NIST Special Publication 1207 

Net-Zero Energy Residential Building 

Component Cost Estimates and 

Comparisons 

Joshua Kneifel 

Eric O’Rear 

This publication is available free of charge from: 

http://dx.doi.org/10.6028/NIST.SP.1207 

 

 

 

 

 

NIST Special Publication 1207 

Net-Zero Energy Residential Building 

Component Cost Estimates and 

Comparisons 

Joshua Kneifel 

Eric O’Rear 

Applied Economics Office 

Engineering Laboratory 

This publication is available free of charge from: 

http://dx.doi.org/10.6028/NIST.SP.1207 

October 2016 

U.S. Department of Commerce 

Penny Pritzker, Secretary 

National Institute of Standards and Technology 

Willie May, Under Secretary of Commerce for Standards and Technology and Director 
 

 

 

 

 

 

Certain commercial entities, equipment, or materials may be identified in this 

document in order to describe an experimental procedure or concept adequately. 

Such identification is not intended to imply recommendation or endorsement by the 

National Institute of Standards and Technology, nor is it intended to imply that the 

entities, materials, or equipment are necessarily the best available for the purpose. 

National Institute of Standards and Technology Special Publication 1207 

Natl. Inst. Stand. Technol. Spec. Publ.1207, 38 pages (October 2016) 

CODEN: NSPUE2 

This publication is available free of charge from: 

http://dx.doi.org/10.6028/NIST.SP.1207 
 

 

 

 

 

Abstract 

Homeowners and builders have increasingly strived to build low energy homes. As 

building materials, equipment, and methods have improved and renewable energy 

systems have become commonplace, the goal of net-zero energy homes has become 

technologically viable. Such an example of these capabilities is on display in the NetZero Energy Residential Test Facility (NZERTF), located at the National Institute of 

Standards and Technology (NIST) in Gaithersburg, Maryland. While the NIST NZERTF 

has shown that net-zero energy performing homes are technologically feasible using 

conventional technologies, questions related to costs continue to arise. Economic 

performance evaluation is reliant on accurate construction cost data, which may change 

significantly over time as industry learns how to implement energy-efficiency measures 

into building design and more energy-efficient technology diffuses into the marketplace. 

In order to update the underlying data in NIST’s economic analysis, a NIST-funded 

contract was completed to estimate the costs of building components designed to meet 

current Maryland building energy code based on 2015 IECC as well as higher efficiency 

building components that are either currently installed in the NZERTF or will be installed 

in the NZERTF in the near future. 

The purpose of this study is to summarize the cost estimates generated by the outside 

contractor. These estimates will then be compared to those from multiple existing data 

sources. Findings from this study will help provide a reasonable range of cost estimates 

for different building components that can be used for future research related to the lowand net-zero energy building designs – in particular, research related to the NZERTF and 

the Building Industry Reporting and Design for Sustainability (BIRDS) software tool. 

Keywords 

Building economics; cost estimation; energy efficiency; residential buildings; low-energy 

buildings; net-zero energy buildings 

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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 estimate the construction costs of energy efficiency measures (EEMs) in 

new residential construction. The intended audience is researchers and policy makers in 

the residential building sector, and others interested in residential building energy 

efficiency. 

Disclaimers 

The policy of the National Institute of Standards and Technology is to use metric units in 

all of its published materials. Because this report is intended for the U.S. construction 

industry that uses U.S. customary units, it is more practical and less confusing to include 

U.S. customary units as well as metric units. Measurement values in this report are 

therefore stated in metric units first, followed by the corresponding values in U.S. 

customary units within parentheses. 

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Acknowledgements 

The authors wish to thank all those who contributed ideas and suggestions for this report. 

They include Dr. Cheyney O’Fallon and Dr. David Butry of EL’s Applied Economics 

Office (AEO), Dr. Harrison Skye of EL’s Energy and Environment Division, and Dr. 

Nicos S. Martys of EL’s Materials and Structural Systems Division. A special thanks to 

OCMI for developing the cost estimates that are the basis of this document. 

Author Information 

Joshua D. Kneifel 

Economist 

National Institute of Standards and Technology 

Engineering Laboratory 

100 Bureau Drive, Mailstop 8603 

Gaithersburg, MD 20899-8603 

Tel.: 301-975-6857 

Email: joshua.kneifel@nist.gov 

Eric G. O’Rear 

Economist 

National Institute of Standards and Technology 

Engineering Laboratory 

100 Bureau Drive, Mailstop 8603 

Gaithersburg, MD 20899-8603 

Tel.: 301-975-4570 

Email: eric.orear@nist.gov 

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Table of Contents 

Abstract............................................................................................................................... i
 Preface...............................................................................................................................iii
 Acknowledgements ........................................................................................................... v

Author Information .......................................................................................................... v
 Table of Contents ............................................................................................................ vii
 List of Figures................................................................................................................... ix

List of Tables .................................................................................................................... ix
 List of Acronyms.............................................................................................................. xi

1 Introduction............................................................................................................... 1
 2 Cost Data Sources ..................................................................................................... 3
 

2.1.1 OCMI .......................................................................................................... 3
 

2.1.2 VESTA........................................................................................................ 3
 

2.1.3 Building Component Cost Community (BC3) ........................................... 4
 

2.1.4 National Residential Efficiency Measures Database .................................. 4
 

2.1.5 RS Means.................................................................................................... 5
 

2.1.6 SunShot....................................................................................................... 5
 

2.1.7 Structural Insulation Panel Association (SIPA).......................................... 5
 

3 Building Component Alternatives........................................................................... 7
 

3.1 Building Envelope................................................................................................ 7
 

3.1.1 Exterior Wall Assembly.............................................................................. 7
 

3.1.2 Roof/Ceiling Assembly............................................................................... 8
 

3.1.3 Basement Insulation.................................................................................... 9
 

3.1.4 Air leakage Rate.......................................................................................... 9
 

3.1.5 Windows ..................................................................................................... 9
 

3.2 Systems............................................................................................................... 10
 

3.2.1 Domestic Hot Water System..................................................................... 10
 

3.2.2 HVAC System .......................................................................................... 10
 

3.2.3 Renewable Energy Systems...................................................................... 12
 

4 Building Component Cost Comparisons .............................................................. 15
 

4.1 Building Envelope Cost Estimates..................................................................... 15
 

4.1.1 Building Envelope Cost Estimates – OCMI ............................................. 15
 

4.1.2 Building Envelope Cost Estimates – Alternative Sources........................ 19
 

4.2 Building System Cost Estimates ........................................................................ 22
 

4.2.1 Domestic Hot Water System Cost Estimates............................................ 22
 

4.3 HVAC System Cost Estimates........................................................................... 23
 

4.3.1 Renewable Energy System Cost Estimates............................................... 26
 

4.3.2 Cost Comparison by Building Design - Building Systems....................... 28
 

5 Building Design Cost Comparisons....................................................................... 31
 

6 Summary, Limitations, and Future Research...................................................... 33
 

6.1 Results Summary................................................................................................ 33
 

6.2 Limitations and Future Research........................................................................ 35
 

7 References................................................................................................................ 37
 

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List of Figures 

Figure 1-1 NIST Net-Zero Energy Residential Test Facility............................................. 1
 

List of Tables 

Table 3-1 Building Component Alternatives: Exterior Wall Assembly............................ 8
 

Table 3-2 Building Component Alternatives: Roof/Ceiling Assembly............................. 8
 

Table 3-3 Building Component Alternatives: Basement................................................... 9
 

Table 3-4 Building Component Alternatives: Air leakage Rate........................................ 9
 

Table 3-5 Building Component Alternatives: Windows ................................................. 10
 

Table 3-6 Building Component Alternatives: Water Heater ........................................... 10
 

Table 3-7 Building Component Alternatives: HVAC Components ................................ 12
 

Table 3-8 Building Component Alternatives: Renewable Energy Systems .................... 13
 

Table 4-1 Building Envelope Area by Component.......................................................... 15
 

Table 4-2 OCMI Exterior Wall Cost Estimates............................................................... 16
 

Table 4-3 OCMI Roof/Ceiling Insulation Cost Estimates............................................... 17
 

Table 4-4 OCMI Basement Insulation Cost Estimates.................................................... 17
 

Table 4-5 OCMI Air Leakage Rate Cost Estimates......................................................... 18
 

Table 4-6 OCMI Window Cost Estimates....................................................................... 18
 

Table 4-7 OCMI Building Envelope Cost Estimate including Mark-Up ........................ 19
 

Table 4-8 Alternative Building Envelope Cost Estimates including Mark-Up ............... 21
 

........................................................................................................................................... 22
 

Table 4-9 Range in Building Envelope Cost Estimates including Mark-Up for NREMD
 

Table 4-10 Water Heater Cost Estimates with Mark-Up................................................. 23
 

Table 4-11 Heat Pump Cost Estimates - OCMI................................................................ 24
 

Table 4-12 Heat Pump Cost Estimates – Alternative Sources......................................... 25
 

Table 4-13 Ventilation Cost Estimates - OCMI ............................................................... 25
 

Table 4-14 Ventilation Cost Estimates – Alternative Sources......................................... 26
 

Table 4-15 Ground-Source Loop Cost Estimates ............................................................ 26
 

Table 4-16 Solar Thermal System Cost Estimates .......................................................... 27
 

Table 4-17 Solar PV System Cost Estimates................................................................... 28
 

Table 4-18 Alternative Building System Cost Estimates ................................................ 29
 

Table 5-1 Alternative Building Design Cost Estimates including Mark-Up................... 31
 

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List of Acronyms 

ACH Air changes per hour 

AEO Applied Economics Office 

ASHRAE American Society for Heating, Refrigeration, and Air-Conditioning 

BC3 Building Component Cost Community 

BIRDS Building Industry Reporting and Design for Sustainability 

COP Coefficient of Performance 

CPUC California Public Utilities Commission 

DEER Database for Energy Efficiency Resources 

DOE Department of Energy 

EER Energy Efficiency Ratio 

EL Engineering Laboratory 

HRV Heat Recovery Ventilator 

HSPF Heating Seasonal Performance Factor 

HVAC Heating, Ventilation, and Air Conditioning 

ICC International Code Council 

IECC International Energy Conservation Code 

LBNL Lawrence Berkeley National Laboratory 

NAHB National Association of Home Builders 

NIST National Institute of Standards and Technology 

NREL National Renewable Energy Laboratory 

NREMD National Residential Energy Measure Database 

NZERTF Net-Zero Energy Residential Test Facility 

OC on center 

OCMI O’Connor Construction Management Inc. 

