LIFE CYCLE ASSESSMENT OF RESIDENTIAL BUILDINGS Luis Ochoa1, Robert Ries2, H. Scott Matthews3, and Chris Hendrickson, M4 ABSTRACT Residential building construction represented about 4.2% of the US Gross Domestic Product in 2000, and residences consumed nearly 20% of total US energy consumption. However, design and construction of residential buildings is often not conducted with an analysis of the life cycle costs and environmental impacts. In this paper, we outline an approach to a life cycle analysis for residences, using the results of a typical construction cost estimate to map into tools for environmental life cycle assessment (using the Carnegie Mellon economic input-output life cycle assessment model) and for resources required during the use phase of residences (using the DOE Energy Saver model). In essence, material costs are mapped into input-output sectors and the EIO-LCA model applied to assess environmental impacts. Similarly, operating inputs such as electricity or natural gas are estimated from the Home Energy Saver model and mapped into EIO-LCA sectors. The result of using our toolset is a life cycle assessment based upon the construction cost estimate. We are limited in the life cycle assessment to the building costs and the impacts calculated by the Carnegie Mellon economic input-output life cycle assessment. KEY WORDS Environmental life cycle assessment; residences; buildings INTRODUCTION Residences comprise an important sector of construction, a significant demand for resources, a major investment by individuals and families, and a major cause of pollution. Figure 1 shows the relative importance of residences for various economic and environmental impacts, including gross domestic product, electricity, energy, global warming, hazardous waste and toxic emissions (Ochoa, 2002). Residences have a disproportionate environmental impact relative to their share of economic activity. The impacts in Figure 1 make evident the need and desirability for better practices in managing the life cycle of residential buildings, including design, selection of raw inputs and manufacturing of building materials, materials transportation, construction procedures, 1

2

3

4

Graduate Student, Dept. of Civ. And Envir. Engrg., Carnegie Mellon Univ., Pittsburgh, PA 15213. E-mail: [email protected] Assistant Professor, Dept. of Civ. And Envir. Engrg., University of Pittsburgh., Pittsburgh, PA 15213. Email: [email protected] Assistant Professor of Civ. And Envir.Engrg. and Engrg. and Public Policy at Carnegie Mellon University, Carnegie Mellon Univ., Pittsburgh, PA 15213. E-mail: [email protected] Head, Dept. of Civ. And Envir. Engrg., Carnegie Mellon Univ., Pittsburgh, PA 15213. E-mail: [email protected]

1

Copyright ASCE 2005

Construction Research Congress 2005 Downloaded 13 Jun 2012 to 128.237.190.83. Redistribution subject to ASCE license or copyright. Visit http://www.ascelibrary.org

optimization of consumption patterns along the usage phase, and convenient disposal strategies (e.g., recycling, reuse, landfill). 0.00%

40% 35%

U.S. Total

30% 0.00%

25%

0.01%

0.08% 36.5%

20%

12.9%

15% 10%

4.9%

0.00% 5% 0%

0.00%

22.4% 19.2% 13.3%

2.9% 2.4%

1.8%

1.3%

1.9%

GDP

Electricity

Energy

GWP

6.4%

Construction

Usage

Haz. Waste RCRA

TRI Air

Disposal

Figure 1: Total Residential Building Impacts for Construction, Usage and Disposal Relative to US Totals for Gross Domestic Product (GDP), Electricity Use, Energy Use, Global Warming Potential (GWP) Emissions, Hazardous Waste Generation and Toxics Releases to Air (TRI Air) in 1997 (Ochoa, 2002). Different efforts have been conducted for improved residential design, some of which have considered a whole life cycle scenario, while others have just focused on some of the life cycle stages. However, most of these studies have not considered the indirect effects that exist among the building elements with the other sectors in the economy (from a market commodities perspective). This consideration may bring unexpected effects that better represent what is really happening in a more comprehensive and realistic scenario. In this paper, we describe our approach using a construction cost estimate for a typical residence to map into a tool for energy analysis, the Home Energy Saver (DOE 2004), and a tool for environmental life cycle assessment, the Carnegie Mellon economic input-output life cycle assessment model (Hendrickson, 1998; GDI, 2004). The result of using our toolset is a full life cycle assessment based upon the construction cost estimate. This model is illustrated for a typical residence in Pittsburgh, PA. Details concerning the model and additional example applications appear in Ochoa (2005).

