Greenbelt Homes Pilot Program:

Summary of Building Envelope 

Retrofits, Planned HVAC 

Equipment Upgrades, and 

Energy Savings

J. Wiehagen, M. Del Bianco, and D. Mallay

Partnership for Home Innovation

May 2015
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Greenbelt Homes Pilot Program:

Summary of Building Envelope Retrofits, Planned HVAC 

Equipment Upgrades, and Energy Savings

Prepared for:

The National Renewable Energy Laboratory

On behalf of the U.S. Department of Energy’s Building America Program

Office of Energy Efficiency and Renewable Energy

15013 Denver West Parkway

Golden, CO 80401

NREL Contract No. DE-AC36-08GO28308

Prepared by:

Home Innovation Research Labs

Partnership for Home Innovation

400 Prince George’s Boulevard

Upper Marlboro, MD 20774

NREL Technical Monitor: Stacey Rothgeb

Prepared under Subcontract No. KNDJ-0-40335-05

May 2015
The work presented in this report does not represent 

performance of any product relative to regulated 

minimum efficiency requirements.

The laboratory and/or field sites used for this work are 

not certified rating test facilities. The conditions and 

methods under which products were characterized for 

this work differ from standard rating conditions, as 

described.

Because the methods and conditions differ, the reported 

results are not comparable to rated product performance 

and should only be used to estimate performance under 

the measured conditions.
Contents

List of Figures ............................................................................................................................................ iii

List of Tables .............................................................................................................................................. iv

Definitions.................................................................................................................................................... v

Executive Summary................................................................................................................................... vi

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

1.1 Pilot Program Background............................................................................................................... 3

1.2 Phase 2 Pilot Program Building Envelope Upgrades....................................................................... 4

2 Greenbelt Homes, Inc. Pilot Program Research Investigation ........................................................ 7

3 Retrofit Designs and Construction Process...................................................................................... 8

3.1 Design Details and Bid Process....................................................................................................... 8

3.2 Additional Analysis Required.......................................................................................................... 9

4 Crawlspace and Attic Upgrades........................................................................................................ 12

4.1 Crawlspace Retrofits...................................................................................................................... 12

4.1.1 Frame-Vinyl Pilot Home Crawlspace Upgrades............................................................... 12

4.1.2 Block and Frame-Brick Crawlspace Upgrades................................................................. 13

4.1.3 Frame-Brick and Frame-Vinyl Attic Upgrades ................................................................ 14

5 Wall, Window and Door, and Exhaust Fan Upgrades..................................................................... 16

5.1 All Pilot Homes—Window Replacement...................................................................................... 16

5.2 Block Home Window and Wall Upgrades..................................................................................... 17

5.2.1 Window Upgrades ............................................................................................................ 17

5.2.2 Block Building Insulation................................................................................................. 19

5.3 Frame-Brick Window and Door Replacement............................................................................... 20

5.4 Frame-Vinyl Wall, Window, and Door Upgrades......................................................................... 20

5.4.1 Window Replacements..................................................................................................... 21

5.4.2 Frame-Vinyl Wall Insulation Upgrades............................................................................ 24

5.5 All Pilot Homes—Exhaust Fan Installation................................................................................... 24

5.6 Energy Upgrade Feature and Monitoring Description................................................................... 26

6 Infiltration Testing .............................................................................................................................. 27

7 Heating Season Comparison............................................................................................................. 30

8 Monitored Data—Indoor Temperature and Energy Use ................................................................. 33

8.1 Monitoring Summary..................................................................................................................... 33

8.2 Indoor Temperature Measurements in Pilot Homes...................................................................... 34

8.3 Energy Use Data ............................................................................................................................ 37

8.3.1 Heating Energy Use .......................................................................................................... 38

8.3.2 Heating Degree Day Normalization.................................................................................. 38

8.3.3 Temperature Difference Normalization and Take-Back Energy Use ............................... 40

9 HVAC System Analysis for Phase 3 Retrofits ................................................................................. 49

10 Cost Savings of Building Envelope Improvements ........................................................................ 51

10.1 Retrofit Cost Complexity.................................................................................................. 51

10.2 Energy Savings Investment............................................................................................... 52

10.3 Prioritizing Energy-Efficiency Measures ......................................................................... 54

11 Energy-Efficiency Measure Lessons Learned................................................................................. 56

11.1 Crawlspace Upgrades ....................................................................................................... 56

11.2 Attic Upgrades.................................................................................................................. 56

11.3 Windows........................................................................................................................... 57

11.4 Exterior Insulation and Weather-Resistive Barriers ......................................................... 57

11.5 Claddings.......................................................................................................................... 58

11.6 Ventilation Fan ................................................................................................................. 59

11.7 Design and Implementation Process................................................................................. 59

i
12 Summary of Research Questions..................................................................................................... 60

13 Next Steps ........................................................................................................................................... 63

References................................................................................................................................................. 64

Bibliography .............................................................................................................................................. 65

Appendix A: Pilot Program Retrofit Options, Estimated Costs, and Estimated Energy Savings .... 66

Appendix B: Units by Construction Type............................................................................................... 67

Appendix C: Total Energy Use and Heating Energy Use in Each Pilot Home.................................... 69

Appendix D: Greenbelt Homes, Inc. Pilot Program Phase 3: Heating Systems Overview................ 74

ii
List of Figures

Figure 1. FB building (2 of 4 homes in set) .............................................................................................. 1

Figure 2. FV building (1st home of 4 in set) ............................................................................................. 1

Figure 3. B building (1st home of 4 in set) ............................................................................................... 1

Figure 4. B/BV (2 of 4 homes in set).......................................................................................................... 1

Figure 5. Original design of B homes ..................................................................................................... 10

Figure 6. Painted B home with circa 1980 window upgrades............................................................... 10

Figure 7. FV building crawlspace prior to upgrades ............................................................................. 13

Figure 8. FV crawlspace after upgrades................................................................................................. 13

Figure 9. B building crawlspace prior to upgrades ............................................................................... 13

Figure 10. Building crawlspace after repair/retrofits............................................................................. 13

Figure 11. Typical attic of the wood-framed buildings.......................................................................... 14

Figure 12. Foam board at attic storage area .......................................................................................... 14

Figure 13. Wood sheathing installed over the foam board to maintain an attic storage area .......... 14

Figure 14. Insulation baffles at edge of new storage area.................................................................... 15

Figure 15. Gable end wall air sealing...................................................................................................... 15

Figure 16. Exterior top plate air sealing.................................................................................................. 15

Figure 17. Completed attic retrofit .......................................................................................................... 15

Figure 18. Window rough opening prior to window installation.......................................................... 18

Figure 19. New replacement window installed over sill flashing and foamed.................................... 18

Figure 20. Window trim installed to the block rough opening and caulked ....................................... 18

Figure 21. Window flashing integrated with foam insulation............................................................... 18

Figure 22. Replacement window installed in a BV unit......................................................................... 19

Figure 23. BV building with new windows and trim .............................................................................. 19

Figure 24. Block building with 2-in. rigid foam and furring.................................................................. 19

Figure 25. Block building with exterior insulation installed................................................................. 20

Figure 26. Completed block building with all energy upgrades installed........................................... 20

Figure 27. Replacement window in FB unit............................................................................................ 20

Figure 28. FB replacement window—flashing and caulking ................................................................ 20

Figure 29. Typical front elevation, FV building ...................................................................................... 21

Figure 30. Window sill flashing on an FV unit........................................................................................ 21

Figure 31. Foam board extends beyond original window trim............................................................. 21

Figure 32. Additional window trim and foam sealing............................................................................ 22

Figure 33. Replacement window installed and flashed......................................................................... 22

Figure 34. Additional window trim and foam sealing........................................................................... 22

Figure 35. Replacement window installed and flashed......................................................................... 22

Figure 36. WRB installed over foam sheathing (not shown)................................................................ 23

Figure 37. WRB wrapped into window opening..................................................................................... 23

Figure 38. Window trim flashing integrated with WRB ......................................................................... 23

Figure 39. Original building paper on frame building ........................................................................... 24

Figure 40. Foam sheathing installed....................................................................................................... 24

Figure 41. WRB installed over foam sheathing...................................................................................... 24

Figure 42. New siding installed following windows, doors, insulation, and WRB............................. 24

Figure 43. Core from B home for an exhaust fan................................................................................... 25

Figure 44. Exhaust fan hood and sleeve adaptor.................................................................................. 25

Figure 45. Interior exhaust fan grille ....................................................................................................... 25

Figure 46. Graphical representation of air leakage in pilot homes...................................................... 29

Figure 47. NOAA heating ranks—2010–2011 ......................................................................................... 30

Figure 48. NOAA heating ranks—2011–2012 ......................................................................................... 30

Figure 49. NOAA heating ranks—2012–2013 ......................................................................................... 30

Figure 50. NOAA heating ranks—2013–2014 ......................................................................................... 30

Figure 51. Graphical representation of ambient weather factors ........................................................ 32

Figure 52. Average winter period temperature difference from base year ......................................... 48

iii
List of Tables

Table 1. Estimated Phase 2 Energy Cost Savings for Envelope Measures by Building Type............ 5

Table 2. Selected Envelope Upgrades by Building Type........................................................................ 6

Table 3. Simulated Energy Savings of Various Insulation Methods for B Units ................................ 11

Table 4. Summary of Wall Insulation Upgrades for GHI Pilot Homes ................................................. 16

Table 5. Summary of Energy Features for Each Pilot Home ................................................................ 26

Table 6. Results of Guarded Blower Door Testing—Net Leakage to the Outside.............................. 28

Table 7. Monthly Ambient Temperature for Four Heating Seasons..................................................... 31

Table 8. Monthly HDDs for Four Heating Seasons ................................................................................ 31

Table 9. Average Seasonal Indoor Temperature and Relative Humidity for Pilot Homes................. 35

Table 10. Heating Period Average Indoor Temperature and Relative Humidity by Building Type... 37

Table 11. Measured Energy Use in Pilot Homes Over Four Heating Seasons ................................... 37

Table 12. Estimated Heating Energy Use in Pilot Homes Over Four Heating Seasons..................... 38

Table 13. HDD Normalized Heating Energy............................................................................................ 39

Table 14. HDD Normalized Heating Energy Savings Over Base Year (%)........................................... 40

Table 15. HDD Normalized Heating Energy Savings Over Base Year (kWh) ...................................... 40

Table 16. TD Normalized Heating Energy............................................................................................... 41

Table 17. TD Normalized Heating Energy Savings Over Base Year (%).............................................. 42

Table 18. TD Normalized Heating Energy Savings From Base Year (kWh) ........................................ 42

Table 19. Summary Heating Energy Use for Each Season, 23 of 28 Pilot Homes ............................. 43

Table 20. Summary of Energy Savings Building Type and Upgrade................................................... 44

Table 21. Heating Energy Savings by Building Using Combined Measured Data ............................. 47

Table 22. Cost Estimates (Installed) for Heating Systems.................................................................... 50

Table 23. Cost Analysis of Building Upgrades ...................................................................................... 53

Table 24. Individual Unit Savings and Cost............................................................................................ 54

Table 25. Homeowner Reponses to Energy and Comfort Questionnaire ........................................... 61

Table 26. Heating Season Total Energy Use in Each Pilot Home ........................................................ 70

Table 27. Heating Season Estimated Energy Use ................................................................................. 72

Unless otherwise noted, all figures and tables were created by Home Innovation Research Labs.

iv
Definitions

A&E Architectural & Engineering Firm

B GHI Block buildings constructed of 8-in. CMU with exterior paint

BA Building America 

BV GHI Block Buildings constructed of 8-in. CMU with exterior vinyl 

siding over furring strips and up to 3⁄4-in. foam board

CMU Concrete Masonry Unit

EBB Electric Baseboard

EEM Energy-Efficiency Measure 

EIFS Exterior Insulation and Finishing System

FB GHI Frame-Brick Veneered Buildings

FV GHI Frame-Vinyl Buildings

GHI Greenbelt Homes, Inc. (A Nonprofit Housing Cooperative)

HDD Heating Degree Day

HVAC Heating, Ventilating, and Air Conditioning

kWh Kilowatt Hour (Measure of Electricity Usage)

PHI Partnership for Home Innovation

SPF Spray Polyurethane Foam

TD30 Temperature Difference Normalization to a 30°f average seasonal 

temperature difference based on actual measured temperature 

differences in a given heating period

WRB Weather-Resistive Barrier

v
Executive Summary

In fall 2010, Greenbelt Homes, Inc. (GHI) undertook a multiyear pilot energy-efficiency retrofit 

project— a 1,566-home cooperative of circa 1930 to 1940 homes in Greenbelt, Maryland. GHI 

established this pilot project to serve as a basis for decision making for the rollout of a decadelong community-wide upgrade program that will incorporate energy-efficiency improvements to 

the building envelope and equipment with the modernization of other systems such as plumbing, 

mechanical equipment, and cladding. The community upgrade was fully funded by the 

cooperative through its membership without outside subsidies; thus, this project presents a 

unique opportunity to evaluate and prioritize the wide range of benefits of high-performance 

retrofits based on the consumers’ experience with—and acceptance of—the retrofit measures 

implemented during the pilot project. The authors address the complex interactions between 

benefits, tradeoffs, construction methods, project management implications, realistic upfront 

costs, financing, and other considerations. This approach serves as a case study for energy 

retrofit projects to include high-performance technologies based on the long-term value to the 

homeowners.

The three predominant wall construction methods for townhomes in the GHI community are 

materials common to the area and climate zone, including: (1) 8-in. concrete masonry unit block,

(2) wood frame with brick veneer, and (3) wood frame with vinyl siding. 

The pilot project has three phases focused on identifying the added costs and energy savings 

benefits of improvements planned for implementation during a planned community-wide retrofit 

program commencing in 2015. Phase 1 provided a baseline evaluation of the current operation, 

use, environmental conditions, and energy costs for a representative set of 28 townhomes sited in 

seven buildings. Phase 2 included the installation of the building envelope improvements identified 

in Phase 1, continued monitoring of the energy consumption for the heating season for comparative 

evaluation of the performance before and after the improvements, and energy simulations 

supporting recommendations for heating, ventilating, and air conditioning and water heating 

upgrades to be implemented in Phase 3.

The U.S. Department of Energy Building America team Partnership for Home Innovation wrote 

a report on Phase 1 of the project that summarized a condition assessment of the homes and 

evaluated retrofit options within the constraints of the cooperative provided by GHI. Phase 2 was

completed following monitoring in the 2013–2014 winter season; the results are summarized in 

this report. Phase 3 upgrades of heating equipment will be implemented in time for the 2014–2015 

heating season and are not part of this report.

This report:

• Summarizes the Phase 2 activities that include crawlspace, attic, and wall upgrades, 

testing, and an energy use summary. 

• Includes an analysis (requested by GHI) of interior insulation options, which have been 

of interest to some GHI members seeking to maintain the exterior “block” profile of the 

original buildings. 

vi
• Includes analyses of heating and cooling system options, community impacts, costs, and 

benefits.

After the Phase 2 crawlspace, attic, and wall upgrades were completed and the bath ventilation 

fans were installed, tests showed the frame-vinyl pilot homes had reduced air infiltration by an 

average of 36% (12–7.7 ACH50), the frame-brick pilot homes by an average of 10% (8.1–7.3

ACH50), and the block homes by an average of 31% (4.9–3.4 ACH50). 

Following is a list of GHI building types and corresponding pilot home upgrades with resultant 

reductions in energy use as measured in the tests. 

• GHI uninsulated block buildings that had only crawlspace and window/door upgrades. 

This yielded a 10% heating energy reduction, primarily from the window/door upgrades 

and reduced infiltration.

• One uninsulated block unit, which included a new ductless heat pump with the upgrade 

package. This achieved a 43% heating energy reduction. This savings was attributed 

primarily to the operation of the ductless heat pump rather than the baseboard resistance 

heaters, and secondarily to the envelope improvements. 

• GHI block homes with vinyl siding and 1⁄2-in. exterior insulation board between the 

furring. The homes had only crawlspace/basement and window/door upgrades. These

yielded a 29% heating energy reduction that was attributed primarily to the window 

upgrades and reduced infiltration. 

• GHI block homes (both end units), which originally had vinyl siding and 1⁄2-in. exterior 

insulation board between furring. The homes had crawlspace and window/door upgrades 

and all existing siding and insulation removed and upgraded with 2-1⁄2-in. exterior rigid 

insulation. New siding was also installed. These measures achieved a 46% heating energy 

reduction that was attributed primarily to the wall insulation, window upgrades, and 

reduced infiltration.

• GHI block home (one interior unit), uninsulated, which had crawlspace and window/door 

upgrades and 2-1⁄2-in. rigid insulation added to the exterior and new siding installed. 

These yielded a 61% heating energy reduction that was attributed primarily to the wall 

insulation, window upgrades, and reduced infiltration.

• GHI frame-brick (end units in two buildings) that had crawlspace, attic, and window/door 

upgrades. These improvements achieved a 34% heating energy reduction that was

attributed to attic insulation, and window upgrades, and reduced infiltration.

• GHI frame-brick (interior units in two buildings) that had crawlspace, attic, and 

window/door upgrades. These improvements yielded a 40% heating energy reduction that 

was attributed to attic insulation, window upgrades, and reduced infiltration.

• GHI frame-vinyl (end units in two buildings) that had crawlspace floor insulation and air 

sealing, attic, window/door, and 1-in. exterior insulating sheathing upgrades. This 

achieved a 42% heating energy reduction that was attributed to attic and wall insulation,

window upgrades, and reduced infiltration.

vii
• GHI frame-vinyl (interior units in two buildings) that had crawlspace floor insulation and 

air sealing, attic, window/door, and 1-in. exterior insulating sheathing upgrades. These 

improvements yielded a 46% heating energy reduction that was attributed to attic and 

wall insulation, window upgrades, and reduced infiltration.

When looking at the overall cost of the upgrades implemented during the pilot program and 

evaluating these costs solely on the basis of energy savings, the simple paybacks are long—29–

70 years. However, with the costs of the upgrades, including new crawlspace vapor barriers, 

windows, and siding (which are replaced on a regular schedule and financed separately), the 

payback periods are reduced by 11–34 years. Based on the type of upgrades—and given the 

more than 30-year periods between major improvements—payback periods of 30 years or longer 

are acceptable.

