Internal Roof and Attic 

Thermal Radiation Control 

Retrofit Strategies for 

Cooling-Dominated Climates

A. Fallahi, H. Durschlag, D. Elliott, J. Hartsough, 

N. Shukla, and J. Kosny

Fraunhofer Center for Sustainable Energy Systems

December 2013
NOTICE

This report was prepared as an account of work sponsored by an agency of the United States government. 

Neither the United States government nor any agency thereof, nor any of their employees, subcontractors, or 

affiliated partners makes any warranty, express or implied, or assumes any legal liability or responsibility for the 

accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or 

represents that its use would not infringe privately owned rights. Reference herein to any specific commercial 

product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily 

constitute or imply its endorsement, recommendation, or favoring by the United States government or any agency 

thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the 

United States government or any agency thereof.

Available electronically at http://www.osti.gov/bridge

Available for a processing fee to U.S. Department of Energy

and its contractors, in paper, from:

U.S. Department of Energy

Office of Scientific and Technical Information

P.O. Box 62

Oak Ridge, TN 37831-0062

phone: 865.576.8401

fax: 865.576.5728

email: mailto:reports@adonis.osti.gov

Available for sale to the public, in paper, from:

U.S. Department of Commerce

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22161

phone: 800.553.6847

fax: 703.605.6900

email: orders@ntis.fedworld.gov

online ordering: http://www.ntis.gov/ordering.htm

Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste
iii

Internal Roof and Attic Thermal Radiation Control Retrofit Strategies 

for Cooling-Dominated Climates

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:

A. Fallahi, H. Durschlag, D. Elliott, J. Hartsough, N. Shukla, and J. Kosny

Fraunhofer Center for Sustainable Energy Systems (CSE)

Building Energy Efficiency Group

5 Channel Center Street

Boston, MA 02210

NREL Technical Monitor: Chuck Booten

Prepared under Subcontract No. KNDJ-0-40345-02

December 2013
iv

[This page left blank]
v

Contents

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

List of Tables ............................................................................................................................................ viii

Abbreviations ............................................................................................................................................. ix

Acknowledgment ........................................................................................................................................ 1

Executive Summary.................................................................................................................................... 2

1 Introduction........................................................................................................................................... 4

2 Field Testing.......................................................................................................................................... 8

2.1 Instrumentation ..................................................................................................................13

2.2 Radiation Control Technology Installations......................................................................17

2.2.1 Radiant barrier with enclosed airspace ..................................................................17

2.2.2 Interior Radiation Control Coating (IRCC)...........................................................18

3 Experimental Data Analysis .............................................................................................................. 20

3.1 External and Internal Air Temperature Comparisons........................................................20

3.2 Experimental Attic Air Temperature Comparisons...........................................................29

3.3 Experimental Heat Flux Comparison.................................................................................44

4 Energy Modeling................................................................................................................................. 47

4.1 Model Description .............................................................................................................47

4.2 Calibration of Whole Building Energy Model...................................................................50

4.3 Prediction of the Cooling Energy Consumption................................................................53

4.4 Modeling Results...............................................................................................................53

5 Cost Effectiveness Analysis.............................................................................................................. 56

6 Conclusions ........................................................................................................................................ 58

References................................................................................................................................................. 60

Appendix A- Historical Energy Consumption Data ............................................................................... 62
vi

List of Figures

Figure 1. Location of site............................................................................................................................ 8

Figure 2. Location of thermistor arrays and heat flow transducers inside the tested attics (Right); 

Bird view image of the duplexes in Austin, TX (Left)........................................................................ 9

Figure 3. Estimated brick wall construction: 2 in. brick, 1 in. air gap, 1⁄2 in. OSB, 2×4 stud wall with

batt insulation, gypsum wall board (left); Estimated clapboard siding: clapboard, battens, 1⁄2 in. 

OSB, 2×4 stud wall with batt insulation, gypsum wall board (right). ............................................ 10

Figure 4. Existing insulation conditions in Duplex 1. Note the inconsistent levels of loose-fill 

insulation............................................................................................................................................. 10

Figure 5. Existing insulation conditions in Duplex 2. Note the inconsistent levels of loose-fill 

insulation............................................................................................................................................. 11

Figure 6. Existing insulation conditions in Duplex 2 (left) and Duplex 1 attic over living space 

(above right) and over garage (below right). ................................................................................... 12

Figure 7. Visible gaps around ducts entering attic. .............................................................................. 12

Figure 8. Location of the vents for attics over living spaces in Duplex 1........................................... 13

Figure 9. Location of the vents for attics over living spaces in Duplex 2........................................... 13

Figure 10. Diagrams of the attic sensor distributions for a RB combined with an enclosed 

reflective air space (upper diagram), and IRCC and baseline (lower diagram). .......................... 15

Figure 11. Thermistors installed on interior, exterior and attic to capture surface temperatures. .. 16

Figure 12. DAQ Components. .................................................................................................................. 17

Figure 13. Installation of RB with enclosed airspace from Fi-Foil Company (Silver Shield). ........... 18

Figure 14. Installation of IRCC from Solec-Solar Energy Corporation (LO/MIT-II MAX) (left) and 

from STS Coating, Inc. (HeatBloc-Ultra) (right)............................................................................... 19

Figure 15. Measured exterior air temperature on one of the test houses........................................... 21

Figure 16. Average daily roof surface temperatures recorded during the April measure period. ... 22

Figure 17. Average daily roof surface temperatures recorded during the June/July measure period.23

Figure 18. Average daily roof surface temperatures recorded during the July/August measure 

period................................................................................................................................................... 24

Figure 19. Maximum roof surface temperatures recorded during the April measure period. .......... 25

Figure 20. Maximum roof surface temperatures recorded during the June/July measure period... 26

Figure 21. Maximum roof surface temperatures recorded during the July/August measure period.27

Figure 22. Average interior air temperatures recorded during the April measure period................. 28

Figure 23. Average interior air temperatures recorded during the June/July measure period. ....... 29

Figure 24. Example of attic air temperatures recorded in four test attics (center location) during 

the April measure period. .................................................................................................................. 30

Figure 25. Average daily attic air temperatures recorded in four test attics (center location) during 

the April measure period. .................................................................................................................. 31

Figure 26. Average daily attic air temperatures recorded in four test attics (center location) during 

the June/July measure period........................................................................................................... 32

Figure 27. Average daily attic air temperatures recorded in two IRCC attics (center location) during 

the July/August measure period....................................................................................................... 33

Figure 28. Maximum daily attic air temperatures recorded in four test attics (center location) 

during the April measure period....................................................................................................... 34

Figure 29. Maximum daily attic air temperatures recorded in four test attics (center location) 

during the June/July measure period. ............................................................................................. 35

Figure 30. Maximum daily attic air temperatures recorded in two IRCC attics (center location) 

during the July/August measure period. ......................................................................................... 36

Figure 31. Differences in daily attic air temperatures recorded between three test attics using 

radiation control technologies and a baseline attic, during the April measure period............... 37

Figure 32. Differences in daily attic air temperatures recorded between three test attics using 

radiation control technologies and a baseline attic, during the June/July measure period. ..... 38

Figure 33. Differences in maximum daily attic air temperatures recorded between three test attics 

using radiation control technologies and a baseline attic, during the April measure period.... 39

Figure 34. Differences in maximum daily attic air temperatures recorded between three test attics 
vii

using radiation control technologies and a baseline attic, during the June/July measure 

period................................................................................................................................................... 40

Figure 35. Daily temperatures on the top surface of the attic insulation recorded in four test attics 

using radiation control technologies and a conventional base case, during the April measure 

period................................................................................................................................................... 41

Figure 36. Daily temperatures on the top surface of the attic insulation recorded in three test attics 

using radiation control technologies and a conventional base case, during the June/July

measure period................................................................................................................................... 42

Figure 37. Daily temperatures on the top surface of the attic insulation recorded in two test attics 

using radiation control technologies and a conventional base case, during the July/August 

measure period................................................................................................................................... 43

Figure 38. Heat fluxes recorded in four test attics using radiation control technologies and a 

conventional base case, during the April measure period. Positive heat flow direction is from 

conditioned space to the attic........................................................................................................... 44

Figure 39. Heat fluxes recorded in test attics using radiation control technologies and a 

conventional base case, during the June/July measure period. Positive heat flow direction is 

from conditioned space to the attic.................................................................................................. 45

Figure 40. Heat fluxes recorded in test attics using radiation control technologies and a 

conventional base case, during the July/August measure period. Positive heat flow direction 

is from conditioned space to the attic.............................................................................................. 46

Figure 41. Duplex 1 model (above); Duplex 2 model (below)............................................................... 48

Figure 42. Breakdown of household gas consumption. ....................................................................... 50

Figure 43. Comparison of monthly historical gas bill, simulated consumption, and the gas 

consumption by Texas Gas Service calculator. The calibration is limited to the months with 

available historical utility bill............................................................................................................. 51

Figure 44..Breakdown of household electrical consumption............................................................... 52

Figure 45. Comparison of monthly historical electricity bill, simulated consumption, and the 

electricity consumption by Texas Gas Service calculator. The calibration is limited to the 

months with available historical utility bill. ..................................................................................... 53

Figure 46. Modeled utility consumption of baseline house in different U.S. South climates and 

payback period of radiation control strategies. .............................................................................. 56

Unless otherwise noted, all figures were created by the Fraunhofer team.
viii

List of Tables

Table 1. Experimental Results for Cooling Load and Heat Flux Reductions Produced by 

Application of RB.................................................................................................................................. 6

Table 2. Model parameters....................................................................................................................... 49

Table 3. Predicted Energy Saving From RB Technology...................................................................... 54

Table 4: Residential utility price based on considered climates ......................................................... 57

Unless otherwise noted, all figures were created by the Fraunhofer team.
ix

Abbreviations

DAQ

IRCC 

OSB

RB

Data Acquisition

Internal Radiation Control Coating 

Oriented Strand Board

Radiant Barrier
1

Acknowledgment

We would like to acknowledge and extend our sincerest thanks to the City of Austin, Texas, and 

Foundation Community for collaborating and providing us with the test houses, Tim Ashwood 

from Fi-Foil Company, Robert Aresty from SOLEC-Solar Energy Corporation and John Kovacs 

from STS Coatings for providing and installing the two radiation control technologies, Dr. David 

Yarbrough from R&D Services, Inc. (RIMA liason), and Dr. Mario Medina from the University 

of Kansas for assistance and technical guidance.
2

Executive Summary

This project evaluates the cooling energy savings and cost effectiveness of radiation control 

retrofit strategies for residential attics in U.S. cooling-dominated climates. Usually, in residential 

applications, radiation control retrofit strategies are applied below the roof deck or on top of the 

attic floor insulation. They offer an alternative option to the addition of conventional bulk 

insulation such as fiberglass or cellulose insulation. Radiation control is a potentially low-cost 

energy efficiency retrofit strategy that does not require significant changes to existing homes. In 

this project, two groups of low-cost radiation control strategies were evaluated for southern U.S. 

applications. One uses a radiant barrier composed of two aluminum foils combined with an 

enclosed reflective air space and the second uses spray-applied interior radiation control coatings 

(IRCC).

