construction.
Load-bearing also called Nebraska - pioneered by the Nebraskan settlers in the USA. In this method, the bales themselves take the weight of the roof, which means there is no other structural framework. They are placed together like giant building blocks, pinned to the foundations and to each other with coppiced hazeland have a wooden roof plate on top. This is the simplest and very fast method but rather for smaller constructions where maximum unsupported (unbraced) wall length is 6m.
Post and beam also called Timber Frame, has become predominant style, as is more readily acceptable to building officials, lenders and insurers. Straw bales are used as infill panels between or around a structural frame and the weight of the roof is carried by a wood. This method requires a high level of carpentry skill and uses substantially more timber than a load-bearing design, but provides a bigger stability for the construction.
Irrespective of the style, all strawbale buildings are plastered. Straw, being a breathable material, functions best when used with similar materials. Various mixtures of materials as earth, sand and lime are covering the straw and make it fireproof.
Benefits of building with straw
- Thermal insulation - straw provides very good insulation at an affordable cost.
- Sound insulation - strawbale walls have very good acoustic insulation. Two recording studios in USA are built of strawbales for their sound proofing quality and insulation.
- Sustainability - straw is a renewable natural product and by using it, means small environmental footprint.
- A Healthy Living Environment - straw is natural and harmless. Walls are breathable and do not give off harmful fumes such as formaldehydes, as many modern materials. Strawbale house is highly recommended for allergy sufferers.
- Energy saving - the most significant saving on strawbale houses is in the long-term fuel reductions due to the high level of insulation. Heating costs can be reduced by up to 75% annually compared with modern style housing.
- Information Guide to Straw Bale Building. Amazon Nails 2001
- Buildings of Earth and Straw: Structural Design for Rammed Earth and Straw-Bale Architecture. Bruce King
- Centre for Alternative Technology (CAT) www.cat.org.uk
A few words about Natural Building
Because of its versatility and widespread availability, earth and straw have been used as construction materials throughout the world since antiquity and particularly soil is one of the oldest building materials; the first freestanding human dwellings may have been built of sod or wattle-and-daub. About 10,000 years ago, the residents of Jericho were using oval, hand formed, sun dried bricks (adobes), which were probably a refinement of earlier cob.
Earthen homes are common in Africa, the Middle East, India, Afganistan, Asia, Europe, South and Cetral America. One-third of the world's population is currently living in homes made of unbaked earth.
A simply definition for natural building, would be any building system which gives value on social and enviromental sustainability. Easy-to-learn techniques based on locally available, raw, renewable and recycled resources, ideally gathered from the site vicinity makes natural building very unique subject which rely heavily on human labor and creativity instead of on capital, high technology, and specialized skills.
Earth construction takes many forms, including adobe, rammed earth, and wattle and daub. By adding a straw, the number of functional methods of natural constructions is expanded to Straw bale, Light straw-clay, Straw bricks and Cob. This provides a wide range of possibilities to choose one's own method for natural construction according to the climate zone and the availability of raw materials.
All the techniques of Natural Building are very flexible and forgiving medium. It needs dedication more than physical strength and willingness to experiment, more than skills. Building with natural materials is an easy way to go on a big adventure!
Climate and Materials
The right method for natural building varies according to the climate of each place. Temperature and availability of materials for construction are playing the main role. For the desert areas the ideal technique is cob which holds the night's cool throughout the day, slowly heating up to release the day's warmth at night. For cold climate the insulation is needed and here with a help is coming a straw which is an amazing isolator for walls, straw bale technique is a solution for this kind of climate.
Availability of materials is important for choosing the type of foundations. Stone is the best and will still be the best a few thousand years from now, after the home has returned to the elements. Collected stones are placed on the ground like puzzle. To eliminate chemicals elements even within the foundations, cob or earthen mortar is used to avoid the moving of stones.
In dry climates a good option for foundation is the use of agricultural bags filled with earth tamped. This concept was originally presented as a Superadobe technology by architect Nader Khalili to NASA for building habitats on the moon and Mars!
- The Cob Builders Handbook. Becky Bee
- Natural Building Colloquium (The Case for Natural Building). Michael Smith