NIST Technical Note 1688 

Prototype Residential Buildings for Energy and 

Sustainability Assessment 

Joshua D. Kneifel 

 

U.S. Department of Commerce

National Institute of Standards and 

Technology 

Applied Economics Office 

Engineering Laboratory 

Gaithersburg, MD 20899 
 
Prototype Residential Buildings for Energy and 

Sustainability Assessment 

Joshua D. Kneifel 

Sponsored by: 

National Institute of Standards and Technology 

Engineering Laboratory 

September 2011 

U.S. DEPARTMENT OF COMMERCE 

Gary Locke, Secretary 

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY 

Dr. Patrick D. Gallagher, Director 

U.S. Department of Commerce

National Institute of Standards and 

Technology 

Applied Economics Office

Engineering Laboratory 

Gaithersburg, Maryland 20899

NIST Technical Note 1688
ii 
iii 

Abstract

Residential building energy efficiency is becoming increasingly important in U.S. energy 

policy. Analyzing the effectiveness of potential energy efficiency improvements in the 

residential sector involves running whole building energy simulations for alternative 

building designs. Such analysis requires detailed building design characteristics including 

climate, fuel type, energy technologies, and design improvements. For broad studies of 

the U.S. residential sector, prototypical designs representing “typical” homes are 

necessary to provide the basis for this detailed analysis. 

This report defines two prototype detached residential house designs based on the 2009 

International Energy Code Council (IECC) code. These prototypes can be used as 

baselines from which to analyze homes built to older IECC codes as well as to estimate 

the energy savings and sustainability from increasing residential building energy 

efficiency beyond current energy codes. These prototypes can also be used as a 

framework for developing additional prototype designs. 

Keywords 

Building economics; life-cycle costing; energy efficiency; residential building; prototype 

building designs; sustainability assessment
iv 
v 

Preface 

This study was conducted by the Applied Economics Office in the Engineering 

Laboratory (EL) at the National Institute of Standards and Technology (NIST). The study 

is designed to document the assumptions and approaches implemented in creating two 

“prototypical” residential house designs to use as the basis for energy, life-cycle cost, and 

sustainability estimates for new and existing residential buildings. The intended audience 

is researchers in the residential building sector concerned with energy efficiency and 

sustainability. 

Disclaimer 

Certain trade names and company products are mentioned in the text in order to 

adequately specify the technical procedures and equipment used. In no case does such 

identification imply recommendation or endorsement by the National Institute of 

Standards and Technology, nor does it imply that the products are necessarily the best 

available for the purpose. 
vi 
vii 

Acknowledgements

The author wishes to thank all those who contributed ideas and suggestions for this 

report. They include Ms. Barbara Lippiatt and Dr. Robert Chapman of EL’s Applied 

Economics Office, Dr. William Healy of EL’s Building Environment Division, Dr. Nicos 

S. Martys of EL’s Materials and Construction Research Division, Philip Kerrigan of 

Building Science Corporation, and S. Craig Drumheller and Joseph Wiehagen of the 

National Association of Home Builders (NAHB) Research Center. 

 

Author Information

Joshua D. Kneifel 

Economist 

National Institute of Standards and Technology 

100 Bureau Drive, Mailstop 8603 

Gaithersburg, MD 20899-8603 

Tel.: 301-975-6857 

Email: joshua.kneifel@nist.gov 

 
viii 
ix 

Contents

Abstract ............................................................................................................................. iii

Preface ................................................................................................................................ v

Acknowledgements ......................................................................................................... vii

Author Information ........................................................................................................ vii

List of Acronyms ............................................................................................................. xii

1 Introduction ............................................................................................................... 1

1.1 Background .......................................................................................................... 1

1.2 Purpose ................................................................................................................. 1

1.3 Literature Review ................................................................................................. 1

1.4 Approach .............................................................................................................. 2

2 One-Story Building Design Specification................................................................ 4

2.1 Building Envelope ................................................................................................ 4

2.1.1 General Assumptions .................................................................................. 4

2.1.2 Climate Zone-Specific Assumptions .......................................................... 7

2.2 Heating, Ventilating, and Air Conditioning Equipment ...................................... 9

2.3 Operating Conditions ........................................................................................... 9

2.4 Mechanical Ventilation and Air Infiltration ......................................................... 9

2.5 Domestic Hot Water ........................................................................................... 10

2.6 Lighting .............................................................................................................. 12

2.7 Appliances and Miscellaneous Electrical Loads ................................................ 14

2.8 Internal Mass ...................................................................................................... 15

2.9 Occupancy .......................................................................................................... 16

2.10Internal Heat Gains............................................................................................. 17

3 Two-Story Building Design Specification ............................................................. 18

3.1 Building Envelope .............................................................................................. 18

3.1.1 General Assumptions ................................................................................ 18

3.1.2 Climate Zone-Specific Assumptions ........................................................ 21

3.2 Heating, Ventilating, and Air Conditioning Equipment .................................... 23

3.3 Operating Conditions ......................................................................................... 23

3.4 Air Infiltration and Mechanical Ventilation ....................................................... 23

3.5 Domestic Hot Water ........................................................................................... 24

3.6 Lighting .............................................................................................................. 26

3.7 Appliances and Miscellaneous Electrical Loads ................................................ 28

3.8 Internal Mass ...................................................................................................... 29

3.9 Occupancy .......................................................................................................... 30

3.10Internal Heat Gains............................................................................................. 31

4 Recommendations for Future Research ............................................................... 32

4.1 Expansion of Current Prototypes ....................................................................... 32

4.2 Location-Specific Factors .................................................................................. 32

4.3 Additional Building Sizes .................................................................................. 32

4.4 Additional Building Designs .............................................................................. 34
x 

4.5 Heating Fuel Type .............................................................................................. 34

4.6 Additional Energy Codes ................................................................................... 34

4.7 Parametric Designs beyond Current Code ......................................................... 35

References ........................................................................................................................ 36

Appendix .......................................................................................................................... 38

List of Figures

Figure 2-1 Building material layers for exterior wall ........................................................ 5

Figure 2-2 Building material layers for ceiling .................................................................. 6

Figure 2-3 Building material layers for roof ...................................................................... 6

Figure 2-4 Building material layers for slab-on-grade ...................................................... 7

Figure 2-5 Domestic Hot Water Load Profiles as a Proportion of Peak Flow Rate, By 

Hour of the Day ................................................................................................................ 11

Figure 2-6 Electrical Equipment Load Profiles as a Proportion of Peak Wattage, By Hour 

of the Day .......................................................................................................................... 15

Figure 3-1 Building material layers for exterior wall ...................................................... 19

Figure 3-2 Building material layers for ceiling ................................................................ 20

Figure 3-3 Building material layers for roof .................................................................... 20

Figure 3-4 Building material layers for slab-on-grade .................................................... 21

Figure 3-5 Domestic Hot Water Load Profiles as a Proportion of Peak Flow Rate, By 

Hour of the Day ................................................................................................................ 25

Figure 3-6 Domestic Hot Water Load Profiles as a Proportion of Peak Use, By Hour of 

the Day .............................................................................................................................. 29

Figure 4-1 Square footage of new 1-story single-family housing ................................... 33

Figure 4-2 Square footage of new 2-story single-family housing ................................... 34

Figure 1 ASHRAE 90.1 Climate Zones by County ......................................................... 38

List of Tables 

Table 2-1 Material Parameter Calculation Approach ........................................................ 4

Table 2-2 2009 IECC energy code requirements for exterior envelope ............................ 8

Table 2-3 Hot Water Consumption .................................................................................. 10

Table 2-4 Domestic Hot Water Daily Internal Heat Gains .............................................. 12

Table 2-5 Annual Lighting Electricity Consumption ...................................................... 13

Table 2-6 Lighting Load Profile as Proportion of Peak Wattage in Use, by Hour of the 

Day .................................................................................................................................... 13

Table 2-7 Appliance and MEL Electricity Consumption ................................................ 14

Table 2-8 Occupancy Load Profile as a Proportion of Maximum Occupancy, and Total 

Occupants, By Hour of the Day ........................................................................................ 16

Table 2-9 Heat Gain Comparison-Reference and Prototype Designs ............................. 17

Table 3-1 Material Parameter Calculation Approach ...................................................... 18

Table 3-2 2009 IECC energy code requirements for exterior envelope .......................... 22

Table 3-3 Hot Water Consumption .................................................................................. 24

Table 3-4 Domestic Hot Water Internal Heat Gains ........................................................ 26
xi 

Table 3-5 Annual Lighting Electricity Consumption ...................................................... 27

Table 3-6 Lighting Load Profiles as a Proportion of Peak Wattage in Use, By Hour of the 

Day .................................................................................................................................... 27

Table 3-7 Appliance and MEL Electricity Consumption ................................................ 28

Table 3-8 Occupancy Load Profile as a Proportion of Maximum Occupancy, By Hour of 

the Day .............................................................................................................................. 30

Table 3-9 Heat Gain Comparison-Reference and Prototype Designs ............................. 31

Table 4-1 Additional Prototype Sizes .............................................................................. 32

Table 4-2 Size Distribution of New Housing in Square Footage .................................... 33
xii 

List of Acronyms 

AFUE Annual Fuel Utilization Efficiency

AHS American Housing Survey

ASHRAE American Society of Heating, Refrigerating and Air-Conditioning Engineers

BA Building America

CBECS Commercial Building Energy Consumption Survey

CFA Conditioned Floor Area

COP Coefficient of Performance

DHW Domestic Hot Water

DOE Department of Energy

EIA Energy Information Administration

EL Engineering Laboaratory

ELA Effective Leakage Area

EPS Expanded Polystyrene

HVAC Heating, Ventilating, and Air Conditioning

ICC International Code Council

IECC International Energy Conservation Code

IRC International Residential Code

MEL Miscellanous Electric Load

NBR number of bedrooms

NAHB National Association of Home Builders

NIST National Institute of Standards and Technology

NREL National Renewable Energy Laboratory

OAE Office of Applied Economics

PNNL Pacific Northwest National Laboratory

RECS Residential Energy Consumption Survey

SEER Seasonal Energy Efficiency Ratio

SF Square Feet

SHGC Solar Heat Gain Coefficient

SLA Specific Leakage Area

VT Visible Transmittance

XPS Extruded Polystyrene

 
1

1 Introduction 

1.1 Background 

Previous research on residential building energy efficiency has created energy modeling 

parameters for predicting energy use for both new and existing residential buildings. 

