ADOBE, RAMMED EARTH AND WOOD:

AN ENERGY-BASED ENVIRONMENTAL ANALYSIS OF RESIDENTIAL CONSTRUCTION

IN PHOENIX, ARIZONA

 

Candace L. Gossen

Solar 7.83 Consultants

2323 SE Tamarack

Portland, Oregon 97214

ABSTRACT

More than 90% of the new single-family dwellings built in the Phoenix Metropolitan Area consists of wood frame construction. Using adobe and rammed earth as alternatives in residential wall construction are the main focus of this study. The study examines the "process" of home construction, concentrating on the environmental impacts of energy embodied in the four stages: extraction, transportation, construction, and operation. These four stages were applied to three prototypes built in the Phoenix Area throughout one year. The results are compared to determine which has the lowest environmental costs and most likely to benefit sustainability.

The study requires a comparative analysis rather than a definite choice of a better prototype. The information provides assistance to the builder/designer with options about environmental impacts and the whole energy spectrum. Wherein previous research based on performance standards of operation, we must also consider environmental impacts and externalities.

 

1. INTRODUCTION

Many studies have compared the economics of materials and building performance. Little research on the study of energy embodied in materials exists. Moving into a new paradigm, the natural environment, there is a need to understand how energy is consumed. Current building practices make extensive use of wood, and tree growth cannot sustain the growing demand. To achieve sustainability we need to consider alternative methods of building construction and materials. Earth materials (e.g.,

 

dirt, adobe, aggregate) are local to Arizona, and are also effective as thermal mass in the hot arid desert. They can help reduce the reliance on wood products and the environmental degradation involved in processing the wood material.

Society is becoming more conscious about environmental sustainability, but economics hinder even the best intentions. It is now becoming important that the building industry make responsible decisions involving energy consumption relative to the materials necessary in building a house. By the same token there should be a responsibility not only to create performance standards in operation, but also to chose building materials that have the fewest impacts on the environment. For example, a house that consumes less energy has less of an environmental impact. A house that demands fewer wood materials in the building process, also destroys fewer trees that are necessary in the absorption of pollutants in our air. Power plants have both direct and indirect impacts on the air, land, and water we need to exist. These resources are depleting, pollution is increasing, degradation is evident, and the population of the world continues growing. There is an urgent need for alternatives to today’s building practices. The purpose of this study is to evaluate the relative environmental impacts of alternative building practices, and to suggest new approaches that are more environmentally compatible with their local environment.

 

2. RESEARCH DESIGN

The Phoenix metropolitan area is one of the fastest growing cities in the United States. The majority of building construction is residential and is using fast, easy methods of

 

construction for economic gain. The area is also plentiful in local materials for adobe and rammed earth construction. This could support a more sustainable use of our natural resources and promote less environmental degradation by current practices. The study area encompasses a 50 mile radius including Phoenix and its fast-growing suburbs.

1) The study focuses on four segments called "process" for adobe, rammed earth, and wood-frame type wall construction in residential designs. The first segment addresses the extraction of soil and all of the equipment required to do so. The equipment required is specified as diesel machinery and electric generated equipment.

2) Category two is the transportation of the bricks (as in the Adobe prototype) to the job site. Transportation includes all vehicles and their consumption of fossil fuel. 3) The third category identifies the energy embodied in building materials. The study analyzes the actual Btu’s expended per wall construction material created. For a relative comparison to energy, it is further translated into Btu’s per gallon of gasoline.

4) The fourth category of the four segments of "process" is the energy used to operate the house on an annual basis, given in kilowatt hours. This last category was computed using a DOE2.1D program entitled "Energy Consumption Analysis of a Typical Residential Unit with Different Wall Materials." This program was developed by the United States Department of Energy in order to compare typical residential construction and its annual energy consumption.

Phoenix, Arizona was chosen to enable a comparison to the actual operating conditions where all three prototypes are built.

