BY MAURA KELLER
From insulating the walls of a library in Edinburgh, Scotland, or constructing a historic manor in the French countryside, to building a charming guest cottage in Finland, using straw as a building block has been embraced by people across the globe for centuries.
In the U.S., building with straw bales was made possible by the invention of the horse-powered baling machine in the 1870s. According to Catherine Wanek, author and photographer of The New Straw Bale Home, The Hybrid House, and Designing with Sun, Wind, Water and Earth, transient farm workers across the American Midwest immediately saw the potential of stacking straw bales to craft temporary shelter.
“The first known permanent straw-bale houses were built by settlers in the sandhills of Nebraska in the 1890s. Homesteading rolling grasslands with few trees and soil too sandy for sod homes, some pioneers used what was at hand, stacking bales for walls and plastering them with local ‘gumbo mud,’” Wanek says. “These proved to be comfortable shelters, and some of these structures are still standing today.”
Opposite: One of the first bale homes owned by the Simonton family, 1890s settlers in western Nebraska, made from baled meadow grass.
As Wanek explains, straw is plentiful — essentially a by-product of food production — as it’s the leftover stalk of wheat, rice, oats, barley, rye, etc., after the grain is harvested. It’s also a natural, non-toxic material, especially compared with manufactured insulation materials. It also has much lower “embodied energy” (the energy used to make and deliver a material to the building site).
“Bale walls are seismically resistant, and in an earthquake are amazingly resilient. Bale walls also reduce sound transfer, which is an advantage in urban environments,” Wanek says. “And counterintuitively, they are actually fire-resistant, too. Once plastered, bales are essentially air-tight, so that even if exposed to fire, there’s not enough oxygen within the wall system to support combustion.”
Perhaps the biggest benefit of straw bales is in the creation of an insulated wall system. As Wanek points out, measured in a variety of tests — from Sandia National Labs in New Mexico to the Oak Ridge National Laboratory in Tennessee — their insulation value, also known as R-value, equals or surpasses that of fiberglass insulation. The thickness of a bale, around 22 inches when plastered, delivers a super- insulated wall system of R-30 – R-40.
“In practice, depending on the habits of the inhabitants, super insulation can reduce our heating and cooling needs by 60 to 80% over conventional materials,” Wanek says. “This enhances comfort, reduces energy bills, and shrinks our carbon footprint in two ways. Saving energy saves the burning of fossil fuels, and since straw is basically carbon, encapsulating straw inside walls sequesters literally tons of carbon per home, until the house reaches the end of its life, decades in the future.”
AESTHETICALLY SPEAKING
While pioneers typically built their homes with a single-story hipped-roof design (often with a room in the attic) — using the minimum of lumber and allowing bales to directly support the roof — contemporary builders generally opt for a wooden or steel structure, using bales to fill in the walls, floor to ceiling. According to Wanek, this “post-and-beam” approach allows for multiple-storied structures and is easier to get code approval. Although straw-bale construction is accepted in the International Building Code (IBC), building codes vary state to state, and even county by county.
This compact Craftsman style home is built on a small urban lot in Capitola, California and features straw bale insulation, passive solar design, solar hot water, Photovoltaic panels, water harvesting, and permaculture landscape. Decorative earth/clay interior plasters. Energy star appliances. Total energy bills average $12/month.
This compact Craftsman style home is built on a small urban lot in Capitola, California and features straw bale insulation, passive solar design, solar hot water, Photovoltaic panels, water harvesting, and permaculture landscape. Decorative earth/clay interior plasters. Energy star appliances. Total energy bills average $12/month.
A straw bale home in Pagosa Springs, CO
“Depending on regional climate zones, house foundations might be an insulated concrete slab in cold and dry climates, or might be elevated above the ground to allow air flow and reduce the chances of flooding in wet regions and conditions,” Wanek says.
“In all climates, it’s essential to raise the bale walls well above the potential for moisture, which typically means elevating them at least six to 10 inches above the ground level, and also a few inches above the final floor level.”
Outside and in, bale walls must be plastered, which functionally seals the bales from insects, vermin, precipitation, and fire. The coats of plaster should be permeable, to allow moisture vapor to move through the wall and evaporate on the outside. Permeable plasters can be clay, lime, gypsum, or lime-cement stucco.
“Impermeable coatings, like an elastomeric stucco or ferrous cement, impede this vapor movement, potentially allowing moisture to condense inside the wall,” Wanek says.
EMBRACING CHALLENGES
The enemy of straw bales, and most building materials, is moisture. So dry climates are much more friendly to bale construction than wet, rainy climates. “That said, straw-bale homes have been successfully built in the American South as well as cold coastal climates like Washington state, Nova Scotia, and Denmark,” Wanek says. “In these challenging climates, straw bale walls are often protected from driving rain with a ‘rain screen’ or wooden shiplap siding.”
During construction, keeping the bales dry until they are under the roof also is challenging. In addition, finding an architect and building team that has experience with bale construction is a distinct advantage.
“While straw-bale building seems simple, there are many tricks of the trade that will save time and money, so doing your homework by reading, consulting, and even volunteering on someone else’s build, always pays off,” Wanek says. “A well- designed straw-bale home is a resilient home. Given the uncertainty of modern life, and the potential for an occasional failure of the electrical grid, a super- insulated structure with passive design is a resilient structure that can remain reasonably comfortable in times of both cold and hot weather.”