The main goal of this study, conducted by the U.S. Department of Energy (DOE) Building 

America team, Fraunhofer Center for Sustainable Energy Systems (Fraunhofer CSE), was to 

answer the following three research questions:

• What are the potential reductions in annual cooling energy consumption and cooling 

loads from using a Radiant Barrier (RB) assembly that includes an enclosed reflective air 

space in residential attics? 

• What is the energy performance of an attic-applied IRCC? 

• What are the cost benefits of these radiation control technologies in residential retrofit 

applications located in the southern climate zone?

Both experimental and numerical analyses were used to answer these research questions. 

Working with the City of Austin, Texas, and Foundation Communities, test houses were selected

to apply IRCC and RB systems for field testing and performance analysis. During the 2012 

cooling season, thermal performance measurements were completed on four housing units in two 

residential duplexes. One test attic was retrofitted using RBs and two were retrofitted using 

IRCCs. The fourth unmodified attic was used as a base case for comparisons. All test houses 

were occupied during the testing. The plan was to keep internal load schedules in the test units as 

close as possible.

In general, measured test data confirmed prior results from other research organizations. A 3.4°C 

reduction of the average attic air temperature was observed for the multifoil RB (two reflective 

layer of ε=0.03 and ε=0.04) during mid-summer 2012. The recorded data showed a 34% 

reduction of the attic-generated cooling loads. The potential whole building cooling energy 

savings for this technology may be close to 4% (assuming approximate steady-state heat transfer,

an average attic temperature of 35°C, and internal air temperature of 25°C). This is based on the 

report that in U.S. residential houses, roofs and attics generate an average 12% cooling energy 

contributions. In that light, potential whole building cooling energy savings may reach about 4% 

depending on other building parameters and HVAC system efficiency. 

A 2.4°C reduction of the average attic air temperature was observed for the IRCC test sites. This 

can be equivalent to a 24% reduction of the attic-generated cooling loads and the potential whole 

building cooling energy savings for this technology may be close to 3%. Based on the recorded 
3

data, the energy performance of two IRCC systems with emissivity of 0.17 and 0.19 seems to be 

very similar (there were minor differences in construction). To better characterize these 

technologies, more precise calorimetric field experiments should be considered in the future.

An EnergyPlus computer model calibrated against both pre-retrofit and post-retrofit energy 

consumption data was used to predict the potential cooling energy savings. The results from 

EnergyPlus were well below the range of observed cooling energy savings approximated on the 

measurements performed during this experiment. The modeled whole-building cooling energy 

savings was 1.3% and 0.8% for RB and IRCC respectively (compared with 4% and 3% during 

this experiment). The discrepancies could be partially due to EnergyPlus limitation that uses 

simplified numerical algorithm for attic thermal analysis. 

To evaluate the payback period, the heating and cooling loads were modeled for the baseline 

house with R-19 attic insulation using EnergyPlus in four southern U.S. locations. Having these 

modeled loads, one upper limit and one lower limit for the radiation control strategies load 

savings were assumed. The upper limit was obtained from the literature and the lower limit has 

cooling energy savings close to this report’s field study data. Taking the upper limit of energy 

savings, RB and IRCC systems yielded the shortest payback times for Miami, Florida and 

Phoenix, Arizona—about 3.5 years and 5 years, respectively. When saving levels are similar to 

recorded levels during this experiment (lower limit saving), the payback times are 16 and 22 

years, for RBs and IRCC, respectively, for the same locations.
4

1 Introduction

According to the Reflective Insulation Manufacturers Association (RIMA)

1

, radiation control 

techniques can be grouped in three main product types: a) reflective insulations; b) radiant 

barriers (RB); and c) Interior Radiation Control Coatings (IRCC). Each of these product types is 

represented in ASTM Committee C 16 and have standards in print. The “insulation” market 

share for all products is estimated to be between 1% and 2%. This report will focus on the use of 

RB and low-emittance (low-e) coatings. In this project, the Fraunhofer team worked closely with 

RIMA and three companies Fi-Foil, Solec, and STS Coatings, Inc..Interaction between RIMA 

and Fraunhofer CSE was supported by R&D Services—simultaneously a member of the 

Building America team led by Fraunhofer CSE and technical advisor to RIMA.

In this report, the physical principles that make RBs and IRCCs work are explained; their 

thermal performance is discussed based on results of numerical analysis and full-scale field 

testing.

Attic RBs and IRCCs present a unique way of increasing the thermal performance of existing or 

new insulation within the space between the roof deck and ceiling level in residential and small 

commercial buildings. These systems may also be successfully applied in the space between 

roofs and suspended ceilings in commercial buildings. Attic RBs save energy by reducing the 

transfer of heat from the hot roof to the attic floor insulation in the summer. The transfer of heat 

from the attic floor insulation to the roof in the winter is also reduced. Aluminum surfaces, like 

those found in RB applications, have thermal emittances in the range of 0.03 to 0.06. Therefore, 

there is very little radiant transfer across a space bounded by a RB. 

Most often, RBs are aluminum foil laminates or aluminized synthetic films sheets. The foils are 

laminated to paper, most commonly to Kraft paper, synthetic films, oriented strand board (OSB), 

or plywood. For the aluminized synthetic films, a thin layer of aluminum particles are deposited 

on the films through a vacuum process. These laminates and films are characterized by having at 

least one low-e surface of 0.1 or less (ASTM C 1313, 2010).

IRCCs are low-e coatings or paints that, when applied (i.e., sprayed or painted) to building 

surface (e.g., OSB, plywood, metal siding, or plasterboard), decrease the emittance of these 

surfaces to 0.25 or less (ASTM C 1321, 2009). Both RBs and IRCCs have received considerable 

attention due to their potential to reduce the radiant heat transfer across vented spaces between 

roofs and ceilings of buildings (e.g., attic spaces in residential buildings). In the case of RBs, 

aluminum is used because it is inexpensive and is a surface that, once exposed to air, becomes 

covered with a layer of a transparent oxide that protects it from the atmosphere and allows it to 

maintain a constant emittance for long periods of time (Lenntech, 2010).

 1 The Reflective Insulation Manufacturers Association-International (RIMA-I) is a trade association organized to 

support and encourage the use of reflective technology to conserve energy use in buildings. The Association has 25 

members of which 20 are from the United States and 5 are international. Approximately 20 of the members would 

be considered small businesses. (Dupont, Louisiana Pacific, Sealed Air, Pactiv and Roy-o-Martin are not small 

businesses.)
5

In some cases, an RB can include an enclosed air space in order to provide thermal resistance to 

the path between the roof sheathing and the attic floor. This project uses an RB with an enclosed 

air space, which is a common configuration with multilayer products such as Silver Shield from 

Fi-Foil Company. In some cases, there is an R-value 2 3 associated with the reflective insulation 

component application. In the configuration considered in this research, the thermal performance 

of interior-facing RB has to be combined with the low thermal conductive performance of the 

enclosed air cavities.

Low-e coatings (IRCCs) have similar heat reduction principles as RBs in residential attics. RB

coatings are also being studied in this project at Austin, Texas. This is a crucial project for the 

industry since there are very few examples of directly measured savings due to spray-applied or 

liquid-applied attic IRCCs.

A recently completed review of prior research on RBs (Medina, 2012) indicates a reduction in 

summer ceiling heat loads between 23% and 45%. Winter heat load reductions were equal to 

approximately 40% of the summer reduction. Although the industry does not have software to 

evaluate energy savings, there is an ASTM Consensus method for calculating RB performance 

(ASTM C 1340, “Standard Practice for Estimation of Heat Gain or Loss through Ceilings Under 

Attics Containing Radiant Barriers by Use of a Computer Program”). This program is called 

“AtticSim” and was developed by Kenneth Wilkes. In the past, it has been used by Oak Ridge 

National Laboratory to generate input for two editions of DOE RB fact sheets. 

Currently, RBs and IRCCs are difficult to numerically analyze using whole building energy 

simulation tools. In the past, DOE 2.2, EnergyPlus, and BEopt have not had the capability for 

detailed attic modeling. Recently, there has been an effort to link C 1340 to DOE 2.2 and provide 

modeling of attic RBs. However, the status of this project is unclear. Current DOE-sponsored 

work with AtticSim is limited to attic RBs and does not extend to evaluations of reflective 

insulation assemblies. Additionally, Fraunhofer CSE used AtticSim to analyze the thermal 

performance of complex attic configurations. The organizations listed above have utilized

AtticSim in their research because it is an in-house program that has the recognition of being a 

consensus program.

Medina (2012) reviewed over sixty published papers from various sources. These included peerreviewed journals, peer-reviewed conference proceedings, national and state laboratory reports, 

MS theses, and Ph.D. dissertations. Based on the report, experimental results highlighting 

cooling load and ceiling heat flux reductions produced by RBs vary depending on nominal 

ceiling insulation R-value, testing protocol, climate zone, ventilation type, occupancy and duct 

inclusion in the attics. Medina (2012) reported that in attics with nominal insulation levels of R11, R-19 and R-30, average space cooling reductions are 14%, 20% and 6%, respectively. He 

also reported the average reduction in heat flow produced by installing RBs in attics with 

 2 Thermal resistances calculated for an enclosed air space with one surface having emittance 0.03 and a second 

surface with emittance 0.9 are 1.99 and 3.43 (ft2•h•°F/Btu) when heat directions are up at 45o and down at 45o

, 

respectively. The thermal resistance values in the report do not include the effect of the air space between the 

product and the roof sheathing of the RB effect due to a low-emittance surface facing the attic floor.

3 http://www.rimainternational.org/index.php/technical/library/residential-commercial/ .
6

insulation levels of R-11, R-19 and R-30 are 45%, 30% and 23%. The aforementioned savings 

are listed in below in Table 1.

According to Medina (2012), laboratory-controlled experiments of IRCC applied in a flat system 

configuration with an insulation level of R-19, produced average heat flow reductions of 32% 

(vs. the same system without the application of any coatings). 

Table 1. Experimental Results for Cooling Load and Heat Flux Reductions Produced by 

Application of RB.