2.1 Operating Programs

DOE2.1D--developed by Lawrence Berkeley Laboratory and the University of California is used to project the annual energy consumed for an operating house. The program was modified by Acrosoft International, Inc. to make it available and usable. The program allows the programmer to specify conditions relative to building materials, climate data relative to certain regions in the United States, and to certain mechanical equipment. For this study, Phoenix climate data were input for a total period of one year for all three prototypes. The mechanical equipment was used at minimum levels for heating and cooling, as well as other required electrical devices. The only changing variables between the building prototypes were the specific heat, conductivity, and density of each material used in the walls. The program did not allow the full dimension of 24 inches for the wall thickness of rammed earth. Therefore the program only computed on the maximum allowance of 13 inches. Adobe was input as

specified, and the wood framing was the most difficult. A standard house with current performance standards requires specific insulation values in order to be considered "Climate Crafted Housing" in Arizona. Therefore the wood variables were input, but in order to create a functioning wall for the program, insulation values, and other wall materials and thickness were input as well. This was the first noticeable difference in the materials, because adobe, and rammed earth wall materials can operate alone as finished products. Wood must have other materials in order to complete a functioning wall.

2.2 Energy Embodied Research

The third segment of "process" is the embodied energy for each construction material, as well as the energy expended during the actual construction of the walls for each prototype. In 1981 the Department of Energy sponsored research called the "Handbook of Energy Use for Building Construction" DOE/CE/20220-1( 1 ). The handbook provides building designers with information to determine the energy required for building construction and to evaluate the energy required for alternative materials, assemblies, and methods. The research identifies the energy required for manufacturing and delivering of raw materials to the construction jobsite for over 400 different building materials and products. Unfortunately, there is still very little information concerning adobe, and none on rammed earth.

2.3 Air Emissions

In the flow charts, on the following pages, the final stage is the noted environmental impacts. One part of these charts, as well as Table 4, is the air emissions as noted in separate elements including CO, Nox, HC, Pm, Co2, and So2. These emissions are from the machinery necessary to process each building prototype, whether it be from stationery diesel equipment, mobile diesel equipment, electric generated equipment, or electric generated power. These figures were taken from various sources(2,3,4). Emissions' statistics for stationery equipment were collected from the Arizona Department of Environmental quality table 3.3-1, for industrial equipment (45-600hp) diesel engines(4). The mobile lab profiles from ADEQ 929101-2D dated 4/3/92 were used for all mobile equipment(4). The electric generated equipment and the electric generated power emissions were taken from a collaborative of sources compiled into a program operated by the Arizona Corporation Commission(5). These sources included APS & AEPCO operated units: data from LCP filing of April 1989 TEP base load from FERC Form 1(6) and SRP data from EIA-412 in April 1989. Also included is the EIA "Cost &

 

 

Quality of Fuels for Electric Utility Plants 1988," Table 50 gas units from FERC Form 1. For coal units the So2 and Nox statistics came from the EPA NEDS Point Source Listing 1985 from American Gas Association.

 

2.4 Land, Water, Trees, and Fossil Fuel Impacts

The land degradation noted in Table 4, relative to coal operated power plants, is referenced to research by Martin Pasqualetti and Byron Miller. In the paper titled "Land Requirements for the Solar and Coal Options," it is noted that the total land disturbed due to the operation of Navajo Generating Station is 6.62 ac per NW (7). This includes all land affected for the generating station site, ash disposal area, evaporation ponds, well field and pipeline, station access roads, railroad, transmission lines, mines, and limestone source. Navajo Generating Station was chosen for this study due to the consistent operation of this plant, information available, and more closely related to electric power supply to Phoenix through this generating station.

The water statistics in Table 4 also relate to the generation of power. The figure cited as 0.790 gal per kwh expended is the total evaporation of water. This number is applied to the total electric consumption per building prototype. The tree loss is relative to the amount of board feet required per prototype. This affects the amount of trees per individual houses built in Phoenix during the study year.

Fossil fuel consumption is listed by two sub-titles, diesel and coal. The diesel noted is the direct consumption per piece of equipment necessary to process each natural element into a building construction material and into a finished product of a built house. The coal is relative to Navajo Generating Station and the amount required to supply electric power.