PNNL Pacific Northwest National Laboratory 

PV photovoltaic 

SEER Seasonal Energy Efficiency Ratio 

SFCE Square Foot Cost Estimator 

SHGC Solar Heat Gain Coefficient 

SIP Structural Insulation Panel 

WHD whole house dehumidifier 

XML Extensible Markup Language 

XPS Extruded polystyrene 

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1 Introduction 

Homeowners and builders have increasingly strived to build low energy homes. As building 

materials, equipment, and methods have improved and renewable energy systems have become 

commonplace, the goal of net-zero energy homes has become technologically viable. Such an 

example of these capabilities is on display in the Net-Zero Energy Residential Test Facility 

(NZERTF), located at the National Institute of Standards and Technology (NIST) in 

Gaithersburg, Maryland (see Figure 1-1). In the completion of its second phase (February 2015 

through January 2016), the facility demonstrated that a home of similar size, aesthetics, and 

amenities to those in the surrounding communities can generate as much energy as it consumes 

on an annual basis using conventional technology while meeting the needs of a family of four. 

The facility will subsequently serve as a test bed to facilitate the development and improvement 

of methods of test and performance metrics for existing and future energy-efficient technologies. 

Figure 1-1 NIST Net-Zero Energy Residential Test Facility 

While the NIST NZERTF shows that net-zero energy homes are technologically feasible using 

conventional technologies, a recurring question remains, “What does it cost?” Since 2012, NIST 

has pursued this question in a number of studies focusing on the life-cycle costs of alternative 

levels of energy-efficiency in residential buildings. 

Some analyses have taken a nationwide perspective and focused on state residential building 

energy codes, which are based on different editions of the International Energy Conservation 

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Code (IECC), and the potential gains of state adoption of more restrictive energy codes. Kneifel 

and O’Rear (2015) analyzed 9120 whole-building energy simulations included in the Building 

Industry Reporting and Design for Sustainability (BIRDS) new residential database. The 

database covers 10 building types in 228 cities located across the U.S. for 9 study periods. The 

performance of buildings designed to meet current state residential energy codes is compared to 

their performance when meeting 2012 IECC requirements for their state. 

Other analyses have focused on the performance of the NIST NZERTF relative to Maryland 

code requirements. Kneifel (2014) uses cost estimate data from a NIST-funded contract (Matlock 

2013) to estimate the cost performance of the NZERTF relative to the same house built to meet 

Maryland residential energy code, which was based on 2012 IECC for residential buildings at the 

time of construction. 

Kneifel and O’Rear (2015) combined cost data developed in Kneifel (2014) and Kneifel et al. 

(2015), and compared the sustainability performance (energy, economic, and environmental) 

metrics of the NIST NZERTF design to a 2015 IECC compliant building design using wholebuilding energy simulation, life-cycle costing, and life-cycle impact assessment. Additionally, a 

preliminary analysis was conducted to evaluate the impacts of incrementally adopting 

energy-efficient measures on a building design’s sustainability performance. 

Kneifel et al. (2016) expanded on Kneifel and O’Rear (2015) by analyzing sustainability 

performance of the 75 million records in the recently released BIRDS v3.0 database that 

analyzes 240 000 building designs based on the NIST NZERTF across multiple of study periods, 

home financing options, levels of building construction quality, and discount rates. Building 

design specifications included in the database are based on the five most recent IECC editions, as 

well as other design cases which lead to low-energy or net-zero energy performance. 

Economic performance evaluation is reliant on accurate construction cost data, which may 

change significantly over time as industry learns how to implement energy-efficiency measures 

into building design and more energy-efficient technology diffuses into the marketplace. In order 

to update the underlying data in NIST’s economic analysis, a NIST-funded contract (OCMI 

2016) was completed to estimate the costs of building components designed to meet current 

Maryland building energy code based on 2015 IECC as well as higher efficiency building 

components that are either currently installed in the NZERTF or will be installed in the NZERTF 

in the near future. This study will summarize the cost estimates developed in (OCMI 2016), as 

well as compare those estimates to cost data used in Kneifel’s 2014 study (Kneifel 2014), the 

data from two residential construction cost databases (National Renewable Energy Laboratory 

2012, RS Means 2016), solar PV system installation cost data collected by Barbose and 

Darghouth (2015), and an industry report on structural insulation panels (SIPs) produced by RS 

Means (RS Means 2006). Recommendations on an average/best guess estimate will be 

generated, as well as a reasonable range of cost estimates for future analysis related to net-zero 

energy home design – particularly related to the NZERTF and BIRDS. 

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2 Cost Data Sources 

The cost estimate data sources considered in this study include: (1) two cost reports developed 

under NIST-funded contracts; (2) two public construction cost databases; (3) one subscriptionbased construction cost database; (4) an annual report on average installed solar PV costs; and 

(5) a structural insulated panel industry (SIP) association report. Each of these data sources are 

described in detail below. 

2.1.1 OCMI 

O’Connor Construction Management, Inc. (OCMI) developed cost estimates for NIST on 

energy-efficiency measures that were incorporated into the NZERTF design or will be installed 

in the NZERTF in the near future. Cost estimates were derived using OCMI’s internal cost 

database and predefined scopes of work provided by NIST on the NZERTF and the 2015 IECC 

for the current construction market for Gaithersburg, MD. A full quality control process 

including independent internal reviews was implemented to verify those cost estimates. OCMI 

also obtained external estimates from subcontractors capable of completing the installation of a 

given building component. When subcontractors could not be identified or were not willing to 

participate, OCMI used industry pricing databases (Sayer and RS Means) for the external 

estimate. OCMI compared the external estimates to the internal estimates for confirmation or 

identification of line item differences. The differences were investigated and consolidated into 

final cost estimates for each component alternative, which are the basis for this study and will be 

compared to alternative data sources to determine the potential variability in these cost estimates. 

The cost estimates assume all building components are installed by a subcontractor with a 30 % 

mark-up, general conditions mark-up of 10 %, and overhead and profit mark-up of 10 % 

(compounding to 21 %). 

2.1.2 VESTA 

Kneifel (2014) used the cost estimates reported in Matlock (2013), a government contracted 

report completed by Multinational Group, LCC. The report documented the approach used to 

estimate the costs of constructing the NZERTF and a comparable 2012 IECC Maryland codecompliant design. Multinational Group hired a LEED-certified contractor (VESTA) to create a 

bid as though it was a private sector project in Maryland being built to meet both the NZERTF 

design as being operated during the demonstration phase (proving net zero energy performance 

over an entire year), as well as a Maryland code-compliant design built according to the 2012 

design specifications for ASHRAE Climate Zone 4. The cost estimates to the contractor for each 

house design were delivered to NIST in spreadsheet form with the report, which include the subcontractor mark-up that are not specified in the report. VESTA assumes a general contractor 

mark-up for overhead and profit of 17.5 %, which is included in the estimates reported in Kneifel 

(2014). For direct comparison purposes, the general contractor mark-up is changed to match the 

OCMI mark-up of 21 % and the estimates are inflated from 2014 to 2016 dollars (factor of 

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1.0111) using the RS Means historical construction cost indexes (RS Means 2016a). The 

inflation factor is different for the cost of the solar PV system. See Section 2.1.6 for details. 

2.1.3 Building Component Cost Community (BC3) 

The Building Component Cost Community (BC3) database was developed by Pacific Northwest 

National Laboratory (PNNL), and provides costs for primary building components, including 

walls, fenestration, equipment, and energy-efficiency measures (BC3 2016). BC3 is a publicly 

available repository of building component costs, and includes three cost databases. PNNL 

developed a residential energy efficiency measure (EEM) database through a contract with 

Faithful and Gould (2012) that includes the incremental costs of meeting different requirements 

across editions of IECC, as well as detailed cost data for building components. The American 

Society for Heating, Refrigeration, and Air-Conditioning Engineers (ASHRAE) developed an 

economic database for the energy-efficient design of low-rise residential buildings through a 

contract with the National Association of Home Builders (NAHB) Research Center (National 

Association of Home Builders 2009). The California Public Utilities Commission (CPUC) 

developed the Database for Energy Efficiency Resources (DEER) database (California Energy 

Commission 2008) focused on residential building costs in California. All three databases can be 

used depending on the specific cost data needed for a given cost analysis. BC3 estimates are 

national average costs to the general contractor including the sub-contractor mark-up (unknown 

values), and are adjusted using the location factor for Washington, D.C. (0.9992) developed for 

BC3 and the OCMI general contractor mark-up of 21 % and RS Means construction cost index 

for 2011 data of 1.0834 (RS Means 2011). The inflation factor is different for the cost of the 

solar PV system. See Section 2.1.6 for details. 

2.1.4 National Residential Efficiency Measures Database 

The National Residential Efficiency Measures Database (NREMD) is a publicly available, 

centralized resource of residential building retrofit measures and costs for the U.S. building 

industry (National Renewable Energy Laboratory 2012). With support from the U.S. Department 

of Energy (DOE), the National Renewable Energy Laboratory (NREL) developed an online tool 

(National Renewable Energy Laboratory 2016) to help users of the database to determine the 

most cost-effective retrofit measures for improving the energy-efficiency of existing homes. This 

database of retrofit measures provides information in a standardized format (Extensible Markup 

Language (XML)) that improves consistency and accuracy of cost estimates to support building 

science research and development. NREL developed a set of rules to construct a list of measures 

based on component properties and action types. Version 1 of the Database was publically 

released in February 2010. The second and third versions were released in October 2010 and July 

2012, respectively. See (National Renewable Energy Laboratory 2012) for details on the 

structure of the database, information regarding the collection and processing of underlying data, 

and information utilized in developing and assembling the database. The NREMD provides 

national average and range of cost estimates, which include the sub-contractor mark-up. Note 

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that the sub-contractor mark-up values are unknown for this database. The general contractor 

mark-up is assumed to match the OCMI mark-up of 21 % and the estimates are inflated from 

2014 to 2016 dollars (factor of 1.0111) using the RS Means historical construction cost indexes 

(RS Means 2016a). 

2.1.5 RS Means 

RS Means Online (RS Means 2016) includes two residential construction cost databases that can 

be used to estimate the cost of energy-efficiency measures: (1) residential new construction and 

(2) residential square foot assemblies. These datasets include the most widely used construction 

assemblies and units, but do not always include less common building components or the same 

level of detail for differentiating some higher efficiency equipment. RS Means cost data includes 

both the “bare total” without any mark-up, as well as a “total O&P” estimate that includes 

subcontractor mark-up. For this study, the “bare total” estimate is used and adjusted using the 

OCMI 30 % sub-contractor and 21 % general contractor mark-up for consistency across 

estimates. No location factor or construction cost indexing is necessary since the RS Means data 

is for 2016 construction data for the College Park, Maryland location (includes ZIP codes 

beginning with 208 and 209). 

