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NBS BUILDING SCIENCE SERIES 134

Determining Cost-Effective Insulation

Levels for Masonry and Wood-Frame Walls

in New Single-Family Housing

U.S. DEPARTMENT OF COMMERCE • NATIONAL BUREAU OF STANDARDS '^'.^Z
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards' was established by an act ot Congress on March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology

and facilitate their effective application for public benefit. To this end, the Bureau conducts

research and provides: (1) a basis for the Nation's physical measurement system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety. The Bureau's technical work is per- formed by the National Measurement Laboratory, the National Engineering Laboratory, and

the Institute for Computer Sciences and Technology.

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provides engineering measurement traceability services; develops test methods and proposes

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'Headquarters and Laboratories at Gaithersburg, MD, unless otherwise noted; mailing address Washington, DC 20234. ^Some divisions within the center are located at Boulder, CO 80303.
NBS BUILDING SCIENCE SERIES 134 0 » * Determining Cost-Effective Insulation

Levels for Masonry and Wood-Frame

Walls in New Single-Family Housing

Stephen R. Petersen

Kimberly A. Barnes

Bradley A. Peavy

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

Washington, DC 20234

ItATlONAL BUUUO

or 3TANDA£I>S

I.fURART SEP 1 6 1981

/ 10-6 acc -

no. f^^l

Prepared for the Office of the Assistant Secretary for Conservation and Solar Applications

Department of Energy

Washington, DC 20545

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Issued August 1981
Library of Congress Catalog Card Number: 81-600083

National Bureau of Standards Building Science Series 134

Nat. Bur. Stand. (U.S.), Bldg. Sci. Ser. 134, 126 pages (Aug. 1981)

CODEN: BSSNBV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1981

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402

Price $4.75

(Add 25 percent for other than U.S. mailing)
ABSTEIACT

Economically optimal insulation methods and resistance levels for three

different types of walls in a one-story, single-family residence are calculated

for a wide range of geographic locations, energy prices, heating and cooling

equipment efficiencies, and financial evaluation criteria. The three basic

wall types examined are 8-in concrete block walls, brick and block walls, and

wood-frame walls with lightweight siding. Changes in annual heating and cooling

requirements for an 1176 ft^ prototype house resulting from several different

insulation resistances in each wall type are calculated using the NBS Load

Determination program and Test Reference Year climate data for a number of

geographic locations. Changes in heating requirements are correlated with

heating degree days to provide estimates of energy savings in all geographic

regions of the continental United States. Cooling requirements are not found

to vary significantly with the thermal resistance of the walls under a typical

operating profile except in the southwestern desert. An index number system

is developed to quickly determine insulation levels based on the data generated

in the report.

Key words: building design; building economics; energy conservation; exterior

wall; HVAC calculations; insulation; life-cycle cost analysis;

masonry; mass.

Cover: In residential construction, the

economically optimal level of insulation

for masonry walls is likely to be different

from that for wood-frame walls.

iii
PREFACE

The work in this report was conducted as an interdisciplinary research project

by the Building Economics and Regulatory Technology Division and the Building

Thermal Performance Division within the Center for Building Technology, National

Engineering Laboratory, at the National Bureau of Standards. This effort was supported by the Department of Energy (DoE) under Interagency Agreement

No. 77-A -01-6010, Task Order A008-BCS.

This report extends to additional wall types and climatic areas the work

reported in NBSIR 79-1789, Economic Analysis of Insulation in Selected Masonry

and Wood-Frame Walls . That report was sponsored by the Department of Housing

and Urban Development and built upon concurrent research in economic analysis

of insulation in masonry walls sponsored by DoE.

iv
ACKNOWLEDGMENTS

The authors would like to acknowledge the helpful contributions of those who

reviewed and commented on this document. Their suggestions have contributed to

making this a more useful and accurate report.

We would especially like to thank the following people at the National Bureau

of Standards for their helpful comments: James G. Gross, James P. Barnett,

John S. Stroik, E. Thomas Pierce, and Harold E. Marshall, all with the Center

for Building Technology (CBT), and Robert E. Chapman, with the Center for

Applied Mathematics. Appreciation is extended to Tamami Kusuda, also with CBT,

and Paul R. Achenbach for their technical support of this project. Special

thanks are also due to Tracey Kistler for the attentiveness given to the drafts

and final typed version of this report. The authors remain responsible for any errors or omissions.

V
TABLE OF CONTENTS

Page

LIST OF TABLES viii

LIST OF FIGURES x

SI CONVERSION xlii

EXECUTIVE SUMMARY xiv

1. INTRODUCTION 1

1.1 Statement of Problem 1

1 . 2 Scope • 3

1.3 Approach 4

1.4 Organization 5

2. WALL TYPES EXAMINED AND INSULATION METHODS CONSIDERED 7

2.1 Description of Wall Types Examined 7 2.2 Insulation Methods 13

2.2.1 Insulation in Masonry Walls 14

2.2.1.1 Insulation on the Inside Surface 14

2.2.1.2 Insulation in Cavity (Brick and Block Walls) .. 15

2.2.1.3 Insulation in Cores (Concrete Block Walls) .... 18

2.2.1.4 Insulation on the Outside Surface 18

2.2.2 Insulation in Wood-Frame Walls 19

3. THERMAL ANALYSIS PROCEDURES 23

3.1 Description of Single-Family House Prototype 24

3.2 Thermal Modeling Procedures 28

3.3 Climatic Variation Considerations 30

4. THERMAL ANALYSIS OF WALL INSULATION 33

4.1 Insulation in 8-in Block Walls 34

4.1.1 Base Case (Open Cores, 100 Ib/ft^ Concrete,

a = 0.50) 34

4.1.2 Solar Absorptance Variations 37

4.1.3 Concrete Density Variations 39

4.1.4 8-in Block Walls (Insulated Cores) 42

4.2 Insulation in Brick and Block Walls 47

4.2.1 Insulation on Inside Surface 47

4.2.2 Insulation in Cavity 50

vi
TABLE OF CONTENTS (con't)

Page

4.3 Thermal Analysis of Wood-Frame Walls 50

4.4 Reductions in AHR and ACR , 54

4.4.1 Generalized Data Analysis 54

4.4.2 Correlation with Climate Data 56

5. ECONOMIC ANALYSIS OF WALL INSULATION 59

5.1 Calculating the Present Dollar Value of Energy Savings 60

5.2 Criteria for Economic Optimization 62

5.3 Calculation of Optimal Insulation Levels: Examples 64

6. INDEX NUMBER SYSTEM TO DETERMINE OPTIMAL INSULATION LEVELS 71

7. SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS FOR FURTHER RESEARCH 81

7.1 Summary 81

7.2 Conclusions 82

7.3 Recommendations for Further Research 83

REFERENCES 85

APPENDIX A Glossary of Selected Technical Terms A-1

APPENDIX B Graphical Representations of Annual Heating and Cooling

Requirements for Selected Cities B-1

APPENDIX C Solar Absorptances of Walls by Color C-1

vii
LIST OF TABLES

Table Page

1 Base 8-in Block Wall Description 8

2 Base Brick and Block Wall Description 9

3 Base Wood-Frame Wall Description 10

4 Insulation Levels Examined and Cost Data for Insulation in 8-in

Block Walls 16

5 Insulation Levels Examined and Cost Data for Insulation in Brick

and Block Walls 17

6 Insulation Levels Examined and Cost Data for Insulation in

Wood-Frame Walls 21

7 Prototype House Parameters 25

8 Operational Profile of Prototype House 27

9 Attic and Window Glazing Specifications by City 29

10 Heating Degree Days and Cooling Degree Hours Based on Test

Reference Year (TRY) Data 31

11 Annual Heating and Cooling Requirements for Prototype House:

8-in Block Walls, No Insulation in Cores 35

12 Annual Heating and Cooling Requirements for Prototype House:

8-in Block Walls, a = 0.25 38

13 Annual Heating and Cooling Requirements for Prototype House:

8-in Block Walls, a = 0.75 40

14 Annual Heating and Cooling Requirements for Prototype House in

Washington, D.C: 8-in Block Walls, Variation in Concrete

Density 43

15 Calculation of AHR and ACR for Prototype House in Washington, D.C.

Interpolated to Same U-Values: 8-in Block Walls, Three Concrete

Densities 44

16 Annual Heating and Cooling Requirements for Prototype House:

8-in Block Walls, Insulation in Cores 45

17 Annual Heating and Cooling Requirements for Prototype House:

Brick and Block Walls, Insulation on Inside Surface 48

viii
LIST OF TABLES (con't)