Nominal Insulation Level 

(R-value)

Saving Range (%) Average Saving (%)

Cooling Load 

Reduction

R-11 11-16 14

R-19 13-27 20

R-30 Below 164 6

Ceiling Heat Flux 

Reduction

R-11 34-60 45

R-19 16-43 30

R-30 20-25 23

In this project, Fraunhofer CSE worked with a team of local companies in order to field test three 

radiation control technologies:

1. In collaboration with RIMA, Foundation Communities and City of Austin, the three following 

building enclosure technologies were installed in test houses in the Austin project in September

2011: 

a. Two low-cost IRCC, a non-thickness dependent, low-e coating. IRCCs are usually 

applied by spray to roof deck boards.

b. RB integrated with sheathing material and air cavity; in this project; two layers of 

aluminum and an enclosed air space.

2. Test instrumentation (necessary to install during the retrofit process) was installed in two 

duplex houses that were selected for the field testing (each half of the duplex represented a 

separate housing unit). Attics between separate units (two tenants per duplex) were thermally 

divided and insulated. The following test configuration was installed:

a. First duplex: IRCC coating and baseline attic

b. Second duplex: IRCC coating system and RB system.

3. Cost data from installation of the tested radiation-control technologies were collected.

These systems were installed in two duplexes in Austin. One unit, where none of the radiation 

control technologies were installed, established the baseline. The other three units underwent 

modifications to incorporate the systems described above, taking care to minimize alterations to 

existing conditions so that a direct comparison could be done post-retrofit. All units had heat flux 

transducers and thermistors installed to monitor both surface and air temperatures. 

 4 Based on Medina, 2010, when the attic insulation levels were R-30, the range of space cooling load reductions 

produced by the RBs ranged from -1% to 16%. The -1% indicates that there was one case in which the reported 

space cooling load once the RBs was installed was higher than before the RB was installed.
7

Comparisons of attic air temperatures were made to assess system performance. Although heat 

flux is an indicator of the heating or cooling loads, air temperature reflects the unique conditions 

of each unit as well as the loads. These unique conditions included varying parameters within the 

four units that could not be changed or controlled. Notable variations between the four cases 

include:

• Ventilation of conditioned space – Occupants operating windows and adjusting 

HVAC systems varied the flow rate greatly

• Air leakage through ceiling – Craftsmanship of ceiling construction varied by 

apartment (i.e. holes around pipes, ducts, etc.)

• R-value of attic – Construction and insulation type and thickness varied between 

duplexes

• Internal temperatures – Occupants adjusted the thermostat causing non-uniform 

temperatures between units.

Finally, representative computer models were constructed to further enhance understanding of 

the radiation control systems. Comparisons to the utility consumption data were made from the 

simulation results.
8

2 Field Testing

The test houses consisted of two duplex houses in Austin, which were closely located to each 

other (< 0.1 miles apart, see Figure 1 and Figure 2). The duplexes were both constructed of 2×4 

wood framing with brick or wood cladding. Figure 3 shows best estimates of the wall 

composition. Duplex 1 was built between 1987 and 1997 and Duplex 2 was a pre-1987 

construction. Each duplex has two attached, unconditioned garages. The windows were operable,

single glazed in non-thermally-broken aluminum frames. 

Figure 1. Location of site.

The attics over the garages are separated from the attics over the houses and were not installed 

with the radiant control technologies. In order to thermally separate the test units, the attics over 

the houses were divided by insulated walls for the purpose of this field study. The ceilings were 

flat in Duplex 1 and vaulted in Duplex 2. Overall, the insulation was very non-uniform in all test 

attics. In several places, the loose-fill cellulose could reach depths such that the R-values equal 

approximately R-30 but were lower at other places. Duplex 1 had loose-fill cellulose and loosefill fiberglass near the garage and Duplex 2 had a layer of batt insulation with loose cellulose on 

top. Four different test cases (see Figure 2) were established:

1. Duplex 1

A. Nothing added to the east attic (used as baseline)

B. IRCC (LO/MIT) added to the west attic

2. Duplex 2

A. RB added to the east attic

B. IRCC (HeatBloc-Ultra) added to the west attic.
9

Source: maps.google.com

Duplex 2

Source: maps.google.com

Duplex 1

Unfortunately, there was no opportunity to measure the performance of the four units prior to the 

retrofits in order to establish a baseline in each unit without radiation control technologies. There 

was an option to make the aforementioned insulation levels consistent; however, this would have 

made the utility bill calibration comparison impossible. For this reason, it was decided to 

maintain post-retrofit conditions, such as infiltration and insulation, as closely as possible to the 

pre-retrofit conditions. The only exception to this was the addition of rigid polyisocyanurate

insulation in the attic as a divider to thermally separate the two units. Considering the attic air 

temperature difference created by applying these technologies is small, the applied insulating 

divider isolates the effect of each technology from each other.

Figure 2. Location of thermistor arrays and heat flow transducers inside the tested attics (right); 

Bird view image of the duplexes in Austin, TX (left).
10

Figure 3. Estimated brick wall construction: 2 in. brick, 1 in. air gap, 1⁄2 in. OSB, 2×4 stud wall with 

batt insulation, gypsum wall board (left); Estimated clapboard siding: clapboard, battens, 1⁄2 in. 

OSB, 2×4 stud wall with batt insulation, gypsum wall board (right).

Duplex 1 consisted mainly of loose-fill cellulose insulation. It was blown between and leveled 

with 2×8 joists. The cellulose distribution was more even than in the other duplex. However, the 

areas above and close to the garage were blown with loose-fill fiberglass insulation on top of 

cellulose. The fiberglass thickness varied from less than 1 in. to over 10 in. above garage area.

Figure 4. Existing insulation conditions in Duplex 1. Note the inconsistent levels of loose-fill 

insulation.

Duplex 2 had a vaulted ceiling and had two layers of insulation in the attic. The first layer is 

fiberglass batt installed between and leveled with 2×4 joists and the second layer on top is loose 

fill cellulose insulation. However, the loose fill cellulose is not evenly distributed; at some 

locations there is close to 1 in. cellulose insulation in the middle of the attic and over 6 in. along 

the eaves.
11

Figure 5. Existing insulation conditions in Duplex 2. Note the inconsistent levels of loose-fill 

insulation.

When field testing began, there was an option to evenly distribute the insulation; however, this 

would change the thermal condition of the attics and would make it difficult to use a historical 

utility bill for comparison and calibration of the EnergyPlus models.

Poor craftsmanship was evident in the partition between the attic and spaces below. Large holes 

were noticed in the plywood where ducts entered from the HVAC closet in Duplex 2, shown in 

Figure 7. This allowed air to flow from the garage, where the utility closet was located, to the 

attic. Measured air leakage values were also quite high in the living space due to the uninsulated, 

unsealed door linking the garage and kitchen. Therefore, the garage was unintentionally semiconditioned. Ventilation in the attic over the living spaces in Duplex 1 is through soffit vents and 

ridge vents (Figure 8). The venting area is approximately 15.5 ft2 (approximately equivalent to 

1:50 ventilation rate). Duplex 2 has sparsely distributed soffit vents and gable end vents (Figure 

9). The venting area is approximately 12 ft2 and the ventilation rate is estimated to be 1:75.

A blower door test was attempted in the living space, indicating air changes per hour to be 

between 4 and 7 ACH. However, the confidence in these results was low since there was great 

difficulty in pressurizing the houses. This was due to the air leakage between the living space 

and the garage. 

Historical utility data of the houses for existing condition configurations were collected and used 

for energy performance comparisons of each individual attic, as well as calibration of the 

computer energy model discussed in Chapter 4.
12

Existing insulation in Duplex 2 attic

Existing conditions in Duplex 1 attic over the 

garage

Existing conditions in Duplex 1 attic over the 

garage

Figure 6. Existing insulation conditions in Duplex 2 (left) and Duplex 1 attic over living space 

(above right) and over garage (below right).

Figure 7. Visible gaps around ducts entering attic.
13

Figure 8. Location of the vents for attics over living spaces in Duplex 1.

Figure 9. Location of the vents for attics over living spaces in Duplex 2.

2.1 Instrumentation

Each partitioned attic has been instrumented to measure thermal energy flows and included

thermistor arrays for the test attics and heat flux transducers on the ceiling between the living 

zone and the attic zone. In addition, a weather station was installed to measure outdoor climatic 

parameters. The attic instrumentation diagram is illustrated in Figure 10 for the two different 

installed technologies.

Soffit Vent Ridge Vents

Soffit Vent Gable-end Vent
14

Unit 2A

Foi

~4 ~4 

Temperature Sensor 

Heat Flux 
15

Figure 10. Diagrams of the attic sensor distributions for a RB combined with an enclosed reflective air space (upper diagram), and IRCC 

and baseline (lower diagram).

Units 1A, 1B ~4 ~4 

Temperature Sensor 

Heat Flux 
16

The team measured temperatures using shielded thermistors. Two arrays of thermistors were 

installed at each attic: one on the underside of the south-facing roof and the other under the 

north-facing roof. To measure surface temperatures, thermistors were bonded to surfaces using 

epoxy resin (see Figure 11).

Figure 11. Thermistors installed on interior, exterior and attic to capture surface temperatures.

Heat flux transducers measured the energy flow through the attic floors. Each attic transducer 

was first installed on a 1 ft×1 ft gypsum board panel and then placed on the ceiling gypsum 

board. To keep a flat contact surface between two gypsum boards without any air gap, shallow 

grooves were cut into the 1 ft×1 ft gypsum panels to place the heat flow transducer and the wires, 

and then secured with epoxy. This method allowed good contact without damaging interior 

finishes of the building. The location of the heat flow transducers was close to the thermistor

array as shown in Figure 10. Pictures of these technologies in-situ can be found in Figure 11.

The temperature sensors used for this experiment were 10K Ohm thermistors. The thermistor 

sensors were acquired as leaded elements that were soldered to lengths of shielded twisted-pair,

two-conductor cables, and the tips were encapsulated with thermally conductive epoxy (Resinlab 

EP1200). The completed assembly was then calibrated using a Fluke 9171 Metrology Well and a 

Keithley 2700 Digital MultiMeter through seven temperature points.

The heat flux transducers are HFS-4 Heat Flux transducers (Omega Engineering). They were

calibrated between two pieces of gypsum in a Laser Comp Fox 304 heat flow meter. For each HF 

transducer, seven different temperature gradients were established across the heat flow meter. 

