Appendix G

ENVIRONMENTAL IMPACTS OF A SINGLE FAMILY BUILDING SHELL -

FROM HARVEST TO CONSTRUCTION

July 17, 2002

Prepared by:

Jamie Meil, ATHENA Sustainable Materials Institute¹
Bruce Lippke, University of Washington
John Perez-Garcia, University of Washington
Jim Bowyer, University of Minnesota

¹ Meil is vice president, Athena Sustainable Materials Institute, Toronto, Canada; Lippke is director, Rural Technology Initiative, and Perez-Garcia is associate professor, College of Forest Resources, University of Washington, Seattle, WA; Bowyer is director Forest Products Management Development Institute, Dept. of Wood and Paper Science, University of Minnesota, St. Paul MN.

TABLE OF CONTENTS

1.0 INTRODUCTION
2.0 METHODOLOGY
    2.1 BACKGROUND
    2.2 INTEGRATING CORRIM LCI DATA
    2.3 HOUSE DESIGNS
        2.3.1 Minneapolis
        2.3.2 Atlanta
3.0 IMPACT INVENTORY
    3.1 BILL OF MATERIALS FOR HOUSE CONSTRUCTION
    3.2 RESOURCE EXTRACTION
    3.3 ENERGY CONSUMPTION
    3.4 AIR EMISSIONS
    3.5 WATER EMISSIONS
    3.6 SOLID WASTE AND SOLID WASTE INDEX
4.0 IMPACT ASSESSMENT
    4.1 GLOBAL WARMING POTENTIAL INDEX
    4.2 AIR AND WATER POLLUTION INDICES
    4.3 RESOURCE USE INDICES
5.0 DISCUSSION
    5.1 DISCUSSION OF MINNEAPOLIS RESULTS
    5.2 DISCUSSION OF ATLANTA RESULTS
6.0 SUMMARY OF PRELIMINARY RESULTS
    6.1 MINNEAPOLIS PRELIMINARY RESULTS
    6.2 ATLANTA PRELIMINARY RESULTS
7.0 FUTURE WORK
    7.1 EVALUATION OF BUILDING OPERATION
    7.2 BUILDING USE AND DISPOSAL
        7.2.1 Life Expectancy and Durability
        7.2.2 Use, Recycle and Disposal Module
    7.3 INTEGRATED ANALYSIS FRAMEWORK
        7.3.1 Standard unit of use vs. standard unit of supply
        7.3.2 Carbon storage integrated across forest resources and construction
        7.3.3 The impact of increased forest management intensity
8.0 REFERENCES

LIST OF FIGURES

LIST OF TABLES

1.0 INTRODUCTION

This section describes the methodology by which the individual product LCI databases developed by CORRIM were used to support the development of an integrated LCI for a single family building shell. CORRIM is a member of the ATHENA™ Sustainable Materials Institute (the Institute). The Institute maintains a model for simulating residential construction and developing LCI data for a constructed building using an array of building materials for which comprehensive LCI data are available. The Institute has modified and expanded its ATHENA™ software to accept U.S. wood product production LCI data and to simulate construction activity in two different U.S. end markets - Minneapolis and Atlanta. This section also presents results of an environmental comparison of typical single-family houses in each market location constructed of wood and of alternative materials (steel frame in Minneapolis and concrete block in Atlanta). The environmental assessment was limited to the structural components used in each of the comparable designs. Life cycle stages from resource extraction through on-site construction are considered in these analyses.

The assessment results include a large number of output measures including energy consumption, air and water emissions and generation of solid wastes. Results are summarized in terms of four index measures: 1) initial embodied energy (initial embodied energy includes the direct and indirect energy associated with extraction, manufacturing and on-site construction activity stages, including all transportation within and between these three stages), 2) greenhouse gas emissions (both fuel and process generated, but excluding CO2 from the combustion of biomass), 3) measures of air and water pollution, and 4) solid waste emissions. A fifth index - environmental measures associated with resource extraction - will be developed in future work.

2.0 METHODOLOGY

2.1 BACKGROUND

Since the early 90s the Institute has been developing an environmental life cycle assessment decision support tool known as ATHENA™. A primary objective has been to assist the building community in making more informed decisions regarding the selection of design and material mixes that will minimize a building's life cycle environmental impact. Used in conjunction with product and process LCI databases, it can also assist in the evaluation of the environmental effectiveness of alternative manufacturing and forest management process changes.

The Athena™ model encompasses steel, wood and concrete structural products and assemblies, and covers life cycle stages from natural resource extraction, through manufacturing of individual products, to on-site construction, including all related transportation. It provides a full environmental life cycle inventory within the boundaries selected, as well as selected measures of environmental impact.

Prior to the CORRIM research effort, the model and databases were Canadian in scope representing average or typical manufacturing technologies used in Canada and appropriate modes and distances for transportation. The original model was regionalized into six geographic centers represented by Vancouver, Calgary, Winnipeg, Toronto, Montreal and Halifax end use markets. Over the past year the model has been expanded to include the two major US wood product producing regions (the US Pacific Northwest and US Southeast) and two U.S. end-use markets represented by Minneapolis and Atlanta.