Table Page

18 Annual Heating and Cooling Requirements for Prototype House:

Brick and Block Walls, Insulation in Cavity 51

19 Annual Heating and Cooling Requirements for Prototype House:

Wood-Frame Walls 52

20 Change in AHR/ft^ of Wall Area Normalized to AU = 0. 1 Btu/(ft2)(h)

(°F) 55

21 Regression Equations for Five Wall Insulation Variations 57

22 Example #1: Albuquerque - 8-in Block Walls (1000 ft^) Insulated

on Inside Surface 66

23 Example #1: Incremental Life-Cycle Savings and Costs 66

24 Example #2: Phoenix - Brick and Block Walls (1000 ft^) Insulated

in Cavity 68

25 Example #2: Incremental Life-Cycle Savings and Costs 68

26 Example #3: Wood-Frame Walls (1000 ft^) in 6000 HDD33 Climate ... 70

27 Example #3: Incremental Life-Cycle Savings and Costs 70

28 Modified Uniform Present Worth Factors (UPW*) 74

29 Unit Energy Prices (Metered) and Corresponding Price per

Million Btu Output from Furnace 75

30 Breakpoint Ratios for 8-in Block Walls (Insulation on Inside

Surface) 76

31 Breakpoint Ratios for Brick and Block Walls (Insulation on Inside Surface) 77

32 Breakpoint Ratios for Brick and Block Walls (Insulation in

Cavity) 78

33 Breakpoint Ratios for Wood-Frame Walls 79

ix
LIST OF FIGURES

Figure Page

1 Details of Three Major Wall Types Examined 12

2 Floor Plan of 1176 ft^ Single-Family House Used in Analysis 26

3 Relationship Between AHR, ACR, and U-value : 8-in Block Walls

(Washington, D.C.) 36

4 Effects of Solar Absorptance on AHR and ACR: 8-in Block Walls

(Washington, D.C.) 41

5 Relationship Between AHR, ACR, and U-value: 8-in Block Walls,

Insulation in Cores (Washington, EVC.) 46

6 Relationship Between AHR, ACR and U-value: Brick and Block Walls

(Washington, D.C.) 49

7 Relationship Between AHR, ACR, and U-value: Wood-Frame Walls

(Washington, D.C.) 53

8 Heating Degree Days (base 55°F) Map of United States 58

9 Economic Optimization Criteria for Insulation 63

B.l Albany, New York: Relationship Between Annual Heating and

Cooling Requirements and Wall U-value for an 117 6 ft^ House (8-in

Block Walls and Wood-Frame Walls) B-2

B.2 Albuquerque, New Mexico: Relationship Between Annual Heating and

Cooling Requirements and Wall U-value for an 1176 ft^ House (8-in

Block Walls and Wood-Frame Walls) B-3

B.3 Atlanta, Georgia: Relationship Between Annual Heating and

Cooling Requirements and Wall U-value for an 1176 ft^ House (8-in

Block Walls and Wood-Frame Walls) , B-4

B.4 Indianapolis, Indiana: Relationship Between Annual Heating and

Cooling Requirements and Wall U-value for an 1176 ft^ House (8-in

Block Walls and Wood-Frame Walls) B-5

B.5 Jackson, Mississippi: Relationship Between Annual Heating and

Cooling Requirements and Wall U-value for an 1176 ft^ House (8-in

Block Walls and Wood-Frame Walls) B-6

B.6 Jacksonville, Florida: Relationship Between Annual Heating and

Cooling Requirements and Wall U-value for an 1176 ft^ House (8-in

Block Walls and Wood-Frame Walls) B-7

X
LIST OF FIGURES (con't)

Page

B.7 Madison, Wisconsin: Relationship Between Annual Heating and

Cooling Requirements and Wall U-value for an 1176 ft^ House (8-in

Block Walls and Wood-Frame Walls) B-8

B.8 Phoenix, Arizona: Relationship Between Annual Heating and

Cooling Requirements and Wall U-value for an 1176 ft^ House (8-in

Block Walls and Wood-Frame Walls) B-9

B.9 Salt Lake City, Utah: Relationship Between Annual Heating and

Cooling Requirements and Wall U-value for an 1176 ft2 House (8 -in

Block Walls and Wood-Frame Walls) B-10

B.IO Tampa, Florida: Relationship Between Annual Heating and Cooling

Requirements and Wall U-value for an 1176 ft^ House (8-in Block

Walls and Wood-Frame Walls) B-11

B.ll Washington, D.C: Relationship Between Annual Heating and

Cooling Requirements and Wall U-value for an 1176 ft^ House (8-in

Block Walls and Wood-Frame Walls) B-12

B.12 Albuquerque, New Mexico: Relationship Between Annual Heating and

Cooling Requirements and Wall U-value for an 1176 ft2 House (8 -m

Block Walls and Brick and Block Walls) B-13

B.13 Atlanta, Georgia: Relationship Between Annual Heating and

Cooling Requirements and Wall U-value for an 1176 ft^ House (8-in

Block Walls and Brick and Block Walls) B-14

B.14 Indianapolis, Indiana: Relationship Between Annual Heating and

Cooling Requirements and Wall U-value for an 1176 ft^ House (8-in

Block Walls and Brick and Block Walls) B-15

B.15 Jacksonville, Florida: Relationship Between Annual Heating and

Cooling Requirements and Wall U-value for an 1176 ft^ House (8-in

Block Walls and Brick and Block Walls) B-16

B.16 Madison, Wisconsin: Relationship Between Annual Heating and

Cooling Requirements and Wall U-value for an 1176 ft^ House (8-in

Block Walls and Brick and Block Walls) B-17

B.17 Phoenix, Arizona: Relationship Between Annual Heating and

Cooling Requirements and Wall U-value for an 1176 ft^ House (8-in

Block Walls and Brick and Block Walls) B-18

B.18 Tampa, Florida: Relationship Between Annual Heating and Cooling

Requirements and Wall U-value for an 1176 ft^ House (8-in Block

Walls and Brick and Block Walls) B-19

xi
LIST OF FIGURES (con' t)

Washington, D.C.: Relationship Between Annual Heating and

Cooling Requirements and Wall U-value for an 1176 f t^ House (8-in

Block Walls and Brick and Block Walls)

xii
SI CONVERSION

In view of the presently accepted practice of the building industry in the

United States and the structure of the NBS Load Determination computer program

used in this report, common U.S. units of measurement have been used throughout

this report. In recognition of the position of the United States as a signatory to the General Conference of Weights and Measures, which gave official

status to the metric SI system of units in 1960, appropriate conversion factors

have been provided in the table below. The reader interested in making further

use of the coherent system of SI units is referred to:

NBS SP330, 1972 Edition, "The International System of Units" E380-72

ASTM Metric Practice Guide (American National Standard Z210.1).

Metric Conversion Factors

Length:

Area:

Volume:

Fluid Capacity:

Temperature

:

Temperature

Interval

:

Mass:

Mass per unit

length:

Mass per unit area

:

Mass per unit

vo lume

:

Energy:

Heat flow rate;

Specific heat:

U-value

:

R-value

:

1 inch (in) = 25.4 millimeters (mm)

1 foot (ft) = 0.3048 meter (m)

1 ft2 = 0.092903 m2

1 ft3 = 0.028317 m3

1 gallon (gal) = 3.78541 litres (L)

1°F = 9/5°C + 32

1°F = 5/9°C or K

1 pound (lb) = 0.453592 kilogram (kg)

1 lb/ft = 1.48816 kg/m

1 lb/ft2 = 4.88243 kg/m^

1 lb/ft3 = 16.0185 kg/m3

1 Btu = 1.05506 kilojoules (kJ)

1 Btu/h = 0.293071 Watt (W)

1 Btu/(lb)(°F) = 4.1868 kJ/(kg)(K)

1 Btu/(ft2)(h)(°F) = 5.67826 W/(m2)(K)

1 (f t2)(h)(°F)/Btu = 0.176110(m2)(K)/W

xiii
EXECUTIVE SUMMARY

This report examines both the energy and dollar-value savings and the

additional costs attributable to thermal insulation in the exterior walls

of new masonry and wood-frame single-family housing. Based on these savings

and costs, economically optimal insulation methods and corresponding thermal

resistance (R) values are determined. Economically optimal insulation methods

and R-values are defined as those having the greatest present-value, lifecycle, net savings of all the alternatives considered. Since net savings are determined in part by climate and energy costs, optimal insulation methods and

R-values for exterior walls can vary significantly with both geographic location and the space heating equipment used. In addition, significant differences in insulation costs between masonry and wood-frame walls and somewhat

smaller differences to the potential energy savings may result in differences

in the optimal method and R-value between wall types as well.

Three distinct wall types are examined in this report: (1) 8-in concrete block

walls; (2) brick and block cavity walls; and (3) wood-frame walls. All three

walls are evaluated in an otherwise identical 1176 square-foot (28 ft x 42 ft)

single-story house. An expanded output version of the National Bureau of

Standards Load Determination program (NBSLD) and hourly Test Reference Year

(TRY) climate data for each location are used to calculate the annual heating

and cooling requirements (AHR, ACR) of the house and reductions in those

requirements due to increasing levels of insulation.