2

Copyright ASCE 2005

Construction Research Congress 2005 Downloaded 13 Jun 2012 to 128.237.190.83. Redistribution subject to ASCE license or copyright. Visit http://www.ascelibrary.org

EXISTING RESIDENTIAL ANALYSIS AND DESIGN TOOLS Different approaches have been taken for determining the environmental impacts of residential buildings, suggesting different ways towards better sustainable practices. Some existing tools include: • LEED (Leadership in Energy and Environmental Design) by U.S. Green Building Council (GBA 2004) is a checklist of desirable practices for residential design and construction. Buildings conforming to good practice can be certified as ‘green buildings.’ • BEES (Building for Environmental and Economic Sustainability) is a listing of life cycle environmental impacts for different building material and component choices (NIST 2004). • Life cycle assessment tools have been developed by a variety of researchers and consulting firms to trace the impacts of different products and processes and to effect design improvements (Curran 1996, Heijings 2002). An application of these methods to a US residence appears in Keoleian (2001). • Energy analysis is a major concern of residential design due to the large life cycle energy uses. Model systems for energy analysis include ECOLOGUE-SEMPER (Ries 2001), ENERGY-10 (DOE 2004b) and DAEC (Assessment of Durability, Adaptability and Energy Conservation of Buildings) (Langford 2002). While numerous tools exist, there is still a need for a general purpose life cycle assessment tool that includes both direct and indirect impacts and is easy to use. MODEL FRAMEWORK The activities that encompass the life of a residential building are varied. In this work they are divided into construction, usage and disposal. For the construction phase, a construction cost estimate is used as input in the format used by RS Means (2000). The various material demands are mapped from the RS Means categories to economic input output sectors as defined by the Census Bureau. For the usage phase, we estimate home improvement and remodeling expenditures based upon Census (2001a, b, c), Mediamark (2000) and National Association of Home Builders (NAHB 2002) data and energy usage from the Home Energy Saver model (DOE 2004a). Disposal phase characterization is done in the RS Means (2000) format using the other construction economic sector. For each phase, the expected material and energy uses are converted to dollar amounts and their environmental impacts are assessed using the EIO-LCA model (Hendrickson 1998, Hendrickson 2005, GDI 2004). Figure 2 represents the overall architecture of the model. Table 1 illustrates the type of mapping from cost sectors to economic input-output sectors required for application of the model. In this case, we start with Census data from 1998 for typical residential material expenditures. The different material categories are grouped into economic input-output sectors and the dollar amounts converted to 1997 amounts (using the deflator 112.8/115.1 = 0.98 from RS Means, 2000) less a 10% markup representing the difference between expenditures and producer prices.

3

Copyright ASCE 2005

Construction Research Congress 2005 Downloaded 13 Jun 2012 to 128.237.190.83. Redistribution subject to ASCE license or copyright. Visit http://www.ascelibrary.org

CONSTRUCTION PHASE CHARACTERIZATION (RSMeans)

USAGE PHASE HOME IMPROVEMENT & REMODELING (Mediamark, Census, NAHB) USAGE PHASE ENERGY CONSUMPTION (Home Energy Saver)

INVENTORY (eio-lca)

RESULTS

DISPOSAL PHASE CHARACTERIZATION (RSMeans)

Figure 2: Structure of the Residential Life Cycle Assessment Model Showing Data Flows. Table 1: EIO-LCA Mapping of Improvement Materials Cost to Economic Input-Output Sectors (EION Sector) from a Household in the U.S. ACTIVITY FROM CENSUS

Bathroom or kitchen faucets Other bathroom or kitchen plumbing fixtures Insulation for ceiling, floor, and/or walls Exterior light fixtures Interior light fixtures Clean-air filter Down spouts/gutters Wooden Yard fence * Metallic Yard fence *

EION SECTOR

EION SECTOR DESCRIPTION

(1) 400200 400200

(2) Plumbing fixture fittings and trim Plumbing fixture fittings and trim

362000

Mineral wool

550300 550300 490300 400700 200903 370103

Wiring devices Wiring devices Blowers and fans Sheet metal work Wood products n.e.c. Steel wiredrawing and steel nails and spikes Converted paper products, n.e.c. Paint and allied products Paint and allied products

