Byggmeister Test Home: 

Analysis and Initial Results of 

Cold Climate Wood-Framed 

Home Retrofit

C. Gates

Building Science Corporation

January 2013
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iii

Byggmeister Test Home: 

Analysis and Initial Results of Cold Climate Wood-Framed Home Retrofit

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: 

C. Gates

Building Science Corporation 

30 Forest Street

Somerville, MA 02143

NREL Technical Monitor: Cheryn Metzger

Prepared under Subcontract No. KNDJ-0-40337-00 

January 2013 
iv

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v

Contents

List of Figures ............................................................................................................................................ vi

List of Tables .............................................................................................................................................. vi

Definitions.................................................................................................................................................. vii

Executive Summary................................................................................................................................. viii

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

1.1 Context and Relevance to Other Homes.......................................................................................... 1

2 Retrofit Measures for Belmont Two-Family ....................................................................................... 3

2.1 Enclosure Measures for Belmont Two-Family................................................................................ 4

2.1.1 Above-Grade Walls ............................................................................................................ 4

2.1.2 Roof or Attic ....................................................................................................................... 5

2.1.3 Foundation Walls................................................................................................................ 6

2.1.4 Basement Floor................................................................................................................... 7

2.1.5 Windows and Doors............................................................................................................ 7

2.1.6 Water Management System................................................................................................ 8

2.1.7 Air Barrier System.............................................................................................................. 9

2.1.8 Other Enclosure Measures................................................................................................ 10

2.1.9 Enclosure Retrofit Costs................................................................................................... 11

2.2 Mechanical System Measures for the Belmont Two-Family......................................................... 13

2.2.1 Mechanical System Construction Costs............................................................................ 15

2.3 Deciding Which Measures To Include in the Retrofit ................................................................... 15

2.3.1 The Planning Process........................................................................................................ 15

2.3.2 Basement Decisions.......................................................................................................... 16

2.3.3 Mechanical System Decisions.......................................................................................... 16

2.4 Cost Effectiveness of the Retrofit Measures Package.................................................................... 17

3 Testing and Analysis for Belmont Two-Family ............................................................................... 19

3.1 Measurements................................................................................................................................ 19

3.2 Energy Modeling ........................................................................................................................... 20

3.3 Actual Energy Use for January 2011 Through May 2011 ............................................................. 22

3.4 Occupant Feedback........................................................................................................................ 23

4 Conclusions ........................................................................................................................................ 24

References................................................................................................................................................. 25

Appendix A: Belmont Two-Family: Final Blower Door Test............................................................... A-1

Appendix B: Belmont Case Study: HERS as Planning, Goal-Setting Tool for a Deep Energy 

Retrofit............................................................................................................................................... B-1

Appendix C: Belmont Two-Family: Yearly Site Energy Use Data Generated by BEopt .................. C-1

Appendix D: Belmont Two-Family: Monthly Average Site Energy Use Data Generated by 

BEopt ................................................................................................................................................. D-1
vi

List of Figures

Figure 1. Pre- and post-retrofit Belmont Two-Family.............................................................................. 2

Figure 2. Insulating sheathing on the Belmont Two-Family................................................................... 5

Figure 3. Belmont Two-Family roof and attic insulation......................................................................... 6

Figure 4. Belmont Two-Family basement wall insulation....................................................................... 7

Figure 5. Belmont Two-Family outie windows......................................................................................... 8

Figure 6. Belmont Two-Family sump pump installed (before basement wall was insulated)............. 9

Figure 7. Belmont Two-Family, showing the roof membrane that was sealed to exterior insulating 

sheathing............................................................................................................................................. 10

Figure 8. Belmont Two-Family porch deck attachment (from below) ................................................. 11

Figure 9. Belmont Two-Family natural gas furnace in basement with air-conditioner coil 

attached............................................................................................................................................... 13

Figure 10. Belmont Two-Family ERV for upper unit in attic kneewall space...................................... 14

Figure 11. Belmont Two-Family DHW storage tank for solar thermal with backup electric tanks... 14

Figure 12. Belmont Two-Family BEopt optimization results, cost versus energy use...................... 18

Figure 13. Belmont Two-Family BEopt optimization results, source energy use.............................. 18

Figure 14. Belmont Two-Family: Setting up blower door testing ........................................................ 20

Unless otherwise noted, all figures were created by BSC.

List of Tables

Table 1. Belmont Two-Family Enclosure Measures and Cost.............................................................. 12

Table 2. Belmont Two-Family Mechanical System Measures and Cost.............................................. 15

Table 3. Retrofit Measures Included ....................................................................................................... 16

Table 4. Blower Door Testing for the Belmont Two-Family.................................................................. 20

Table 5. Final Energy Model Site Energy Use for Belmont Two-Family (MMBtu/yr).......................... 21

Table 6. Energy Use Reduction by Component for Belmont Two-Family (MMBtu/yr)....................... 21

Table 7. January 2011–May 2011 Actual Site Energy Use .................................................................... 22

Table 8. January 2011–May 2011 BEopt Projected Site Energy Use ................................................... 22

Unless otherwise noted, all tables were created by BSC.
vii

Definitions

ACH Air changes per hour 

ACH 50 Air changes per hour at 50 pascal test pressure

AFUE Annual fuel utilization efficiency

ASHP Air source heat pump

ASHRAE American Society of Heating, Refrigerating, and Air Conditioning 

Engineers

BEopt Building Energy Optimization 

BSC Building Science Corporation 

Btu British thermal unit

ccSPF Closed-cell spray polyurethane foam

cfm Cubic feet per minute

cfm 50 Cubic feet per minute at 50 pascal test pressure

DEAP Duclos, Eldrenkamp and Panish Energy Group

DER Deep energy retrofit

DHW Domestic hot water

EER Energy efficiency ratio

ERV Energy recovery ventilator

ft2 Square foot

ft3 Cubic foot

gal Gallon

HERS Home Energy Rating System 

HRV Heat recovery ventilator

kBtu Thousand Btus

kW Kilowatt

kWh Kilowatt-hour

MMBtu Million British thermal units

PV Photovoltaic

SEER Seasonal energy efficiency ratio

SHGC Solar heat gain coefficient

THC Thousand Home Challenge

yr Year
viii

Executive Summary

The Building Science Corporation seeks to further the energy efficiency market for retrofit 

projects in the New England area by supporting projects that are based on solid building science 

fundamentals and verified implementation. The Building Science Corporation has been working 

with Byggmeister, a partner on its Building America Program team, on retrofit projects.

Byggmeister is a Boston-area design-build firm that specializes in energy efficient retrofits and 

new construction. The DEAP (Duclos, Eldrenkamp and Panish) Energy Group, which is 

associated with Byggmeister, conducts energy analysis for projects during design and performs 

monitoring after completion. 

With the high exposure of energy efficiency and retrofit terminology currently being used in the 

general media, it is important to have evidence that measures being proposed will in fact benefit 

the homeowner through a combination of energy savings, improved durability, and occupant 

comfort. Concrete data from specific projects can close the gap between “hype” and reality. 

This technical report describes a deep energy retrofit project for a two-family wood framed home 

located in Belmont, Massachusetts. Built in the 1920s, this home is referred to in this report as 

the “Belmont Two-Family.” The report examines the retrofit measures for the enclosure and 

mechanical systems and the decision making that took place during project planning. Because 

the retrofit project is complete, projected and actual energy use data are compared for the 5 

months immediately following the retrofit. Occupant reactions and experiences are also 

described.

The retrofit measures implemented for the Belmont Two-Family resulted in a home with 

airtightness of 0.93 air changes per hour at 50 pascal test pressure, a Home Energy Rating 

System index of 44 (excluding photovoltaics), and initial energy use significantly less than the 

energy models projected. The home is on track to meet the Thousand Home Challenge. In these 

ways, the project meets or exceeds the energy goals established for the retrofit. 

Energy modeling tools were found to be useful during the planning stage for investigating the

relative cost effectiveness of retrofit measures. They were less effective, however, in projecting

actual energy use. Discrepancies between the results of different tools need to be better 

understood, and interactions among retrofit measures are not effectively handled by the energy 

modeling tools at this time. 

During the first few months after the retrofit, the homeowner had questions about the effective 

operation of the mechanical equipment. With the increased airtightness and R-values, the 

equipment needs to be operated differently to realize the potential energy savings. This 

information needs to be better understood and disseminated by everyone involved with retrofit 

projects. 