The analysis of the measured data also highlights the complexity of comparative evaluation of 

the energy use (energy savings) before and after the home retrofits, especially because the 

occupants’ preferences for thermostat setting levels changed after the retrofit. The high energy 

costs prior to the retrofit may have led to lower thermostat settings during the winter in an effort 

to conserve energy; however, envelope improvements helped lower heating energy consumption, 

which led to a higher thermostat setting for improved comfort. This was the case in most of the 

GHI pilot homes. During the latest winter season after the upgrades, the highest average indoor 

temperatures were recorded even though the average outdoor temperature was lower than in any 

of the previous three monitored winter periods.

viii
1 Introduction

A multiyear energy-efficiency retrofit pilot project has been undertaken by Greenbelt Homes, 

Inc. (GHI), a 1,600-unit housing cooperative of circa 1930 to 1940 homes located in Greenbelt, 

Maryland. The three dominant materials of construction of the approximately 800- to 1,200-ft2

townhome units in the community are:

• Frame (2 × 4) with brick veneer (frame-brick or FB, Figure 1)

• Frame (2 × 4) with vinyl siding (frame-vinyl or FV, Figure 2)

• Eight-inch concrete masonry unit block; painted (block or B, Figure 3) or clad with vinyl 

siding (block-vinyl or BV, Figure 4).

Figure 1. FB building

(2 of 4 homes in set)

Figure 2. FV building

(1st home of 4 in set)

Figure 3. B building

(1st home of 4 in set)

Figure 4. B/BV

(2 of 4 homes in set)

1
A detailed summary of the community and of the pilot homes is provided in an initial baseline 

performance report (Wiehagen et al. 2013). The GHI pilot project was envisioned with three 

phases focused on identifying the added costs and energy savings benefits of energy-efficient

features for a set of representative pilot homes. Based on the outcome of the pilot project, select 

energy-efficiency upgrades are to be installed in all units outside of the pilot program during a 

planned community-wide replacement program commencing in 2015. Phase 1 of the pilot project 

consisted of a baseline evaluation of the current operation, use, environmental conditions, and 

energy costs for a representative set of 28 townhomes (units) sited in seven buildings: six block 

units (designated B1 through B6), six block-vinyl units (BV1 through BV6), eight frame-vinyl 

units (FV1 through FV8), and eight frame-brick units (FB1 through FB8). Phase 2 consisted of 

installing the building envelope improvements identified in Phase 1, continuing to monitor the 

energy consumption for the heating season both before and after installation, and performing 

energy simulations supporting recommendations for heating, ventilating, and air conditioning 

(HVAC) and water heating upgrades to be implemented in Phase 3. Monitoring will continue 

through the 2014–2015 heating season.

The U.S. Department of Energy’s Building America (BA) team Partnership for Home Innovation 

(PHI) wrote a report on Phase 1 that summarized a condition assessment of the homes and 

evaluated retrofit options for the homes within the constraints of the cooperative provided by 

GHI (Wiehagen et al. 2013). Retrofit options, estimated costs, and estimated energy savings for 

the pilot homes are summarized in Appendix A.

With the support of National Renewable Energy Laboratory staff, the homes were monitored for 

energy use and indoor temperature and humidity. The recorded data from the energy meters and 

utility meter readings and the monitored energy usage were compared with the computer 

simulation. The results showed that the predictive capability of the software was within 11% of 

actual for the subject set of buildings after three outliers were removed (Wiehagen et al. 2013).

Phase 1 of the GHI pilot program efforts conducted during 2010–2011 included a field 

assessment (which included existing conditions), energy simulations of select options for 

projected savings, building envelope energy improvements, cost estimates, recommendations for 

upgrades, installation and maintenance of monitoring equipment, and maintenance of the data 

produced. Results were published in a report to the GHI community (NAHBRC 2011).

Phase 2 consisted of installing the building envelope improvements identified in Phase 1 and was 

implemented over 3 years. Crawlspace improvements were completed in 2011; attic 

improvements were completed in 2012; and wall, window, door, and exhaust fan upgrades were

completed in 2013. Energy consumption and indoor temperature and humidity were monitored

throughout the staged envelope upgrades. Bath exhaust fans with timed controls were added to 

the work in Phase 2 to provide some mechanical air exchange and to vent the largest source of 

moisture in the homes. An analysis of heating and cooling system upgrades, including simulation 

results and example system installation, was completed in 2013 in preparation for system 

installation and testing in 2014. One aspect of the Phase 2 effort was to evaluate different types 

of heating—and in some cases cooling—equipment for estimated savings and costs.

2
The phases were organized in this sequence to encompass a systems approach to building retrofit 

that evaluated the benefits of envelope improvements independently of any equipment 

improvements. The goal of the GHI buildings committee was to identify envelope improvements 

that would reduce energy consumption, provide a higher level of comfort to members, and 

demonstrate actual costs and payback periods. Based on this investigation, GHI members would 

have much better information to guide their decisions about the large investment necessary for a 

community-wide upgrade. 

GHI has created a reserve fund that is used for replacing the windows, doors, siding, and roofs at 

obsolescence. However, the reserve funds were not intended to cover energy upgrades such as air 

sealing, insulation, or HVAC improvements other than replacing the electric baseboard (EBB) 

heaters as required. This combination of the reserve funds and the opportunity for long-term 

investment in energy upgrades is the primary impetus for the pilot project. The energy-efficiency 

improvements that were not budgeted in reserve funds yielded energy savings that will be 

analyzed; this analysis will provide the estimate of the costs and payback periods for the 

members to make reasonable and informed decisions.

1.1 Pilot Program Background

GHI is a nonprofit entity that was organized to purchase or otherwise acquire, operate, and 

manage housing projects in Greenbelt in the interest of and for the housing of its members (GHI 

2012). A nine-member board of directors hears the five standing committees, makes decisions 

for the corporation, and hires the general manager. The board of directors and management

recognized the impending need to replace numerous components nearing the end of their useful 

lives. In the interest of good governance, the directors and managers polled the community 

members for their input on features that they would like to see incorporated into the scheduled 

renovations. Increased comfort and decreased energy costs achieved with limited lifestyle 

disruption were the overwhelming responses from members who voted to support the pilot 

program—a 28-unit demonstration project of energy-efficient features that could be incorporated 

with the façade and systems updates planned for 2015–2025.

The GHI pilot program was established in 2010 to form the basis for decision making for the 

rollout of a 10-year community upgrade program incorporating energy-efficient buildings and 

equipment with the modernization of other systems and building components such as plumbing 

pipes, windows, and siding replacement. The goals for such capital improvements are to:

• Improve member comfort and “livability.”

• Emphasize the use of sustainable, environmentally friendly energy sources, technologies, 

and products where economically feasible.

• Reduce overall life cycle costs, including preventive and corrective maintenance, for 

heating, cooling, and domestic hot water systems.

• Minimize disruption to households as improvements are being made.

• Implement the program while maintaining the unique and historic character of the GHI 

homes.

3
The pilot program was developed by the buildings committee to have three phases focused on 

identifying the added costs and benefits of energy-efficient features that would be installed 

during the planned replacement timetable commencing in 2015.

Because building envelope energy retrofits necessarily include some surface finish tasks after the 

insulation and air sealing are installed, it is prudent to schedule these tasks with other retrofit 

work, such as siding replacement or interior gut/rehab. Thus, the cost of the energy-efficient

component can be separated from the cost of the façade upgrade, which was going to be 

undertaken regardless.

1.2 Phase 2 Pilot Program Building Envelope Upgrades

Improvement to the walls’ thermal resistance 

from the exterior was identified as a primary 

pathway to long-term energy efficiency and 

member comfort. The FV units are constructed 

of 2 × 4 walls with R-13 wall cavity insulation, 

horizontal board sheathing, tar paper, and vinyl 

siding. The FB units are constructed of 2 × 4

walls with R-13 wall cavity insulation, 

horizontal board sheathing, tar paper, a capillary 

break/drainage cavity, and brick veneer. The 

block units (B) are constructed of 8-in. concrete 

masonry units (CMUs) that have been painted or 

vinyl-sided (BV). Some B units have interior 

furring, air space, and foil backed plaster board 

beneath a plaster finished wall. Others have no 

insulation with plaster directly applied to the 

masonry. The pre-retrofit summary of energy 

features, most of which were installed during the 

1980s upgrades following the oil crisis, is 

included in Appendix B.

In keeping with the owners’ desire to minimize 

lifestyle interruption and maximize benefits from 

scheduled façade replacement work, externally

applied insulation measures were explored.

Computer-generated Building Energy Optimization software v1.2 (NREL 2015) simulations 

were used to identify the energy-efficiency measures (EEMs) that would provide the optimal 

benefits at the least cost. Simulated building savings indicated that these homes could benefit 

from energy cost savings ranging from 9% to 28%—depending on building construction type—

with the implementation of Phase 2 upgrades only (see Table 1). These initial estimates were 

evaluated to provide the largest energy savings with the lowest investment cost before the 

heating (and cooling) systems were analyzed. The cost analysis contains the residential 

electricity cost scheduled by PEPCO, the owner of the local transmission service, at an average 

cost per kilowatt-hour of $0.15 (Pepco). Because the homes are all electric, the energy 

conversions to source energy reflect similar savings percentages.

Q2. Why did we need a pilot program? 

Couldn’t we get reliable information from 

prior industry studies and from modeling?

A2. To decide whether we want to make specific 

improvements to the energy efficiency and 

comfort of our units, we need to know what the 

actual costs and energy savings are for 

alternative improvements used in our particular 

types of homes. The pilot program is providing us 

with: (a) reliable cost and benefit information on 

the energy used in the pilot homes; (b) actual 

installation costs and energy saving data; and (c) 

life cycle costs and payback periods. In addition, 

it is revealing challenges for installing and 

maintaining new, alternative energy-efficiency 

improvements to our homes; helping us learn 

about logistics of such improvements (such as 

how to handle storage in attics during and after 

attic insulation is installed); and teaching us how 

to minimize disruption and inconvenience to 

members during construction.

Response of the Buildings Committee to FAQ by 

the GHI membership.

4
Table 1. Estimated Phase 2 Energy Cost Savings

for Envelope Measures by Building Type

Building Type

Block

8-in. CMU (B) FB FV

Per Building Average Estimates (4 units)

Pre-Retrofit Use, Whole House

(4 homes in building) $9,734 $7,508 $7,730

Post-Retrofit Savings, Whole House

(4 homes in building) Envelope Only $2,680 $702 $1,331

Average Savings, Whole House

(4 homes in building) 27.5% 9.4% 17.2%

Appendix A contains the cost and feature matrix that was developed for the GHI building 

committee’s consideration in providing pilot study recommendations to the membership. EEMs

presented for consideration included overall foundation/floor insulation values between R-5 (B, 

BV, and FB, foundation walls) and R-19 (FV, floors); wall insulation values of R-13 to R-18; 

and an attic insulation value of R-38 (FB and FV). The flat concrete roofs of the B and BV units 

were updated between 1996 and 2004 with R-26 rigid insulation and ethylene propylene diene 

methylene membranes. Improved crawlspace ground vapor barriers and mechanical ventilation 

via timed bath fan exhaust were included with the Phase 2 upgrades to maintain or improve 

indoor air quality after the retrofit.

Overall, the goal of the U.S. Department of Energy’s BA program is to “reduce [existing] home 

energy use by 30%-50% compared to the pre-retrofit energy use” and “develop market-ready 

energy solutions that improve efficiency of new and existing homes in each U.S. climate zone, 

while increasing comfort, safety, and durability (DOE undated).” The GHI pilot program

facilitates the integration of specific data on the energy reduction, cost, and constructability of 

the installed envelope energy retrofit measures. These data will inform the GHI board of 

directors and members about solutions that serve the needs and budgets of the community 

members. Further savings attributed to any heating (or cooling) system upgrades will be 

evaluated following Phase 3 of the pilot program.

A summary list of the upgrades that were suggested and approved by GHI for implementation in 

the pilot program is contained in Table 2. The pilot program consists of seven four-unit 

buildings—one B painted, two buildings with mixed units of B painted and BV, two FV, and two 

FB buildings. Selected energy-efficiency upgrades by building type are noted in Table 2. In 

addition, siding, windows, and doors were scheduled for replacement with the launch of the 

community-wide upgrade.

Because unanticipated complications arose during the bidding process, the crawlspace 

improvements were implemented in fall 2011, the attic improvements in fall 2012, and the wall 

upgrades (except for the EIFS, which has not been implemented) in fall 2013.

5
Table 2. Selected Envelope Upgrades by Building Type

B or BV Buildings FB Buildings FV Buildings

Crawlspacea Repair side wall and slab 

ceiling rigid insulation

Repair side wall and 

slab ceiling rigid 

insulation

Remove FGb batts and 

install R-19 SPFc

Repair and seal GVBd Repair and seal GVB Re-grade and repair 

and seal GVB

Attic n/a

Install 2-in.

XPSe/oriented strand 

board for storage

Install 2-in.

XPS/oriented strand 

board for storage

Air-seal exterior wall 

top plates

Air-seal exterior wall 

top plates

Install an additional 

8- to12-in. (R-38) blown 

cellulose around storage 

area

Install an additional

8- to 12-in. (R-38) 

blown cellulose around 

storage area

Weather strip and 

insulate attic access 

panel

Weather strip and 

insulate attic access 

panel

Walls

Add 2-in. polyisocyanurate

(R-12) and new vinyl siding, 

or, add 3.5-in. expanded 

polystyrene and EIFSf, or 

leave as is (control building)

n/a

Remove vinyl siding, 

install 1-in. XPS (R-5), 

WRBg, and new vinyl 

siding

Windows

Remove and reinstall new 

vinyl sliding windows U =

0.30, solar heat gain 

coefficient = 0.30 with 

flashing and trim included

Remove and reinstall 

new vinyl sliding 

windows U = 0.30, solar 

heat gain coefficient =

0.30 with flashing and 

trim included

Remove and reinstall 

new vinyl sliding 

windows U = 0.30, 

solar heat gain 

coefficient = 0.30 with 

flashing and trim 

included

Doorsh

Remove existing, install 

new prehung insulated door, 

flash, and trim.

Remove existing, install 

new prehung insulated 

door, flash, and trim.

Remove existing, 

install new prehung

insulated door, flash, 

and trim. a Crawlspace of the B, BV, and FB units are monolithic poured concrete from stem walls through first floor slab.

b Fiberglass

c SPF is spray polyurethane foam

d GVB is ground vapor barrier e XPS is extruded polystyrene

f EIFS is exterior insulating finishing system, a wall finishing system that combines typically expanded 

polystyrene foam attached to the wall and covered with a synthetic stucco. The insulation can be installed at 

various thicknesses depending on the level of insulation desired.

gWRB is weather-resistive barrier h Some members elected to keep the existing doors.

6
2 Greenbelt Homes, Inc. Pilot Program Research Investigation

With support from the BA program through the PHI BA team, the GHI pilot program was 

crafted to investigate the potential for energy upgrades to be cost-effective and improve the 

livability of the homes. The phased approach described previously facilitates the research 

investigation. This report focuses on the Phase 2 effort and links the Phase 1 simulation estimates 

and baseline energy measurements with the improvements implemented in Phase 2, the planning 

for specific HVAC modifications, and the resultant energy use measurements. The following 

specific research questions serve as the basis for the investigation:

• How does the energy use for the homes with energy retrofits compare with the preretrofit energy use for space heating and total consumption?

• Can either enhanced energy savings or “take-back” energy consumption be identified 

from the pre- and post-retrofit measurements?

• What is the difference between the average indoor air temperatures for the homes with 

energy retrofit and the pre-retrofit home (and occupants) measurements?

• How does the realized energy savings for the efficiency retrofits compare with the 

realized installation cost of the retrofits?

• What is the homeowner perspective on the home comfort following the energy retrofits?

• How does the relative humidity within the home change from the pre- to the post-retrofit 

conditions?

• What is the change in the crawlspace environmental conditions from the pre- to postretrofit conditions?

• What is the comparison between the metered energy use data (electric utility meter) and 

the measured daily energy use and can this relationship be standardized for similar 

analysis in homes in heating climates to avoid costly instrumentation?

7
3 Retrofit Designs and Construction Process

A primary goal of the pilot project is to develop the process to implement energy retrofit 

upgrades throughout the GHI cooperative. This process, typically handled by a remodeler or 

trades contractor in an individual home, is much broader and more complicated when it is 

implemented community wide.

3.1 Design Details and Bid Process

Using pilot homes and members as willing participants in the process, the perceived path to 

completion of the pilot retrofits consisted of GHI’s engagement of the services of an architectural 

and engineering firm (A&E) to define the existing conditions and recommended upgrades to 

each building type. Once the details were developed, these were formatted into a scope of work 

and placed out for bid. But because of the uniqueness of the construction and details of the GHI 

buildings, the reliance of the A&E industry on generic details that were not applicable to the 

actual conditions, and boilerplate requirements for contractors working in the GHI cooperative,

the details did not provide the intended design and instructional framework for the energy 

upgrades. Several rounds of GHI requesting proposals resulted in bids that were considerably 

higher than estimated, which stalled progress. The process was originally envisioned as:

1. A&E submits design, including details of existing conditions and integration details for 

the proposed thicker walls and window and door components.

2. GHI requests bids of contractors based on A&E-produced plans.

3. Build from plans and specifications after GHI accepts the bid.

GHI found that the process wasn’t as straightforward as desired. Causes ranged from 

unfamiliarity with unique or uncommon building construction types to a delayed selection of 

window and door style/type decisions that are dependent on individual homeowners and GHI’s 

insurance and unique working hours specifications. Because of the bidding process, the window 

supplier and installation subcontractor and installation methodology were selected by GHI 

independently of consultation with the general contractor or with the PHI team. This caused the 

prime contractor to be delayed in installing windows or doors and in resolving the discontinuity 

in the drainage plane caused by the selected window installation method—a block frame

(retrofit) window that might have been more efficiently installed as a flanged window.

Adding to the complexity of the bid process was the selection of an EIFS as one of the exterior 

finishes intended for the B buildings. This system was originally considered as a solution that 

might be more flexible in providing details that would more closely resemble the look of the 

original block construction. The EIFS installation was postponed indefinitely because of the cost 

and complexity of integrating it with the windows and door components in a retrofit situation, 

but the concept may be revisited once the other wall upgrades have been completed.

The shortcomings of the design-bid-build process flow are often obvious in many retrofit 

projects where construction modifications are made after the work has been initiated. In this 

case, the variation in building types and the wide range of the scope of work created a significant

challenge to define all details of the upgrades before the bid process was initiated.

