EMV Group A, Deliverable 16 EUL Research - Residential Insulation - PDA
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EMV Group A, Deliverable 16 EUL Research – Residential Insulation Draft Report Prepared for: California Public Utilities Commission Submitted by: Guidehouse Inc. 101 California Street Suite 4100 San Francisco, CA 94111 415.356.7100 guidehouse.com Reference No.: EUL2021-2 June 29, 2021 ©2021 Guidehouse Inc.
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This study was conducted by Guidehouse under contract to the California Public Utilities
Commission. Principal authors include:
Robert Slowinski
Brian Chang
Lucas Schroyer
Karen Maoz
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Table of Contents
Executive Summary ...................................................................................................... 1
1. Introduction ............................................................................................................... 8
1.1 Measure Background and Data Sources ............................................................................8
1.2 Study Objectives .................................................................................................................10
2. Study Methodology ................................................................................................. 11
2.1 Program Data Collection and Database Analysis ............................................................11
2.2 Participant Survey ...............................................................................................................12
2.3 Contractor Interviews..........................................................................................................13
2.4 Analysis Methodology.........................................................................................................14
3. Results ..................................................................................................................... 16
3.1 Response Demographics ...................................................................................................16
3.1.1 Age of Homes ......................................................................................................... 16
3.1.2 Location of Upgrades ............................................................................................. 18
3.1.3 Existing Insulation Type ......................................................................................... 19
3.1.4 Motivation for Upgrades......................................................................................... 20
3.2 Insulation Degradation and Performance .........................................................................20
3.2.1 Natural Degradation of Insulation Materials ......................................................... 21
3.2.2 Factors Affecting Insulation Performance ............................................................ 21
3.2.3 Degradation and Performance – Findings from Literature Review ................... 22
3.2.4 Newly Installed Insulation ...................................................................................... 24
3.3 Age of Existing Insulation on Upgrade ..............................................................................24
3.3.1 Age by Program Administrator .............................................................................. 25
3.3.2 Age by Insulation Location .................................................................................... 25
3.3.3 Age by Insulation Type .......................................................................................... 26
4. Conclusions ............................................................................................................. 28
4.1 EUL Determination .............................................................................................................28
4.2 Applicability of RUL.............................................................................................................29
Appendix A. Online Participant Survey Guide ........................................................ A-1
Appendix B. Contractor Interview Guide ................................................................ B-1
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List of Figures and Tables
Figures
Figure E1. Survey Results: Age of Replaced Insulation by PA ...................................................... 4
Figure 3-1. Participant Survey Responses by PA.......................................................................... 16
Figure 3-2. Surveyed Home Age Distribution – Decade Home Constructed .............................. 17
Figure 3-3. Original and Previously Upgrade Insulation by Decade of Home Construction ...... 18
Figure 3-4. Proportion of Upgrades by Installation Location......................................................... 19
Figure 3-5. Participant Motivations for Insulation Upgrades ......................................................... 20
Figure 3-6. Survey Results: Age of Replaced Insulation by PA ................................................... 25
Figure 3-7. Survey Results: Age of Replaced Insulation by Home Location ............................... 26
Figure 3-8. Survey Results: Age of Replaced Insulation by Insulation Type .............................. 27
Tables
Table E1: EUL Findings Summary, by Stratification Type (all values in years) ............................ 6
Table 2. Home Upgrade Project Participant Data, 2013-2018 ..................................................... 11
Table 3. Home Upgrade Program Insulation Contractors, 2013-2018 ........................................ 12
Table 4. Survey Responses for Existing Insulation Type by Location ......................................... 20
Table 5. EUL Findings Summary by Stratification Type (All Values in Years) ............................ 28
Disclaimer
This report was prepared by Guidehouse Inc (“Guidehouse”) for the California Public Utilities
Commission. The work presented in this report represents Guidehouse’s professional judgment
based on the information available at the time this report was prepared. Guidehouse is not
responsible for the reader’s use of, or reliance upon, the report, nor any decisions based on the
report. GUIDEHOUSE MAKES NO REPRESENTATIONS OR WARRANTIES, EXPRESSED
OR IMPLIED. Readers of the report are advised that they assume all liabilities incurred by them,
or third parties, as a result of their reliance on the report, or the data, information, findings and
opinions contained in the report.
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Executive Summary
Introduction and Objective (Pages 8-10)
This document outlines the effective useful life (EUL) research 1 conducted by Guidehouse, Inc.
(Guidehouse) on behalf of the California Public Utilities Commission (CPUC) for residential
insulation energy efficiency measures. Residential insulation is a long-lived measure that has a
deemed measure life of 20 years 2 which is the maximum allowed measure life by the CPUC. 3 In
California, Program Administrators (PAs) incentivize wall insulation, attic/roof/ceiling insulation,
and floor insulation. These installations are typically retrofits, but incentives are also given for
high-performing building envelopes in new construction projects. In addition, some insulation
projects are standalone, but most are included as a part of whole building retrofit projects. This
study includes data from both types of projects.
The primary objective of this EUL research was to address several key questions:
1. What is the estimated EUL of residential insulation projects?
2. Does the evidence support limiting the measure life of new insulation to the existing
insulation’s RUL 4, or does it support using the full EUL value, similar to a new
installation?
3. Should separate EUL values be defined for different types of insulation, or insulation
installed in different geographic regions?
Methodology (Pages 11-15)
The research team utilized a three-pronged approach to determine the answers to the study
questions.