This technical report contributes to several basic areas of research. These include the 

combination of measures that is feasible, affordable, and acceptable to homeowners as well as 

expectations versus results. 
1 

1 Introduction

The Building Science Corporation (BSC) seeks to further the energy efficiency market for 

retrofit projects in the New England area by supporting projects that are based on solid building 

science fundamentals and verified implementation.

1

 BSC has been working with Byggmeister, a 

partner on its Building America Program team,2 on retrofit projects. Byggmeister is a Bostonarea design-build firm that specializes in energy efficient retrofits and new construction. DEAP

(Duclos, Eldrenkamp and Panish) Energy Group, which is associated with Byggmeister, 

conducts energy analysis for projects during design and performs monitoring after completion. 

With the high exposure of energy efficiency and retrofit terminology currently being used in the 

general media, it is important to have evidence that measures being proposed will in fact benefit 

the homeowner through a combination of energy savings, improved durability, and occupant 

comfort. Concrete data from specific projects can close the gap between “hype” and reality. 

This report explores the retrofit efforts and results for a test home called the “Belmont TwoFamily”. This typical, wood framed, two-family home was built in 1925 in Belmont, 

Massachusetts (see Figure 1). This test home contributes to several basic areas of research. These 

include the combination of measures that is feasible, affordable, and acceptable to homeowners,

as well as expectations versus results. In particular, this report examines the package of measures 

considered, the planning process used, and the construction costs reported. In addition, because 

the retrofit is complete, initial energy use results are available for analysis. 

The Belmont Two-Family was a participant in the National Grid Deep Energy Retrofit Pilot 

Program (National Grid 2009).

3

 The program’s goal is to achieve, ideally, at least 50% better 

energy performance than a code-built or Energy Yardstick home4

; the program offers financial 

incentives and technical support to participants. BSC has partnered with National Grid by 

furnishing technical guidance and program support. 

1.1 Context and Relevance to Other Homes 

The current owner purchased the Belmont Two-Family in 2009 to renovate and then to serve as 

an extended family home with the owner’s immediate family in the upper unit and his parents in 

the lower unit. When an older home such as this is purchased at a bargain price, an energy 

retrofit can be combined with the renovation project. The older home can be brought up to date 

in terms of energy and HVAC standards as well as modifications needed to meet modern living 

standards. Given the continuing lower prices in the current home market, this type of situation is 

likely to continue to generate a strong market for energy retrofits in the near future. For this type 

of retrofit project, the home is likely to be unoccupied during construction. Although this 

removes certain constraints, the project schedule can be a driving force to meet an established 

move-in date for the new owner. These conditions contribute to the decisions made during 

planning of the energy measures for this type of energy retrofit. 

 

1 For more information, see www.buildingscience.com. 2 For more information, see www.buildingamerica.gov.

3 For more information, see http://www.powerofaction.com/der.

4 For more information, see 

https://www.energystar.gov/index.cfm?fuseaction=home_energy_yardstick.showgetstarted.
2 

Figure 1. Pre- and post-retrofit Belmont Two-Family 

Pre-retrofit photo provided by National Grid.
3

2 Retrofit Measures for Belmont Two-Family

Although many of the energy efficiency measures for a retrofit are the same as for new 

construction, the underlying constraints differ. For new construction, the owner has a clean slate 

for implementing the most important energy efficient aspects—detailing the air barrier; 

incorporating ventilation and ductwork for heating and cooling; selecting, installing, and air 

sealing windows; and using large amounts of insulation. These can be implemented according to 

standard proven details. For a retrofit, though, the reality of existing conditions results in special 

case details for nearly all portions of the building. The decision to retrofit a building implies that 

something about the existing building needs to be preserved—all or parts of the exterior, all or 

parts of the interior, just the structural framing, or a combination. This complicates everything—

from installing an effective air barrier to ventilating the newly air-tightened house.

For the Belmont Two-Family, certain existing elements of the interior, such as window and door 

moldings, wood floors, and plaster over lath walls were elegant and retained where possible. On 

the other hand, some interior partitions were to be removed or relocated and bathrooms and 

kitchens were to be completely gutted, so there were opportunities to introduce retrofit measures 

that required invasive construction methods. 

From the beginning of the project, the owner was committed to creating a home with exceptional 

energy efficiency that would demonstrate what was possible and serve as an information

resource for others interested in energy efficient homes. The energy goals of the project evolved 

during the planning phase as a result of energy and cost modeling and the availability of rebates 

and incentives, as well as the constraints of the house itself. The project started out targeting 

either Passive House certification5 or net zero energy status, then cut back somewhat to a deep 

energy retrofit (DER). In the end, designers and the homeowner settled on participating in 

National Grid’s Deep Energy Retrofit Pilot Program (plus photovoltaic [PV] panels). The home 

also became a participant in the Thousand Home Challenge (THC).

6

Passive House certification requires meeting stringent performance requirements that include 

upper limits on air infiltration (≤0.6 air changes per hour at 50 pascal test pressure [ACH 50]), 

the annual heating requirement (≤4.65 kBtu/ft2∙yr), and total source energy demand (≤38.1 

kBtu/ft2∙yr) (Straube 2009). Net zero energy means producing at least as much energy on site as 

is used over the course of a year. A DER is typically a package of specific energy efficiency 

measures that addresses all components (e.g., exterior walls, attic/roof, windows, and doors). 

THC is a performance-oriented program that sets a specific upper limit for total yearly site 

energy use.

In addition to the specific performance goals incorporated by participating in the DER program 

and in THC, the contract between the owner and Byggmeister added two specific performance 

goals: air infiltration of 1,000 cubic feet per minute at 50 pascal test pressure (cfm 50) or less and 

a Home Energy Rating System (HERS) index of 55 or less.

7

 5 For more information about the Passive House methodology and certification in the United States, see 

http://phaus.org 6 For more information about this program, developed and directed by the Affordable Comfort Institute (one of 

BSC’s Building America team partners), see http://thousandhomechallenge.org. 7 HERS was developed by the Residential Energy Services Network. A net zero energy home scores a HERS index 

of 0.
4

Regardless of the specific energy efficiency goals being targeted, a set of measures is used to 

improve performance levels. The measures can be broken into two groups: building enclosure 

measures and mechanical system measures. Enclosure measures address energy efficiency by 

reducing heat loss or gain, reducing air infiltration, and improving durability and indoor air 

quality. Mechanical measures address energy efficiency primarily by upgrading the efficiency of 

equipment.

The enclosure measures, though, add new requirements to the mechanical systems. Because of 

increased airtightness, ventilation must be provided and combustion safety must be ensured. 

Also, because of the reduced load conditions resulting from the improved enclosure, the 

mechanical systems can and should be downsized.

With the test home located in Massachusetts, the retrofit measures that are described in this 

document are discussed in the context of cold-climate (U.S. Department of Energy Zone 5A) 

conditions.

2.1 Enclosure Measures for Belmont Two-Family

Enclosure retrofit measures are described based on the enclosure component or the function as 

follows: above-grade walls, roof or attic, foundation walls, basement floor, windows and doors, 

water management system, air barrier system, and other enclosure measures.

The National Grid Deep Energy Retrofit Program has desired project characteristics for 

qualification, including fenestration, airtightness, and opaque enclosure guidelines. For 

reference, the program’s targets for opaque R-value, fenestration, and airtightness are 

summarized as follows (National Grid 2009, p. 6–7):

Insulation - targets for effective R-value: roof-R60, above grade wall-R40, below 

grade wall - R20, basement floor - R10. Thermal bridging needs to be considered 

fully in estimation of thermal performance and minimized to the extent possible.

Air Sealing Target – Ideal whole house sealed to achieve 0.1 (zero point 1) cfm

50 /sq. ft. of thermal enclosure surface area (6 sides) with high durability 

materials.

Windows and Doors - target R5 (U ≤ 0.2) whole-unit thermal performance, 

infiltration resistance performance of ≤ 0.15 cfm/sq ft. of air leakage, per 

AAMA11 standard infiltration test.

When it was accepted into the National Grid DER Pilot program, these became the target Rvalues for the enclosure measures for the Belmont Two-Family. 

2.1.1 Above-Grade Walls

To provide at least nominal R-40 walls, insulating sheathing was applied over the exterior board 

sheathing and the wall cavities were filled with cellulose insulation. 