These studies specify a majority of the parameters required to create a residential 

building energy simulation model, which are useful when the building design is known. 

However, prototype residential building designs that represent “typical” residential 

buildings are required to consistently analyze energy efficiency improvements across the 

U.S. building stock. 

1.2 Purpose 

The purpose of this report is twofold. First, it develops and documents prototype 

residential building designs. These prototype designs provide a consistent basis for 

running building energy simulations across the U.S. residential building stock for 

different climate zones and varying levels of energy efficiency. Second, this report can be 

used as a basis for adding more prototype building designs or for developing more 

detailed designs of the prototypes reported here. 

1.3 Literature Review 

Previous research on prototype building designs has focused on commercial buildings. 

The National Renewable Energy Laboratory (NREL) has documented 16 commercial 

prototypical buildings for 16 U.S. climate zones.1

 These 256 reference commercial 

buildings are based on the Commercial Building Energy Consumption Survey (CBECS) 

database and the American Society of Heating, Refrigerating and Air-Conditioning 

Engineers (ASHRAE) 90.1 Standard, and represent greater than 70 % of the U.S. 

building stock. These prototypes have become the basis for significant research on energy 

efficiency measures in commercial buildings. 

Two reports from the Building America (BA) program of the DOE Building 

Technologies Program -- Hendron and Engebrecht (2010) and Hendron (2006) -- 

document the assumptions for energy efficiency performance comparison for new and 

existing residential buildings, respectively. These reports define total loads and load 

profiles for energy and water usage within a home based on the number of bedrooms, 

bathrooms, and square footage. Since the focus of this study is on new residential 

buildings, Hendron and Engebrecht (2010) will be a primary source of information for 

the prototype designs. 

 

1

 Field, Deru, and Studer (2010) 
2

Persily et al. (2007) define a suite of over 200 homes that represent approximately 80 % 

of the U.S. housing stock, including detached, attached, manufactured, and apartment 

buildings for use in indoor air quality research. The prototypes are based on the 

Residential Energy Consumption Survey (RECS) and American Housing Survey (AHS) 

databases. The study defines the conditioned floor area (CFA) and dimensions of 3 

different detached homes: 107.0 m2 (1152 ft2), 180.4 m2 (1942 ft2), and 275.5 m2

(2966 ft2).2

Pacific Northwest National Laboratory (PNNL) published a report for the DOE Building 

Energy Codes Program that analyzes the state-level impacts of the adoption of 2009 

IECC for residential buildings.3 The study uses EnergyGauge (based on the DOE-2 

whole building energy simulation software) to determine the energy use and cost savings 

for a two-story, 223 m2

 (2400 ft2) house.4 

The literature has not yet documented the details of the assumptions made in designing 

prototype residential buildings. This report will document the assumptions for two such 

prototypes to be used for simulating energy use and measuring sustainability in detached 

homes. 

1.4 Approach 

Prototype residential building designs are based on a number of sources, including the 

research described above by Building America. Additional resources are RS Means cost 

databases, U.S. Census and EIA housing stock data, and a collection of ASHRAE 

standards and IECC codes. The prototype buildings are designed in the EnergyPlus V6.0 

simulation software.5

Two prototypical residential building designs are documented in this report: one-story 

and two-story detached homes. The framework for these designs is the 2009 IECC 

Residential Code for One- and Two-Story Dwellings. IECC code defines the thermostat 

control, window specifications, exterior envelope R-values (m2-K/W), minimum lighting 

efficiency, maximum infiltration rates, mechanical ventilation, internal and structural 

mass, and heating, ventilating, and air-conditioning (HVAC) system requirements. 

 

2

 Persily et al. (2007) does not create 3-dimensional representations of the prototypical homes because it 

was not required for their analysis. 

3

 PNNL (2009) 

4

 The report does not specify the reasoning behind the building design selection. 

5

 Department of Energy (2010)
3

Although 2009 IECC defines the general framework for modeling, the code does not 

address the building’s plug loads, occupancy, or geometry. Also lacking is a number of 

small, but important details and assumptions required to effectively simulate the energy 

use of a residential building. 

One source of this additional information is the Building America Research Benchmark 

Definition (2010), which is used for the annual loads, load profiles, and internal heat 

gains for lighting, occupancy, and domestic hot water. 

Prototypical building size and geometry are selected based on four sources. The 

American Housing Survey (AHS) and the EIA Residential Energy Consumption Survey 

(RECS) are used to determine typical square footage and number of bedrooms for onestory and two-story residential detached buildings. The Annual 2010 Characteristics of 

New Housing released by the U.S. Census Bureau’s Manufacturing, Mining, and 

Construction Statistics Division (MCD) and RSMeans Square Foot Costs (2011) are used 

to determine appropriate prototype building geometries. Selections are comparable to 

Persily et al. (2007). 

Other codes and standards are needed to establish additional specifications: International 

Residential Code (IRC), ASHRAE 90.2-2007, ASHRAE 62.2-2010, and the ASHRAE 

Fundamentals Handbook. Their use will be defined in detail where appropriate in the 

remainder of the document. 
4

2 One-Story Building Design Specification 

The first building design represents a typical 1-story, 3-bedroom, slab-on-grade detached 

house with no garage. This design was chosen because it is the simplest building design 

and can be used as the framework for more detailed single-story house designs. In the 

remainder of this section, each aspect of the building design and operation will be 

defined. 

2.1 Building Envelope 

There are some building envelope assumptions that are constant regardless of the 

building location’s climate while other assumptions are climate specific. The following 

two subsections will define each set of assumptions separately. 

2.1.1 General Assumptions 

The prototype is a 2009 IECC compliant 1-story 3-bedroom slab-on-grade house. The 

dimensions are 19.5 m x 7.6 m (64 ft x 25 ft) for a total of 148.6 m2 (1,600 ft2

) of 

conditioned floor area (CFA). The house is oriented 19.5 m (64 ft) east to west and 7.6 m 

(25 ft) north to south. The first floor has a 2.4 m (8 ft) high ceiling. The roof slope is 

assumed to be 4:12 with 0.3 m (1ft) overhangs on the north and south sides of the 

building. There is assumed to be no garage in the prototype. 

The house is built to meet 2009 IECC for low-rise residential buildings. The EnergyPlus 

parameters for the materials used in the exterior envelope (excluding the roof) are 

estimated using an average transmittance with the surface-weighted path fractions. In 

other words, using a simple weighted average of parameter values based on the 

percentage of framing in the surface. The roof controls for varying materials by splitting 

the roof into two separate surfaces. The framing percentage for each surface type is 

shown in Table 2-1. 

Table 2-1 Material Parameter Calculation Approach 

Construction Pct. Frame Approach 

Exterior Wall 23 % surface-weighted path fractions 

Ceiling 11 % surface-weighted path fractions 

Roof 11 % split into separate surfaces 

The exterior wall is assumed to be 3.8 cm x 8.9 cm (1.5 in x 3.5 in) wood-framed 41 cm 

(16 in) on center (OC) with cavity insulation (9 cm (3.42 in) fiberglass batts at 

0.67 m2·K/W (R-3.8 ft2·0F·h/Btu) per 2.5 cm (1 in). The material layers for the exterior 
5

wall are defined in Figure 2-1. The construction is made of 5 or 6 layers depending on 

IECC requirements: wood siding, a felt air barrier, rigid insulation (if required), plywood 

sheathing, 3.8 cm x 8.9 cm (1.5 in x 3.5 in) framing with batt insulation in wall cavity, 

and gypsum wall board (GWB). 

Figure 2-1 Building material layers for exterior wall 

The average conductance (U-factor) of the framing/insulation combination material is 

calculated by the following equation from ASHRAE Fundamentals Handbook (2009): 

U AVG UFRAME UINSULATION = 23%* + 77%*

For this material, 23 % of the wall area is framing with the remaining 77 % being the 

wall cavity that is filled with cavity insulation. 

The interior ceiling is assumed to be 1.3 cm (0.5 in) GWB with 3.8 cm x 14.0 cm (1.5 in 

x 5.5 in) ceiling joists. There is blown-in cellulose insulation in the open cavity plus any 

additional inches of blown-in insulation as required by 2009 IECC. The amount of 

blown-in insulation varies by climate zone, and will be described in Section 2.1.2. The 

average material U-factor is calculated in the same manner as the exterior wall for the 

wood frame/cavity layer. Framing accounts for 11 % of the ceiling surface. The material 

layers for the ceiling are defined in Figure 2-2. 