Thermal performance data are generated for 11 locations for wood-frame and 8-in

block walls and 8 locations for brick and block walls:

8-in Block Brick & Block Wood Frame

Albany, New York X X

Albuquerque, New Mexico X X X

Atlanta, Georgia X X X

Indianapolis, Indiana X X X

Jackson, Mississippi X X

Jacksonville, Florida X X X

Madison, Wisconsin X X X

Phoenix, Arizona X X X

Salt Lake City, Utah X X

Tampa, Florida X X X

Washington, D.C. X X X

Based on these results, generalized relationships between reductions in overall

wall U-values and reductions in AHR are developed and correlated with heating

degree days. Sensitivity analyses with regard to exterior wall color and wall

density are made for the 8-in block walls. The effects of changing the position of the insulation from the inside surface to the cavity of the brick and

block walls on AHR and ACR are also calculated.

Representative costs for the most common insulating methods are estimated in

1980 dollars for a wide range of commonly available R-values using Means

xiv
Building Construction Cost Data for 1980. A methodology is outlined for

determining the present dollar value of energy savings from each additional

level of insulation, sensitive to energy prices, projected energy price esca- lation rates, a discount rate, and the expected useful life of the insulation.

An index number system is devised to assist the reader in determining optimal

insulation levels for each wall type and geographic location, as well as for

different economic factors, with a minimum of computational requirements.

Some of the conclusions reached in this study may be of considerable interest

to the building community and could have a significant impact on insulation

practices in new home construction.

(1) Because of the higher cost of insulating masonry walls relative to woodframe walls, the economically optimal level of insulation in much of the

South and Southwest is no more than R-3 (a reflective air space provided

by furring and foil-backed wall board). R-11 or R-13 mineral wool insulation is generally cost effective in similar houses with wood-frame

walls in the same locations (with the exception of a gas-heated house

in southern Florida).

(2) Free-standing framing on the inside of masonry walls with 2 x 3-in studs,

insulated with mineral wool batts or blankets, is generally a more costeffective method of reducing heat loss than the use of furring strips and

rigid foam insulation. If rigid foam insulation is used, optimal insulation levels in masonry walls tend to be significantly lower than those

for wood-frame walls insulated with mineral wool. If framing and mineral

wool are used in masonry walls, optimal insulation levels tend to be quite

similar to those for wood-frame walls, except in the mildest heating

climates (i.e., the South and Southwest). In the colder climates, the

optimal insulation level may be as high as R-23 if high cost heating

fuels are used.

(3) Reductions in annual heating requirements due to insulating exterior walls

are similar for both wood-frame and masonry walls in regions with more

than 3000 heating degree days (base 65°F). In milder regions, the reductions tend to be less for the insulation in masonry walls. However, these

differences are generally small in absolute terms.

(4) Changes in annual cooling requirements due to increasing insulation levels

in exterior walls tend to be insignificant except in extremely hot climates like the Arizona desert. In fact, cooling requirements may increase

if the house is kept closed up, especially in the spring and fall. Small

reductions in annual cooling requirements may occur if air conditioning is

only used when the outdoor dry bulb temperature is higher than the thermostat setpoint. These reductions or increases in annual cooling requirements are not generally large enough to have any effect on the optimal

level of insulation except in the mildest heating climates (especially

southern Arizona).

(5) In climates typified by mild winter or summers, increased mass in exterior

walls can significantly improve the thermal performance of those walls.

XV
However, in these regions, heating or cooling requirements tend to be

small to begin with and thus absolute energy savings are small. As more

severe climates are encountered, the advantages of mass in terms of

reducing annual energy usage are sharply reduced.

(6) Insulation in the cavity of a brick, and block wall generally performs

significantly better than the same insulation placed on the inside surface

of the same wall. If the installed cost per resistance unit of cavity

insulation is approximately the same or less than for insulation on the

inside surface, cavity insulation is generally more cost effective.

(7) Insulation in the core of concrete blocks is generally less cost effective

than mineral wool insulation installed on the inside wall surface, primarily because of thermal bridging effects and a higher first cost per

equivalent R-value.

(8) The color of the exterior surface of walls may have more effect on annual

heating and cooling requirement than mass. However, unless the location

of the house is clearly dominated by either heating or cooling loads, the

advantage of a given color in one season will be offset by the disadvantage of the same color in the opposite season. >

!

Facing page: Past guidelines for insulation

in residential buildings were based in large

part on the analysis of energy savings and

costs for insulation in wood-frame housing.

xvi
1 . INTRODUCTION

1 .1 STATEMENT OF PROBLEM

Life-cycle cost analysis has been frequently used to demonstrate that the

increased use of thermal insulation in residential construction is generally

a cost-effective means of reducing the impact of rapidly rising energy

1
prices. ' As a result, Government Agencies and Industry sources have

significantly upgraded their standards and/or recommendations for Insulation

usage In new and existing housing. ^ Where R-30 attic Insulation and R-1 9 wall

Insulation were virtually unheard-of ten years ago, both of these have become

common practice In many parts of the United States today.

Current guidelines and standards for residential Insulation are based in large

part on the analysis of energy savings and Insulation costs in wood-frame

housing. While such guidelines and standards tend to be differentiated by

climate and fuel type (in order to recognize differences in the dollar values

of the energy savings accrued), little attention has been given to differentiation by construction type. For example, while R-30 or R-38 insulation may be

economically justified in open attics, such resistance levels will be considerably more costly and thus inappropriate in some flat roofs and cathedral-type

ceilings. Similarly, R-11 or R-1 9 wall insulation may be justified in a con- ventional wood-frame wall, while somewhat different resistance levels may be

more appropriate for masonry wall construction.

The purpose of this report is to develop economic guidelines for insulating

load-bearing masonry and wood-frame walls in single-family residences.^ Economically optimal Insulation guidelines for load-bearing masonry walls are likely to be different from those for wood-frame walls in residential

construction for two distinct reasons:

For examples of this, see the following: U.S. Department of Energy, Office

of Conservation and Solar Energy, Economic Analysis, Energy Performance Standards for New Buildings , Doc. 9568.00 (Washington, D.C.: U.S. Department of

Energy, November 1979); Stephen R. Petersen, Retrofitting Existing Housing

for Energy Conservation: An Economic Analysis , NBS BSS 64 (Washington,

D.C»: National Bureau of Standards, December 1974); and J. E. Snell,

P. R. Achenbach, and S. R. Petersen, "Energy Conservation in New Housing

Design," Science , Vol. 192, June 25, 1976, pp. 1305-1311.

For examples of recently published standards, see: U.S. Department of

Agriculture, Farmers Home Administration, "Thermal Performance Standards"

(Washington, D»C., 1979); and U.S. Department of Housing and Urban Development, "Minimum Property Standards for One- and Two-Family Dwellings"

(Washington, D.C., 1979).

NAHB Research Foundation, Inc., "Annual Builder Practices Survey," Rockvllle,

Md. 20850.

It is assumed that the type of wall construction to be used has already been

selected at this point. This report does not compare the costs of

alternative methods of wall construction.

2
(1) The cost of insulating a load-bearing masonry wall is substantially more

expensive than insulating a wood-frame wall to the same U-value because there

is no stud space suitable for installing relatively low-cost blanket or batt

insulation materials.

(2) The greater weight of the masonry wall relative to the wood-frame wall

gives it some natural advantage in terms of dampening the effects of the diurnal climate on space heating and cooling loads. As a result, the potential

reduction in energy requirements due to insulation in masonry walls may be

somewhat different than the equivalent thermal resistance value in wood-frame

walls, especially if the insulation is located toward the outer surface of the

wall.

Both of these differences will be examined in some detail in this report in

order to provide a suitable basis for a life-cycle cost analysis of insulation

in masonry walls.

1.2 SCOPE

In this report, economic guidelines for insulating load- bearing masonry walls

and wood-frame walls are developed, based on a life-cycle cost analysis of the

increased construction costs and corresponding energy savings related to the

increased use of insulation. Two basic types of masonry construction are

examined: 8-in concrete masonry units, ^ typical of masonry construction in

Florida and the Southwest, and a composite (or cavity) construction made of

4-in face brick and 4-in blocks,^ more typical of load- bearing masonry wall

construction in other parts of the United States. (While brick veneer walls

are not explicitly examined, implications for these walls are discussed in

subsections 4.1,1 and 5.3.) For the 8-in block wall, insulation will be con- sidered both in the hollow cores of the blocks and on the inside wall surface,

covered with 0.5-in gypsum wallboard. For the brick and block wall, insulation

is considered both on the inside wall surface and in the cavity between the

brick and block. Economic guidelines for insulation in conventional wood-frame

wall construction are developed using the same methodology.