The specific components of the exterior wall upgrade were as follows: 

• Existing cedar shingles and remaining building paper were removed to expose the board 

sheathing; board sheathing was replaced where damaged.

• Cellulose was blown into the wall cavities from the outside through cores in the board 

sheathing where the interior plaster walls were to be retained. In areas where there was no 

existing finished wall (e.g., at the attic gables), netted cellulose was applied from inside. 
5 

• Housewrap was applied over the board sheathing. 

• Insulating sheathing (4 in.) was applied over the housewrap; the seams of the insulating 

sheathing were staggered, both vertically and horizontally, and the seams were taped on 

both layers (see Figure 2). 

• Vertical wood strapping was applied over the insulating sheathing and attached to the 

wall studs using long screws. For this type of installation, the screws need to be hotdipped galvanized screws sized to extend 11⁄2 in. into the existing wall studs (or as 

required by code).

• Fiber cement lap siding was attached to the wood strapping. 

Figure 2. Insulating sheathing on the Belmont Two-Family

Photo by David Connelly Legg 

2.1.2 Roof or Attic 

Before the retrofit, the attic space was used for storage. As part of the renovation, living space 

for the upper unit was created in the attic including a bedroom, a full bathroom, and a sitting 

area. Also, ductwork and mechanical equipment was located in the space behind the attic 

kneewalls. The formerly vented attic, then, was changed to an unvented attic. 

With a targeted nominal R-value of R-60 for the roof, three layers of 2-in.-thick foil-faced 

polyisocyanurate insulating sheathing were applied over the existing roof sheathing. Netted dry 

cellulose was blown into the 7-in.- deep rafter bays. The seams of the insulating sheathing were 

staggered and taped (see Figure 3). 
6

Figure 3. Belmont Two-Family roof and attic insulation

The specific components of the roof upgrade were as follows: 

• Existing roofing shingles and old underlayment were removed, exposing the existing roof 

sheathing; sheathing was replaced where there was damage. 

• The overhangs at the eaves and rakes were sawed off (known as a “chainsaw retrofit”) so 

that the planes of the roof and wall sheathing meet to form a corner. The exterior 

insulating sheathing on the wall was extended up to the corner.

• Self-adhered roofing membrane was applied over the existing roof sheathing. The 

membrane was lapped down over the face of the outside layer of insulating sheathing on 

the wall and sealed to it. 

• The insulating sheathing on the roof was installed over the membrane, extending over the 

top of the wall insulating sheathing; the seams of the insulating sheathing were staggered 

between layers and were taped to minimize air passage channels. 

• A new layer of plywood sheathing was installed, attached through the insulation to the 

existing rafters using long screws. The plywood was covered with ice and water shield 

for the entire roof. For this type of installation, the screws need to be hot-dipped 

galvanized sized to extend 11⁄2 in. into the existing rafters (or as required by code).

• New overhangs for the eaves and rakes were constructed and attached back to the 

building structure through the insulating sheathing.

• New asphalt shingles were installed. 

• On the interior, the 7-in. rafter bays were netted and filled with cellulose. 

2.1.3 Foundation Walls

The test home has a full basement that was to be used for storage, mechanical equipment, and 

laundry. With exposed stone foundation walls, the existing basement before the retrofit was 
7

damp and subject to minor flooding. The targeted nominal R-value for basement walls is R-20 

and the only feasible option was to insulate from the inside (Lstiburek 2006). 

The specific components of the foundation wall upgrade were as follows:

• Two to three inches of closed-cell spray foam (ccSPF) insulation was applied directly 

onto the stone foundation wall; the spray foam extended up over the mud sill and rim 

joist and down onto the basement floor.

• A metal stud interior perimeter wall with gypsum wall board was installed inside the 

ccSPF.

• The space between the wall board and the ccSPF was filled with dense packed mineral 

wool (see Figure 4).

After the retrofit, the total insulation R-value is approximately R-40. 

. 

Figure 4. Belmont Two-Family basement wall insulation

2.1.4 Basement Floor

It is recommended that basement floors be insulated to at least nominal R-10. For a retrofit, this 

particular measure can be problematic because adding 2 in. of insulation to the floor raises the 

floor elevation, often resulting in a ceiling height problem. It can also seem unnecessary to the 

homeowner because the ground temperature at that level is moderate, which means that the 

energy loss through the floor is relatively low. An untreated basement floor, though, can be a 

source of moisture from condensation and possible capillary wicking from below in addition to 

heat loss (Lstiburek 2006). 

This measure was not included for the Belmont Two-Family.

2.1.5 Windows and Doors 

The targeted R-value for doors and windows was R-5 or more (a U-value of 0.2 or less). New 

triple glazed, flanged vinyl windows were installed with a U-value of 0.2, a solar heat gain 
8

coefficient (SHGC) of 0.25, and visual transmittance of 0.42. These windows were installed as 

“outie” windows (see Ueno 2010), meaning that the outside plane of the windows is at the 

outside of the exterior wall. The installation for this project nailed the flanges to strapping 

surrounding the windows that was applied over the insulating sheathing; the strapping was 

attached through the insulating sheathing to the wall framing by long screws. With windows in 

an outie installation, it is necessary to extend the existing interior jamb, head, and sill window 

trim to reach the position of the new windows (see Figure 5).

Figure 5. Belmont Two-Family outie windows

New insulated exterior doors were installed as well. 

2.1.6 Water Management System

The water management system needs to be coordinated among all the components of the 

enclosure (BSC May 2009a). For the roof, the ice and water shield underlayment over the 

plywood sheathing is the drainage plane. The eave overhangs extend the water management 

system beyond the roof/wall intersection. 

The drainage plane for the exterior walls is the outer layer of insulating sheathing. To serve this 

function, all seams of the insulating sheathing were taped to prevent water from passing through 

the seams. The window flashing and sill pan were integrated with the outer surface of the 

insulating sheathing. The gap between the insulating sheathing and the lap siding that is created 

by the vertical strapping furnishes space for drainage as well as ventilation to assist drying. 

In the basement, the primary water management concern was to handle bulk and capillary water 

that penetrates through the foundation walls. Because water does not pass through ccSPF, the 

basement wall treatment prevents water from entering the basement interior until it reaches the 

floor. To handle water at the bottom of the foundation wall, a subslab interior perimeter drainage 

system connected to a new sump pump was installed (see Figure 6). In addition, a short segment
9 

of drainage mat was installed along the base of the foundation wall when the trench was created 

for the subslab drainage system. The drainage mat forms a channel that directs the water from 

behind the ccSPF down to the subslab drainage system. 

Figure 6. Belmont Two-Family sump pump installed (before basement wall was insulated)

Photo by David Connelly Legg 

Because the basement slab insulation was not used in this project, there was a risk of 

condensation on the basement floor slab and capillary action or diffusion of water through the 

basement slab. An application of an epoxy coating was applied to the slab to prevent diffusion. If 

this does not control moisture sufficiently, a dehumidifier will need to be installed in the 

basement.

2.1.7 Air Barrier System

The air barrier system separates indoor (conditioned) air from outdoor (unconditioned) air. To be 

effective, it must be continuous over all six sides of the building. The retrofit plan needs to 

identify the air barrier for each component of the enclosure and how it is to be continuously 

transitioned to the air barrier of adjacent components (Lstiburek 2005). 

For the Belmont Two-Family, the air barrier system consists of the following components: 

• Self-adhered roofing membrane over the existing roof sheathing (roof) 

• The taped outer layer of exterior insulating sheathing on the exterior walls (wall) 

• The ccSPF on the inside of the stone foundation walls (foundation wall)

• The existing concrete basement slab (basement floor). 

Transitions between these components were as follows:

• Roof to exterior wall. The roofing membrane was extended down and sealed onto the 

outer layer of the insulating sheathing at the top of the walls (see Figure 7). This simple 

transition was possible because there were no overhangs or eaves (i.e., the chainsaw 

retrofit).
10

• Exterior wall air barrier (the outer layer of insulating sheathing) to foundation wall 

(ccSPF on the interior side). This was complex and labor intensive because there were 

so many layers between the outer layer of insulating sheathing and the interior ccSPF on 

the foundation wall. Sealant was required between the layers of insulating sheathing at all 

edges and between the insulating sheathing and the board sheathing and mud sill. In 

addition, the ccSPF was extended up over the interior side of the mud sill. To be 

effective, each of these transitions needed to be continuous. 

• Foundation wall to concrete basement slab. The transition was created by extending 

the ccSPF down onto the concrete slab.