2.1.6 SunShot 

Lawrence Berkeley National Laboratory (LBNL) publishes “Tracking the Sun,” an annual report 

on trends in the solar PV system market (Barbose and Darghouth 2015). Given the fast-changing 

market conditions in the solar PV market that has led to significant reductions in the installed 

cost of a solar PV system, it is necessary to use the most up-to-date cost data. The installed cost 

includes all expenditures associated with the system including the sub-contractor and contractor 

mark-up (unknown values). Installed cost data is available by type of system (residential, 

commercial, or utility), size, and location, allowing for more precise estimates than cost 

databases that focus on national average costs with location factors. Additionally, general 

construction costs have been increasing over time while solar PV system costs are trending 

downward. Therefore, the historical installed cost data for Maryland in Barbose and Darghouth 

2015 is used to develop an inflation factor for solar PV system cost estimates for the BC3 (0.63) 

and VESTA (1.00) data sources. 

2.1.7 Structural Insulation Panel Association (SIPA) 

RS Means generated a report for BASF (RS Means 2006) that compares the time and effort 

required to install residential structural insulation panels (SIPs) to those of typical wood-framed 

residential wall construction. Within this report characteristics of SIPs are explained in detail, 

including the SIP assembly and differences in material and labor. 

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3 Building Component Alternatives 

The construction cost data in OCMI (2016) includes line item cost estimates for 13 building 

components with a range of one to six alternatives for each component, totaling 37 building 

component cost estimates. Seven of the building components are associated with the building 

envelope (e.g., exterior enclosure), while 6 are associated with building systems (e.g., heating 

and cooling equipment and renewable systems). Each component alternative is discussed in 

detail below. 

3.1 Building Envelope 

The OCMI cost estimates include one to four alternatives for each aspect of the building 

envelope: exterior wall assembly, roof/ceiling assembly, basement insulation, whole house air 

leakage rate, and fenestration (i.e., windows). Since the building envelope of the NZERTF would 

be difficult to change over the lifetime of the facility, the focus of the alternatives selected is to 

allow for comparison between current Maryland residential energy code requirements and the 

specifications of the NZERTF. In some cases, additional alternatives may also be reported. Each 

is discussed in Section 3.1.1 through Section 3.1.5. 

3.1.1 Exterior Wall Assembly 

Two types of exterior wall assemblies are considered: (1) framing installed first (constructed onsite or prefabricated) and then insulation installed second (i.e. “stick-built” framing) and (2) 

prefabricated assembly with continuous insulation within plywood structure (i.e., structural 

insulation panels or SIPs). The exterior wall “stick-built” framing estimates include three 

alternatives: 5.1 cm x 10.2 cm – 40.6 cm studs on center (OC) (2 in x 4 in – 16 in OC), 5.1 cm x 

15.2 cm – 40.6 cm studs OC (2 in x 6 in – 16 in OC), and “advanced framing” that uses 5.1 cm x 

15.2 cm studs installed 61.0 cm studs OC (2 in x 6 in – 24 OC). These three alternatives will be 

referenced as 2x4-16OC, 2x6-16OC, and 2x6-24OC, respectively, for the remainder of this 

study. 

The exterior wall insulation alternatives for “stick-built” wall framing include: (1) R-13 batt 

fiberglass insulation in the wall cavity and R-5 of extruded polystyrene (XPS) rigid exterior 

insulation (R-13+5); (2) R-20 of cellulose insulation in the wall cavity (R-20); and (3) R-20 

cellulose insulation in the wall cavity with R-24 of polyisocyanurate rigid exterior insulation (R20+24).1 The first two are both compliant with 2015 IECC requirements while the third is the 

insulation installed in the NZERTF. The line item estimation by OCMI allows for an additional 

alternative between the performance of the Maryland code and NZERTF designs to be estimated 

1 Units for R-value are h·ft2·°F/Btu for customary units and K·m2/W for metric units. The conversion is 1 

h·ft2·°F/Btu = 0.176110 K·m2/W. 

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by adding R-12 of the exterior rigid insulation to the R-20 cellulose in the wall cavity (R-20+12), 

which is an alternative included in the BIRDS low-energy residential database. 

Given the dependency between the structural support and the insulation alternatives, it is 

necessary to consider the installed costs of the entire assembly. The combinations of framing and 

wall insulation that are estimated by OCMI are shown in Table 3-1. Also included in the wall 

insulation alternatives is a SIP with R-44 of rigid insulation (R-44 SIP), which includes both the 

structural sheathing in place of framing and the insulation in an assembly that is installed as a 

single unit. 

Table 3-1 Building Component Alternatives: Exterior Wall Assembly 

Exterior 

Wall 

MD Code Alt. MD Code 1 Alt. MD Code 2 Incremental 

Alt.* 

NZERTF Alt. - SIPs 

Insulation** RSI-2.29+0.88 RSI-23.52 RSI-3.52 RSI-3.52+2.11 RSI-3.52+ 4.23 

(R-13+5) (R-20) (R-20) (R-20+12) (R-20+24) RSI-3.52 SIP 

Framing*** 5.1x10.2-40.6OC 5.1x15.2-40.6OC 5.1x15.2-61.0OC 5.1x15.1-61.0OC 5.1x15.2-61.0OC (R-44 SIP) 

(2x4-16OC) (2x6-16OC) (2x6-24OC) (2x6-24OC) (2x6-24OC) 

*Alternative calculated using line item cost estimate for NZERTF wall assembly. 

** RSI-value units is kelvin square meters per watt (K·m2/W). R-value units is degree Fahrenheit square feet hours per Btu 

(ft2

·°F·h/Btu) 

***Framing characteristics are expressed in centimeters (inches) 

3.1.2 Roof/Ceiling Assembly 

As with wall assemblies, the roof assembly alternatives include both “stick-built” framing and 

SIPs. Three different approaches to insulating the attic space are shown in Table 3-2: (1) 

cellulose insulation on the attic floor (R-49) to meet 2015 IECC requirements; (2) R-45 cellulose 

insulation in the roof rafter cavity in combination with R-30 polyisocyanurate rigid exterior 

insulation (R-45+30) to match the specifications of the NZERTF; and (3) prefabricated SIP 

assembly with comparable levels of thermal performance to that of the NZERTF (R-75 SIP). An 

additional alternative can be estimated using the OCMI line item estimates for an incremental 

increase in thermal performance between the Maryland-code compliant and NZERTF designs 

(R-45+15). 

Table 3-2 Building Component Alternatives: Roof/Ceiling Assembly 

Roof/Ceiling MD Code Incremental Alt.* NZERTF Alt. - SIPs 

Insulation** RSI-8.63 RSI-7.92+2.64 RSI-7.92+5.28 RSI-13.21 SIP 

(R-49) (R-45+15) (R-45+30) (R-75 SIP) 

*Alternative calculated using line item estimate for NZERTF roof assembly.
 

** RSI-value units is kelvin square meters per watt (K·m2/W). R-value units is degree Fahrenheit
 

square feet hours per Btu (ft2·°F·h/Btu).
 

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3.1.3 Basement Insulation 

Three alternatives for basement insulation are shown in Table 3-3: (1) the 2015 IECC compliant 

option of R-10 rigid insulation in the basement wall assembly with no insulation under the slab 

(R-10/R-0); (2) the insulation installed in the NZERTF with R-22 rigid insulation in the 

basement wall assembly and R-10 rigid insulation in the basement slab assembly (R-22/R-10); 

and (3) an incremental alternative that installs R-22 in the basement wall assembly with no 

insulation under the basement slab assembly (R-22/R-0). 

Table 3-3 Building Component Alternatives: Basement 

Basement MD Code Alt. MD Code* Incremental 

Alt.* 

NZERTF 

Wall 

Insulation** 

RSI-1.76 

(R-10) 

RSI-1.76 

(R-10) 

RSI-3.87 

(R-22) 

RSI-3.87 

(R-22) 

Slab 

Insulation** 

RSI-0.0 

(R-0) 

RSI-0.0 

(R-0) 

RSI-0.0 

(R-0) 

RSI-1.76 

(R-10) 

*Alternative calculated using line item estimate for NZERTF basement wall
 

assembly.
 

** RSI-value units is kelvin square meters per watt (K·m2/W). R-value units is degree
 

Fahrenheit square feet hours per Btu (ft2·°F·h/Btu).
 

3.1.4 Air leakage Rate 

Two alternatives for the air leakage rate are shown in Table 3-4: (1) spray-on air barrier 

membrane that reduces the air leakage rate to 3.0 air changes per hour at 50 Pa using a blower 

door test to meet 2015 IECC requirements (3.0 ACH), and (2) peel-and-stick air barrier 

membrane that reduces the air leakage rate to 0.63 air changes per hour at 50 Pa using a blower 

door test to meet the measured performance of the NZERTF (0.63 ACH). 

Table 3-4 Building Component Alternatives: Air leakage Rate 

Air leakage MD Code NZERTF 

ACH 3.0 ACH 0.63 ACH 

3.1.5 Windows 

Two alternatives for windows are shown in Table 3-5: (1) window with specifications that meet 

2015 IECC U-value and SHGC requirements (U-0.35/SHGC-0.40) and (2) windows comparable 

in performance to those installed in the NZERTF (U-0.20/SHGC-0.25). 

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Table 3-5 Building Component Alternatives: Windows 

Windows MD Code NZERTF 

Thermal USI-2.00 (U-0.35) USI-1.14 (U-0.20) 

Performance 

SHGC=0.4 SHGC=0.25 

3.2 Systems 

The OCMI cost estimates include two or more alternatives for each of the building systems: 

domestic hot water system, heating, ventilation, and air conditioning (HVAC) system, and 

renewable energy systems. The electrical system is not considered because energy-efficiency for 

lighting in residential buildings is primarily increased by replacing light bulbs with CFLs or 

LEDs without changing the electrical system design, which is a straightforward cost estimate that 

does not require the expertise of a construction cost estimator. 

Duplicate HVAC systems were installed in the NZERTF, including ground-source (geothermal) 

loops, small-duct, high-velocity ductwork as well as two separate solar thermal systems. 

Additional equipment has been (e.g., small-duct high-velocity heat pump), or will be installed 

(e.g., ground-source heat pump and gas storage water heater), over the lifetime of the facility to 

test alternative system configurations. Therefore, there are additional alternatives considered that 

allow for both comparisons between current Maryland residential energy code requirements and 

the specifications of the NZERTF, as well as future system configurations. Each system 

component alternative is discussed in detail below. 