Annual space heating and cooling requirements are calculated for an 1176

square-foot, one-story house, with each wall type examined individually over a

For the remainder of this paper concrete masonry units will be simply

referred to as "blocks."

When insulation is placed between the brick and block, this composite wall

type will be refer^^ed to as "cavity wall" construction. The term "brick and

block" will be used to describe the general wall construction.

3
range of insulation levels. An expanded output version of the National Bureau

of Standards Load Determination computer program (NBSLD),^ and Test Reference

Year weather data^ are used in calculating these requirements

.

In general, only the least costly means of insulating a wall to different

levels of thermal performance need be considered in determining the optimal

insulation level, provided that other (non-thermal) performance criteria are

satisfied. However, in this report, alternative means of insulating masonry

and wood-frame walls are considered in order to provide a broader basis for

evaluating insulation methods.

Calculations of annual space heating and cooling requirements were made for

11 widely dispersed locations for the prototype house with 8-in block and woodframe walls, and in 8 of those 11 locations for the prototype house with

the brick and block walls. Based on these calculations, a method for calculating heating and cooling requirements in other locations throughout the

continental United States is developed. Some sensitivity analyses related to

both the weight of the wall and the solar absorptivity of its exterior surfaces

are made for the 8-in block wall.

The two basic insulation materials considered for increasing the thermal

resistance of load-bearing masonry walls were rigid foam and mineral wool

blanket. In addition, loose-fill insulation poured into the hollow cores of

8-in blocks is examined. However, the methodology presented is flexible enough

to allow the reader to consider many variations in insulating materials, based

on their thermal resistance characteristics and general suitability for

installation in sidewalls.

1 .3 APPROACH

Incremental changes in annual space heating and cooling requirements due to

increased levels of thermal resistance in exterior walls are calculated for

each wall type in a wide range of climates for a 1176 square-foot, single-story

house. The present-dollar values of life-cycle energy savings corresponding to

these changes are then calculated, based on current and projected energy costs,

equipment efficiencies, a discount rate, and the expected lifetime of the insulation. Initial costs of the different insulation types and resistance values

examined are also estimated, based on current (1980) construction cost data.

For a description of NBSLD, see T. Kusuda, NBSLD, The Computer Program for

Heating and Cooling Loads in Buildings , NBS BSS 69 (Washington, D.C.:

National Bureau of Standards, 1976). For a description of the expanded

output version, see Stephen R. Petersen and James P. Barnett, Expanded NBSLD

Output for Analysis of Thermal Performance of Building Envelope Components , NBSIR 80-2076 (Washington, D.C.: National Bureau of Standards, July 1980).

See E. Stamper, "Weather Data," ASHRAE Journal . February 1977, p. 47.

4
Incremental savings and costs due to increased insulation usage are compared

on a present-value, life-cycle basis in order to determine the economically

optimal level of insulation, i.e., that insulation method and resistance value

which has the greatest cumulative net savings in any given installation. An

indexing format is developed which allows the user to quickly determine the

optimal insulation method and resistance value for each of the wall types

examined.

1.4 ORGANIZATION

This report has six sections in addition to this introductory section.

Section 2 begins by detailing the wall types and insulation methods to be considered. Section 3 outlines the thermal analysis procedures used to calculate

the reduction in annual heating and cooling requirements attributable to

increased insulation usage in each wall type. The prototype house and operational profile used in the analysis are described. In addition, the climatic

variations used in the analysis are discussed. Section 4 provides the results

of the thermal analysis in terms of calculated annual heating and cooling

requirements for the prototype house, varied by wall type, wall U-value, and

geographic location. The changes in annual heating and cooling requirements

attributable to a reduction in U-value of 0.1 Btu/ (f t^ ) (h) ( °F) are calculated

for each wall type, insulation method, and climate. Regression equations are then calculated based on heating degree days to allow interpolation of the

thermal analyses to other geographic regions.

In section 5, the economic criteria for determining optimal insulation levels

are presented. Three example problems are solved in order to demonstrate the

calculation procedures. In section 6 an index number calculation procedure is

introduced in order to facilitate the computation process, so that optimal

insulation methods and resistance levels can be quickly identified. Finally,

a summary, conclusions, and recommendations for further research are presented

in section 7

.

This report also contains three appendices which are intended to provide

additional information related to the material covered in the main body of

the report. Appendix A contains a glossary of selected technical terms used

in this report. Appendix B provides graphical representations of the results

of the thermal analysis described in section 4 for the 11 cities used in that

analysis. Appendix C contains a brief guide to the relationship between the

surface color and solar absorptance of various exterior wall coverings.

5
Facing page: The thermal performance of

a masonry wall can be expected to vary with

concrete density, wall weight, the specific

heat of its components, and the relative

placement of the insulation within the wall.

6
2. WALL TYPES EXAMINED AND INSULATION METHODS CONSIDERED

2.1 DESCRIPTION OF WALL TYPES EXAMINED

Basic descriptions of the three wall types modeled in this report are provided

in table 1 for the 8-in concrete block wall, table 2 for the brick and block

wall, and table 3 for the wood-frame wall. The descriptions include the thickness, specific heat, thermal resistance, and weight of each wall component and

the resistance, thermal transmission coefficient (U ) , weight, and thermal mass

of the overall wall on a square-foot basis.

7

1
Table 1. Base 8-in Block Wall Description^

A. 100 lb/ft3 Concrete Block Wall

Component Specific Heat Overall Wall Core Area (71%) Web Area (29%)

Description Btu/(lb °F) R Ib/f R Ib/ft^ R Ib/ft^

Outside air film^ 0.17 0.17 0.17

8-in block 0.21 1.88 36.2 1.79 25.0 2.11 63.5

0.75-in air space*^ 0.96 0.96 0.96

0.50-in gypsum board 0.20 0.45 2.1 0.45 2.1 0.45 2.1 Inside air film 0.68 0.68 0.68

Total 4.14 38.3 4.05 27.1 4.37 65.6

U = 1/R 0.242 0.247 0.229

Thermal Mass (Btu/ft^ "F) 8.02 5.67 13.76

B. 80 lb/ft3 Block Wall

Component Specific Heat Overall Wall Core Area (71%) Web Area (29%)

Description Btu/(lb °F) R Ib/ft'^ R Ib/ft-^ R Ib/f t^

Outside air film^ 0.17 0.17 0.17

8-in block 0.21 2.39 28.9 2.16 20.0 3.05 50.8

0.75-in air space'^ 0.96 0.96 0.96

0.50-in gypsum board 0.20 0.45 2.1 0.45 2.1 0.45 2.1 Inside air film 0.68 0.68 0.68

Total 4.65 31.0 4.42 22.1 5.31 52.9

U = 1/R 0.215 0.226 0.188

Thermal Mass (Btu/ft^ °F) 6.49 4.62 11.09

C. 120 lb/ft3 Concrete Block Wall

Component Specific Heat Overall Wall Core Area (71%) Web Area (29%)

Description Btu/(lb °F) R Ib/ft^ R Ib/ft^ R Ib/ft-^

Outside air film^" 0.17 0.17 0.17

8-in block 0.21 1.52 43.4 1.54 30.0 1.47 76.2

0.75-in air space^ 0.96 0.96 0.96

0.50-in gypsum board 0.20 0.45 2.1 0.45 2.1 0.45 2.1 Inside air film 0.68 0.68 0.68

Total 3.78 45.5 3.80 32.1 3.73 78.3

U = 1/R 0.265 0.263 0.268

Thermal Mass (Btu/ft^ 9.53 6.72 16.42

3 Actual thickness of 8-in block is 7.625 in. Total thickness of wall is 8.875 in.

Winter design value (wind speed = 15 miles/hour).

0.75-in air space between block and gypsum board includes 0.75-in wood furring strips,

24 inches on center, having approximately the same resistance value as the air space.

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10
Component weights, thermal resistances, and specific heats are based on the

ASHRAE Handbook of Fundamentals .-^ Three different concrete densities are exam- ined in the description of the 8-in block wall: 80 Ib/ft-^ (lightweight), 100

Ib/ft-^ (medium weight), and 120 Ib/ft-^ (heavyweight). However, an initial sen- sitivity analysis of the thermal performance of these three densities shows

little difference after adjustment for differences in the overall U-value.^

As a result, the 100 lb/ft-* concrete is used as the base case for both the

8-in block wall and brick and block wall. Detailed drawings of each wall

type examined are shown in figure 1.

The three basic wall types examined in this report range widely in weight,

from approximately 5.6 Ib/ft^ of wall area for the wood-frame wall to 61.7

Ib/ft^ for the brick and block wall. The 8-in block wall (100 Ib/ft^ concrete)

is approximately halfway between these two extremes at 38.3 Ib/ft^. Such a wide variation in weight per unit wall area can be useful in determining the

relationship between wall weight and thermal performance for walls with identical U-values. For example, the 5.6 Ib/ft^ of wall area for the wood-frame wall

is based on the use of lightweight siding (e.g., wood or aluminum). If brick

veneer is used, the resulting wall weight is nearly identical to the 8-in

block wall. Thus, the thermal analysis of the latter wall system provides a good basis for estimating the thermal performance of brick veneer walls.

