BUILDING WITH STRAW#1: BRIEF HISTORY OF STRAW
Actualizată în: 3 Sept. 2020
AN ACCESSIBLE RAW MATERIAL, USED FOR HUNDRED OF YEARS AROUND THE WORLD
Thousands of years ago, our ancestors had at their disposal only local resources to build their shelters. Among the most encountered and accessible materials were clay, straw, grass, and reed, which were easily manufactured to form light structures and a roof over their heads. It’s estimated that the first straw constructions have appeared for the first time in Africa as far back as the Paleolithic (1.000.000-10.000 B.C.).
Closer to us, on the European continent, a lot of houses that have been built with straw and reed, over 200 hundred years ago, are still standing in the present day., the oldest house made out of straw bales dates back 400 years ago. In the Nordic region of Europe and Russia, straw has been used for the rooftops of houses, a technique encountered also in Japan, where straw was used as flooring in the form of tatami: straw ties weaved with grass and underlined on the edges with cloth.
In colder climates, such as North America, straw was used as thermal insulation material in the traditional tents of village people, being inserted between the inner cloth layer and the outer layer made out of leather. The second most common traditional method of utilizing straw in constructions was mixture with clay and some other binding agents, in different formulas, resulting in construction elements like mud bricks, mud walls plastered with clay and jute and other similar techniques very frequently used also in our country by our ancestors.
Starting the mid-1800’s, along with the development of mechanized baling, farmers of The Great American Plains, mainly Nebraska, turned to straw bales as the main construction material. In comparison with lumber, which was difficult to transport and very expensive, straw bales were a cheap and efficient solution, used not just for building houses, but also stores, farms, churches, and public buildings.
The technique, for areas with low seismic activity, was pretty simple: straw bales stacked one on top of the other and hardened with wooden sticks, plastered on both sides with clay, under a simple thatched roof. Many of these houses are still standing until the present day, despite the fact that they are located in an area with a high level of precipitations and humidity. In spite of all that, the straw bales stand in a good condition, an example being the “Pilgrim Holiness Church” from Arthur, Nebraska, built in 1928 and refurbished in 1976 with the same local materials (the plaster and finishing were made out of local clay, “gumbo mud”).
Another example of European straw-bale house, that presents itself in a great condition, is the Feuillette house from France, built in 1921 by Feuillette, a french engineer who was looking for new cheaper construction methods, as a response to the housing crisis caused by World War I.
The house was bought by “Centre National de la Paille” (CNPC, National Center for Straw Construction) with the purpose of preserving it in the patrimony as a key element in developing straw-bale constructions in France.
WHAT IS STRAW?
Straw is made of dried stems of cereal plants like rice, wheat, oat, barley, rye, etc. after being harvested and stored in a bale or a bundle, that come in different shapes (square, rectangular, or round). They do not contain the grain ending (as in the case of hay) and thus they have a low nutritional value and aren’t that appealing for pests. From a chemical point of view, straw contains mostly cellulose, hemicellulose, and lignin - just like wood - but unlike wood, straw has a very high level of silicate.
Romania is the first country in the EU regarding wheat export and it has been harvesting on average 2 million hectares annually. Reported to one hectare, out of a wheat crop results around 5 tons of wheat grains and 4 tons of straw. This means that annually, in Romania, approximately 8.4 tons of straw arise just out of wheat, without taking into consideration other cereal crops mentioned above. In other words, as raw material, straw is available from abundance and at relatively minimal costs, around 50 EURO/ton, at which we add transportation and taxes.
The size and weight of a straw bale differ, from rectangular bales with 2 or 3 strings to the round ones of large dimensions. The density of a regular bale depends on the type of straw, their level of humidity, and the compression level of the bailing machine, but generally, it should have a density between 40-80 kg/m3.
With the production of wheat straw only, throughout one year in Romania, it would be possible to build 1.600.000 houses of 100 square meters.
In general, straw is considered a residual product in agriculture and most of the time they are either left on the field to decompose, either they are grinded and mixed with the soil for the next crop or they’re burned, this being the only way for farmers to get rid of them. Nevertheless, these kinds of methods create trouble for the environment, because through burning, straw release back into the atmosphere all the CO2 absorbed in the growing phase, through photosynthesis. Moreover, the European Committee has been discouraging farmers that burn straw on the fields, by cutting their subventions.
Straw can still have other uses in other domains. In zootechnics, they are used as bedding for birds or animals, in the energetic field they can be exploited as pellets (with a caloric power of 4kW/Kg), as soil fertilizer and compost for the mushrooms crops and, not lastly, in the ecological construction sector, where they are going through a technological and cultural renaissance.
This article is part of a series dedicated to straw and its building applications. Don't miss the other articles!