3.2.1 Domestic Hot Water System 

Two alternatives for the domestic water heater are shown in Table 3-6: (1) an electric water 

heater that meets the federal minimum efficiency requirement of 95 % (ElectWH) and (2) a heat 

pump water heater comparable in performance to that installed in the NZERTF (HPWH) with a 

rated coefficient of performance (COP) of 2.33. 

Table 3-6 Building Component Alternatives: Water Heater 

Domestic Hot Water System MD Code NZERTF 

Water Heater ElectWH HPWH 

3.2.2 HVAC System 

The HVAC systems described in Table 3-7 include up to three different components depending 

on the system type. These three components are: (1) a heat pump with ductwork, (2) a ground10
 

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source loop, and (3) ventilation equipment and/or ductwork. All HVAC system costs estimates 

include the cost of a heat pump with rectangular ductwork. A total of six different 2-ton heat 

pump options are considered. The first four are air-to-air heat pump units with one of the four 

following characteristics: (1) a federal minimum efficiency Seasonal Energy Efficiency Ratio 

(SEER) rating of 13 Btu/W-hr and a Heating Seasonal Performance Factor (HSPF) of 

7.7 Btu/W-hr (SEER 13/HSPF 7.7); (2) a comparable efficiency to that of the system installed 

in the NZERTF (SEER 15.8/HSPF 9.05/DM) with dedicated dehumidification mode; (3) a 

comparable efficiency to that of the system installed in the NZERTF without dedicated 

dehumidification mode (SEER 15.8/HSPF 9.05); and (4) an efficiency level comparable to that 

of the Lennox XP 25 series (SEER 23.5/HSPF 10.2). 

Heat pump option 1 is a single-speed, “standard efficiency” system which meets IECC 

requirements, has a SEER of 13 Btu/W-hr for cooling mode, and a HSPF of 7.7 Btu/W-hr for 

heating mode. Heat pump options 2 and 3 are multi-speed heat pump systems with SEER and 

HSPF ratings of 15.8 Btu/W-hr and 9.06 Btu/W-hr, respectively. The former includes 

dehumidification-only mode which helps to reduce the humidity in the house, making it more 

comfortable for the occupants. The latter does not include this feature. The fourth heat pump 

option is an air-to-air heat pump with a SEER rating of 23.5 Btu/W-hr and a HSPF rating of 10.2 

Btu/W-hr. 

The remaining two heat pump options considered are water-to-air heat pumps. The first is 

comparable to that of Water Furnace 3 with an Energy Efficiency Ratio (EER) of 22.3 Btu/W/hr 

and is representative of entry-level ground-source heat pumps. The second (EER 43) has a 

performance comparable to the Climate Master Trilogy 40 Q with an EER of 43 Btu/W/hr, and 

the capability of both space conditioning and water heating. In the case of a water-to-air heat 

pump, a ground-source loop is required for heat exchange. Three ground-source loops sized to 

match a 2-ton water-to-air heat pump are considered: vertical U-loop, horizontal loop, and 

“slinky” loop. All three have been installed in the ground surrounding the NZERTF. 

Under current Maryland code, outdoor air ventilation is required for all new residential building 

construction. Two approaches for providing dedicated outdoor air ventilation are considered. The 

first incorporates supply only utilizing the heat pump ductwork, while the second uses a balanced 

system with dedicated ductwork with energy recovery equipment. Three alternative setups are 

considered for the latter approach: (1) a heat recovery ventilator (HRV) only; (2) a HRV with 

additional economizer (HRV+ECO); and (3) a HRV with a whole-house dehumidifier (WHD) 

(HRV+WHD). The purpose of these three different combinations is to allow for consideration of 

different HVAC configurations. For example, an air-to-air heat pump without dehumidification 

only mode may require the HRV with a WHD in order to maintain the indoor relative humidity 

level. 

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Table 3-7 Building Component Alternatives: HVAC Components 

Components Type Characteristics / Efficiency 

Heat Pumps Air-to-Air 

Air-to-Air 

Air-to-Air 

Air-to-Air 

SEER 13 / HSPF 7.7 

SEER 15.8 / HSPF 9.05 with Dehumidification Only Mode 

SEER 15.8 / HSPF 9.05 without Dehumidification Only 

SEER 23.5 / HSPF 10.2 

Water-to-Air EER 22.3 

Water-to-Air EER 43 

GroundSource Loop Vertical 

Horizontal 

Slinky 

2 - 150’ Bore Holes 

4 - 230’ trenches and tubing (6’ deep) 

2 - 130’ trenches with 801’ tubing (5’ deep) 

Ventilation Dedicated Outdoor Air 

Separate Ductwork 

No Energy Recovery 

HRV 

HRV with Economizer 

HRV with Whole House Dehumidifier 

Conversion: 1’ = 0.3048 m 

3.2.3 Renewable Energy Systems 

Two different types of renewable energy systems have been installed in the NZERTF, a solar 

thermal system and solar photovoltaic system. Two different indirect solar thermal systems are 

currently installed on the porch roof of the NZERTF: (1) two flat plate solar collector panels with 

303 L (80 gal) storage tank and (2) two flat plate solar collector panels with 454 L (120 gal) 

storage tank. Both solar thermal systems are indirect systems that use a glycol/water mix in the 

solar thermal loop to allow for year-round operation and a heat exchanger that transfers energy 

from the solar loop fluid to the water in the storage tank. OCMI developed cost estimates for the 

303 L (80 gal) solar thermal system as well as two alternatives, replacing the flat plate collectors 

with evacuated tube collectors and replacing the entire solar thermal system and installing a 

2.0 kW solar PV system in its place on the porch roof. The latter was included because the 

electricity generation from the PV system may be a more cost-effective use of the porch roof 

area than using it for pre-heating domestic water with the solar thermal system. OCMI developed 

an estimate for the 10.2 kW solar photovoltaic system with two inverters currently installed on 

the roof of the NZERTF as well as estimates for down-sizing the solar PV system to 2.55 kW, 

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5.1 kW and 7.6 kW with appropriately matched inverters. Each of these renewable system 

alternatives is shown in Table 3-8. 

Table 3-8 Building Component Alternatives: Renewable Energy Systems 

System Alternative 

Solar Two Panels w/ 80 gal 

Thermal storage tank 

System 

Two Panels w/ 120 gal 

storage tank 

Replaced with 2.5 kW 

Solar PV System 

Solar PV 

System 

2.5 kW 

5.1 kW 

7.6 kW 

10.2 kW 

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4 Building Component Cost Comparisons 

The OCMI cost estimate for each of the alternatives described in Chapter 3 is reported in this 

chapter. These costs are compared to the cost estimates from other data sources discussed in 

Chapter 2. Any cost estimates reported on a per unit basis are converted to total costs using the 

specifications of the NZERTF (e.g., exterior wall area). Cost comparisons are focused on the 

incremental total costs to account for differences in fixed costs across data sources. All cost 

estimates are total installed costs, which include both material and labor costs. Mark-ups for 

overhead and profits are also included, and adjusted where necessary to remain consistent across 

data sources. 

4.1 Building Envelope Cost Estimates 

OCMI cost estimates for the building envelope are estimated on a per square foot basis. In order 

to compare the OCMI estimates to other data sources (i.e., VESTA), it is necessary to calculate 

the total costs for each building component. This is accomplished by multiplying the cost per 

unit of area by the area for each building envelope component in the NZERTF, which are shown 

in Table 4-1. 

Table 4-1 Building Envelope Area by Component 

Building 

Envelope 

Area 

Exterior 

Wall 

Basement 

Wall 

Basement 

Floor 

Roof Ceiling Exterior 

Framing 

Total 

Exterior 

Area 

Windows 

m2 303.4 151.7 148.8 187.2 135.8 303.4 490.6 38.6 

(ft2) (3266) (1633) (1602) (2015) (1462) (3266) (5281) (416) 

Conversion: 1 m2 = 10.76391 ft2 

4.1.1 Building Envelope Cost Estimates – OCMI 

OCMI cost estimates per unit of area are shown in Table 4-2. The cost of exterior wall 

construction is lowest with R-20 2x6-24OC, followed by R-13+5 2x4-16OC. This is because 

R-20 thermal performance is achieved using only batt or loose-fill insulation, which is far less 

expensive than the rigid insulation that must be paired with batt insulation to achieve comparable 

thermal performance. R-20 2x6-16OC is comparable in cost to R-13+5 2x4-16OC because the 

lower insulation costs are offset by the greater costs for the framing. The NZERTF design 

(R-20+24 2x6-24OC) is significantly more expensive than either of the Maryland-code 

compliant designs due to the additional rigid insulation. The line item estimation by OCMI 

allows for estimating the cost of an incremental energy efficiency measure between the 

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Maryland-code compliant and NZERTF designs (R-20+12 2x6-24OC).2 Comparing the 

insulation costs per ft2 for the R-20 2x6-24OC and R-20+12 2x6-24OC exterior wall 

constructions, reveal that use of the additional R-12 rigid insulation increases ft2 costs by roughly 

$1.43. The change in cost using the structural insulation panel for the wall assembly (R-44 SIP) 

is almost a factor of 10 greater than R-20+24. Even after combining the wall framing and 

insulation costs, R-44 SIP is approximately five times more expensive than R-13+5 and three 

times more expensive than R-20+24. 

Table 4-2 OCMI Exterior Wall Cost Estimates 

Building Envelope 

Cost ($/ft2)* 

R-13+5 R-20 R-20 R-20+12 R-20+24 R-44 SIP 

2x4-16 2x6-16 2x6-24 2x6-24 2x6-24 

Exterior Wall 

Insulation $1.71 $1.44 $1.44 $2.87 $4.19 

$29.62 

Framing $4.76 $5.06 $4.71 $4.71 $4.71 

Total / ft2 $6.47 $6.50 $6.15 $7.58 $8.90 $29.62 

Total $21 131 $21 229 $20 086 $24 756 $29 067 $96 739 

Delta Cost $0 $65 -$1078 $3592 $7904 $75 575 

*Conversion: 1 US$/m2 = 0.09290304 US$/ft2 

Table 4-3 OCMI Roof/Ceiling Insulation Cost Estimates 

Building 

Envelope 

Cost ($/ft2)* 

R-49 R-45+15 R-45+30 R-75 SIP 

$/ft2 $2.30 $3.74 $5.90 $23.25 

Roof/Ceiling Total $3363 $7536 $11 889 $46 849 

Delta Cost $0 $4173 $8526 $43 486 

*Conversion: 1 US$/m2 = 0.09290304 US$/ft2 

shows the four OCMI cost estimates for each of the roof/ceiling alternatives. The cost of the 

insulation in the attic space is lowest for the Maryland code-compliant design (R-49), which is a 

result of not requiring any rigid insulation. The NZERTF design (R-45+30) is significantly more 

expensive than the Maryland code-compliant design, while the cost of the incremental alternative 

design (R-45+15) is approximately the midpoint between the Maryland code-compliant and 

NZERTF designs. The structural insulation panel for the roof assembly (R-75 SIP) is nearly five 

2 Note that this alternative has been estimated for use in future analysis (e.g. BIRDS database) and will not be 

discussed further. 