 

3. COMPARATIVE ANALYSIS

3.1 Documentation -- Flow Charts

The flow charts show the procedure followed for each step in the process, beginning with material extraction, transportation, construction and operation of the three building prototypes (adobe, rammed earth, and wood frame). Each shape of the flow chart signifies a separate function. The rectangle signifies the material. The indented rectangle symbolizes the equipment required in each procedure. Following the arrows to the squares shows the action that each piece of equipment takes. The circle is the energy expended by each action, and the final ellipse is

the environmental impact by the action. Each chart follows in vertical format in process, but also follows horizontally in action.

Fig. 1 Adobe Construction Diagram

 

3.2 Adobe (See Fig. 1)

Beginning with the extraction process, one must find the proper soil mixture in order to create an adobe brick. In Arizona, adobe soil is plentiful, especially near the Phoenix Area within the 50 mile radius used in the study. The equipment used in mechanical adobe processing are mostly electric generated and produce approximately 5,000 bricks per 6 hour shift. Production is random depending on the demand from construction. The operation cited in this study operates at 115,000 kwh monthly, or 5,750 kwh per 5,000 bricks for one house constructed(1). In the construction phase it is noted that the energy embodied per adobe brick = 2,500 Btu’s at 5,000 bricks per house = 12,500,000 Btu’s expended. In relation to fossil fuels, the energy embodied in 5,000 bricks would equal 116 gallons of gasoline.

The operation of the adobe house consumes approximately 11,069 kwh annually. Using Navajo Generating Station statistics from a document "An Evaluation of Alternative Control Strategies to Remove Sulfur Dioxide and Carbon Dioxide at Existing Large Coal-Fired Facilities" Report EA 1989, per kwh there is 10,239 Btu’s expended. Therefore an adobe house would equal 113,335,491 Btu’s expended divided by 22.07 million Btu’s per ton of coal = 5.135 tons of coal per one year of operation.

Fig. 2 Rammed Earth Construction Diagram

3.3 Rammed Earth (See Fig. 2)

 

The process for rammed earth has two options, either to transport in the aggregate needed, or to dig out the site. It is common to use "5/8" minus aggregate which is a byproduct of the granite mining process. The diesel equipment necessary in this process consumes 2,500 gallons of diesel in 8 days, which is 33 gallons per house constructed. Ninety-Six tons of aggregate is needed of each house, as compared to 1,472 tons produced daily. The emissions are based on mobile vehicles in figures by ADEQ(4). The construction of the walls consumes 100 gallons of diesel with the emissions given on the flow chart. The fourth

 

 

procedure, operation of the constructed house would consume 9,639 kwh annually. Although the DOE2.1D program only allowed for 13 inches width of the walls. In comparison a normal rammed earth wall is 24 inches wide. Using again the statistics from Navajo Power Plant, this documents the rammed earth prototype as using 4.47 tons of coal annually.

3.4 Wood Frame (See Fig. 3)

There is quite an extensive network involved in the timber industry and that is why this study was quite specific in only documenting sawnwood, or lumber used in framing a house. For an average 1,500 sf house there is 14,307.6 b.f. used in the walls and roof. In comparison both the adobe and rammed earth prototypes used 1,900 b.f. for the roof framing only.

In the extraction process, all of the equipment required are noted on the flow chart. There are generally 12-16 loggers daily that work for one particular cut or sale area. As an average there is among 6-25,000 b.f. cut daily over 160 acres in 7 days(8). Diesel is used as an energy source and the statistic base is the same as used for adobe and rammed earth. Total skidding, loading and hauling for production of one house consumes 119.52 gallons of diesel per 14,307.6 b.f. of lumber, or 20 trees.

Once the timbers are cut then they must be milled. The procedure for milling follows in diagram and consumes 3.3 b.f./kwh of production. Multiplying for 14,307.6 b.f. for requirements of one house that would equal to 47,215.08 x 10,239 Btu’s = 21.9 tons of coal for electric generate power.

The transportation of this cut timber and lumber was traced by consumption in Arizona versus import and export factors. It was found that most of the lumber used in the state is from the Pacific Northwest mills. To transport to Arizona there are two methods, by rail and by truck. The total traveled miles from Oregon is 1,419 miles by one train comprising 100 cars and 4 engines on average depending on total weight of cargo.

