What Is 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.

What Types of Straw Bale Insulation Exist?

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.  

What is the R-Value of Straw Bale Insulation?

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.

How To Finish Straw Bale Walls

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.