8
Fortunately, the oversight of the GHI project manager, the dedication of the GHI buildings 

committee, the attention to detail by the general contractor, and the continued support of the BA

program allowed for ongoing and timely decisions that accommodated the many questions that 

arose during the upgrades. Without these partners and their level of commitment to the project 

success, project costs would likely have increased significantly and durability concerns may have 

arisen. Cost increases would have been incurred from added materials and labor for window 

installation, siding trim details over thick foam, and other issues. Durability concerns might have 

arisen, such as from the location of the drainage plane, window flashing, flashing of thicker foam 

integrated with existing roof flashing, attachment of furring strips through thick foam, and siding 

attachment to furring strips. The partners helped to resolve many of these issues and achieve 

outcomes that can be repeated in other community-wide upgrades.

The team continued to communicate during the retrofit process for each building, working 

through details as they arose and reviewing the solutions after the installation to document 

opportunities for changes and improvements in preparation for the community-wide upgrade. 

This approach will enable future work to be estimated more precisely and installed with more 

defined steps and sequencing—all aspects that enhance affordability.

By a similar approach, after the completion of the crawlspaces, PHI translated a new 

construction scope of work for the construction of crawlspaces to one that could serve as an 

inspection, design, build, and quality management system report to aid in the retrofit of existing 

building foundations. GHI will use this report (Del Bianco et al. 2013) to guide the improvement

program in assessing crawlspace retrofit needs and solutions as the community-wide upgrade is 

initiated after the pilot program’s results are reviewed.

3.2 Additional Analysis Required

Another development that arose after the start of the pilot project was a renewed interest in 

maintaining the original exterior façade and look of the buildings, especially the B buildings. The 

pilot homes (B1 to B4), which had been anticipated at the outset of the pilot program to be 

retrofitted with EIFS, emerged at the center of an inquiry supported by the Maryland Historical 

Trust to investigate opportunities to leave the exterior of the B buildings unchanged and insulate 

their interiors. The issue raised with the Maryland Historical Trust suggested that the historical 

significance of the B buildings might be lost by covering the painted CMU of one B building in the

pilot program. Figure 5 shows the original drawings of the B buildings, including the casement 

style windows. The block is shown unpainted. Figure 6 shows a B building after the 1980 

upgrades, which included the change to a slider type window.

9
Figure 5. Original design of B homes

Figure 6. Painted B home with circa 1980 window upgrades

Although the specifics of building cladding types, including the use of EIFS on the exterior of 

the B buildings, had been vetted by the community nearly 2 years earlier, the interior insulation 

options were raised as alternatives to exterior claddings. The Maryland Historical Trust

recognizes part of the community as a “Greenbelt Historic District,” the originally developed 

inner core of GHI, which was known for “the predominant building type of multistoried 

apartment houses.” The National Historic Trust comments that, “Settled in 1937 as a cooperative 

New Deal era community, Greenbelt is now nationally recognized for its unique design and 

strong sense of place,” inferring that the historical recognition is designated by the community 

and its infrastructure and orientation rather the architecture per se (Maryland Historic Trust).

The Maryland Historical Trust provided a grant to an architectural firm (through GHI) to study 

alternative cladding methods. The PHI BA team was asked to provide a follow-up analysis of 

10
interior insulation options consistent with the study that was originally performed using exterior 

insulation options. Results are covered in Table 3.

Table 3. Simulated Energy Savings of Various Insulation Methods for B Units

Type of Usage

Existing 

Usage 

(kWh)

Insulation System Upgrade Option

Exterior 

EIFS/Glass FiberReinforced 

Concrete

R-12 Addedb

Interiora

R-5 Added

Interiora

R-7.5 

Added

End Unit, Heating Energy, 

kWh 8,001 3,016 4,756 4,074

End Unit, Heating Energy 

Savings 62% 41% 49%

Interior Unit, Heating 

Energy, kWh 4,481 1,628 2,824 2,407

Interior Unit, Heating 

Energy Savings 64% 37% 46%

Whole Building, Heating 

Energy, kWh 24,964 9,288 15,160 12,962

Whole Building, Heating 

Energy Savings 63% 39% 48%

a Assume 8% of end unit and 12% of an interior unit wall area are left uninsulated because of kitchen and bath 

features.

b EIFS/glass fiber reinforced concrete upgrades are exterior-applied insulation systems of equal R-value.

If an internal wall insulation upgrade option were selected, the small interior area of the B homes 

(844–1,596 ft2) would require that members and their possessions be moved out of the homes for 

the 7- to 14-day period that would be required to complete the interior retrofit of insulation and 

gypsum with a painted finish. Cabinetry and appliances in the kitchens and baths that span 

exterior wall surfaces would preclude those areas from being retrofitted from the inside, because 

removing and reinstalling these are neither affordable nor practical. GHI required that temporary 

storage and relocation be included in the project’s estimated cost; thus, retrofitting from the 

inside was more expensive than the cost estimates attached to the exterior applications in the B 

and BV CMU units. 

Because the interior insulation options had higher costs and lower energy savings, these were 

determined to be less cost-effective than an exterior insulation option. These results provided the 

GHI administration with additional detailed information to make an informed decision about 

energy-efficiency upgrades in the community.

This additional analysis provided confirmation of the original direction for the pilot program in 

terms of cost-effective energy-efficiency upgrades.

11
4 Crawlspace and Attic Upgrades

The work was undertaken in stages because of the complicated bidding process and the extensive 

range of the energy upgrade. All activities were originally intended to be performed over a 6-

month period that would include crawlspace, attic, wall, and window and door upgrades. Even 

so, the work scope was deemed sufficiently extensive and complicated for such a large pilot 

program that a staged process was initiated to tackle different building components. The pilot 

homes are configured in sets of four attached homes.

4.1 Crawlspace Retrofits

In fall 2011, crawlspace upgrades were commenced and completed for all pilot homes. The 

crawlspace retrofits (refer to Table 2) were performed on each of the seven building sets (28 

homes) based on its condition. The B and FB buildings have monolithic poured concrete 

crawlspace foundations from the stem walls through the first-floor slabs. The walls were

insulated with 2-in. XPS foam board in the 1980s; it deteriorated over time in some locations. 

The porch slab extensions on each home also have crawlspaces beneath that communicate with 

the home crawlspace, but these areas had previously been covered with a sheet of foam board, 

much of which had deteriorated. The crawlspaces are effectively semiconditioned, but the 

monolithic concrete construction prevents direct communication with the home.

The FV homes have wood frame floors that sit on concrete blocks and brick stem walls. The 

floors are insulated, resulting in unconditioned crawlspaces. Automatic vents allow ventilation in 

the crawlspaces, which close when the temperature falls below freezing.

Each crawlspace foundation has a ground vapor barrier that in all cases that were inspected had

deteriorated over the years. Of the 28 pilot homes, two have a basement level that is above grade 

on the back side to the rear yard. These basement foundations abut the concrete crawlspace of 

the adjoining two homes in the building. 

4.1.1 Frame-Vinyl Pilot Home Crawlspace Upgrades

The insulation and the ground vapor barriers in the FV homes’ crawlspaces had deteriorated 

extensively (Figure 7).

Repairs and upgrades consisted of insulation and ground vapor barrier improvements (Figure 8). 

The fiberglass batt insulation in the floor joists had been disturbed to the point where they had to 

be removed and replaced. Three to 4 in. of SPF insulation was installed in place of the fiberglass 

batts at the underside of the first-floor decks. The SPF provided an air seal in addition to a 

thermal resistance value of approximately R-6 per inch. The value of the new insulation brought 

the R-value of the floors to R-19 from an inconsistent R-11. The contractor also removed and 

replaced all ground vapor barriers and sealed the new ones to the walls and columns of the 

foundations.

12
Figure 7. FV building crawlspace

prior to upgrades

Figure 8. FV crawlspace

after upgrades

4.1.2 Block and Frame-Brick Crawlspace Upgrades

The B, BV, and FB buildings are constructed of 5-in. concrete slabs supported by 8-in. integral 

poured concrete foundation walls. The crawlspace walls were insulated with rigid XPS in a 1980 

renovation to provide a sealed, conditioned crawlspace. Water heaters that service the units are 

housed in the boiler rooms that allow access to the crawlspaces and are open to the crawlspaces 

in each building. 

Some of the insulating foam boards had fallen off the foundation walls and some of the exterior 

porch slabs had not been insulated in the earlier retrofit, so these areas were noted for insulation 

installation. The ground vapor barrier required repair and sealing to the foundation walls to 

mitigate ground surface moisture entering the crawlspace (Figure 9 and Figure 10).

Figure 9. B building crawlspace

prior to upgrades

Figure 10. Building crawlspace

after repair/retrofits

13
4.1.3 Frame-Brick and Frame-Vinyl Attic Upgrades

Attics of the wood-framed buildings were constructed with 2 × 8 floor and ceiling rafters and 

originally were insulated with about 6 in. of blown insulation (R-19) at the attic floor. Figure 11

shows typical attic framing and floor.

Figure 11. Typical attic of the wood-framed buildings

Most attics were sheathed with boards, which provided a storage area. This feature impeded 

installation of additional insulation in that area if a storage platform were to be maintained. The 

solution was to add 2 in. of rigid foam and wood sheathing on top of the approximately 192 ft2 of 

surface of the storage area that was to remain.

1 Figure 12 shows the insulation board at the attic 

access and Figure 13 shows the protective sheathing over the foam board. The added XPS 

provided an additional R-10 of thermal resistance at the storage areas.

Figure 12. Foam board at attic storage area Figure 13. Wood sheathing installed over the 

foam board to maintain an attic storage area

1 To avoid damage to the ceiling below, the existing flooring was left and insulation board and a durable surface 

added to keep some area for storage.

14

 
Dams made from rigid foam boards were installed around the storage area to hold back the 

blown insulation that was added to the attics because the depth of the blown-in insulation 

exceeded the storage deck level by approximately 5 in. (Figure 14).

The attic retrofit included air sealing the exterior gable end top plates (Figure 15) and the exterior 

eave top plates (Figure 16), repairing eave baffle installation, and weather stripping the attic 

access hatches. The completed insulated attic storage area and surrounding insulation are shown 

in Figure 17.

Figure 14. Insulation baffles at edge of new 

storage area

Figure 15. Gable end wall air sealing

Figure 16. Exterior top plate air sealing Figure 17. Completed attic retrofit

The attic upgrades included insulation over and air sealing around the access hatch, and in some 

cases covers for the attic hatch. 

15
5 Wall, Window and Door, and Exhaust Fan Upgrades

GHI staff planned to request a second set of bids for the wall insulation, window and door 

replacement, and bath exhaust fan installation in the selected pilot homes according to the 

original pilot home study plan, with one notable exception. The installation of the EIFS system 

was postponed indefinitely because bids for that project were received that significantly 

exceeded earlier estimates from contractors and because issues were raised with covering the 

original block buildings.2

An outline of the wall efficiency upgrades for the pilot homes is shown in Table 4.

Table 4. Summary of Wall Insulation Upgrades for GHI Pilot Homes

Pilot Home 

Reference

Building Type

Existing Condition Wall Efficiency Upgrades

B1–B4 Block, uninsulated Window and door replacement, exterior insulation 

postponed indefinitely, bath exhaust fans

BV1 and 

BV2

Block, existing vinyl 

siding, 3⁄4 in. of foam board 

between furring

Window and door replacement, remove existing 

wall coverings, add 2 in. of insulation board and 

new siding, bath exhaust fans

B5 and B6 Block, uninsulated Window and door replacement, add 2 in. of 

insulation board and new siding, bath exhaust fans

BV3–BV6

Block, existing vinyl 

siding, 3⁄4 in. of foam board 

between furring

Window and door replacement, bath exhaust fans

FB1–FB8 Frame, brick veneer, 

existing cavity insulation Window and door replacement, bath exhaust fans

FV1–FV8 Frame, vinyl siding, 

existing cavity insulation

Window and door replacement, remove existing 

wall coverings, add 1 in. of insulation board and 

new siding, bath exhaust fans

The wall upgrades were completed by the end of 2013.

5.1 All Pilot Homes—Window Replacement

Windows were replaced on all pilot homes, except in a few cases where the windows had been 

recently replaced. The procurement process established by GHI resulted in selection of a window 

manufacturer that installed its own product. The window procurement process functioned in 

parallel with other wall upgrades; the integration of the window replacement with the new 

exterior insulation and siding was detailed during the installation process—not an ideal approach 

and one that will be addressed before the community-wide upgrades begin. When evaluated 

across all of the pilot homes, the window installation was complicated by:

2 The pilot building (Units B1 through B4) was determined, based on energy simulation estimates, to show the 

greatest energy savings of any of the pilot homes following the wall insulation upgrades. This building has little 

insulation and high utility bills showed high energy use (refer to Appendix C for a summary of energy 

measurements over previous heating periods).

16

 
• The different types of buildings into which the windows were installed, i.e., 8-in. thick B, 

BF, and wood frame with vinyl siding and trim

• The requirement that little or no interior work be required. i.e., all replacement windows 

were mounted to the interior (because the prime contractor was tasked to perform interior 

rework)

• The complete window integration, including all flashing and trim details, which had to be 

completed by the window installer independently of the siding contractor.

These requirements resulted in multiple integration details that required resolution during the wall 

insulation and siding upgrades. Of these details, the one that appeared most problematic was the 

use of window flashing material around the rough opening before the window was installed. 

The window manufacturer/installer had a well-defined methodology for installing replacement 

windows:

1. Remove the existing replacement window.

2. Install the new window from the exterior using the interior window trim as the frame’s 

backstop.

3. Apply SPF around the new window from the exterior.

4. Flash the window to meet the existing exterior window trim or wall cladding.

5. Caulk all seams, cuts, and joints in the flashing to protect against water intrusion.

To enhance the long-term durability and provide moisture protection from window leaks and to 

accommodate the detail of the additional thickness of exterior insulation the window 

manufacturer/installer was asked to modify its typical installation to include sill pan flashing 

with flexible, self-adhering flashing to integrate the new window flashing/trim with the wall 

insulation.

5.2 Block Home Window and Wall Upgrades

Wall efficiency upgrades in the block buildings (both uninsulated B and BV with 3⁄4-in. foam 

board insulation with vinyl siding) included replacement windows and doors. On one building

the upgrade included 2-in. foam board insulation and new vinyl siding. 

5.2.1 Window Upgrades

The window replacement details included installing the replacement window into the original 

wood window frames and integrating the window trim flashing with the exterior wall. In the B 

buildings that do not have exterior insulation, the windows were flashed directly to the block 

edge and caulked. This method was used for all the replacement window upgrades installed in 

the 1980s. Figure 18 shows the window framing after the old replacement window was removed. 

The interior trim, which will provide the interior finish and backstop for the frame of the new 

replacement window, is visible. Flexible flashing was used over the original window sill and the 

edges of the window were spray foamed to provide an air seal (Figure 19).

17
Figure 18. Window rough opening prior to 

window installation

Figure 19. New replacement window installed 

over sill flashing and foamed

Where the block was to remain uncovered, the window trim was installed to the inside of the 

window rough opening and caulked at all trim edges and joints (Figure 20).

When insulation was to be added to the exterior of the block buildings, an entirely different detail 

was developed. In this case, the window flashing was integrated with the foam insulation under the 

furring strips and taped (Figure 21). In all cases the window trim flashing (and caulking) serves as 

the primary water barrier.

Figure 20. Window trim installed to the block 

rough opening and caulked

Figure 21. Window flashing integrated with 

foam insulation

The BV3–BV6 units in the pilot program had window and door upgrades; however, the existing 

siding was left unaltered. The energy savings and air infiltration results will be evaluated based 

on the crawlspace improvements and window replacements only. Because each of these units 

had been clad by different siding contractors and existing window details were not standard at 

the outset, the windows were installed with counter-flashed window trim that was integrated with 

the existing siding. Figure 22 shows the replacement window installed before the new flashing;

Figure 23 shows a completed window installed with new flashing trim.

18
Figure 22. Replacement window installed

in a BV unit

Figure 23. BV building with new windows

and trim

5.2.2 Block Building Insulation

The B building upgraded with exterior insulation consisted of BV units on the end and 

uninsulated B units in the middle (Figure 4). The existing siding on the end units, furring, and 

insulation board were removed and discarded. Two-inch-thick polyisocyanurate rigid foam 

(polyiso) was specified on all units in the building. The polyiso was tacked in place on the wall 

using adhesive, taped to serve as a WRB, and then permanently fastened with concrete screws 

spaced at 24 in. along furring strips placed at 16 in. along the length of the building (Figure 24). 

The screw holes were predrilled for the 4-in. × 1⁄4-in. drill bit fasteners that were to fasten through 

the furring strip and 2 in. of polyiso into the CMU walls. No anchors were required.

Figure 24. Block building with 2-in. rigid foam and furring

After this assembly was completed, 1⁄2-in. XPS foam was installed between the furring strips with 

adhesive to create a smooth, solid surface behind the vinyl siding as recommended by the vinyl 

siding manufacturer to preserve the warranty. Figure 25 shows the polyiso insulation, furring 

strips, additional insulation, and window flashing using the flashing trim. The vinyl was installed 

conventionally—secured to the furring with roofing nails. Figure 26 shows the finished product.

19
Figure 25. Block building with exterior 

insulation installed

Figure 26. Completed block building with all 

energy upgrades installed

5.3 Frame-Brick Window and Door Replacement

The pilot program includes two FB buildings (eight units). These units were to have window and 

door replacements as well as the crawlspace improvements (similar to that of the block 

buildings). The window replacements were integrated with the original window framing, similar 

to the replacements that were implemented in the 1980s. Figure 27 and Figure 28 show the new 

window installed in an FB unit.

Figure 27. Replacement window in FB unit Figure 28. FB replacement window—flashing 

and caulking

5.4 Frame-Vinyl Wall, Window, and Door Upgrades

Energy retrofits to the FV buildings (Figure 29), in addition to the crawlspace and attic 

improvements outlined earlier, consisted of removing the existing siding and windows, installing

replacement windows and doors, and installing 1-in. rigid foam board insulation, a WRB, and 

new siding. Both FV buildings (eight units) were improved with these same features. As is 

common with remodeling efforts, the homeowners made some decisions that directly affected

the work scope after the work had already commenced. In this case, the decision to cover an 

inoperable exterior trash door was made while the job was in progress, thus requiring onsite

20
changes to the siding installation. Similar changes were necessary for some windows where the 

interior trim was not the standard installation that had been encountered in previous units.