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times more expensive than R-45+30. However, much of this higher cost is attributed to the 

additional cost of the structural rafters. 

Table 4-3 OCMI Roof/Ceiling Insulation Cost Estimates 

Building 

Envelope 

Cost ($/ft2)* 

R-49 R-45+15 R-45+30 R-75 SIP 

$/ft2 $2.30 $3.74 $5.90 $23.25 

Roof/Ceiling Total $3363 $7536 $11 889 $46 849 

Delta Cost $0 $4173 $8526 $43 486 

*Conversion: 1 US$/m2 = 0.09290304 US$/ft2 

Table 4-4 shows OCMI cost estimates for the three basement insulation alternatives. The cost of 

the basement insulation (wall and floor combined) is seven times greater for the NZERTF design 

(R-22/R-10) relative to the Maryland code-compliant design (R-10/R-0), while the design with 

the wall insulation of the NZERTF with no insulation under the slab (R-22/R-0) is almost five 

times the Maryland-code compliant design. The alternative Maryland code-compliant design that 

uses XPS to meet the R-10 requirement (Alt. R-10/R-0) is almost four times as expensive. 

Table 4-4 OCMI Basement Insulation Cost Estimates 

Building Envelope 

Cost ($/ft2)* 

R-10 / R-0 Alt. R-10 / R-0* R-22 / R-0 R-22 / R-10 

Wall Insulation $1.22 $2.94 $5.81 $5.81 

Basement 

Floor Insulation 

Total 

$0.00 

$1992 

$0.00 

$7552 

$0.00 

$9488 

$2.88 

$14 101 

Delta Cost $0 $5560 $7496 $12 109 

* Conversion: 1 US$/m2 = 0.09290304 US$/ft2 

**Uses R-10 of XPS in place of concrete block polystyrene to match NZERTF specs. 

Table 4-5 shows the two air leakage rate alternatives. The cost of the air leakage rate for the 

NZERTF design (0.61 ACH) is significantly more expensive than the Maryland-code compliant 

design (3.0 ACH). Note that the wall and roof SIPs are assumed to meet the NZERTF air 

leakage rate at no additional cost. 

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Table 4-5 OCMI Air Leakage Rate Cost Estimates 

Building Envelope 

Cost ($/ft2)* 

3.0 ACH 0.61 ACH 

Air Leakage Membrane $0.96 $2.49 

Rate Total $5070 $13 150 

Delta Cost $0 $8080 

Note: Assumes SIPs meet 0.61 ACH50 

*Conversion: 1 US$/m2 = 0.09290304 US$/ft2 

Unlike the rest of the building envelope components, which are priced out on a cost per unit of 

area, OCMI estimated the total cost for the windows as shown in Table 4-6. The use of higher 

efficiency windows by the NZERTF design (U-0.20/SHGC 0.25) drives up costs by roughly 

45 % relative to the Maryland-code compliant design (U-0.30/SHGC 0.40). 

Table 4-6 OCMI Window Cost Estimates 

Building Envelope 

Cost ($) 

U-0.30 / SHGC 0.40 U-0.20 / SHGC 0.25 

Windows $18 560 $26 880 

Delta Cost $0 $8320 

OCMI assumes that the building envelope construction will be bid by subcontractors and the 

subcontractor will include a 30 % mark-up for their overhead and profit. Table 4-7 shows the 

costs for the Maryland-code compliant and NZERTF designs for each component of the building 

envelope accounting for the subcontractor mark-up. The incremental costs for the entire building 

envelope of the NZERTF design to the general contractor is $58 463 more expensive than the 

Maryland-code compliant design. After accounting for the general conditions and overhead and 

profit mark-ups by the general contractor (10 % and 10 %, respectively, for a total of 21 %), the 

cost to the homebuyer is $70 740. The compounding mark-up from the subcontractor (30 %) and 

general contractor (21 %) increases the total incremental costs for the building envelope by 

57.3 % ($25 748) from $44 971 to $70 740. 

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Table 4-7 OCMI Building Envelope Cost Estimate including Mark-Up 

Building 

Envelope 

Area 

(ft2)* 

MD 

Code 

NZERTF 

Exterior Wall 3266 $33 239 $45 723 

Basement Insulation 1633 $3134 $22 182 

Roof/Ceiling 2015 / 1462 $5289 $18 701 

Air Leakage Rate 5281 $7975 $20 684 

Windows 416 $24 128 $42 282 

Total Incremental Costs $65 194 $123 613 

Cost Difference to General 

Contractor $0 $58 463 

Cost Difference to Homebuyer $0 $70 740 

*Conversion: 1 m2 = 10.76391 ft2 

4.1.2 Building Envelope Cost Estimates – Alternative Sources 

The VESTA cost estimates for the building envelope were reported in total costs while the cost 

estimates from BC3, NREMD, and RS Means are on a per unit of area basis. In some cases, an 

exact match is not possible (e.g., window U-factor and SHGC) and the cost data for the 

component with the closest match to those specifications is selected. There is no data for the 

exterior framing in the alternative data sources, but since the change in costs is minimal and 

negative for the OCMI estimate it is reasonable to assume the change in cost will be 

approximately zero for the estimates for the alternative data sources. The total cost estimates 

including mark-ups are reported in Table 4-8 for each building envelope component for each 

available data source as well as a comparison to the OCMI estimates. 

Estimates across the different data sources are similar for exterior wall insulation, roof/ceiling 

insulation, and exterior framing. The additional costs from building to the NZERTF design for 

the exterior wall assembly is comparable with a range of -18 % to +2 % relative to the OCMI 

estimate. The roof/ceiling insulation cost estimates are similar for the OCMI and alternative data 

sources, with the additional cost to meet the NZERTF roof and ceiling assembly ranging 

+/- 20 %. There is no data for the exterior framing in the alternative data sources, but since the 

change in costs is minimal and negative for the OCMI estimate it is reasonable to assume the 

change in cost will be approximately zero. 

Significant differences are realized for the air leakage rate, windows, and basement wall and 

floor insulation. The air leakage rate cost estimate is higher for OCMI than the alternative data 

sources except for RS Means. The reason for these differences is the assumed method to reach 

the lower air leakage rate through the building envelope. The OCMI and RS Means estimates are 

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based on changing the type of continuous air barrier installed on the exterior of the house while 

the BC3, NREMD, and VESTA estimates assume the use of spray foam insulation in 

combination with or in lieu of the air barrier. The use of spray foam on areas of high air leakage 

could reduce air leakage more significantly while using less material and labor, leading to lower 

costs to meet the target air leakage rate. The cost estimates for changing the windows vary 

significantly, -46 % to +73 %, which could be driven by the underlying source of the data in 

combination with the window characteristics. Since the performance specifications (U-factor and 

SHGC) of the windows installed in the NZERTF cannot be matched exactly, it is possible that 

the cost of windows can vary significantly. 

The largest differences in costs across the alternative sources are for the additional costs incurred 

by building to the NZERTF design specifications for the basement wall insulation and basement 

floor insulation, with estimates being 53 % to 76 % and 44 % to 55 % lower, respectively. Some 

of these additional costs are a result of the assumed insulation approach to reach the R-10 

basement wall requirement for the MD Code design. If the R-10 requirement is met using R-10 

of XPS instead of concrete block polystyrene, then it leads to the OCMI estimate being 24 % to 

62 % higher. The remaining difference may be due to some unforeseen complexity in the 

insulation installation. The difference in the estimates for the basement floor insulation may be 

due to the lack of available cost data for the specific installation of insulation under a basement 

slab. The wall insulation cost data is used from the alternative cost data sources to develop the 

cost estimate, potentially not accounting for the complexities of installation under the slab. 

Excluding wall framing, cost estimates were completed for all building envelope components 

using the BC3 and NREMD databases.3 RS Means does not have detailed data for windows, for 

which an average of the other alternatives is used as a proxy. VESTA does not have a line item 

breakdown for the basement insulation as well as additional costs for a combination of the roof 

and wall framing. In total, the additional costs for the building envelope range from $50 708 to 

$75 411 with an average of $61 108, which is 13 % lower than the OCMI estimate. The sum of 

the minimum cost differences for each building envelope component is $37 646, which is the 

lowest potential estimate at 47 % lower than the OCMI estimate. The sum of the maximum cost 

differences for each building envelope component is $73 884, which is less than the VESTA 

estimate at $75 411 and 7 % higher than the OCMI estimate. 

3 Since the total cost estimates are not comparable across data sources, the total for each building design is excluded. 

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Table 4-8 Alternative Building Envelope Cost Estimates including Mark-Up 

Building 

Envelope Data Source MD Code NZERTF Additional Cost 

Additional 

Cost 

(OCMI) 

Difference 

relative to 

OCMI 

Percent 

Difference 

relative to 

OCMI 

VESTA $2447 $12 846 $10 399 $12 741 -$2342 -18% 

Exterior BC3 $11 188 $23 786 $12 598 $12 741 -$143 -1% 

Wall NREMD $14 473 $26 052 $11 579 $12 741 -$1163 -9% 

RS Means $7038 $19 985 $12 947 $12 741 $206 2% 

VESTA NA NA NA -$257 NA NA 

Exterior BC3 NA NA NA -$257 NA NA 

Framing NREMD NA NA NA -$257 NA NA 

RS Means NA NA NA -$257 NA NA 

VESTA NA NA NA $11 790 NA NA 

Basement BC3 $3315 $7743 $4427 $11 790 -$7363 -62% 

Wall NREMD $5996 $11 579 $5582 $11 790 -$6208 -53% 

RS Means $3802 $6575 $2773 $11 790 -$9017 -76% 

VESTA NA NA NA $7 258 NA NA 

Basement BC3 $0 $3252 $3252 $7 258 -$4005 -55% Floor NREMD $0 $4057 $4057 $7 258 -$3201 -44% 

RS Means $0 $3730 $3730 $7 258 -$3528 -49% 

VESTA $3059 $19 330 $16 272 $13 412 $2860 21% 

Roof / BC3 $3159 $16 549 $13 389 $13 412 -$22 0% 

Ceiling NREMD $3332 $14 032 $10 700 $13 412 -$2712 -20% 

RS Means $5166 $17 751 $12 586 $13 412 -$826 -6% 

VESTA $1835 $8319 $6484 $12 710 -$6226 -49% Air Leakage BC3 $2144 $12 140 $9996 $12 710 -$2714 -21% Rate NREMD $0 $3477 $3477 $12 710 -$9233 -73% 

RS Means $1246 $13 624 $12 378 $12 710 -$332 -3% 

VESTA $26 915 $40 373 $13 458 $13 087 $370 3% 

BC3 $12 245 $19 289 $7044 $13 087 -$6043 -46% Windows NREMD $18 435 $41 083 $22 648 $13 087 $9561 73% 

RS Means $17 723 NA NA $13 087 NA NA 

VESTA $75 411 $70 741 $4669 7%
 

BC3 $50 708 $70 741 -$20 034 -28%
 

NREMD $58 043 $70 741 -$12 699 -18%
 

Total RS Means $60 272 $70 741 -$10 469 -15%
 

Average $61 108 $70 741 -$9354 -13% 

Min* $37 646 $70 741 -$33 096 -47%
 

Max* $73 884 $70 741 $3143 4%
 

*The min and max estimates are the sum of the minimum and maximum estimates for each building component, 

which does not include the VESTA roof and wall framing costs. 

