The seven homes in Shirehampton, Bristol were constructed as part of an EU-funded joint research project with the University of Bath and the architectural firm Modcell. The team behind the project insist the houses are a good way to meet the UK’s housing needs in a sustainable way, as well as bring straw housing from a niche market used by the ecologically-minded, into the broader general construction market.
While the homes in Bristol look like conventional brick homes, the walls are thick and timber-framed, filled with straw bales and covered in wooden boards. Knowing this, many people might think the walls would not be fire-proof. But densely packed straw bales have a tendency to smolder, rather than erupt in flames.
“I think there’s a lot of misconception about using straw – stories about the three little pigs and the big bad wolf, concerns about fire resistance,” Professor Pete Walker from the University of Bath told the BBC. Professor Walker led the project in developing and testing straw bale construction, including the testing of weight-bearing, structural, and thermal qualities in straw bales.
The project was researched over a period of three years, focusing on various aspects of straw, and its performance capabilities when used in construction. Walker says the new home construction must reduce energy consumption by “50% and its carbon emissions by 80% by 2050.” This means major changes are needed in construction methods.
“As a construction material, straw is a low-cost and widely available food co-product that offers real potential for ultra-low carbon housing throughout the UK. Building with straw could be a critical point in our trajectory towards a low-carbon future,” says Walker.
Straw house construction is as old as humankind
Straw houses were being built on the African plains during the Paleolithic era, and straw-thatched roofs have been used in Northern Europe and Asia for centuries. It is well documented that in the sandhills of Nebraska, homesteaders in the 1800s used straw to build homes because of a lack of trees for lumber. New Englanders used stacked straw bales in the 1890s to insulate blocks of ice, keeping the ice for summer use. So using straw in construction isn’t really a brand new idea.
Straw is the leftover stalks of grains, such as wheat, oats, and rice. This abundant waste is used for animal bedding. In the UK, almost 4.0 million tons of straw are leftover from agricultural production, according to the Agricultural and Horticultural Development Board. It takes about seven tons of straw bales to built a three-bedroom home. “They’re also a very efficient insulator, so they should reduce energy bills by as much as 90 percent compared to other houses around this site,” Prof Walker added.
The positive aspects of building with straw bales
Straw bale construction has a number of advantages, particularly in achieving energy efficiency. As far as the insulation quality of straw bales over traditional insulating materials, straw bales can give a home an insulation rating of R-30 to R-35 or more. The thicker the bale, the better the R-value. And speaking of thickness, bales are at least 18-inches thick. Not only do thicker walls give added aesthetic appeal to a home, but the thicker walls help to reflect sunlight throughout a room.
Straw has low embodied energy. This means little energy was used to manufacture the straw because sunlight was the main energy source in growing the product. Other than baling and transporting the straw, the energy required is small. When we think of traditional insulating materials such as fiberglass, the energy savings are evident.
Properly maintained, straw bale houses are 100 percent sustainable and can last up to 100 years, or the life of the house. When the time comes to tear down the walls, the straw can be plowed back into the earth. And believe it or not, but well-compacted straw bales are more flame retardant than wood construction. This is because dense straw bales tend to smolder. And straw lends itself to any number of architectural styles.
There are some negative aspects of building with straw bales
First of all, building a house using straw bales is not a conventional method of home construction, and new construction techniques are needed. While they are not difficult to learn, it is necessary that the builder understand what is involved. And a big consideration is local building codes. The codes can vary from country to country and town to town. Always check the codes.
Another consideration is the climate. Building a straw bale home in a region with high humidity and lots of wet weather is not advisable because moisture is detrimental to straw as well as other building materials. Experienced builders of straw bale homes will tell you it is imperative to avoid allowing any moisture to enter the walls from the roof. If the straw bale walls are kept absolutely dry, they will last for the life of the house.
Lastly, because the walls are thicker, actual living space is cut down in a straw bale home. If straw bales have to be shipped over a long distance, there is the added cost of transportation to consider, as well as the possible pollution of the building material itself. In summing up the pros and cons of using straw bales as a sustainable and environmentally friendly building material, the potential for using a waste product over cutting down more trees is a definite plus. And being proactive in adapting to a warming climate is always smarter than doing nothing.