An online survey that yielded quality responses from 210 respondents 5 of individual
Home Upgrade Program (HUP) participants’ experiences. Notably, every project in the
dataset included a roof insulation upgrade, with a small percentage also including wall
and/or floor insulation upgrades as well.
1
This research plan is part of the steps listed in the Effective Useful Life (EUL) Study Work Plan and accompanying
Measure Prioritization document, https://pda.energydataweb.com/#!/documents/2191/view.
2
Database of Energy Efficiency Resources. Accessed June 2019. www.deeresources.com
3
Decision D.09-05-037, http://docs.cpuc.ca.gov/PublishedDocs/WORD_PDF/FINAL_DECISION/101543.PDF
and www.deeresources.com
4
Remaining useful life. RUL is often used when a measure is installed on top of “host” equipment that has a high
impact upon its expected lifetime.
5
Of 467 total survey responses, 210 respondents had usable, informed data encompassing 237 unique installation
locations.
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Phone interviews with seven insulation contractors6 characterized their expertise with
various types of insulation installed in various locations, as well as the factors affecting
the longevity of each installation.
Information from a literature review was used to support the conclusions obtained by the
online survey and telephone interviews.
The failure mode for insulation is unique as compared to other types of measures. If a
refrigerator fails, for example, the end of the useful life is immediately obvious to the
homeowner. When an air conditioner’s performance degrades beyond a certain point, such
performance degradation is easily tested by a Heating, Ventilation, and Air-Conditioner (HVAC)
technician. But for insulation measures, the impact is rarely as sudden or as catastrophic. For
this reason, quantification of insulation EUL requires one of the following:
An intrusive site visit process—entering a home and physically examining materials in
the roof, wall or floor—and repeating the process at a large number of installations
Time-consuming and/or expensive testing, often involving a laboratory and complex
equipment and heat transfer analysis
The use of proxy characteristics that are likely to reflect the amount of time that
insulation was installed and effective
Previous retention studies 7 measured the proportion of insulation measures that were still in
place, operational, and effective nine years after installation. The study’s analysis8 required
extrapolation of the data in order to estimate the ultimate lifetime of the materials. While the raw
nine-year survival data pointed towards estimated EULs that exceeded 20 years 9, ultimately, the
research team decided to retain the previous (and current, but undocumented) value of 20
years10 due to study limitations such as the small sample size and usage of projected data.
Insulation contractors interviewed for this study expressed that insulation performance
degradation is most affected by human behavioral factors unrelated to the insulation material
itself. Contractors reported that work on HVAC systems and the installation of ceiling “can
lights,” TV or cable wires, speaker systems, camera systems, and alarm systems are the main
6
Phone interviews lasted approximately 30 minutes each, and engaged contractors in various geographic regions,
ranging from a few hundred completed projects per year to 5,000 completed projects per year.
7
Retention Studies provide the percentage of the measures that are in place and operable at a point in time.
Retention studies identify technology design, define operable conditions, and describe how operable conditions could
be measured.
8
Megdal & Associates. Measure Retention Study – 1996 and 1997 Residential Weatherization Programs. CALMAC.
December 2005. http://www.calmac.org/publications/9-year_Retention_Study-Id_991__1996_and_1997_RWRI-
rev12-21.pdf
9
EUL values were estimated to range from 85 to 290 years, based on the nine-year survival rate. See DEER2008
EUL Database Definitions. https://www.cpuc.ca.gov/WorkArea/DownloadAsset.aspx?id=11483
10
Database for Energy Efficient Resources, accessed June 2019. www.deeresources.com
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reasons for performance degradation, especially when the homeowner or installer did not take
similar care in replacing the disturbed insulation as with the installation itself. Less frequently,
rodent or other pest infestations may cause material damage or create thermal bridges 11 that
reduce the effectiveness of the installed insulation. Literature from insulation manufacturers also
indicated that these factors, as well as moisture infiltration, are common reasons for insulation
performance degradation. 12,13,14
Furthermore, it is often difficult or impossible to measure the existing performance of installed
insulation, either due to inaccessibility of the material or the lack of any kind of nameplate or
record of the original install. Given the timeline and budget of the research plan, laboratory
testing would be both time consuming and cost prohibitive. The previous research on insulation
EUL (conducted in the mid-2000s) used a similar, survey data-driven research methodology to
the one outlined here. Given these constraints, the research team believes that using actual
installation and removal data is an accessible means of quantifying EUL—if a homeowner or
contractor made the decision that a costly upgrade was required, that data can be used as an
indicator that the useful life of the insulation had been eclipsed. Such a method provides an
estimate of how long the typical insulation project accrues real energy and demand savings.
The research team believes that using actual installation and removal data from customers over
a long period of time – while similar to previous research which also used survey-data – is a
more reliable method, since it characterizes real insulation retrofits and replacements over 50+
years old, rather than relying on projections based on nine years of survival data. In fact, the
results of this research build upon the previous research, offering credence to a potentially
longer insulation EUL than the current 20-year official value.
Results (Pages 16-27)
Of the 210 online survey respondents, over 80% consisted of only roof insulation upgrades. The
remainder of projects consisted of roof upgrades plus a combination of wall and/or floor
insulation upgrades. A majority of projects had loose-fill or blown cellulose insulation, while
fiberglass or other insulation types made up a significant minority. There were few projects with
existing spray-in-place or rigid foam board insulation. This finding is consistent with the
responses of all seven insulation contractors interviewed.
11
Thermal bridges are areas of reduced insulation quality or effectiveness where a disproportionate amount of heat is
transferred, reducing the effectiveness of the overall insulation assembly.