Figure 7. Belmont Two-Family, showing the roof membrane that was

sealed to exterior insulating sheathing

The blower door test results (590 cfm 50 or 0.93 ACH 50) indicate that even though the air 

barrier system was complicated and difficult to implement, the implementation was thorough and 

yielded excellent results. 

2.1.8 Other Enclosure Measures

The chimney and the fireplaces were removed. The porch roofs and porch decks were removed 

and rebuilt and attached after the insulating sheathing had been applied over the house (see 

Figure 8). This approach prevents thermal bridging where these attach to the house. 
11

Figure 8. Belmont Two-Family porch deck attachment (from below)

2.1.9 Enclosure Retrofit Costs

The costs of renovating and those of including a DER with the renovation differ significantly. At 

one point during project planning, it seemed that the performance improvement part of the 

project might need to be deferred because of cost. This would have severely limited the type of 

energy upgrades that could be made in the future. Fortunately, the availability of rebates, grants 

and other financial incentives allowed the project to go forward with the original plans, even 

enabling the addition of a PV component. 

Table 1 summarizes the pre-retrofit condition, retrofit enclosure measures implemented, and the 

construction cost for the enclosure measures for the Belmont Two-Family.

The costs given in Table 1 are the actual construction costs to the owner for the enclosure 

measures before rebates or other incentives were applied. In some cases, the actual cost to the 

owner will, of necessity, include more than just the cost of the enclosure measure. For example, 

because the roofing and siding must be removed so that the insulating sheathing can be applied

to the exterior, new roofing shingles and usually new siding will be needed as well. The 

additional costs for shingles and siding are not included in the table.
12

Table 1. Belmont Two-Family Enclosure Measures and Cost

Parameter Existing Condition Enclosure Measures Construction Cost (number 

of units)

Roof or Attic Vented attic; fiberglass 

batts on attic floor

R-63: 6-in.

polyisocyanurate exterior 

insulating sheathing with 7-

in. netted cellulose filling 

rafter cavities; asphalt 

shingles; unvented attic

$28,055; excludes new roof 

shingles

(approximately 1,708 ft2 roof 

deck area at $16.50/ft2)

Above-Grade 

Walls

No insulation in 2 × 4 

wall cavity

R-40: 4-in.

polyisocyanurate exterior 

insulating sheathing with 4-

in. dry cellulose insulation 

in wall cavities; fiber 

cement lap siding over 

vertical strapping

$45,138; excludes new siding 

and trim

(approximately 3,262 ft2 at 

$14.00/ft2

)

Foundation 

Wall Stone wall, uninsulated

R-20: 3-in. ccSPF covered 

with mineral wool 

insulation within a metal 

stud perimeter wall 

$9,051

(approximately 1,112 ft2 at 

$8.14/ft2)

Basement 

Floor

Concrete floor, 

uninsulated

No insulation; subslab 

drainage system, sump, and 

sump pump added for water 

management

No separate construction cost 

available 

(approximately 1,200 ft2

)

Windows and 

Doors Wood, single glazed

U-value = 0.25, SHGC =

0.25 vinyl, krypton/argon 

blend, triple glazed, low-E 

windows; new insulated 

doors

$40,305

(55 windows, 5 doors at

$596.45/window and

$1,500/door)

Water 

Management 

System`

Roofing felt under 

asphalt shingles; 

building paper under 

wood shingles on walls; 

overhangs at eave and 

rake

Ice and water shield under 

shingles; taped insulating 

sheathing behind lap siding; 

subslab drainage, sump, 

and sump pump

No separate construction cost 

available

Air Barrier 

System/ 

Airtightness

None/

5,700 cfm 50 or 15.2 

ACH 50 (attic and 

basement closed) 

Self-adhered membrane 

over existing sheathing 

(roof), exterior insulating 

sheathing taped (walls), 

ccSPF (foundation walls 

and mud sill), with taped, 

sealed, or spray foam 

transitions;

590 cfm 50 or 0.93 ACH 50

$3,000 for testing and sealing; 

air barrier materials combined 

with other costs

Other 

Enclosure 

Measures

Removed chimney roof 

penetration; porch roofs, 

stairs, landing at back 

rebuilt to allow continuous 

exterior wall insulation 

behind

No separate construction cost 

available
13

2.2 Mechanical System Measures for the Belmont Two-Family

Replacing outdated, inefficient mechanical equipment is a major source of energy savings for a 

retrofit. With improved R-values and airtightness of the house after the retrofit, smaller and more 

energy efficient systems can be installed (Ueno 2008). Because of the improved airtightness, it is 

important for occupant safety and indoor air quality that the installed mechanical systems have 

controlled, outside-supplied combustion air and exhaust venting. In addition, the improved 

airtightness introduces the need for mechanical ventilation.

The mechanical systems retrofit measures include upgrades to heating, cooling, ventilation, and 

domestic hot water (DHW). These generally work together as an interdependent system. 

The existing systems for the Belmont Two-Family consisted of old and outdated equipment, all 

of which needed to be replaced. Heat was produced by two oil boilers, one for each unit, with 

steam radiators. There was no cooling. Atmospheric natural gas water heaters generated hot 

water, and only spot exhaust was provided.

As part of the retrofit planning, the team decided to switch to forced air heating and cooling. 

Because so much of the interior was opened up for the renovation, installing ductwork was not a 

major obstacle. With all interior space including the attic, the kneewall space and the basement 

being within the thermal enclosure layer, all ductwork is located in conditioned space. 

Figure 9. Belmont Two-Family natural gas furnace in basement with air-conditioner coil attached

For each unit, a new heating/cooling system was installed. The lower unit’s systems are in the 

basement; the upper unit’s systems are in the kneewall attic space. Each system consists of a 

96.7 annual fuel utilization efficiency (AFUE) direct vent, closed combustion natural gas 

variable speed furnace with an Air-Conditioning, Heating, and Refrigeration Institute-rated 
14

14 seasonal energy efficiency ratio (SEER)/12 energy efficiency ratio (EER) coil attached to the 

air handler and an outdoor unit at the back of the house (see Figure 9). 

Ventilation is supplied by one energy recovery ventilator (ERV) for each unit. The ductwork for 

the ERVs is independent of the air handler’s ductwork. The supply air is ducted to common 

space and the exhaust is taken from the bathrooms. The ERV for the lower unit is located in the 

basement; the ERV for the upper unit is located in the kneewall attic space (see Figure 10).

Figure 10. Belmont Two-Family ERV for upper unit in attic kneewall space

DHW combines a 77-ft2 solar thermal collector system with a 100-gal common tank and a 

separate 40-gal electric heat backup tank for each unit (see Figure 11). 

Figure 11. Belmont Two-Family DHW storage tank for solar thermal with backup electric tanks
15

2.2.1 Mechanical System Construction Costs 

Table 2 summarizes the existing and retrofit mechanical system measures, and gives the 

approximate cost to the owner for the new equipment.

Table 2. Belmont Two-Family Mechanical System Measures and Cost

Parameter Existing 

Conditions

Mechanical System 

Measure

Approximate 

Construction Cost

Heating System

Two oil boilers in 

basement with 

steam radiators

For each unit, 96.7 AFUE 

direct vent, closed 

combustion natural gas 

furnace 

$15,995 (2 units for 

heating, including 

ductwork)

Cooling System None

For each unit, 14 SEER/12 

EER coil installed at airhandling unit and 

connected to outdoor unit 

$3,000 

(2 outdoor units) 

Ventilation Spot exhaust only ERV installed for each unit

$7,084

(2 units, including 

dedicated ductwork)

DHW

Atmospheric 

natural gas water 

heater

Solar thermal with single 

storage tank and, for each 

unit, electric backup tank

$14,070

Site-Generated 

Electricity None 4.3 kW (21 panels) $37,810

2.3 Deciding Which Measures To Include in the Retrofit

As in most construction projects, the final decision about the measures to include is primarily 

driven by cost—initial cost, operational cost, or some combination. It can also be observed that 

the measures eliminated because of cost are probably an indicator of their value as perceived by 

the homeowner.

For this project, specific performance goals—air infiltration level and HERS index—were also 

significant factors in the decision process. 

2.3.1 The Planning Process

For this test home, the owner was committed to ultra-high energy efficiency from the start, even 

considering Passive House certification. As a result, all of the measures of a DER that showed 

progress toward the project’s performance goals were considered. To evaluate the performance, 

the project’s energy consultant, DEAP Energy Group, developed a REM/Rate energy model for 

use during the planning process. The model was developed to show projected energy use 

changes for incremental application of measures.