Sheathing

Felt

Average of 

Insulation/ 

Wood Frame 

GWB

Wood Siding

Rigid Insulation 

(if required)
6

Figure 2-2 Building material layers for ceiling

The roof construction is assumed to be 3.8 cm x 14.0 cm (1.5 in x 5.5 in) rafters with 

1.3 cm (0.5 in) plywood sheathing, felt paper, and asphalt shingles. There is no insulation 

in the rafters, which makes it unnecessary to calculate an average U-factor. Instead the 

roof is split into two surfaces for energy simulation, one with framing (23 % of roof area) 

and one without framing (77 % of roof area). The material layers for the roof with 

framing are defined in Figure 2-3. 

Figure 2-3 Building material layers for roof

The foundation is a 10 cm (4 in) concrete slab. The floor finish is assumed to be 40 % 

carpet, 40 % hardwood, 15 % vinyl tile, and 5 % ceramic tile (based on RSMeans Square 

Foot Costs). Some climate zones require rigid insulation to be placed on the slab edge, 

which will be described in Section 2.1.2. The material layers for the slab are defined in 

Figure 2-4. The EnergyPlus Slab preprocessor is used to simulate the heat transfer 

between the ground and the slab, which recommends simulating horizontal insulation 

under the slab instead of vertical insulation on the edge of the slab for “slab-on-grade” 

foundations because the energy transfer that occurs on the vertical edges of the slab are 

significantly smaller than the energy transfer from the surface area contacting the ground. 

The Slab preprocessor assumes that the bottom of the slab is flush with the grade. 

Blown-In 

Insulation 

GWB

Average of 

Insulation/ 

Wood Frame 

Shingles 

Wood Frame

Sheathing 

Felt 
7

Figure 2-4 Building material layers for slab-on-grade

Window glazing area is assumed to be 15 % of conditioned floor area and is split 

between the four exterior walls based on wall area. Two 1.2 m (4 ft) high windows on 

each side of the house (8 in total) are assumed to be located equal distance from the wall 

edge. The width of the windows is based on the fraction of total wall area represented by 

each side. There are assumed to be two 0.9 m x 2.0 m (3 ft x 6 ft 8 in) – 4.4 cm (1.75 in) 

solid pine wood doors, located in the center of the wall on the north and south walls. 

Windows are defined in EnergyPlus using the “Simple Glazing System,” which requires 

only 3 parameters: U-factor (W/ (m2·K)), solar heat gain coefficient (SHGC), and visible 

transmittance (VT). These parameters vary by climate zone, and will be described in 

Section 2.1.2. 

2.1.2 Climate Zone-Specific Assumptions 

The exterior envelope performance requirements of 2009 IECC vary depending on the 

climate zone. Table 2-2 is an abridged version of Table 402.1.1 found in Chapter 4: 

Residential Energy Efficiency of the 2009 IECC. A map of the climate zones by county is 

found in the appendix. 

Floor Finish 

Concrete 

Rigid Insulation 

(IECC Requirement) 

Rigid Insulation 

(Simulated in E+) 
8

Table 2-2 2009 IECC energy code requirements for exterior envelope 

Climate Zone 

Fenestration 

U-Factor 

(W/m2·K) 

Glazed 

Fenestration 

SHGC 

Ceiling 

R-Value Wood Frame Wall R-Value Slab Edge R-Value Slab Depth 

1 1.2 0.30 5.3 (30) 2.3 (13) 0 (0) 0 (0) 

2 0.65 0.30 5.3 (30) 2.3 (13) 0 (0) 0 (0) 

3 0.50 0.30 5.3 (30) 2.3 (13) 0 (0) 0 (0) 

4 except Marine 0.35 NR* 6.7 (38) 2.3 (13) 1.8 (10) 0.61 m (2 ft) 

5 and 4 Marine 0.35 NR* 6.7 (38) 3.5 (20) or 2.3+0.88 (13+5)** 1.8 (10) 0.61 m (2 ft) 

6 0.35 NR* 8.6 (49) 3.5 (20) or 2.3+0.88 (13+5)** 1.8 (10) 1.21 m (4 ft) 

7 and 8 0.35 NR* 8.6 (49) 3.7 (21) 1.8 (10) 1.21 m (4 ft) 

*NR = No Requirement 

**13+5 means R-13 cavity insulation plus R-5 insulated sheathing. 

*** R-value Units: m2

·K/W (ft2·0F·h/Btu) 

Although EnergyPlus requires three parameters for defining window performance, 2009 

IECC only specifies two: U-factor and SHGC. The U-factor is restricted to below 1.2 in 

Zone 1 and becomes stricter the colder the climate zone, restricting the U-factor to below 

0.35 in Zones 7 and 8. The SHGC must be less than 0.30 for Zones 1 through 3, but has 

no requirement for Zones 4 through 8. The SHGC for the standard reference design 

specified in 2009 IECC is 0.40 for Zones 4 through 8. The visible transmittance is not 

restricted in 2009 IECC for any climate zones, and is assumed to be 0.16 for Zone 1, 0.22 

for Zone 2, 0.46 for Zone 3, and 0.40 for Zones 4 through 8.6

The insulation R-values for the exterior walls, ceiling, and foundation increase as the 

climate zone gets colder. The exterior wall R-value ranges from R-13 in Zones 1 through 

4 to R-21 in Zones 7 and 8. The first R-13 is met with high density cavity insulation in 

the wall cavity. Additional R-value is met by adding rigid insulation to the exterior of the 

wall. The ceiling R-value ranges from R-30 in Zones 1 through 3 to R-49 in Zones 6 

through 8. Additional cellulose blown-in insulation is used to reach the required R-value. 

R-10 insulation under the foundation is required in Zones 4 through 8 only, which is met 

by adding 2 in of extruded polystyrene (XPS) below the slab.

 

6

 Visible transmittance values are based on window characteristics defined in the ASHRAE Fundamentals 

Handbook (2009). 
9

2.2 Heating, Ventilating, and Air Conditioning Equipment 

The HVAC system in the prototype building design is a single-speed unitary system with 

an air conditioner with a Seasonal Energy Efficiency Ratio (SEER) rating of 13,7

 and a 

gas furnace with annual fuel utilization efficiency (AFUE) of 78 % (both current 

minimum federal energy efficiency requirements). No dehumidification option or 

economizer is included in the system. The supply fan is assumed to cycle, and has a total 

efficiency of 70 %. The supply fan motor efficiency is 90 %. The ductwork is assumed to 

be within the conditioned space, which leads to zero energy loss from the ductwork. This 

assumption assists in simplifying the model, and will be relaxed in future research to 

account for split systems and the resulting duct leakage.8

2.3 Operating Conditions 

The thermostat setpoints are based on the standard reference designs defined in 2009 

IECC, which are 23.9°C (75°F) cooling and 22.2°C (72°F) heating. 

2.4 Mechanical Ventilation and Air Infiltration 

The mechanical ventilation rate is based on ASHRAE Standard 62.2-2010. The 

Minimum Outdoor Air Flow Rate (liters per second) is based on ASHRAE 62.2-2010 

equation 4.1b: 

0.05 ∗   3.5 ∗ 

  1

For the prototype design’s 148.6 m2 (1600 ft2) and 3 bedrooms, the total house ventilation 

rate is 0.02162 m3 per second (46 ft3 per minute). The ASHRAE 62.2-2010 requirements 

have a built-in 0.15 ACH of air leakage. Door infiltration is assumed to be included in the 

ACH.9

The prescriptive maximum air leakage of 7 air changes per hour (ACH) at 50 pascals 

specified in Section 402.4.2.1 of the 2009 IECC is not defined under normal operating 

conditions. For this reason, leakage is based on ASHRAE 62.2-2010. 

Table 405.5.2(1) of the 2009 IECC specifies that “residences with mechanical ventilation 

that are test in accordance with ASHRAE 119, Section 5.1, the measured air exchange 

rate combined with the mechanical ventilation rate...shall not be less than” the ASHRAE 

 

7

 The 13 SEER rating converts to a Coefficient of Performance (COP) of 3.28 for the EnergyPlus 

simulation based on the following equation:   
0.02 ∗   1.12 ∗ /3.412. 

8

 The 2009 IECC prescriptive requirements include a duct tightness post-construction test showing duct 

leakage less than or equal to 226.5 L/min (8 CFM) per 9.29 m2 (100 ft2) at 25 Pascal (Pa).

9

 According to the ASHRAE Fundamentals Handbook, “In residences...air exchange associated with a door 

can be estimated based on air leakage through cracks between door and frame.
10

62.2-2010 minimum outdoor air flow rate. As assumed in ASHRAE 62.2-2010, the air 

infiltration rate is assumed to be 0.15 ACH. 

The standard reference design in 2009 IECC assumes the attic is vented with venting 

equivalent to 1 unit per 300 units of the ceiling area, which converts to an effective 

leakage area (ELA) of 4954.8 cm2

 (5.33 ft2). 