12
Ezeonu M., J.A. Noble, R.B. Simmons, D.L. Price, S.A. Crow and S.G. Ahearn. “Effect of relative humidity on
fungal colonization of fiberglass insulation,” Applied and Environmental Microbiology, vol. 60, no. 6, pp. 2149-2151,
Jun. 1994.
13
Price, D.L., Simmons, R.B., Ezeonu, I.M. et al. “Colonization of fiberglass insulation used in heating, ventilation and
air conditioning systems,” Journal of Industrial Microbiology, vol. 13, pp. 154–158, May 1994.
https://doi.org/10.1007/BF01584000
14
US Department of Energy, Office of Energy Efficiency and Renewable Energy, “Insulation Fact Sheet,” 2008.
https://web.ornl.gov/sci/buildings/docs/factSheets/Insulation-FactSheet-2008.pdf
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Figure E1 shows the calculated age of replaced insulation across four PAs. The team received
more survey responses from participants in northern California 15 than southern California16. Still,
the team did not find considerable variation across PAs for median age values which ranged
between 30.5 and 33 years. The combined median age of replaced insulation across all PAs
was 31 years.
Figure E1. Survey Results: Age of Replaced Insulation by PA
50
45
40
35
Age (Years)
30
25 Median
20 Mean
15
10
5
30,5 29,1 31,0 31,1 33,0 40,2 32,0 35,0 31,0 32,3
0
BayREN PG&E SoCalGas SoCalREN Combined
(n = 74) (n = 79) (n = 37) (n = 9) (n = 199)
N = 199, from 210 valid responses minus 11 participants that indicated “No Previous Insulation.”
Source: Guidehouse
Figure E2 shows the calculated age of replaced insulation, by material type. Loose-fill and batt
or blanket insulation were the most common insulation types with median age values of 32.0
and 31.0 years respectively. Only seven participants reported that their existing insulation was
spray foam or foam-in-place. This type of insulation has a much higher median and mean age,
though it had a low response count and a correspondingly larger confidence interval 17. The
median age value across all material types is 32.0 years.
15
Bay Area Regional Energy Network (BayREN) and Pacific Gas and Electric (PG&E)
16
SoCal Gas and Southern California Regional Energy Network (SoCalREN)
17
Although the statistically estimated value is shown, the confidence interval shows the range in which the true
average value of the entire population is likely to lie. Larger confidence intervals indicate less certainty of the actual
value.
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Figure E2. Survey Results: Age of Replaced Insulation by Insulation Type
Median Mean
70,0
60,0
50,0
Age (Years)
40,0
30,0
20,0
10,0
31,0 33,5 32,0 33,1 52,0 44,3 32,0 33,7
0,0
Batt/Roll Loose-Fill/Blown-In Spray Foam/Foam-in- Combined
(n = 65) (n = 137) Place (n = 209)
(n = 7)
N = 209, from 256 insulation location data points minus: 19 locations with “No Previous Insulation”; 27 locations with
unspecified type; and 1 location with type Foam Board/Rigid Foam. The team removed this type because there was only
one data point.
Source: Guidehouse
While the research team believes that insulation EUL values are likely to be similar across
insulation types (roof/wall/floor), given the lack of specific data on non-roof/attic removals, the
team recommends that the research findings only inform changes to the roof/attic EUL value.
The roof/attic EUL findings are based on a substantial set of survey data (210 responses), and
since the majority of customer replacements involve roof/attic insulation, a change to this
insulation measure will be impactful in characterizing building envelope lifecycle savings as
accurately as possible.
Conclusions (Pages 28-29)
Based on the qualitative evidence provided by insulation contractors and backed up by the
quantitative data collected from 2013-2018 Home Upgrade Program participants, the research
team concludes that the existing roof/attic insulation EUL value of 20 years is low. Should the
CPUC choose to reevaluate the current 20-year EUL cap, this study could be used as a
datapoint. Additionally, the values cited here include an assumption that the aggregate “time
between replacements” is a reasonable proxy for insulation EUL, given the lack of cost-effective
alternative testing methods. The research team also acknowledges that—due to its less
definitive failure modes—even worn-out insulation often continues to accrue real energy
savings.
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The team believes that the presented results are not inconsistent with the previous studies, but
result from a more rigorous method, since this research characterized actual replacements
rather than attempting to project EUL from a shorter retention study. Past studies did not
recommend changing the EUL value, although the previous research team indicated that their
recommendation of ‘no change’ was impacted more by the sample size and the implications of
extrapolating based on nine years, rather than the quality of the data itself. By assessing the
age of insulation upon replacement, rather than relying on projected data, this study provides
increased certainty that the EUL of insulation is longer than the current 20 years.
Given these considerations, the median EUL calculated from all survey participants is 32.0
years. The calculated mean is 33.1 years, with a 90% confidence that the mean EUL is at least
31.5 years. Additionally, the median values across each PA, across each insulation location
within the home, and across each type of insulation material are all just above 30 years, as
shown in Table E1.
Table E1: EUL Findings Summary, by Stratification Type (all values in years)
EUL Lower
Confidence
# of EUL EUL Bound
Stratification by PA Interval
Participants (median) (mean) (90%
(90%)
confidence)
BayREN 74 30.5 29.1 2.2 27.0
PG&E 79 31.0 31.1 2.2 28.9
SoCal Gas 37 33.0 40.2 5.9 34.3
SoCalREN 9 32.0 35.0 9.3 25.7
EUL Lower
Confidence
Stratification by # of EUL EUL Bound
Interval
Material Type Installations (median) (mean) (90%
(90%)
confidence)
Batt/Roll 65 31.0 33.5 3.2 30.3
Loose-fill/Blown-in 137 32.0 33.1 2.2 30.9
Foam Board/Rigid Foam 1 61.0 61.0 n/a n/a
Spray foam/Spray-in-
7 52.0 44.3 16.2 28.1
place
The median EUL estimates should be used in accordance with the EUL definition outlined in the
California Evaluation Protocols. However, mean values are also provided in order to be able to
calculate 90% confidence intervals.