The NREMD database includes a range of values leading to the minimum and maximum values 

shown in Table 4-9. The additional costs of constructing the building envelope to meet the 

NZERTF requirements vary by +/- 20 % to +/- 58 % relative to the average value depending on 

the building envelope component. The minimum total additional costs vary by +/- 27 % relative 

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to the average value and -40 % to 4 % relative to the OCMI estimate, which are similar to the 

minimum and maximum values estimated in Table 4-8 at -47 % and 7 %. 

Table 4-9 Range in Building Envelope Cost Estimates including Mark-Up for NREMD 

Building 

Envelope 

MD 

Code NZERTF Additional Cost 

Percent 

Variation 

Additional 

Cost 

(OCMI) 

Difference 

relative to 

OCMI 

Percent 

Difference 

relative to 

OCMI 

Exterior 

Wall 

Average 

Min 

Max 

$14 473 

$9221 

$18 194 

$26 052 

$17 367 

$33 495 

$11 579 

$8 146 

$15 301 

-30 % 

32 % 

$12 741 

$12 741 

$12 741 

-$1163 

-$4595 

$2560 

-9% 

-36% 

20% 

Exterior 

Framing 

Average 

Min 

Max 

NA 

NA 

NA 

NA 

NA 

NA 

NA 

NA 

NA 

-$257 

-$257 

-$257 

NA 

NA 

NA 

NA 

NA 

NA 

Basement 

Wall 

Average 

Min 

Max 

$5996 

$4549 

$7650 

$11 579 

$8684 

$14 679 

$5582 

$4135 

$7029 

-26 % 

26 % 

$11 790 

$11 790 

$11 790 

-$6208 

-$7655 

-$4761 

-53% 

-65% 

-40% 

Basement 

Floor 

Average 

Min 

Max 

$0 

$0 

$0 

$4057 

$3245 

$4868 

$4057 

$3245 

$4868 

-20 % 

20 % 

$7258 

$7258 

$7258 

-$3201 

-$4013 

-$2389 

-44% 

-55% 

-33% 

Roof / 

Ceiling 

Average 

Min 

Max 

$3332 

$2221 

$4443 

$14 032 

$10 461 

$17 604 

$10 700 

$8240 

$13 161 

-23 % 

23 % 

$13 412 

$13 412 

$13 412 

-$2712 

-$5172 

-$250 

-20% 

-39% 

-2% 

Air 

Leakage 

Rate 

Windows 

Average 

Min 

Max 

Average 

Min 

Max 

Total 

$0 

$0 

$0 

$18 435 

$11 588 

$23 175 

$3477 

$1471 

$5482 

$41 083 

$28 442 

$51 090 

Average 

Minimu 

Maximu 

$3477 

$1471 

$5482 

$22 648 

$16 855 

$27 915 

$58 043 

$42 092 

$73 758 

-58 % 

58 % 

-26 % 

23 % 

-27 % 

27 % 

$12 710 

$12 710 

$12 710 

$13 087 

$13 087 

$13 087 

$70,741 

$70,741 

$70,741 

-$9233 

-$11 239 

-$7228 

$9561 

$3767 

$14 828 

-$12 699 

-$28 649 

$3,016 

-73% 

-88% 

-57% 

73% 

29% 

113% 

-18% 

-40% 

4% 

Note: Minimum and maximum are the sum of the minimum and maximum values for each building component. 

4.2 Building System Cost Estimates 

OCMI cost estimates for building systems include components of the domestic hot water system, 

HVAC system, and renewable energy systems. OCMI developed detailed line item estimates, 

allowing for isolation of the costs for individual pieces within a building system, such as 

alternative heat pumps, ventilation equipment, or water heaters. This section will report these 

OCMI estimates and compare them to the alternative data sources when available. 

4.2.1 Domestic Hot Water System Cost Estimates 

Cost estimates including the subcontractor and contractor mark-ups for domestic water heaters 

are shown in Table 4-10. OCMI estimated the cost for two water heaters, an electric water heater 

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that meets minimum federal efficiency requirements, and a heat pump water heater comparable 

to that installed in the NZERTF. Based on these estimates, the heat pump water heater is $1587 

more expensive than the electric water heater. The alternative data sources do not include the 

cost of plumbing, which is assumed to be constant across the two alternatives. Therefore, the 

difference in costs across data sources should be directly comparable. As shown in the table, the 

OCMI estimated difference in cost is slightly lower (15 %) than the NREMD estimate, but 

higher (12 %) than the BC3 estimate. There was no cost estimate in VESTA for the water heater 

and RS Means does not have cost data on residential heat pump water heaters. 

Table 4-10 Water Heater Cost Estimates with Mark-Up 

DHW Electric 

Water Heater 

Heat Pump Water 

Heater 

Difference 

OCMI $2345 $3933 $1587 

VESTA NA NA NA 

BC3 $1009 $2355 $1346 

NREMD $747 $2532 $1785 

($494 to $975) ($1773 to $3292) ($798 to $2798) 

RS Means $1826 NA NA 

Range NC NC $1346 to $1785 

Includes 30 % subcontractor mark-up. 

NC = Not Comparable 

4.3 HVAC System Cost Estimates 

OCMI cost estimates for the HVAC system include heating and cooling equipment, ventilation 

equipment, and ground-source heat exchanger loops. The OCMI estimates will be explained in 

detail and then compared to available estimates for alternative data sources. 

OCMI estimated the cost of six heat pumps, four air-to-air heat pumps and two water-to-air heat 

pumps, including the ductwork for the system. The more efficient the air-to-air heat pump, the 

greater the cost of the installed system. One of the heat pump system estimates includes 

dehumidification-only mode, which will allow for comparison of the system operated during the 

first year of operation for the NZERTF, to the installation of a whole-house dehumidifier, which 

was operated during the second year. See Section 3.2.2 for additional details. 

Table 4-11 includes the contractor cost of each heat pump system, cost of each system adjusted 

for a 21 % contractor mark-up, and the difference in costs relative to the MD Code building 

component design. Based on Table 4-11, the following is revealed: (1) increases in heat pump 

efficiency correspond with increases in cost; (2) inclusion of the dehumidification-only mode 

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option raises the price of an air-to-air heat pump by $750; (3) the typical high-efficiency waterto-air heat pump is similar in price to the highest efficiency air-to-air heat pump; (4) the waterto-air heat pump with a variable speed compressor and water heating is significantly more 

expensive than any other heat pump. The difference in cost between the MD Code and NZERTF 

building component designs is $1930. 

Table 4-11 Heat Pump Cost Estimates - OCMI 

Heat Pump Contractor Cost Price w/ Mark-Up Diff. from 

MCC 

HP13/7.7 $16 677 $26 233 $0 

HP15.8/9.05 No Dehum $17 007 $26 752 $519 

HP15.8/9.06 w/ Dehum $17 904 $28 163 $1930 

HP23.5 $22 754 $35 792 $9559 

Geo Water Furnace 3 EER 22.3* $22 032 $34 656 $8423 

Climate Master Trilogy 40 Q EER 43** $33 264 $52 324 $26 091 

*Must be combined with ground-source loop.
 

** Must be combined with ground-source loop; includes DHW capabilities
 

Table 4-12 shows the cost estimates available from the alternative data sources. Notice that some 

cost data is not available for some of the heat pump alternatives depending on the data source, 

and those with available data cannot be compared directly to the OCMI estimates because it is 

uncertain whether the costs include all the same line items. However, it is reasonable to compare 

the cost difference across systems for each data source. VESTA is the only data source with cost 

estimates for both the Maryland code-compliant heat pump and NZERTF heat pump, and 

includes the cost of installing the ductwork. According to VESTA, the cost difference is 

estimated at $11 623. The BC3 and NREMD data sources have data for the heat pump installed 

in the NZERTF except for the dehumidification mode capability. The difference between the 

MD Code and NZERTF heat pump is $709 and $1246, respectively. 

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Table 4-12 Heat Pump Cost Estimates – Alternative Sources 

Heat Pump 

Price w/ Mark-Up 

VESTA BC3 NREMD* RS Means 

Air-to-Air 13/7.7 $16 516** $1558 $3439 

($2368 to $4675) 

$5348 

Air-to-Air 16.5/9.1 No Dehum 

NA $2267 $4685 

($3401 to $6407) 

NA 

Air-to-Air 16.5/9.1 w/ Dehum $28 139** NA NA NA 

Air-to-Air 23.5 

NA NA $6204 

($4343 to $8534) 

NA 

Water-to-Air EER 22.3 

NA $5348 $9002 

($5824 to $12 636) 

$3854 

Water-to-Air EER 43 NA NA NA NA 

*Closet match 

**Includes cost of ductwork 

Cost estimates for the ventilation component of the HVAC system include a dedicated outdoor 

air system built into the heat pump ductwork and 3 system alternatives that include separate 

ductwork. The system installed in the NZERTF is an HRV system with separate ductwork. The 

two other alternatives incorporate an economizer and a dehumidifier into the HRV system. As 

displayed in Table 4-13, use of a separate ductwork for whole-house ventilation increases 

ventilation costs by $3736. Inclusion of an economizer, a dehumidifier, or both, will only lead to 

further increases in ventilation costs. 