Wallpaper/covering

240706

Exterior painting Interior painting

300000 300000

TOTAL MATERIAL COST FOR HOUSEHOLD (1998 DOLLARS) (3) 4.9

MATERIALS COST IN 1997 DOLLARS (- 10% MARKUP) (4) 4.3

3.6

3.2

1.8 1.8 3.1 2.1 1.5 1.9

1.6 1.6 2.8 1.9 1.3 1.7

1.9

1.7

3.8 5.4 9.9

3.3 4.7 8.8

* The activity “Yard fence” was divided into two categories for a better environmental approach Column (4) = (3) * 0.9 * 0.98

4

Copyright ASCE 2005

Construction Research Congress 2005 Downloaded 13 Jun 2012 to 128.237.190.83. Redistribution subject to ASCE license or copyright. Visit http://www.ascelibrary.org

EXAMPLE APPLICATION A typical residence in Pittsburgh, PA is assessed following the methodology described above. The residence is a two story building with 2,000 sq. ft. (186 sq. m.) of living space and a wood frame. CONSTRUCTION PHASE The construction phase analysis is based upon a detailed summation of material requirements for the construction. As an example, the analysis for category “Foundation” is shown in Table 2. Table 2: Concrete Footing Foundation Example: EIO-LCA Mapping for Pittsburgh Case Concept

Corresponding

EIO Sector Description

(1)

EIO Sector (2)

(3)

Concrete, 3000 psi Forms, footing, 4 uses Reinforcing, 1/2" diameter bars, 2 each Keyway, 2" x 4", beveled, 4 uses Dowels, 1/2" diameter bars, 2' long, 6' O.C.

361200 200600 370101 200200 370101

EIO Sector Increased Economic Activity in 2001 Year Dollars (4) 381 118

Ready-mixed concrete Veneer and plywood Blast furnaces and steel mills 59 Sawmills and planing mills, general 32 Blast furnaces and steel mills 9

After having mapped the rest of the building categories, Table 3 shows the consolidated construction material requirements for the typical residence considered. The expenditures shown in Table 3 are input into the EIO-LCA model (GDI 2004) for the life cycle impact analysis. USAGE PHASE The usage phase involves impacts due to remodeling but mainly the energy inputs for cooling, heating and electrical systems. For this Pittsburgh example, we modeled a residence with central gas furnace, no air conditioning, and R-11 attic insulation. Based on the DOE Home Energy Saver (Session id 282940), the electricity consumption per year was 7,000 kW-hr and the natural gas consumption was 1,300 therms. These annual consumptions were then multiplied by the 50 year residence life time. DISPOSAL PHASE We estimated the impact of demolition expenditure of $3,500 in the EIO-LCAsector 110900 (Other Construction, including demolition). This is likely an overestimate relative to the construction phase since on-site activities are included, but the disposal phase is small even with this overestimate.

5

Copyright ASCE 2005

Construction Research Congress 2005 Downloaded 13 Jun 2012 to 128.237.190.83. Redistribution subject to ASCE license or copyright. Visit http://www.ascelibrary.org

Table 3: Construction Material Purchases and EIO Sectors for Pittsburgh Case EIO Sector

EIO Sector Description

(1) 90002 170100 200200 200300 200501 200502 200600 240701 270406 280100 280200 300000 310300 320400 350100 360300 360600 361200 361400 362000 370101 370103 370200 380700 400100 400200

(2) Sand and gravel Carpets and rugs Sawmills and planing mills, general Hardwood dimension and flooring mills Millwork Wood kitchen cabinets Veneer and plywood Paper coating and glazing Chemicals and chemical preparations, n.e.c. Plastics materials and resins Synthetic rubber Paint and allied products Asphalt felts and coating Miscellaneous plastics products, n.e.c. Glass and glass products, except containers Ceramic wall and floor tile Vitreous china plumbing fixtures Ready-mixed concrete Gypsum products Mineral wool Blast furnaces and steel mills Steel wiredrawing and steel nails and spikes Iron and steel foundries Rolling, drawing, and extruding of copper Enameled iron and metal sanitary ware Plumbing fixture fittings and trim Heating equipment, except electric and warm air furnaces Metal doors, sash, frames, molding, and trim Sheet metal work Hardware, n.e.c. Coating, engraving, and allied services, n.e.c. Switchgear and switchboard apparatus Wiring devices Environmental controls Total