While the use of a stucco exterior on masonry or wood-frame walls is not

explicitly analyzed, the effect of stucco on the thermal performance of walls

is primarily related to a change in wall U-value rather than wall weight.^

The thermal performance of the wall can also be expected to vary with the

specific heat of its components and the relative placement of the insulation

in the wall. The "thermal mass" of the wall, which is the sum of the weight

of each component multiplied by its specific heat, is a better indicator of

the ability of the wall to store and release heat in a dynamic operating environment than weight alone. No parametric measure has been defined to include

the effects of the relative placement of the insulation within the wall. As

will be seen, insulation placement can have a significant impact on the actual

thermal performance of a wall design.

The solar absorptance (a) of the exterior wall surface, which is a function of

its color, is also an important variable in the analysis of the thermal performance of wall constructions. For this reason, the same value for solar absorptance is used for establishing the basic performance data for each wall

variation examined in this report. This base value is 0.5, which corresponds

ASHRAE Handbook of Fundamentals (New York: American Society of Heating,

Refrigerating and Air-Conditioning Engineers, Inc., 1972).

^ See section 4.1.3,

^ See section 4.1.1.

^ See section 4.1.3.

11
0.75-in 8- in concrete

airspace block

Figure 1. Details of three major wall types examined.

12
to a medium coloring (i.e., buff or beige). Appendix C contains a short guide

to the relationship between surface color and solar absorptance. A limited

sensitivity analysis is performed for the 8-in block wall in order to demonstrate the extent of variation in wall performance due to a higher (0.75) and

lower (0.25) solar absorptance.

In tables 1 to 3, the core and web cross sections of the block walls are described separately. Similarly, in the wood-frame walls, the stud space and

studs are described separately. Preliminary investigation into alternative

modeling techniques showed that modeling the core (stud space) and web (stud) cross sections separately is more realistic than modeling the wall as homogeneous in mass and thermal resistance. This latter approach is easier and faster

but exaggerates the thermal response characteristics of the wall in terms of

dampening wall heat losses and gains over the heating and cooling seasons,

respectively.

2.2 INSULATION METHODS

Practical insulation methods for exterior walls vary both by wall type and by

the level of overall thermal resistance desired. Since the placement of the

insulation vis a vis the thermal mass in masonry walls can have a significant

effect on the dynamic thermal performance of those walls, this factor should

be considered as well. In this subsection, several approaches to the insulation of both masonry walls and wood-frame walls will be briefly examined. For

all wall types, the base case (i.e., uninsulated) wall is assumed to be covered

with 0.5-in gypsum wallboard enclosing a non-reflective air space (R-value ~ 0.96 (ft2)(h)(°F)/Btul).

For each insulation method discussed, an estimated installed cost (in 1980

dollars) is given. All costs include contractor overhead and profit. These

costs are based on the 1980 Means Building Construction Cost Data .^ In all cases where the use of increased insulation reduces usable floor space and/or

increases window and door framing costs, these factors are included in estimating the installed insulation cost. The implicit cost of reduced inside floor

space can be estimated by calculating the cost per incremental square foot of

floor area (rather than average cost per square foot) in a new house. Extending the end wall of a house 28 feet wide (the width of the house studied

in this report) by 2 feet will result in approximately 52 square feet of

ASHRAE Handbook of Fundamentals , p. 358.

Means Building Construction Cost Data, 1980 (Duxbury, Mass.: Robert Snow

Means Company, Inc., 1979).

13
increased floor space at a cost of approximately $260, or $5 per square

foot.^ This provides a cost adjustment factor for insulation methods which

increase the thickness of a wall beyond the base design value.

In general, for all masonry walls insulated on the inside surface and for

wood-frame walls, the first increase in thermal resistance considered in this

report is the use of foil-backed gypsum board together with the existing air

space formed by the furring strips or studs. This reflective foil backing on

one side of the air space has an emissivity of approximately 0.05, which

results in an R-value of approximately 3.0 (f t^) (h) ( °F ) /Btu.^ The foil-backed

gypsum board is generally considered first in this report because of its relatively low cost per resistance unit. However, if the air space is filled with

conventional insulating materials in order to further increase the thermal

resistance of the wall, the foil backing is no longer considered since it has

no thermal resistance value without an adjoining air space.

2.2.1 Insulation in Masonry Walls

2.2.1.1 Insulation on the Inside Surface

Both concrete block and brick and block walls can be insulated on the inside

surface before covering the wall with gypsum wallboard. Two basic methods are referenced here:

( 1 ) Rigid foam insulation over, between, or beneath furring strips. ^ Rigid foam insulation beneath 0. 75-in furring strips is preferred in

this report because it reduces insulation cutting and fitting time.

This cost is for the structural modifications only since the actual inside

finished area is assumed to remain constant. Based on Means Building Construction Cost Data, 1980 , this cost includes the extension of footings,

slab, walls, and roof.

ASHRAE Handbook of Fundamentals , p. 358. In fact, this R-value varies

between 2.8 and 3.6 (ft^)(h)(°F) /Bt u depending on the mean temperature of

the air space and the temperature differential across the air space. However, dynamic changes in the resistance of the air space cannot currently be

modeled by the NBSLD computer program. Convection currents (i.e., air circulation) within the furring (stud) space can significantly reduce the effective resistance of any insulating method. The extent to which convection

currents reduce the effective resistance of the reflective foil is not

known

.

Alternatively, the furring strips can be eliminated (except at the top and

bottom of the wall), and the wallboard can be glued directly to the foam

insulation. This will reduce the cost of insulating with rigid foam but may

reduce wall performance over time and increase wiring costs. As a result,

it is not considered further in this report.

14
reduces thermal bridging, and provides an air space that can be used

with foil-backed gypsum board, thereby reducing costs and increasing

wall performance relative to the other two approaches. This approach

is currently finding widespread use in Florida.

(2 ) Framing with free-standing 2 x 3-in studs in place of furring strips

and insulating with mineral wool batts . While this second approach

may appear redundant (in terras of creating a second "wall")* it is

generally less costly than the first approach for two reasons: (i)

mineral wool insulation materials (in standard sizes, e.g., R-11,

R-19) are much less expensive than rigid foam insulation materials

per unit of thermal resistance; and (ii) much of the cost of the

framing is offset by omitting the furring strips. Typically, R-11

mineral wool insulation would be the sraallest insulation resistance

used with this approach since the cost differential above lower

R-values (e.g., R-7 ) is relatively small. In such a case, the

interior framing would stand away from the block wall approximately 1 inch in order to accomodate the standard 3.5-in, R-11

insulation batts without compression. By moving the framing out

further from the wall, R-19 or greater resistances can be used in

a similar manner.

Table 4 shows several levels of thermal resistance for both methods used with

8-in block walls, along with corresponding U-values and estimated installed

costs. Table 5 shows similar data for brick and block walls.

2.2.1.2 Insulation in Cavity (Brick and Block Walls)

Only rigid foam insulation is considered for insulating the cavity area of a brick and block wall in this report. A 1-in air space between the insulation

and the outer wall is recommended to avoid moisture penetration from the outside wall.-*- (Moisture-resistant, loose-fill insulating materials are also

sometimes poured into the cavity. However the R-value per inch for these

loose-fill materials is typically less than half that of rigid foam insulation,

with a higher cost per unit of resistance.) Maximum cavity width depends on

the wall design. However, 4.5 -in is considered to be a practical maximum.

2

Thus, with a rigid foam insulation having an R-value per inch of approximately

5.25 (f t^ ) (h) ( °F) /Btu (e.g., extruded polystyrene), a maximum practical insulation R-value would be approximately R-18. (Some rigid foam insulation materials have R-values per inch as high as 7.0 (f t2)(h)( ''F)/Btu .) Since this

insulation is located toward the outside of much of the wall mass, its thermal

performance can be expected to be somewhat greater than the same insulation

resistance on the inside surface of the wall.

^ "BIA Technical Notes on Brick Construction - 21," Brick Institute of America,

McLean, Va

.

2 Ibid.

15
Table 4, Insulation Levels Examined and Cost Data for

Insulation in 8-in Block Walls

Insulation

Resistance U-vaiue

De scription (^rf^Mn^v. J:';/Dtu iitu/ t^ MnM r ) LO S L/ r t

Base Case (0,75-in air space 0.242 0

and u.j-in waiiboara;

Foil-backed wallboard K~J U . i dZ t n in . i U

Mineral Wool in R-11 0.074 $0.75

2 X 3-in framing^

R-13 0.066 $0.80

R-19 0.046 $1 .00

Rigid Foam on Inside Surface K~ / $U .o i (R-value includes R-3

foil-backed wallboard) R-9 0.082 $0.76

R-12 0.066 $1.00

R-15 0.055 $1.23

R-18 0.047 $1.46

Loose fill in cores R-12.