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Usage of RUL: Although it does settle or degrade over time, existing insulation does not appear
to constitute "host equipment" in quite the same way that an existing furnace would host an
upgraded furnace fan. In the furnace example, a customer might install an efficient fan on a 10-
year-old furnace. When the furnace inevitably fails at the end of its useful life, the customer is
highly unlikely to continue using the fan. In that case, limiting the fan's EUL to 1/3 of the EUL of
the host furnace makes sense.
In the case of augmenting insulation, however, there are two important differences:
The new insulation often fixes the flaws in the old. As discovered, the degradation in the
performance of insulation is often tied to thermal bridging caused by human or animal
intervention. In those cases where the existing insulation is to remain in place, the
addition of new insulation is expected to fix the existing flaws of the entire installation.
According to their self-described protocols, contractors will carefully fill any problem
spots—ensuring that the final installation meets the project’s goals.
The existing insulation—when augmented—is not removed at the end of its original EUL.
Instead, the old and new insulation comprise a new, complete assembly. When new
insulation is installed in addition to the old, the resulting R-value 18 of the overall
assembly is designed to meet or exceed the required code. Furthermore, contractors
indicated that for the majority of projects, they do not remove existing insulation, 19 and
typically do so only in case of an animal infestation, to enable more thorough air sealing,
or for other health considerations. Customer survey data indicated that nearly two-thirds
of insulation projects involved augmentation, rather than complete tear-outs. The
rationale motivating that decision is that typically, the existing insulation combined with
the new insulation will still provide full longevity for the entire envelope system.
For these reasons, the research team recommends that RUL not be used in the case of new
insulation added to existing insulation. Instead, the full original EUL value should be employed.
The team recommends that this RUL recommendation apply to all types of insulation –
roof/attic, wall, and floor, because this conclusion originates from qualitative interviews with a
group of insulation contractors that routinely install and are able to characterize installations of
all types.
For more information please contact:
Rob Slowinski
robert.slowinski@guidehouse.com
303-728-2540
guidehouse.com
18
R-value is a measure of insulation’s resistance to heat transfer (°F·ft2·h/BTU). The higher the R-value, the more
effective the insulation.
19
Contractor estimates on the frequency of full insulation tear-outs ranged from 1% of the time to 25% of the time.
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1. Introduction
This study details the process and findings of Guidehouse’s investigation on the effective useful
life (EUL) of residential insulation measures in California. EUL is defined as the median number
of years since installation that an implemented measure is still in place and operable. 20 The
primary focus of this EUL research is to update the existing default EUL values used in the
statewide portfolio, including an update to the Database of Energy Efficiency Resources
(DEER). 21
Guidehouse (also referred to as the research team) prepared this study (EMV Group A,
Deliverable 16 EUL Research, Residential Insulation) for the California Public Utilities
Commission (CPUC). In June 2019, the research team conducted a high impact measures
analysis, ranking measures from two datasets. The first approach used the Uncertain Measure
List, 22 which is at the measure category level. The second approach used the measure-level
detail in the California Energy Data and Reporting System (CEDARS) extract for 2017.23 The
prioritization process designated residential insulation as a high priority measure. 24
1.1 Measure Background and Data Sources
Each program administrator (PA) in California offers incentives for building envelope measures
through the Home Upgrade Program, a whole building retrofit program. In particular, the PAs
incentivize roof insulation (also sometimes referenced as ceiling or attic insulation), wall
insulation, and floor insulation. 25 These installations are typically retrofits of existing
construction, but incentives are separately given for high achieving building envelopes in new
construction projects. Some insulation projects are standalone, but most are included as a part
of whole building retrofit projects. This study includes data from both types of projects.
20
California Public Utilities Commission, California Energy Efficiency Evaluation Protocols: Technical,
Methodological, and Reporting Requirements for Evaluation Professionals, April 2006,
http://www.cpuc.ca.gov/WorkArea/DownloadAsset.aspx?id=5212.
21
DEER contains estimates of the energy-savings potential of select energy-efficient technologies and measures in
residential and non-residential applications. The database also contains information on the costs and benefits of
energy-efficient measures.
22
Energy Division maps the thousands of measures in annual claims to 288 standardized measure groups for the
purposes of aggregation and consistency across programs, PAs, and years. In a given program year, each measure
associated with one or more claims is assigned a single measure group, allowing for application and comparison
between evaluations of one year and claims of another. The Uncertain Measure List can be found here:
http://www.cpuc.ca.gov/general.aspx?id=4137
23
CEDARS, “Confirmed Claims Dashboards for 2017 (Cost Effectiveness Output),” California Energy Data and
Reporting System, 2018, online at https://cedars.sound-data.com.
24
Measure prioritization for EUL research,
https://pda.energydataweb.com/api/downloads/2191/Measure%20Prioritization.pdf.
25
Note that not each PA has standalone insulation projects in each program year. Guidehouse originally considered
including windows, but there are few little-to-no rebated high efficiency windows across the portfolio.
