page_title: Straw-bale construction
section_title: Method
hierarchical_section_title: Straw-bale construction / Method
caption_attribution_description: English: Building a straw-bale house Français&#160;: Construction d'une maison en paille
context_page_description: Straw-bale construction is a building method that uses bales of straw as structural elements, building insulation, or both. This construction method is commonly used in natural building or "brown" construction projects. Research has shown that straw-bale construction is a sustainable method for building, from the standpoint of both materials and energy needed for heating and cooling.
  Advantages of straw-bale construction over conventional building systems include the renewable nature of straw, cost, easy availability, naturally fire-retardant and high insulation value. Disadvantages include susceptibility to rot, difficulty of obtaining insurance coverage, and high space requirements for the straw itself. Research has been done using moisture probes placed within the straw wall in which 7 of 8 locations had moisture contents of less than 20%. This is a moisture level that does not aid in the breakdown of the straw. However, proper construction of the straw-bale wall is important in keeping moisture levels down, just as in the construction of any type of building.
context_section_description: Straw bale building typically consists of stacking rows of bales (often in running-bond) on a raised footing or foundation, with a moisture barrier or capillary break between the bales and their supporting platform. There are two types of straw-bales commonly used, those bound together with two strings and those with three.  The three string bale is the larger in all three dimensions. Bale walls can be tied together with pins of bamboo or wood (internal to the bales or on their faces), or with surface wire meshes, and then stuccoed or plastered, either with a lime-based formulation or earth/clay render. The bales may actually provide the structural support for the building ("load-bearing" or "Nebraska-style" technique), as was the case in the original examples from the late 19th century. The plastered bale assembly also can be designed to provide lateral and shear support for wind and seismic loads.
  Alternatively, bale buildings can have a structural frame of other materials, usually lumber or timber-frame, with bales simply serving as insulation and plaster substrate, ("infill" or "non-loadbearing" technique), which is most often required in northern regions and/or in wet climates. In northern regions, the potential snow-loading can exceed the strength of the bale walls. In wet climates, the imperative for applying a vapor-permeable finish precludes the use of cement-based stucco. Additionally, the inclusion of a skeletal framework of wood or metal allows the erection of a roof prior to raising the bales, which can protect the bale wall during construction, when it is the most vulnerable to water damage in all but the most dependably arid climates. A combination of framing and load-bearing techniques may also be employed, referred to as "hybrid" straw bale construction.
  Straw bales can also be used as part of a Spar and Membrane Structure (SMS) wall system in which lightly reinforced 5 - 8 cm (2 - 3") gunite or shotcrete skins are interconnected with extended "X" shaped light rebar in the head joints of the bales. In this wall system the concrete skins provide structure, seismic reinforcing, and fireproofing, while the bales are used as leave-in formwork and insulation.
  The University of Bath has completed a research programme which used ‘ModCell’ panels - pre-fabricated panels consisting of a wooden structural frame infilled with straw bales and rendered with a breathable lime-based system - to build 'BaleHaus', a straw bale construction on the university's campus. Monitoring work of the structure carried out by architectural researchers at the university has found that as well as reducing the environmental footprint, the construction offers other benefits, including healthier living through higher levels of thermal insulation and regulation of humidity levels. The group has published a number of research papers on its findings.
  Typically "field bales" (bales created on farms with baling machines) have been used, but recently higher-density "precompressed" bales (or "straw-blocks") are increasing the loads that may be supported.   Field bales might support around 900 kg per linear meter of wall (600 lb./ lin. ft.), but the high density bales bear up to 6000 kg per linear meter of wall (4,000 lb./lin.ft.), and more. The basic bale-building method is now increasingly being extended to bound modules of other oft-recycled materials, including tire-bales, cardboard, paper, plastic, and used carpeting. The technique has also been extended to bags containing "bales" of wood chips or rice hulls.
  Straw bales have also been used in very energy efficient high performance buildings such as the S-House in Austria which meets the Passivhaus energy standard. In South Africa, a five-star lodge made from 10,000 strawbales has housed luminaries such as Nelson Mandela and Tony Blair. In the Swiss Alps, in the little village of Nax Mont-Noble, construction works have begun in October 2011 for the first hotel in Europe built entirely with straw bales. The Harrison Vault, in Joshua Tree, California, is engineered to withstand the high seism
caption: Straw bale construction
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