5

0.112 $0.63

^ Framing or furring area equals approximately 10 percent of net wall area. Costs include adjustment for decreased floor area.

16
Table 5. Insulation Levels Examined and Cost Data for

Insulation in Brick and Block Walls

Insulation

Description

Resistance

{ft^)(,h){ F)/Btu

U-value

Btu/(f f^^ChX F) Cos t/ f t^

Base Case (0.75-in air space

and 0.3-in wallboard;

0.201 0

A. Insulation on Inside

Foil-back wallboard R-3 0. 142 $0. 10

1. Mineral Wool in

2 X 3-in framing

R-13

r\ n "7 n U. U/U

0. 062

$U. /5

$0. 80

R-19 0. 045 $1. 00

2. Rigid Foam (R-value

includes R-3 foilback wallboard;

R-7

R-y

0.091

U. U/ /

$0.61

$U. / b

R-i Z U. UoZ $ 1 . UU

R-15 0. 053 $1. 23

R-18 0. 045 $1. 46

B. Insulation in Cavity

1. Rigid Foam R-4 0. Ill $0.51

R-6 0.091 $0.66

R-9 0.071 $0.90

R-12 0.059 $1. 13

R-15 0.050 $1.36

R-18 0.043 $1.57

17
Insulation resistance levels in the cavity of a brick and block wall that are examined in this report are shown in part B of table 5, along with estimated

1980 insulation cost data.

2.2.1.3 Insulation in Cores (Concrete Block Walls)

Loose-fill insulation (e.g., perlite or vermiculite) can be poured into the

hollow cores of concrete blocks during construction. However, the effectiveness of such an insulating technique is somewhat limited because of the thermal

bridging between cores. (Approximately 29 percent of the cross section of the

8-in block wall modeled is solid concrete.) Perlite has a somewhat higher

resistance value per inch of thickness than vermiculite (approximately 2.7 vs. 2.2 (f t^) (h)

(

°F) /Btu) and thus the former is modeled in the thermal analysis.

While poured insulation may be practical in the cores of 8-in blocks, it is

not considered practical in the smaller cores of the 4-in blocks used in brick

and block walls because of its relatively high cost per effective resistance

unit (R).

A cost of $0.63/ft^ of wall area is estimated for poured insulation in 8-in

block walls, based on Means. ^ The use of perlite insulation reduces the

U-value of an otherwise uninsulated 8-in block wall from approximately 0.242

to 0.112 Btu/( f t^) (h) ( °F) . ^ Note, however, that a greater reduction in

U-value can be achieved at lower cost by insulating the wall on the inside.

Table 5 shows that a U-value of 0.091 Btu/(ft2)(h)(°F), using rigid foam insulation plus reflective foil wallboard, costs only about $0.58 per square foot.

Rigid foam inserts which can be placed in the cores of 8-in blocks are also

available. However, insufficient thermal performance data are available at

this time to adequately model the use of such inserts. Thus these inserts are

not evaluated in this report.

2.2.1.4 Insulation on the Outside Surface

Rigid foam insulation can be placed on the outer surface of a masonry wall in

order to enhance the thermal storage characteristics of the walls. However,

this requires that the insulation be covered with a weatherproof covering

(e.g., stucco or aluminum siding) at considerable additional cost. Since a major benefit of masonry walls is low exterior maintenance, this additional

covering serves little purpose other than to protect the insulation. In such

a case, exterior insulation is difficult to justify on a cost effectiveness

basis relative to the insulation methods discussed above, despite its somewhat

Means Building Construction Cost Data, 1980 .

See table 4.

See B. Peavy, F. Powell and D. Burch, Dynamic Thermal Performance of an Experimental Masonry Building , NBS BSS 45 (Washington, D.C.: National Bureau

of Standards, 1972).

18
enhanced thermal performance. For this reason it has not been explicitly

evaluated in this report. (Some insight into the superior performance of

insulation on the outside wall surface can be gained from examination of the

cavity-insulated brick and block wall.)

2.2.2 Insulation in Wood-Frame Walls

As mentioned in the introduction, wood-frame walls have a natural advantage

over load-bearing masonry walls when insulation is considered because of the

empty stud space between the exterior sheathing and inside paneling. Since

this stud space is open during construction, mineral wool insulation batts can be easily and relatively inexpensively installed at that time. Typically,

R-11 mineral wool insulation is used in a nominal 2 x 4-in stud space because

it has been engineered to fit snugly into a 3.5-in stud space having 16- or 24-in stud centers. A denser R-13 mineral wool batt is also produced to fit

into the same space. In general, no less than R-11 insulation is recommended

for use in wood-frame walls for two reasons: (1) if the stud space is not

filled, convection currents tend to degrade the actual performance of the

wall;^ and (2) the extra cost involved in using R-11 mineral wool insulation

relative to some lower level (e.g., R-7 ) is usually quite small so that the

R-11 insulation tends to be more cost effective (in terms of reducing energy

costs) than the lower level.

In order to increase the thermal resistance of a wood-frame wall beyond R-13,

two basic options are available:

(1) The use of nominal 2 x 6-in studs in place of 2 x 4-in studs, which

allows the use of a thicker insulation batt. (The additional framing

cost can be minimized if the 2 x 6-in studs are placed 24-in on center, which also reduces thermal bridging.) Typically, a 6-in, R-19

mineral wool batt is used in this case. However, since the actual stud

space is only 5.5 in, this results in a slight compression of the batt,

thereby reducing its effective thermal resistance to R-18.-^

(2) The use of rigid foam insulation (e.g., polystyrene or polyisocyanurate)

instead of the more conventional asphalt-impregnated fiberboard sheathing. This rigid insulation is available in several thicknesses and

If the exterior covering is justified primarily for aesthetic, rather than

protective, purposes (i.e., it would have been used whether or not the exterior wall was to be insulated) , this approach would more likely be preferred

to the use of rigid foam insulation on the inside wall surface.

G. J. Tietsma and B. A. Peavy , The Thermal Performance of a Two-Bedroom

Mobile Home , NBS BSS 102 (Washington, D.C.: National Bureau of Standards,

1978).

Based on private correspondence with a representative of the Owens-Corning

Fiberglas Corporation.

19
resistance values. It can be used in conjunction with 2 x 4-in studs

and mineral wool insulation to achieve a total insulation resistance

approximately equivalent to that using 2 x 6-in studs and R-19 mineral

wool batts. Or it can be used with 2 x 6-in studs and R-19 mineral

wool batts to increase the total insulation resistance significantly

beyond the 2 x 6-in stud wall with conventional sheathing (e.g., R-23

to R-27).

Rigid foam insulation typically costs three or four times more per resistance

unit than mineral wool batts (although the substitution for the conventional

sheathing reduces its effective cost in this application somewhat) . At the same time, the increased cost of 2 x 6-in studs instead of 2 x 4-in studs must

be attributed to the insulation cost if R-19 mineral wool batts are used. As

a result, the cost per unit of resistance above R-13 is typically significantly

higher than the unit cost below R-13.

Table 6 shows five alternative levels of insulation for wood-frame walls

examined in this report, along with the corresponding overall wall U-value and

representative 1980 insulation costs. In table 6, the R-18 insulation level is

based on R-13 mineral wool plus R-5 rigid foam sheathing, since the cost of

this system is shown to be less than using 2 x 6-in studs and R-19 mineral

wool. However, in some cases, the latter system may have a cost advantage

over the former. For either case, the resulting U-value for the net wall area

is approximately the same.

20
Table 6. Insulation Levels Examined and Cost Data for

Insulation in Wood-Frame Walls

uefacripu-L on

Insulation

Resistance

<'fi-2wuV°F'> \TZ j\njK r /R^1l J

/

DLU

U-value

n LU/ \1L J Kiij ^ V ) Cost

Base Case (3.5-in air space) 0.213 $ 0

Foil-backed wallboard R-3 0.152 $0. 10

Mineral Wool R-11 0.078 $0.30

R-13 0.071 $0.35

«R-19a 0.055 $0.55

Mineral Wool (R-18 plus

Rigid Foam Sheathing (R-5)) «R-23 0.045 $0.90

^ R-19 mineral wool in a nominal 2 x 6-in stud wall compresses to R-18.

21
Facing page: To calculate the thermal

response of walls of significantly different

weights and construction types, a dynamic

simulation program such as NBSLD was needed.

22
3. THERMAL ANALYSIS PROCEDURES

In this section, the basic modeling procedures used to calculate the reduction

in space heating and cooling loads attributable to the various levels of insulation examined are discussed. This includes a description of the prototypical

house used in the thermal analysis, the NBSLD computer program used to calculate space heating and cooling loads, and the climate data used to represent

different geographic locations.

