PNNL-24936 Rev-1

Cost-Effectiveness Analysis of 

the Residential Provisions of 

the 2015 IECC for South Dakota

February 2016

VV Mendon

M Zhao

ZT Taylor

E Poehlman

Cost-Effectiveness Analysis of the 

Residential Provisions of the 2015 

IECC for South Dakota

VV Mendon

M Zhao

ZT Taylor

E Poehlman

February 2016

Prepared for

the U.S. Department of Energy

under Contract DE-AC05-76RL01830

Pacific Northwest National Laboratory

Richland, Washington 99352
*Authors’ Note

The present report is a revision of a previous report of the same name published in October 2015. The 

previous report was revised to update numbers reported in certain results tables.
PNNL-24936 Rev-1

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Acronyms and Abbreviations

BC3 Building Component Cost Community

BECP Building Energy Codes Program

CPI Consumer Price Index

DOE U.S. Department of Energy

EIA Energy Information Administration

ERI Energy Rating Index

ICC International Code Council

IECC International Energy Conservation Code

LCC Life-Cycle Cost

NAHB National Association of Home Builders

PNNL Pacific Northwest National Laboratory
PNNL-24936 Rev-1

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Highlights

The 2015 IECC provides cost-effective savings for residential buildings in South 

Dakota. Moving to the 2015 IECC from the 2009 IECC base code is cost-effective 

for residential buildings in all climate zones in South Dakota.

The average statewide economic impact (per dwelling unit) of upgrading to the 2015 IECC is shown in 

the table below based on typical cost-effectiveness metrics.

1

Metric Compared to the 2009 IECC

Life-cycle cost savings of the 2015 

IECC $9027.42

Simple payback period of the 2015 

IECC 2.9 years

Net annual consumer cash flow in 

year 1 of the 2015 IECC2 $501.29

Annual (first year) energy cost 

savings of the 2015 IECC ($) $588.93

Annual (first year) energy cost 

savings of the 2015 IECC (%) 25.5%

 

1 A weighted average is calculated across all climate zones in the state.

2 The annual cash flow is defined as the net difference between annual energy savings and annual cash outlays 

(mortgage payments, etc.), including all tax effects but excluding up-front costs (mortgage down payment, loan fees, 

etc). First-year net cash flow is reported; subsequent years' cash flow will differ due to the effects of inflation and 

fuel price escalation, changing income tax effects as the mortgage interest payments decline, etc.
PNNL-24936 Rev-1

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Cost-Effectiveness Results for the 2015 IECC for South 

Dakota

This section summarizes the cost-effectiveness analysis in terms of three primary economic metrics:

 Life-Cycle Cost (LCC): Full accounting over a 30-year period of the cost savings, considering energy 

savings, the initial investment financed through increased mortgage costs, tax impacts, and residual 

values of energy efficiency measures

 Consumer Cash Flow: Net annual cost outlay (i.e., difference between annual energy cost savings and 

increased annual costs for mortgage payments, etc.)

 Simple Payback Period: Number of years required for energy cost savings to exceed the incremental 

first costs of a new code, ignoring inflation and fuel price escalation rates

LCC savings is the primary metric used by the U.S. Department of Energy (DOE) to assess the 

economic impact of residential building energy codes. Simple payback period and the Consumer Cash 

Flow analysis are reported to provide additional information to stakeholders. Both the LCC savings and 

the year-by-year cash flow values from which it is calculated assume that initial costs are mortgaged, that 

homeowners take advantage of mortgage interest tax deductions, that individual efficiency measures are 

replaced with like measures at the end of their useful lifetimes, and that efficiency measures may retain a 

residual value at the end of the 30-year analysis period.

1. Life-Cycle Cost 

The Life-Cycle Cost (LCC) analysis computes overall cost savings per dwelling unit resulting from 

implementing the efficiency improvements of a new energy code. LCC savings are based on the net 

change in overall cash flows (energy savings minus additional costs) resulting from implementing a new 

energy code. LCC savings are summed over an analysis period of 30 years. Future cash flows are 

discounted to "present values" using a discount rate that accounts for the changing value of money over 

time. LCC savings is the economic metric used by DOE for decision making purposes.