2.5 Domestic Hot Water 

The BA Benchmark functions defined in Table 2-3 are used instead of 2009 IECC to 

estimate the hot water consumption of each piece of equipment and activities. Total hot 

water consumption based on the BA Benchmark is 303 liters (80 gallons). These 

estimates are used for the analysis because they break down consumption by end use; the 

2009 IECC estimate is for total hot water consumption only. The clothes washer and 

dishwasher use only hot water 48.9°C (120°F) while the showers, baths, and sinks use hot 

water that is tempered to 40.6°C (105°F), as shown in Table 2-3. Since some of the water 

consumed is tempered with cold water, the total hot water drawn from the hot water tank 

is 273 liters (72.5 gallons) per day. 

Table 2-3 Hot Water Consumption 

Equipment Water Temp. Function 

Liters (Gallons) 

Liters (Gallons) 

Per Day 

Clothes Washer 48.9°C (120°F) 28+10* NBR (7.5+2.5*NBR) 56.8 (15) 

Dishwasher 48.9°C (120°F) 10+3* NBR (2.5+0.833*NBR) 18.9 (5) 

Showers 40.6°C (105°F) 53+18* NBR (14.0+4.67*NBR) 106.0 (28) 

Baths 40.6°C (105°F) 13+4* NBR (3.5+1.17*NBR) 26.5 (7) 

Sinks 40.6°C (105°F) 47+16* NBR (12.5+4.16*NBR) 94.6 (25) 

Total: 303 (80) 

The BA Benchmark total water use, daily water use load profiles, and sensible 

(temperature-based) and latent (humidity-based) loads for hot water use are used to 

estimate the real time hot water use and the resulting internal heat gains. The daily load 

profile, or proportion of peak flow rate by hour of the day, for each hot water use 

category can be seen in Figure 2-5. 
11

Figure 2-5 Domestic Hot Water Load Profiles as a Proportion of Peak Flow Rate, 

By Hour of the Day

Internal heat gains from hot water for the clothes washer and dishwasher are assumed to 

be zero for both sensible and latent loads. Any heat gains for this equipment are included 

in the equipment electricity use heat gains. The sensible and latent load fractions for 

shower, bath, and sinks are reverse engineered from internal heat gains estimated using 

the BA Benchmark functions in Table 2-4. 

0.0

0.2

0.4

0.6

0.8

1.0

1 3 5 7 9 11 13 15 17 19 21 23

Clothes Washer

0.0

0.2

0.4

0.6

0.8

1.0

1 3 5 7 9 11 13 15 17 19 21 23

Dish Washer

0.0

0.2

0.4

0.6

0.8

1.0

1 3 5 7 9 11 13 15 17 19 21 23

Bath

0.0

0.2

0.4

0.6

0.8

1.0

1 3 5 7 9 11 13 15 17 19 21 23

Shower

0.0

0.5

1.0

1 3 5 7 9 11 13 15 17 19 21 23

Sinks
12

Table 2-4 Domestic Hot Water Daily Internal Heat Gains 

Equipment 

End Use 

Sensible Load Latent 

Function 

kWh (Btu) 

Heat Gain 

kWh (Btu) 

Load 

Fraction 

Function 

kWh (Btu) 

Heat Gain 

kWh (Btu) 

Load 

Fraction 

Showers 0.22+0.07*NBR

(741+247*NBR) 

0.4 (1482) 0.1947 0.21+0.07* NBR

(703+235*NBR) 

0.4 (1408) 0.0055 

Baths 0.05+0.02* NBR

(185+62*NBR) 

0.4 (1371) 0.7262 0 (0) 0 (0) 0.0000 

Sinks 0.09+0.03*NBR

(310+103*NBR) 

0.2 (619) 0.0917 0.04+0.01* NBR

(140+47*NBR) 

0.1 (281) 0.0012 

Based on 2009 IECC, the water heater must meet federal energy efficiency requirements. 

The water heater is assumed to be a gas water heater with a perfectly mixed storage tank 

with an efficiency of 76 %,10 a firing rate of 10 551 W,11 and a setpoint temperature of 

48.9°C (120°F). The heat loss coefficient from the water heater to the ambient 

temperature in the internal space is assumed to be 2.1 W/K.12

2.6 Lighting 

The lighting load profiles and electricity consumption are based on the simplest profile in 

the BA Benchmark, which varies by time-of-day, but not from day-to-day. Total 

electricity use is estimated based on the two-stage process defined in the BA Benchmark 

as expressed in Table 2-5. The baseline lighting estimate is based on 86 % incandescent 

and 14 % fluorescent use. The lighting requirements in 2009 IECC require 50 % high 

efficacy lighting, which is met by using 50 % compact fluorescent lamp (CFL) lighting. 

The BA Benchmark adjustment functions shown on the right in Table 2-5 are used to 

adjust the total electricity consumption estimate to represent the greater efficiency 

required by 2009 IECC. The baseline total lighting electricity consumption is estimated at 

1918 kWh. The 2009 IECC-compliant lighting decreases lighting electricity consumption 

by 26 % to 1415 kWh. 

 

10 Minimum federal efficiency requirement for gas water heaters 

11 Based on the BA Benchmark for a 3 bedroom/2 bathroom house with a gas unit 

12 Based on NIST expert recommendation
13

Table 2-5 Annual Lighting Electricity Consumption 

Lighting 

Use 

Category 

Baseline 2009 IECC-Compliant 

Function kWh Function kWh 

Hard-wired 0.8*(CFA*0.737+467) 1317 1,317*[(FINC+0.14) + (FCFL-0.14)*0.27] 971 

Plug-In 0.2*(CFA*0.737+467) 329 329*[(FINC+0.14) + (FCFL-0.14)*0.27] 243 

Exterior CFA*0.17 272 272*[(FINC+0.14) + (FCFL-0.14)*0.27] 201 

Total CFA*0.737+467+ CFA*0.17 1918 1,918*[(FINC+0.14) + (FCFL-0.14)*0.27] 1415 

The load profile (proportion of peak wattage in use) for interior lighting can be seen in 

Table 2-6. The total wattage parameter for lighting in EnergyPlus is reverse engineered 

from the peak consumption load profile and the total electricity consumption estimate. 

The load profile for exterior lighting assumes the lights are on sunset to sunrise. 

Table 2-6 Lighting Load Profile as Proportion of Peak Wattage in Use, by Hour of 

the Day 

Hour Load Profile Hour Load Profile 

1:00 0.067 13:00 0.119 

2:00 0.067 14:00 0.119 

3:00 0.067 15:00 0.119 

4:00 0.067 16:00 0.206 

5:00 0.187 17:00 0.439 

6:00 0.394 18:00 0.616 

7:00 0.440 19:00 0.829 

8:00 0.393 20:00 0.986 

9:00 0.172 21:00 1.000 

10:00 0.119 22:00 0.692 

11:00 0.119 23:00 0.384 

12:00 0.119 24:00 0.16 
14

2.7 Appliances and Miscellaneous Electrical Loads 

The electrical equipment in the house includes a refrigerator, clothes washer, clothes 

dryer, dishwasher, electric range, and a combination of variable miscellaneous electrical 

loads (MELs). MELs encompass electronics such as computers, televisions, stereos, and 

other plug loads. The electricity consumption for each category is based on the BA 

Benchmark functions seen in Table 2-7. Electricity consumption is usually a function of 

the number of bedrooms in the home (NBR). 

Table 2-7 Appliance and MEL Electricity Consumption 

Equipment Function kWh 

Refrigerator Constant 669 

Clothes Washer 52.5+17.5*NBR 105 

Clothes Dryer 418+139* NBR 835 

Dishwasher 103+34.3* NBR 206 

Electric Range 302+101* NBR 605 

Variable MELs 1281+ (196* NBR) + (0.345*CFA) 2421 

Total: 4841 

The BA Benchmark load profiles in Figure 2-6 create a real-time variation in electricity 

consumption for each category. Appliances such as the electric range and dishwasher 

have a significant variation in time-of-day use while refrigerator use only varies slightly 

over a day. 
15

Figure 2-6 Electrical Equipment Load Profiles as a Proportion of Peak Wattage, By 

Hour of the Day

2.8 Internal Mass 

Instead of defining individual interior surfaces and furniture, internal mass is estimated 

based on ASHRAE 90.2-2007 recommendations. There is assumed to be 3.6 kg (8 lb) of 

5 cm (2 in) thick wood per square foot of conditioned space for contents for a total of 

5806 kg (12 800 lb). There is assumed to be 2.3 kg (5 lb) of 1.3 cm (0.5 in) gypsum wall 

board (GWB) per square foot of conditioned space for the internal structure for a total of 

3629 kg (8000 lb). 

EnergyPlus estimates internal mass in terms of square meters of material open to the zone 

air. Based on the total weight of the two materials (wood and GWB) and their weight per 

0.00

0.02

0.04

0.06

0.08

0.10

1 3 5 7 9 11 13 15 17 19 21 23

Clothes Washer

0.00

0.05

0.10

0.15

1 3 5 7 9 11 13 15 17 19 21 23

Dishwasher

0.00

0.02

0.04

0.06

1 3 5 7 9 11 13 15 17 19 21 23

Refrigerator

0.00

0.02

0.04

0.06

0.08

0.10

1 3 5 7 9 11 13 15 17 19 21 23

Clothes Dryer

0.00

0.05

0.10

0.15

0.20

1 3 5 7 9 11 13 15 17 19 21 23

Range

0.00

0.02

0.04

0.06

0.08

1 3 5 7 9 11 13 15 17 19 21 23

MELs
16

inch, it is possible to determine the comparable surface area needed to match the amount 

of internal mass required. Assuming the wood density is equivalent to that of white oak, 

753 kg per m3 (47 lb per ft3), the 5 cm (2 in) thick wood weighs 38 kg per m2 (7.833 lb 

per ft2) and would require 151.8 m2 (1634 ft2) of content mass. Assuming GWB density 

of 10 kg per m2 (2.08 lb per ft2), a total of 357.3 m2 (3846 ft2) of structural mass is 

required to meet the standard recommendation. 

