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Straw bale home construction is a green building method that uses bales of straw as structural support, insulation, or both. Generally, this method of building has numerous advantages over conventional building systems because straw is a renewable source, low cost, easily available, and has a high insulation value. The two forms of straw bale construction are load-bearing (Nebraska style) which uses the bales of straw as structural support and non-load bearing (infill) which uses the bales of straw as insulation between traditional wood framed walls. Non-load bearing straw bale homes is easier to obtain permits and working with building code officials because officials view straw bales as an alternative insulation material, but since the structural elements are familiar, infill straw bale is less intimidating to contractors not already familiar with this type of construction. The construction process for a non-load bearing straw bale home is very similar to a convention home build, and it is typically less expensive to build.
During the 21st century, society is aware of climate change, more intense storm systems (i.e. hurricane Katrina), and other environmental impacts that could potentially harm mankind. In an effort to combat such impacts, technology is now even more present in the construction industry, and society is beginning to turn towards sustainable resources and green building materials as an alternative to conventional construction.
While buildings are our place of residency, employment, and playground that protect us from nature's extremes, green building is the practice of creating and using healthier and more resource-efficient models of construction, renovation, operation, maintenance, and demolition ("Green Building," 2009). In the United States, buildings account for 39% of total energy use, 12% of total water consumption, 68% of total electricity consumption, and 38% of carbon dioxide emissions ("Why Build Green," 2009). Construction has an impact on the natural environment, human health, and the economy. By utilizing an alternative more sustainable resources into building construction, buildings will benefit society, the economy, and the environment from minimizing strain on local infrastructure, reducing operating costs while optimizing life-cycle performance, and preserving our natural resources from protecting ecosystems, reducing waste streams, and improving air and water quality ("Why Build Green," 2009). Straw bale home construction is an example of a green building method. Straw is a renewable resource, relatively inexpensive, and when put into practical use, extremely energy efficient ("Choosing Green Materials and Products," 2009). Straw bale construction uses bales of straw as structural elements, insulation, or both ("Straw Bale Construction," 2009).
Straw has been used in construction since the early 20th century in many types of buildings because it provides excellent tensile strength, great insulation value, and additional structural integrity. There are some 75+ year-old buildings still inhabited today (Jacoby, 2001). Straw bale home construction started in the Midwestern United States, especially in Nebraska because the grass in plentiful ("Straw Bale Construction," 2009). This green building approach has been put into more practical use at the turn of the 21st century. The United States currently wastes 200 million tons of straw each year, and the United States Department of Agriculture indicates that American farmers annually harvest enough straw to build about 4 million, 2,000 square foot homes each year which is roughly 4 times the number of houses currently constructed (Jacoby, 2001). Generally, straw bale construction has numerous advantages over conventional building systems because straw is a renewable resource, eco-friendly, strong and durable, completely biodegradable, inexpensive, readily available, and has a high insulation value ("Straw Bale Construction," 2009). Currently, there are two forms of straw bale home construction. The most common, load-bearing or Nebraska style, uses the bales of straw as structural support while non-load bearing or infill uses the bales of straw as insulation between traditional posts and beamed framed walls (Hart, 2009).
Non-load bearing straw bale construction is more beneficial than conventional home construction because straw bales has a high sound absorption coefficient, high insulating qualities with an average R-values of 42 while an R-value of 19 is considered to be super insulated, and this method of construction can incorporate conventional building methods as well (Jacoby, 2001). However straw bale builders face many drawbacks. The design and construction of the straw bale home requires careful detailing to prevent liquid water infiltration, requires breathable finishes, generally plaster over the straw, requires educating the owner, the builder, permitting officials, and requires close interaction with building code officials in regions that do not currently have codes for straw bale home construction. Financing a straw bale home is rather difficult because banks are less likely to lend because it is an alternative method, unknown conditions exist, or there is a lack of building codes in place (Phyers, n.d.). In the recent years, this is rapidly changing, and building code officials are more likely to permit non-load bearing straw homes because the structural system is an independent element, because it utilizes conventional techniques, and it can be engineered according to load requirements and building codes (Jacoby, 2001).
Most residential post and beam house framing in North America today is built using stud construction or timber framing, and it could incorporate exposed timber throughout the structure (Post And Beam House: Timber Framing versus Standard Stud Construction, 2008). Non-load bearing straw bale construction uses post and beam framing and/or stud construction as the structural support then uses straw bales to infill as an independent element. This method of construction does not rely on bales to carry any of the building loads other than the weight of the bales themselves (Jacoby, 2001). Figure 1 on the proceeding page is a detail of a non-load bearing house. The drawing depicts a slab-on-grade foundation, size of timber to be used, orientation of the straw bales, and number of straw bale layers needed to reach the height of the ceiling. Non-load bearing straw bale construction is easier obtaining permits and working with building code officials because officials view straw bales as an alternative insulation material, and since the structural elements are familiar, infill straw bale is less intimidating to contractors not already familiar with this type of construction (Overview of Straw Bale Construction, 2000).