Figure 29. Typical front elevation, FV building

5.4.1 Window Replacements

As with the established installation method, the window upgrades were made using replacement 

windows installed to an interior stop bead so that no interior trim work or painting was required. 

Sill flashing was installed at PHI’s request after the window was removed (Figure 30).

The existing windows were removed and the new windows installed after the siding was 

removed and 1-in. XPS was installed. This resulted in a wall thicker than that of the original 

window jamb trim (Figure 31).

Figure 30. Window sill flashing on an FV unit Figure 31. Foam board extends

beyond original window trim

21
If the existing trim is undamaged, removing it is not preferable for a variety of reasons, including 

avoidance of disposal and disturbance of old paint layers. For aesthetic purposes, a new 1-1⁄4-in.

thick pine board was installed over the original picture frame trim of the windows and covered 

with the window counter flashing that was custom made onsite of aluminum coil stock with a 

vinyl surface coating. SPF was applied as an air seal (Figure 32). An integral flashed edge butted 

the XPS foam board. Next, a WRB was installed over the foam sheathing and taped to the 

window trim counter flashing (Figure 33 and Figure 34).

The interior of the window required only caulking to finish (Figure 35).

Figure 32. Additional window

trim and foam sealing

Figure 33. Replacement window

installed and flashed

Figure 34. Additional window

trim and foam sealing

Figure 35. Replacement window 

installed and flashed

22
For the second of the two FV buildings, a slightly different installation method was employed to 

integrate the window with the new foam board. Once the existing siding was removed, the foam 

board was installed and covered with a WRB (Figure 36) with overlap that would be folded into 

the window opening before the replacement window was installed (Figure 37).

Figure 36. WRB installed over foam sheathing 

(not shown)

Figure 37. WRB wrapped into

window opening

The window was installed with SPF for air sealing and with the trim’s counter flashed edge taped 

to the WRB (Figure 38).

Figure 38. Window trim flashing integrated with WRB

This window installation methodology was somewhat more acceptable to the trade contractors.

The driving force behind the use of the installation details was that the windows had to be 

installed independently of all other wall upgrades. This was because the contractor’s 

independence was based on the separateness of the contract. This approach is often not ideal but 

23
is common in residential retrofit projects. The requirement that as little interior work as possible 

be performed also drove the windows installation method because the windows had to be inset 

rather than installed as new construction flanged at the face of the added wall thickness, which 

would have been the ideal installation for ease of detailing.

5.4.2 Frame-Vinyl Wall Insulation Upgrades

After the siding was removed, foam board insulation was installed over the existing wall. Figure 

39 shows the wall with the siding removed and the building paper installed over the board 

sheathing. One-inch-thick foam sheathing was installed (Figure 40) over the wall and covered 

with a WRB (Figure 41). This procedure was used because the foam was often installed in 

smaller pieces because the irregular openings in the building would have required extensive tape 

and detailing to completely seal out air and moisture. New siding was installed to complete the 

exterior (Figure 42).

Figure 39. Original building paper

on frame building

Figure 40. Foam sheathing installed

Figure 41. WRB installed over

foam sheathing

Figure 42. New siding installed following 

windows, doors, insulation, and WRB

5.5 All Pilot Homes—Exhaust Fan Installation

An important aspect to the energy upgrades was the installation of exhaust fans in the bathrooms 

of the pilot homes. Few fans had been installed and interior humidity could be quite high in 

winter in some homes, particularly the B homes. The exhaust fans were specified to reduce 

24
interior relative humidity, which was expected to increase during the heating season as building 

infiltration decreased after new efficiency features were installed. The fans and a controller allow 

the occupants to control operation and satisfactorily mitigate excess relative humidity.

Installing the fans was challenging, especially in the B homes where core drilling in the allconcrete envelope was necessary. Because these homes are constructed with block walls and 

poured concrete floor and roof decks, the least-cost approach was to core drill the bathroom wall. 

One such core wall bore is shown in Figure 43.

Figure 43. Core from B home for an exhaust fan

The through-the-wall fan selected for installation did not include an exterior hood cover; thus, 

the fan hood that was used (Figure 44) required an adaptor to match with the fan duct diameter. 

An air seal at the hood junction and around the fan and grille (Figure 45) was effected using tape 

and SPF, respectively. The fan was wired to a timer switch via surface wire placed in conduit, as 

was commonly the wiring detail in the B buildings.

Figure 44. Exhaust fan hood and sleeve adaptor Figure 45. Interior exhaust fan grille

25
5.6 Energy Upgrade Feature and Monitoring Description

A summary of the upgrades performed on each of the 28 GHI homes in the pilot program is 

shown in Table 5. The nomenclature for each type of building and unit within the building is 

used throughout the analysis part of the investigation. Double horizontal lines in Table 5 denote 

the end of one building and start of another.

Table 5. Summary of Energy Features for Each Pilot Home

GHI Pilot 

Home

Crawlspace 

Wall 

Insulation

Crawlspace 

Floor 

Insulation

Wall 

Insulation

Attic 

Insulation, 

Air Seal

Windows Bath Fan

B-1   

B-2   

B-3   

B-4   

BV-1    

B-5    

B-6    

BV-2    

BV-3   

BV-4   

BV-5   

BV-6   

FB-1   

FB-2    

FB-3    

FB-4    

FB-5  

FB-6    

FB-7    

FB-8    

FV-1     *

FV-2     

FV-3     

FV-4     

FV-5     

FV-6     

FV-7     

FV-8     

B is Block building (6 homes), uninsulated; BV is Block building with vinyl siding (6 homes); FB is Frame 

building with brick veneer (8 homes); FV is Frame building with vinyl siding (8 homes); 

Note: Unit B4 had a ductless heat pump installed in fall 2012.

26
6 Infiltration Testing

To quantify the convective losses from building leakage, each home was blower-door tested at 

the time it was originally assessed. Results indicate the volume of air leakage to the outside (or 

adjacent units) when the home is depressurized with a fan. Air leakage measurements indicate 

energy losses from unconditioned air leaking into the home or conditioned air leaking out of the 

home. Air leakage measurements are made at a standard pressure (50 Pascals) to compare 

buildings. The measurement of air leakage volume is divided by the volume of the house to 

establish a standard metric for each home—the number of house air changes per hour at the 50 

Pascal pressure (ACH50). 

An appropriate amount of fresh outdoor air is desirable for good indoor air quality, but excessive 

air leakage simply wastes energy. Building codes and standards differ on the maximum air 

leakage rate that is desirable in homes; generally, 7 ACH50 is understood as a maximum target. 

New residential building codes for climate zone 4 require no more than 3 ACH50, but a 

ventilation system must be installed to add fresh air into the house. Older homes are very 

leaky—10 ACH50 or higher is very common. This much leakage wastes energy and causes 

comfort problems. The goal of the GHI pilot program was to reduce energy-wasting leakage to 

around 7 ACH50. 

Largely because of the method and material of construction, the CMU B buildings were the most 

airtight as a group and required very little air sealing beyond the best practice details associated 

with installing new windows, doors, and fans. The frame walls of the FB and FV buildings allow 

air leakage between the house and the attic because of wiring holes through wall top plates and 

continuous balloon framing. In balloon-framed construction the exterior wall studs extend from 

the first floor to the second-level ceiling as one length. The sheathing on these homes is usually 1

× 6 in. or 1 × 8-in. boards that allow air leakage where boards meet. The FV homes also had air 

leakage to the crawlspace via abandoned wiring holes and gaps in the wood flooring’s tongueand-groove joints. (The flooring served as sheathing and finished floor.) The closed-cell SPF 

installed at the crawlspace ceiling in November 2011 should have stopped air leakage through 

the floor. In fact, the FV and FB homes showed an average 15% improvement in air sealing after 

the crawlspace insulation was installed. 

Table 6 summarizes the results of all blower door tests conducted on the homes after the floor 

insulation was upgraded (November 2011) in the FV homes, the attic insulation upgrades 

(November 2012) in the FB and FV homes, and finally the window and wall upgrades 

(November 2013) performed to some extent in all pilot homes. A lower ACH50 number 

indicates less air leakage into and out of the home.

For each unit, an unguarded blower door test was performed to first measure total house leakage, 

and then a modified guarded blower door test3 was performed with the adjacent unit(s) 

3 In this case, a modified guarded test was performed that refers to a test with one adjacent unit at a time

depressurized, which eliminates any leakage between units. The leakage measured in a guarded test will be the 

leakage to outside.

27

 
depressurized to measure net leakage to outdoors. All reported blower door test results are net 

leakage to outdoors (Table 6).

Table 6. Results of Guarded Blower Door Testing—Net Leakage to the Outside

Pilot Home

Original 

Test-In 

Data

(ACH50)

Following 

Crawlspace 

Upgrades

(ACH50)

Following 

Attic 

Upgrades

(ACH50)

Following 

Window and

Wall Upgrades

(ACH50)

Percent 

Change 

From 

Original

B-1 4.7 2.7 43%

B-2 3.3 2.9 13%

B-3 2.4 1.7 30%

B-4 4.8 2.9 40%

BV-1 7.2 5.9 18%

B-5 4.3 2.8 34%

B-6 8.4 4.3 48%

BV-2 4.8 3.2 33%

BV-3 7.5 4.8 36%

BV-4 3.5 3.2 10%

BV-5 4.3 3.6 17%

BV-6 4.0 2.9 26%

FB-1 10.4 8.8 9.2 11%

FB-2 6.8 6.4 6.5 4%

FB-3 7.4 6.4 5.8 21%

FB-4 8.0 7.7 7.2 10%

FB-5 6.1 5.9 6.2 -2%

FB-6 8.8 7.4 7.8 11%

FB-7 11.9 10.2 10.0 16%

FB-8 5.5 5.4 5.5 0%

FV-1 9.7 9.6 8.6 7.4 24%

FV-2 13.1 10.7 8.4 8.5 35%

FV-3 9.3 9.7 8.4 6.8 27%

FV-4 14.1 10.6 10.5 8.6 39%

FV-5 14.0 13.3 11.4 10.4 26%

FV-6 14.8 8.3 7.0 5.8 61%

FV-7 10.1 9.2 7.9 7.1 30%

FV-8 11.2 10.4 9.5 6.8 39%

All Block 4.9 3.4 31%

Frame-Brick 8.1 7.3 7.3 10%

Frame-Vinyl 12.0 10.2 9.0 7.7 36%

Note: Windows were not replaced in FB-1 and FB-5. Bath fans were added to the homes, which will slightly add 

to infiltration losses.

28
After the floor was insulated in the FV buildings, the average reduction in air infiltration rates 

was about 15% across all eight FV homes. After the crawlspace was air sealed, the range of 

reduction was quite large; one home sustained a small increase in infiltration rate, a few homes 

experienced little change, and one home retested with a large decrease in infiltration. However, 

following the attic air sealing and insulation upgrades all the FV homes showed a decrease in the 

infiltration rate compared to the original tests; the overall average reduction was 26%. For the FB

homes, the average reduction in the infiltration rate was 10% after the attic upgrades.

After the window, door, and wall insulation upgrades, the final infiltration tests showed a 

significant decrease in infiltration rates across all homes. Twenty-two of the 28 homes remained

at or achieved the 7 ACH50 or lower goal. Homes with limited air sealing opportunities caused 

by inaccessibility in additions or attics had higher air leakage rates. Figure 46 graphically 

summarizes the infiltration test results.

Figure 46. Graphical representation of air leakage in pilot homes

29
7 Heating Season Comparison

Comparing energy data gathered over multiple heating seasons requires an analysis of the 

severity of the heating season during which the data are gathered. A review of average 

temperature data over a span of three winter periods shows that not all heating seasons are alike. 

The variations between winter seasons are shown in Figure 47 (2010–2011), Figure 48 (2011–

2012), Figure 49 (2012–2013), and Figure 50 (2013–2014) range from below normal to much 

above normal the next winter season and back to above normal during the third winter period to 

below normal in the most recent winter period (National Oceanic and Atmospheric 

Administration). For the 2013–2014 heating season, the time period is 1 month earlier to keep 

the similar formatting in previous years.

Figure 47. NOAA heating ranks—2010–2011 Figure 48. NOAA heating ranks—2011–2012

Figure 49. NOAA heating ranks—2012–2013 Figure 50. NOAA heating ranks—2013–2014

Over the past 4 years of the pilot program, GHI members experienced significantly different 

heating seasons during which the energy use for heating an occupied home was also expected to 

vary considerably. Therefore, temperature severity was commonly reported in context with 

energy use for heating. Calculating heating degree-days (HDDs) is a common method used to 

30
establish a perspective for gauging energy usage for heating a home. To calculate an HDD the 

average of the daily maximum and daily minimum temperatures is subtracted from 65°F and the 

difference is aggregated throughout the heating season. The more HDDs in a season, the colder 

the daily average temperatures are. The baseline used to compute HDDs is 65°F, which is a 

moderate temperature thought to require neither supplemental heating nor cooling. The weather 

data for this report were obtained from a National Weather Service station located at College 

Park Airport, which is within 5 miles of the GHI project center (station KCGS) and verified to 

the data from measurements made near the GHI main office. Table 7, Table 8, and Figure 51

summarize the weather data for each of the four heating seasons monitored through Phases 1 and 

2 of the pilot program.

Table 7. Monthly Ambient Temperature for Four Heating Seasons

Average 

Temperature 

°F, 2010–2011

Average 

Temperature 

°F, 2011–2012

Average 

Temperature 

°F, 2012–2013

Average 

Temperature 

°F, 2013–2014

October 59.8 56.6 60.0 59.9

November 48.6 51.2 44.3 44.9

December 34.8 43.3 44.7 41.4

January 33.1 39.6 39.4 29.9

February 41.3 41.9 37.6 35.4

March 46.5 55.4 43.4 40.4

April 60.2 55.7 57.6 54.2

Average 46.3 49.1 46.7 43.7

Table 8. Monthly HDDs for Four Heating Seasons

Monthly HDDs

2010–2011

Monthly HDDs

2011–2012

Monthly HDDs

2012–2013

Monthly HDDs

2013–2014

October 191 264 143 217

November 493 413 629 609

December 940 676 626 736

January 993 787 795 1089

February 666 671 797 828

March 570 314 667 761

April 213 304 255 338

Total 4,064 3,427 3911 4578

HDDs represent the number of degrees that a day’s average temperature is below 65°F, in this table summed over a 

monthly period. For example, October 2010 with 191 HDDs averaged 6.2°F per day below 65°F; January 2014 with 

1089 HDDs averaged 35.1°F per day below 65°F.

31
For the heating period analyzed, the second winter season had about 20% fewer HDDs than the 

first season, the third heating season had about 4% fewer HDDs than the first season, and this 

last heating season had about 9% more HDDs than the baseline first heating season.

Figure 51. Graphical representation of ambient weather factors

0

150

300

450

600

750

900

1050

1200

1350

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep

Average Daily Temperature, 

Heating Degree Days (65F Base)

°F

Avg. Daily Temp. (2010-2011) Avg. Daily Temp. (2011-2012) Avg. Daily Temp. (2012-2013) Avg. Daily Temp. (2013-2014)

HDD 2010-2011 HDD 2011-2012 HDD 2012-2013 HDD 2013-2014

32
8 Monitored Data—Indoor Temperature and Energy Use

The GHI pilot program has now been through four heating seasons that have been monitored to 

catalog energy use, interior temperatures, and relative humidity. The baseline heating season 

(2010–2011) was the second most severe that the area has seen in the last 4 years. This latest 

heating season had colder average temperatures than the previous three winters. The recorded 

indoor conditions (temperature and humidity) and the measured energy use during the winter 

periods followed several phases of building improvements that were implemented in the homes. 

A summary of improvements for each unit by construction type is covered in Table 2 and 

Appendix B. An overall summary of the building improvements made before each heating 

season include:

• Season 1, 2010–2011: baseline year, no improvements made

• Season 2, 2011–2012: crawlspace improvements to all 28 pilot homes

• Season 3, 2012–2013: attic upgrades to 16 pilot homes (FB and FV only), one ductless 

(mini-split) heat pump installed in one block home

• Season 4, 2013–2014: window upgrades in all pilot homes, exterior insulation added to 

FV (8) homes and one block home building (four homes—BV-1, B-5, B-6, and BV-2).

8.1 Monitoring Summary

Temperature and humidity were monitored in each home on the first and second floors and in the 

basement where applicable (BV-5 and BV-6). Crawlspaces were also monitored. Because the 

pilot study had 28 homes, an effort was made to incorporate a wireless system to record 

temperatures. The first system selected consisted of wireless transmitters from Onset, the Hobo 

ZW series of data loggers. These loggers communicated with a receiver that was located in the 

crawlspace of the homes and required biweekly data downloads via a site visit. This technology 

proved to be somewhat unreliable and these sensors were eventually replaced by wireless sensors 

from Omnisense. The Omnisense sensors communicate with a gateway that was installed in each 

building. The gateway connects to the Internet and transmits data to online storage immediately. 

This technology obtained a much more reliable and consistent data stream. 

Energy data were recorded through use of Wattnode energy transducers that were installed in the 

electrical panel. Current transformers connected to specific circuits were used to measure the 

whole-house energy, the primary heating circuits, water heaters, and dryers. The pulse output 

was connected to a Campbell Scientific data logger that transmitted data to National Renewable 

Energy Laboratory offices. In addition to the energy data recorded, utility meters were generally

read biweekly.

Not all homes could have direct energy monitoring because of the electrical panel’s location; in 

many cases heating was supplied by portable heaters that could not be monitored. Therefore, the 

total energy use of the home was used as the primary energy metric for analysis. An estimate of 

heating energy was developed using swing season estimates of baseline energy use where the 

data were consistent.

33
Energy data analysis is based on the measured electrical energy data and the electricity meter 

data. Measured electrical energy was reconciled with the utility meter data in all cases. Where 

measured data were not available for a particular home, the biweekly utility data were used.

All homes have EBB heaters. Some homes have wall thermostats to control some heaters; the 

rest of the heaters are controlled by an integral thermostat. One home has a ducted heat pump 

system and another home had a ductless heat pump that was installed before winter 2012. The 

homes are all-electric; natural gas is not available in the community.

The timeframe for the heating season analysis was December 1 through March 21, a period of 

111 days. This timeframe was selected to minimize variations caused by warm periods when 

windows might be open for part of the day. 