Once the systems reached equilibrium, the heat flow was measured by the meter, and the voltage 

Thermistors epoxied to the surface 

Thermistor underside the shingle 

Thermistors on RB surface 

Interior Thermistors wired to 

the arrays instide the attic
17

was measured with a USB-TEMP 24-bit data acquisition unit (Measurement Computing). A 

linear relationship was determined, and a heat flux coefficient was generated.

The data acquisition units employed were Measurement Computing USB-TEMP units with 24-

bit resolution. The RH was measured with RH-USB (Omega Engineering). Weather recorded by 

a HOBO U30 (Onset) included wind speed and direction, rain fall, temperature, humidity, global 

radiation.

Figure 12. DAQ Components.

2.2 Radiation Control Technology Installations

As stated earlier, two types of low-cost radiation control strategies for southern U.S. applications 

were installed in tested attics: a) RB composed of an RB combined with an enclosed reflective 

air space, and b) spray-applied IRCC. Attic configurations are shown in Figure 10, where the 

IRCCs and RB were installed in the attic over the living spaces

2.2.1 Radiant barrier with enclosed airspace

Fi-Foil’s Silver Shield is an insulating product composed of multiple layers of low-e materials 

designed to reduce radiant heat transfer. The inside layer is a metalized polymer with emissivity 

of 0.04 and the outside layer is reinforced aluminum foil kraft paper with emissivity of 0.03 

bonded with a fire-retardant adhesive. The layers expand when installed to form a reflective air 

space to provide enhanced thermal performance (see Figure 13) and protect the low-e surface 

from the performance reducing effects of dust accumulation. Since metalized and foil-based 

aluminum products have a near zero water vapor permeance, Silver Shield is perforated to allow 

water vapor transmission. 

In addition to the reflective properties of the product in attic application, the enclosed air space 

provides an R-value that increases the thermal performance of the attic insulation system. This 

product application reduces direct roof-deck level thermal loads and indirect attic floor heat 

transfer. This improves the thermal performance of HVAC ducts, and improves comfort levels in 

both winter and summer conditions.

Fi-Foil was installed in Duplex 2A by two to three labors. Equipment included scissors or utility

knife, stapler, and measuring tape. Installation began approximately 1 in. to 2 in. above the attic 

floor mass insulation. The product was stapled every 4 in. to 8 in.. A 3 in. to 6 in. opening was 

Temperature Sensor Array Heat Flow Transducer Weather Station
18

left at the ridge and sections of Silver Shield were cut out for roof vents. Each end of the product 

was enclosed by folding the ends over twice to form a 3⁄4 in. reflective air space.

Figure 13. Installation of RB with enclosed airspace from Fi-Foil Company (Silver Shield).

2.2.2 Interior Radiation Control Coating (IRCC)

IRCC changes the emissivity of the surface where it is applied. Most building products such as 

plywood, brick, and plasterboard have high emissivities (0.70-0.95). When heated, they radiate 

most of their heat to cooler surfaces. LO/MIT IIMax can lower their surface emissivity, reducing 

their ability to radiate heat. Two IRCC products were applied in this project: LO/MIT-II MAX

and HeatBloc-Ultra (see Figure 14).
19

I. LO/MIT-II MAX from Solec-Solar Energy Corporation

LO/MIT-II Max is a silver-colored, non-thickness dependent and low-e coating. When 

applied to building materials such as plywood, it lowers their surface emissivity to 0.17 

or lower. LO/MIT-IIMax is water-based and is classified by ASTM as an Interior 

Radiation Control Coating System (IRCCS).

The coating was mixed thoroughly with a squirrel-cage mixer and pumped up through the 

gable end of Duplex 1. Alternatively, buckets could also be brought into the attic for 

application. The job was completed by one applicator in roughly three hours (including 

setup and cleanup time), covering the complete undersurface of the roof decking, 

including rafters, joists and gables/dividing walls. The worker used a filtered respirator 

and a Tyvek coverall suit for applicator protection. One coat was all that was required. 

Coverage was roughly 400 ft2 of spray surface per gallon. After installation, the 

applicator can be cleaned up with water and soap. 

No maintenance or re-coat is needed for the life of the roof deck. LO/MIT-IIMAX does 

not deteriorate or lose its optical properties over time and will not delaminate. It is 

permeable to moisture and is Class A Fire Rated for flame spread and smoke.

II. HeatBloc-Ultra from STS Coatings, Inc.

HeatBloc-Ultra is an aluminum-colored, water-based, low-e coating. When applied to 

building materials such as plywood, OSB or plasterboard, HeatBloc-Ultra lowers surface 

emissivity to 0.19 or lower. It is classified by ASTM as an IRCC.

In Duplex 2, the install time required approximately three hours from set-up to 

completion and clean-up. The crew consisted of two workers—one installer in the attic 

applying the material while another outside with the equipment and materials. Workers 

used safety precautions including a full-faced respirator, spray suit, hard hat and head 

lamp.

Figure 14. Installation of IRCC from Solec-Solar Energy Corporation (LO/MIT-II MAX) (left) and 

from STS Coating, Inc. (HeatBloc-Ultra) (right).
20

3 Experimental Data Analysis

As mentioned in the earlier sections, during the cooling season 2012, thermal performance 

measurements were performed on two residential duplexes (four housing units). Since the major 

goal of this project was to evaluate the energy effects of RBs and IRCCs, these field tests

focused on thermal and energy performance of the attics. As a result, three test attics were 

modified using RBs and IRCCs and tested. The fourth attic stayed unmodified and was used as a 

baseline for comparisons. To reiterate, the primarily goal was to investigate performance of the 

attic thermal components, not an attempt of the complete whole building energy retrofit. 

Therefore, results presented herein should not be considered as whole building retrofit strategies. 

However, the findings of this project can be useful in the future for development of energy 

conservation strategies for whole buildings, including building retrofit projects.

A major goal of this part of analysis was the thermal performance comparisons of three radiation 

control technologies used in the field testing. This section shows thermal performance data 

collected during three different time periods of significantly different exterior temperatures and 

levels of insolation—April, June/July, and July/August 2012. Note that all test housing units 

were occupied during the testing by families. Each of these families had different occupation 

habits and thermal comfort preferences. In each house, thermostat temperature setups were close, 

but not identical. Also, individual schedules for using the AC were different. In addition, the 

duplexes—even though they had been similarly built in relatively close time periods—had attics 

with different structural components, thicknesses, types of attic floor insulation and levels of 

attic ventilation.

In the following sections, the recorded test data is presented and compared for all four test units. 

Significant attention was paid to the comparison of the attic air temperatures, which were

considered (due to the listed above differences in the attic construction) as a best indicator of the 

performance differences between analyzed technologies.

The following data is summarized and analyzed below:

• External and Internal Air Temperature Comparisons

• Experimental Attic Temperature Comparison

• Experimental Heat Flux Comparison

• Theoretical Heat Flux Comparison.

3.1 External and Internal Air Temperature Comparisons

As mentioned earlier, thermal performance comparisons were conducted for three major time 

periods: 1) April - when exterior air temperature was below 30°C for most of the day, reaching 

10°C during the nights; 2) June/July – with the highest daily temperature peaks, and 3) 

July/August, with typical summer temperatures and insolation levels. The overnight temperatures 

during the mid-summer months were relatively close with minimal oscillating between 12°C and 

15°C.

 
21

Figure 15. Measured exterior air temperature on one of the test houses.

As shown in Figure 15, the weather data displays the external temperature varying between 10°C 

during the night, and approximately 52°C during the day. It was also observed that during the 

mid-summer months, minimum night temperatures stayed above 20°C.

As mentioned in previous sections, the orientations of test houses were very close and all test 

attics had similar roof finish materials using plywood decks and asphalt shingles. These facts 

helped in thermal performance comparisons for the top parts of the roof assemblies. Figures 16-

21 show basic comparisons of the top of the roof temperatures in all four test units. These 

temperatures represented the top-level boundary conditions for the roof/attic structures. They 

were critical for calculation of the thermal loads generated by the roof and estimation of the 

overall performance of the attic thermal system (insulation, attic ventilation rates, and radiation 

control technologies).

0

10

20

30

40

50

60

4/12/2012 0:024/13/2012 3:274/14/2012 6:52

4/15/2012 10:174/16/2012 13:424/17/2012 17:074/18/2012 20:326/14/2012 23:57

6/16/2012 3:226/17/2012 6:47

6/18/2012 10:126/19/2012 13:376/20/2012 17:026/21/2012 20:276/22/2012 23:52

6/24/2012 3:176/25/2012 6:42

6/26/2012 10:076/27/2012 13:326/28/2012 16:576/29/2012 20:226/30/2012 23:47

7/2/2012 3:127/3/2012 6:37

7/4/2012 10:027/5/2012 13:277/6/2012 16:52

7/27/2012 20:177/28/2012 23:42

7/30/2012 3:077/31/2012 6:32

8/1/2012 9:57

8/2/2012 13:22

External Temperature (°C)

Temperature (C)
22

Figure 16. Average daily roof surface temperatures recorded during the April measure period.

Figure 16 displays the averages of the roof surface temperatures recorded in April 2012. 

Although they varied greatly by day, up to 20°C for the period, the temperature trends were not 

large or consistent. At times, the roof of Duplex 2 was on average 1°C-2°C warmer than that of 

Duplex 1. 
23

Figure 17. Average daily roof surface temperatures recorded during the June/July measure period.

For most of the June month, the average temperatures recorded on the roof surfaces were

between 15°C and 20°C higher than temperatures recorded during the April period. As seen in 

Figure 17, in June the roof temperatures of Duplex 2 were typically 1°C to 2°C warmer than 

Duplex 1. This small difference was most likely caused by notable differences in attic ventilation 

systems used in both duplexes. The other reason might have been the different structural 

components in both duplexes, which interfered in a different way with radiation heat exchange 

between the roof deck surface and the top of the attic floor insulation. In addition, Unit 2A 

typically had the highest roof temperature. This roof used an aluminum foil RB with two 

enclosed air gaps just under the roof deck surface (one enclosed space between two RB layers, 

and one enclosed layer between RB and underside of the roof deck). For this reason, the 

temperature balance in this area was different, compared to other test attics. The greater roof 

surface temperature might have been a consequence of this fact.
24

Figure 18. Average daily roof surface temperatures recorded during the July/August measure 

period.

The temperatures of Duplex 2 were consistently higher than Duplex 1, as seen in Figure 18. This 

was the most pronounced during the hotter months of June and July. In general, however, the 

roof surface temperatures were very similar with differences seldom reaching 3°C. 