The planning process went through several iterations. The initial concept was to target either the 

passive house standard or net zero energy status. Energy modeling created the more realistic goal 

of a DER. Acceptance into the National Grid DER Pilot Project set specific goals for the retrofit 

measures and—with the associated financial incentive—designers were able to include PV. At 

each step along the way, the energy model was used to inform the process (Duclos and 

Eldrenkamp 2011). Table 3 presents the measures that were included in or eliminated from the 

final plan.
16

Table 3. Retrofit Measures Included

Retrofit Measure Belmont Two-Family

Roof or Attic Included

Above-Grade Walls Included

Foundation Wall Included

Basement Floor Not included

Windows and Doors Included 

Airtightness Included

Water Management Included

Heating Included

Cooling Included

Mechanical Ventilation Included 

DHW Included 

On-Site Power Generation Included

2.3.2 Basement Decisions

Except for the basement measures, all enclosure measures were included. Insulating the 

basement is the retrofit measure most often left out of a retrofit project. In this case, the basement 

floor was not insulated. Logistically, this would have been a difficult measure to implement 

because there was insufficient head height in the basement to allow insulation over the existing 

slab and still include a laundry room on that level. In addition, replacing the existing slab and 

excavating down far enough to allow application of 2 in. of insulation would have required 

underpinning of the existing stone foundation walls. 

The energy modeling done during planning projected only 2.3 MMBtu/yr (or about 2%) 

reduction of total energy use by insulating the basement floor once the basement wall insulation 

was included. Given the difficulty of implementing this measure for this project, it was 

eliminated.

Although the reduction in energy use might not be significant in this case, the impact on indoor 

air quality could be important. Without the underslab insulation, there is potential for 

condensation on the basement floor or capillary action or diffusion through the slab. To reduce 

this risk, BSC suggested installing a dehumidifier in the basement and painting the existing slab

with an epoxy coating to resist hydrostatic pressure and capillary moisture transport through the 

slab. The epoxy coating was included. The conditions of the basement floor will be monitored to 

determine if a dehumidifier is necessary.

2.3.3 Mechanical System Decisions

To meet the airtightness goals of the project, including a mechanical ventilation system was a 

given. Decisions about the rest of the mechanical system, however, underwent the same energy 

modeling process that was applied to the enclosure decisions. 

The overall plan was to replace the two existing oil burners and steam radiator systems with 

forced air heating and cooling systems. Determining the system type required further analysis 

with the help of energy modeling and cost comparisons. For heating, the options were an air 

source heat pump (ASHP) or a gas unit (with air conditioning). For the air conditioning, the 

choice was between a coil integrated unit with an air handler and a ducted/ductless mini-split

unit.
17

Alternative DHW systems were also considered during planning and evaluated by energy 

modeling. Options included indirect water heater, ASHP with electric backup, standard gas 

DHW, and solar thermal with electric backup using tanks of varying sizes. 

In each case, the options were modeled and the final HERS score for the selected packages were 

compared to identify systems that met the goals of the project. 

2.4 Cost Effectiveness of the Retrofit Measures Package

As described earlier in this section, planning for the retrofit was a combination of energy 

modeling, cost analysis, and desired goals and targets of the homeowner. These considerations

were balanced by analyzing the modeling results. 

At approximately the time that this retrofit was completed, a new version of Building Energy 

Optimization (BEopt, an hourly energy simulation program used as a primary Building America 

performance analysis tool), was released. Support for energy retrofits is a new feature in BEopt. 

The tool includes an optimization capability that uses user-supplied cost data and energy use 

information for a specified set of energy saving measures to determine combinations of measures 

that are optimal or near optimal in terms of cost effectiveness. On a graph that plots the average 

source energy savings per year against the annualized energy related costs, the optimal packages 

are those that form the lower bound of the plotted data points. BEopt uses a sequential searching 

technique so that not every possible combination of options is simulated.

Even though the project was already completed, a BEopt optimization simulation was performed. 

This simulation included the measures implemented as well as some of those that were 

considered during planning. BEopt does not currently support comparisons between different 

types of mechanical systems (e.g., between a heat pump system and a gas furnace), so this type 

of decision cannot be evaluated using BEopt’s optimization feature. The optimization feature 

can, however, help with decisions such as the amount of insulation to apply or the AFUE needed 

for a gas furnace.

For the BEopt optimization prepared for this report, the default cost values for the Chicago 

Retrofit were used with user option costs adjusted relative to the similar default options.

8

Although the costs do not represent the Boston-area costs, the BSC team believes that the 

optimal and near optimal selections would be the same. The utility rates used were the state 

average values for Massachusetts supplied by BEopt.

Options selected for the optimization of the enclosure included different amounts of exterior 

insulation on the above-grade walls and on the roof and different amounts of interior insulation 

on the basement walls. The targeted R-values for the walls and roof could not be achieved 

without exterior insulation so no options without exterior insulation were included. Because 

mechanical equipment was located in the basement and in the attic kneewall area, all options 

selected included the basement and all of the attic space within the thermal layer of the 

enclosure. 

For the mechanical equipment, options included different AFUE and SEER values for 

heating/cooling, energy factor values for the water heater, and amount (including “NONE”) of 

solar collectors and PV panels. For the mechanical ventilation, the operating modes of 50% and 

100% of ASHRAE 62.2 were included (ASHRAE 2010).

 8 The BEopt v1.1 simulation program includes default costs for a Chicago-area retrofit as a sample cost selection set.
18

The BEopt optimization, which simulated 58 of a possible 4,096 total combinations of options, 

calculated a set of options for maximum savings (energy use) that differed from the implemented 

measures only in selecting 50% instead of 100% of ASHRAE 62.2 for the ERV. This is an 

operating mode change instead of any change in the measures implemented. The BEopt 

optimization for minimum cost reduced the amount of insulation on the roof and on the basement 

walls, reduced the AFUE and SEER for the heating and cooling, and eliminated the PV panels. 

The difference in source energy use between the “maximum savings” and “minimum cost” 

projected by BEopt was 73.5 MMBtu/yr after the PV-generated electricity was subtracted (see 

Figures 12 and 13).

Figure 12. Belmont Two-Family BEopt optimization results, cost versus energy use

Figure 13. Belmont Two-Family BEopt optimization results, source energy use
19

3 Testing and Analysis for Belmont Two-Family

Various types of testing and analysis were performed during the planning phase of the retrofit 

project and immediately after the retrofit was complete. Monitoring of actual conditions and 

energy use is ongoing. 

3.1 Measurements

Blower door testing was performed before and after the retrofit project (see Figure 14). The two 

units of the house have separate front and rear entrances. The first-floor unit has an interior 

connection to the basement; the upper unit has an interior connection to the third floor. There is 

also an exterior entrance (bulkhead) to the basement. The initial blower door testing was done by 

DEAP Energy Group using two blower doors with several different setups (e.g., interior 

basement door open and closed, and attic door open and closed). Testing of the two units with 

the attic and basement closed resulted in 5,700 cfm 50. With the original living space volume of 

22,507 ft3 (which excludes the basement and attic), this represents existing air infiltration 

conditions of 15.2 ACH 50. It should be noted that the pre-retrofit testing was performed on a 

windy day so that the results are approximate.

Once the retrofit was complete, the BSC team performed blower door testing using two blower 

doors and both guarded and unguarded testing setups. For unguarded testing, the blower door 

was run in one unit with the windows and doors open to the exterior for the other unit. For the 

guarded testing, all doors, windows, and other openings to the exterior were closed and the 

second blower door was used to keep the pressure the same in both units. 

For the unguarded case, the infiltration for the lower unit was 971 cfm 50 and the upper unit was 

928 cfm 50. Because there was no attempt to air seal between the units as part of the renovation 

project, much of this infiltration occurs between units. In most multifamily housing, air sealing 

between units would be important for indoor air quality and for controlling energy use, but for 

this extended family configuration, this was not a concern. This situation would need to be 

corrected for future use of the building as multifamily housing by air sealing the common 

interior walls and the common floor/ceiling. 

For the guarded case, which eliminates the infiltration between units by keeping both units at the 

same pressure, the infiltration for the lower unit was 312 cfm 50 and the upper unit was 278 cfm

50, so total building shell infiltration was 590 cfm 50. The guarded testing included the basement 

in the lower unit and the attic in the upper unit. The total volume for this test, then, was 38,035 

ft3

, resulting in 0.93 ACH 50 (see Appendix A).