23
3.1 DESCRIPTION OF SINGLE-FAMILY HOUSE PROTOTYPE

In order to calculate accurately the effects of wall insulation on annual

heating and cooling requirements, it is necessary to model the building in

which the walls to be insulated are located. Table 7 provides the basic specifications of an 1176 ft^, one-story, single-family house used in the NBSLD

simulation of space heating and cooling requirements. This house, shown in

figure 2. is modeled after the "compact" ranch-style house proposed by S. R.

Hastings^ as typical of one-story, single-family houses built in the United

States, although it is somewhat smaller than the average house size of approximately 1500 ft^. (However, the average figure includes multistory houses as well.) The house is modeled as one room^as it has been determined through

previous analysis at NBS^ that this method more closely approaches the actual

thermal performance of a single-story house than modeling uncoupled rooms within the house. (Thermal coupling of rooms is a difficult problem and has

not yet been incorporated into the NBSLD computer program.) The ceiling is

modeled with an insulated attic; the level of insulation depends on the climatic location examined. The floor is modeled as a concrete slab weighing

20,000 lb and is essentially adiabatic (i.e., does not transmit heat into the

ground) .-^ This floor weight was selected to represent the internal mass of

the house, including internal partitions, fixtures, and furnishings, rather

than an actual slab on grade. As a result, the building modeled is more

representative of a house over a heated basement or well-insulated crawl space

than a house actually built on a concrete floor slab. The house has approximately 0.6 air changes per hour at an outdoor temperature of 45 "F and a wind

speed of 7.5 miles per hour. However, the actual air change rate in any hour

is dependent upon the inside-outside temperature differential and wind speed.

The base house is oriented with the long walls facing north and south. Of the

127 ft^ of glass area, 72 ft^ face south and 55 ft^ face north. (The glass to

gross wall area ratio is approximately 11 percent.) The south-facing glass

includes a sliding glass door.

Operational assumptions are shown in table 8. Note that a night setback from

68° to 60°F is assumed during the heating season. This night setback, together

with the internal mass and south-facing windows, gives the house some advantage

from a "passive" solar aspect. The hourly internal heat release profile is

also shown in table 8.

S. R. Hastings, Three Proposed Typical House Designs for Energy Conservation

Research , NBSIR 77-1309 (Washington, D.C.: National Bureau of Standards,

1977).

See S. R. Petersen and J. P. Barnett, Expanded NBSLD Output for Analysis of

Thermal Performance .

This is accomplished by modeling a very high thermal resistance beneath the

slab in order to isolate it from the ground temperature.

24
Table 7. Prototype House Parameters^

Floor and ceiling areas = 1176 f t^

Glass area = 127 ft^ (72 ft^ south, 55 ft^ north)

Wall area: gross (including windows and doors) = 1120 ft^

net = 973 ft^

Wood door (1) =20 ft^

Outside dimensions = 28 ft x 42 ft

Solar absorptance of exterior walls = 0.50

Floor weight = 20,000 Ib^

Shading coefficients for glass: single = 0.8, double = 0.7,

triple = 0.6.

^ Based on ranch house design in S . R. Hastings, Three Proposed

Typical House Designs.

^ Representative of interior mass of house.

25
0)

•H

„0--83

26
Table 8. Operational Profile of Prototype House

Thermostat settings:^

Heating Periods: 68°F day

60°F night (11 p.m. - 7 a.m.)

Cooling Periods: 78°F

Relative Humidity:^

Lower Bound 20%

Upper Bound 60%

Occupants: 2 adults, 2 children

Hourly Lighting, Equipment, and Occupant Heat Release

Schedule (Btu/h)

Hour Lights Equipment Occupants

1 0 703 1200

2 0 703 1200

3 0 703 1200

4 0 703 1200

5 0 703 1200

6 0 1984 1200

7 2088 2935 1200

8 2088 3927 1200

9 48 2356 480

10 48 2522 480

11 48 2356 480

12 48 3638 480

13 48 2563 480

14 48 1984 480

15 48 1984 480

16 48 2108 828

17 48 1984 828

18 48 2687 1200

19 48 2894 1200

20 1044 3349 1200

21 1044 4134 1200

22 2088 2563 1200

23 2088 2894 1200

24 2088 1984 1200

No cooling or heating is required when indoor temperature is

between heating and cooling thermostat settings.

Humidif ication is assumed during heating periods only,

dehiamidif ication is assumed during cooling periods only.

27
Since this study is limited to the analysis of wall insulation, the

specification of the other shell components was held constant for each of the

11 geographic locations examined in this report. However, attic insulation

levels and window glazing specifications (e.g., single, double, triple) were

adjusted in each location in order to conform approximately with 1978 HUD

Minimum Property Standards^ for those locations. Table 9 provides these specifications for each of the 11 locations considered in this report. Details

regarding the selection of these 11 locations are provided in section 3.3.

3.2 THERMAL MODELING PROCEDURES

NBSLD-X0,2 an expanded output version of the National Bureau of Standards Load

Determination Program, NBSLD,-^ was used to simulate the heating and cooling

loads of the prototype house with its various wall modifications on an hourly

basis for an entire year. Test Reference Year (TRY)^ weather tapes were used

to provide typical hourly climate data for the locations considered, consistent

with the requirements of the basic NBSLD program. The annual heating requirements and annual cooling requirements reported represent the thermal energy

output to the conditioned space from the heating and cooling equipment. Actual

purchased energy requirements are calculated outside of the NBSLD simulation,

based on estimates of seasonal heating and cooling equipment efficiencies.

Because NBSLD can calculate the thermal response of walls of significantly

different weights and construction types to a relatively high degree of accuracy, this program is well suited for the thermal analyses needed for a study of

this nature. In addition, it has been successfully validated in a number of

studies at NBS and elsewhere.^

U.S. Department of Housing and Urban Development, "Minimum Property Standards

for One- and Two-Family Dwellings."

S. R. Petersen and J. P. Barnett, Expanded NBSLD Output for Analysis of

Thermal Performance .

T. Kusuda, NBSLD, The Computer Program for Heating and Cooling Loads .

E. Stamper, "Weather Data."

NBS studies include: B. Peavy, F. Powell and D. Burch, Dynamic Thermal

Performance of an Experimental Masonry Building ; and B. Peavy, D. Burch,

F. Powell and C. M. Hunt, Comparison of Measured and Computer-Predicted

Thermal Performance of a Four Bedroom Wood-Frame Townhouse , NBS BSS 57

(Washington, D.C,: National Bureau of Standards, 1973). Other studies

include Roberts, Nail, Rogers and Greenburg, "Comparison of ComputerPredicted Thermal Loads with Measured Data from Three Occupied Townhouses ,

ASHRAE Transactions , Vol. 83, Part I (New York: American Society of Heating,

Refrigerating and Air Conditioning Engineers, Inc., 1978).

28
Table 9. Attic and Window Glazing Specifications by City

Window

Glazing

Attic Insulation

Al bany Double R-30

Albuquerque Double R-30

Atlanta Single R-19

Indianapolis Double R-30

Jackson Single R-19

Jacksonville Single R-19

Madison Triple R-38

Phoenix Single R-19

Salt Lake City Double R-30

Tampa Single R-19

Washington, D.C, Double R-30

29
Three specific changes to the standard NBSLD program were made to improve the

modeling of heating and cooling loads for the prototype house: (1) All glass

areas of the house are assumed to be 50 percent shaded from May through September. (2) The direct solar heat gain is modeled so that 90 percent is distributed directly to the floor, with the remaining 10 percent evenly distributed

to the other interior surfaces. This solar distribution in effect simulates

the solar gain of interior partitions and furniture rather than of the inside

of the exterior surfaces of the house when the house is modeled as a single

room. (3) Cooling loads are divided into two parts: those cooling loads which

occur when the outdoor temperature falls below the thermostat setting and those

cooling loads which occur when the outdoor temperature is equal to or greater

than the thermostat setting (78°F). This distinction is important because the

direction of heat flow through the walls during cooling periods depends in part

on whether the outdoor temperature is higher or lower than the inside temperature. When heat flow is outward during cooling periods, increased thermal

resistance will increase cooling loads rather than reduce them. Moreover,

when the outdoor temperature is lower than the indoor temperature, cooling

loads can often be eliminated by increased natural ventilation.

3.3 CLIMATIC VARIATION CONSIDERATIONS

Eleven locations were selected for the NBSLD analysis of space heating and

cooling loads. These locations are shown in table 10, along with heating

degree day and cooling degree hour data calculated from the Test Reference Year

weather tapes used in the analysis. (Two different calculation bases are shown

for both heating degree days and cooling degree hours, as it will be shown in

section 4.4 that the second calculation base in each case is useful in interpolating annual heating and cooling requirements to other locations in the

United States.) Four of these eleven locations were selected because they are located in the south and southwest regions of the United States where the use

of concrete block construction is common (Tampa, Jacksonville, Phoenix^and

Albuquerque). The other locations were selected to provide a broader range of

climate data for the thermal analysis. Even though it is recognized that loadbearing masonry wall construction is not common in single-family houses in many

regions of the United States, the more complete data base that results may provide useful information to some potential users of this report, such as standards-making organizations.