2.9 Occupancy 

Occupancy is based on the BA Benchmark constant daily occupancy load profile seen in 

Table 2-8. The profile changes over the hours of the day, but does not vary across days. 

The house is treated as a single zone with an average internal heat gain of 385.8 

Btu/person/hr (113 watts per person). The average number of people varies between all 

three family members being at home during the night to only 0.73 people present during 

the middle of the day. 

Table 2-8 Occupancy Load Profile as a Proportion of Maximum Occupancy, and 

Total Occupants, By Hour of the Day 

Hour Load Profile People Hour Load Profile People 

1:00 1.000 3.00 13:00 0.242 0.73 

2:00 1.000 3.00 14:00 0.242 0.73 

3:00 1.000 3.00 15:00 0.242 0.73 

4:00 1.000 3.00 16:00 0.242 0.73 

5:00 1.000 3.00 17:00 0.295 0.89 

6:00 1.000 3.00 18:00 0.553 1.66 

7:00 1.000 3.00 19:00 0.897 2.69 

8:00 0.883 2.65 20:00 0.897 2.69 

9:00 0.409 1.23 21:00 0.897 2.69 

10:00 0.242 0.73 22:00 1.000 3.00 

11:00 0.242 0.73 23:00 1.000 3.00 

12:00 0.242 0.73 24:00 1.000 3.00 
17

2.10 Internal Heat Gains 

Previous sections have addressed specific internal heat gain categories, but it is of interest 

to summarize these heat gains and determine if they are comparable to the 2009 IECC 

standard reference design specifications. The total internal heat gains specified by 2009 

IECC are based on the following equation. Based on 2009 IECC, total internal heat gains, 

IGain, should be 20 001 kWh/day (68 292 Btu/day) for the one-story prototype. 

CFA NBR IGain = 17,900 + 23 8. * + 4104 *

Internal heat gains originate from domestic hot water use, electrical equipment use, 

lighting, and human occupancy. Table 2-9 gives internal heat gains resulting from each 

category based on an EnergyPlus simulation of the prototype. The simulated internal heat 

gains of 20 412 kWh/day (69 694 Btu/day) are slightly higher than the 2009 IECC 

standard reference design (2 %). 

Table 2-9 Heat Gain Comparison-Reference and Prototype Designs 

Equipment BA Benchmark 

kWh (Btu) 

2009 IECC 

kWh (Btu) 

Prototype Design 

kWh (Btu) 

Lighting NA NA 3558 (12 150) 

Equipment 9742 (33 264) NA 9739 (33 253) 

Occupancy 5602 (19 126) NA 5602 (19 128) 

Hot Water 1512 (5161) NA 1512 (5163) 

Total NA 20 001 (68 292) 20 412 (69 694) 
18

3 Two-Story Building Design Specification 

The second building design represents a typical 2-story, 3-bedroom, slab-on-grade 

detached house with no garage. This design was chosen because it is the simplest 

building design and can be used as the framework for more detailed 2-story house 

designs. In the remainder of this section, each aspect of the building design and operation 

will be defined. 

3.1 Building Envelope 

There are some building envelope assumptions that are constant regardless of the 

building location’s climate while other assumptions are climate specific. The following 

two subsections will define each set of assumptions separately. 

3.1.1 General Assumptions 

The prototype is a 2009 IECC compliant 2-story, 3-bedroom, slab-on-grade house. The 

dimensions are 12.2 m x 7.6 m (40 ft x 25 ft) for a total of 185.8 m2

 (2000 ft2) of 

conditioned floor area. The house is oriented 12.2 m (40 ft) east to west and 7.6 m (25 ft) 

north to south. The first and second floors have 2.4 m (8 ft) high ceilings. The roof slope 

is assumed to be 4:12 with 0.3 m (1 ft) overhangs on the north and south sides of the 

building. There is assumed to be no garage in the prototype. 

The house is built to meet 2009 IECC for low-rise residential buildings. The EnergyPlus 

parameters for the materials used in the exterior envelope (excluding the roof) are 

estimated using an average transmittance with the surface-weighted path fractions. In 

other words, using a simple weighted average of parameter values based on the 

percentage of framing in the surface. This approach is reasonable for materials with 

similar R-values and thickness. The roof and interior floor control for varying materials 

by splitting the surface into two separate surfaces. The framing percentage for each 

surface type is shown in Table 3-1. 

Table 3-1 Material Parameter Calculation Approach 

Construction Pct. Frame Approach 

Exterior Wall 23 % surface-weighted path fractions 

Top Floor Ceiling 11 % surface-weighted path fractions 

Roof 11 % split into separate surfaces 

Interior Floor 13 % split into separate surfaces 
19

The exterior wall is assumed to be 3.8 cm x 8.9 cm (1.5 in x 3.5 in) wood-framed 41 cm 

(16 in) on center (OC) with cavity insulation (9 cm (3.42 in) fiberglass batts at R-3.8 per 

2.5cm (1 in)). The material layers for the exterior wall are defined in Figure 3-1. The 

construction is made of 5 or 6 layers depending on IECC requirements: wood siding, a 

felt vapor barrier, rigid insulation (if required), plywood sheathing, 3.8 cm x 8.9 cm 

(1.5 in x 3.5 in) framing with batt insulation in wall cavity, and gypsum wall board 

(GWB). 

Figure 3-1 Building material layers for exterior wall

The average conductance (U-factor) of the framing/insulation combination material is 

calculated by the following equation from ASHRAE Fundamentals Handbook (2009): 

U AVG U FRAME U INSULATION = 23% * + 77% *

For this material, 23 % of the wall area is framing with the remaining 77 % being the 

wall cavity that is filled with cavity insulation. 

The second floor ceiling is assumed to be 1.3 cm (0.5 in) GWB with 3.8 cm x 14.0 cm 

(1.5 in x 5.5 in) ceiling joists. There is blown-in cellulose insulation in the open cavity 

plus any additional inches of blown-in insulation as required by 2009 IECC. The amount 

of blown-in insulation varies by climate zone, and will be described in Section 3.1.2. The 

average material U-factor is calculated in the same manner as the exterior wall. Framing 

accounts for 11 % of the ceiling surface. The material layers for the ceiling are defined in 

Figure 3-2. 

Sheathing

Felt

Average of 

Insulation/ 

Wood Frame 

GWB

Wood Siding

Rigid Insulation 

(if required)
20

Figure 3-2 Building material layers for ceiling

The roof construction is assumed to be 3.8 cm x 14.0 cm (1.5 in x 5.5 in) rafters with 

1.3 cm (0.5 in) plywood sheathing, felt paper, and asphalt shingles. There is no insulation 

in the rafters, which makes it unrealistic to calculate an average U-factor. Instead the roof 

is split into two surfaces for energy simulation, one with framing (23 % of roof area) and 

one without framing (77 % of roof area). The material layers for the roof with framing 

are defined in Figure 3-3. 

Figure 3-3 Building material layers for roof

The interior floor/ceiling (first floor ceiling/second floor ceiling) construction is assumed 

to be 3.8 cm x 19.1 cm (1.5 in x 7.5 in) floor joists with 1.6 cm (5/8 in) plywood 

subflooring and 100% carpet finish. The framing accounts for 13 % of the floor. No 

insulation is required for interior surfaces because there is no thermal benefit from 

restricting thermal transfer within the same zone. 

The foundation is a 10 cm (4 in) concrete slab. The floor finish is assumed to be 40 % 

carpet, 40 % hardwood, 15 % vinyl tile, and 5 % ceramic tile (based on RSMeans Square 

Foot Costs). Some climate zones require rigid insulation to be placed on the slab edge, 

which will be described in Section 3.1.2. The material layers for the slab are defined in 

Figure 2-4. The EnergyPlus Slab preprocessor is used to simulate the heat transfer 

between the ground and the slab, which recommends simulating horizontal insulation 

Blown-In 

Insulation 

GWB

Average of 

Insulation/ 

Wood Frame 

Shingles 

Wood Frame

Sheathing 

Felt 
21

under the slab instead of vertical insulation on the edge of the slab for “slab-on-grade” 

foundations because the energy transfer that occurs on the vertical edges of the slab are 

significantly smaller than the energy transfer from the surface area contacting the ground. 

The Slab preprocessor assumes that the bottom of the slab is flush with the grade. 

Figure 3-4 Building material layers for slab-on-grade

Window glazing area is assumed to be 15 % of conditioned floor area and is split 

between the four exterior walls based on wall area. Two 1.2 m (4 ft) high windows on 

each side of the house for each floor (16 in total) are assumed to be located at an equal 

distance from the wall edge. The width of the windows is based on the fraction of total 

wall area represented by each side. There are assumed to be two 0.9 m x 2.0 m (3 ft x 6 ft 

8 in) – 4.4 cm (1.75 in) solid pine wood doors, located in the center of the wall on the 

north and south walls. Windows are defined in EnergyPlus using the “Simple Glazing 

System,” which requires only 3 parameters: U-factor (W/m2

·K), solar heat gain 

coefficient (SHGC), and visible transmittance (VT). These parameters vary by climate 

zone, and will be described in Section 3.1.2. 

