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In simple terms strawbale construction is using bales of straw in the construction of a building. More specifically it’s a wall with the majority of its volume stacked straw bales that are air-sealed on both sides with plaster (or sheathing or other air barrier). Strawbale construction is a natural building method that works well in many climates. Any region where grain is grown will provide abundant straw to use as a building material.
Load-bearing vs. Infill:
A strawbale building can be built either so the straw carries the weight of the roof or some other structural frame (most frequently wood) does while using straw primarily as insulation. When the straw is carrying the growing of the roof we call it load-bearing or Nebraska style. When another structure holds the weight of the roof and upper stories it’s called strawbale infill. In all load-bearing straw walls the straw/plaster is responsible for the shear resistance of the building as well. This is only the case in some strawbale infill walls.
Straw is a proven and ancient building material which has been used in various forms (light straw clay, cob, thatched rooves, etc.) for millennia. Using baled straw is a more recent technique, but not as recent as you may think. Once several mechanical balers became available in the mid 1800s it didn’t take long for people to figure out that straw bales made great building blocks. The first recorded strawbale building was a schoolhouse, built in Nebraska in the 1890s. Between then and WWII an estimated 70 strawbale buildings were built in Nebraska, many of them with native prairie grass rather than straw. The technique spread and in 1921 a strawbale house was built in France. After WWII cement became more readily available and strawbale building fell to the wayside for a time.
Strawbale construction never went away completely and articles appeared in Popular Mechanics in 1960 and the book Shelter published in 1973. The renaissance of strawbale houses began in the 1980s and grew in the 1990s. People looking for a way to build on a budget began the renaissance since the materials are inexpensive. The modern strawbale renaissance has grown alongside the field of building science and both are still growing. Strawbale buildings have now been built in all 50 states and many countries around the world. They are most popular in the Southwestern United States and Australia.
The advantages of strawbale construction break into four basic categories; environmental, economic, aesthetics and performance.
Straw is an environmentally friendly building material for a few reasons. Straw is a byproduct of grain production and is often considered a waste product. People use it for animal bedding or compost, but sometimes just burn it to get rid of it. In contrast, building a house with it puts it to much better use. Building is one of the highest uses of straw, if not outright the best.
Another environmental advantage is straw takes more carbon out of the atmosphere than producing it puts into the atmosphere. It’s a carbon sink. When the grain crop is growing carbon is absorbed from the atmosphere and is captured in the straw until it decomposes or is burned. Keeping straw intact inside the walls of a building keeps the carbon out of the atmosphere.
The manufacturing process of some insulation materials (fiberglass, foam, etc.) damages the environment, while others are fine (such as cellulose). This means the environmental impact of strawbale construction depends on the alternative it is chosen over.
The low cost of straw is what attracts some people to strawbale homes. While straw is very inexpensive compared to other building materials building with straw is labor intensive. If you provide some or all of this labor yourself you can save a lot of money over conventional construction, but if you pay for the labor expect to spend about the same for a strawbale house as you would for a comparable conventional home.
Most types of natural buildings can look any way you want, strawbale is no exception. Many people who build strawbale houses like an organic look with walls that are mostly, but not perfectly flat, but that’s not the only option. You can make a strawbale building look as whimsical or as conventional as you want. Bill and Athena Steen wrote a whole book on The Beauty of Straw Bale Homes which I recommend. In their introduction they strongly recommend building strawbale homes to look different than conventional homes, but in a beautiful way.
Straw is an insulator. It’s admittedly not the best insulator per inch but it might be the best insulator per dollar. The thick walls of a strawbale house paired with its insulative properties make for a well insulated home. Insulation, though usually the performance advantage mentioned first by strawbale advocates, isn’t the only performance advantage of strawbale construction. One key performance area that I value is indoor air quality. Many conventional building materials off-gas chemicals that negatively impact human health; however, straw doesn’t and neither do any of the plaster materials commonly used with strawbale construction. Finally, strawbale buildings that are built right can be high performers when it comes to air sealing. This is because the walls have two air control layers (one on each side of the bales) rather than one as is the case with many buildings.
The performance characteristics, especially as it relates to indoor air quality are what first drew me to strawbale construction, and natural building in general. With all of these advantages there is a lot to like about strawbale construction.
The one challenge that has to do with the building method itself is moisture. The others all have to do with people’s perception of strawbale construction.
The biggest key to building with straw bales is keeping them dry — before, during and after construction. Make sure that you get bales that are dry and have been kept dry since they were baled. The straw should be golden colored with no dark or gray spots in it. If you are uncertain you can use a moisture meter to test it. You should get readings at or below 20%. Make sure the bales are kept dry and off the ground during construction. If building with the infill method, build the structure and roof first so that the straw can be stored under the roof. In order to keep the straw dry after construction is completed make sure to use best practices for water sealing, air sealing and vapor control. Good detailing includes, but isn’t limited to, good roof overhangs, good air sealing and vapor permeable wall systems.
The other challenges are dealing with people’s perceptions of strawbale construction, because strawbale construction is uncommon people may not know about it or how to deal with it. Examples include building inspectors, subcontractors, bankers and insurance agents. Mitigating this will require you to do some research and educate others. You’ll want to talk with your building department before starting your project (assuming your building in an area where codes are enforced). Communicate to them what you want to do and that you want to build well. You may also need to educate subcontractors, especially electricians about working with straw bales. When it comes to banks and insurance companies, do some research to find out who might provide a loan and insurance. This can be a challenge because even if the person you’re dealing with likes the idea of strawbale construction they are likely using a computer program with check boxes — none of the options for them to check will be “straw”. If you can, ask people in your area who live in strawbale houses who their bank and insurance agency are.
Strawbale construction doesn’t come without challenges, but in most cases those challenges are worth the effort to overcome.
What about building codes?
Since 2015 a provision has been made in the IRC model building code for residential construction published by the International Code Council. It’s an optional appendix that must be actively adopted by a building code jurisdiction before it’s valid for that area. In addition, several places have their own strawbale codes, some of which have been around longer than the IRC Appendix S. If there isn’t a specific provision for strawbale construction in your local building code, all building codes have a provision for using alternative methods if approved by the building official. In order to get this approval you may need to have an engineer provide a stamped set of drawings. If you’re not building immediately, you can also ask that when the next version of the code is adopted in your area that the strawbale appendix also be adopted.