Straw Bale Spiral
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| Written by Nick Moser |
| Tuesday, April 8th 2008 |
| Straw Bale Spiral |
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This article discusses the technique of building with bales of straw, including the history and variations of the style, using my current construction project as an example. When crops such as wheat, straw, barley or other grains are harvested, the nutritional value is held in the seed heads at the end of long, thin stalks of straw. The straw has little organic material, and is made mostly of silica to transfer water and nutr
Bale it, Build it. In the 1840's a machine was invented to compress hay into square bales, making it easier to transport feed from hay farms to livestock miles away. It became popular in the late 1870's, when automatic threshers and balers became an easy way to harvest feed and store it for months without taking up much space. While hay is valuable feed for livestock, straw lacks the organic material needed by animals. Instead, it is packed with silica which is much stronger than the grasses in hay. Inadvertently the machine that was invented to bale valuable hay also paved the way for the modern straw bale house.
In the early 1900's the prevalence of all this excess baled straw made it inevitable that somebody would begin to stack them like bricks and put a roof on top. And this is exactly what the original 'Nebraska-style' straw bale house was. The oldest still-standing bale house in America is the Burke farm in Alliance, Nebraska. It was built in 1903 and is still in great condition through tornadoes, blizzards, and droughts. Since then the technique of building with bales of straw has matured, different styles developed, and the results well-tested as a great and economic way to build. Style There are several different styles of straw bale houses. The original, or 'Nebraska-style' is made by stacking the bales on top of a shallow foundation or footing. The bales are stacked like bricks, staggering the gaps every other row. Windows and doors are framed as the walls go up, and then a roof is placed atop the bale walls. Once the weight of the roof has settled the bales a bit, the windows are placed in and the walls are plastered. This style of straw bale house is also known as load-bearing, since the weight of the roof is held by the bales themselves. Tests have shown that bales without any other support can hold 400 lbs/linear foot.
Another style is using the bales as insulating fill between a wood frame structure. A traditional frame house, timber-frame or stick (2x4), holds the weight of the roof and is attached to the foundation. Timber framing is the ideal framing for this style since stick frames have less room between posts, making it difficult to fit bales between. In this case the benefit of the straw bales is the insulation. The average straw bale wall has an R- value (insulative value) of around 45. For reference, the average house with wall insulation has a value of R=20. Combined with the bales' high thermal mass the houses are slow to heat from summer sun and resist the cold winds in the winter, holding heating inside.
The last style is the use of straw bales in construction materials other than the standard field bales. The simplest is just a straw bale that has been re-compressed using high powered hydraulic presses. These increase the R=value up to 70 and can hold up to 4,000 lbs/linear foot! There are several enterprising companies that have devised ways to use straw by pressing it into sheets, to be used as flooring or in the place of drywall, or even into 2x4's to be used as wall studs. Design naturally. More often than not, straw bales are used as part of a natural building project that uses other natural materials, such as adobe bricks, natural stucco or cob. This is because natural materials mix extremely well with the use of straw bales. For example, to maintain a dry wall, the inside and outside coverings must be able to breathe, which clay-based plasters do well while cement plasters do not. Clay and wood bind well with the bales of straw, while metal conducts moisture and cause the bales to mildew and rot. Building with straw bales forces certain important passive solar techniques such as large overhangs, which are necessary to keep the bale walls dry. Building with straw bales is part of an overall commitment to using natural materials.
This is the commitment that I have made recently on a piece of land in east Texas. The plan is to build a small (700 sq. ft.) house in the form of a spiral. The design started as the Fibonacci numbers plotted onto the coordinate plane, which makes a spiral that as it extends outwards tends towards the Fibonacci spiral, or Golden Spiral. The Fibonacci numbers are taken by adding one number to the one previous to it to obtain the following number. The series begins as follows: 1, 1, 2, 3, 5, 8, 13, 24...etc. When the average ratio of one number to the one previous is calculated we get 1:1.618. This is known as the Golden Ratio. The Parthenon, the hu
The process. For Texas, the essential part of this is staying cool in the summer. I am using a hybrid of the straw bale techniques in order to have almost half of the structure as an open-air porch. While t
Each of the brown dots in the diagram is a post, holding the weight of the roof where there is not a wall bearing the load. Recently I found a small scale mill that sells cured cedar posts cut locally. The large center post is a large cedar found on the building site itself, curing as I write. From the center post going outwards will be the rafters holding the roof. The mill also has these long, 15' beams made of Texas pine also cut within 10 miles of the site. Also sold at the mill are raw planks of cedar made when round logs are cut square before being cut into rough lumber. These planks, with the bark on one side and cut flat on the other, will be used for both closing the roof as well as for the decking on the porch. Cedar not only is incredibly aromatic and beautiful with its rich red hues, but is naturally resistant to rotting and can be placed in the ground without a concrete footing.
The roof will be, of course, alive. Using lightweight soil and drought- resistant sedum, local grasses and mosses, I will continue the high insulation of the straw bales with a living roof capable of R=3 per inch of soil. I plan on using 4 inches of soil, thus R=12 for the roof with plants absorbing most of the sun's heat before it even attempts to heat the house. Keep an eye out for a future article on the myriad benefits of a living roof.
After the walls and roof are up, the walls will be plastered with
Final touches. While each straw bale project is unique in design, materials, and process, there is one thing that remains true in each. Straw was once considered a waste product. Each project has taken straw bales and recognized their real value. Through creative thinking we can eliminate it as a waste product. There is no such thing as waste. It does not exist. I have begun to see wasted wood that is not used because it has bark on one side as a resource. I see clay pits that are wasted soil because they will not grow crops as a resource. I see straw standing in the fields as a resource that can be used to create beautiful, healthy, sustainable living space. Works Consulted "House of Straw - Straw Bale Construction Comes of Age." April 1995 Last update: May 21, 2009
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ients up the stalk to the developing seed heads.Straw is a necessary by-product of all grain crops, and because it is a by-product of a valuable product is has long been considered waste.
man face, sunflowers, mollusk shells, hurricanes, and pine trees all are built according to the Golden Ratio.
he main living space is load-bearing straw-bale, the roof is supported over the porch area with posts.
a mix of straw, clay and sand.