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The EULs of insulation measures are more difficult to quantify than for other energy efficiency
measures; for insulation, there is no fixed nameplate to display information about the installation
date or original efficiency. Similarly, insulation rarely fails with a sudden or catastrophic event
alerting the homeowner of the urgent need for replacement. Rather, the effectiveness of
insulation measures often highly depends on initial installation quality, the insulative properties
of the material, and the type of product installed.
The current EUL of insulation measures is deemed to be 20 years.26 Between 2004 and 2006, a
number of retention studies were performed to estimate insulation EUL values prior to the
DEER2008 update. 27,28,29,30 These studies measured the proportion of insulation measures that
were still in place, operational, and effective 9 years after installation, and used this data to
calculate ex post EUL values. These values ranged between 85 and 291 years, but report
authors recommended adopting ex ante EUL values of 20. Another 2007 study cited in
DEER2008 documentation recommended an insulation EUL value of 25 years; 31 ultimately, the
values were set at 20 years based on these studies and due to a cap instituted by the CPUC.32
In addition, Resolution E-4818 reaffirmed that EUL values for add-on equipment measures are
limited to the Remaining Useful Life (RUL) values of the host equipment. 33 The same resolution
declared that wall, floor, and ceiling insulation added to existing insulation is a retrofit add-on
equipment measure. The only exception to this is when the add-on measure—in this case,
insulation—is part of a new installation in which case the EUL of the add-on equipment is limited
by the EUL of the host equipment. 34
To study the EUL of insulation measures in California, the research team requested tracking
data from five PAs. The request covered residential insulation measures that were installed as
part of the Home Upgrade Program between 2013 and 2018. The team received data for 10,471
insulation projects from this request.
26
Database of Energy Efficiency Resources, accessed June 2019. www.deeresources.com
27
See DEER2008 EUL Database Definitions. https://www.cpuc.ca.gov/WorkArea/DownloadAsset.aspx?id=11483
28
Megdal & Associates. Measure Retention Study – 1996 and 1997 Residential Weatherization Programs. CALMAC.
December 2005. http://www.calmac.org/publications/9-year_Retention_Study-Id_991__1996_and_1997_RWRI-
rev12-21.pdf
29
SDG&E. 1995 Residential Weatherization Retrofit Incentives: Ninth Year Retention Evaluation. CALMAC. March
2004. http://www.calmac.org/publications/aPY95_RWRI_9th_Year_Retention_Evaluation.pdf
30
SDG&E. 1996 Residential New Construction Program: Ninth Year Retention Evaluation. CALMAC. March 2006.
http://www.calmac.org/publications/2006_PY96PY97_RNC_9th_Year_Retention_Evaluation.pdf
31
GDS Associates, Inc. Measure Life Report: Residential and commercial/Industrial Lighting and HVAC Measures.
Consortium for Energy Efficiency. June 2007. https://library.cee1.org/content/measure-life-report-residential-and-
commercialindustrial-lighting-and-hvac-measures
32
Decision D.09-05-037, http://docs.cpuc.ca.gov/PublishedDocs/WORD_PDF/FINAL_DECISION/101543.PDF
and www.deeresources.com
33
Decision 15-12-002, http://docs.cpuc.ca.gov/PublishedDocs/Published/G000/M156/K191/156191759.docx
34
Approval of the Database for Energy-Efficient Resources updates for 2020 and revised version 2019 in Compliance
with D.15-10-028, D.16-08-019, and Resolution E-4818, www.deeresources.com
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Guidehouse used the tracking data to compile lists of program participants and installation
contractors. The research team then conducted telephone interviews with contractors to gather
information from their experiences installing insulation projects on a large scale and to provide
insights into the standard practice in California. The team also conducted an online survey of
program participants to gauge their individual experiences and gather additional quantitative
detail on the amount of time between the installation of their house’s original insulation and their
recent insulation upgrade. Section 2 provides details both the customer survey and contractor
interviews. Appendix A and Appendix B present copies of the customer survey guide and the
contractor interview form, respectively.
1.2 Study Objectives
This EUL research aimed to address the following key questions:
1. What is the estimated EUL of residential insulation projects?
2. Does the evidence support limiting new insulation’s measure life to the existing
equipment’s RUL or does it support using another measure life estimate, such as the
new insulation’s EUL value?
3. Should separate EUL values be defined for different types of insulation, or insulation
installed in different geographic regions?
Using primary data is imperative for providing California-specific data, establishing the credibility
of the research, and for making a persuasive case regarding the existing EUL estimates and
policy cap. The results of this study may also support updates to the existing default EULs used
in the statewide portfolio, including an update to the EUL values in DEER.
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2. Study Methodology
This chapter describes the methodology used in this study. The first three sections detail the
team’s data collection efforts from PAs, Home Upgrade Program participants, and insulation
contractors. The final section describes the methodology for analyzing responses and
determining EUL.
2.1 Program Data Collection and Database Analysis
The first part of the study involved collecting and analyzing tracking data of residential insulation
upgrades completed by each PA. Guidehouse requested data on all roof, wall, and floor
insulation upgrades completed as part of the Home Upgrade Program between 2013 and 2018.
The data request included individual project information (such as the location of upgrades and
customer contact information) and contractor information (such as company name, total annual
rebate amounts, and contractor contact information).
Table 2 shows the number of projects for which customer data was received from four PAs.
Some PAs included projects that consisted only of duct insulation upgrades; the team removed
these duct insulation projects from consideration.