3.1.2 Climate Zone-Specific Assumptions 

The exterior envelope performance requirements of 2009 IECC vary depending on the 

climate zone. Table 3-2 is an abridged version of Table 402.1.1 found in Chapter 4: 

Residential Energy Efficiency of the 2009 IECC. A map of the climate zones by county is 

found in the appendix. 

Floor Finish 

Concrete 

Rigid Insulation 

(IECC Requirement) 

Rigid Insulation 

(Simulated in E+) 
22

Table 3-2 2009 IECC energy code requirements for exterior envelope 

Climate Zone Fenestration 

U-Factor 

(W/m2·K) 

Glazed 

Fenestration 

SHGC 

Ceiling 

R-Value 

Wood Frame Wall R-Value Slab Edge 

R-Value 

Slab Depth 

1 1.2 0.30 5.3 (30) 2.3 (13) 0 (0) 0 (0) 

2 0.65 0.30 5.3 (30) 2.3 (13) 0 (0) 0 (0) 

3 0.50 0.30 5.3 (30) 2.3 (13) 0 (0) 0 (0) 

4 except Marine 0.35 NR* 6.7 (38) 2.3 (13) 1.8 (10) 0.61 m (2 ft) 

5 and 4 Marine 0.35 NR* 6.7 (38) 3.5 (20) or 2.3+0.88 (13+5)** 1.8 (10) 0.61 m (2 ft) 

6 0.35 NR* 8.6 (49) 3.5 (20) or 2.3+0.88 (13+5)** 1.8 (10) 1.21 m (4 ft) 

7 and 8 0.35 NR* 8.6 (49) 3.7 (21) 1.8 (10) 1.21 m (4 ft) 

*NR = No Requirement 

**13+5 means R-13 cavity insulation plus R-5 insulated sheathing. 

*** R-value Units: m2

·K/W (ft2·0F·h/Btu) 

Although EnergyPlus requires three parameters to define windows, 2009 IECC only 

specifies two: U-factor and SHGC. The U-factor is allowed to be as high as 1.2 in Zone 1 

to as low as 0.35 in Zones 7 and 8. The SHGC must be less than 0.30 for Zones 1 through 

3, but has no requirement for Zones 4 through 8. The SHGC for the standard reference 

design specified in 2009 IECC is 0.40 for Zones 4 through 8. The visible transmittance is 

not restricted in 2009 IECC for any climate zones, and is assumed to be 0.16 for Zone 1, 

0.22 for Zone 2, 0.46 for Zone 3, and 0.40 for Zones 4 through 8.13

The insulation R-values for the exterior walls, ceiling, and foundation increase as the 

climate zone gets colder. The exterior wall R-value ranges from R-13 in Zones 1 through 

4 to R-21 in Zones 7 and 8. The first R-13 is met with high density cavity insulation in 

the wall cavity. Additional R-value is met by adding rigid insulation to the exterior of the 

wall. The ceiling R-value ranges from R-30 in Zones 1 through 3 to R-49 in Zones 6 

through 8. Additional cellulose blown-in insulation used to reach the required R-value. 

R-10 insulation under the foundation is required in Zones 4 through 8 only, which is met 

by adding 10 cm (2 in) of extruded polystyrene (XPS) below the slab.

 

13 Visible transmittance values are based on window characteristics defined in the ASHRAE Fundamentals 

Handbook (2009). 
23

3.2 Heating, Ventilating, and Air Conditioning Equipment 

The HVAC system in the prototype building design is a single-speed unitary system with 

an air conditioner with a Seasonal Energy Efficiency Ratio (SEER) rating of 13,14 and a 

gas furnace with annual fuel utilization efficiency (AFUE) of 78 % (both current 

minimum federal energy efficiency requirements). No dehumidification option or 

economizer is included in the system. The supply fan is assumed to cycle, and has a total 

efficiency of 70 %. The supply fan motor efficiency is 90 %. The first and second floors 

are assumed to be a single zone, with the HVAC equipment located on the first floor. The 

ductwork is assumed to be within the conditioned space, which leads to zero energy loss 

from the ductwork. These two assumptions assist in simplifying the model, and will be 

relaxed in future research to account for split systems and the resulting duct leakage.15

3.3 Operating Conditions 

The thermostat setpoints are based on the standard reference designs defined in 2009 

IECC, which are 23.9 °C (75°F) cooling and 22.2 °C (72°F) heating. 

3.4 Air Infiltration and Mechanical Ventilation 

The mechanical ventilation rate is based on ASHRAE Standard 62.2-2010. The 

Minimum Outdoor Air Flow Rate (liters per second) is based on ASHRAE 62.2-2010 

equation 4.1b: 

0.05 ∗   3.5 ∗ 

  1

For the prototype design’s 185.6 m2 (2000 ft2

) and 3 bedrooms, the total house ventilation 

rate is 0.0236 m3 per second (50 ft3 per minute). The ASHRAE 62.2-2010 requirements 

have a built-in 0.15 ACH of air leakage. Door infiltration is assumed to be included in the 

ACH.16

The prescriptive maximum air leakage of 7 air changes per hour (ACH) at 50 pascals 

specified in Section 402.4.2.1 of the 2009 IECC is not defined under realistic conditions. 

For this reason, leakage is based on ASHRAE 62.2-2010. 

Table 405.5.2(1) of the 2009 IECC specifies that “residences with mechanical ventilation 

that are test in accordance with ASHRAE 119, Section 5.1, the measured air exchange 

rate combined with the mechanical ventilation rate...shall not be less than” the ASHRAE 

 

14 The 13 SEER rating converts to a Coefficient of Performance (COP) of 3.28 for the EnergyPlus 

simulation based on the following equation:   
0.02 ∗   1.12 ∗ /3.412. 

15 2009 IECC prescriptive requirements include a duct tightness post-construction test showing duct 

leakage less than or equal to 226.5 L/min (8 CFM) per 9.29 m2

 (100 ft2) at 25 Pascal (Pa). 

16 According to the ASHRAE Fundamentals Handbook, “In residences...air exchange associated with a 

door can be estimated based on air leakage through cracks between door and frame.
24

62.2-2010 minimum outdoor air flow rate. As assumed in ASHRAE 62.2-2010, the air 

infiltration rate is assumed to be 0.15 ACH. 

The standard reference design in 2009 IECC assumes the attic is vented with venting 

equivalent to 1 unit per 300 units of the ceiling area, which converts to an effective 

leakage area (ELA) of 3096.8 cm2

 (3.33 ft2). 

3.5 Domestic Hot Water 

The BA Benchmark functions defined in Table 3-3 are used instead of 2009 IECC to 

estimate the hot water consumption of each piece of equipment and activities. Total hot 

water consumption based on the BA Benchmark is 303 liters (80 gallons) which are the 

same as in the 1-story prototype because the number of bedrooms is equal. These 

estimates are used for the analysis because they break down consumption by end use; the 

2009 IECC estimate is for total hot water consumption only. The clothes washer and 

dishwasher use only hot water 48.9°C (120°F) while the showers, baths, and sinks use hot 

water that is tempered to 40.6°C (105°F), as shown in Table 3-3. Since some of the water 

consumed is tempered with cold water, the total hot water drawn from the hot water tank 

is 273 liters (72.5 gallons) per day. 

Table 3-3 Hot Water Consumption 

Equipment Water Temp. Function 

Liters (Gallons) 

Liters (Gallons) 

Per Day 

Clothes Washer 48.9°C (120°F) 28+10* NBR (7.5+2.5*NBR) 56.8 (15) 

Dishwasher 48.9°C (120°F) 10+3* NBR (2.5+0.833*NBR) 18.9 (5) 

Showers 40.6°C (105°F) 53+18* NBR (14.0+4.67*NBR) 106.0 (28) 

Baths 40.6°C (105°F) 13+4* NBR (3.5+1.17*NBR) 26.5 (7) 

Sinks 40.6°C (105°F) 47+16* NBR (12.5+4.16*NBR) 94.6 (25) 

Total: 303 (80) 

The BA Benchmark total water use, daily water use load profiles, and sensible 

(temperature-based) and latent (humidity-based) loads for hot water use are used to 

estimate the real-time hot water use and the resulting internal heat gains. The daily load 

profiles, or proportion of peak flow rate by hour of the day, for each hot water use 

category can be seen in Figure 3-5. 
25

Figure 3-5 Domestic Hot Water Load Profiles as a Proportion of Peak Flow Rate, 

By Hour of the Day

Internal heat gains from hot water for the clothes washer and dishwasher are assumed to 

be zero for both sensible and latent loads. Any heat gains for this equipment are included 

in the equipment electricity use heat gains. The sensible and latent load fractions for 

shower, bath, and sinks are reverse engineered from internal heat gains estimated using 

the BA Benchmark functions in Table 3-4. 