Table 1 shows the LCC savings (discounted present value) over the 30-year analysis period for the 

2015 IECC compared to the 2009 IECC.

Table 1. Life-Cycle Cost Savings of the 2015 IECC compared to the 2009 IECC

Climate Zone Life-Cycle Cost Savings ($)

5A $9,411.33

6A $8,997.11

State Average $9,027.42
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2. Consumer Cash Flow

The Consumer Cash Flow results are derived from the year-by-year calculations that underlie the 

Life-Cycle Cost savings values shown above. The specific cash flow values shown here allow an 

assessment of how annual cost outlays are compensated by annual energy savings and the time required 

for cumulative energy savings to exceed cumulative costs, including both increased mortgage payments 

and the down payment and other up-front costs.

Table 2 shows the per-dwelling-unit impact of the improvements in the 2015 IECC on Consumer

Cash Flow compared to the 2009 IECC.

Table 2. Consumer Cash Flow from Compliance with the 2015 IECC Compared to the 2009 IECC

Cost/Benefit 5A 6A State 

Average

A

Down payment and other 

up-front costs $97.32 $154.78 $150.58

B

Annual energy savings 

(year one) $582.02 $589.48 $588.93

C Annual mortgage increase $53.53 $85.14 $82.83

D

Net annual cost of 

mortgage interest 

deductions, mortgage 

insurance, and property 

taxes (year one)

$3.12 $4.95 $4.82

E 

=

[B-(C+D)]

Net annual cash flow 

savings (year one) $525.38 $499.38 $501.29

F

=

[A/E]

Years to positive savings, 

including up-front cost 

impacts

0.19 0.31 0.30

Note: Item D includes mortgage interest deductions, mortgage insurance, and 

property taxes for the first year. Deductions can partially or completely offset 

insurance and tax costs. As such, the "net" result appears relatively small or is 

sometimes even negative.

3. Simple Payback Period

The simple payback period is a straightforward metric including only the costs and benefits directly 

related to the implementation of energy-saving measures associated with a code change. It represents the 

number of years required for the energy savings to pay for the cost of the measures, without regard for 

changes in fuel prices, tax effects, measure replacements, resale values, etc. The simple payback period is 

useful for its ease of calculation and understandability. Because it focuses on the two primary 

characterizations of a code change—cost and energy performance—it allows an assessment of cost 

effectiveness that is easy to compare with other investment options and requires a minimum of input data. 
PNNL-24936 Rev-1

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DOE reports the simple payback period because it is a familiar metric used in many contexts. However, 

because it ignores many of the longer-term factors in the economic performance of an energy-efficiency 

investment, DOE does not use the payback period as a primary indicator of cost effectiveness for its own 

decision-making purposes.

Table 3 shows the simple payback period for the 2015 IECC for South Dakota. The simple payback

period is calculated by dividing the incremental construction cost by the first-year energy cost savings

assuming time-zero fuel prices. It estimates the number of years required for the energy cost savings to 

pay back the incremental cost investment without consideration of financing of the initial costs through a 

mortgage, the favored tax treatment of mortgages, the useful lifetimes of individual efficiency measures, 

or future escalation of fuel prices. 

Table 3. Simple Payback Period for the 2015 IECC Compared to the 2009 IECC

Climate Zone Payback Period (Years)

5A 1.9

6A 3.0

State Average 2.9
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Overview of the Cost-Effectiveness Analysis Methodology

This analysis was conducted by Pacific Northwest National Laboratory (PNNL) in support of the U.S. 

Department of Energy’s (DOE) Building Energy Codes Program. DOE supports the development and 

implementation of energy efficient and cost-effective residential and commercial building energy codes. 

These codes help adopting states and localities establish minimum requirements for energy-efficient 

building design and construction, as well as ensure significant energy savings and avoided greenhouse gas 

emissions. 

The present analysis evaluates the cost-effectiveness of the prescriptive path of the 2015 edition of the 

International Energy Conservation Code (IECC), relative to the 2009 IECC. The analysis covers one- and 

two-family dwelling units, town-homes, and low-rise multifamily residential buildings covered by the 

residential provisions of the 2015 IECC. The IECC's simulated performance path and the new Energy 

Rating Index (ERI) path included in the 2015 IECC are not in the scope of this analysis due to the large 

variety of building configurations those paths allow. While buildings complying via these paths are 

generally considered to provide equal or better savings compared to the prescriptive requirements, the 

intent of these paths is to provide additional design flexibility at a cost dictated by the builder or 

homeowner. DOE has established a methodology for determining energy savings and cost-effectiveness 

of various residential building energy codes (Taylor et al. 2012). The LCC analysis described in that 

methodology balances upfront costs with longer term consumer savings and is therefore DOE's primary 

economic metric for its decision making processes.