Table 2. Home Upgrade Project Participant Data, 2013-2018
Program Number of Number of Projects with Valid
Administrator (PA) Projects* Participant Email Address
Bay Area Regional
Energy Network 2,434 1,958
(BayREN)
Pacific Gas & Electric
2,738 1,742
(PG&E)
Southern California
1,942 1,586
Gas (SoCal Gas)
Southern California
Regional Energy 857 460
Network (SoCalREN)
Total 7,971 5,746
* Includes all projects with roof, wall, or floor insulation. Does not include projects that only included duct
insulation.
Source: Guidehouse
The research team cleaned the tracking data to compile a list of participant contacts for the
online survey. This involved removing around 2,200 participants who either did not provide an
email address or did not have a valid and unique email address. Table 2 shows the number of
participants with valid email addresses for each PA. Invalid email addresses included those with
incorrect formats and those with default text such as “none” or “NA.” The team also removed
participants who had duplicate email addresses if the address appeared to be contractor or
company email rather than a personal address.
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The team analyzed the tracking data to compile a list of insulation contractors to contact for
telephone interviews. Table 3 shows the number of contractors identified from each PA. The
team identified 261 unique companies that have installed insulation as part of the Home
Upgrade Program between 2013 and 2018. Table 3 also shows the proportion of projects
(sorted by number of participants or total rebates) that were completed by the 10 largest
contractors within each PA. A relatively small number of contractors account for a large majority
of the projects. Therefore, the team sorted the pool of contractors from largest to smallest and
focused on interviewing the largest contractors.
Table 3. Home Upgrade Program Insulation Contractors, 2013-2018
Program Number of Contractors Proportion of Projects by
Administrator (PA) Identified Top 10 Contractors
BayREN 101 68%
PG&E 66 76%
SCE 54 85%*
SoCal Gas 58 88%
SoCalREN 60 72%*
Average 67.8 77.8%
* Based on proportion of total rebates awarded as opposed to the number of projects.
Source: Guidehouse
2.2 Participant Survey
Guidehouse designed and fielded a customer survey to determine the average age of existing
insulation before replacement. The goal of the survey was to determine the following:
What is the average age of existing insulation before augmentation or replacement?
Is there any variability in the lifetime of insulation by geographic region or by PA?
Does the type of insulation installed (loose-fill, fiberglass batt, etc.) impact its useful life?
Does insulation installed in a roof have a different EUL than insulation installed in a wall
or in a floor?
The first part of the survey included qualification questions to ensure that the participant had
direct knowledge of the referenced insulation upgrade project. Only responses from customers
who were directly knowledgeable about their projects were used in the analysis.
The second section of the survey aimed to collect demographics of a customer’s house and
insulation project; it included questions like:
In what year was your home built?
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Was the previous insulation in your home original to the home’s construction or has it
been replaced or upgraded previously? 35
Did your recent insulation upgrade involve new insulation in the roof, walls, floor, or any
combination thereof?
The third portion of the survey collected more detailed information about each home’s original
insulation:
Type of existing insulation (loose-fill or blown cellulose, fiberglass or other batts, rigid
foam boards, or spray-in-place insulation)
Condition of existing insulation (worn out, removed and replaced, existing insulation
augmented)
Age of prior insulation (either original to home or installed in a specific year or decade)
Motivation for each upgrade (comfort issues, part of a larger remodel, code requirement)
The survey was fielded in February and March 2020 and yielded 467 participant responses. Of
these, 210 customer responses passed the initial qualification questions that screened for
whether the participant had knowledge of their insulation upgrades, which exceeded the target
of 100 responses. The 210 customer responses consisted of 237 installations (including some
customers with installations in multiple locations—roof and walls, for example). Most customers
had loose-fill existing insulation, and more customers had roof insulation installed than any other
type. Further details of the survey analysis can be found in Section 3, and a detailed survey
guide can be found in Appendix A.
2.3 Contractor Interviews
In contrast to individual homeowners, insulation contractors have experience with a much larger
number of projects and a greater diversity of project types. The goal of contractor interviews
was to gain insight into these contractors’ wealth of knowledge about the condition and age of
existing insulation in California projects.
From the compiled list of contractors summarized in Table 3, Guidehouse sorted by geographic
region and contractor size (gauged by number of projects or awarded incentives). The team
spoke with seven contractors in various geographic regions; the contractors ranged from a few
hundred completed projects per year to 5,000 completed projects per year. Collectively, the 7
interviewed contractors accounted for approximately 13% of kWh and 8% of natural gas savings
associated with all Home Upgrade Projects for the PAs in Table 2 from 2013 to 2018. Each
interview lasted around 30 minutes and detailed the following:
35
Data from homes that had no insulation prior to the 2013-2018 retrofit projects was not used in calculating
insulation EUL.
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The contractor’s evaluation and decision-making process (whether a project should
proceed and what types of upgrades to recommend)
The typical types of insulation encountered, categorized by roof/wall/floor installations
The typical condition and age of existing insulation
Specific factors affecting the age, performance, or durability of each type of insulation
and each installation location (roof/wall/floor)
Most of the interviewed contractors reported that between 90% and 100% of their insulation
work was with single-family homes and that a small percentage was with multifamily or
commercial projects. One contractor reported that only 70% of their work was with single-family
homes, while the remaining 30% was with multifamily homes.
To assess the existing insulation of a home, contractors reported primarily using visual and
physical inspections of insulation type, thickness, and depth. Many also reported using thermal
infrared heat guns. Other commonly reported aspects of energy audits included blower door
tests and constructing energy models. Several contractors noted the importance of inspecting
for air sealing prior to installing insulation.
Sections 3.2 presents findings from the interviews specific to the evaluation of insulation EUL.
