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:
luis-o@alumni.cmu.edu
Assistant Professor, Dept. of Civ. And Envir. Engrg., University of Pittsburgh., Pittsburgh, PA 15213. Email: robries@pitt.edu
Assistant Professor of Civ. And Envir.Engrg. and Engrg. and Public Policy at Carnegie Mellon University,
Carnegie Mellon Univ., Pittsburgh, PA 15213. E-mail: hsm@cmu.edu
Head, Dept. of Civ. And Envir. Engrg., Carnegie Mellon Univ., Pittsburgh, PA 15213. E-mail:
cth@cmu.edu
1
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
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
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
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-LCA sector 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
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
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
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.
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