This Lesson Plan was very closely adapted from: 

http://www.unm.edu/~abqteach/ArchiCUs/99-02-08.htm. 

Much of the text is directly taken from this source.

 

 

STRAW BALE BUILDING

Background Information:

Straw bale construction is not new although it may seem to be. It has been used for over 100 years, and it is recently making a comeback in the residential construction trade.

Before 1936 all known straw-bale structures in the United States used the walls to support the roof. This was known as the "Nebraska Style" (1). After 1936, strawbales were used as infill material. The bales are placed inside a roof support structure, such as post and beam, or concrete for their insulation values and not as support for the roof (2).

Dr. William Henry Burritt built a two story mansion using straw bales in 1936, (See http://www.unm.edu/~abqteach/Image45.gif). The first house, which used mostly wood for the structural support and the straw as in-fill material, burned the day Dr. Burritt moved in. He rebuilt his house this time mainly using concrete instead of wood for the structural parts. This house remains in good standing condition today.

Another straw bale process of building uses the bales by encasing them in mortar much like brick laying, http://www.unm.edu/~abqteach/Image46.gif. There was a general store built in 1948 using this technique (3). Another technique for building non-load-bearing walls is to compress the bales. This is an example of typical construction practices of today, (See http://www.unm.edu/~abqteach/Image47.gif and http://www.unm.edu/~abqteach/Image48.gif).

Straw bale building slowed between the early 1950's and early 1980's, most likely due to the increased availability of mass-produced building materials. Straw bale building is not limited to dry areas. Straw bale homes have been built in Washington State, which receives 75" of rain annually. Until 1991 straw bale structures were given the lowest possible building permit and were generally not bank financed. In 1991, Virginia Carabelli of Tesuque, New Mexico built the first insured and bank financed straw bale home. In addition, around this time, Tony Perry organized the Straw Bale Construction Association, SBCA. The SBCA sponsored small-scale fire tests and transverse load tests to incorporate straw bale building practices into New Mexico building codes. A copy of New Mexico's straw-bale construction guidelines and codes located on the Internet at http://www.earthbuilding.com/nm-straw-bale-code.html.

Straw bale building uses building materials from a by-product of wheat and rice grain production. The straw can be grown in a short period in contrast to lumber, which takes years to produce usable material. Therefore, it is a fast, sustainable building material. This type of building does not require expensive tools or specialized laborers. Building with straw bales is less labor intensive than concrete block, adobe or stone. The straw is very forgiving and lends itself to the creativity of the builder.

A clear advantage of straw-bale construction is insulation. A straw bale has a better insulation value or R-Value, than the most modern well insulated homes.

Product

R-Value/per inch

Wood
Brick
Fiberglass batt.
Straw with the grain
Straw against the grain

 

1
.2
3.0
2.4
3.0

 

A 3-string bale stacked flat, which is 23" wide, has an R-Value of 54.7. If that bale were stacked on edge, 16" wide, the R-Value would be 49.5. These values are 2 to 3 times greater than an well-insulated modern framed house (4).

Each year grain farmers battle with the remains of their harvest, straw. Straw does not decompose very rapidly and becomes a burden for the farmers. The burning of straw in California produced more Carbon Monoxide or CO than all the electrical power generating plants in the state combined produced. There is 1 million tons of rice straw burned, which produces 56,000 tons of CO. Burning 97,000 tons of wheat straw produces 5,000 tons of CO. The straw does not decompose very rapidly and becomes a burden for the farmers. It is estimated that if all the straw left after harvest was baled instead of burned, 5 million 2,000-sq. ft. homes could be built every year. This would help the farmers and help the homeless while reducing the amount of CO in the air (5).

The affordability of straw bale homes is cheaper or at most comparable to modern building practices. If the owner becomes the builder, the structure can cost between $5 to $20 per sq. ft.; $20 to $50 if the owner sub contracts part of the work out. Expect to pay $50 to $80 for a contractor to build the entire house. Today a typical two by four framed house will cost $75 to $100 per sq. ft. Another benefit of straw bale is fire safety.

In the mid 1980's the National Research Council of Canada carried out fire rating tests on plastered straw bales and found them more resistant than conventional building materials. A mortar encased bale passed the test with a maximum temperature rise of only 110 degrees F. for 4 hours. The plaster coating withstood 1850 degrees F. for 2 hours before a small crack appeared. In 1993, the state of New Mexico found similar results in their tests. The first test on an unplastered wall section met the standard requirements by exposing the face panel to 1000 degrees F. within 5 minutes and increasing the temperature to 1500 degrees after 30 minutes. The temperature rise on the unheated side was 1.97 degrees F. It took 30 minutes to burn through the center of the test wall, not the middle of the exposed bale. It burned through at a joint where 2 bales met; the rest of the bale was only charred half way through. The second test was exposing 1942 degrees F. to a plastered wall section. The temperature rise on the unheated side was only 10 degrees F. Neither flames nor gases penetrated the wall (6). Straw-bale construction has recently made a great comeback in the residential sector. All the research and testing is really stacking up to support straw-bale construction. Self-sustaining building practices are becoming more of a necessity.

 

Lesson Plan

 

Objective:

Students will be able to:

  • Comprehend terminology
  • Identify the processes needed to construct a straw bale home.
  • Evaluate the benefits of straw bale built structures.
  • Create a floor plan and section view of a straw bale structure.
  • Incorporate New Mexico Standard Straw-bale Codes into their house designs.
  • Complete a model replica of straw bale construction.

 

Activities:

  • The students will build wall sections using clay or another medium to signify the straw bales and tooth picks to represent the rebar.
  • They will finish the walls with a mud plaster finish.
  • Students will design a straw-bale structure using straw-bale-building codes.
  • Students will create a section of a portfolio for straw-bale construction that includes:
                Sketches

                Articles and research Material

                Lecture notes

                Pictures

                Poster and Presentation Boards

 

Materials:

  • Slide projector
  • Articles and Internet information and sources.
  • Guest speakers from straw bale construction companies and SBCA, if available.
  • Straw-bale model medium such as marshmallows or clay
  • Toothpicks to represent the rebar
  • Mud and aggregate

 

Evaluation:

  • In class discussion with visual-verbal presentation of drawings and models
  • Verbal quizzes
  • Project design
  • Class and self-critique of structures
  • Test taking
  • Identification of materials and practices
  • Wall building project evaluation
  • Portfolio grade based on the following:
  • Fluency and clarity of communication
  • Imagination, innovation and creativity
  • Understanding process
  • Detail and overall aesthetics
  • Technical competence

 

 

Notes and Bibliography

1.   Steen A.S, Steen B., Bainbridge D., Eisenberg D. The Straw Bale House. Chelsea Green Publishing Company: Vermont, 1994. Pg. 3.
2.   http://www.earthbuilders.com/nm-straw-bale-code.html
3.   Steen A.S, Steen B., Bainbridge D., Eisenberg D. The Straw Bale House.Chelsea Green Publishing Company: Vermont, 1994. Pg. 6
4.   Steen A.S, Steen B., Bainbridge D., Eisenberg D. The Straw Bale House.Chelsea Green Publishing Company: Vermont, 1994. Pg. 25.|
5. Steen A.S, Steen B., Bainbridge D., Eisenberg D. The Straw Bale House.Chelsea Green Publishing Company: Vermont, 1994. Pg. 27.
6. Steen A.S, Steen B., Bainbridge D., Eisenberg D. The Straw Bale House.Chelsea Green Publishing Company: Vermont, 1994. Pg. 41.

 

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