Table 4-13 Ventilation Cost Estimates - OCMI 

Ventilation Contractor 

Cost 

Price w/ 

Mark-up 

Diff. from 

MCC 

DOA $557 $876 $0 

HRV $2932 $4612 $3736 

HRV w/Econ $3308 $5203 $4327 

HRV w/Dehumid. $3762 $5918 $5041 

HRV w/Econ & Dehumid. $4138 $6509 $5633 

Only the VESTA and NREMD data sources have cost data for an HRV system. The estimates 

based on VESTA is $14 681 while the estimates based on NREMD is $2102 with a range from 

$1760 to $2583. 

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Table 4-14 Ventilation Cost Estimates – Alternative Sources 

Ventilation 

Price w/ Mark-up 

VESTA BC3 NREMD RS Means 

DOA NA NA NA NA 

HRV $14 681 NA $2102 

($1760 to $2583) 

NA 

HRV w/Econ NA NA NA NA 

HRV w/Dehumid. NA NA NA NA 

The water-to-air heat pumps must be combined with ground-source heat exchanger loops. Three 

cost estimates were developed for each of the loop options available. The estimates in Table 4-15 

include mark-up. The cost estimates based on VESTA are significantly lower than the OCMI 

cost estimates. For both data sources, the vertical system has the greatest cost because it requires 

drilling a deep well to install the vertical U-tube instead of a long trench. 

Table 4-15 Ground-Source Loop Cost Estimates 

Ground-Source Loops Vertical 

U-Tube 

Horizontal 

U-Tube 

Slinky 

OCMI $27 778 $24 506 $24 539 

VESTA $19 575 $12 846 $12 846 

BC3 NA NA NA 

NREMD NA NA NA 

RS Means NA NA NA 

4.3.1 Renewable Energy System Cost Estimates 

Two types of renewable energy systems are considered: solar thermal and solar PV systems. 

OCMI estimated the cost for two solar thermal systems, one using flat plate collectors and 

another using evacuated tube collectors. Both systems include the same pumping loop, heat 

exchanger, and storage tank. An alternative to a solar thermal system is to install additional solar 

PV panels to generate electricity instead of pre-heating water going to the domestic water heater. 

The cost estimates in Table 4-16 include all mark-up. The OCMI cost estimate shows that the 

flat plate collector system ($6824) is cheaper than the evacuated tub collector system ($9304). 

The cost estimates from VESTA ($4894) and BC3 ($7134) for the flat plate collector system are 

similar to the OCMI estimate. The OCMI solar PV system alternative is significantly more 

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expensive at $20 265 while the alternative cost estimate based on data from SunShot is only 

$7800. 

Table 4-16 Solar Thermal System Cost Estimates 

Solar 

Thermal 

2 Panels w/ 80 

gal tank 

2 Panels w/ 120 gal 

tank 

Evac. Tubes w/ 

80 gal tank 

Replace w/ 

2 kW PV 

OCMI $6824 NA $9304 $20265 

VESTA $4894 $7341 NA NA 

BC3 $7134 NA NA NA 

NREMD NA NA NA NA 

RS Means NA NA NA NA 

SunShot NA NA NA $7800 

The solar PV system installed on the NZERTF is a 10.2 kW system, which includes four 

horizontal rows of eight 320 W panels with two inverters. The OCMI cost estimates include 4 

incremental increases in the size of the installed system (2.55 kW, 5.1 kW, 7.65 kW, and 

10.2 kW). These incremental increases are based on adding an additional string of panels, with 

adjustments to the size and number of inverters accordingly. 

Table 4-17 shows the solar PV system installation cost estimates compiled from the different 

cost data sources. All cost estimates include markup and are absent of any federal or state 

incentives like the Solar Investment Tax Credit. Both the OCMI and BC3 data sources show that 

system costs increase with system size. The discrepancies in the cost estimates between the two 

data sources are rather significant. Even though both the OCMI and VESTA cost estimates were 

developed specifically for the NIST NZERTF, the difference in the estimated cost of a 10.2 kW 

system is more than $24 843. The BC3 cost estimate also shows lower costs than the OCMI 

estimate at $41 598. The most up-to-date data source is SunShot, which estimates the 10.2 kW 

system to cost $39 780 ($3.90/W). Based on the alternative cost estimates, it appears that the 

OCMI estimate is relatively high at $5.76/W of installed capacity for the 10.2 kW system. 

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Table 4-17 Solar PV System Cost Estimates 

Solar PV 2.55kW 5.1 kW 7.65 kW 10.2 kW 

OCMI $22 944 $32 571 $45 486 $58 723 

VESTA NA NA NA $33 880 

BC3* $10 399 $20 799 $31 198 $41 598 

NREMD NA NA NA NA 

RS Means NA NA NA NA 

SunShot** $9 945 $19 890 $29 835 $39 780 

Range $9945 to $22 944 $19 890 to $32 571 $29 835 to $45 486 $33 880 to $58 723 

*Includes the installed cost of PV panels and inverters only. 

**Based on the average price of installed capacity for Maryland ($3.90/W) 

4.3.2 Cost Comparison by Building Design - Building Systems 

Table 4-18 shows the cost estimates for each building system component for the Maryland Code 

design and NZERTF design, the cost difference between the two designs, and the total building 

system cost differences between the two designs for each of the alternative data sources. As in 

the case for RS Means window cost data, for data sources missing cost estimates for a given 

system component, the average of the other alternative data sources is used as a proxy. 

The difference in building system costs for OCMI is higher than any of the alternative data 

sources at $71 616. However, once this estimate is adjusted to use solar PV cost data that seems 

more accurate (SunShot), the estimate decreases to $52 673 and brings it in line with the 

alternative cost estimates. The alternative data sources range from $49 719 to $66 950 with an 

average of $59 069, which is within 12 % of the OCMI estimate with the adjusted solar PV cost 

data. The extreme minimum and maximum are only slightly outside these estimates at $43 237 to 

$76 821. 

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Table 4-18 Alternative Building System Cost Estimates 

Building 

Envelope 

Data 

Source 

MD Code NZERTF Difference 

OCMI $2345 $3933 $1588 

VESTA NA NA NA Domestic Hot 

Water System BC3 $1009 $2355 $1346 

NREMD $747 $2532 $1785 

RS Means $1826 NA NA 

OCMI $26 233 $28 163 $1930 

Heating and VESTA $16 516 $28 139 $11 623 

Cooling BC3 $1558 $2267* $709 

Equipment NREMD $3439 $4685* $1246 

RS Means $5348 NA NA 

OCMI $876 $4612 $3736 

VESTA $0 $14 681 $14 681 Ventilation 

Equipment BC3 NA NA NA 

NREMD $0 $2102 $2102 

RS Means NA NA NA 

OCMI $0 $5639 $5639 

VESTA $0 $5200 $5200 Solar Thermal 

BC3 $0 $7134 $7134 System 

NREMD NA NA NA 

RS Means NA NA NA 

OCMI $0 $58 723 $58 723
 

VESTA $0 $33 880 $33 880
 

BC3 $0 $41,598 $41,598 Solar PV System 

NREMD NA NA NA 

RS Means NA NA NA 

SunShot $0 $39 780 $39 780 

OCMI $29 454 $101 070 $71 616
 

OCMI using SunShot for Solar PV $52 673 

VESTA** $66 950 

Total Building BC3** $59,179 

System Costs NREMD** $49 719 

Sum of Average $59 069 

Sum of Minimum $43 237 

Sum of Maximum $76 821 

*Heat Pump does not include cost of dehumidification mode capability.
 

**For missing values, used the average of the other alternatives for that category.
 

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5 Building Design Cost Comparisons 

The total additional costs to meet the NZERTF specifications relative to the Maryland-code 

compliant specifications shown in Table 5-1 are calculated by combining the results from Table 

4-8 on the building envelope and Table 4-18 on the building systems. The total cost to the 

homeowner using the OCMI estimate with the adjusted solar PV costs is $123 414 with the 

alternative data source estimates ranging from $107 762 (-13 %) to $142 360 (+15 %). The 

average of the alternative data sources is within 1.4 % at $125 591. The most extreme 

combinations of cost estimates lead to a minimum of $80 883 (-34 %) and a maximum of 

$150 705 (+22 %). 

Table 5-1 Alternative Building Design Cost Estimates including Mark-Up 

Incremental 

Costs 

Difference to 

Homeowner 

Difference to 

Contractor 

Difference to 

Subcontractor 

OCMI $142 357 $117 651 $90 501 

OCMI using SunShot $123 414 $101 995 $78 458 

VESTA* $142 360 $117 653 $90 502 

BC3* $109 886 $90 815 $69 858 

NREMD* $107 762 

($89 439 to $126 540) 

$89 059 

($73 916 to $104 579) 

$68 507 

($56 859 to $80 445) 

Average $125 591 $103 435 $79 565 

Min Combination $80 883 $66 845 $51 420 

Max Combination $150 705 $124 550 $95 808 

*Proxies required when no value is available. 

Note: Assumes subcontractor mark-up is the same as OCMI assumption. 

These additional costs of reaching net-zero energy performance can be put into perspective by 

comparing the change in the total costs of purchasing a home in the Gaithersburg, Maryland 

area. Assuming the specifications of a 2015 IECC compliant design, the cost of constructing a 

2700 ft2, luxury two-story home in Gaithersburg, MD would cost approximately $418 965 

($155.17/ft2)

4

. Adding together the incremental costs from Table 5-1, the cost of the constructing 

a code-compliant home in Gaithersburg, and the cost of land in the area, will give the total cost 

to the homeowner of constructing a net-zero energy home. The lot size is assumed to be 0.4 acres 

with a cost of $100 000, which is a conservative estimate based on current listings of land lots 

4 The RS Means Online Square Foot Calculator was used to generate this cost. The RS Means calculator accounts 

for differences in construction cost based on location in the U.S. The user has the ability to account for these 

location-based adjustments in their cost calculations by clicking on a dropdown and selecting from a list of U.S. 

cities. Since Gaithersburg, MD is not included as an option, the city of College Park, MD was chosen given its close 

proximity to Gaithersburg relative to other Maryland cities listed in the dropdown. 

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for sale southwest of the NIST campus in the Quail Run community between Darnestown, MD 

and Kentlands, MD vary from $260 000 per acre to $753 000 per acre according to Redfin 2016. 

Table 5-2 shows the total cost to the homeowner of building a net-zero home in the Gaithersburg 

area, as well as the required monthly mortgage payment given the different data sources. 