1. Estimation of Energy Usage and Savings

In order to estimate the energy impact of residential code changes, PNNL developed a single-family 

prototype building and a low-rise multifamily prototype building to represent typical new residential 

building construction (BECP 2012, Mendon et al. 2013 and Mendon et al. 2014). The key characteristics 

of these prototypes are described below:

 Single-Family Prototype: A two-story home with a 30-ft by 40-ft rectangular shape, 2,400 ft2 of 

conditioned floor area excluding the basement (if any), and window area equal to 15% of the 

conditioned floor area equally distributed toward the four cardinal directions.

 Multifamily Prototype: A three-story building with 18 units (6 units per floor), each unit having 

conditioned floor area of 1,200 ft2and window area equal to approximately 23% of the exterior wall 

area (not including breezeway walls) equally distributed toward the four cardinal directions.

These two building prototypes are further expanded to cover four common heating systems (natural 

gas furnace, heat pump, electric resistance and oil-fired furnace), and four common foundation types 

(slab-on-grade, heated basement, unheated basement, crawlspace), leading to an expanded set of 32 

residential prototype building models. This set is used to simulate the energy usage for typical homes 

built to comply with the requirements of the 2015 IECC and those built to comply with the requirements 

of the 2009 IECC for one location in each climate zone in the state using DOE’s EnergyPlusTM software, 

version 8.0 (DOE 2013). A detailed discussion of the code provisions considered in this analysis is given 

by Mendon et. al. (2013 and 2015). Energy savings of the 2015 IECC relative to the 2009 IECC,
PNNL-24936 Rev-1

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including space heating, space cooling, water heating and lighting, are extracted from the simulation 

results. 

2. Fuel Prices

The energy savings from the simulation analysis are converted to energy cost savings using the most 

recent state-specific residential fuel prices from DOE’s Energy Information Administration (EIA 2014a, 

EIA 2014b, EIA 2014c). The fuel prices used in the analysis are shown in Table 4.

Table 4. Fuel Prices used in the Analysis

Electricity

($/kWh)

Gas

($/Therm)

Oil 

($/MBtu)

$0.11 $1.08 $18.74

3. Financial and Economic Parameters 

The financial and economic parameters used in calculating the LCC and annual consumer cash flow 

are based on the latest DOE cost-effectiveness methodology (Taylor et al. 2015) to represent the current 

economic scenario. The parameters are summarized in Table 5 for reference.

Table 5. Economic Parameters used in the Analysis

Parameter Value

Mortgage interest rate (fixed rate) 5.00%

Loan fees 0.6% of the mortgage amount

Loan term 30 years

Down payment 10% of home value

Nominal discount rate (equal to mortgage rate) 5.00%

Inflation rate 1.60%

Marginal federal income tax 15%

Marginal state income tax 0.00%

Property tax 1.10%

4. Aggregation Scheme

Energy results, weighted by foundation and heating system type, are provided at the state level and 

separately for each climate zone within the state. The distribution of heating systems for South Dakota is 

derived from data collected by the National Association of Home Builders data (NAHB 2009) and is 
PNNL-24936 Rev-1

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summarized in Table 6. The distribution of foundation types is derived from the Residential Energy 

Consumption Survey data (EIA 2009) and is summarized in Table 7. The single-family and multifamily 

results are combined for each climate zone in the state and the climate zone results are combined to 

calculate a weighted average for the state using housing starts from the 2010 U.S. Census data (Census 

2010). The distribution of single- and multifamily building starts is summarized in Table 8.