In summary, data presented in Figures 16, 17, and 18 indicate notable differences in thermal 

performance of the top of the roof in all four test units. These differences were caused by 

dissimilar ventilation rates followed by varying structural and insulation components in 

Duplexes 1 and 2. However, yielded temperature differences between these individual units did 

not exceed 2°C for most of the time during the summer 2012. The highest temperature of Duplex 

2A’s roof was caused by the aluminum foil RB containing two enclosed air gaps (one enclosed 

space between two RB layers, and one enclosed layer between RB and underside of the roof 

deck). This thermal system was installed just under the roof deck surface reducing the amount of 

heat transmitted from the roof surface down to the attic space.
25

Figure 19. Maximum roof surface temperatures recorded during the April measure period.

Roof-generated daily peak-hour thermal loads were a function of the maximum roof 

temperatures. The higher the roof surface temperature, the higher thermal load was transmitted to 

the attic space. As seen in Figure 19, the maximum roof surface temperatures for all four test 

units in April were very similar and varied greatly between 40°C and 70°C. Similarly, as in 

earlier figures, the temperatures of Duplex 2 were typically higher than in Duplex 1.
26

Figure 20. Maximum roof surface temperatures recorded during the June/July measure period.

Again, when the weather becomes warmer in June, the roof temperatures of Duplex 2 were

greater than Duplex 1. The maximum roof temperatures in June for Duplex 2 were up to 5°C 

hotter than Duplex 1. This was most likely due to general differences in construction of both 

types of attics and thermal behavior of the RB combined with the enclosed air gaps, installed 

under the roof deck in the test house 2A.
27

Figure 21. Maximum roof surface temperatures recorded during the July/August measure period.

It is clear from Figure 21 that the differences between the houses became more pronounced when 

looking at the maximum roof surface temperatures. The maximum roof surface temperatures in 

July varied by 3°C-4°C across Units 1B, 2A, and 2B. This was similar to previous charts where 

the foil technology in 2A had the hottest roof temperature and the IRCC in 2B had slightly 

higher roof temperature than in Unit 1B. 
28

Figure 22. Average interior air temperatures recorded during the April measure period.

As mentioned earlier, all test units were occupied during the testing. Each of these families had 

different occupation habits and thermal comfort preferences. In each of these houses, thermostat 

setups were close but not identical. As shown in Figure 22, the beginning of the cooling season 

for residents of Unit 2A was most likely on April 15. Also, individual schedules for using AC

were different for each test unit. In April, the internal air temperatures were close to 25°C, as 

seen in Figure 22.
29

Figure 23. Average interior air temperatures recorded during the June/July measure period.

Figure 23 displays that the internal temperatures were close to 25°C in June, as well. Most likely,

residents of Units 1A and 2A preferred interior temperatures slightly above 25°C, while residents 

from Units 1B and 2B preferred temperatures closer to 24°C.

3.2 Experimental Attic Air Temperature Comparisons

Typically in residential attic applications, RBs and IRCCs work by reducing the amount of 

thermal radiation that is transferred across the air space between the roof deck and the top of the 

attic floor insulation. Since the amount of thermal radiation increases as the temperature of the 

emitting surface increases, it is critical to keep it as low as possible. This surface can be directly 

roof deck, foil-laminated roof deck boards, roof deck boards coated with IRCC, or RB material 

facing the interior of the attic. An application of multifoil RB in the case of Unit 2A showed that 

sometimes it was possible to apply radiation control technology, increase the roof deck 

temperature and at the same time reduce the air temperature in the attic. As depicted in Figures 

17–21, this technology generated a slightly higher roof surface temperature compared to other 

test attics. However, when attic air temperatures were compared, the recorded attic temperature 

for Unit 2A was significantly lower comparing to other attics; see Figures 25, 26, 27, 28, and 29

below.
30

In this project, due to the structural differences between the test attics and due to the fact that the

attic floor insulations were not uniform in all the units, measurements of the attic air

temperatures in the center-of-the-attic location were used as one of indirect indicators of the attic 

system thermal performance. The second potential performance indicator considered in this 

project was heat flux measured on the ceiling level. However, as shown in Figures 22 and 23, the 

internal air temperatures were not identical in all test units. That is why direct comparisons of 

measured heat fluxes cannot be used as a full indicator of the attic system thermal performance.

Figure 24. Example of attic air temperatures recorded in four test attics (center location) during 

the April measure period.

The charts in Figure 24 display the general appearance of attic temperature data collected for 

Duplexes 1 and 2. The temperatures varied between 13°C during the night and 47°C during the 

daytime. About a one-hour time delay was observed between maximum temperature peaks 

recorded in 2A’s attic (with multifoil system) and other attics.
31

Figure 25. Average daily attic air temperatures recorded in four test attics (center location) during 

the April measure period.

The differences in attic temperature in April were small and not consistent, as seen in Figure 25.

Attic air temperature oscillated between about 33°C and 22°C during the April measure period. 

During the warmest days, attic 2A, containing multifoil RB, was the coolest attic among all 

tested units.
32

Figure 26. Average daily attic air temperatures recorded in four test attics (center location) during 

the June/July measure period.

Figure 26 shows that the attic of Duplex 1 was typically hotter than Duplex 2 in June 2012. This 

is consistent with the observation that the roof of Duplex 1 was cooler than Duplex 2. It is good 

to remember that there were some differences between both duplexes, such as the roof deck 

construction—rafters versus trusses—and the levels of ventilation in the attics, determined by 

measuring the area of the soffit vents. An average baseline attic temperature for the considered 

time period was 35.7°C, while for the coolest attic 2A was only 33.4°C. This was a 2.3°C 

difference. 
33

Figure 27. Average daily attic air temperatures recorded in two IRCC attics (center location) during 

the July/August measure period.

For the hottest month of the year, Figure 27 shows that the average attic temperature was very 

similar between the two IRCC technologies. The temperature in 2B was slightly lower than 1B, 

by approximately 1°C. This might be caused by construction differences between Duplexes 1 and 

2.
34

Figure 28. Maximum daily attic air temperatures recorded in four test attics (center location) 

during the April measure period.

The maximum attic air temperatures were similar in April, generally varying by a degree or less, 

as seen in Figure 28. During the last, warmest day of the period the temperature difference 

between the hottest (1A) and coolest attic (2A) was close to 8°C. Average attic air temepratures 

were within 3.6°C.
35

Figure 29. Maximum daily attic air temperatures recorded in four test attics (center location) 

during the June/July measure period.

Figure 29 depicts the maximum daily attic air temperatures for June/July 2012. These 

temperatures reflect differences in attic-generated peak-hour cooling loads during the day. It is 

clear that different types of reflective insulation work effectively in southern U.S. climates. In 

June, the base case attic, 1A, had consistently higher maximum daily attic air temperatures. Units 

1B and 2B were quite similar, but were generally a lower maximum temperature than the base 

case (over 3°C on avarage). The fact that 1B and 2B appeared similar was a different pattern than 

previously observed. However, examining the hotter time period in July may confirm that 2B 

generally had lower attic temperatures than 1B. Finally, 2A,the house with the foil technology 

installed, had the lowest maximum temperatures across this period by approximately 7°C, while 

compared to the baseline attic, 1A.
36

Figure 30. Maximum daily attic air temperatures recorded in two IRCC attics (center location) 

during the July/August measure period.

As shown in Figure 30, the attic with the IRCC technology installed in the Duplex 2 had lower 

maximum temperatures across this time period, while comparing to the similar attic in Duplex 1. 

Even for hottest summer days, 2B and 1B had very similar maximum attic temperatures with 

differences not exceeding 1°C.
37

Figure 31. Differences in daily attic air temperatures recorded between three test attics using 

radiation control technologies and a baseline attic, during the April measure period.

As mentioned earlier, field measurements of the attic air temperatures were used in this project, 

as one of the indirect indicators of the attic system thermal performance. It can be said that the 

attic air temperature represented thermal condition equilibrium incorporating radiation, 

ventilation, and convection effects together. This temperature also reflected structural differences 

between all test attics. 

Figure 31 displays the difference between the average attic air temperatures for the houses with 

technology—Units 1B, 2A and 2B—and the base case attic. The most extreme values indicate 

the greatest differences from the base case. The only consistent observation in this chart is that 

the attic in Unit 2A had the most different attic temperature from the base case.
38

Figure 32. Differences in daily attic air temperatures recorded between three test attics using 

radiation control technologies and a baseline attic, during the June/July measure period.

The chart in Figure 32 indicates that the foil technology was thermally more effective than both 

IRCC technologies. An average temperature difference between this attic and the base case was

about 3.4°C, while for the IRCC technologies, it was about 2°C. In addition, the IRCC in 2B was

usually more different from the base case than the 1B case.

It is important to note that 3.4°C reduction of the average attic air temperature caused by the 

multifoil RB can be an equivalent to more than 34% reduction of the attic-generated cooling 

loads—assuming approximate steady-state heat transfer, average attic temperature of 35°C (as 

shown in Figure 26) and internal air temperature of 25°C. It has been reported that for U.S. 

residential houses, roofs and attics generate an average of 12% cooling energy contributions 

(Huang et al., 1996). In that light, potential whole building cooling energy savings may reach 

about 4%, depending on other building parameters and HVAC system efficiency.

Similarly, a 2.4°C reduction of the average attic air temperature due to the IRCC technology can 

be an equivalent to more than 24% reduction of the attic-generated cooling loads. Potential 

whole building cooling energy savings for this technology may be close to 3%.
39

Figure 33. Differences in maximum daily attic air temperatures recorded between three test attics 

using radiation control technologies and a baseline attic, during the April measure period.

Figure 33 displays the difference from the base case for the maximum attic temperatures. Unit

2A, being the most extreme, had temperatures that varied the most from the base case. The 

maximum air temperatures for the attic using the multifoil system were on average about 7°C 

lower from the base case attic.

Surprisingly, the IRCC attic, 1B, showed more difference from the base case than 2B. This was

different from previous observations, where 2B generally had lower temperatures than 1B and 

the base case had very high attic temperatures. 
40

Figure 34. Differences in maximum daily attic air temperatures recorded between three test attics 

using radiation control technologies and a baseline attic, during the June/July measure period.

Figure 34 shows clear superiority of the multifoil radiation control technology used in the attic 

2A. For this attic, maximum air temperatures were, on average, about 8.5°C lower than the base 

case attic. It can be also observed that IRCC systems reduced maximum attic air temperature by 

over 6°C. 

Following earlier analyses performed for the average attic temperature, a 8.5°C reduction of the 

maximum attic air temperature caused by the multifoil RB can be an equivalent to over 30% 

reduction of the attic-generated peak-hour cooling loads, considering maximum attic temperature 

of 53°C (as in Figure 29) and internal air temperature of 25°C. 

Again, attic air temperature recorded in Unit 2A was the most different from the base case. 