400300 400500 400700 420300 420402 530300 550300 620300 All

EIO Sector Increased Economic Activity in 1997 Dollars (3) 329 2,290 10,438 6,394 13,990 919 4,756 458 55 190 436 1,930 370 859 509 527 96 1,689 2,521 861 168 83 58 38 1,359 173 846 852 566 424 28 440 565 114 55,331

6

Copyright ASCE 2005

Construction Research Congress 2005 Downloaded 13 Jun 2012 to 128.237.190.83. Redistribution subject to ASCE license or copyright. Visit http://www.ascelibrary.org

PHASES CONSOLIDATION Table 4 summarizes the life cycle environmental impact inventory for the typical Pittsburgh residence. As expected, the usage phase dominates most impact categories. In an actual study, the design characteristics of the residences could now be altered to estimate differences from these typical values. Table 4: Environmental Impact Analysis for an Example Pittsburgh Case Study. CONCEPT

UNITS

External Costs (Median) Electricity Used Energy Used Ores Iron Copper Bauxite Uranium & Vanadium Fuels Bituminous Coal Natural Gas LNG LPG Light Fuel Oil Heavy Fuel Oil Kerosene Fertilizers Hazardous Waste Generated RCRA Conventional Pollutants in Air SO2 CO NO2 VOC PM10 Global Warming Potential CO2 CH4 N2O CFCs Weighted Toxics Releases Air Releases Land Releases Underground Releases

$ Kw-hr MJ Kg Kg Kg Kg $ MJ MJ MJ MJ MJ MJ MJ $ Kg Kg Kg Kg Kg Kg Kg Equivalent kilograms of CO2 “ “ “ Equivalent kilograms of H2SO4 “ “

Construction

Usage

Disposal

2,000 32,000 590,000 6,000 1,000 4,000 0 0 550,000 150,000 230,000 0 17,000 81,000 14,000 0 80 2,000

18,000 390,000 13,000,000 9,000 3,000 5,000 200 0 13,000,000 4,000,000 9,000,000 1,000 65,000 130,000 220,000 6 10 3,000

90 800 18,000 400 100 300 3 0 17,000 5,000 6,000 4 700 4,000 400 0 0 50

Total (50 years) 20,000 430,000 14,000,000 15,000 4,000 9,000 300 0 14,000,000 4,000,000 10,000,000 1,000 83,000 220,000 230,000 6 90 5,000

700 100 300 200 100 100 43,000 38,000 4,000 70 100 100 4 20 2

6,000 3,000 1,000 2,000 200 200 581,000 524,000 56,000 200 200 300 5 20 2

30 5 10 10 0 10 1,000 1,000 100 0 0 13 0 1 0

7,000 3,000 1,000 2,000 300 300 620,000 560,000 60,000 300 300 400 8 40 4

CONCLUSIONS This work proposes a model to conduct the life cycle assessment of a U.S. residential building, from a construction materials and energy consumption standpoint, along three lifecycle phases: construction, usage, and disposal. It illustrates a case study for a typical residence in Pittsburgh, PA. The model strives to take into consideration life cycle costs and environmental impacts considering direct and indirect relationships among economy components.

7

Copyright ASCE 2005

Construction Research Congress 2005 Downloaded 13 Jun 2012 to 128.237.190.83. Redistribution subject to ASCE license or copyright. Visit http://www.ascelibrary.org