Appendix B contains the contractor interview guide.
2.4 Analysis Methodology
As considered in Section 1.1, the EUL of insulation measures is more nuanced than for other
types of measures. If a refrigerator fails, for example, the end of the useful life is immediately
obvious to the homeowner. When an air conditioner’s performance degrades beyond a certain
point, such performance degradation is easily tested by an HVAC technician. But for insulation
measures, the impact is rarely as sudden or catastrophic.
Furthermore, insulation contractors are somewhat split on whether insulation materials degrade
on their own (see Section 3.2.1). Most commonly, degradation of insulation performance is
caused by human behavioral factors perhaps unrelated to the insulation itself. Insulation
contractors report that the installation of ceiling can lights or speaker wires are a main culprit in
performance degradation, especially when the homeowner or installer did not take similar care
in replacing the disturbed insulation as with the installation itself. Less frequently, rodent or other
pest infestations may cause material damage or create thermal bridges that reduce the
effectiveness of the installed insulation.
While code-mandated insulation R-values36 increase over time, it is often difficult or impossible
to measure the on-site efficiency of installed insulation, either due to inaccessibility of the
36
R-value is a measure of how well certain building insulation materials can resist the flow of heat and is the
commonly used metric defining how insulative a material is.
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material or the lack of any kind of nameplate or record of the original install. Regardless of the
exact culprit of performance degradation, the values cited in this report include an assumption
that the aggregate “time between replacements” is a reasonable proxy for insulation EUL, given
the lack of cost-effective alternative testing methods. To report on such data, the research team
collected survey data on the age of previously installed insulation at the time of each Home
Upgrade Program project and used it to estimate EUL.
For each location in which insulation was upgraded between 2013 and 2018, the survey asked
participants whether or not there was existing insulation in that location. If preexisting insulation
was encountered, the survey asked whether or not it was in place at the time of the home’s
construction or if it was the result of a previous upgrade. If the existing insulation was original to
the home, then the year of the home’s construction was used as a proxy for age of the
insulation. Otherwise, the survey asked participants to provide the year of their previous
upgrade, which the team used to calculate the age of existing insulation upon upgrade. After
cleaning the data, Guidehouse used the median value of this age across all participants to
estimate EUL. Section 3.3 presents the results of this analysis.
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3. Results
This section presents key findings from the interviews of insulation contractors and the online
survey of Home Upgrade Program participants. Section 3.1 discusses the demographics of the
responses. Section 3.2 discusses the findings that inform insulation degradation factors and
EUL estimates based on the age of the replaced insulation. Section 3.3 and Section 4 discuss
the team’s determinations on EUL and RUL based on the results.
3.1 Response Demographics
Guidehouse received 467 responses to the customer survey. Of these, 210 participant
responses passed the initial qualification and screening questions that ensured the participant
had direct knowledge of the referenced insulation upgrades. Figure 4 shows the breakdown of
these 210 responses by PA.
Figure 3-1. Participant Survey Responses by PA
90
80
Number of Participants
70
60
50
40 84
77
30
20 39
10
10
0
BayREN PG&E SoCalGas SoCalREN
Total count: n = 210 participants
Source: Guidehouse
3.1.1 Age of Homes
The research team asked both insulation contractors and Home Upgrade participants about the
age of homes requiring insulation upgrades. Contractors reported working primarily with homes
built prior to 2000 and in particular with homes built prior to 1978, when the first building energy
efficiency standards were implemented in California.37 One contractor said that they specialized
37
California Energy Commission, Past Building Energy Efficiency Standards, 2020.
https://www.energy.ca.gov/programs-and-topics/programs/building-energy-efficiency-standards/past-building-energy-
efficiency
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in homes built between the 1920s and 1950s. Otherwise, contractors reported working on a
wide range of homes built between approximately 1940 and 1980.
The contractor responses were largely matched by the participant survey data. Each participant
in the survey provided the year or decade bin in which their home was built. Figure 5 shows the
distribution of these responses. The figure shows that most respondents had homes built
between 1940 and 2000. Only a few participants reported that their homes were built before
1940 or after 2000.
Figure 3-2. Surveyed Home Age Distribution – Decade Home Constructed
60
50
Number of Responses
40
30
50
20 41 42
28
10 20
1 4 4 11 9
0
Source: Guidehouse
Survey participants also noted whether their home had original insulation or previously
upgraded insulation at the time of their home upgrade. Original insulation refers to the insulation
that was present at the time of the home’s construction. Previously upgraded insulation means
that the insulation in place at the time of the home upgrade between 2013 and 2018 was not the
insulation original to when the home was built; the existing insulation had been installed in a
prior retrofit. Figure 6 shows how the proportion of original and previously upgraded insulation
varied across homes of different ages. Older homes had a relatively larger proportion of
previously upgraded insulation than newer homes. Newer homes primarily had original
insulation in place at the time of the home upgrade.
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Figure 3-3. Original and Previously Upgrade Insulation by Decade of Home Construction
60
Number of Responses
50
40
30
20
10
0
Unknown Original Previously Upgraded
Source: Guidehouse
3.1.2 Location of Upgrades
Guidehouse asked participants and contractors about roof, wall, and floor insulation projects.
While the CPUC’s historic convention has been to use the same EUL value for each type of
insulation project, inquiring about each insulation location separately may justify additional
stratification if the data suggests different EULs for different types of installations.