Given the hotter temperatures in June, Unit 2B was typically the next most different attic 

temperature, as seen in Figure 34.
41

Figure 35. Daily temperatures on the top surface of the attic insulation recorded in four test attics 

using radiation control technologies and a conventional base case, during the April measure 

period.

The insulation surface temperatures were quite similar, as seen in Figure 35. Generally, the 

temperatures in Unit 2A were less extreme than for the other units. Maximum day temperatures 

were about 4°C lower than the conventional base case attic. In addition, 2A’s attic stayed warmer 

during the night. The top of the insulation temperature was about 1°C warmer from all other 

attics. This was due to the additional thermal insulation of the two encased air cavities generated 

by the multifoils RB system; the first one between roof deck and aluminum foil and the second 

one between two foils. 

In ideal conditions (when measurement perimeters were highly controlled and the insulation 

layer is uniform), temperature measurements on the top of the attic insulation could be a very 

good direct indicator of the technology thermal performance. However, in this experiment, due 

to the differences in construction, thicknesses of insulation and types of insulation in the 

individual attics, direct thermal performance comparisons were not possible using top insulation 

surface temperatures. 
42

Figure 36. Daily temperatures on the top surface of the attic insulation recorded in three test attics 

using radiation control technologies and a conventional base case, during the June/July measure 

period.

In the hot month of June, the insulation surface temperatures were still quite similar. Again, Unit

2A appears to have less extreme temperatures, as shown in Figure 36. Maximum day 

temperatures on top of the attic insulation were about 4°C to 5°C lower comparing to the 

conventional base case attic. As mentioned earlier, these temperatures reflected the atticgenerated peak hour cooling loads. Like April, during the night, the top of the insulation 

temperature stayed about 1°C warmer comparing to all other test attics. This fact made 

temperatures very close on average in all test attics, which may not have necessary reflected the

relationships between attic generated peak-hour cooling loads (in contrast to daytime when 

insulation surface temperature is a good peak-hour thermal performance indicator).
43

Figure 37. Daily temperatures on the top surface of the attic insulation recorded in two test attics 

using radiation control technologies and a conventional base case, during the July/August 

measure period.

In Figure 37, in the very hot month of July, Unit 2A appeared somewhat less extreme than 2B 

and 1B, which showed the greatest changes in temperatures. Still, maximum day temperatures on 

top of the attic insulation were about 4°C to 5°C lower comparing to other attics. During the 

night, top of the insulation temperature stayed about 1°C warmer in attic 2A, compared to all 

other test attics.
44

3.3 Experimental Heat Flux Comparison

Figure 38. Heat fluxes recorded in four test attics using radiation control technologies and a 

conventional base case, during the April measure period. Positive heat flow direction is from 

conditioned space to the attic.

Because of different attic configurations and internal air temperatures, the heat fluxes measured 

on the ceiling level were not good indicators of performance compared to attic temperatures.

There were four factors that can affect this measurement: ventilation rates, R-values, internal 

temperatures, and air leakage through the attic ceiling. Figure 38 shows that the heat flux in 1A 

was typically larger than the other houses.
45

Figure 39. Heat fluxes recorded in test attics using radiation control technologies and a 

conventional base case, during the June/July measure period. Positive heat flow direction is from 

conditioned space to the attic.

In June, the measured heat flux in the house with IRCC technology was significantly higher than 

in the house with the foil technology, as seen in Figure 39. The largest differences are between 

units 2A and 2B. Heat fluxes measured in unit 2A were between 40% and 50% lower than heat 

fluxes measured for unit 1B.
46

Figure 40. Heat fluxes recorded in test attics using radiation control technologies and a 

conventional base case, during the July/August measure period. Positive heat flow direction is 

from conditioned space to the attic.

Again, in July and August, the attic with the multifoil technology generated lower heat flux 

compared to the IRCC system unit 1B. This was a relatively large effect. Interestingly, heat 

fluxes measured on ceilings in the same Duplex 2 were within less than 20% difference only.
47

4 Energy Modeling

4.1 Model Description

The two duplexes in Austin were modeled using EnergyPlus 7.1 and SketchUp 8.0, with the 

Legacy OpenStudio Plug-in version 1.0.8 to generate the EnergyPlus input data files. The houses 

were each modeled as three zones representing the living space, attic, and garage (a total of six

zones in each duplex). Other parameters are listed in Table 2.

Outside boundary conditions came from a weather file for Austin’s climate. Wall and ceiling 

constructions were modeled in THERM to determine the effective thermal conductivity of the 

assembly layer containing the wood studs and insulation. As stated earlier, Duplex 1 was built 

between 1987–1997 and Duplex 2 was built prior to 1987. Compared to parameters listed in 

ASHRAE HOF Chapter 15, operable single-glazed windows with non-thermally broken 

aluminum frames, such as those installed in the duplexes, were confirmed. Solar heat gain 

coefficients were set to 0.79 in the model and U-factors were 0.92 Btu/h·ft2·°F (5.2 W/m2·K).

Window construction was also kept consistent throughout the models.

Roofs were modeled as shingles and plywood with addition of the appropriate paint or foil layer 

where applicable. A no-mass material was specified in EnergyPlus to represent the IRCC and RB 

technologies. The absorptance of the material was lowered to decrease the amount of radiant 

transfer to other surfaces in the attic zone. Because of the non-uniform levels of insulation on the 

attic floor, an average value was calculated for use in the model. The team determined that both 

duplexes had approximate R-20, despite having different compositions—7.5 in. of loose 

cellulose in Duplex 1 while 3.5 in. of batt insulation plus an average of 3.5 in. of loose cellulose 

in Duplex 2, both with framing factors of 25%. Attic ventilation rates were estimated based on 

measurements of the area of attic vents in each of the test houses (Atherton, 2011).

Cooling setpoints were kept for modeling purposes at 76.1°F (24°C) for all four units. The 

heating setpoint was 68°F (20°C). Considering stratification of the temperatures, these 

temperatures were very close to that which was measured in 2012 in the test houses. However, it 

is important to notice that due to a change of some tenants followed by a possible change of 

space conditioning preferences, measured temperatures in two units were about 1°C higher from 

the other two. Two HVAC systems were added to each building, one per conditioned zone in 

each duplex. The Unitary Template in EnergyPlus was used to model the forced air system with 

a 2.5 rated coefficient of performance (COP) single-speed direct expansion cooling coil and 

natural gas heating coil with an efficiency of 70%. Considering the losses due to duct leakage 

and the condenser unit, the overall COP of the system was reduced in the model from the 

manufacturer’s COP. The natural gas water heater had a thermal efficiency of 80%. The models 

were calibrated against gas consumption data obtained from utility bills during winter. The 

maximum hot water flow was obtained through calibration of gas consumption with the amount 

reported by Texas Gas Service calculator for a typical residential single family house in Austin.
48

Figure 41. Duplex 1 model (above); Duplex 2 model (below).
49

Table 2. Model Parameters.

Model Parameters Duplex 1 Duplex 2

Unit A

(Baseline)

Unit B

(IRCC)

Unit A

(RB)

Unit B

(IRCC)

Zones 3; Attic, Living, 

Garage

3; Attic, Living, 

Garage

3; Attic, Living, 

Garage 

3; Attic, Living, 

Garage 

Infiltration 

(ACH)

Attic 10 10 10 10

Living 1.2 1.2 1.2 1.2

Garage 1.2 1.2 1.2 1.2

Construction Wall assembly Siding, Plywood,

2x4 wood studs 

with semi-rigid 

insulation, 

Gypsum

Siding, Plywood

2x4 wood studs 

with semi-rigid 

insulation, 

Gypsum

Siding, Plywood

2x4 wood studs 

with semi-rigid 

insulation, 

Gypsum

Siding, Plywood

2x4 wood studs 

with semi-rigid 

insulation, 

Gypsum

Wall R-Value

(whole assembly)

 10 10 10 10

Roof assembly Shingle, Plywood Shingle, 

Plywood, IRCC ( 

LO/MIT;ε=0.17)

Shingle, 

Plywood

RB (Fi-Foil; ε

=0.03)

Shingle, Plywood, 

IRCC ( HeatBlocUltra; ε= 0.19)

Ceiling R-value

(whole assembly)

20.2 20.2 20.2 20.2

Attic Framing 

Factor

0.25 0.25 0.25 0.25

Window type Single glazing Single glazing Single glazing Single glazing

Glazing 

Ratio

North 14.01% 14.01% 2.80% 2.80%

South 31.30% 31.30% 9.51% 9.51%

East/

West

1.90% 1.90% 12.32% 12.32%

Window U-Factor 

(Btu/h·ft2·°F)

0.92 0.92 0.92 0.92

Window SHGC 0.79 0.79 0.79 0.79

HVAC 

Setpoints (°F)

Cool 75.2 75.2 75.2 75.2

Heat 68 68 68 68

People 2.5 2.5 2.5 2.5

Lighting (W) 1100 1100 1100 1100

Electrical Equipment (W/ft2) 0.46 0.46 0.46 0.46

Water Heater Thermal Eff. 0.8 0.8 0.8 0.8
50

4.2 Calibration of Whole Building Energy Model

In order to predict energy consumption of the duplexes with reliable accuracy, the EnergyPlus 

models were calibrated against historical utility bills obtained for tested houses. For this purpose, 

the computer-generated energy consumptions were compared with historical energy bills for 

both heating and cooling seasons. 

It is important to mention that, due to complexity of the test attics and the fact that buildings 

were occupied during the testing, it was impossible to validate the thermal simulation algorithm 

used for attics by EnergyPlus. Therefore, EnergyPlus simulation results (cooling energy savings) 

presented in this study need to be confirmed in the future either by more accurate computer 

models (like ATTICSIM–ASTM C1340) or by calorimetric field measurements with use of the 

test huts. Additionally, due to limited amount of available historical bill data, the comparison 

was done only for duplex 1B. 

During the heating season, the main sources of energy consumption were a furnace for space 

heating and a water heater for domestic hot water. Based on Texas Gas Service’s home energy 

calculator, for a typical single family house with similar characteristics to the test houses, close 

to 50% of total gas consumption was space heating, approximately 35% water heating and 15% 

was cooking, as shown in Figure 42. Therefore, to capture these main sources of gas 

consumption, a water heater, furnace and gas equipment were considered in the model. Figure 43

compares the simulated gas consumption with historical energy bill and Texas Gas Service for 

duplex 1B. There was a relatively good agreement between EnergyPlus-generated gas 

consumption and historical gas service data. Note that EnergyPlus used the actual weather file

which is the observed weather data for the duration of the modeling. Figure 43(a) and 43(b)

compare gas consumption of duplex 1B with historical gas bill before and after applying the 

radiation technology, respectively. The data confirms proper selection of the building enclosure 

and HVAC system parameters for whole building energy consumption simulations.