In the Pittsburgh case study the environmental stressors most important for the construction phase were soil toxicity, ores depletion, and polluted air, which highlights the need for greener construction materials, as well as for greener manufacturing processes. As for the usage phase, all type of efforts directed towards the optimization of energy consumption for the housing sector should be encouraged: Energy-efficient electro-domestic appliances, construction materials with better insulation properties, ecological awareness in architectural design, etc. In this point it is also very important the way in which cleaner technologies for generating energy (solar, wind, biomass and geothermal) will evolve in the medium and long terms. Contribution of the disposal phase was definitely minor in scope. ACKNOWLEDGMENTS The authors would like to thank the Green Design Industrial Consortium and the Universidad Michoacana (UMSNH) for financial support for this paper. REFERENCES Census (2001a) U.S. Census Bureau, Manufacturing, Mining, and Construction Statistics. “Residential Improvements and Repairs Statistics.” Census (2001b) U.S. Census Bureau , Statistical Abstract of the United States: 2000. “No. 1209. Housing Units–Characteristics by Tenure and Region: 1997.” (Last accessed April 2, 2002) Department of Commerce, Washington, D.C. Census (2001c) U.S. Census Bureau, Statistical Abstract of the United States: 2000. “No. 1223. Expenditures by Residential Property Owners for Improvements and Maintenance and Repairs by Type of Property and Activity: 1980 to 1998.” (Last accessed April 2, 2002) Department of Commerce, Washington, D.C. Curran (1996) Curran, Mary Ann, “Environmental Life Cycle Assessment,” McGraw-Hill. DOE (2004a) US. Department of Energy, “Home Energy Saver.” (Last accessed October 10, 2004), Washington, D.C. DOE (2004b) US Dept. of Energy, “Energy-10,” http://www.nrel.gov/buildings/energy10/ (Last accessed November 8, 2004). GBA (2004) Green Building Alliance, “Leadership in Energy and Environmental Design,” http://www.usgbc.org/LEED/leed_homes.asp (Last accessed November 8, 2004). GDI (2004) Green Design Institute, “Economic Input-Output Life Cycle Assessment Software,” (Last accessed October 20, 2004), Carnegie Mellon, Pittsburgh, PA. Heijings (2002) Heijungs, R. and Suh, S., “The Computational Structure of Life Cycle Assessment,” Kluwer Academic Publishers. Hendrickson (2005) Hendrickson, C.T. et. al., “Environmental Life Cycle Assessment Using Economic Input-Output Analysis,” (forthcoming). Hendrickson (1998) Hendrickson, C., A. Horvath, S. Joshi and L.B. Lave, "Economic InputOutput Models for Environmental Life Cycle Analysis," Envir. Science & Techn., April.

8

Copyright ASCE 2005

Construction Research Congress 2005 Downloaded 13 Jun 2012 to 128.237.190.83. Redistribution subject to ASCE license or copyright. Visit http://www.ascelibrary.org

Keoleian (2001) Keoleian, Greg et. Al., “Life-Cycle Energy, Costs and Strategies for Improving a Single-Family House,” Journal of Industrial Ecology. 4(2), 135-157. Langford (2002) Langford, David A., Iain MacLeod, Branka Dimitrijevic, Tom W. Maver, “Assessment of Durability, Adaptability and Energy Conservation of Buildings,” Intl. J. Journal of Envir. Technol. and Management- Vol. 2, No.1/2/3 pp. 142-159. Mediamark (2000) Mediamark Research Inc., “Top-Line Reports.” (Last accessed April 1, 2002). NAHB (2002) National Association of Home Builders, “The Strength of a Nation Lies in the Homes of its People.” (Last accessed April 8, 2002). NIST (2004) National Institute of Standards and Technology, “Building for Environmental and Economic Sustainability,” http://www.bfrl.nist.gov/oae/software/bees.html (last accessed November 8, 2004). Ochoa (2005) Ochoa, Luis, “A Method for Environmental Life Cycle Assessment of Residential Buildings,” Unpublished PhD Dissertation, Carnegie Mellon, (forthcoming). Ochoa (2002) Ochoa, L., Hendrickson, C., and Matthews, S., “Economic Input-output Lifecycle Assessment of U.S. Residential Buildings.” Journal of Infrastructure Systems, ASCE, Volume 8, Number 4, pp. 132-138, December. Ries (2001) Ries, Robert and A. Mahdavi, “Integrated Computational Life-Cycle Assessment of Buildings,” J. of Computing in Civil Engineering, 15(1), 59-66. RSMeans (2000a) RSMeans Company, Inc. (2000). “RSMeans Residential Cost Data 2001.” Kingston, MA.

9

Copyright ASCE 2005

Construction Research Congress 2005 Downloaded 13 Jun 2012 to 128.237.190.83. Redistribution subject to ASCE license or copyright. Visit http://www.ascelibrary.org