8.2 Indoor Temperature Measurements in Pilot Homes

All 28 pilot homes were instrumented with temperature and humidity recorders for four heating 

seasons beginning with 2010–2011. In most cases, the first-floor sensor was in the living room 

near a wall thermostat. The second-floor sensor was installed in the main bedroom. As expected, 

the variation in temperatures between levels varied widely among homes; therefore, an average 

of the first- and second-floor temperatures is summarized for the most useful information. Table 

9 summarizes the indoor temperatures and relative humidity for each pilot home. The change in 

the average temperature from Season 1 (baseline) to each of the subsequent seasons is shown in 

the columns on the right.

34
Table 9. Average Seasonal Indoor Temperature and Relative Humidity for Pilot Homes

Pilot Home 

Unit

I.D.

Heating Season Average Daily Temperatures and Relative Humidity

(December 1 Through March 21) Temperature Change

Indoor Air Average of 1st and 2nd From Base

Floor, °F Indoor Relative Humidity, %

2010–

2011

2011–

2012

2012–

2013

2013–

2014

2010–

2011

2011–

2012

2012–

2013

2013–

2014

2011–

2012

2012–

2013

2013–

2014

B-1 69.9 68.3 70.0 71.9 – 42.2 40.1 42.5 –1.5 0.1 2.1

B-2 68.5 68.0 67.9 66.9 – 43.1 43.2 45.2 –0.5 –0.6 –1.6

B-3 59.9 63.2 64.8 61.0 67.5 66.7 68.4 73.0 3.3 4.9 1.1

B-4 72.0 71.5 71.5 72.5 32.1 43.2 41.8 44.3 –0.6 –0.5 0.5

B1/4 Crawl 60.7 63.9 62.7 61.2 64.7 62.6 60.4 55.8 3.2 2.0 0.5

BV-1 66.3 66.0 66.7 68.2 44.3 49.1 49.2 45.0 –0.3 0.4 1.9

B-5 57.4 58.5 61.4 70.3 63.4 62.1 62.4 43.8 1.1 4.0 12.9

B-6 62.1 65.8 62.3 66.4 48.3 45.1 43.9 46.9 3.8 0.3 4.4

BV-2 62.7 70.2 70.7 69.5 37.2 40.9 41.1 39.3 7.4 8.0 6.8

BV1/2 Crawl 56.3 62.0 61.4 60.9 – 52.7 50.6 39.7 5.6 5.1 4.6

BV-3 68.7 69.0 69.2 70.4 42.8 48.8 42.0 46.1 0.3 0.5 1.7

BV-4 63.2 64.4 63.7 54.6 54.4 54.9 54.2 47.6 1.1 0.5 –8.6

BV-5 68.7 70.5 69.0 69.3 29.1 40.0 42.4 38.8 1.8 0.2 0.5

BV-6 66.7 68.7 67.4 64.5 40.9 46.7 42.6 50.7 1.9 0.7 –2.2

BV3/6 Crawl 56.0 60.2 59.4 54.5 83.2 61.8 58.7 60.6 4.3 3.5 –1.5

FB-1 69.8 70.9 69.7 71.8 26.0 30.8 32.6 36.5 1.1 –0.2 2.0

FB-2 64.8 66.6 68.9 69.1 31.1 33.7 29.6 34.5 1.8 4.1 4.2

FB-3 66.5 68.3 68.5 65.6 39.1 46.8 39.8 40.1 1.8 2.0 –1.0

FB-4 55.6 58.3 57.4 57.5 43.3 46.9 45.8 40.4 2.6 1.8 1.9

FB1/4 Crawl 56.4 59.7 60.6 59.2 65.3 44.9 40.4 40.7 3.2 4.2 2.8

FB-5 65.4 67.7 66.8 62.8 35.8 44.5 40.5 42.3 2.2 1.4 –2.6

FB-6 64.7 66.0 65.4 69.7 39.2 50.4 48.1 47.6 1.3 0.6 5.0

FB-7 52.2 57.3 56.3 52.8 37.7 45.5 41.4 40.2 5.0 4.0 0.5

FB-8 65.3 64.9 64.1 64.3 39.6 48.3 46.2 41.2 –0.4 –1.2 –1.0

FB5/8 Crawl 54.4 60.2 58.8 55.6 63.2 51.1 49.0 50.6 5.8 4.5 1.2

35
Pilot Home 

Unit

I.D.

Heating Season Average Daily Temperatures and Relative Humidity

(December 1 Through March 21) Temperature Change

Indoor Air Average of 1st and 2nd From Base

Floor, °F Indoor Relative Humidity, %

2010–

2011

2011–

2012

2012–

2013

2013–

2014

2010–

2011

2011–

2012

2012–

2013

2013–

2014

2011–

2012

2012–

2013

2013–

2014

FV-1 60.0 63.4 66.4 69.7 43.6 45.5 38.8 37.3 3.5 6.4 9.7

FV-2 68.1 69.6 69.3 70.0 33.9 34.8 35.9 36.0 1.4 1.2 1.8

FV-3 68.3 67.6 65.6 72.7 37.1 41.7 44.4 38.0 –0.7 –2.7 4.5

FV-4 68.9 67.2 67.7 69.1 35.9 41.0 39.5 41.7 –1.6 –1.2 0.2

FV1/4 Crawl 50.7 55.6 54.5 53.3 75.0 71.2 72.8 70.3 4.9 3.8 2.6

FV-5 68.8 69.4 68.4 66.7 28.7 35.1 34.4 34.5 0.6 –0.5 –2.1

FV-6 64.3 63.2 59.8 62.8 37.2 38.9 46.8 44.5 –1.1 –4.6 –1.6

FV-7 66.1 68.0 67.6 68.0 36.8 43.6 38.0 35.4 1.9 1.5 1.9

FV-8 63.1 64.8 62.5 63.7 34.8 46.5 48.2 45.4 1.7 –0.6 0.6

FV5/8 Crawl 51.3 53.3 51.5 49.0 55.4 56.4 54.2 2.0 0.2 –2.3

BV5 & BV6 average includes basement; n/a = data not available; Shaded rows indicate change in or no occupancy.

2010–2011 Heating Season truncated based on available data in some homes, subsequent heating seasons from December 1 through March 21. * Rows shaded in yellow indicate homes omitted from the building averages.

36
A summary of the temperatures and humidity for each building type for the heating period 

December 1 through March 21, in the pilot program is shown in Table 10.

Table 10. Heating Period Average Indoor Temperature and Relative Humidity by Building Type

Indoor Temperature Indoor Relative Humidity

Season 

1

Season 

2

Season 

3

Season 

4

Season 

1

Season 

2

Season 

3

Season 

4

B Uninsulated 68.1 68.4 67.9 69.4 40.2 43.4 42.3 44.7

BV 66.6 68.9 68.9 69.3 38.4 44.7 43.7 42.3

FB 64.6 66.1 65.8 65.8 36.3 43.0 40.4 40.4

FV 66.0 66.7 65.9 67.8 36.0 40.9 40.8 39.1

Average (23 of 28)* 66.1 67.2 66.8 67.6 37.1 42.8 41.5 41.4

Average Outdoor T 38.4 44.1 41.0 36.1

HDDs 2,953 2,351 2,653 3,201

8.3 Energy Use Data

A general rollup of the total energy use over the four heating seasons of the pilot program is 

shown in Table 11. As indicated previously, the time period for the heating season is from 

December 1 through March 21. The four heating seasons were differentiated as:

• Season 1—Baseline season

• Season 2—Crawlspace upgrades in all pilot homes

• Season 3—Attic upgrades in FB (eight) and FV (eight) homes—one B/uninsulated in 

which was installed a ductless heat pump

• Season 4—window upgrades in all homes, exterior insulation in FV and on four of the 12 

B homes.

Table 11. Measured Energy Use in Pilot Homes Over Four Heating Seasons

Unit Type No. of 

Units

Average/Home Actual Energy Use (kWh)

Season 1 Season 2 Season 3 Season 4

B, Uninsulated 4 8,414 5,938 6,391 6,991

BV 4 8,275 6,722 8,245 7,786

FB 7 6,179 4,591 4,997 5,403

FV 8 5,431 3,838 4,186 4,496

Notes: 

Seasonal period is from December 1 through March 21.

Five homes are not included in the study because of very uncommon use patterns or changes in occupancy.

37
The data in Table 11 represent actual energy use without normalization to any weather or indoor 

temperature factors. As noted from the weather data previously, Season 2 was much milder than 

any of the other heating seasons. Also, Season 4 was the coldest on average of the four heating 

seasons. 

The data need to be normalized to compare performance across seasons, in particular to evaluate 

the savings associated with the energy upgrades. For this report, normalization to HDDs and to 

indoor-outdoor temperature difference is used to evaluate the energy use of each pilot home 

across seasons.

8.3.1 Heating Energy Use

Although an attempt was made to monitor the heating circuits in each home, portable space 

heaters were so common that much of the heating energy was missed. A combination of the 

measured heating circuits (where available) and the measured energy use during swing seasons 

(when little or no heating and cooling are used) were used to adjust the building energy data and

estimate the heating energy. In cases where the monitored heating circuits were known to 

represent nearly all the heating energy, the correlations were excellent. Therefore, the 

methodology was used for all pilot homes. Table 12 shows the heating energy summary for the 

defined heating period of 111 days (December 1 through March 21) for each of the four winter 

periods.

Table 12. Estimated Heating Energy Use in Pilot Homes Over Four Heating Seasons

Unit Type No.

Average/Home Estimated Heating Energy 

(kWh)

Season 1 Season 2 Season 3 Season 4

B, Uninsulated 4 6,968 4,552 4,931 5,530

BV 4 6,095 4,542 5,605 5,505

FB 7 4,471 2,953 3,388 3,789

FV 8 3,555 2,301 2,418 2,697

Notes: 

Seasonal period is from December 1 through March 21.

Five homes were excluded from the study because of very uncommon use patterns or changes in occupancy.

8.3.2 Heating Degree Day Normalization

The simple ratio-based HDD normalization methodology uses a constant HDD value for all 

seasons applied to the normalization factor for each individual season.

4 The chosen HDD 

constant is 3000, which for the period of the analysis (December 1 through March 21) represents 

about 66%–75% of all the annual HDD. HDD normalization uses the following formula:

EHDD3000s = (AEs/HDDs)*3000

where

4 For a more complete analysis of HDD normalization, refer to 

http://web.ornl.gov/sci/buildings/2012/1985%20B3%20papers/009.pdf (accessed 9/4/14)

38

 
EHDD3000s = Energy use for 3000 HDD in a particular season

AEs = Actual energy used in a particular season

HDDs = the heating degree days in a particular season.

An HDD normalization is most useful when the sample set is large. This methodology accounts

for the changes in heating demand across seasons, but not for differences in interior 

temperatures. HDD normalization is commonly used because it uses readily available data;

indoor temperature data across seasons are often unavailable. Table 13 summarizes the energy 

use of the pilot home types based on a normalized 3000 HDDs.

Table 13. HDD Normalized Heating Energy

Unit Type No.

Average/Home Heating Energy 3000 HDD 

Normalized, kWh

Season 1 Season 2 Season 3 Season 4

B, Uninsulated, All 4 7,080 5,808 5,576 5,183

B1, B2 2 6,585 4,554 6,155 5,956

B4 1 10,565 9,563 6,836 6,017

B6 1 4,586 4,562 3,157 2,803

BV, All 4 6,193 5,796 6,338 5,159

BV3, BV5 2 6,770 4,871 5,473 5,788

FB, All 7 4,543 3,769 3,831 3,551

FV, All 8 3,612 2,936 2,734 2,527

All—Homes in each building type, excluding five units with atypical occupancy

B1, B2—block, original uninsulated, one outside and one inside unit, no wall insulation added

B5—block, original uninsulated, interior unit, exterior insulation added during Phase 2 upgrades

B4—block, uninsulated, no wall insulation added, ductless heat pump installed prior to Season 3

BV3, BV5—block, original vinyl siding, one outside and one inside unit, no wall insulation added

Using the HDD normalized heating energy, Table 14 shows the heating energy savings by 

percent (for the analysis period), and Table 15 shows the savings in energy. 

39
Table 14. HDD Normalized Heating Energy Savings Over Base Year (%)

Unit Type

Average/Home Heating Energy HDD Normalized 

Savings

Season 1 Season 2 Season 3 Season 4

B, Uninsulated, All – 18% 21% 27%

B1, B2 – 31% 7% 10%

B4 – 9% 35% 43%

B6 – 1% 31% 39%

BV, All – 6% –2% 17%

BV3, BV5 – 28% 19% 14%

FB, All – 17% 16% 22%

FV, All – 19% 24% 30%

All—Homes in each building type, excluding five units with atypical occupancy

B1, B2—block, original uninsulated, one outside and one inside unit, no wall insulation added

B6—block, original uninsulated, interior unit, exterior insulation added during Phase 2 upgrades

B4—block, uninsulated, no wall insulation added, ductless heat pump installed prior to season 3

BV3, BV5—block, original vinyl siding, one outside and one inside unit, no wall insulation added

Table 15. HDD Normalized Heating Energy Savings Over Base Year (kWh)

Unit Type

Average/Home Heating Energy Normalized 

Savings (kWh)

Season 1 Season 2 Season 3 Season 4

B, Uninsulated, All – 1,272 1,505 1,897

B1, B2 – 2,031 430 630

B4 – 1,002 3,729 4,548

B6 – 24 1,429 1,783

BV, All – 397 –145 1,034

BV3, BV5 – 1,899 1,296 982

FB, All – 774 711 991

FV, All – 675 877 1,084

All—Homes in each building type, excluding five units with atypical occupancy

B1, B2—block, original uninsulated, one outside and one inside unit, no wall insulation added

B6—block, original uninsulated, interior unit, exterior insulation added during Phase 2 upgrades

B4—block, uninsulated, no wall insulation added, ductless heat pump installed prior to Season 3

BV3, BV5—block, original vinyl siding, one outside and one inside unit, no wall insulation added

8.3.3 Temperature Difference Normalization and Take-Back Energy Use

A known inaccuracy of the HDD normalization is the interior temperature variation across 

homes. The HDD normalization methodology assumes that the indoor temperature is the same in 

all cases; i.e., across homes and seasons. This assumption may work well with large groups of 

homes; however, it is less applicable to GHI homes. The large difference in construction types 

and the wide range of indoor temperatures make this assumption much less applicable. 

40
Many GHI homeowners have acknowledged that they set their thermostats lower than they might 

otherwise because of the high heating bills. This leads to the assumption that with lower costs for 

heating, homeowners would set their thermostats to a higher, more comfortable temperature. 

This assumption cannot be individually validated (many homes do not have central thermostats

that control all the heating), but the measured data do provide perspective. 

Using the average indoor and ambient temperatures for the heating period, the measured data can 

be normalized to this seasonal temperature difference. The methodology develops a factor based 

on the actual temperature difference for each season and then normalizes all homes and seasons 

to a 30°F temperature difference. A 30°F temperature difference is assumed from an average of 

38°F outdoor temperature for the referenced period and a common 68°F interior temperature. 

This methodology is represented by the formula:

EDT30s = (AEs/(Tindoor–Tambient)*30

where

EDT30s = Energy use for 30°F temperature difference in a particular season

AEs = Actual energy used in a particular season

Tindoor = Average indoor temperature (for the season)

Tambient = Average outdoor temperature (for the season)

Based on the temperature difference (TD) normalization, Table 16 summarizes the results for 

each building type. 

Table 16. TD Normalized Heating Energy

Unit Type No.

Average/Home Heating Energy 30°F 

Normalized, kWh

Season 1 Season 2 Season 3 Season 4

B, Uninsulated, All 4 7,390 5,501 5,379 4,887

B1, B2 2 6,298 4,435 5,808 5,638

B4 1 9,288 8,207 5,958 5,305

B6 1 7,678 4,928 3,941 2,967

BV, All 4 8,009 5,512 6,084 4,983

BV3, BV5 2 7,822 4,429 5,184 5,518

FB, All 7 6,021 3,924 4,055 3,849

FV, All 8 4,515 3,081 2,875 2,549

All—Homes in each building type, excluding five units with atypical occupancy

B1, B2—block, original uninsulated, one outside and one inside unit, no wall insulation added

B6—block, original uninsulated, interior unit, exterior insulation added during Phase 2 upgrades

B4—block, uninsulated, no wall insulation added, ductless heat pump installed prior to Season 3

BV3, BV5—block, original vinyl siding, one outside and one inside unit, no wall insulation added

Using the HDD normalized heating energy, Table 17 shows the heating energy savings by 

percent (for the analysis period), and Table 18 shows the savings in energy.

41
Table 17. TD Normalized Heating Energy Savings Over Base Year (%)

Unit Type

Average/Home Heating Energy HDD 

Normalized Savings

Season 1 Season 2 Season 3 Season 4

B, Uninsulated, All – 26% 27% 34%

B1, B2 – 30% 8% 10%

B4 – 12% 36% 43%

B6 – 36% 49% 61%

BV, All 31% 24% 38%

BV3, BV5 43% 34% 29%

FB, All 35% 33% 36%

FV, All 32% 36% 44%

All—Homes in each building type, excluding five units with atypical occupancy

B1, B2—block, original uninsulated, one outside and one inside unit, no wall insulation added

B5, B6—block, original uninsulated, interior units, exterior insulation added during Phase 2 upgrades

B4—block, uninsulated, no wall insulation added, ductless heat pump installed prior to Season 3

BV3, BV5—block, original vinyl siding, one outside and one inside unit, no wall insulation added

Table 18. TD Normalized Heating Energy Savings From Base Year (kWh)

Unit Type

Average/Home Heating Energy 30°F Normalized 

(kWh)

Season 1 Season 2 Season 3 Season 4

B, Uninsulated, All – 1,889 2,011 2,503

B1, B2 – 1,862 489 659

B4 – 1,081 3,330 3,983

B6 – 2,751 3,737 4,711

BV, All 2,497 1,925 3,026

BV3, BV5 3,394 2,639 2,305

FB, All 2,097 1,966 2,173

FV, All 1,435 1,640 1,966

All—Homes in each building type, excluding five units with atypical occupancy

B1, B2—block, original uninsulated, one outside and one inside unit, no wall insulation added

B6—block, original uninsulated, interior unit, exterior insulation added during Phase 2 upgrades

B4—block, uninsulated, no wall insulation added, ductless heat pump installed prior to Season 3

BV3, BV5—block, original vinyl siding, one outside and one inside unit, no wall insulation added

Because of the colder winter of Season 4 following the upgrades and the warmer temperatures in 

many of the homes, normalizing to temperature difference combines the effects of the winters 

with the variable indoor temperatures, and demonstrates a much higher level of savings.

