Indigenous Construction Material
Monday, May 14, 2012
We are very familiar with straw and mud. Explore the countryside and you will see dried stalks of threshed grains, especially wheat and rice everywhere. Straw is used as a fodder, for covering floors, and thatching roofs, and in weaving mats, screens, baskets, ornaments, hats, fans and more. You can also see mud houses dotting the countryside landscape.
Building homes and other living structures with straw is also tradition dating as back as to the start of civilization. Since prehistory, human beings are using straw as a construction material. The incorporation of machine compressed bales seems to have started in early last century though. Compressed straw bales are being used like bricks in the buildings.
Having grown up in the rural Punjab myself (I come from a rustic village situated on the bank of River Jhelum where it passes along the foot of the Salt Range), straw and mud have a special place rooted deep in to my cultural perceptions and this personal bond encourages a more intimate relationship between the straw and me.
Earlier we have discussed how mud engineering is reviving in Pakistan. Thanks to Dr. Norbert Pintsch and his mud architecture projects that focus on architecture constructed of mud brick, rammed earth, compressed earth block and other methods of earthen construction. The proliferation of concept to use mud and improved techniques in order to raise the level of living in the population was discussed here on these pages some time ago. Now we have a look at straw as indigenous construction material.
Straw engineering has been introduced (I say re-introduced) in Pakistan after the devastating earthquake of 2005. Remember MW 7.6 quake that killed an estimated 100,000 people, razed over 780,000 buildings and rendered more than 3.5 million homeless mainly due to poorly constructed buildings in the area. Some 11 straw bale houses have been built in earthquake hit areas of Pakistan. A project to compress straw into bales is also working in village Jabbori – a heaven like village on the bank of River Siran in district Mansehra that suffered severe damage and loss of life in the 2005 earthquake. The awareness about the straw engineering and appropriate technology is growing fast.
What is more, Builders Without Borders (BWB) - an international network of ecological builders who form partnerships with communities and organizations around the world to create affordable housing from local materials and to work together for a sustainable future - believe the solution to homelessness is not merely housing, but training of local population to make houses for them. With the help of non-profit groups, BWB is offering help in the form of educational materials and has donated books and training materials for use at local level.
Renowned engineer Darcey Donovan is the spirit behind the concept of promoting straw engineering in Pakistan. Donovan has a B.S. in Mechanical Engineering from Stanford University, an M.S. in Civil Engineering from the University of Nevada, Reno, and is a licensed Professional Civil Engineer practicing since 1986. She is very keenly working to see straw engineering takes off in the earthquake affected areas in northern Pakistan.
There are many reasons to use straw as a building material. Close examination of eco-architect Laurie Baker’s straw buildings reveals that “using natural materials and showing them off will lead to a greener building. Such strategies reduce the use of energy-guzzling materials such as cement, steel, aluminum and glass.” Straw engineering is earthquake resistant, consumes less energy and produces lesser emission. Straw (wheat, rice) is locally available in abundance.
Straw is economical, practical, functional and attractive alternative. It is easy to work with. Straw is especially useful in hot climates like we have in Pakistan and in earthquake prone areas. Straw is a natural material that is found everywhere, especially where other building materials such as bricks, stone or wood are scarce due to affordability and or availability.
Straw engineering is a construction method that uses compressed straw bales as structural elements, building insulation, or both. There are two major types of construction with compressed straw bales: load bearing and non load bearing. A pillar and beam framework that supports the basic structure of the building, with the compressed bales of straw used like normal bricks, is the most common non-load bearing method. On the other hand there are many load- bearing compressed straw bale buildings that are standing just fine. It is estimated that “the method and materials (mud, straw) can produce buildings at half the cost of conventional earthquake-resistant buildings in Pakistan.
Some unfounded myths say that that straw building have a greater risk for fire, can be easily infested by pests and straw gets wet and ultimately decompose? Empirical observations and laboratory tests show that this is not true. Canadian and American materials laboratories have found that “the straw bale structure wall has proven to be exceptionally resistant to fire.” What is more, walls can be mud plastered as early as possible to increase their fire resistance. Similarly, pests are more of an imagined concern than a real threat. Once the walls are properly mud plastered or sided, there is no way for bugs or rodents to get into the bales.
Moisture threats can be handled easily with proper design and construction methods. So long as the dry compressed bales are installed and are properly sealed with the plaster and protected from water infiltration, they will perform well. With proper construction techniques, water will not enter the building thus making decomposition impossible. Rice straw, in particular, has a high silica content which increases its resistance to decay.
Focus of straw engineering is on architecture with the help of compressed straw bales, rammed earth, compressed mud blocks and other earthen construction materials. The proliferation of concept to use straw and appropriate technology in order to improve the quality of life is a very welcome idea and we in Pakistan need that. This can go a long way not only in the form of changing the look of population centers, rural as well as urban, but also in solving environmental problems related to use of energy and other finite resources. We already have convincing engineering evidence that straw buildings are safe and sound to start.
posted by S A J Shirazi @ 10:20 AM,
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