2.2 INTEGRATING CORRIM LCI DATA

Regional LCI data developed as part of the CORRIM project for forest harvesting and for production of softwood lumber, plywood and oriented strand board (OSB) are described in separate reports included within the Appendices. Using detailed surveys, raw data were collected from forestry and mill operations in each of the producing regions and then modeled in SimaPro (a LCA practitioners' tool for conducting product life cycle inventories). SimaPro generates complete life cycle inventory data for each product including a summary of all raw material and energy inputs as well as resultant process and fuel related emissions to air, water and land.
To maintain consistency across U.S. wood products studied as part of CORRIM and the alternative building materials already modeled in Athena™, the LCI for each product was input to Athena™ free of any electricity or gate-to-market transportation related burdens. US average and regional electricity grid flows from and to nature were incorporated in Athena™. Similarly, transportation distances determined in the CORRIM project were input to Athena™. Athena™ includes a transportation energy use and emissions module to calculate the impacts from transportation. Each regional LCI product profile was imported to the Athena™ software. The non-wood building material LCI profiles already in Athena™ were recalculated to reflect US average electricity generation and use.

The Athena™ model contains algorithms to estimate on-site construction effects associated with structural assemblies and systems. On-site activities can be significant and can range from 2 to 30% of the embodied energy of the materials making up an assembly. These on-site effects calculations were not changed to reflect the new regions; however, the on-site effects relationships are less a function of regional location and more a function of material and structural assembly type.

2.3 HOUSE DESIGNS

Single-family home designs for Minneapolis and Atlanta were reviewed with Softplan® CAD files detailing the elevations, floor plans and specified materials (Appendix F).

Some material specification refinements were made such as determining the working gauge for steel products, the use of either plywood or OSB sheathing materials where they could be interchanged, and the specific strength of concrete to be used in various applications. For the purposes of wood and alternative material comparison, plywood was selected as the default sheathing material for this phase of the analysis.

The house designs were specified to be as close as possible to "as built" in each end market; i.e., no attempt was made to optimize material use in construction. In the Minneapolis market, the primary structural material alternative to wood was determined to be steel, although insulated concrete form is gaining in popularity. For Atlanta, the alternative material design to wood was determined to be concrete block.

It is important to note that while the designs in a region were intended to produce identical insulation properties with no difference in energy use over the life of a building (i.e. the standard unit of use having equal properties), in practice there will be differences affecting energy consumption over the life of a building. Similarly, maintenance requirements may be different. These differences will be considered in future work.

2.3.1 Minneapolis

Table 1 summarizes the similarities and differences in alternative house designs for Minneapolis. The primary structural difference between the Minneapolis wood and steel house designs is the use of materials for floors and walls. Both designs share the same basement and roof elements. It should be noted that the basement walls were furred out over their full height using the partition wall system as specified above for each material design.

Table 1: Summary of Alternative House Designs for Minneapolis

2.3.2 Atlanta

As shown in Table 2, the only major difference between the Atlanta wood and concrete house designs is their respective exterior wall structure; all other structural elements are common between the two designs.

Table 2: Summary of Alternative House Designs for Atlanta

3.0 IMPACT INVENTORY

3.1 BILL OF MATERIALS FOR HOUSE CONSTRUCTION

The bill of materials produced by the ATHENA™ construction model appears in Table 3. The bill of materials determines the flow of materials and all associated energy use, emissions, and solid wastes from raw materials extraction or harvest, through each stage of transport and processing, and continuing through the completion of the designed house.

Table 3: Bill of Materials for Alternative House Designs for Minneapolis and Atlanta

3.2 RESOURCE EXTRACTION

For each product in the bill of materials, the raw materials needed to provide that quantity are evaluated. Table 4 lists the extracted resources derived by tracing the products in the bill of materials back to the resources required for their production (see LCI data for each stage of processing, Appendices A to E).

Table 4: Raw Materials Needed to Produce Alternative House Designs for Minneapolis and Atlanta

The flow of wood from the forest to products used in construction and co-products is provided in Figures 1 and 2.

Figure 1: Wood Flow Chart to Construct a House in Minneapolis

Figure 2: Wood Flow Chart for Construction of a Wood-Framed House in Atlanta

3.3 ENERGY CONSUMPTION

Energy consumption is analyzed for each stage of processing: extraction, product manufacturing, and construction. Energy consumed in transportation is an important subcategory included with manufacturing. Embodied energy is reported in gigajoules. Embodied energy includes all energy, direct and indirect, used to transform or transport raw materials into products and buildings, including inherent energy contained in raw or feedstock materials that are also used as common energy sources. For example, natural gas used as a raw material in the production of various plastic (polymer) resins is part of the embodied energy of plywood. In addition, the model captures the indirect energy use associated with processing, transporting, converting and delivering fuel and energy.

Table 5 lists the energy consumed by source for each alternative house design and stage of processing.

Table 5: Energy Consumption by Stage of Processing for Alternative House Designs for Minneapolis and Atlanta

* Electricity (kWh) is produced primarily from the reported natural gas and coal (MJ)

3.4 AIR EMISSIONS

The air emissions produced by each stage of processing are provided in Table 6.

Table 6: Emissions to Air by Stage of Processing for Alternative House Designs for Minneapolis and Atlanta