Summarizing the energy use measurements for the pilot homes (24 of 28 units), the energy 

reduction resulting from the envelope upgrades is obvious (Table 19).

42
Table 19. Summary Heating Energy Use for Each Season, 23 of 28 Pilot Homes

Heating Energy (kWh)

Actual Use HDD Normalized TD Normalized

Season 1 (Base) 111,982 113,784 139,868

Season 2 75,457 96,287 96,166

Season 3 85,204 96,348 97,243

Season 4 92,235 86,443 86,811

Season 4 Savings Over Base 18% 24% 38%

Table 19 clearly demonstrates that overall across the pilot homes, the efficiency upgrades 

resulted in substantial energy savings. This is borne out even in actual consumption data, where 

the latest heating season was the most demanding in the study. 

Breaking out each of the building types, Table 20 provides a comparative perspective on heating 

energy use and savings based on the building and upgrades. The project includes seven 

buildings, each with four attached units. The letter-identified header columns (A through I) 

indicate the units in a particular building type that are analyzed together. 

43
Table 20. Summary of Energy Savings Building Type and Upgrade

Building Type (Number of Units)

Unit ID and Location

Upgrade Features

A B C D E F G H I

Block (2) B1 

Outside B2 Inside 

CW,W,D,F

Block (1) B4 

Outside 

CW,W,D,F DHP 

S3

Block (2) BV3 

Outside BV5 

Inside CW,W,D,F

Block (2) BV1, 

BV2 Outside 

CW,W,D,F 2.5EI

Block (1) B6 

Inside CW,W,D,F 

2.5EI

Brick (4) FB1, 

FB4, FB5, FB8 

Outside 

CW,W,D,F

Brick (3) FB2, 

FB3, FB6 Inside 

CW,W,D,F

Vinyl (4) FV1, V4, 

FV5, FV8 Outside 

F,W,D,F, 1EI

Vinyl (4) FV2, V3, 

FV6, FV7 Inside 

CF,W,D,F, 1EI

Heating Energy, Actual

Season 1, Base Year, kWh 12,962 10,398 13,325 11,054 4,513 19,282 12,012 16,499 11,937

Season 2, 2a Upgrades, kWh 7,138 7,494 7,634 10,534 3,575 13,347 7,326 11,046 7,363

Season 3, 2b Upgrades, kWh 10,886 6,045 9,680 12,738 2,792 13,679 10,039 12,289 7,055

Season 4, 2c Upgrades, kWh 12,710 6,420 12,352 9,667 2,991 16,249 10,275 13,216 8,356

Season 4 Savings Over Base, % 2% 38% 7% 13% 34% 16% 14% 20% 30%

Season 4 Savings Over Base, kWh 253 3,978 973 1,387 1,522 3,034 1,737 3,283 3,581

Average Savings Per Home, kWh 126 3,978 487 694 1,522 758 579 821 895

Heating Energy 30°F Normalized

Season 1, Base Year, kWh 12,595 9,288 15,645 16,392 7,678 25,803 16,345 21,830 14,292

Season 2, 2a Upgrades, kWh 8,870 8,207 8,858 13,191 4,928 17,887 9,580 14,873 9,773

Season 3, 2b Upgrades, kWh 11,617 5,958 10,368 13,969 3,941 17,084 11,303 14,691 8,312

Season 4, 2c Upgrades, kWh 11,276 5,305 11,035 8,899 2,967 17,112 9,828 12,686 7,704

Season 4 Savings Over Base, % 10% 43% 29% 46% 61% 34% 40% 42% 46%

Season 4 Savings Over Base, kWh 1,319 3,983 4,610 7,493 4,711 8,691 6,517 9,143 6,589

Average Savings Per Home, kWh 659 3,983 2,305 3,746 4,711 2,173 2,172 2,286 1,647

Heating Energy 3000 HDD Normalized

Season 1, Base Year, kWh 13,171 10,565 13,539 11,232 4,586 19,593 12,205 16,764 12,129

Season 2, 2a Upgrades, kWh 9,109 9,563 9,741 13,442 4,562 17,031 9,349 14,095 9,395

Season 3, 2b Upgrades, kWh 12,310 6,836 10,947 14,404 3,157 15,468 11,352 13,896 7,978

Season 4, 2c Upgrades, kWh 11,912 6,017 11,576 9,060 2,803 15,228 9,630 12,386 7,832

44
Building Type (Number of Units)

Unit ID and Location

Upgrade Features

A B C D E F G H I

Block (2) B1 

Outside B2 Inside 

CW,W,D,F

Block (1) B4 

Outside 

CW,W,D,F DHP 

S3

Block (2) BV3 

Outside BV5 

Inside CW,W,D,F

Block (2) BV1, 

BV2 Outside 

CW,W,D,F 2.5EI

Block (1) B6 

Inside CW,W,D,F 

2.5EI

Brick (4) FB1, 

FB4, FB5, FB8 

Outside 

CW,W,D,F

Brick (3) FB2, 

FB3, FB6 Inside 

CW,W,D,F

Vinyl (4) FV1, V4, 

FV5, FV8 Outside 

F,W,D,F, 1EI

Vinyl (4) FV2, V3, 

FV6, FV7 Inside 

CF,W,D,F, 1EI

Season 4 Savings Over Base, % 10% 43% 14% 19% 39% 22% 21% 26% 35%

Season 4 Savings Over Base, kWh 1,259 4,548 1,963 2,172 1,783 4,364 2,575 4,378 4,298

Average Savings Per Home, kWh 630 4,548 982 1,086 1,783 1,091 858 1,095 1,074

CW-crawlspace walls; CF-crawlspace floor; W-windows; D-doors; F-bath vent fans;

2.5EI- 2.5-in. exterior insulation board; 1EI- 1-in. exterior insulation

Upgrades: 2a- crawlspace, 2b- attics, 2c- windows/doors/wall insulation where applicable

Note that BV5 has a basement foundation that was insulated similar to the crawlspace using wall insulation.

45
Tables of the energy use in each pilot home across four heating periods are available in 

Appendix C.

The energy use summary outlined in Table 20 is divided into three sections: actual heating 

energy use, TD30, and normalized HDD heating energy use. Note that heating energy is 

estimated using a combination of measured and swing-season use. Heating energy use and 

savings are based on the analysis period December 1–March 21 in each heating season and 

generally represent a minimum level of savings for heating energy. In the following bullets 

summary results are given for the TD normalization; this approach accounts for the changing 

ambient conditions and the changing indoor temperature settings. Heating energy use results for 

GHI building types recorded after the pilot home upgrades and testing follow. Column data 

identified by the top header letter row and the middle table section Heating Energy, 30°F 

Normalized (in Table 20) were used.

• Column A: GHI uninsulated B buildings that had only crawlspace and window/door 

upgrades. This yielded a 10% energy reduction, attributed primarily to the window/door 

upgrades and a reduction in infiltration. 

• Column B: Same as column A but with a ductless heat pump added—a 43% energy 

reduction, attributed primarily to the ductless heat pump and secondarily to the envelope 

improvements. 

• Column C: GHI BV homes with 1⁄2-in. of exterior insulation board between the furring. 

The homes had only crawlspace (BV3)/basement (BV5) and window/door upgrades, 

which yielded a 29% energy reduction, attributed primarily to the window upgrades and a 

reduction in infiltration. 

• Column D: GHI BV homes (both end units) with 1⁄2-in. of exterior insulation board 

between furring. The homes had crawlspace and window/door upgrades, all existing 

siding and insulation removed, and 2-1⁄2 in. of exterior rigid insulation with new siding 

installed. These measures achieved a 46% energy reduction, attributed primarily to the 

wall insulation, window upgrades, and infiltration reduction.

• Column E: GHI B home (one interior unit), uninsulated, which had crawlspace and 

window/door upgrades and 2-1⁄2 in. of rigid insulation added to the exterior, and new 

siding installed. This yielded a 61% energy reduction, attributed primarily to the wall 

insulation, window upgrades, and infiltration reduction.

• Column F: GHI FB (end units in two buildings) that had crawlspace, attic, and 

window/door upgrades. These improvements achieved a 34% energy reduction, attributed 

to the infiltration reduction, attic insulation, and window upgrades.

• Column G: GHI FB (interior units in two buildings) that had crawlspace, attic, and 

window/door upgrades, which yielded a 40% energy reduction, attributed to the 

infiltration reduction, attic insulation, and window upgrades.

• Column H: GHI FV (end units in two buildings) that had crawlspace floor insulation and 

air sealing, attic, window/door, and 1 in. of exterior insulating sheathing upgrades. This 

achieved a 42% energy reduction, attributed to the infiltration reduction, attic and wall 

insulation, and window upgrades.

46
• Column I: GHI FV (interior units in two buildings) that had crawlspace floor insulation 

and air sealing, attic, window/door, and 1 in. of exterior insulating sheathing upgrades. 

This yielded a 46% energy reduction, attributed to the infiltration reduction, attic and 

wall insulation, and window upgrades.

Table 21 summarizes the heating energy savings by the type of building in the pilot home 

program and combines the data from Table 20.

The data set also highlights the complexity of energy savings in existing homes, especially in the 

thermostat settings. That is, where high energy costs may have led to lower thermostat settings in 

winter to conserve energy, envelope improvements help to lower heating energy use and may 

therefore lead to a higher thermostat setting. This appears to be the case in some of the GHI 

homes (Figure 52) where the average indoor temperature is higher in the latest winter period 

after all of the envelope upgrades.

Table 21. Heating Energy Savings by Building Using Combined Measured Data

Building Type (4 homes per building)

Measurement 

Period kWh 

Savings

Cost Savings

Measurement 

Period HDD

Simulation 

HDDc

Uninsulated B Building With 

Crawlspace, Windows, Bath Fan EEMs

a 2,638 (10%) $396 $523

BV Building With Crawlspace, 

Windows, Bath Fan EEMs

a 9,220 (29%) $1,383 $1,828

Uninsulated BV Building With 

Crawlspace, Windows, Walls With 2-1⁄2-

in. Exterior Insulation, Bath Fan EEMs

b

16,916 (53%) $2,537 $3,353

FB With Crawlspace, Attic, Windows, 

Bath Fan EEMs 8,691 (37%) $1,304 $1,723

FV With Crawlspace, Attic, Windows, 1-

in. Exterior Insulation, Bath Fan EEMs 7,866 (44%) $1,180 $1,559

a This building configuration not simulated

b Two homes uninsulated, two homes with vinyl siding, all upgraded with similar insulation and vinyl siding c Measured savings over period with 3,201 HDDs, Simulation HDD with 4,230 HDDs.

47
Figure 52. Average winter period temperature difference from base year

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Block Block/Vinyl Frame/Brick Frame/Vinyl

Average Heating Period Temperature Difference, °F

Season 2 from Base

Season 3 from Base

Season 4 from Base

48
9 HVAC System Analysis for Phase 3 Retrofits

One aspect of the energy upgrades for the GHI pilot program is an evaluation of heating system 

options. Currently the homes are heated with EBB heaters unless the homeowner has installed an 

alternative heating system. Typically the GHI cooperative is responsible for heating equipment,

but it does not support (install or maintain) cooling equipment. In conjunction with the 

evaluation of the envelope upgrades, GHI wanted to consider alternatives to the EBB heating 

equipment.

The PHI BA team researched and analyzed alternative heating and cooling systems. PHI recently 

completed a report covering the technical perspective of HVAC performance for the GHI 

building committee. The report points out that it does not consider the comfort, livability, 

control, convenience, and resale of the units; these features’ contributions to equipment solutions 

are best defined by the members. The report is contained in its entirety as Appendix D. 

Air-source heat pumps and high-velocity delivery systems, ground-source heat pumps, ductless 

mini-split heat pumps, electric radiant panels, and EBB heat were all considered in the analysis. 

Propane, oil, and wood were rejected from consideration because of their high cost; natural gas 

was rejected because of the high cost of infrastructure expansion.

Heat gain and loss were calculated before and after the Phase 2 EEMs along with the estimated 

energy savings over an existing condition. Theoretical duct layouts were included in the report so 

that those costs could be estimated. The layouts will also help members visualize the changes to 

their homes’ interiors posed by the ductwork bulkheads and the air handling equipment. Some of 

the cost estimates were derived from actual installations recently performed in other GHI 

members’ homes. In other cases, estimates were derived from bids offered by various HVAC 

companies. 

Table 22 contains the installed HVAC cost estimates that appear in the report.

A challenge for the community-wide effort is that most homes will require the smallest unit size 

manufactured, which typically is not manufactured in high efficiencies. On the other hand, a 

whole-building HVAC solution would have introduced a bookkeeping and allocation burden on 

GHI that it was reluctant to undertake.

The HVAC system analysis concludes that converting the EBB heat in the GHI homes is rarely 

cost-effective on purely an energy basis, even without envelope upgrades. The switch to a heat 

pump system, however, may be undertaken for comfort or long-term performance against rising 

utility prices. The switch to HVAC equipment, however, will incur much higher maintenance 

costs compared to EBB heating units.

49
Table 22. Cost Estimates (Installed) for Heating Systems

Type of System Average Size Efficiency Estimated Cost Building 

Type

Air-Source Heat 

Pumpa 18,000–24,000 Btu 16 SEERb

/

9.0 HSPFc

$16,000–

$18,000 Any

Ground-Source Heat 

Pump 18,000–24,000 Btu 18–27 EERd

/

4.5 COPe $25,000 Any

Ground-Source Heat 

Pump With Ductless 

Fan Coils

18,000–24,000 Btu 18–27 EER/

4.5 COP

$23,000–

$29,000 Any

Ground-Source Heat 

Pump With Ductless 

Console

18,000–24,000 Btu 18–27 EER/

4.5 COP

$25,000–

$40,000 Any

Ductless Mini-Split 

Heat Pump 18,000–24,000 Btu 16 SEER/9.0 HSPF $10,000–

$18,000 Any

High-Velocity Split 

System Heat Pumpa 24,000 Btu 15 SEER/8.2 HSPF $16,000–

$18,000 Any

Electric Radiant 

Panelsf 8–12 kW 100% $2,400–$3,200 Any

EBB Heat 4–7 kW 100% $610–$720 FV

EBB Heat 7–9 kW 100% $720–$1,380 FB

EBB Heat 7–12 kW 100% $720–$1,840 B, BV

a Highest efficiency available in the size.

b Seasonal energy-efficiency ratio c Heating season performance factor

d Energy-efficiency ratio e Coefficient of performance

f

Unit size (1.5 kW) times the quantity required per home (6–8).

50
10 Cost Savings of Building Envelope Improvements

The cost of the Phase 2 envelope improvements came in considerably higher than originally 

estimated. GHI staff members are compiling actual costs, with the intention of isolating those

associated with various envelope upgrades. Several factors are involved in pricing estimates, 

especially for the unique circumstances of the GHI cooperative:

• Contractors were asked to bid on a wide range of building envelope improvements from 

crawlspace insulation using SPF to vent fans installed through block walls to foam 

insulation installed on exterior walls using furring strips. A wide range of work scopes 

can drive up costs because of uncertainty in any one area.

• The community has established hours during which work can be conducted to 

accommodate the membership and administrative staff. Weekends and every other Friday 

were not allowable workdays.

• Demolition and disposal costs can vary significantly from area to area—these costs were 

difficult to capture independently of the retrofit work.

• Procuring uncommon materials for the jobsite increased time and cost.

• Uncommon work scopes increase costs. One example was installing furring over foam 

into block.

• Home occupants (GHI members) and the administrative staff interacted with contractors, 

adding a layer of oversight not common in residential retrofits.

Identifying factors unique to the GHI cooperative that may have affected estimates for the retrofit 

work will help GHI determine opportunities to lower costs in future community-wide retrofits.

10.1 Retrofit Cost Complexity

The GHI pilot program was initiated as an opportunity to evaluate the cost of upgrades in 

comparison with the energy cost savings and isolate the highest performing, lowest cost upgrades 

to deploy. This approach is used in BA and other programs to help in the decision process to 

invest in energy-saving technologies. The investment is expected to demonstrate a payback 

based solely on energy savings. This approach is reasonable and common for many homeowners

and informs the decision process. However, this approach masks a number of complexities of the 

energy retrofit market:

• Some upgrades, such as windows and doors, have an energy benefit; however, costs are 

affected by other factors such as aesthetics, frame quality, and ease of use.

• Siding may be replaced in a home regardless of any concerns over insulation. Separating 

the siding costs from the insulation installation can be difficult, especially if more than a 

thin layer of foam is used, which requires other trim details (as was the case with GHI).

• Installation of siding over insulation on a building that did not previously have siding is 

considered an energy upgrade and is thus included in the cost of the upgrade. In this case, 

the cost of the finish has a large implication on affordability. 

51
• Crawlspace upgrades will be performed to improve durability and insulation. However, 

crawlspace upgrades often show little benefit, especially for the GHI concrete monolithic 

foundations that required insulation repair. Durability improvements come at a cost that 

does not accrue to energy savings.

• Ventilation fans, a necessary upgrade during some energy retrofits, will not contribute to 

energy savings, and may in fact reduce savings.

• Retrofit upgrades in older homes that do not have air conditioning and have EBB heating 

(GHI homes) may not demonstrate the full range of energy savings achievable in new 

homes.

• Home resale value from appreciation that may result from improved energy efficiency is 

yet to be defined adequately. 

For these and other reasons, such as homeowner comfort, associating the cost of upgrades with 

energy savings is a complex process in which separating energy cost upgrades from other costs is 

a significant challenge.

10.2 Energy Savings Investment

The GHI pilot program aimed to evaluate the cost of each envelope upgrade with its attendant 

energy savings. However, because of the broad scope of each activity in the construction phases 

that were involved in the upgrades and the different types of buildings, costs are hard to flesh out 

and assign to a specific energy-efficient feature and its accompanying energy savings. 

Table 23 shows an initial compilation of the costs and a comparison with the energy savings.

The last two Simple Payback rows in Table 23 highlight the importance of timing this energy 

retrofit project with the wider home improvement project that is in progress at GHI members’ 

homes. When EEMs are included with planned renovations, the cost of the energy-efficient

component is more easily isolated from the expense of cladding, window, and door removal and 

installation. The additional costs of insulation and air sealing was less than 50% of the gross 

project cost, for all but the B building (BV1, B5, B6, BV2), which included the cost of siding. 

The energy savings, based on an estimated full heating season (which added 20% to the number 

of HDDs) have been realized from the EEM investments. These savings will pay for the 

unfunded project costs in 9.5 to 28.6 years, depending on building type and installation details. 