The construction of the framing for a wood frame house embodies approximately 105,376,199 Btu’s that is equivalent to 970 gallons of gasoline. Today only 74% of an actual timber is usable. For an average "16" diameter by 16' long log, approximately 199 b.f. is obtained.

The operation of a wood frame house is dependent on other elements beside just the dimension lumber; including plywood, insulation, and finish materials. In the DOE2.1D

 

 

 

Fig. 3 Wood Frame Construction Diagram

program all current R values represent what is called locally "a climate crafted home," built to save 25% of the energy consumption of competitive homes. After

construction, the wood frame house would consume approximately 12,236 kwh annually, or 125,284,404 Btu’s equaling 5.67 tons of coal yearly.

4. CONCLUSIONS

This study requires a comparative analysis rather than a definitive answer or choice of a better prototype. The study concludes that:

  • Rammed Earth option #1 (to excavate the site out) had the fewest environmental impacts.
  • A rammed Earth house operates with the least energy consumed on an annual basis for the Phoenix Area.
  • The largest consumption of energy is from electric generated machinery.
  • Largest amounts of air emissions are from electric generated power.
  • Land degradation and water evaporation must be considered in electric generated power, which is relative to the operation of the construction industry.
  • The fewest amounts of trees required were equal for adobe, and rammed earth, with a ratio of 7:1 for a wood framed house to an adobe or rammed earth house (this includes lumber for the roof framing only).
  • Fossil fuels were consumed for all three prototypes, diesel for on site machinery and coal for electric generated power. The least impact is the more efficient piece of machinery.
  • The adobe and rammed earth houses require more labor but require less in costs of materials as compared to wood framing.

The analysis of wood framing included only dimension lumber. Although to form a complete wall, including wood framing, insulation, finish materials and other products necessary to have an operational structure. As compared to adobe and rammed earth, the soil is the finished product, thus lessening the need to exploit product.

4.1 Outcome

The worksheet entitled "totals" give the numbers comparatively among the three prototypes in this study. It shows the higher emissions of carbon and sulfur are relative to fossil fuel machinery and electric generated power. Wood framing encompasses the greater degradation. Comparatively there is a choice of three trees per house for the adobe and rammed earth houses, and twenty for the wood framing. In comparison, 70 tons of soil for adobe and 300 tons of soil for rammed earth are required. Water is consumed through electric generation by Navajo Power Plant for all prototypes, as well as coal being consumed for the production of electric energy.

 

 

Table 4. Comparative Analysis of Individual Prototypes

5. REFERENCES

(1) Stein, R.G., 1981. "Handbook of Energy Use for

Building Construction," USDOE/CE1220220-1. March 1981.

(2) Environmental Protection Agency, 1989. "An Evaluation of Alternative Control Strategies to Remove Sulfur Dioxide and Carbon Dioxide at Existing Large Coal-fired Facilities." NEDS Point Source Listing 1985. Report 1989-January 3, 1989.

(3) Arizona Department of Environmental Quality, 1992. "Emission Factors for Gasoline and Diesel Powered Industrial Equipment." Emission Factor Ratings,

Table 3.3-1.

(4) Arizona Department of Environmental Quality, 1990. "Air Quality Control for Arizona." Office of Air Quality. Annual Report, August 1991.

(5) Arizona Corporation Commission. Interview with David Berry, by author. Written interview 6 October 1992.

(6) Environmental Inspection Agency, 1992. "Cost & Quality of Fuels for Electric Utility Plants 1988," table 50 gas units. FERC Form 1. Arizona Public Service, Co.

(7) Pasqualetti, M. and Miller, Byron A., 1984. Land Requirements for the Solar and Coal Options. The Geographical Journal, volume 150, number 2, July 1984.

(8) Arizona Public Service & Arizona Electric Power Cooperative operated units: data from LCP filing of April 1989.

(9) Georgia-Pacific. Clemet Falls, Oregon 1992. Interview with Peter Hess, Norm Edwardson, by author. Telephone interview January 1992.

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