Because the blower door test results are indicative of the effective integration of all of the retrofit 

measures, they yield one quantifiable metric of the success of the retrofit package. This value 

was also used as input for the energy modeling at the end of the project.
20

Figure 14. Belmont Two-Family: Setting up blower door testing

Table 4 summarizes the blower door testing results for the Belmont Two-Family.

Table 4. Blower Door Testing for the Belmont Two-Family

Pre-Retrofit Results (cfm 50)

Lower Unit Upper Unit Combined Conditions

2,900 0 2,900 Basement and attic doors closed

0 4,000 4,000 Basement and attic doors closed

3,400 2,300 5,700 (15.20 ACH 50) Basement and attic doors closed

Post-Retrofit Results (cfm 50)

971 0 971 Basement door closed, unguarded

0 928 928 Basement door closed, unguarded

312 278 590 (0.93 ACH 50) Basement and attic doors open, guarded

3.2 Energy Modeling

Energy modeling was used extensively during the planning phase of the retrofit project. DEAP 

Energy Group developed a REM/Rate energy model for the house at the beginning of the project. 

Using this model, the HERS rating, annual energy consumption (in million British thermal units 

per year) and peak heating loads were generated for alternative scenarios to help with the 

decision process. 

In an unusual move, the homeowner and Byggmeister agreed to include HERS and airtightness 

goals in the construction contract. The HERS goal was 55 and the air tightness goal was 1,000 

cfm 50. The energy modeling was used to develop different approaches that could be used to 

reach these goals. In the initial model, the variables included levels of insulation in the walls and 

roof, wall and slab treatment in the basement, airtightness metrics, SHGC and U values for 

windows and doors, and mechanical configurations to create different scenarios.
21

The REM/Rate model was updated throughout the project with the final model including final 

infiltration values, actual appliance ratings, and PV panels (Duclos and Eldrenkamp 2011). 

Appendix B contains a presentation of the results for the final energy model. Table 5 summarizes 

the projected yearly energy use generated by the final REM/Rate model.

When the project was nearing completion, BSC created an energy model for the project using 

BEopt. BEopt support for the retrofit type became available during the last quarter of 2010. 

Using BEopt 1.0 (subsequently updated to version 1.1), the expected energy use for the Belmont 

Two-Family was generated based on the measures that were implemented. For those options that 

were not related to a retrofit measure, the default values were used. These results were compared 

to the REM/Rate results, to the THC goals, and to the actual energy use. This information can 

provide further evidence of the relevance, accuracy, and appropriate use of energy use modeling 

tools during retrofit planning and assessment. Because energy use or energy savings are 

important components in calculating cost effectiveness, it is particularly important that this be 

validated for the energy modeling programs being used. 

To compare the BEopt results with the final REM/Rate energy model information, the projected 

yearly site energy use was divided into the categories of DHW, natural gas for heating, and all 

electricity use, along with total site energy use. The output was derived from the average site 

energy use data generated by BEopt (see Table 5 and Appendix C).

Table 5. Final Energy Model Site Energy Use for Belmont Two-Family (MMBtu/yr)

Annual 

Heating 

(gas)

Annual 

Cooling DHW Other

Total Site 

Energy 

Consumed

Total On-Site 

Generated 

Energy

Total Site 

Energy 

Use

REM/Rate 41.7 4.0 3.1 54.7 106.2 –19.2 87.0

BEopt v1.1 44.8 0.8 4.8 31.1 81.5 –17.8 63.7

The heating, DHW, and on-site generated energy projections are similar for the BEopt and 

REM/Rate models. The other BEopt energy use projections are significantly lower than the 

REM/Rate projections. Because BEopt does not support multifamily houses, the BEopt model 

assumes a 5-bedroom, 3.5-bath single-family house. The distinction between single-family and 

multifamily energy use assumptions would account for some of this discrepancy. For example, 

having two kitchens and two distinct families using two sets of other appliances would be 

expected to increase the total energy use.

On the other hand, the overall relative reductions in energy use of the REM/Rate and BEopt 

energy models are in agreement, even if the actual numbers generated are not the same (see 

Table 6). REM/Rate predicts an 83% reduction in energy use; BEopt predicts an 88% reduction.

Table 6. Energy Use Reduction by Component for Belmont Two-Family (MMBtu/yr)

Site Energy 

(MMBtu)

PreRetrofit 

(Existing)

DER 

Insulation, 

Ventilation,

Windows (4)

Airtightness, 

Air-Handling 

Unit, Solar 

Thermal (9)

Appliances 

and Compact 

Fluorescent 

Lamps (11)

PV

Panels 

(12)

REM/Rate Model 508 168 114 106 87

BEopt v1.1 Model 524 172 85 81 64
22

The REM/Rate projection for annual consumption of non-site-generated site energy is 87.0 

MMBtu/yr or 25,588 kWh/yr. The BEopt projection for annual consumption of non-sitegenerated site energy is 64 MMBtu/yr or 18,823 kWh/yr. Both of these projections are generated 

using standard benchmark energy use factors (e.g., set points, miscellaneous loads, and appliance 

use assumptions).

Using the projection of the REM/Rate energy model, the project applied to and was accepted as a 

candidate for the THC program. Within the program, the candidate is given a specific energy use 

threshold for yearly site energy use. This threshold is computed based on location, number of 

people and number of households, area of conditioned space, and heating fuel type. The THC 

threshold for the Belmont Two-Family is 17,006 kWh/yr. This is lower than the projections of 

BEopt and REM/Rate. Although an energy efficient enclosure and mechanical system and onsite energy generation are expected to be required to stay below the threshold, it is also expected 

that behavior, lifestyle, and community-based solutions will be necessary. These behavior-based 

criteria were not incorporated into the energy models. 

3.3 Actual Energy Use for January 2011 Through May 2011

Since January 2011, the owner of the Belmont Two-Family has been reporting monthly energy 

use information. Table 7 summarizes the use from January through May 2011. The homeowner 

maintains a THC tracking spreadsheet.

Table 7. January 2011–May 2011 Actual Site Energy Use

January February March April May 

DHW (kWh) 251 251 114 110 96

Gas (kWh) 2,316 1,706 1,067 366 91

Electricity used 

except DHW 

(kWh)

782 692 783 783 739

Total kWh of 

energy used 3,349 2,649 1,964 1,259 926

Electricity from 

PV (kWh) –303 –376 –590 –534 –585

Total site energy 

kWh 3,046 2,273 1,374 725 341

Monthly projections from REM/Rate are not available for comparison to the actual energy use. 

BEopt monthly projections can be extracted from the hourly output of BEopt, however. These 

projections were used to generate the information in Table 8 (see Appendix D).

Table 8. January 2011–May 2011 BEopt Projected Site Energy Use

January February March April May 

DHW (kWh) 259 183 164 124 62

Gas (kWh) 3,198 2,590 2,108 1,320 435

Electricity Used Except DHW (kWh) 831 747 708 643 629

Total kWh of Energy Used 4,288 3,520 2,980 2,086 1,126

Electricity from PV (kWh) –346 –415 –461 –462 –519

Total Site Energy (kWh) 3,942 3,105 2,519 1,624 606
23

Such a small sample of comparative data is not statistically significant, but continued monitoring 

of monthly results could help improve understanding of the applicability of the lower level 

information that BEopt provides. Of particular note for this test case is that the owner is very 

interested in the behavior aspect of reducing energy use, as encouraged by the tenets of the THC.

If the projected energy use represents “average behavior” for a house of the specified geometry 

and options, the actual energy use might be expected to show a general lower energy use pattern 

than that projected by BEopt. Deviations such as specific weather conditions, though, can affect 

the actual use for any given month. 

3.4 Occupant Feedback

The owner of the Belmont Two-Family maintains a website where he includes information about 

his retrofit experiences along with other local energy issues. In addition, there were some email 

exchanges with Byggmeister while adjustments were being made after the homeowner first 

occupied the house. Here is a summary of some of the issues discussed:

• Upgrading of insulation and inclusion of solar thermal both appear to be cost effective for 

this particular project. PV cells, though, are probably not cost effective without 

substantial incentives. 

• If planning a retrofit that goes beyond current code requirements, blower door testing (to 

assess current status) and energy modeling in the planning are important first steps. 