Monthly mortgage payments were calculated based on a 30-year loan payback period and 80 % 

financing of the initial investment cost of the total property at 4.88 % APR (Annual Percentage 

Rate). The OCMI estimate leads to mortgage payments that are $754 more expensive than those 

for the house built to Maryland code compliance. 

The table reveals that the differences in monthly mortgage payments for the net-zero energy 

home across the alternative sources, with the largest difference being only $183 (OCMI and 

NREMD). Although proxy data was used in cases where no data was available for some sources, 

Table 5-2 does highlight the importance of not only using accurate cost data when formulating 

cost estimates of net-zero energy building designs, but also the importance of using cost data that 

is consistent with existing industry cost trends. 

Table 5-2 Alternative Building Design Cost Estimates including Mark-Up 

Data Source Cost to Homeowner 

(Sale Price) 

Mortgage Payment 

(Monthly)* 

Additional Mortgage 

Payment 

MD Code NZERTF MD Code NZERTF Relative to 

MD Code 

Relative to 

OCMI 

OCMI $518 965 $661 323 $2748 $3502 $754 $0 

OCMI using SunShot $518 965 $642 380 $2748 $3401 $653 -$101 

VESTA $518 965 $661 325 $2748 $3502 $754 $0 

BC3 $518 965 $628 851 $2748 $3330 $582 -$172 

NREMD $518 965 $626 727 $2748 $3319 $571 -$183 

Average $518 965 $644 121 $2748 $3411 $663 -$91 

Min Combination $518 965 $599 848 $2748 $3176 $428 -$326 

Max Combination $518 965 $669 670 $2748 $3546 $798 $44 

*Assumes 30-year mortgage, 80 % financing, and 4.88 % APR. 

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6 Summary, Limitations, and Future Research 

This study compares the recent cost estimates developed by OCMI related to building 

components incorporated into a Maryland 2015 IECC code-compliant design, as well as higher 

efficiency building components currently incorporated or soon to be incorporated in the NIST 

NZERTF, to alternative cost data sources related to these buildings. The purpose of this study is 

to reveal differences in component cost estimates across data sources, as well as provide 

reasonable ranges for building component cost approximations that can be incorporated into 

future studies related to low-energy and net-zero energy residential building designs. 

6.1 Results Summary 

The alternative cost estimates for the building envelope reveal similarities across data sources for 

the exterior wall assembly and the roof/ceiling insulation building component categories. The 

additional costs incurred by building to the NZERTF design specifications ranges between -18 % 

and 2 % for the exterior wall assembly, and -20 % to 21 % for roof/ceiling insulation, relative to 

the OCMI estimates. More noticeable differences, however, are realized for the air leakage rate, 

windows, and basement (wall and floor) insulation. Air leakage rate cost estimates differ by as 

much as -73 % relative to OCMI, with RS Means showing the least amount of deviation (-3 %). 

These differences are primarily linked to differences in the assumed approach to achieving the 

lower air leakage rate. 

The wide range in window cost estimates across the alternative data sources (-46 % to 73 %) is 

likely the result of differences in the underlying cost data, as well as the use of proxy data in 

cases where window specifications cannot be matched exactly across data sources. Of any of the 

building envelope components the biggest differences in incremental costs between OCMI and 

the alternative data sources are for basement wall and floor insulation, with OCMI estimates 

being 56 % to 76 % and 44 % to 55 % lower, respectively. Alternative assumptions for the 

method to reach the R-10 basement wall requirement for the Maryland code-compliant design 

are partly responsible for these considerable differences. The additional costs of building the 

entire building envelope to that of the NZERTF specifications range from $50 708 to $75 411. 

The average incremental cost ($61 108) is roughly 13 % lower than that of the OCMI estimate. 

The significant differences in cost estimates do not occur for the building envelope only, but for 

the domestic hot water system, HVAC system, and renewable energy systems as well. According 

to the OCMI estimates, changing to a heat pump water heater from a minimum efficiency 

electric water heater would cost the homeowner an additional $1587. This incremental cost 

estimate is about 15 % lower than the NREMD estimate and 12 % higher than the BC3 estimate. 

The HVAC system configurations considered in this study include at least two out of the three 

system components: heat pumps for heating and cooling, ventilation equipment, and groundsource heat exchanger loops. Data sources show that increases in heat pump system efficiency 

coincide with increases in system costs. Differences in cost for the Maryland code-compliant 

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heat pump and NZERTF heat pump based on VESTA estimates ($11 623) is roughly six times 

greater than the difference based on OCMI ($1930). Similar trends are seen with regards to the 

ventilation system and ground-source loop options. The addition of the HRV system with 

separate ductwork (based on the NZERTF specifications) leads to an additional cost of $14 681 

based on VESTA estimates, which is roughly four times higher than the incremental cost found 

using OCMI data ($3736). The difference in costs for the ground-source heat exchanger loops 

differ by as much as $11 660 between the VESTA and OCMI data sources depending on the 

loop type. 

The two types of renewable energy systems considered in this study are solar thermal and solar 

PV systems. OCMI estimates suggest that at an additional cost of $6824 the two-panel flat plate 

collector system with 80-gallon storage tank is the least expensive solar thermal system 

configuration. Both the VESTA and BC3 estimates for the same system are close to OCMI 

estimates with cost estimates of $4894 and $7134, respectively. In regards to a roof-mounted 

solar PV system, the alternative data sources reveal that system costs increase with system size. 

However, large discrepancies between the data sources exist for a 10.2 kW system with OCMI 

estimate being roughly $25 000 higher than the VESTA estimate for a similar system. OCMI 

estimates are slightly more than $17 000 higher than BC3 and almost $19 000 more than 

SunShot. 

The differences in total building system cost (sum of domestic hot water, HVAC, and renewable 

energy systems) between the Maryland code-compliant and NZERTF designs is highest with 

OCMI data with an estimated cost of $71 616. This falls outside of the $49 719 to $66 950 cost 

range defined by the alternative data sources. The OCMI estimates only fall within this range 

when it is adjusted using the SunShot estimate for the 10.2 kW solar PV system instead of the 

original OCMI estimate. 

The incremental building envelope and building systems costs incurred by the homeowner for 

building to NZERTF specifications relative to the code-compliant design range between 

$107 762 and $142 360, with an average cost of $125 591. The magnitude of this cost gap, 

however, is reduced once the total costs of building the property is calculated and converted into 

a monthly mortgage payment. Assuming a 30-year mortgage at 4.88 % with 20 % down 

payment, monthly payments range between $3319 and $3502 across the alternative data sources, 

with an average monthly payment of $3411. Regardless of the data source, the additional 

mortgage payment of purchasing a home designed to reach net-zero energy performance relative 

to Maryland code compliance is between $400/month and $800/month based on the 

characteristics of the NIST NZERTF. 

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6.2 Limitations and Future Research 

The analysis in this study is limited in scope and would be strengthened by including more 

accurate, up-to-date data sources as they become available. Recent technological innovation and 

improvements in production efficiency should be considered in the future because they have 

been found to be two key drivers behind declining installed costs of building products. Since all 

of the cost data sources, except OCMI and RS Means Online, are based on data before 2016, it is 

probable that the costs of some building components have fallen as a result of these factors 

and/or others. 

Also limiting the scope of this study is the lack of consistency in building specifications across 

data sources, as well as the lack of available cost data for all building components considered. In 

a few instances, building component cost data from an alternative source was compared to the 

corresponding OCMI estimate despite the specifications of the component not matching exactly 

between the two sources. As a result, the accuracy of the cost comparison can be improved in the 

future with additional data and information. A majority of the alternative data sources had 

missing estimates for multiple building components. The use of proxy data to fill in these gaps 

also limits the accuracy of the analysis. Future analyses should consider only using data sources 

that: (1) include cost data on all building components being considered in the study; and (2) have 

a one-to-one matching of building component specifications with the other data sources being 

used. These two requirements help to ensure that a direct comparison can be made across 

alternative data sources. 

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7 References 

Barbose, G. and N. Darghouth (2015). Tracking the Sun VIII: The Installed Price of Residential 

and Non-Residential Photovoltaic Systems in the United States. Berkeley, CA, Lawrence 

Berkely National Laboratory. 

California Energy Commission (2008). "DEER - Database for Energy Efficient Resources." from 

http://www.energy.ca.gov/deer/. 

Faithful and Gould (2012). Residential Energy Efficiency Measures: Prototype Estimate and 

Cost Data Revision 6.0, National Renewable Energy Laboratory. 

Kneifel, J. (2014). Life-Cycle Cost Comparison of the NIST Net Zero Energy Residential Test 

Facility to a Maryland Code-Compliant Design. NIST SP 1172. National Institute of Standards 

and Technology. Gaithersburg, MD. 

Kneifel, J. and E. O'Rear (2015). "Benefits and Costs of Energy Standard Adoption for New 

Residential Buildings: National Summary." NIST Special Publication 1194. 

Kneifel, J. and E. O'Rear (2015). "Sustainability Performance of the NIST Net-Zero Energy 

Residential Test Facility Relative to a Maryland Code-Compliant Design." NIST Special 

Publication 1187. 

Kneifel, J., et al. (2016). "Evaluating the Sustainability Performance of Alternative Residential 

Building Designs using the BIRDS Low-Energy Residential Database." NIST Special 

Publication 1205. 

Kneifel, J., et al. (2015). "Simulated versus Measured Energy Performance of the NIST Net Zero 

Residential Test Facility Design." NIST Special Publication 1182. 

Matlock, T. (2013). NIST Net Zero Energy Residential Test Facility: Final Report, Multinational 

Group, LLC. 

National Association of Home Builders (2009). Economic Database in Support of ASHRAE 90.2 

(Energy-Efficient Design of Low-Rise Residential Buildings) 1481 RP, NAHB Resarch Center. 

National Renewable Energy Laboratory (2012). National Residential Efficiency Measures 

Database - Development Document, v3.0. Golden, CO, National Renewable Energy Laboratory. 

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National Renewable Energy Laboratory (2016). "National Residential Efficiency Measures
 

Database." from http://www.nrel.gov/ap/retrofits/.
 

OCMI (2016). NIST Net Zero Residential Test Facility Internal EEM Cost Estimate, Prepared
 

by: O'Connor Construction Management, Inc.
 

Redfin (2016). Land/Lots for Sale in Gaitherburg, MD and surrounding area. from
 

https://www.redfin.com/.
 

RS Means (2006). "BASF Corporation - Time & Motion Study." from
 

http://www.sips.org/technical-information/sips-vs-sticks-cost-data.
 

RS Means (2011). "CostWorks Databases." from http://www.meanscostworks.com/.
 

RS Means (2016). "CostWorks Databases." from http://www.meanscostworks.com/.
 

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