Table 6. Heating Equipment Shares

Heating System

Share of New Homes (percent)

Single-Family Multifamily

Natural Gas 57 68

Heat Pump 40 25

Electric Resistance 3 4

Oil 0 3

Table 7. Foundation Type Shares

Foundation Type Slab-on-grade Heated Basement Unheated 

Basement Crawlspace

Share of New Homes (percent) 22 47 16 16

Table 8. Construction by Building Type and Climate Zone

Climate Zone

Share of New Homes (percent)

Single-Family Multifamily

5A 8 5

6A 92 95
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Incremental Construction Costs

In order to evaluate the cost-effectiveness of the changes introduced by the 2015 IECC over the 2009 

IECC, PNNL estimated the incremental construction costs associated with these changes. For this 

analysis, cost data sources consulted by PNNL include: 

 Building Component Cost Community (BC3) data repository (DOE 2012)

 Construction cost data collected by Faithful+Gould under contract with PNNL (Faithful + Gould 

2012)

 RS Means Residential Cost Data (RSMeans 2012) 

 National Residential Efficiency Measures Database (NREL 2014)

 Price data from nationally recognized home supply stores

The consumer price index (CPI) is used to adjust cost data from earlier years to the study year (BLS 

2015). The estimated costs of implementing the prescriptive provisions of the 2012 IECC over the 2009 

IECC are taken from an earlier PNNL study that evaluated the cost-effectiveness of the 2012 IECC 

(Lucas et al. 2012). The additional costs of implementing the prescriptive provisions of the 2015 IECC 

over the 2012 IECC are taken from the National 2015 IECC Cost-Effectiveness study (Mendon et.al. 

2015). The national scope costs from those studies are adjusted to reflect local construction costs in South 

Dakota using location factors provided by Faithful+Gould (2011). 

Table 9 and Table 10 show the incremental construction costs associated with the 2015 IECC 

compared to the 2009 IECC for an individual dwelling unit. Table 9 shows results for a house and Table 

10 shows results for an apartment or condominium. These have been adjusted using a construction cost 

multiplier, 0.829, to reflect local construction costs in South Dakota based on location factors provided by 

Faithful + Gould (2011).

Table 9. Total Construction Cost Increase for the 2015 IECC Compared to the 2009 IECC ($)

Single-family Prototype House

Climate Zone Crawlspace Heated Basement Slab Unheated Basement

5A $1,327.41 $1,545.38 $1,366.39 $1,327.41

6A $2,379.65 $2,379.65 $2,418.63 $2,379.65
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Table 10. Total Construction Cost Increase for the 2015 IECC Compared to the 2009 IECC ($)1

Multifamily Prototype Apartment/Condo

Climate Zone Crawlspace Heated Basement Slab Unheated Basement

5A $751.04 $782.67 $751.04 $751.04

6A $1,135.70 $1,135.70 $1,135.70 $1,135.70

 

1

In the multifamily prototype model, the heated basement is added to the building, and not to the individual 

apartments. The incremental cost associated with heated basements is divided among all apartments equally.
PNNL-24936 Rev-1

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Energy Cost Savings

Table 11 shows the estimated annual per-dwelling unit energy costs of end uses regulated by the 

IECC, which comprise heating, cooling, water heating, and lighting, that result from meeting the 

requirements of the 2015 and the 2009 IECC.

Table 11. Annual (First Year) Energy Costs for the 2015 IECC and the 2009 IECC

Climate Zone

2015 IECC 2009 IECC

Heating Cooling Water 

Heating Lighting Total Heating Cooling Water Heating Lighting Total

5A $742.46

(-42.2%)

$253.52

(-6.5%)

$284.50

(-0.8%)

$145.92

(-11.8%)

$1426.40

(-29.0%) $1,284.96 $271.01 $286.93 $165.51 $2,008.42

6A $700.12

(-44.1%)

$221.08

(-6.1%)

$285.33

(-1.1%)

$140.95

(-11.8%)

$1347.47

(-30.4%) $1,253.21 $235.42 $288.45 $159.87 $1,936.95

Average $703.22 $223.45 $285.27 $141.31 $1,353.25 $1,255.54 $238.02 $288.34 $160.28 $1,942.18

Table 12 shows the first year energy cost savings as both a net dollar savings and as a percentage of 

the total regulated end use energy costs. Results are weighted by single- and multifamily housing starts, 

foundation type, and heating system type. 

Table 12. Total Energy Cost Savings (First Year) for the 2015 IECC Compared to the 2009 IECC

Climate Zone First Year Energy Cost Savings First Year Energy Cost Savings 

(percent)

5A $582.02 24.4

6A $589.48 25.6

Average $588.93 25.5
PNNL-24936 Rev-1

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