• There have been some questions about the interaction between the mechanical ventilation 

and the operation of the air handler. 

• There has been some discussion that suggests a need to consider how to effectively use 

natural ventilation during the “shoulder seasons.”

This summary illustrates two issues that should be addressed with each retrofit project and are 

areas for further study:

• To an owner, cost effectiveness can involve more than a straight calculation of initial 

costs and dollars saved in energy use. Indoor air quality, durability, and combustion 

safety should apply to every job but might not show up in the cost-effectiveness 

calculations. An individual’s weighting of goals also do not compute; for example, 

meeting the THC objectives is an important goal for this project, but this could not be 

achieved without the PV panels, which otherwise appear not to be cost effective. If an 

energy model is used during planning, it needs to provide sufficient transparency or 

flexibility to allow optimizing cost effectiveness with a broader definition of cost.

• A better way to describe the interactions among the various components of the 

mechanical systems, as well as with the high performance enclosure, needs to be 

developed. Example questions to be considered include (1) what are the constraints of a 

DER and (2) when is natural ventilation undermining the energy use reduction? This

type of information needs to be better understood by everyone on the project. There 

should also be a period of follow-up with the owner.
24

4 Conclusions

This report examined the planning, construction, and initial energy use results of a package of 

retrofit measures for a case study involving the renovation of a wood framed, two-family,

suburban New England home built in the 1920s. 

With a blower door test result of 0.93 ACH 50 and a REM/Rate generated HERS index of 44, the 

retrofit package that was applied to the Belmont Two-Family is successful from an energy use 

point of view. The house is on track to meet the THC, which usually results in 15%–30% of the 

Home Energy Yardstick estimation for the same household. 

The question of whether there will be condensation in the basement, resulting from not including 

the basement floor insulation portion of the retrofit measures package, cannot be addressed until

at least a year’s worth of monitoring data is available. If it becomes necessary to run a 

dehumidifier in the future, it will raise the energy use somewhat.

An energy model used in combination with a proposed package of retrofit measures proved to be 

an effective planning tool for this project. Cost effectiveness of proposed energy reduction 

measures was estimated during planning using the projected energy use and initial costs, 

particularly of mechanical equipment. In this case, the homeowner wanted to include certain 

additional measures and was able to take advantage of incentive programs so that the final 

package went somewhat beyond the most cost-effective solution. 

The energy modeling tools used during the project yielded good relative information about 

energy use, but should not be expected to predict actual use. Furthermore, they do not model 

interactions and durability issues. For example, failure to include sufficient exterior insulation 

might result in condensation in the wall or roof, shortening their lives. This type of interaction is 

not effectively supported in the energy modeling tools that were used. 

During the first few months after the retrofit, questions about effective operation of the 

mechanical equipment requires follow-up with the owner. The increased airtightness and Rvalues will slow temperature swings, which will affect system operation and require a different 

pattern of operation from the past. 

This project met the goals of the retrofit and identified areas for further study. In addition, it will 

yield measurable longer term information about the retrofit measures through ongoing 

monitoring.
25

References

ASHRAE (2010). ASHRAE Standard 62.2-2010: Ventilation and Acceptable Indoor Air Quality 

in Low-Rise Residential Buildings. Atlanta, GA: ASHRAE.

BSC (May 2009a). Info-301: Drainage Plane/Water Resistive Barrier. Accessed January 7, 

2011: http://www.buildingscience.com/documents/information-sheets/drainage-plane-waterresistive-barrier. 

Duclos, M.; Eldrenkamp, P. (2011). “Modeling and Marketing the Deep Energy Retrofit.” 

Presented at the Better Buildings by Design 2011 Conference, Burlington, Vermont, February 8–

9, 2012. Accessed June 14, 2011: 

www.efficiencyvermont.com/for_our_partners/bbd/archive.aspx.

Lstiburek, J. (July 2005). “Understanding Air Barriers” ASHRAE Journal (47); pp. 24–30.

Lstiburek, J. (October 2006). BSD-103: Understanding Basements. Accessed January 7, 2011:

http://www.buildingscience.com/documents/digests/bsd-103-understanding-basements/. 

National Grid (2009). “Deep Energy Retrofit Multifamily and Single-Family Pilot Guidelines.” 

Accessed May 16, 2011: www.powerofaction.com/media/pdf/der_desc.pdf.

Straube, J. (2009). BSI-025: The Passive House (Passivhaus) Standard: A Comparison to Other 

Cold Climate Low-Energy Houses. Accessed June 15, 2011: 

www.buildingscience.com/documents/insights/bsi-025-the-passivhaus-passive-house-standard/. 

Ueno, K. (2010). “Residential Exterior Wall Superinsulation Retrofit Details and Analysis.” 

Performance of the Exterior Envelopes of Whole Buildings XI. Atlanta, GA: ASHRAE.

Ueno, K. (June 2008). RR-0110: HVAC Equipment Sizing Strategies: Taking Advantage of HighPerformance Buildings. Accessed January 7, 2011: 

www.buildingscience.com/documents/reports/rr-0110-hvac-equipment-sizing-strategiestaking-advantage-of-high-performance-buildings/view.
A-1

Appendix A: Belmont Two-Family: Final Blower Door Test
BUILDING LEAKAGE TEST
 

Date of Test: 2010.09.23 Technician: CG, KN 

Test File: 2010-09-23 Gilbert Rd Apt 1 guarded 

Customer: Brownsberger Building Address: 118-120 Gilbert 

118-120 Gilbert Belmont, MA 

Belmont, MA 

Phone 

Test Results 

1.	 Airflow at 50 Pascals: 312 CFM ( +/- 3.6 %) 

(50 Pa = 0.2 w.c.) 

0.08 CFM per ft2 floor area 

2. Leakage Areas:	 28.3 in2 ( +/- 18.1 %) Canadian EqLA @ 10 Pa 

14.0 in2 ( +/- 26.5 %) LBL ELA @ 4 Pa 

3. Minneapolis Leakage Ratio:	 0.04 CFM50 per ft2 surface area 

4.	 Building Leakage Curve: Flow Coefficient (C) = 18.0 ( +/- 39.2 %) 

Exponent (n) = 0.730 ( +/- 0.092 ) 

Correlation Coefficient = 0.96984 

5.	 Test Settings: Test Standard: = CGSB 

Test Mode: = Depressurization 

Equipment = Model 3 Minneapolis Blower Door, S/N 4 

Infiltration Estimates 

1.	 Estimated Average Annual Infiltration Rate: 

2.	 Estimated Design Infiltration Rate: Winter: 34.7 CFM 

Summer: 14.7 CFM 

3.	 Recommended Whole Building Mechanical 93.4 CFM 

Ventilation Rate: (based on ASHRAE 62.2) 

Cost Estimates 

1.	 Estimated Cost of Air Leakage for Heating: 

2. Estimated Cost of Air Leakage for Cooling: 

A-2
BUILDING LEAKAGE TEST Page 2 

Date of Test: 2010.09.23 Test File: 2010-09-23 Gilbert Rd Apt 1 guarded 

Building Conditions 

Inside Temperature: 75 deg F Heating Fuel: Gas 

Outside Temperature: 77 deg F Heating Fuel Cost: 

# of Stories 3.0 Heating Efficiency: 

Heating Degree Days: 5641 

Wind Shield: M Cooling Fuel Cost: 

# of Occupants 7.0 Cooling SEER: 

Cooling Degree Days: 275 

# of Bedrooms: 5.0 

Volume: Ventilation Weather Factor: 1.07 

Surface Area: 7468 ft2 Energy Climate Factor: 18.0 

Floor Area: 4092 ft2 

Design Winter Wind Speed: 18.0 mph Design Winter Temp Diff: 61 deg F 

Design Summer Wind Speed: 7.0 mph Design Summer Temp Diff: 13 deg F 

Comments 

apartment 1 guarded 

A-3
BUILDING LEAKAGE TEST Page 3 

Date of Test: 2010.09.23 Test File: 2010-09-23 Gilbert Rd Apt 1 guarded 

Data Points: Data Entered Manually 

Nominal 

Building 

Pressure (Pa) 

Fan Pressure 

(Pa) 

Nominal 

Flow 

Temperature 

Adjusted 

Flow % Error 

Fan 

Configuration 

Baseline 

Std Dev (Pa)

 0.6 n/a +/- 0.00

 -86.5 60.4 463 464 -0.6 Ring B

 -79.1 54.5 440 441 0.8 Ring B

 -71.8 47.3 410 411 0.8 Ring B

 -64.4 42.1 387 388 3.0 Ring B

 -63.3 34.0 348 349 -6.2 Ring B

 -55.7 33.0 343 344 1.4 Ring B

 -0.1 n/a +/- 0.00 

A-4
BUILDING LEAKAGE TEST
 

Date of Test: 2010.09.23 Technician: CG, KN 

Test File: 2010-09-23 Gilbert Rd Apt 2 guarded 

Customer: Brownsberger Building Address: 118-120 Gilbert 

118-120 Gilbert Belmont, MA 

Belmont, MA 

Phone 

Test Results 

1. Airflow at 50 Pascals: 278 CFM ( +/- 4.4 %) 

(50 Pa = 0.2 w.c.) 

