Dec 12, 2020
What if we told you that one of the best insulating materials for your home could be sourced for free from local farmers. That it is a 100 percent natural material with zero volatile organic compounds that could off-gas into your home? Sounds too good to be true? Before the days of fiberglass, cellulose, or spray foam insulation, most homes were completely un-insulated from the outside temperature. This reality led to frigid interior temperatures during the winter and unbearably hot home interiors in the summer. However, some families might have enjoyed homes with better insulation and thermal performance than even the most high-performance structures built today.
Straw bales have been used for decades as a quick and efficient way to build a home's walls. The first documented use of straw bales for a building was an 1896 Nebraska schoolhouse. Many people might think straw bale homes would decompose in just a couple of years. But, there are examples of straw bale homes that are well over 100 years old and show zero decomposition issues. Straw bales are great for high-performance insulation for any home. Besides being a natural and renewable material, straw bales also offer some of the highest R-values of all insulating materials. Below, we provide a complete guide on straw bale insulation.
As its name implies, straw bale insulation is made from the leftover stalks of certain grain crops such as wheat, rice, and barley. For those not well-versed in crops, hay refers to baled grasses and weeds, whereas straw is strictly the leftover stalks of grains left in the fields post-harvest. Whereas hay is generally much finer and more prone to decomposition, the thick blades of straw are much more durable and offer improved insulation properties.
Because it is nutritionally empty, straw has little to no value as animal feed. Though it can (and should) be worked back into the soil to improve soil fertility, many farmers worldwide burn their leftover straw. In China, burning rice and wheat straw is a significant contributor to urban air pollution. Similarly, burning wheat straw in Mexico is shown to increase greenhouse gas emissions and accelerate climate change.
Instead of burning straw to prepare fields for subsequent harvests, straw bales could become an essential part of the transition to natural building alternatives. The Food and Agriculture Organization (FAO) of the United Nations estimates that about 800 to 1000 million tons of rice straw are produced per year, with similar volumes for wheat worldwide. Straw bales can be used for building walls or be manufactured into insulation panels for installation in other types of homes.
Straw is a natural and renewable material with excellent insulation properties. Compared to other types of insulation alternatives, straw bales have a much lower environmental impact. Preserving straw bales as home insulation or as walls can capture an enormous amount of carbon dioxide, thus helping combat global climate change.
Straw bale homes are unique in that they have their insulation already built into the house walls. Straw bales are an average of 18 to 24 inches thick, meaning that straw bale homes have incredibly thick walls. When full-sized straw bales are used for walls, the structure might achieve an R-value of up to R-60, significantly higher than any other insulation alternative.
Another way to utilize straw bale insulation with full-sized bales sourced from local farmers is to use straw bales as in-fill in post and beam construction. Straw bales can be cut or trimmed to size with a simple chainsaw if you don't want massive 20-inch walls. Even a 10-inch straw bale in-fill for insulation would offer significantly higher insulation value than most other alternatives.
Today, many companies are beginning to produce prefab straw insulation panels. These panels are designed to fit in most existing homes, allowing homeowners to update their existing insulation. Eco Cocon is one company producing all-natural straw panels that offer excellent insulation properties.
Straw bales have an R-value of anywhere between R 2.38 per inch to R 0.94 per inch, which is similar to fiberglass and stone wool. It is slightly lower than cellulose and closed-cell spray foam insulation. The actual R-value of straw bale insulation will depend mostly on how tightly packed (or baled) it is. This tightness determines the amount of space and air pockets in between each blade of straw. Because of straw bale walls' thickness, when using full-sized bales, this type of construction or insulation can often offer R-values upwards of R-60.
Let's take an average R-value of 2.0 per inch for straw bales. Find the recommended R-values for insulating your walls, ceilings, and attic according to your region. The ENERGY STAR program offers a helpful guide that you can find here. For example, if you need an R-16 insulation value for your walls, you should look for straw bale insulation panels that are 8-inches thick.
The 2015 version of the International Residential Code (IRC) for single and two-family dwellings includes stipulations for straw bale buildings, including straw bale insulation. This essentially that there is a national straw bale building code. Andrew Morrison, a leader in the world of straw bale homes, has said that the IRC forms the basis for most Residential Building Codes in the US. He went on to say that once the jurisdictions adopt the 2015 IRC, straw bale code will be present for almost every jurisdiction in the United States. This update will mean that homebuilders will be able to refer to the national code to obtain permits and move forward with their construction process.
Straw bales can cost anywhere from $0 to $12 apiece. In some areas, farmers might give them away if they have an excess supply taking up space in their barns. Others might charge a nominal fee. If you are planning on hiring a contractor to build a full straw bale home, you can expect to pay an average of 10 to 12 percent higher costs. However, the energy savings due to the increased insulation performance should pay back that cost within a few years.
Straw bale insulation can be used in both walls, ceilings, and attics as long as some stucco or plaster sufficiently protects it. It can be added to home interiors or exteriors with walls if a water-proof plaster is used on top of the insulation. Because of issues with rotting, you cannot use straw bale insulation to insulate home foundations.
Straw bale insulation, when adequately protected from rain and extended exposure to moisture, can easily last for decades or even centuries. There are living examples of 100-year old straw bale homes. Eco Cocon offers a 25-year warranty on their straw bale insulation panels. However, they mention that "as long as the installation standards are followed, an EcoCocon building should have a life expectancy that can be measured in centuries.
One of the unheralded advantages of straw bale walls is that they also act as a great foundation for earthen and mineral plasters. Both clay, lime, and other natural materials adhere very well to the textured, uneven straw bales' surfaces. Earthen and mineral plasters not only offer an unmatched aesthetic for home interiors and exteriors, but they also help reduce the amount of volatile organic compounds (VOCs) in the home.
Strawbale panels can be installed similar to any other type of batt-type insulation, such as fiberglass or cellulose. If you plan on building a full straw bale wall, you will need to take extra care to connect the straw bale walls to the foundation and top plate that subsequently connects to the roof. This fabrication ensures a solid structure and will most likely be required by code. Extra care should also be taken when electrically wiring a straw bale home. You can find a more detailed video on how to build with straw bales here.
The main benefits or advantages of straw bale home are:
On the downside, straw bale insulation offers a few drawbacks or situational disadvantages that should be considered.
Tobias runs an agroecology farm and a natural building collective in the mountains of El Salvador. He specializes in earthen construction methods and uses permaculture design methods to integrate structures into the sustainability of the landscape.