The construction process for a non-load bearing straw bale home is relatively simple. This process is not much different than a conventional home build. In a non-load bearing straw bale home build, typically just the perimeter walls are infilled with straw bales, and all structural components must be constructed first. This includes the foundation (this could vary depending on the current building code as noted in the building code section in the proceeding pages), the
Figure 1: Detail of Post & Beam Straw Bale House
stud walls and floor joists are constructed, and finally the roof is installed. Interior walls can be constructed before or after the straw bales are infilled. Some building codes require non-load bearing straw bale structure to install the straw bales "in the dry." Simply stated, the straw bales can only be placed once the roof is constructed and finished roofing is installed. Then, the straw bales can then be placed between the structural elements and around all openings including windows and doors. Depending on the ceiling height, there are typically about 7-8 straw bale layers needed to reach the ceiling height. Any remaining interior walls will then be constructed to allow for electrical and plumbing rough-in. Electrical can be installed two different ways, hidden or exposed. If the electrical is to be hidden, conduit is run between the straw bale layers per building code while if the electrical is to be exposed, the conduit is run above the ceiling, in the roof before being exposed down the side of the wall. A cement/lime plaster and stucco is to be applied to the interior and exterior respectively. All windows and doors are installed before the remaining finishes are applied (i.e. drywall, trim, paint). Finish plaster is applied to the interior and exterior before the remaining finish elements are completed. (Overview of Straw Bale Construction, 2000).
Straw bales are an inexpensive building material. The material cost for straw bales walls are substantially lower than conventional stud walls. Generally, the cost of a straw bale wall is approximately 1/5 of the total home construction cost opposed to 1/2 of conventional home construction cost (Overview of Straw Bale Construction, 2000). However hired labor is very expensive (Jacoby, 2001). It is especially in the plastering process because it is a technical and time consuming process, but it is recommended to have community helpers or volunteers to assist with the plastering process to reduce labor costs (Overview of Straw Bale Construction, 2000). In comparison to the actual cost of a non-load bearing straw bale home to a conventional home, it depends on the how "green" the building will be. A straw bale home can be built for as little as $15 a square foot, to a typical range of $43-$73 a square foot, to upwards of $100 a square foot (Phyers, n.d.). In relation to the average home size of 2200 square feet, the cost of a straw bale home is $33,000, $94,600-$160,600, and $220,000 respectively. Non-load bearing straw bale homes is typically higher in cost because stud framing does still exist in the exterior to carry the load.
Non-load bearing and load-bearing straw bale houses each have individual structural characteristics but while under testing conditions, have similar results. Researchers have been testing straw bales or straw bale structures in comparison to convention homes while under extreme wind conditions (i.e. hurricane), fire rating properties, and during an earthquake. All of these are acceptable tests depending on the region the home is to be built. Straw bales have a unique characteristic. Architects and Engineers have considered straw bales to be a seismic resistant building material (Morrison, 2009). Researching and testing has shown that while induced in gale force winds of up to 75mph, a straw bale structure will have no movement, but when tested in winds of up to 100mph, the structure only moves 1/16" (Morrison, 2009). Furthermore, straw bales are dried straw, 3 times as fire resist as current building material finishes used in conventional homes. Dried straw only contains 8% moisture and lack the oxygen needed to ignite a flame (Morrison, 2009). Straw bales act as a shock absorber rather than rigid and breaking. In non-load bearing straw bales structures, the straw rests against the stud construction to absorb the shock of the earthquake. Even more astonishing, a straw bale cabin was built and placed on an earthquake testing machine. The cabin was tested in conditions many people have not experienced. The machine induced an earthquake with a magnitude of 7.6 on the Richter scale (Ecoville Architecs, 2009).
Many regions of the United States do not have building codes that apply to green materials or straw bale structures. Many building officials lack the knowledge needed to approve a green building, in particular, straw bale housing. The approval rate in an area with insufficient or no green building codes is 50% among the code officials surveyed (DCAT, 2005). Nevertheless, the Midwest and West Coast contain the most straw bale building codes. Typically these codes are for both load-bearing and non-load bearing straw bale houses while some codes only focus on non-load bearing straw bale walls. The cities that currently have straw bale building codes are: Austin, Texas, multiple cities and counties in the state of California, Cortez, Colorado, parts of Nevada, Tucson, Arizona, parts of Nebraska, and the entire state of Oregon (Skillful Means, 2000). Tucson, Arizona is noted for requiring all straw bale houses to house doubled stem concrete block foundation walls filled with concrete rather than a slab-on-grade foundation (Phyers, n.d.). Regions that do not currently have straw bale building code like parts of Maryland and Pennsylvania are likely to adopt a code similar to Cortez, Colorado due to the nature and climate of the region, and they will typically require the use of non-load bearing straw bale structures while referring to load-bearing straw bale walls as experimental. Load-bearing straw bale walls are subject to the interpretation of the Uniform Building (Cortez SB Codes, 1997).
Non-load bearing straw bale home construction is relatively similar to conventional home construction. Straw bales give owners the opportunity to use a renewable resource, which is eco-friendly, strong and durable, completely biodegradable, inexpensive, readily available, and has a high insulation value on the perimeter of the building ("Straw Bale Construction," 2009). This will help reduce energy costs substantially. The overall cost is very similar to a conventional home, but by utilizing an alternative more sustainable resource into home construction, houses will benefit society, the economy, and the environment from minimizing strain on local infrastructure, reducing operating costs while optimizing life-cycle performance, and preserving our natural resources from protecting ecosystems, reducing waste streams, and improving air and water quality ("Why Build Green," 2009). Building codes are starting to accept alternative "green" building methods, and a strong recommendation for a new home builder is to elect to use a non-load bearing straw bale system. The owner will not be disappointed.