0.0

0.2

0.4

0.6

0.8

1.0

1 3 5 7 9 11 13 15 17 19 21 23

Clothes Washer

0.0

0.2

0.4

0.6

0.8

1.0

1 3 5 7 9 11 13 15 17 19 21 23

Dishwasher

0.0

0.2

0.4

0.6

0.8

1.0

1 3 5 7 9 11 13 15 17 19 21 23

Bath

0.0

0.2

0.4

0.6

0.8

1.0

1 3 5 7 9 11 13 15 17 19 21 23

Shower

0.0

0.2

0.4

0.6

0.8

1.0

1 3 5 7 9 11 13 15 17 19 21 23

Sinks
26

Table 3-4 Domestic Hot Water Internal Heat Gains 

Equipment 

End Use 

Sensible Load Latent 

Function 

kWh (Btu) 

Heat Gain 

kWh (Btu) 

Load 

Fraction 

Function 

kWh (Btu) 

Heat Gain 

kWh (Btu) 

Load 

Fraction 

Showers 0.22+0.07*NBR

(741+247*NBR) 

0.4 (1482) 0.1947 0.21+0.07* NBR

(703+235*NBR) 

0.4 (1408) 0.0055 

Baths 0.05+0.02* NBR

(185+62*NBR) 

0.4 (1371) 0.7262 0 (0) 0 (0) 0.0000 

Sinks 0.09+0.03*NBR

(310+103*NBR) 

0.2 (619) 0.0917 0.04+0.01* NBR

(140+47*NBR) 

0.1 (281) 0.0012 

Based on 2009 IECC, the water heater must meet federal energy efficiency requirements. 

The water heater is assumed to be a gas water heater with a perfectly mixed storage tank 

with an efficiency of 76 %,17 a firing rate of 10 551 W,18 and a setpoint temperature of 

48.9°C (120 °F). The heat loss coefficient from the water heater to the ambient 

temperature in the internal space is assumed to be 2.1 W/K.19

3.6 Lighting 

The lighting load profiles and electricity consumption are based on the profile in the BA 

Benchmark that separates the house into living and sleeping zones.20 Total electricity use 

is estimated based on the same two-stage process defined in the BA Benchmark except 

the loads are split equally between the two floors, which can be seen in Table 3-5. The 

baseline lighting estimate is based on 86 % incandescent and 14 % fluorescent use. The 

lighting requirements in 2009 IECC require 50 % high efficacy lighting, which is met by 

using 50 % CFL lighting. The BA Benchmark adjustment functions shown in the right in 

Table 3-5 are used to adjust the total electricity consumption estimation to represent the 

greater efficiency required by 2009 IECC. The baseline annual total lighting electricity 

consumption is estimated at 2281 kWh. The 2009 IECC compliant lighting decreases 

lighting electricity consumption by 36 % to 1411 kWh. 

 

17 Minimum federal efficiency requirement for gas water heaters 

18 Based on the BA Benchmark for a 3 bedroom/2 bathroom house with a gas unit 

19 Based on NIST expert recommendation 

20 Splitting the lighting loads profiles will allow an easier transition if multiple zoning options are 

introduced into the prototypes in the future.
27

Table 3-5 Annual Lighting Electricity Consumption 

Lighting Use 

Category 

Baseline 2009 IECC 

Function Total 

kWh Function Total kWh 

kWh/ 

Floor 

Hard-wired 0.8*(CFA*0.737+467) 1553 1553*[(FINC+0.14) + (FCFL-0.14)*0.27] 1145 573 

Plug-In 0.2*(CFA*0.737+467) 388 388*[(FINC+0.14) + (FCFL-0.14)*0.27] 286 143 

Exterior CFA*0.17 340 340*[(FINC+0.14) + (FCFL-0.14)*0.27] 251 NA 

Total CFA*0.907 + 467 2281 2281*[(FINC+0.14) + (FCFL-0.14)*0.27] 1682 NA 

The load profiles (proportion of peak wattage in use) for interior lighting can be seen in 

Table 3-6. The total wattage parameter for lighting in EnergyPlus is reverse engineered 

from the peak consumption load profiles and the total electricity consumption estimates. 

The load profile for exterior lighting assumes the lights are on sunset to sunrise. 

Table 3-6 Lighting Load Profiles as a Proportion of Peak Wattage in Use, By Hour 

of the Day 

Hour Living Sleeping Hour Living Sleeping 

1:00 0.06 0.6700 13:00 0.1387 0.0667 

2:00 0.06 0.6700 14:00 0.1387 0.0667 

3:00 0.06 0.6700 15:00 0.1387 0.0667 

4:00 0.06 0.6700 16:00 0.2591 0.0835 

5:00 0.1201 0.2667 17:00 0.5486 0.1832 

6:00 0.2402 0.5837 18:00 0.7659 0.2661 

7:00 0.2792 0.6336 19:00 0.9451 0.4992 

8:00 0.2691 0.5333 20:00 1.000 0.7995 

9:00 0.1387 0.2000 21:00 0.9006 1.0000 

10:00 0.1387 0.0667 22:00 0.5178 0.8667 

11:00 0.1387 0.0667 23:00 0.2777 0.4963 

12:00 0.1387 0.0667 24:00 0.1201 0.2000 
28

3.7 Appliances and Miscellaneous Electrical Loads 

The electrical equipment in the house includes a refrigerator, clothes washer, clothes 

dryer, dishwasher, electric range, and a combination of variable miscellaneous electrical 

loads (MELs). MELs encompass electronics such as computers, televisions, stereos, and 

other plug loads. The electricity consumption for each category is based on the BA 

Benchmark functions seen in Table 3-7. Electricity consumption is usually a function of 

the number of bedrooms in the home (NBR). The only category that will see an increase in 

electrical consumption is MELs because one variable in its function is square foot of 

conditioned floor area. 

Table 3-7 Appliance and MEL Electricity Consumption 

Equipment Function kWh 

Refrigerator Constant 669 

Clothes Washer 52.5+17.5*NBR 105 

Clothes Dryer 418+139* NBR 835 

Dishwasher 103+34.3* NBR 206 

Electric Range 302+101* NBR 605 

Variable MELs 1281 + (196* NBR) + (0.345*CFA) 2559 

Total: 4979 

The BA Benchmark load profiles in Figure 3-6 create a real-time variation in electricity 

consumption for each category. Appliances such as the electric range and dishwasher 

have a significant variation in time-of-day use while refrigerator use only varies slightly 

over a day. 
29

Figure 3-6 Domestic Hot Water Load Profiles as a Proportion of Peak Use, By Hour 

of the Day

3.8 Internal Mass 

Instead of defining individual interior surfaces and furniture, internal mass is estimated 

based on ASHRAE 90.2-2007 recommendations. There is assumed to be 3.6 kg (8 lb) of 

5 cm (2 in) thick wood per square foot of conditioned space for contents for a total of 

7257 kg (16 000 lb). There is assumed to be 2.3 kg (5 lb) of 1.3 cm (0.5 in) gypsum wall 

board (GWB) per square foot of conditioned space for the internal structure for a total of 

4536 kg (10 000 lb). 

EnergyPlus estimates internal mass in terms of square meters of material open to the zone 

air. Based on the total weight of the two materials (wood and GWB) and their weight per 

0.00

0.02

0.04

0.06

0.08

0.10

1 3 5 7 9 11 13 15 17 19 21 23

Clothes Washer

0.00

0.02

0.04

0.06

0.08

0.10

0.12

1 3 5 7 9 11 13 15 17 19 21 23

Dishwasher

0.00

0.02

0.04

0.06

1 3 5 7 9 11 13 15 17 19 21 23

Refrigerator

0.00

0.02

0.04

0.06

0.08

0.10

1 3 5 7 9 11 13 15 17 19 21 23

Clothes Dryer

0.00

0.05

0.10

0.15

0.20

1 3 5 7 9 11 13 15 17 19 21 23

Range

0.00

0.02

0.04

0.06

0.08

1 3 5 7 9 11 13 15 17 19 21 23

MELs
30

inch, it is possible to determine the comparable surface area needed to match the amount 

of internal mass required. Assuming the wood density is equivalent to that of white oak, 

753 kg per m3 (47 lb per ft3), the 5 cm (2 in) thick wood weighs 38 kg per m2 (7.833 lb 

per ft2) and would require 189.8 m2 (2043 ft2) of content mass. Assuming GWB density 

of 10 kg per m2 (2.08 lb per ft2), a total of 446.6 m2 (4808 ft2) of structural mass to meet 

the standard recommendations. 

3.9 Occupancy 

Occupancy is based on the BA Benchmark constant daily occupancy load profiles split 

into living and sleeping zones as seen in Table 3-8. The profiles change over the hours of 

the day, but do not vary across days. Separate internal heat gain values are used for each 

type of occupancy. Occupancy in the living and sleeping areas are assumed to emit 

420 Btu/person/hour (123 watts per person) and 350 Btu/person/hour (103 watts per 

person), respectively. 

Table 3-8 Occupancy Load Profile as a Proportion of Maximum Occupancy, By 

Hour of the Day 

Hour Living Sleeping Hour Living Sleeping 

1:00 0.000 1.000 13:00 0.242 0.000 

2:00 0.000 1.000 14:00 0.242 0.000 

3:00 0.000 1.000 15:00 0.242 0.000 

4:00 0.000 1.000 16:00 0.242 0.000 

5:00 0.000 1.000 17:00 0.295 0.000 

6:00 0.000 1.000 18:00 0.553 0.000 

7:00 0.344 0.656 19:00 0.897 0.000 

8:00 0.500 0.383 20:00 0.897 0.000 

9:00 0.409 0.000 21:00 0.897 0.000 

10:00 0.242 0.000 22:00 1.000 0.000 

11:00 0.242 0.000 23:00 0.500 0.500 

12:00 0.242 0.000 24:00 0.000 1.000 
31

3.10 Internal Heat Gains 

Previous sections have addressed specific internal heat gain categories, but it is of interest 

to summarize these heat gains and determine if they are comparable to the 2009 IECC 

standard reference design specifications. The total internal heat gains specified by 2009 

IECC are based on the following equation. Based on 2009 IECC, total internal heat gains, 

IGain, should be 22.8 kWh/day (77 812 Btu/day) for the two-story prototype. 