The high end of the payback range is also the cycle for exterior component replacements used by 

GHI in establishing reserve accounts; thus, the cycle presents a logical high end of the range that 

should be set for acceptable payback metrics for this project. 

52
Table 23. Cost Analysis of Building Upgrades

Building Types

General Upgrade Category BV3–BV6 B1–B4 BV1, B5, 

B6, BV2 FB1–FB8 FV1–FV8

Number of Homes 4 4 4 8 8

Crawlspace $12,003 $8,288 $8,681 $16,331 $32,325

Attic $12,419 $9,904

Ventilation Fan $5,740 $6,925 $6,900 $12,220 $10,910

Wall Insulation $28,630 $31,885

Siding $18,695 $35,115

Ductless Heat Pump $12,000

Permits $1,000 $1,000 $1,000 $2,000 $2,000

Windows/Doors $23,242 $22,784 $26,951 $32,271 $43,732

Total Upgrade Cost $41,985 $50,997 $90,857 $75,241 $165,871

Less Windows/Doors/Sidinga,b ($23,242) ($22,784) ($26,951) ($32,271) ($78,847)

Less Crawlspace Vapor 

Retarderc ($3,000) ($3,000) ($3,000) ($6,000) ($6,000)

Net Cost of Energy Upgrades $15,743 $25,213 $60,906 $36,970 $81,024

Energy Features as Percent of 

Total 37% 49% 67% 49% 49%

TD30 Normalized Savingsd,e $1,383 $915 $2,537 $2,607 $2,360

TD30 Normalized Savingsd,e 

+20%f $1,660 $1,098 $3,045 $3,129 $2,832

Simple Payback, All Upgradesf 25.3 46.4 29.8 24.0 58.6

Simple Payback, Energy 

Upgradesf 9.5 23.0 20.0 11.8 28.6

a Windows and doors and frame buildings with siding have a recurring reserve fund for replacement and are not 

included in the cost of the additional energy feature upgrades.

b Siding is included when installed new as a necessary part of the wall insulation upgrade. c Crawlspace vapor barrier is estimated at $3,000 per building.

d Temperature normalized energy savings, estimated for unoccupied/change occupancy units; energy costs at 

$0.15/kWh. e Savings for Unit B1 and B2 (B2 used for atypical B3) and added to B4 (unit where ductless heat pump added) for 

building savings. f Adjust savings based on full heating season.

Upgrades for each building type:

BV3–BV6: crawlspace walls, windows, doors, bath fan

B1–B4: crawlspace walls, windows, doors, bath fan, B4 ductless heat pump

BV1, B5, B6, BV2: crawlspace walls, windows, doors, bath fan, remove siding BV1 and 2, add 2-1⁄2 in. 

exterior insulation.

FB1–FB8: crawlspace walls, attic, windows, doors, bath fan

FV1–FV8: crawlspace floor, attic, windows, doors, bath fan, remove siding, add 1-in. exterior insulation.

53
This simple payback analysis doesn’t account for the cost of money or its availability, but GHI 

could either finance the EEM upgrades for its members or expect its members to pay for them in 

total when installed, as it did with pilot program participants who ordered upgraded windows. To 

present the figures in Table 23 for individual consumption (the level at which these decisions may 

be made), the savings and the costs were broken down to the averages at the unit level in Table 24. 

Once the average individual monthly savings were calculated, a comparable mortgage payment at 

4.5% annual interest rate and a term of 30 years was calculated and the principal for that payment 

noted. 

Table 24. Individual Unit Savings and Cost

Unit ID

Individual Unit Analysis Based on Building Type

BV3–BV6 B1–B4 BV1, B5, 

B6, BV2 FB1–FB8 FV1–FV8

No. Units 4 4 4 8 8

TD30 Normalized 

Savings/Building

($ at 0.15/kWh)

1,660 1,098 3,045 3,129 2,832

Annual Savings/Unit ($) 414.89 274.48 761.21 391.07 353.97

Monthly Utility Bill Savings ($) 34.57 22.87 63.43 32.59 29.50

Matching Mortgage Payment 

at 4.5%/30 years ($) (34.45) (22.80) (63.34) (32.43) (29.39)

Amount Financed in Matching 

Mortgage Payment ($) 6,800 4,500 12,500 6,400 5,800

EEM Cost (Net Project Cost) 

per Unit ($) 3,936 6,303 15,227 4,621 10,128

Difference Between Financing 

Limit and EEM Cost ($) 2,864 (1,803) (2,726) 1,779 (4,328)

If the homeowner secures a mortgage to pay for the EEMs, two of the five building types indicate 

that the EEMs selected are fiscally prudent investments within the established parameters. In 

particular, no fuel cost escalation has been included in the energy savings estimate and no tax 

benefit has been assumed to accrue to the mortgage payment. Thus, the financing/savings 

calculations shown in Table 24 represent a conservative approach to the EEM analysis. Three 

building types will not be paid for in a 30-year mortgage payment that matches the energy 

savings—B (with heat pump), BV with 2-1⁄2 in. continuous foam and cladding, and FV with SPF 

floor insulation and 1-in. continuous foam. These types will require some revision to the EEM

package because of costs. In all cases there is an even tradeoff of an expense (utility bill) for 

amortization of a debt acquired for investment in EEMs; this is a prudent metric for decision

making. 

10.3 Prioritizing Energy-Efficiency Measures

Based on the GHI bid process, which required a fairly detailed breakout of cost estimates, and the 

resultant implementation sequencing of the Phase 2 envelope upgrades, it should be possible to 

evaluate cost estimates in terms of energy and other benefits. For example, the crawlspace 

upgrades presented considerable bid deviation from estimates because contractors did not want to 

54
remediate the ground vapor barriers and insulation; they preferred removal and replacement. 

Because the B and FB foundations were 75% insulated and naturally sealed from the home 

interiors by the monolithic slab and stem wall construction, these improvements will likely be set 

at a lower priority in future funding decisions. The issues could be remediated by the GHI 

maintenance department. An alternative would be GHI establishing a reserve for crawlspaces and 

limit independent contractors’ unsupervised access to these spaces; much of the debris collection

and degradation within the crawlspaces appear to have been caused by cable, electrical, and 

plumbing trades hired to perform work for GHI or an individual member occupant.

Similarly, the FV crawlspaces will likely require the same level of detail as the pilot buildings. 

The SPF insulation in the floor assembly will provide vital air sealing at the plank-sheathed 

floors and a durable long-lasting thermal barrier. If the crawlspace floors and ground vapor 

barriers cannot be repaired concurrently with the insulation installation, a reserve fund should be 

established for a near-term retrofit.

All upgrades will be evaluated as final costs are compiled and energy savings for the 2013–2014

heating season are logged.

55
11 Energy-Efficiency Measure Lessons Learned

Based on the envelope upgrades implemented in the pilot program, a number of details have been 

identified as critical to the long-term success of the community-wide upgrade. Some issues fall into 

the category of “lessons learned”; others still need solutions. All these factors will require an 

ongoing careful review of the costs to achieve an optimized approach to specific upgrades. 

11.1 Crawlspace Upgrades

Original simulation estimates indicated modest energy savings from upgrades to the crawlspace, 

especially for the B and FB buildings, where some insulation was already installed and where air 

leakage to the home is minimal because the foundation and the slab construction are integrated. 

Conversely, retrofitting the FV buildings is expected to produce higher energy savings and incur 

higher cost because a large amount of SPF was used and the crawlspaces presented tight working 

quarters. Assessment details for the crawlspaces that pertain to the community-wide upgrades

follow:

• Evaluate the cost of the concrete foundation upgrades in B, BV, and FB buildings, the 

scope of work, and the expected benefits to determine their priority.

• Evaluate the drainage issues encountered in the FV crawlspaces to determine if additional 

remediation is necessary.

• Break out costs and savings for the FV crawlspaces to determine if alternative approaches 

would provide similar benefits at a lower cost.

• Separate ground vapor barrier costs from the insulation improvement costs and

investigate avenues for including the barriers and insulation in GHI’s regular home 

maintenance procedures and schedule.

11.2 Attic Upgrades

Attic upgrades included air sealing, insulation, and storage area maintenance and are applicable to 

the FB and FV buildings only. These improvements appear to have reasonable costs relative to the 

estimated benefits (especially when air leakage to the attic is included in the scope). Assessment 

details for the attics that pertain to the community-wide upgrades follow:

• Re-evaluate the cost of the attic upgrades to identify any possible cost optimizations.

• Solicit the GHI membership for interest in maintaining the storage space, the area of 

storage needed, and any optional approaches such as a minimal level versus an enhanced 

level (whose cost would be borne independently by the member).

• Develop specific air sealing details for the attic including sequencing and material 

selections.

• Consider alternative attic insulation options such as exterior roof panels.5

5 SPF in the roof was originally considered and not recommended because of the cost, loss of headroom, ignition 

barrier requirements, and potentially lower overall insulating levels.

56

 
• Review attic access options and detail upgrades based on the specific type of access and 

condition.

11.3 Windows

Window replacements have proven to be the most difficult detail to define for the communitywide upgrade. A cost and energy analysis was initially not as critical for windows because 

window replacements have been built into the replacement reserves. Although no performance 

specifications are part of the window replacement reserves, GHI did need to include a minimum 

performance specification (0.30 U-value/0.30 solar heat gain coefficient) into the bid process. 

Estimates for the window costs to match the reserve replacement funds did not appear to be 

adversely affected by the window specifications. However, the performance specifications were 

in line with the manufacturer’s typical product selection. If higher performing windows had been 

specified (R5 or higher), there would very likely be a significant discrepancy between reserve 

estimates and window costs. 

The window costs are likely to be revisited because during installation the windows were 

integrated with new wall insulation, which necessitated large amounts of aluminum coil stock 

and the use of self-adhering window and sill pan flashing unfamiliar to the window 

manufacturer. Cost estimates for future window installations are expected to increase. 

Assessment details for the windows that pertain to the community-wide upgrades follow:

• A detailed review of window installation options for each building type is required. In 

particular for buildings that receive exterior insulation, review whether windows are 

installed as “innies” or “outies” and the required commensurate trim details.

• Review exterior window trim details for the FV buildings and standardize an approach.

• Review the window type (flanged or replacement) for the B buildings when the windows 

are integrated with exterior insulation. If an “innie” window option is selected, determine 

the window trim flashing details by the window installer versus those of the cladding 

installer.

• Clearly specify the window flashing details for all building types and develop a quality 

control mechanism for ensuring installation consistency.

• Review flashing details for second-story window head flashing that is integrated with 

siding and eave soffits.

• Review sequencing of window removal, replacement, and flashing.

• Review architectural details for exterior trim that is integrated with new wall insulation 

and the WRB.

• Provide clear options for homeowners for window styles and cost differences well in 

advance of planned retrofits to take advantage of bulk purchases.

11.4 Exterior Insulation and Weather-Resistive Barriers

Exterior insulation is expected to demonstrate a large benefit in the overall pilot program. In 

addition to the higher levels of insulation, the air sealing benefits will further support energy 

savings and indoor comfort. Imperfections in the existing cavity insulation from the 1980s 

57
retrofit caused by settling or framing factors will be mitigated with the exterior continuous 

insulation alternative. Assessment details for continuous exterior insulation that pertain to the 

community-wide upgrades follow:

• Review costs and energy savings associated with exterior insulation and specify the 

preferred insulation board for all building types to receive exterior insulation.

• Define the approach to the WRB, the material options, and the installation requirements 

based on the specific materials.

• Clearly specify the integration of the window flashing with the WRB.

• Review insulation thicknesses for each building type and the specific attachment 

methodology based on the insulation thickness.

• Identify all flashing details at the roof, adjacent wall, decks, and chimneys.

• Identify building details where roofing systems intersect with wall insulation systems and 

catalog areas with crossover that may need to be addressed in future maintenance or 

repair work.

11.5 Claddings

Direct attachment of cladding, in particular vinyl siding, over 1-in. foam board is generally 

permitted based on manufacturers’ recommendations and warranty requirements. Beyond this 

thickness furring strips may be required to provide the nail base for the cladding. For the B 

homes that are retrofitted with exterior foam board, furring must be installed to serve as the nail 

base for the cladding. However, design details must be addressed in this case to identify the 

drainage plane and the integration of the furring. Furring is often considered merely as the 

“nailer” for siding and trim; this encourages the installation of more wood than is required,

including horizontal furring. The horizontal furring can then interrupt the drainage plane that is 

provided by the taped rigid foam. If horizontal furring absolutely must be installed, it must be 

flashed if the rigid foam is also serving as the drainage plane. To flash the horizontal furring and 

the rigid foam plane, the vertical furring must stand off from the horizontal furring, or the 

flashing must be installed unencumbered by perpendicular furring directly above the horizontal 

piece. 

Vinyl siding manufacturers require a continuous rigid backing for the product that isn’t met with 

furring only. According to CertainTeed (2013): 

1. Install all siding and accessories over a smooth, flat surface. Always install siding over 

a rigid sheathing, and never install it over open studs. 2. Vinyl siding is not a watertight 

material. Install a weather-resistant barrier, like CertainTeed CertaWrap, and flash around 

all windows and doors before installing vinyl siding and trim.

When the voids between the spacing of the furring are filled with additional rigid foam, the 

drainage plane location becomes obscured and interrupted by all of the smaller foam panels that 

fit between the furring. The contractor used 2-in. foam and furring at 16-in. spacing on the block 

building and then filled in between the furring with 1⁄2-in. rigid foam panels adhered and tacked 

to the underlying foam. Alternative sidings and rigid foam details are under investigation.

58
Furthermore, rigid foam can provide sufficient edge definition (or architectural relief) and 

support against denting under polyvinyl chloride-coated aluminum coil stock that has been 

brake-folded into trim just as well as wood at window sills and frames. The added benefit of the 

thermal resistance and the lower cost (than the 1x pine trim) recommends its use for future 

buildings. Assessment details for the cladding that pertain to the community-wide upgrades

follow:

• Review details and scope of work to attach cladding directly over foam board (for FV 

buildings) and to attach cladding over furring (for B and BV buildings).

• Identify the drainage plane location for each system and identify a continuous pathway 

for various trade contractors.

• Review architectural relief options that use alternatives to wood products.

• Review window trim details to optimize the requirements for the community-wide 

upgrade.

11.6 Ventilation Fan

Bath exhaust fans were identified as an important feature in the energy retrofits. Most GHI 

homes have no exhaust fans. The upgrades to the insulation and the reduction in infiltration rates 

make exhaust fans much more critical to the home’s long-term performance and the occupants’ 

comfort. Assessment details for the exhaust fan that pertain to the community-wide upgrades

follow:

• Plan to install the exhaust fan before the attic upgrades are started.

• Establish a fan and control specification that can be met with a wide range of products.

• Establish multiple ducting paths and hood locations to accommodate field conditions.

• Provide the homeowners instructions on the use of the fans and controller.

• Evaluate the operation of the fan to determine if a higher level of automation is 

necessary.

11.7 Design and Implementation Process

Retrofit upgrades of this breadth and magnitude highlight the shortcomings of the design-bidbuild process flow in which construction modifications are made after the work has been 

initiated. In this case, because building types vary and the scope of work is broad, the challenge 

to define all details of the upgrades before the bid process began was significant. Bid costs were 

complicated by the wide range of retrofit technologies on three building types. Unfamiliarity 

with technologies, such as exterior insulation over concrete block, led to field decisions for 

attachment, air sealing, and integration with other components. Fortunately, the design of the 

pilot program helped to identify these issues before the community-wide upgrade took place.

59
12 Summary of Research Questions

1. How does the energy use for the homes with energy retrofits compare with the preretrofit energy use for space heating and total consumption?

For the homes that had typical use throughout the study and were occupied without change, the 

heating energy during the selected 111-day heating period from December 1–March 21, was 

reduced by 10%–53%, depending on the extent of the efficiency features and using a TD

normalization. Total energy use was reduced by 12%–46% using the same normalization 

methodology. Without any normalization methods, either based on HDDs or using the TD

between the interior and exterior, the actual energy savings was positive for all buildings even 

with a colder winter and generally warmer indoor temperature settings.

2. Can either enhanced energy savings or “take-back” energy consumption be identified 

from the pre- and post-retrofit measurements?

3. What is the difference in the average indoor air temperatures for the homes with energy 

retrofits compared with the pre-retrofit home (and occupants) measurements?

Question 2 is answered by an analysis of the indoor temperatures (Question 3) over multiple 

monitoring periods. Generally, the indoor temperatures were measured warmer by 1°– 3°F+

from the base year before any retrofit measures were installed. The warmer indoor temperatures 

during the last heating season occurred when average outdoor temperatures were on average 2°F 

colder over the measurement period and represent a “take-back” effect in which more 

comfortable indoor temperatures are selected, presumably because of the lower energy costs.

4. How does the realized energy savings for the efficiency retrofits compare with the 

realized installation cost of the retrofits?

When looking at the overall cost of the upgrades implemented during the pilot program and 

evaluating these costs solely on the basis of energy savings, the simple paybacks are long, 29–70 

years. However, for the costs of the upgrades, which include new crawlspace vapor barriers, 

windows, and siding that are replaced on a regular schedule and financed separately, the payback 

periods are markedly reduced by 11–34 years. Based on the type of upgrades, payback periods of 

30 or more years are acceptable, given the more than 30-year periods between major 

improvements.

5. What is the homeowner perspective on the home comfort following the energy retrofits?

GHI pilot homeowners were asked to complete a questionnaire developed by the GHI buildings 

committee to provide qualitative feedback on the retrofits installed during Phase 2 of the pilot 

program for the cooperative membership. Table 25 summarizes the homeowner responses by 

building type.

60
Table 25. Homeowner Reponses to Energy and Comfort Questionnaire

Question/Response FB FV B and BV

Does your home feel any different since the replacements were installed?

No 29% 0% 17%

Yes 71% 100% 83%

Does your home feel less drafty?

No 14% 13% 4%

Yes 71% 88% 22%

Does your home feel warmer?

No 14% 13% 8%

Yes 86% 88% 92%

How do you find the fan sound?

Quiet 43% 75% 17%

Moderate 29% 13% 50%

Loud 0% 0% 0%

Very Loud 0% 0% 0%

Do not notice it 29% 0% 17%

N/A (no fan 

installed) 0% 13% 0%

Overall, the comments provided by the pilot home members were very positive. As expected, 

many comments focused on logistics, selections, and aesthetics, which are aspects of retrofit 

work that is important for homeowners. Feedback on utility costs has not been compiled as of 

this writing.

