The Building Codes
Societal Impact Matrix
Return of The Village
Habitat For Humanity
Curves of Breath & Clay
Overview of Techniques
Nature, Earth & Magic
History of Cob
Cob Q & A
Compressed Earth Blocks
German Clay Building
Earthen Plaster & Aliz
Solar Water Heater
Barefoot Architecture: Creating the Straw Bale/Earthen House
ATHENA and BILL STEEN
Traveling en route to the mountains of southern Sonora or other destinations in Mexico, Ciudad Obregon seemed to be, at best, a place to pass through as rapidly as possible on our way to somewhere else. A modern agricultural city of approximately 400,000 people, Ciudad Obregon was the birthplace of the Green Revolution under the guidance of Dr. Norman Borlaug. Designed in New York by the Richardson Development Company and built mostly after the 1930s, it clearly lacks the colonial charm of nearby Alamos and, with the appearance of Pizza Hut and Kentucky Fried Chicken, its distinction from cities north of the border has become blurred. If we had been asked to choose a place in Mexico where we would like to work, it would have been near the bottom of our list. However, fate and one's imagination rarely coincide, and so it was that we were asked by the Save the Children Foundation of Sonora to help them in their efforts to develop straw-bale housing.
With over three-quarters of a million acres of wheat in cultivation every year, Ciudad Obregon is a perfect place to make use of the staggering amount of straw that is annually burned. Its expansive clay soils are nightmarish, the region is almost treeless and the summer temperatures can consistently exceed 110 degrees. But now, almost four years and many tortillas later, Ciudad Obregon has become a place to which we anxiously return. It is the place where some of the most meaningful work of our lives is taking place, a place where friendships, cultivated over handfuls of mud and straw, have let memories of Mexican beaches and the colonial south fade gently into the past.
The devaluation of the Mexican peso was in many ways the major factor that influenced our early work. The monetary crisis, and the inflation that followed, dictated that most building activities for the average Mexican cease or be drastically reduced in cost. Concrete, which is the dominant building material of the region, became more expensive than ever. For many residents of Aves del Castillo, the neighborhood where we work, one bag of cement is equivalent to one or two day's wages. Lumber, costly and of poor quality, remains even further out of reach.
These circumstances made it all the more necessary to explore less costly materials and methods. We initially concentrated on small (200-300 sq. ft.) structures that were designed to compete in cost with small shacks built from scrap wood and corrugated asphalt panels. We helped build several of these small houses costing between $350 to $500. They were all load-bearing straw-bale buildings that relied heavily on a local bamboo-like reed called carrizo (arundo donax) and the local clay soils. All were set on earthbag foundations with the bags either dirt-filled on rubble trenches or filled with gravel. The walls were finished with earthen plasters and some have a finish coat of lime.
As usual, the roofs required the most ingenuity. Initially, we tried using pallet wood but found the pallets too difficult to disassemble. We then discovered 3" to 4" diameter poles that were discards from timber cutting operations because they were too small for convenient milling. The roof surface or decking was constructed of "carrizo" and covered with a straw/clay mix also used to create the parapets of the walls. We used a mix of powdered marble, white cement and an acrylic water-proofing component as a final coating.
These little houses are affectionately called everything from "casas provisionales" to "casas economicas." By drawing upon modern straw-bale building techniques, traditional Mexican building, classic European methods (straw/clay and cob) and the incredible ingenuity of people confronted with few resources, a straw-earthen building system is unfolding that:
· is truly inexpensive and small in scale
· relies on natural local waste products
· uses few manufactured materials
· has a simple, beautiful aesthetic
· doesn't unnecessarily displace human labor with machines
These early efforts led to two exciting projects. In 1997 and '98 we helped design and build a demonstration center for Save the Children. It's a place where people can see, learn and experience alternative ways of building, food production and other appropriate technologies that are within the reach of everyone. One of the first buildings to go up at the Center was a 5,000 sq. ft. office for Save the Children. It embodies on a larger scale much of what we learned over the previous years, and created an opportunity to use techniques and methods that we had previously utilized on smaller, more informal projects.
1997 also marked the beginning of a formal straw-bale housing program. Through coordination with one of the wealthier families in Obregon, Save the Children can now offer families a low-interest, short-term mortgage program and a group of trained builders to construct housing that will be competitive with the typical poorly-insulated concrete-block housing. Owners of these structures have the option to participate in the construction of their houses to reduce costs.
The first house to be built under this program is an 800 sq. ft. straw-bale building that, including labor, cost 30,900 pesos to build or, depending on the rate of exchange, $4,000 dollars paid back on a 10-year mortgage. In contrast, an uncomfortable government subsidized 300 sq. ft. concrete block structure can run as much as $10,000 dollars, with a 25 year mortgage and a higher interest rate. Short of building one's own home, cheaper housing options are not available.
Both the office building and the aforementioned house follow a similar method of construction. They utilize an infill wall system of straw, clay and carrizo in conjunction with concrete columns, necessitated by the use of concrete in the roof structure.
