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BTS: House of Straw - Straw Bale Construction Comes of Age

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House of Straw - Straw Bale Construction Comes of Age

A demonstration project using affordable, energy-efficient construction techniques with

an emphasis on materials produced near the building site and erected by local labor

resources.

U.S. Department of Energy

Energy Efficiency and Renewable Energy

April 1995

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Introduction

Americans want comfortable, attractive, functional, and durable housing. Yet, many

increasingly find high quality housing beyond their means. Conventional building methods

rely on plentiful resources. With some of these resources dwindling, housing costs are

sky rocketing. The cost of a home includes materials, construction, financing, taxes,

energy consumption, and insurance. This booklet explores recent attempts to reduce

those costs. Construction techniques discussed in this booklet focus on building resource-

efficient and energy-conserving homes, without sacrificing affordability or quality.

In a cooperative demonstration project between the U.S. Department of Energy (DOE),

the U.S. Department of Housing and Urban Development (HUD), and the Navajo Nation,

current home designs on the Navajo reservation were evaluated and recommendations

were made to improve quality and lower the costs. The resulting design utilized straw-

bale wall construction.

Straw-bale building is a practical and perhaps under utilized construction method.

Initiated in the United States at the turn of the century, straw-bale building is showing

new merit in today's marketplace. Walls of straw, easily constructed and structurally

sound, promise to take some of the pressure off of limited forest resources.

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Straw is a viable building alternative, plentiful and inexpensive. Straw-bale buildings

boast superinsulated walls (R-50), simple construction, low costs, and the conversion of

an agricultural byproduct into a valued building material. Properly constructed and

maintained, the straw-bale walls, stucco exterior and plaster interior remain water proof,

fire resistant, and pest free. Because only limited skill is required, a community house-

raising effort can build most of a straw-bale house in a single day. This effort yields a

low-cost, elegant, and energy-efficient living space for the owners, a graceful addition to

the community, and a desirable boost to local farm income. This booklet offers an in-

depth look at one such community house-raising, in addition to a general overview of

straw-bale construction.

Straw-Bale Construction

History of Straw Bale Construction

People have built homes using straw, grass, or reed throughout history. These materials

were used because they were reliable and easy to obtain. European houses built of straw

or reed are now over two hundred years old. In the United States, too, people turned to

straw houses, particularly after the hay/straw baler entered common usage in the 1890s.

Homesteaders in the northwestern Nebraska "Sandhills" area, for example, turned to

baled-hay construction, in response to a shortage of trees for lumber. Bale construction

was used for homes, farm buildings, churches, schools, offices, and grocery stores.

Nebraska historian Roger L. Welsch writes: "It was

inevitable that some settler, desperate for a cheap,

available building material, would eventually see the big,

solid, hay blocks as a possibility. Soon, baled hay was

indeed a significant construction material. The bales,

about three to four feet long and one and one-half to two

feet square, were stacked like bricks, one bale deep, with

the joints staggered. About half used mortar between the

bales; the others simply rested one bale directly on the

other. Four to five wooden rods (in a few cases iron rods)

were driven down through the bales to hold them firmly together. The roof plate and roof

were also fastened to the top bales of the wall with rods or stakes. The most common

roof configuration was some sort of hipped roof. . . .Window and door frames were set as

the walls rose around them. . . .Walls were left to settle a few months before they were

plastered and the windows installed."

Matts Myhrman and Judy Knox, straw-bale construction consultants, have visited many of

these "Nebraska-type" bale structures, built between 1900 and 1940. Myhrman

rediscovered the area's oldest existing bale building, the Burke homestead, constructed

in 1903 outside Alliance, Nebraska. Although abandoned in 1956, the Burke homestead

continues to successfully withstand Nebraska's wide temperature swings and blizzard

force winds. Long-time Nebraskan Lucille Cross recalls the hay-bale house of her

childhood was so quiet that her family, not hearing a tornado outside, just sat there

playing cards, while the tornado wrought havoc all around them.

In Wyoming, straw-bale structures have consistently withstood severe weather and

earthquakes. "The earthquake was in the 1970s and it was either 5.3 or 5.8," Chuck

Bruner, a resident of one of the houses told The Mother Earth News. "There wasn't a

single crack in the house. You can live in this house comfortably during the summer. It

stays nice and cool. We have never needed any air conditioning, and in summer we get

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days up in the 90s. Also, last winter, I only turned our small bedroom heater on twice. If

I had to guess how our utility bills compare to those of our neighbors, I'd have to say our

bill is about half.