6. How does the relative humidity within the home change from the pre- to the post-retrofit

conditions?

Measured indoor relative humidities have remained fairly consistent over the last three of the 

four monitored winter periods, averaging during the latest heating period from 39% to 45%. The 

first-year measured data, which is missing some data early in the heating season, shows a 3%–

5% lower humidity across all homes on average. The combination of envelope improvements, 

including low-e windows and bath fans, appears to have resulted in satisfactory moisture 

performance.

7. What is the change in the crawlspace environmental conditions from the pre- to postretrofit conditions?

Although some data are unavailable for the first season for the crawlspaces, the average seasonal 

relative humidity has remained consistent across all of the monitored periods at about 55%. Dew

point temperatures average approximately 15°F lower than the average air temperatures. 

8. What is the comparison between the metered energy use data (electric utility meter) and 

the measured daily energy use, and can this relationship be standardized for similar 

analysis in homes in heating climates to avoid costly instrumentation?

61
Excellent agreement was found between measured data and utility meter data. Utility meter data 

were compiled biweekly. These data can help to isolate the energy used for heating. Generally, 

the estimated heating energy was higher when using the daily data than with estimates made 

using utility meter data, but the differences were not significant. The average range of heating 

percentage using the daily data was 62%–66% and 57%–66% when using the utility meter data 

estimates. The range, however, was 18%–96% for the daily data and 14%–85% for the utility 

meter data. This extensive data set indicates that use of higher resolution utility data will be 

sufficient for ongoing monitoring efforts at GHI. Furthermore, because all GHI utility meters 

have been converted to smart meters, the resolution of whole-house electric data will be much 

higher should access be given to the data.

62
13 Next Steps

GHI staff, the GHI buildings committee, and the PHI BA team plan to review the results of the 

Phase 2 upgrades, including the energy use during the heating season, the pilot homeowner 

anecdotal responses to the upgrades, the performance of the house following the upgrades, and 

the architectural details that may drive some changes in the selected upgrades for the community.

The homes will continue to be monitored through the Phase 3 heating system upgrades on 

specific units.

All of these review and analysis efforts are focused on achieving recommendations for the 

community-wide upgrade of the GHI portfolio to provide energy savings and durable housing for 

the members.

63
References

CertainTeed (2013). CertainTeed Vinyl Siding Installation Guide, p.70. CTS205. Valley Forge, 

PA: CertainTeed Corporation. Accessed October 28, 2013: 

www.certainteed.com/resources/CTS205.pdf. 

Del Bianco, M.; Wiehagen, J.; Wood, A. (2013). Energy Efficient Crawlspace Foundation 

Retrofit: Mixed Humid Climate. Golden, CO: National Renewable Energy Laboratory. Accessed 

April 1, 2015:

apps1.eere.energy.gov/buildings/publications/pdfs/building_america/crawlspace_found_retrofit.pdf.

“Building America: Bringing Building Innovations to Market.” U.S. Department of Energy. 

Accessed October 28, 2013: http://www1.eere.energy.gov/buildings/residential/ba_index.html.

“GHI Bylaws 2003–2012.” Greenbelt Homes, Inc. Accessed October 28, 2013: 

http://ghi.coop/content/ii-purpose-and-powers.

Guide to Attaching Sheathing, Furring, and/or Cladding through Continuous Foam Insulation to 

Wood Framing, Steel Framing, Concrete and CMU Substrates with TRUFAST SIP TP, SIP LD 

and Tru-Grip Fasteners. (2012). TRU110910-21. Nappanee, IN: NTA, Inc. 

Accessed October 28, 2013:

www.trufast.com/links/pdf/NTA_inc_Engineering_Evaluation_Report_TRU110910-21.pdf.

International Code Conference (2012). International Residential Code 2012.

Excerpt from TABLE R703.4, page 366; “[footnote] z. Where approved by the manufacturer’s 

instructions or test report [vinyl] siding shall be permitted to be installed with fasteners 

penetrating not less than 0.75 inches through wood or wood structural sheathing with or without 

penetration into the framing.”

Maryland Historic Trust. Property Name: Greenbelt Historic District. Accessed October 28, 

2013: http://mht.maryland.gov/nr/NRDetail.aspx?NRID=658&FROM=NRNHLList.aspx

NAHBRC (2011). Greenbelt Homes, Inc. Pilot Project Energy Analysis. Upper Marlboro, 

Maryland: NAHB Research Center. Accessed March 30, 2015: 

http://ghi.coop/sites/default/files/attachments/GHI%20Pilot%20Home%20Energy%20Analysis%

20Report%20by%20NAHBRC.pdf.

“National Temperature and Precipitation Maps.” National Oceanic and Atmospheric 

Administration. Accessed April 1, 2015: http://www.ncdc.noaa.gov/temp-and-precip/usmaps/3/201202.

Pepco, Residential Rate Schedule R. Accessed October 28, 2013: http://www.pepco.com/rateschedules.aspx

“BEopt.” National Renewable Energy Laboratory. Accessed March 30, 2015: 

http://beopt.nrel.gov/downloadBEopt2.

Wiehagen, J.; Del Bianco M.; Wood A. (2013). Greenbelt Homes Pilot Energy Efficiency 

Program Phase 1 Summary: Existing Conditions and Baseline Energy Use. Golden, CO: 

National Renewable Energy Laboratory. Accessed March 30, 2015: 

http://apps1.eere.energy.gov/buildings/publications/pdfs/building_america/greenbelt_homes_pilo

t.pdf.

64
Bibliography

Dow Building Materials. Installing...Residential Sheathing... Accessed October 28, 2013:

http://building.dow.com/na/en/tools/installations/duramate.htm. 

McIlvaine, J., Sutherland, K., and Martin, E. of Florida Solar Energy Center. (2013). Energy 

Retrofit Field Study and Best Practices in a Hot-Humid Climate. Cocoa, FL: BA-PIRC/Florida 

Solar Energy Center. 

www.nrel.gov/docs/fy13osti/57827.pdf

Neuhauser, Ken (2013). Evaluation of Two CEDA Weatherization Pilot Implementations of an 

Exterior Insulation and Over-Clad Retrofit Strategy for Residential Masonry Buildings in 

Chicago. Somerville, MA: Building Science Corporation.

apps1.eere.energy.gov/buildings/publications/pdfs/building_america/evaluation_ceda_pilots.pdf

65
Appendix A: Pilot Program Retrofit Options, Estimated Costs,

and Estimated Energy Savings

66
Appendix B: Units by Construction Type

Construction 

Type General Conditions Total No. of Units

B or BV

8-in. CMU

• Formed concrete crawlspace foundation*, with structural 

concrete first floors over common crawlspaces

• Crawlspaces are 4 ft and retrofitted as closed crawlspaces with 

1–2 in. of rigid XPS foam applied to the perimeter walls

• Crawlspace walls extend under front and rear porch slabs 

(many exposed to ambient conditions)

• Structural concrete floors (1st and 2nd levels)

• Main house and porch slabs lack thermal breaks

• CMU walls, finished with plaster 

• Some interior common walls are wood framed (where party 

walls breach the adjacent units’ footprint).

• Double-glazed vinyl windows (1980)

• Exterior walls are painted (B) or have vinyl siding (BV)

• Flat concrete roofs retrofitted with 3-3⁄4 in. of polyisocyanurate 

insulating tapered sheathing and Ethylene propylene diene 

monomer roofing, R-26

• EBB heating

• Room through-the-wall air conditioning

• Electric water heat

256

FB Veneer

• Formed concrete crawlspace foundations, with structural 

concrete first floors over common crawlspaces 

• Crawlspaces are 4 ft and retrofitted as closed crawlspaces with 

1–2 in. of rigid XPS foam applied to the perimeter walls

• Crawlspace walls extend under front and rear porch slabs 

(many exposed to ambient conditions)

• Structural concrete first floor

• Main house and porch slabs lack thermal breaks

• Balloon- framed 2 × 4 16 in. o.c. walls with plasterboard 

interior finish

• Blown-in cellulose/rock wool insulation in walls (1980)

• Board wall and roof sheathing (1 × 6/1 × 8)

• Exterior brick veneer, no WRB

• Double-glazed vinyl windows (1980)

• Gable roofs with slate shingles

• Ventilated attic with rock wool, cellulose, or fiberglass floor 

insulation, R-16 (1980)

• EBB heating

• Room through-the-wall air conditioning

• Electric water heat

318

67
Construction 

Type General Conditions Total No. of Units

FV Sided

• Common ventilated crawlspace of 8-in. CMU block, 4-1⁄2 

courses high (3 ft)

• 2 × 8 16 in. o.c. floor joists with midspan dropped beam 3, 2 × 

10 in. on CMU piers

• R-11 kraft-faced fiberglass batt insulation in floor joists (1980)

• Balloon-framed 2 × 4 16 in. o.c. walls 

• Blown-in cellulose insulation in walls (1980)

• Board wall and roof sheathing (1 × 6/1 × 8)

• Double-glazed vinyl or aluminum windows (1980)

• Vinyl siding, no WRB

• Gable roof with asphalt shingles 

• Ventilated attic 

• Attics insulated with rock wool, cellulose, or fiberglass floor 

insulation, R-16 (1980)

• EBB heating

• Room through-the-wall air conditioning

• Electric water heat

992

(140 of 

these are 

apartments)

* Several units have full, rear walkout basements of CMU

68
Appendix C: Total Energy Use and Heating Energy Use in Each 

Pilot Home

69
Table 26. Heating Season Total Energy Use in Each Pilot Home

Pilot 

Home

Heating Season Total Energy Use (December 1 Through March 21)

Total Heating Season Energy Use, kWh 30°F Temperature Difference Normalized 3000 HDD Normalized

2010–

2011

2011–

2012

2012–

2013

2013–

2014

2010–

2011

2011–

2012

2012–

2013 2013–2014 2010–2011

2011–

2012

2012–

2013

2013–

2014

B-1 9,436 5,314 8,336 9,697 9,009 6,566 8,646 8,140 9,587 6,781 9,427 9,088

B-2 6,252 4,244 5,073 5,472 6,237 5,312 5,671 5,348 6,352 5,416 5,737 5,128

B-3 1,956 1,774 1,886 2,869 2,737 2,784 2,384 3,466 1,987 2,264 2,133 2,689

B-4 12,472 9,634 8,088 8,595 11,140 10,551 7,971 7,102 12,672 12,294 9,145 8,055

BV-1 8,212 6,799 9,444 7,143 11,257 9,278 11,041 6,701 8,344 8,676 10,680 6,694

B-5 3,174 3,112 4,601 6,176 7,330 6,453 6,785 5,436 3,225 3,971 5,202 5,788

B-6 5,497 4,559 4,067 4,199 9,352 6,283 5,741 4,165 5,585 5,817 4,599 3,935

BV-2 6,044 6,938 8,483 7,020 9,907 7,977 8,577 6,321 6,142 8,853 9,593 6,579

BV-3 8,677 6,353 7,716 8,525 10,200 7,652 8,231 7,480 8,816 8,106 8,725 7,990

BV-4 4,399 3,290 3,720 1,284 6,579 4,865 4,922 2,091 4,470 4,199 4,206 1,203

BV-5 10,166 6,799 7,335 8,455 11,926 7,702 7,888 7,667 10,329 8,676 8,294 7,924

BV-6 8,851 7,750 8,909 8,875 11,261 9,448 10,148 9,402 8,994 9,890 10,074 8,317

FB-1 7,576 6,214 5,458 6,770 8,946 6,948 5,727 5,699 7,698 7,929 6,172 6,344

FB-2 4,727 3,378 5,017 5,248 7,434 4,489 5,404 5,074 4,803 4,310 5,674 4,918

FB-3 6,405 4,564 5,169 4,246 8,684 5,638 5,649 4,332 6,508 5,823 5,846 3,979

FB-4 3,230 2,058 2,434 3,242 8,637 4,350 4,473 4,554 3,282 2,626 2,752 3,038

FB-5 6,490 5,196 5,401 5,059 7,214 6,608 6,292 5,696 6,594 6,630 6,108 4,742

FB-6 7,320 5,638 5,951 6,946 8,454 7,699 7,346 6,221 7,438 7,194 6,729 6,510

FB-7 1,322 1,113 1,448 739 2,781 2,530 2,855 1,337 1,343 1,420 1,637 692

FB-8 7,507 5,087 5,546 6,310 8,463 7,331 7,229 6,727 7,628 6,492 6,271 5,914

FV-1 4,627 3,519 4,777 5,588 8,933 5,448 5,665 5,007 4,702 4,490 5,402 5,237

FV-2 4,995 3,716 3,985 4,010 6,315 4,371 4,229 3,561 5,075 4,742 4,507 3,758

FV-3 4,664 3,133 3,170 3,945 5,861 3,998 3,879 3,237 4,739 3,997 3,585 3,697

FV-4 6,042 4,594 5,065 5,192 7,414 5,949 5,704 4,736 6,139 5,862 5,728 4,866

FV-5 6,362 4,818 4,557 4,830 6,371 5,703 5,002 4,745 6,464 6,148 5,153 4,527

FV-6 4,674 2,152 2,284 2,626 5,498 3,376 3,664 2,963 4,749 2,746 2,583 2,461

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Pilot 

Home

Heating Season Total Energy Use (December 1 Through March 21)

Total Heating Season Energy Use, kWh 30°F Temperature Difference Normalized 3000 HDD Normalized

2010–

2011

2011–

2012

2012–

2013

2013–

2014

2010–

2011

2011–

2012

2012–

2013 2013–2014 2010–2011

2011–

2012

2012–

2013

2013–

2014

FV-7 6,905 5,089 5,799 5,855 7,570 6,378 6,562 5,528 7,016 6,494 6,558 5,487

FV-8 5,177 3,686 3,848 3,923 6,384 5,322 5,386 4,275 5,260 4,704 4,352 3,677

BV5 and BV6 average includes Basement; n/a = data not available

Shaded rows excluded from analysis in the report body.

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Table 27. Heating Season Estimated Energy Use

Pilot 

Home

Heating Season Estimated Heating Energy Use (December 1 Through March 21)

Total Heating Season Energy Use, kWh 30°F Temperature Difference Normalized 3000 HDD Normalized

2010–

2011

2011–

2012

2012–

2013

2013-

2014

2010–

2011

2011–

2012

2012–

2013

2013–

2014

2010–

2011

2011–

2012

2012–

2013

2013–

2014

B-1 7,847 3,923 6,840 8,305 7,493 4,846 7,094 6,971 7,974 5,005 7,735 7,784

B-2 5,115 3,216 4,046 4,404 5,102 4,024 4,523 4,305 5,197 4,103 4,576 4,128

B-3 792 686 746 1,135 1,108 1,076 943 1,372 805 875 844 1,064

B-4 10,398 7,494 6,045 6,420 9,288 8,207 5,958 5,305 10,565 9,563 6,836 6,017

BV-1 6,436 5,023 6,897 5,167 8,823 6,854 8,063 4,847 6,540 6,409 7,799 4,842

B-5 637 575 1,864 3,214 1,471 1,193 2,748 2,829 647 734 2,107 3,012

B-6 4,513 3,575 2,792 2,991 7,678 4,928 3,941 2,967 4,586 4,562 3,157 2,803

BV-2 4,618 5,511 5,841 4,500 7,569 6,337 5,906 4,052 4,692 7,033 6,605 4,217

BV-3 5,253 2,929 4,942 5,608 6,176 3,528 5,272 4,920 5,338 3,738 5,589 5,255

BV-4 1,894 785 1,214 1,117 2,832 1,160 1,606 1,820 1,924 1,001 1,373 1,047

BV-5 8,071 4,705 4,738 6,744 9,469 5,330 5,095 6,115 8,201 6,003 5,358 6,320

BV-6 2,576 1,475 5,879 5,710 3,277 1,798 6,697 6,049 2,617 1,882 6,648 5,352

FB-1 6,371 5,009 4,253 5,564 7,523 5,600 4,463 4,684 6,474 6,392 4,809 5,215

FB-2 3,561 2,109 3,667 3,860 5,601 2,804 3,950 3,732 3,618 2,692 4,147 3,617

FB-3 4,900 2,674 3,614 2,813 6,644 3,304 3,949 2,870 4,979 3,412 4,086 2,636

FB-4 2,459 1,327 1,666 2,418 6,573 2,805 3,062 3,396 2,498 1,693 1,884 2,266

FB-5 4,878 3,675 4,005 3,663 5,422 4,674 4,666 4,124 4,956 4,690 4,529 3,433

FB-6 3,550 2,543 2,758 3,602 4,100 3,473 3,405 3,226 3,608 3,245 3,119 3,376

FB-7 838 669 974 329 1,764 1,521 1,920 594 852 854 1,101 308

FB-8 5,575 3,336 3,754 4,603 6,285 4,808 4,893 4,907 5,665 4,257 4,245 4,314

FV-1 3,659 2,172 3,270 3,741 7,065 3,363 3,878 3,352 3,718 2,772 3,698 3,506

FV-2 2,644 1,910 2,093 2,090 3,343 2,246 2,221 1,856 2,687 2,437 2,367 1,958

FV-3 3,451 1,647 1,503 2,205 4,337 2,101 1,839 1,809 3,507 2,101 1,700 2,067

FV-4 4,465 3,156 3,643 3,765 5,478 4,088 4,102 3,434 4,536 4,028 4,119 3,529

FV-5 4,492 3,200 2,692 2,997 4,498 3,788 2,955 2,945 4,564 4,083 3,044 2,809

FV-6 2,598 2,075 714 1,105 3,056 3,255 1,146 1,247 2,640 2,647 808 1,036

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Pilot 

Home

Heating Season Estimated Heating Energy Use (December 1 Through March 21)

Total Heating Season Energy Use, kWh 30°F Temperature Difference Normalized 3000 HDD Normalized

2010–

2011

2011–

2012

2012–

2013

2013-

2014

2010–

2011

2011–

2012

2012–

2013

2013–

2014

2010–

2011

2011–

2012

2012–

2013

2013–

2014

FV-7 3,244 1,732 2,744 2,957 3,556 2,170 3,105 2,791 3,296 2,210 3,103 2,771

FV-8 3,883 2,517 2,684 2,713 4,788 3,635 3,757 2,956 3,945 3,212 3,035 2,542

BV5 & BV6 average includes Basement; n/a = data not available

Shaded rows excluded from analysis in the report body.

73
Appendix D: Greenbelt Homes, Inc. Pilot Program

Phase 3: Heating Systems Overview

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DOE/GO-102015-4618 ▪ May 2015

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