One of the most exciting innovations to come out of these projects has been the creation of straw/clay blocks. They are more insulative and lighter than regular adobes as well as more resistant to damage by rain or water. These qualities make the blocks a better building material for families or workers who don't have enough training, background or tarps to protect straw bales during a building project. Another advantage is that they can be produced without baling machines. This last fall, members of the Aves del Castillo community made approximately 5,000 straw/clay blocks for the new office building. Women, men and children were paid 1 peso for each block, creating another source of employment for people normally confined to very low-paying agricultural field work.
These blocks were first used in a small house built for the caretaker at the new Center. The walls of this building are load-bearing with a concrete bond beam and a clerestory roof built primarily from pallets nailed together and straw/clay as the insulating material.
We designed the office building around a central courtyard to take advantage of passive cooling strategies. Before the arrival of air conditioning, courtyards were an essential part of desert houses. The exterior walls of the building are built of straw bales, while the walls around the courtyard and all interior walls are built of straw/clay blocks. Around the perimeter of the courtyard is a porch covered with palm thatch, providing a cool refuge from the blazing sun.
The infill bale walls are uniquely constructed. Rather than the conventional technique of pinning the interior of the bales, we have gone to a system where long lengths of carrizo are placed on the inside and outside of the bale walls and then are tied together using a self-locking knot, squeezing and sandwiching the bales between them. At the height of seven courses the two-wire bale walls are compressed using a homemade Mexican "Gripple" system: a 3" diameter pole is laid on top of the seventh course, over which a heavy gauge wire is passed and then tensioned with a fence stretcher, or "come-along."
Using this technique, the wall sections compress in the vicinity of 4 to 5 inches. The poles then became part of the door and window lintels. One more bale is placed on top of the seventh course before the concrete bond beam is poured. To level the uneven surface on top of the seventh course created by the pole, straw/clay blocks are used to adjust the height of the bale walls. The combination of using carrizo, pins and compression creates an externally stable and solid infill wall section.
The walls gain further strength from a very thick coat of earthen plaster that averages somewhere between 3 and 4 inches thick. The mix is comprised of clay-soil slip with a very large amount of chopped straw (the same mix used for making straw/clay blocks). We began using this system because of the cost and difficulty involved in acquiring sand. The high quantity of straw prevents large cracks from forming as the mix dries on the wall. Small cracks remain, but not enough to disturb the strength and integrity of the wall. The addition of manure in finish coats can remove most of the small cracks if desired.
A sufficient quantity of this mixture is applied by hand to the wall to give it the final shape and form. Since our Mexican co-workers like straight, flat walls, this translates into a lot of material. These coatings add a lot of strength as well as mass. Finally when the building is completed, a thin coat of lime plaster, stabilized with prickly pear cactus (nopal), will be used as the exterior finish coat. A variety of lime, gypsum and earth plasters provide the finish coats on the interior of the building.
Prior to the office building, the roofs of earlier straw-bale buildings integrated cardboard boxes filled with loose straw into the concrete. This added insulation and helped decrease the amount of cement needed. In the office, we are experimenting with a variety of roofs primarily using a precast concrete beam called a "vigueta" in conjunction with carrizo and straw/clay. The most exciting of these have been two vaults built of a combination of three overlapping layers of carrizo, a layer of straw/clay and a thin layer of concrete. They are not only beautiful structures, but reduce the amount of form-work, skill, and cement needed.
In contrast to commercial construction here in the United States, the entire office is amazingly being built with little more than three shovels, two hammers, two wheelbarrows, one machete, one handsaw, two plastering trowels, one fence stretcher and a hammer mill to chop straw. Because of the innate difficulty of acquiring tools, this technology has been shaped in a way that only a limited number of simple tools are needed. This limitation has turned out to be more of a benefit than a hindrance. It makes constant creativity a necessity. We have had to learn and discover new solutions rather than running to the store and simply buying our way out. We are regularly reminded by our co-workers that "no tools make the work harder, but too many tools keep it from being enjoyable." Free of heavy machinery and dangerous tools, the work naturally opens itself up for all to participate.
As this building system has grown, so has a group of women workers skilled in plastering, clay paints, and working with straw/clay combinations. They have been building everything from earthen bread ovens to household furniture such as bookshelves, desks and seating made only from straw/clay and carrizo. The furniture is a popular addition since most families can afford very little, if any.
In many respects it has been the close collaboration and friendships, built with people from a totally different context than our own, that has been the biggest contributing factor to the unfoldment of these methods. By stepping outside of our everyday known world, we have been able to sufficiently broaden our perception of how we build to become part of a highly-creative process. Equally important has been the same trust and willingness on the parts of our Mexican co-workers. Consequently, we are involved in an ongoing process which offers very direct and quick feedback. We continue to work and learn together, treasuring the sound of barefoot children playing in the background.
Athena and Bill Steen are directors of The Canelo Project, offering natural building workshops, building innovative simple, straw-earth houses in Mexico and numerous cultural exchange and training programs. They are co-authors of the book The Straw Bale House.
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This article was originally published in The Last Straw Issue #18 and is reprinted with permission. The Last Straw, The Grassroots Journal of Straw Bale and Natural Building, HC66 Box 119, Hillsboro NM 88042; ph 505-895-5400, fax 505-895-3326; firstname.lastname@example.org, www.strawhomes.com
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