Straw: A Renewable Resource

Straw, the stalks remaining after the harvest of grain, is a renewable resource, grown

annually. Each year, 200 million tons of straw are under utilized or just wasted in this

country alone. Wheat, oats, barley, rice, rye, and flax are all desirable straws for bale

walls. Even though the early bale homes used hay for the bales, hay is not recommended

because it is leafy and easily eaten by creatures great and small. Straw, tough and

fibrous, lasts far longer. Straw-bale expert Matts Myhrman estimates that straw from the

harvest of the United States' major grains could be used to construct five million, 2,000

square-foot houses every year! More conservative figures from the U.S. Department of

Agriculture indicate that America's farmers annually harvest enough straw to build about

four million, 2,000 square-foot homes each year, nearly four times the houses currently

constructed.

Building a straw-bale house is relatively simple. A basic 2,000 square-foot house requires

about 300 standard three-wire bales of straw (costing approximately $1,000). Placed on

a foundation, the bales are skewered on rebar pins like giant shiskabobs. After wiring and

plumbing, the walls are sealed and finished. Because grains are grown in almost every

region of the country, straw bales are readily available, with minimal transportation

costs. Lumber from trees, in addition to becoming more scarce and expensive, must be

transported over longer distances.

TYPES OF STRAW BALES

Straw bales come in all shapes and sizes, from small two-string bales to larger three-

string bales and massive cubical or round bales. The medium sized rectangular three-

string bales are preferred for building construction. Three-string bales are better

structurally, have higher R-value, and are often more compact. A typical medium-sized,

three-wire bale may be 23" X 16" X 42" and may weigh from 75 to 85 pounds. The

smaller two-wire bales, which are easier to handle, are roughly 18" X14" X 36" and weigh

50 to 60 pounds. If the current trend continues, it may not be long before "construction-

grade" bales begin to appear.

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The Navajo Project

The Navajo Nation (located in parts of Arizona, New Mexico, and Utah) is the largest

American Indian reservation in the United States. With a population of close to 200,000

people spread over 17 million rural acres, the Navajo community has a continuous need

for adequate housing. This need for housing is complicated by the lack of affordable

electricity to remote homesites, dwindling supplies of firewood, and increasing cost of

building materials and labor. Navajo community leaders wanted housing that boosted the

local economy, used local materials and labor, and maintained the integrity of their

culture.

In 1991, the Navajo Nation asked the DOE for assistance in creating more energy-

efficient, affordable housing. Under the proposal, DOE and HUD provides funds for

technical assistance to review home designs and suggest alternatives, while the Navajo

Nation provide funds for construction of a demonstration house. A team was assembled

in December 1992 to discuss local housing construction, evaluate design options, identify

the needs of home occupants, and inventory community sentiment. In architectural

circles, this process is known as a "design charrette." Charrette participants were

selected for expertise in energy, finance, indigenous materials, passive solar design, and

knowledge of the Navajo community and traditions. The design charrette was conducted

in Gallup, New Mexico and focused on the following design criteria for the prototype

home:

z Energy efficiency;

z Affordability;

z Resource-efficient building

technology;

z Use of local materials;

z Community involvement and

use of local labor;

z Cultural compatibility; and

z Design simplicity, adaptability,

and comfort.

The final design that was agreed upon

was a unique combination of

"Nebraska-style" straw-bale walls and adobe walls with passive solar orientation. This

combination has several benefits. Straw-bale and adobe are inexpensive, locally available

materials that can be used for building by local unskilled labor after only minimal training.

Straw-bale walls are superinsulated (about R-50), and adobe and passive solar

orientation have been used for centuries by Native Americans in the southwest. Because

of the two-foot thick bale walls, the resulting structure has approximately 1,000 square

feet of living space.

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Construction of the demonstration home began in July 1993 near Ganado, Arizona and

was completed in December 1994. The home successfully met the design criteria in the

following ways.

Energy Efficiency. The high elevation desert climate of the Navajo Nation, characterized

by wide daily temperature fluctuations, low humidity, plentiful sunshine, and cold

winters, dictated the design parameters for the prototype home. Well-insulated walls,

good air-leakage control, and taking advantage of the solar radiation were key to

reducing the use and cost of space heating. Unlike a wood frame wall that has many

pieces assembled at the site, bales provide an nearly monolithic layer of straw that is

covered inside with plaster and outside with stucco. Coupled with a simple geometric

design, the monolithic wall coverings result in very little air leakage.

Straw is a form of cellulose that has reasonably good insulating properties; and because

a bale can be up to two feet thick, a straw-bale wall has extremely high thermal

resistance. Recent tests following ASTM procedures resulted in bale R-values between R-

2.4 and R-3.0 per inch, depending on the direction of the straw, and showed that thermal

resistance is affected by moisture and density of the pack (Joseph McCabe, January

1993). Matts Myhrman, another straw-bale expert, suggests that R-2.4 per inch is

representative of straw-bale thermal resistance in the field. Therefore, straw-bale homes

should have lower heating and cooling costs than conventional homes.

METHODS OF BUILDING WITH STRAW

Straw has been used for centuries by builders who recognized its structural integrity. A

piece of straw is simply a tube made of cellulose. Tubes are recognized as one of the

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