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Straw Bale Construction

A straw bale wall is not a straw bale wall until it has been plastered with a complete base coat on both sides of the wall. That said, we will focus more on the straw-part of the wall in this section, and leave the plaster-part of the discussion, for the most part, in the plasters section.

History and Context
While straw construction in baled form has only been around since the 1800s (founded by westward migrants in Nebraska), the use of straw as a building material dates back thousands of years, examples of which can be found across the globe. Modern bale building experienced much of its early development in the southwestern region of the United States, and this has given way to a myth that straw bale construction is only suitable to dry climates, a myth reinforced when building techniques employed in that environment fail when replicated in cold and wet climates without appropriate consideration of and detailing for the forces and realities of such a different environment. We have come to realize over time, with experience and through observation, that by adjusting techniques and best common practices to respond to the extreme conditions of moisture and temperature, straw bale construction is not only highly adaptable for use in cold and wet climates, but its inherent properties allow it to excel as a building medium, helping in part to create highly efficient, resilient, durable, and attractive structures that are healthier for the builder, the occupants and visitors, and environmental and social ecologies, more so than their conventional counterparts.
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To Load or Not To Load
The original straw buildings were of 'load-bearing' design, as there was no abundant source of sod or timber with which to construct their homes. The load in reference here is the roof; the bale walls themselves supported — in part or entirety, depending on the span of the structure and design of the roof — the weight of the roof, requiring no further framing in conjunction with the walls. Now frequently known as 'Nebraska-style' bale buildings, in reference to those original buildings built in the Nebraska sand hills, load-bearing straw bale is the most prevalent form of bale construction worldwide, prized in part for its simplicity and reduction of timber resources. That said, 'non-load-bearing' — that is, walls that carry no structural load — straw bale is far more common in the northeastern United States. Why? A few reasons: for one, there is still a terrific timber resource which allows for the sustainable use of wood for framing. For another, there is a strong vernacular of wood framing in this part of the world, and therefore a great resource of skilled tradespeople available to perform the work. Timber framing in particular has enjoyed a modern renaissance, and marries quite well with straw bale wall systems. See the Framing section for information about frames. Perhaps, though, one of the most common reasons is the climate: in an environment where precipitation can be expected 365 days a year, often without much warning, the practicality of building walls, pre-compressing them (a process of stabilizing the walls to receive the roof load evenly), building the roof assembly, and plastering the walls before the threat of rain is quite difficult, as is creating temporary protective shelter for the walls, especially for larger buildings. There are load-bearing walls in the northeast and in other areas of similar climate, but for now the prevalent style in this area is non-load-bearing.
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On Moisture
Many who question straw's ability to perform well in cold and wet climates point to the vulnerability of straw to moisture. This is to suggest that, somehow, moisture infiltration, via precipitation, condensation, or otherwise, is not a concern for walls insulated with fiberglass, cellulose, or any other insulation material, for that matter. Anyone who has been involved in remodeling in this region will tell you that moisture — sourced in liquid or vapor form, from condensation or direct infiltration — is a major problem for all walls, not just those built of straw. What critics fail to recognize is the inherent benefits of a straw bale wall in dealing with moisture in this environment. The most fundamental — and most misunderstood — property of these walls is their ability to allow for the natural migration of moisture vapor into and out of the wall; this "breathable" capability does not refer to air migration — in fact, avoiding the transmission of air, and its associated moisture content, by achieving a fully sealed wall (via plaster) is a central strategy of avoiding condensation in the wall. The ability of moisture vapor to move throughout vapor-permeable plaster skins, however, is what allows any ambient or atmospheric humidity within the wall to be released. The appropriate choice of plaster is critical in this regard, and as well as in regard to its ability to uptake and release to the atmosphere significant amounts of moisture without passing that moisture on to the straw behind (see the plasters section for more information).
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Other Concerns
Other concerns in this region center mainly on insect and rodent infestation and fire. Again, the inclusion of well-applied plaster skins effectively seals off the wall from air, which in effect starves macro-biologic life as well as potential fire spread. In fact, recent fire testing on straw bale walls has gained it class A fire rating, with plastered bale walls remaining in excess of two hours' fire exposure for a cement-stuccoed wall, and one hour for an earth-plastered wall. Insect and rodent prevention, however, really starts in the selection of the bales themselves; bales, first of all, must be of straw and not hay, and furthermore must be "clean" — devoid of seed heads and weeds that may provide fodder for unwanted pests. Additionally, most straw-inhabiting insects require a certain percentage of moisture, generally inappropriate for building-quality bales, so if bales are sourced, transported, stored, installed, and kept fully dry, the potential of insect infestation is kept to a minimum even before the plaster seal is applied.
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Ready for Winter!
In conclusion, while common practices for straw bale architecture and understanding of the performance of these wall systems are still in development in extreme cold, wet climates, both theory and practice not only point towards the long-term viability of these walls in this climate, but assures numerous benefits that reduce energy consumption, improve quality of life, and enliven the spirit.
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