0.07 CFM per ft2 floor area 

2. Leakage Areas: 28.7 in2 ( +/- 21.2 %) Canadian EqLA @ 10 Pa 

15.3 in2 ( +/- 30.9 %) LBL ELA @ 4 Pa 

3. Minneapolis Leakage Ratio: 0.04 CFM50 per ft2 surface area 

4. Building Leakage Curve: Flow Coefficient (C) = 21.9 ( +/- 45.6 %) 

Exponent (n) = 0.650 ( +/- 0.106 ) 

Correlation Coefficient = 0.96224 

5. Test Settings: Test Standard: = CGSB 

Test Mode: = Depressurization 

Equipment = Model 3 Minneapolis Blower Door, S/N 4 

Infiltration Estimates 

1. Estimated Average Annual Infiltration Rate: 

2. Estimated Design Infiltration Rate: Winter: 37.9 CFM 

Summer: 16.1 CFM 

3. Recommended Whole Building Mechanical 93.4 CFM 

Ventilation Rate: (based on ASHRAE 62.2) 

Cost Estimates 

1. Estimated Cost of Air Leakage for Heating: 

2. Estimated Cost of Air Leakage for Cooling: 

A-5
BUILDING LEAKAGE TEST Page 2 

Date of Test: 2010.09.23 Test File: 2010-09-23 Gilbert Rd Apt 2 guarded 

Building Conditions 

Inside Temperature: 75 deg F Heating Fuel: Gas 

Outside Temperature: 77 deg F Heating Fuel Cost: 

# of Stories 3.0 Heating Efficiency: 

Heating Degree Days: 5641 

Wind Shield: M Cooling Fuel Cost: 

# of Occupants 7.0 Cooling SEER: 

Cooling Degree Days: 275 

# of Bedrooms: 5.0 

Volume: Ventilation Weather Factor: 1.07 

Surface Area: 7468 ft2 Energy Climate Factor: 18.0 

Floor Area: 4092 ft2 

Design Winter Wind Speed: 18.0 mph Design Winter Temp Diff: 61 deg F 

Design Summer Wind Speed: 7.0 mph Design Summer Temp Diff: 13 deg F 

Comments 

apartment 1 guarded 

A-6
BUILDING LEAKAGE TEST Page 3 

Date of Test: 2010.09.23 Test File: 2010-09-23 Gilbert Rd Apt 2 guarded 

Data Points: Data Entered Manually 

Nominal 

Building 

Pressure (Pa) 

Fan Pressure 

(Pa) 

Nominal 

Flow 

Temperature 

Adjusted 

Flow % Error 

Fan 

Configuration 

Baseline 

Std Dev (Pa)

 0.3 n/a +/- 0.00

 -88.2 46.1 405 406 0.8 Ring B

 -82.3 40.3 379 380 -1.4 Ring B

 -65.9 28.5 319 320 -4.1 Ring B

 -64.5 33.6 346 347 5.5 Ring B

 -55.8 165.4 294 295 -1.5 Ring C

 -0.2 n/a +/- 0.00 

A-7
B-1

Appendix B: Belmont Case Study: HERS as Planning, GoalSetting Tool for a Deep Energy Retrofit
Provide

Belmont The DE

case study:

HERS as planning, goal‐setting t l oo for a D

B-2
C-1

Appendix C: Belmont Two-Family: Yearly Site Energy Use Data 

Generated by BEopt
Exported Data for Belmont Two‐Family generated by BEopt v1.1 for Belmont Two‐Family

Avg. Site Electricity Use (kWh/yr)

1‐ Basic Insulation 3 ‐ High Perf Windows 5 ‐ Air Tightness 7 ‐ DHW‐ electric 9 ‐ Solar HW 11

Existing 2 ‐ DER Insulation 4 ‐ ERV 2 6 ‐ High Perf Furnace 8 ‐ Air conditioning 10 ‐ 100% CFL 

Misc. (E) 4074 4074 4074 4074 4074 4074 4074 4074 4074 4074 4074 Vent Fan (E) 30 30 115 30 593 724 724 724 724 724 724 

Lg. Appl. (E) 1426.81 1426.81 1426.81 1426.81 1426.81 1426.81 1426.81 1426.81 1426.81 1426.81 1426.81 

Lights (E) 2960 2960 2960 2960 2960 2960 2960 2960 2960 2960 1732 HVAC Fan/Pump ( 770 632 431 349 354 285 339 339 293 290 301 

Cooling (E) 0 0 0 0 0 0 0 0 249 247 222 

Hot Water (E) 0 0 0 0 0 0 0 4713.22 4713.22 1688.09 1688.09 

Total 9260.81 9122.81 9006.81 8839.81 9407.81 9469.81 9523.81 14237.03 14440.03 11409.89 10167.89 

PV 00000000000

Net (Total ‐ PV) 9260.81 9122.81 9006.81 8839.81 9407.81 9469.81 9523.81 14237.03 14440.03 11409.89 10167.89 

Avg. Site Natural gas Use (Therms/yr)

1‐ Basic Insulation 3 ‐ High Perf Windows 5 ‐ Air Tightness 7 ‐ DHW‐ electric 9 ‐ Solar HW 11

Existing 2 ‐ DER Insulation 4 ‐ ERV 2 6 ‐ High Perf Furnace 8 ‐ Air conditioning 10 ‐ 100% CFL 

Heating (G) 0 0 0 0 0 0 396 396 404 400 429 

Hot Water (G) 250.54 250.54 250.54 250.54 250.54 250.54 250.54 0 0 0 0 

Lg. Appl. (G) 48.92 48.92 48.92 48.92 48.92 48.92 48.92 48.92 48.92 48.92 48.92 

Misc. (G) 10 10 10 10 10 10 10 10 10 10 10 Total 309.46 309.46 309.46 309.46 309.46 309.46 705.46 454.92 462.92 458.92 487.92 

Avg. Site Fuel oil Use (gal/yr)

1‐ Basic Insulation 3 ‐ High Perf Windows 5 ‐ Air Tightness 7 ‐ DHW‐ electric 9 ‐ Solar HW 11

Existing 2 ‐ DER Insulation 4 ‐ ERV 2 6 ‐ High Perf Furnace 8 ‐ Air conditioning 10 ‐ 100% CFL 

Heating (O) 3078 1788 1076 682 728 542 0 0 0 0 0 

Total 3078 1788 1076 682 728 542 0 0 0 0 0 

C-2
D-1

Appendix D: Belmont Two-Family: Monthly Average Site Energy 

Use Data Generated by BEopt
Exported Monthly Data for Belmont Two‐Family generated by BEopt 1.1 using Hourly Output Tool

This represents the average site energy use per hour for the month. To get monthly use, multiply by days/month X 24 hrs/da

Hot Water (E) PV (E) Total (E) Total (G)kWh kWh kWh Btu

Jan 0.34826 0.46456 1.4647 14616Feb 0.26272 0.59696 1.3362 12654Mar 0.22107 0.6195 1.1721 9634

Apr 0.17166 0.64207 1.0646 6233

May 0.08316 0.6982 0.9281 1998

June 0.08419 0.67066 0.9001 1007

July 0.04199 0.7027 1.01 499

Aug 0.02031 0.68726 0.8906 404

Sept 0.05291 0.64289 0.8741 527

Oct 0.14512 0.56144 1.0557 2126

Nov 0.24599 0.45257 1.2221 6780

Dec 0.25303 0.41643 1.3503 10505

D-2
DOE/GO-102013-3759 ▪ January 2013

Printed with a renewable-source ink on paper containing at 

least 50% wastepaper, including 10% post-consumer waste.