Contractors generally reported that roof projects make up the majority of their insulation work
(80%-90% or more) and that wall and floor projects are relatively uncommon. Some contractors
reported larger numbers of wall projects than floor projects, while others reported a roughly
even split between wall and floor projects. Only one contractor reported that floor projects are
more common than wall projects. Kommentar [JA1]: Maybe add
something about CPUC historically
In the participant survey, each participant reported whether their home upgrade included roof, using the same value for these
wall, or floor insulation measures. The 210 projects consisted of 256 separate instances of roof, different insulation types?
wall, or floor upgrades. Figure 7 shows the breakdown between these three locations. All 210
projects included roof insulation, which accounted for 82% of all measures installed. Wall and
floor insulation each accounted for around 9%, which is in line with what contractors reported.
The small number of wall and floor responses made it difficult for the team to draw differentiated
conclusions based on the insulation’s location within the house.
Of the 210 projects, 169 (over 80%) consisted of only roof upgrades, 19 consisted of roof and
wall upgrades, and 17 consisted of roof and floor upgrades. Only five of the projects consisted
of upgrades in all three locations.
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Figure 3-4. Proportion of Upgrades by Installation Location
22
24
Roof (82.0%)
Wall (9.4%)
Floor (8.6%)
210
Source: Guidehouse
3.1.3 Existing Insulation Type
The research team collected information about the type of insulation that was in place prior to
the home upgrade from both contractors and survey participants. Contractors reported that it
was common to find homes with no previously installed insulation, especially in walls and floors
and in homes built prior to the 1960s or 1970s. Existing insulation was most frequently found in
roofs, where contractors reported most often seeing fiberglass batts or small amounts of blown
cellulose or fiberglass. Contractors occasionally found other materials like mineral wool,
rockwool insulation, or vermiculite in roofs.
In walls, most contractors reported finding no existing insulation the majority of the time;
however, the largest contractor reported finding no existing wall insulation only 15% of the time.
In instances where there was existing wall insulation, contractors reported finding fiberglass
batts or sometimes blown cellulose if the home was previously retrofitted. Similarly, all but one
contractor reported almost never finding existing floor insulation. When existing floor insulation
was found, it was usually fiberglass batts.
Table 4 shows the distribution of insulation type across roofs, walls, and floors for the surveyed
participants. All 210 participants reported having existing roof insulation which was most often
loose-fill or blown-in, followed by batt or roll insulation.
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Table 4. Survey Responses for Existing Insulation Type by Location
Insulation Type Roof Wall Floor
Batt or Roll 54 5 6
Foam Board or Rigid Foam 1 - -
Loose-Fill or Blown-In 132 2 3
Spray Foam or Foam-in-Place 5 1 1
No Previous Insulation - 9 10
Not Specified/Unknown 18 7 2
Total 210 24 22
Source: Guidehouse
3.1.4 Motivation for Upgrades
In the online survey, Guidehouse asked participants about their motivation for upgrading
insulation. These responses are shown in Figure 8. The majority of participants said that their
upgrades were part of a larger remodel, while a smaller number said that they were upgrading
primarily to improve home comfort.
Figure 3-5. Participant Motivations for Insulation Upgrades
120
Number of Responses
100 111
80
60 67
40
20
25
4 3
0
House too Part of a Required to Other No
hot or too larger meet code Response
cold remodel
Source: Guidehouse
3.2 Insulation Degradation and Performance
This section presents findings on insulation degradation and performance from the contractor
interviews and literature review.
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3.2.1 Natural Degradation of Insulation Materials
In the contractor interviews, the research team asked about the natural degradation of insulation
materials over time. Specifically, the team asked contractors if they believed that fiberglass or
cellulose insulation will naturally break down and lose its insulative properties.
A majority of the contractors felt that insulation materials do not naturally degrade. They believe
that natural reductions in performance over time are relatively small compared to the reductions
that result from settling or external factors like human disturbances and pests. These
contractors were generally of the opinion that absent external disturbances, properly installed
insulation left on its own will last essentially forever.
However, this was not a consensus opinion. Three contractors expressed a belief that there is
slight degradation over time; they believe that after 25-30 years, effective insulating properties
are diminished and that natural degradation plays a part in this. They commented that like all
things, insulation does tend to fall apart over a long time and that insulation in older homes
generally looks worn out, settled, and diminished.
All contractors agreed that insulation performance does decline over time—and to a greater
extent–as a result of other external factors. These are discussed in the following section.
3.2.2 Factors Affecting Insulation Performance
The team asked contractors about how insulation performance degrades over time. Contractors
responded that the most important factors are human-caused behavioral factors, pests,
improper installation, and settling.
Human behavioral factors refer to homeowners or non-insulation contractors and technicians
shifting or moving insulation for various purposes and not properly replacing it. These factors
were most often discussed in the context of roof insulation because it is the most commonly
insulated location and because it is generally an uncomfortable and tight space in which
homeowners or contractors are eager to exit. Two contractors reported seeing at least one of
these problems in 75%-80% of homes; others did not provide a specific estimate. Specifically,
contractors often brought up:
Work on HVAC systems or the installation of recessed lighting, TV or cable wires,
speaker wires, camera systems, and alarm systems that requires accessing the attic or
roof space. Contractors reported that this was more of a problem with batt insulation
than loose-fill insulation.
Homeowners walking on or moving around insulation in their attics. Specific examples
included using attics for storage or moving around and not replacing insulation during
home remodeling. One contractor reported seeing this issue in 30% of projects.
Pest contamination—especially from rodents—was another frequently mentioned factor. Some
contractors reported finding some level of infestation in 30%-50% of homes, while a few
reported seeing minor infestations in up to 90% of homes. However, contractors generally
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