What Is a Straw Bale House? Definition, Designs, and Examples

A straw bale house is made using straw as either a main structural element, insulation, or both. The buildings are constructed by stacking rows of compact straw bales on a strong foundation before sealing with a moisture barrier and outer plaster layer. They typically have extremely thick walls with efficient thermal mass for low energy bills and year-round comfort.

Straw bale houses are relatively rare, but the practice is picking up steam thanks to the growing sustainable design trends.

Straw is cheap (sometimes free) and the entire process reduces construction waste that can have a negative impact on the environment; any excess straw or natural plaster can, in theory, be used on site in compost or as ground cover to protect the soil. One paper found that straw bale buildings save 40% of construction costs when compared to traditional homes.

What Is a Straw Bale House

Straw is an agricultural byproduct that comes from growing cereal grains like wheat, oats, and rice—the straw itself is made up of the dry stalks of the cereal plants after the grain has been removed. It’s been used for thousands of years as a building material for reinforcing clay or mud structures as an inexpensive, renewable resource with good insulating value.

The modern practice of straw bale building originated in Nebraska during the late 19th century, when early settlers were looking for the quickest method for temporary housing (although, straw and reeds were used as building materials in thatch roofing throughout the Middle East for thousands of years before that). Unsurprisingly, the construction method directly followed the invention of the steam bale engine, which collected and packed straw into the tight, brick-like bales we see today.

Straw Construction Regulations

Whether or not your state has a building code for straw bale construction depends on the region. Those planning to build a straw bale home will want to research the code book for their particular state and check in the alternative building section as well as any local or state addendums.

In California, for example, straw bale homes have their own guidelines; these include a minimum bale wall thickness of 13 inches, a one-story maximum in the case of buildings with load-bearing bale walls (unless it has been designed by a civil engineer or architect licensed by the state), and at least 40 other requirements.

In general, a straw bale home that's covered with plaster, drywall, or stucco is considered to have greater fire resistance than conventional building construction.

How to Build a Straw Bale House

Essentially, there are two ways to build a straw bale house—load bearing and non-load bearing. A load-bearing straw bale house uses straw bales as the primary structural support, making it more reliable in milder climates.

On the other hand, a non-load-bearing straw bale house uses another material, such as lumber, for its primary support. Straw bales are then added to shape the walls and provide insulation, so it’s often a better choice for more unpredictable climates or those that get a lot of snow.

The construction starts with a foundation, something strong like a layer of concrete, on which the straw bales are stacked on top of each other to form the walls. A moisture barrier is then applied to the surface of the walls, usually made up of earthen plasters, stucco cement, or gypsum plasters.

The final layer consists of another plaster made with clay, lime, or cement to provide thermal mass, which can act as the topcoat or be supplemented with paint. Oftentimes, the owner decides to utilize an additional sustainable construction element, like a rammed earth wall, to add a supplementary texture or detail while still maintaining the overall eco-friendly feel of the home.

Additionally, small sections of the interior wall may be left unplastered and opened with a glaze or frame like a window so occupants can see what the straw building looks like inside.

The straw bales are anchored to each other using stakes of wood, bamboo, or rebar so they don’t fall over during construction. To keep the house in good condition, it’s important to periodically inspect the plaster layer for cracks and holes to avoid excessive dampness and subsequent mildew.

Pros and Cons

Overall, straw is a sustainable material that has plenty of redeemable features when it comes to construction, though it may not be suited for everyone or every situation. Take time to look at the risks and rewards (and limitations) while considering a straw bale house.

Pros

Renewable Materials

Straw bale houses are considered eco-friendly thanks to the main material, straw, being a completely renewable byproduct of the agricultural industry.

Straw already has many uses, such as mulch or bedding for animal pens, and can be regrown quickly each year rather than the lengthier time it takes for a tree to mature for lumber.

Harvesting lightweight straw also requires less energy than producing and transporting wood—farmers can even leave it in the fields to protect soils from erosion, add organic matter, or return nutrients to soil.

Cost Efficient

Not only is straw typically less expensive than traditional building materials like wood, concrete, and steel, a straw bale house can cost less to heat or cool due to its high insulation factor.

A 2017 study in the Journal of Building Engineering performed a Life Cycle Assessment with a straw bale wall to investigate its energy and environmental performance. Researchers found that while the wall offered adequate thermal insulation under steady winter conditions, the lightness of the structure could be detrimental for unsteady summer conditions and lead to overheating in warm climates. Overall, the paper concluded that the use of straw bales in walls is capable of reducing both energy and carbon embodied in a building.

Low Fire Hazard

This one may seem far-fetched, but straw bale homes don’t actually pose a higher fire risk than traditional homes (once they’re finished, that is). Since the straw bales are tightly packed, there isn’t much airflow available to sustain a fire.

In fact, straw bale homes are approximately three times more fire resistant than homes built from conventional construction materials.

Biodegradable

The core material of a straw bale house can be returned to the earth at the end of its life. The straw, the natural clay plaster, and most other parts can simply be plowed back into the soil to decompose naturally. 

Low Embodied Energy

Studies in Italy show that the embodied energy (the sum of all the energy required to produce the home) is about half that of a traditional home, while the CO2 equivalent emissions differ by over 40%.

Growing and processing straw doesn’t take much energy outside of the sunlight needed during its growth phase, the bailing process, and transporting the bales to the construction site. 

Cons

Permitting

Apart from dealing with difficult protocols when planning a straw bale house, some states may not even account for them within their building codes; this can make it challenging to obtain a building permit.

Likewise, city officials may find the concept unconventional and be uncomfortable accepting the straw bale house based on the home’s aesthetics compared to the rest of the area. 

Moisture

Straw bale houses are more susceptible to moisture-related problems since straw will decay and weaken if it becomes damp, which can quickly turn dangerous for inhabitants.

Moisture can come from cracks in the plaster, plumbing pipes, damage from flash flooding, or in instances where windowsills or joints have not been properly sealed. For this reason, climates known to be particularly wet or humid may not be ideal for straw bale houses.

No Studs

Since often there is no wood supporting the structure, straw bale houses do not have studs in the walls. Hanging anything on the walls, including shelves, cabinets, or even picture frames, will be a much more complex endeavor than in a regular home.

Pests

Some of the biggest concerns over straw bale houses have to do with insect and rodent issues, though straw bale enthusiasts would argue that selecting and applying the appropriate plaster would take care of either. However, depending on where they came from, straw bales may arrive at the building site already containing grain-eating pests.

Maintenance

The plaster layer that keeps the straw dry and safe from mold or mildew doesn’t last forever. Once it starts to degrade, it must be replaced, meaning maintenance for a straw bale house is required more often than with most other modern homes.

The layer of plaster on the outside ranges from cement stucco, which can cause moisture issues when it cracks, to clay-based earth plasters, which require reapplication regularly.