Figure 42. Breakdown of household gas consumption.
51

a) Gas consumption of duplex 1B before installing radiation control technology. The EnergyPlus 

simulation is based on actual weather file data from 2009.

b) Gas consumption of duplex 1B before installing radiation control technology. The EnergyPlus 

simulation is based on the observed weather data file from 2011.

Figure 43. Comparison of monthly historical gas bill, simulated consumption, and the gas 

consumption by Texas Gas Service calculator. The calibration is limited to the months with 

available historical utility bill.

Using the actual weather data file enabled comparisons to energy consumption results generated 

with a use of the Texas Gas Service’s home energy calculator5

. During the cooling season, the 

main sources of electricity consumption were AC unit for space cooling, lighting and appliances. 

Again, referring to Texas Gas Service’s home energy calculator in Figure 44, for a typical single 

family house, close to 80% of total electricity consumption was for space cooling, 8.5% for 

lighting and close to 11.5% for appliances and others. 

 5 http://www.texasgasservice.com/SaveEnergyAndMoney/HomeEnergyCalculator.aspx
52

Figure 44..Breakdown of household electrical consumption.

a) Electricity consumption of Duplex 1B before installing radiation control technology. The 

EnergyPlus simulation is based on actual weather data file from 2011. High electricity 

consumption during heating season is due to unexpected usage of the electric heater by the 

tenants. A cooling system with COP=2.5 was considered throughout this report; however, as a 

parametric study, cooling system with COP=2 was modeled and compared in this graph.
53

b) Electricity consumption of Duplex 1B after installing the radiation control technology. The 

EnergyPlus simulation is based on actual weather data file from 2012. High electricity 

consumption during heating season is due to unexpected usage of electric heater by the 

tenants. A cooling system with COP=2.5 was considered throughout this report; however, as a 

parametric study, cooling system with COP=2 was modeled and compared in this graph.

Figure 45. Comparison of monthly historical electricity bill, simulated consumption, and the 

electricity consumption by Texas Gas Service calculator. The calibration is limited to the months 

with available historical utility bill.

As Figure 45 shows, EnergyPlus predicted well the electricity consumption during the cooling 

season compared with historical electricity bill and Texas Gas Service’s calculator. However, 

during the heating season, there were discrepancies due to the fact that the test houses were using 

auxiliary electricity for heating. Overall, considering the fact that the historical electricity bill 

was not prorated and both the AC unit set point and consumer behavior were approximated, the 

prediction of energy consumption particularly during the cooling season seemed in good 

agreement with historical bills and Texas Gas Service’s calculator.

4.3 Prediction of the Cooling Energy Consumption

As described, the models’ calibration was based on comparison between electricity and gas 

consumption data with simulated energy use in the models with historical data from the Texas 

Gas Service calculator. The calibrated models were simulated with a TMY3 weather file for 

Austin Mueller Municipal Airport to predict the electricity consumed by AC units during cooling 

season. 

4.4 Modeling Results

In the summer, a higher infiltration rate of the attic reduced the attic temperature by exchanging 

the outdoor air with the attic air that was heated by the roof. The lower attic temperature reduced

the heat flux through the ceiling of the living space. The wall construction and infiltration rate of 

the living space also affected the cooling load placed on the HVAC system. Finetuning the RB

was required to model the emissivity within the attic space accurately and the thermal 

conductivity through the layer, and in the case of the Fi-foil, the air gap between the roof and the 

RB.
54

The results from EnergyPlus using a typical meteorological year (TMY3) indicate that the 

energy consumption is well below the range approximated based on the measurements 

performed during the experiment. In addition, EnergyPlus-generated cooling energy savings are 

at least five times lower than the earlier findings from different U.S. research studies summarized 

(Medina, 2012).

Table 3. Predicted Energy cooling Consumption and Associated Savings from Radiation 

Control Technologies.

Cooling Energy 

Consumption / Test Unit

Without Radiation 

Control Technology

With Radiation Control 

Technology

Annual Cooling Energy 

Savings

1A (Baseline) 4333 kWh N/A N/A

1B (IRCC) 4326 kWh 4308 kWh 0.43%

2A (RB) 4703 kWh 4703 kWh 1.27%

2B (IRCC) 4922 kWh 4922 kWh 0.83%

The modeling results in Table 3 show that cooling energy is saved with the use of radiation 

control technologies. The table lists and compares the modeled annual cooling energy 

consumption of each house before and after implementing the radiation control technology. The 

“Annual Cooling Energy Savings” for each house in Table 3 is calculated by comparing cooling 

energy consumption in “Without Radiation Control Technology” and “With Radiation Control 

Technology” columns. The Fi-Foil shows the highest savings from its lower emissivity and the 

air gap created between the roof and the space between the two layers of the foil. Comparing the 

two duplexes with IRCC installed, the results show that the attic geometry and the amount of 

roof coated with the low-e material make a difference in the performance.

Parametric studies of the convection coefficients, air exchange rate, set point temperature and 

changes of the heat transfer rate through exterior walls and windows were performed in the 

process of calibrating the model. Convection coefficients were specified from the ASHRAE 

Handbook of Fundamentals. The values for horizontal down flow were used and a slight 

improvement was expected from the values EnergyPlus calculated. This was expected since all 

roof surfaces were at angles above horizontal. The air exchange rate made little difference in the 

output of the model. This is likely because the exchange of air has a greater effect on the zone air 

temperature than the surfaces temperatures, which govern radiant heat flow. Heat flow through 

the exterior walls and windows had the greatest effect on the performance of the RB since heat 

flow through the ceiling into the conditioned zone was proportionally less than the other surfaces 

even though the heat flux through the ceiling remained the same.

It should be noted that the above savings have been estimated based on EnergyPlus modeling 

parameters close to existing test house conditions. Depending on HVAC configuration, air 

leakage rate, and building envelope parameters, the savings can increase close to twice the values 

reported in Table 3. However, they will still be significantly lower than the results of earlier 

experimental studies (Medina 2012). This is one of the most surprising findings from this study. 

Recorded temperature and energy consumption data showed that one test unit was notably 

different during the winter 2011, which was evidence of an extensive use of an electric heater. 

The use of a supplemental heater was unexpected, and an electric heater was not instrumented. 

An additional challenge in modeling was caused by the fact that the tenant changed in one of the 
55

test units just before the start of measurements. Also, the inability to control setpoint differences 

between the units made direct comparisons difficult (since test units were occupied by tenants 

with various space conditioning preferences).

One of the conclusions from this study is the fact that it is extremely difficult to conduct a 

detailed performance analysis of a single building enclosure system like RB using field test data 

from occupied vintage housing units. It is still unclear how well energy consumption predictions 

of the building systems containing RBs can be simulated using simplified Energy Plus roof/attic 

algorithm. The team recommends that in the future, a calorimetric type of a field experiment 

(with precisely measured attic air leakage rates, level of attic insulation, and with simple attic 

structural components) be performed in order to further validate EnergyPlus predictions in cases

of RB applications. This experiment will most likely require test huts or similar small and wellinstrumented test structures. 
56

5 Cost Effectiveness Analysis

For the purpose of cost analysis, a range of cooling load savings achievable by applying RB and 

IRCC was assumed. The upper limit of this saving range was obtained from the available review 

of earlier research studies provided (Medina, 2012). Taking R-19 (hr·ft2·°F/Btu) attic insulation 

as a baseline, according to published literatures (Medina, 2012, Stovall et al., 2010), the team 

found that approximately 20% and 14% cooling load saving can be achieved by applying RB and 

IRCC technologies underside of attic roof, respectively. Similarly 4% and 2.4%6 heating load 

saving is possible for RB and IRCC technologies. At some point, these numbers can be 

questioned, considering that in most of the U.S. residential houses, attic-generated cooling loads 

represent approximately 12% of the whole building loads (Huang et al., 1996). That is why the 

lower limit of savings representing 20% of the upper limit was assumed in this study as well. 

This 20% lower limit was chosen since it yields a 4% cooling load reduction for RB, a similar 

level as the cooling energy savings calculated from measured data analysis (see Chapter 3).

In this analysis, the developed EnergyPlus models were used to simulate the energy performance 

of a single-family residence as a baseline house in representative U.S. climates. The same single 

story house was used for development of Model Energy Code (Council of American Building 

Officials, 1995) and ASHRAE 90.2 (ASHRARE 2007).

Figure 46. Modeled utility consumption of baseline house in different U.S. South climates and 

payback period of radiation control strategies.

The simulations were performed for four U.S. climates using weather files. The energy 

performance of this baseline house is presented as utility consumption rate (electricity and gas).

 6 Based on Medina (2010), IRCC heating load saving estimated to be 61% of RB heating load saving
57

To evaluate the payback period, the heating and cooling loads were modeled for the baseline 

house with R-19 attic using EnergyPlus. Having these modeled loads, the radiation control 

strategies load savings suggested by literature (upper limit for the energy savings of 20%, 14%

summer savings, and 4% and 2.4% winter savings for RB and IRCC, respectively, according to 

Medina 2012; and lower limit of 20% of the above savings) were calculated, as well as the 

associated consumptions rate and energy cost savings. It is important to mention that the 

calculated 20% cooling energy savings level (of the data presented in literature—see Medina 

2012) was close to energy savings approximated based on the results of this field study. The 

payback periods were estimated by comparing the cost savings and the installed cost7 of RB and 

IRCC in the attic.

It should be noted that both RB and IRCC contractors provided the same quoting prices for their 

installed products ($0.75 per square foot). Following direct observations performed during the 

installation process, the above cost numbers seem unreasonable due to the fact that not only the 

material usage but also the labor costs were notably different for each of the considered 

technologies. As an example of a similar installation process, the labor cost of painting work and 

air barrier installation work are significantly different according to RS MEANS 2011. Therefore, 

although the payback period has been shown in Figure 46, it should be highlighted that the 

calculations are based on the same quoting price value received from RB and IRCC contractors.

As shown in Figure 46, the climate with higher electricity consumption or higher cooling loads

has shorter payback period since the radiation control strategies provided more savings in 

cooling rather heating season.

Table 4. Residential Utility Price Based on Considered Climates.