CFA NBR IGain = 17900 + 23 8. * + 4104 *

Internal heat gains originate from domestic hot water use, electrical equipment use, 

lighting, and human occupancy. Table 3-9 gives internal heat gains resulting from each 

category based on an EnergyPlus simulation of the prototype. The simulated internal heat 

gains of 21.1 (71 972 Btu/day) are lower than the 2009 IECC standard reference design 

(7 %). The variation is likely a result of the number of bedrooms assumed in the 

prototype.21

Table 3-9 Heat Gain Comparison-Reference and Prototype Designs 

Equipment BA Benchmark 

kWh (Btu) 

2009 IECC 

kWh (Btu) 

Prototype Design 

kWh (Btu) 

Lighting NA NA 3.9 (13 374) 

Equipment 9.9 (33 716) NA 10.1 (34 366) 

Occupancy 5.6 (19 028) NA 5.6 (19 071) 

Hot Water 1.5 (5 161) NA 1.5 (5 183) 

Total NA 22.8 (77 812) 21.1 (71 972) 

 

21 Increasing the number of bedrooms from 3 to 4 would likely result in total internal heat gains above the 

2009 IECC estimate because much of the heat gains are based on the number of bedrooms in the house. 
32

4 Recommendations for Future Research 

4.1 Expansion of Current Prototypes 

These two prototype designs are non-location specific and serve as a basis from which 

additional prototypes can be designed. Alterations to these two prototype designs should 

include selecting the location of the building, changing the square footage, changing the 

foundation type, adding a garage, changing orientation, changing the heating fuel type, 

and designing to meet different editions of the IECC. 

4.2 Location-Specific Factors 

The prototype design is location neutral. For energy simulation, each location requires its 

own weather file as well as specification of the following local parameters: location, 

ground temperature, water mains temperature, and design days.22

4.3 Additional Building Sizes 

Leaving the house dimension ratios the same at approximately 2.56:1 and 1.60:1 for the 

1-story and 2-story prototypes, respectively, the prototypes can be expanded or 

contracted to meet the building sizes described in Table 4-1. 

Table 4-1 Additional Prototype Sizes 

1-Story Prototypes 2-Story Prototypes 

m

2

 (ft2) Dimensions m (ft) BR m2 (ft2) Dimension m (ft) BR 

111.6 (1201) 6.6x16.9 (21.67x55.42) 3 148.8 (1602) 6.8x10.9 (22.37x35.8) 3 

148.6 (1600) 7.6x19.5 (25.0x64.0) 3 202.9 (2184) 7.9x12.8 (26.0x42.0) 4 

176.6 (1901) 8.3x21.3 (27.25x69.75) 3 241.0 (2594) 8.7x13.9 (28.5x45.5) 4 

214.0 (2303) 9.1x23.4 (30.0x76.75) 4 297.9 (3207) 9.7x15.4 (31.75x50.5) 5 

287.3 (3093) 10.6x27.1 (34.75x89.0) 5 418.1 (4500) 11.4x18.3 (37.5x60.0) 6 

These alternative building sizes are based on the U.S. Census’ 2010 Characteristics of 

New Housing database. Figure 4-2 shows the percentile breakdown of the size of new 

single-family detached houses. More detailed information on the new housing data can be 

found in Figure 4-1 and Figure 4-2, which show the square footage frequency (left y-

 

22 An EnergyPlus database can be created with location-specific information readily available. 
33

axis) and cumulative distribution (right y-axis) for 1-story and 2-story single-family 

homes, respectively.23 The building sizes selected for the residential prototypes represent 

the 10th, 30th, 50th, 70th, and 90th percentiles for each distribution. 

Any design with 185.8 m2 (2000 ft2) or less of conditioned floor area is assumed to have 

3 bedrooms. Any design with between 185.8 m2

 (2000 ft2) and 278.7 m2 (3000 ft2) of 

conditioned floor area has 4 bedrooms.24 Any design with 278.7 m2

 (3000 ft2) to 371.6 m2

(4000 ft2) of conditioned floor area is assumed to have 5 bedrooms. Any design with 

greater than 371.6 m2

 (4000 ft2) is assumed to have 6 bedrooms. 

Table 4-2 Size Distribution of New Housing in Square Footage 

Percentile 1-Story 2-Story 

10% 1200 1600

20% 1398 1878

30% 1561 2152

40% 1706 2376

50% 1866 2600

60% 2052 2912

70% 2270 3246

80% 2592 3684

90% 3125 4493

Figure 4-1 Square footage of new 1-story single-family housing 

 

23 Homes with less than 700 square feet are assumed to have 700 and square feet. 

24 Building dimensions and number of bedrooms are based on RECS and AHS data.

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0

100

200

300

400

500

600

0

100-200300-400500-600700-800

900-1000

1100-12001300-14001500-16001700-18001900-20002100-22002300-24002500-26002700-28002900-30003100-32003300-34003500-36003700-38003900-4000

Cumulative Distribution

Frequency

Range
34

Figure 4-2 Square footage of new 2-story single-family housing 

4.4 Additional Building Designs 

The two prototype homes, oriented due south, can be altered in a number of ways to 

account for alternative building designs. A two-car garage can be added to various 

locations around the house (east, southeast, and southwest).25 New west, northwest, and 

northeast side designs can be created by changing the orientation of the house by 180 

degrees. 

Slab-on-grade is not the primary foundation type in some regions in the United States. 

Alternative foundation types can be added to the prototype designs to better represent the 

U.S. housing stock. The slab-on-grade can be replaced with slab-in-grade, crawlspace, or 

a basement (finished and unfinished). 

4.5 Heating Fuel Type 

Although natural gas is the most common heating fuel source in the nation, particular 

regions of the nation, such as the South, tend to use electricity at least as often as natural 

gas. Also, a significant portion of the homes in the Northeast use fuel oil for heating. 

4.6 Additional Energy Codes 

 

25 The most typical garage in the housing stock is an attached two-car garage. 

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0

100

200

300

400

500

600

0

100-200300-400500-600700-800

900-1000

1100-12001300-14001500-16001700-18001900-20002100-22002300-24002500-26002700-28002900-30003100-32003300-34003500-36003700-38003900-40004100-42004300-44004500-46004700-48004900-5000

Cumulative Distribution

Frequency

Range
35

The current number of prototype buildings, designed to comply with 2009 IECC, can be 

modified to meet older IECC codes -- 2000, 2003, and 2006 IECC-- to account for the 

variation in state energy codes across the United States. 

4.7 Parametric Designs beyond Current Code 

Once prototypes for current state energy codes have been created, parametric 

improvements can be simulated to estimate energy savings from additional energy 

efficiency improvements using conventional approaches as well as emerging 

technologies. 
36

References

American Society of Heating Refrigerating and Air-Conditioning Engineers, Inc., 2007, 

ANSI/ASHRAE Standard 62.2-2010, Ventilation and acceptable indoor air 

quality in low-rise residential buildings. 

American Society of Heating Refrigerating and Air-Conditioning Engineers, Inc., 2007, 

ANI/ASHRAE Standard 90.2-2007, Energy-efficient design of low-rise 

residential buildings. 

American Society of Heating Refrigerating and Air-Conditioning Engineers, Inc., 2009, 

ASHRAE handbook – fundamentals. 

Department of Energy, Building Technologies Program, EnergyPlus energy simulation 

software Version 6.0.0, 2010, http://apps1.eere.energy.gov/buildings/energyplus/. 

Energy Information Administration, Commercial building energy consumption survey, 

http://www.eia.doe.gov/emeu/cbecs/. 

Energy Information Administration, Residential energy consumption survey, 

http://www.eia.doe.gov/emeu/recs/. 

Field, K., Deru, M., Studer, D., August 2010, Using DOE commercial reference building 

for simulation studies, Conference paper, presented at SimBuild 2010, NREL/CP550-48588. 

Hendron, R., Engebrecht, C., January 2010, Building America research benchmark 

definition, National Renewable Energy Laboratory, Technical Report NREL/TP550-47246. 

Hendron, R., Engebrecht, C., September 2010, Building America house simulation 

protocols, National Renewable Energy Laboratory, Building Technologies 

Program. 

International Code Council, 2009, International residential code for one- and two-family 

dwellings. 

International Code Council, 2009, International energy conservation code. 

Pacific Northwest National Laboratory, September 2009, Impacts of the 2009 IECC for 

residential buildings at state level, Department of Energy Building Energy Codes 

Program. 
37

Persily, A., Musser, A., Leber, D., August 2006, A collection of homes to represent the 

U.S. housing stock, National Institute of Standards and Technology, NISTIR 

7330. 

RSMeans, 2005, Square foot costs – 27th annual edition, Reed construction data. 

U.S. Census Bureau, National american housing survey, 

http://www.census.gov/hhes/www/housing/ahs/ahs.html. 

U.S. Census Bureau, Manufacturing, Mining, and Construction Statistics Division, 2011, 

Annual 2010 characteristics of new housing, 

http://www.census.gov/const/www/charindex.html. 
38

Appendix 

Figure 1 ASHRAE 90.1 Climate Zones by County