The Navajo Project

he 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 ass&mbled 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: Energy efficiency; Allowability;

Resource-efficient building technology; Use of local materials; Community involvement and use of local labor;

Cultural compatibility; and 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 southyvest. Because of the two-foot thick bale walls, the resulting structure has approximately 1,000 square feet of living space.

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

Straw-bale/adobe prototype home under construction (southwest ctlevation).

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 art 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 d 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-vajues 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 healing and cooling costs than conventional homes.

The Department of Energy, interested in the magnitude of potential energy savings of the wall design options, asked building scientist Jim Hanford of Lawrence Berkeley Laboratory (LBL) to analyze'the thermal characteristics of the various wall materials and project energy savings for the prototype home. The energy efficiency of various building design options was analyzed during the design charrette at Navajo and continued to be evaluated during the construction and testing phases of this project. Hanford's analysis, -which follows, assumes R-2.4 per inch for a straw bale, with sensitivities conducted at R-1.8 and R-3.0 per inch. Table one compares thermal characteristics of the

Ganado floor plan illustrates bask passive solar design principles at work; wrap the building with insulating straw bale exterior walls (except south, which is open to passive solar gain) and incorporate adobe into the house's interior. The insulating perimeter prevents the heat or cool stored in the thermal mass from being lost back to the outside.

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