Climate Elec. Price8 [$/kW.h] Gas Price9 [$/THERM]

Phoenix 0.110 1.31

Houston 0.107 0.79

Atlanta 0.102 1.24

Miami 0.122 1.49

 7 The installed cost based on contractors quotes.

8 Edison Electric Institute Typical Bills and Average Rates Report, January 2011 

9 Department of Energy for monthly “bundled” supply and delivery costs for January 2011
58

6 Conclusions

The major goal of this project was to evaluate the energy effects of RBs and IRCCs in field 

conditions. Major focus was paid on thermal and energy performance of the attics. During the 

cooling season 2012, thermal performance measurements were performed on four housing units 

in two residential duplexes. Three test attics were modified using RBs and IRCCs and tested, 

while the fourth attic stayed unmodified and was used as a base case for comparisons.

Two main goals of this report were thermal performance analysis and cost comparisons of three 

radiation-control technologies used in the field testing. Thermal performance data was collected 

during three time periods of April, June/July, and July/August 2012. Field experiments took 

place in Austin, Texas. All test houses were occupied during the testing by residents. The 

original plan was to keep internal load schedules in the test units as close as possible; however, 

each of these tenants had different occupation habits and thermal comfort preferences. Also, 

individual schedules for operating the AC were different. In addition, the test houses had attics 

with varying structural components, thicknesses and types of attic floor insulation, and levels of 

attic ventilation. All of the above factors made direct comparison of the whole building energy 

consumption impossible.

Measured test data confirmed earlier results from other research organizations. An average 3.4°C 

reduction of the average attic air temperature caused by the multifoil RB was recorded during

mid-summer 2012, and can be equivalent to over 34% reduction of the attic-generated cooling 

loads—assuming approximate steady-state heat transfer, average attic temperature of 35°C (as in 

Fig. 12) and internal air tmperature of 25°C. This is consistent with a range of the cooling load

reductions reported by Medina (2012). It has been also reported that for U.S. residential houses, 

roofs and attics generate an average 12% cooling energy contributions (Huang, et al., 1996). In 

that light, potential whole building cooling energy savings may reach about 4%, depending on 

other building parameters and HVAC system efficiency. 

Similarly, a 2.4°C reduction of the average attic air temparature caused by the IRCC technology 

can be an equivalent to over 24% reduction of the attic-generated cooling loads, and potential 

whole building cooling energy savings for this technology may be close to 3%. Based on the 

recorded data, energy performance of two IRCC systems seems to be very similar considering 

the small differences in construction of both test attics in Duplexes 1 and 2.

An EnergyPlus computer model calibrated against both gas and electricity historical bill data for 

the periods of pre-retrofit and post-retroft was used for prediction of potential cooling energy 

savings. The results from EnergyPlus were well below the range of cooling energy savings 

approximated based on the measurements performed during this experiment. In addition, 

EnergyPlus-generated cooling energy savings were at least four to five times lower than results 

available from the earlier studies (Medina, 2012). The team recommends more work on 

validation of whole building computer models using attic algorithms with RB.

For the purpose of cost analysis, each of the reflective insulation companies participating in the 

project were asked for cost estimates based on the records from installation of their technologies 

in the test houses. Surprisingly, cost data provided by RB and IRCC companies had similar 

prices per square foot of the installed radiation control system in the attic. These uniform costs
59

were used in the following payback time calculations; however, in the future, they should be 

confirmed in additional projects. 

To evaluate the payback period, the heating and cooling loads were modeled for the baseline 

house with R-19 attic insulation using EnergyPlus. With these modeled loads, the radiation 

control strategies load savings suggested by literature was calculated, as well as the associated 

consumptions rate and energy cost savings. This is based on 20% and 14% summer savings, and 

4% and 2.4% winter savings for RB and IRCC, respectively, according to Medina 2012; and 

20% of the above savings, which yields 4% and 2.8% cooling energy savings—close to the 

results of this field study. The payback periods were estimated by comparing the cost savings 

and the installed cost10 of RB and IRCC in the attic. Four southern U.S. locations were used for 

this analysis. When higher energy savings (according to Medina 2012) are considered, RB and 

IRCC systems yielded the lowest payback times for Miami, FL and Phoenix, AZ—about 3.5 

years and 5 years, respectively. When savings levels were similar to results recorded during this 

experiment are considered, the payback times for the same locations are 16 and 22 years, 

respectively for RBs and IRCCs.

 

10 The installed cost based on contractors quotes.
60

References

CABO (1995). Model Energy Code; 1995 Edition. Falls Church, Virginia: Council of American 

Building Officials.

ANSI/ASHRAE 90.2-2007: Energy Efficient Design of Low-Rise Residential Buildings

ASTM Standard C1313. (2010). "Standard Specification for Sheet Radiant Barriers for Building 

Construction Applications". ASTM International, West Conshohocken, PA, DOI: 

10.1520/C1313_C1313M-10.

ASTM Standard C1340. (2010). "Standard Practice for Estimation of Heat Gain or Loss Through 

Ceilings Under Attics Containing Radiant Barriers by Use of a Computer Program". ASTM 

International, West Conshohocken, PA, DOI: 10.1520/C1340_C1340M-10.

ASTM Standard C1321. (2009). "Standard Practice for Installation and Use of Interior Radiation 

Control Coating Systems (IRCCS) in Building Construction". ASTM International, West 

Conshohocken, PA, DOI: 10.1520/C1321-09.

Atherton, S.A. (2011). "Residential Attic Ventilation In A Hot And Humid Climate: Effects Of 

Increased Ventilation On Thermal Performance and Moisture Control", Master Thesis, 

University of Tennessee, Knoxville.

DEG. (2000). "Simulated Attic Radiant Barrier Performance in Six U.S. Locations”. Davis 

Energy Group, Inc., Davis, CA.

DOE (various dates). Building America - Resources for Energy Efficient Homes. U.S. 

Department of Energy. Accessed at: www.buildingamerica.gov. .

DOE (2012). Residential Natural Gas Average Monthly State Costs, Bundled Service – Supply 

and Delivery Costs – As of July 2012. . U.S. Department of Energy. Accessed at:

http://www.northwesternenergy.com/ourcustomers/shared/NaturalGasRates.pdf

Edison Electric Institute (2012). Residential Electric Monthly Costs – July 2012 

750 kWH Bundled Service – Supply & Delivery Costs Accessed at: 

http://www.northwesternenergy.com/ourcustomers/shared/ElectricRates.pdf

Fifoil products technical data sheet. Available at: 

http://www.fifoil.com/Builders/Products/ProductInfo/?ID=3.

Hancock, E., Norton, P., and Hendron, B. (2002). “Building America System Performance Test 

Practices: Part 2, Air Exchange Measurements” NREL Technical Report NREL/TP-550-30270.

Accessed at: http://www.nrel.gov/docs/fy02osti/30270.pdf
61

Huang, J., Hanford, J. and Yang, F. (1996). “Residential Heating and Cooling Loads Component 

Analysis.”. LBNL Technical Report LBNL-44636. Accessed at: 

http://simulationresearch.lbl.gov/dirpubs/44636.pdf.

Lenntech (2010). "Aluminum". Available at: http://www.lenntech.com/periodic/elements/al.htm

Medina, M. (2012) “A Comprehensive Review of Radiant Barrier Research Including 

Laboratory and Field Experiments”, ASHRAE Transactions; 2012, Vol. 118 Issue 1, p400

http://blog.radiantbarrier.com/wp-content/uploads/2012/02/radiant-barrier-research-ashrae.pdf.

Parker, D. S. (2005). “Literature Review of the Impact and Need for Attic Ventilation in Florida 

Homes”. Florida Solar Energy Center Report FSEC-CR-1496-05. Accessed at: 

http://www.fsec.ucf.edu/en/publications/pdf/FSEC-CR-1496-05.pdf.

Parker, D. S. (2003). “Research highlights from a large scale residential monitoring study in a 

hot climate”. Energy and Buildings. 35 (9), pp. 863-87.

Parker, D. and Sherwin, J. (1998). "Comparative Summer Attic Thermal Performance of Six 

Roof Constructions", Proceedings of the 1998 ASHRAE Annual Meeting, Toronto, Canada.

RIMA International (2002). “Understanding and Using Reflective Insulation, Radiant Barriers

and Radiation Control Coating”. Second Edition. Accessed at: 

http://www.rimainternational.org/pdf/handbook.pdf.

RS Means Building Construction Cost data (2011). http://rsmeans.reedconstructiondata.com/

Stovall, T., Yarbrough D. W., Shrestha S., Pearson T. and Arimilli R. V. (2010). “Analysis in 

Support of the Radiant Barrier Fact Sheet 2010 Update”. Proceedings of Thermal Performance of 

Exterior Envelopes of Whole Buildings XI , Florida. Accessed at: 

http://web.ornl.gov/sci/buildings/2012/B11%20papers/141_Stovall.pdf .

Texas Gas Service, Home Energy Calculator. Available at: 

http://www.texasgasservice.com/en/SaveEnergyAndMoney/HomeEnergyCalculator.aspx

Wallace, L.A., Emmerich, S.J., and Howard-Reed, C. (2002).“Continuous measurement of air 

change rates in an occupied house for 1 year: the effect of temperature, wind, fan and windows.” 

2002. Journal of Exposure Analysis and Environmental Epidemiology (12) pp. 296- 306.
62

Appendix A- Historical Energy Consumption Data

Utility data from the four units was made available. This was useful for comparing against 

monthly consumption results from the simulations. The model was calibrated against Unit 1B’s 

electricity data from November 2010-November 2011 and gas data from 2009.

Duplex 1, Unit B Duplex 1, Unit B

Gas

Date Usage (ccf) Billed

26-Jan-09 51 $66.87

24-Feb-09 28 $37.24

25-Mar-09 33 $40.01

24-Apr-09 22 $26.09

26-May-09 16 $19.32

24-Jun-09 17 $19.90

24-Jul-09 15 $20.65

24-Aug-09 13 $18.97

23-Sep-09 13 $17.87

26-Oct-09 16 $21.44

23-Nov-09 19 $24.96

22-Dec-09 41 $41.60

24-Jan-11 49 $45.08

23-Feb-11 58 $51.51

24-Mar-11 29 $32.31

22-Apr-11 23 $28.11

Electric

Date Usage 

(kWh)

Billed

11-Jan 1036 $89.93 

11-Feb 970 $83.79 

11-Mar 737 $62.12 

11-Apr 709 $59.51 

11-May 792 $72.55 

11-Jun 1001 $95.78 

11-Jul 1563 $158.26 

11-Aug 1560 $157.92 

12-Jan 664 -

12-Feb 631 -

12-Mar 603 -

12-Apr 720 -

12-May 968 -

12-Jun 1177 -
DOE/GO-102013-3943 ▪ December 2013

Printed with a renewable-source ink on paper containing at 

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

buildingamerica.gov