The most comprehensive NBSLD analyses of the different wall parameters examined

in this report, including changes in thermal resistance, mass, and color, were

performed for the Washington, D.C. climate. This location was selected because

it represents an approximate average heating climate and cooling climate in the

United States.^ For the brick and block walls, only 8 of the 11 locations

were included in the analysis due to resource constraints. All calculations

Edward A. Arens and William L. Carroll, Geographical Variation in the

Heating and Cooling Requirements of a Typical Single-Family House, and

Correlation of These Requirements to Degree Days , NBS BSS 116 (Washington,

D.C: National Bureau of Standards, November 1978), p. 18.

30
Table 10. Heating Degree Days and Cooling Degree Hours Based on Test Reference Year (TRY) Data

Heating Degree Days Cooling Degree Hours

Location Base 65°F Base 55°F Base 65°F Base 78°F

Albany 7118 4638 16742 1872

Albuquerque 4397 2408 35970 8054

Atlanta 2959 1370 36104 4525

Indianapolis 5886 3719 26320 3854

Jackson 2352 1025 59926 13547

Jacksonville 1239 327 65667 11827

Madison 7311 4765 15911 2239

Phoenix 1571 404 90743 37907

Salt Lake City 6216 3928 30367 7784

Tampa 459 57 76663 12904

Washington, D.C« 4162 2185 37589 7668

31
of annual heating and cooling requirements are based on the entire year

analysis and are not adjusted to remove heating or cooling requirements

occuring out of season.

Facing page: One of the types of insulation

materials considered in this study was rigid

foam.

32
4. THERMAL ANALYSIS OF WALL INSULATION

In this section, the energy savings attributable to reductions in the U-value

of each wall type described in section 3.1 are calculated using the NBS Load

Determination (NBSLD) program and Test Reference Year (TRY) climate data. In

order to reduce the total number of runs needed for a complete analysis of each

case considered, and to provide a more generally useful data set, NBSLD runs

were made only to establish the specific relationship between the thermal performance of the wall and wall U-values for each wall type and climate. Based

on these specific relationships, the wall performance corresponding to any wall

U-value (in the same general range) for a given wall type, climate, and

insulation method can be accurately estimated.

33
A description of the U-values and corresponding insulation resistance levels

actually analyzed using NBSLD, the resulting annual heating and cooling

requirements, and some implications for wall design are discussed in this

section.

4.1 INSULATION IN 8-IN BLOCK WALLS

4.1.1 Base Case (Open Cores, 100 Ib/ft^ Concrete, a =0.50)

Table 11 lists the annual heating and cooling requirements (AHR, ACR) of the

single-family prototype house with the basic 8-in concrete block walls (i.e.,

open cores, 100 Ib/ft^ concrete density, solar absorptance of exterior sur- face = 0.50) for each of the 11 locations shown in table 10. In Washington,

D.C., 5 different U-values were modeled; in the remaining 10 cities, 3

U-values were modeled. The U-values used were selected to establish a general

relationship between AHR, ACR, and wall U-value. The AHR and ACR corresponding

to intermediate U-values can be found by interpolation. In addition, moderate

extrapolation to lower U-values will provide useful results.

The relationships between AHR and U-value and ACR and U-value are shown in

figure 3 for the 8-in block wall in Washington, D. C . Note that AHR are characterized by a straight line, while there is a slight curvature in the ACR

lines. The results for all 11 cities are shown graphically in figures B.l

through B.ll in appendix B. In general, they are also characterized by a linear AHR function and slightly curved ACR relationships.

As discussed in section 3.2, ACR are divided into two parts: ACR"^ include only

cooling loads that occur when the outdoor temperature is equal to or greater

than the air conditioner thermostat setting (78°F); ACR~ include only cooling

loads that occur when the outdoor temperature is below the thermostat setpoint.

These latter cooling requirements result when heat losses through the shell of

the house are insufficient to offset the internal heat gain from occupants,

lights, appliances, and solar heat gain through windows.

As the walls are better insulated, ACR"*" generally decrease, although only

slightly in most cases. At the same time, ACR~ tend to increase, and generally

offset any decrease in ACR"*", so that their sum, ACR''^, tends to increase as well. The only exception to the trends observed in the 11 locations examined

is Phoenix, where the increase in wall insulation does result in a significant

decrease in ACR*^, due to the extremely high daily temperatures during much of

the cooling season in southwestern desert locations. When only the months of

April through October are evaluated (i.e., assuming that the air conditioning

equipment is not operating between November and March) , ACR''^ in Jackson,

Jacksonville, and Tampa decrease as insulation levels in walls are increased.

In the remaining cities studied, ACR''^ increase slightly as the walls are better

insulated.

If windows are assumed to be closed at all times, ACR^ better represent annual

cooling requirements. If windows are opened for natural ventilation when the

outdoor temperature (t^) is below 78°F, ACR^ are better. In fact, actual operating practices are usually somewhere between these two extremes. For example.

34
Table 11. Annual Heating and Cooling Requirements for Prototype House: 8-in Block Walls, No Insulation in Cores

Annual Space Heating and

Cooling^ Requirements

(million Btu)

Overall Wall R-value in U-value Furr ing Space

Location Btu/(ft2)(h)(°F) (f )(h)(°F)/Btu AHR ACR"*" ACR" acrT

Albany 0. 2417 0. 96 51.33 3.10 3.13 6. 23

0. 1443 3. 75 39.46 3. 11 3.86 6. 97 0.0693 1 1. 25 30.07 3. 16 4.73 7. 89

Albuquerque 0. 2417 0. 96 21.89 9. 06 3. 94 13. 00

0. 1443 3. 75 15.28 8.72 4.69 13. 40 0.0693 11. 25 10.33 8.55 5,61 14. 15

Atlanta 0. 2417 0. 96 16.81 9. 37 7.43 16. 80 0.1443 3, 75 12.55 9.22 8.48 17. 70 0.0693 1 1

.

25 9.36 9. 18 9.49 18. 68

Indianapolis 0. 2417 0. 96 41 . 34 6. 32 4. 34 10. 65 0.1443 3. 75 31.26 6. 18 5, 10 11. 28 0.0693 1 1

.

25 23.35 6. 14 6.04 12. 17

Jackson 0. 2417 0. 96 12.46 1 9. 59 8.14 27. 74

0. 1443 3. 75 9.11 18.97 8.87 27, 84 0.0693 1 1

.

25 6,63 18.56 9.58 28, 14

Jacksonville 0.2417 0. 96 3. 50 21.66 11.05 32, 71

0. 1443 3. 75 2.27 21.21 12.01 33, 22 0.0693 1 1

.

25 1.47 20.94 13,03 J J , Q 7

Madison 0. 2417 0. 96 48. 71 3.17 2,20 5. 37

0. 1443 3. 75 36.23 3.17 2,95 6. 12 0.0693 1 1

.

25 26.41 3.21 3,97 7

1 B

Phoenix 0.2417 0. 96 3. 93 36. 44 5, 57 42. 01

0. 1443 3. 75 2. 56 33. 84 6, 30 40. 14

0. 0693 11. 25 1 . 68 31 . 86 7 , 09 38. 96

Salt Lake City 0.2417 0. 96 39.82 7.91 2.84 10. 76

0. 1443 3. 75 29.51 7.76 3,33 11. 09 0.0693 11. 25 21.45 7.73 3.92 11. 65

Tampa 0.2417 0. 96 0.82 24.26 13.91 38. 16 0.1443 3. 75 0.47 23.79 15. 15 38. 94 0.0693 11. 25 0.28 23.51 16.29 39. 80

Washington, D,C. 0.2417 0. 96 21.53 10.70 4.97 15. 67

0. 1618 3. 00 16. 10 10.34 5.53 15. 86

0. 1443 3. 75 14.92 10.26 5.68 15. 94 0.0936 7. 50 11.55 10.06 6.20 16. 27 0.0693 11. 25 9.96 9.98 6.52 16. 49

^ ACrT = ACR"*" + ACR~.

Air space (0.75 in) has an R-value of approximately 0.96 (f t^ ) (h) ( °F ) /Btu.

Insulation density actually modeled is 2.2 lb/ft2 with an R-value per inch

of 5.0 (ft2)(h)(°F)/Btu.

35

during spring and fall, windows and doors may be left open for natural

ventilation more frequently than during the summer months. However, noise,

humidity, air pollution, and security considerations may encourage leaving

windows closed more than they might be otherwise, especially in urban areas.

As a result, the net effect of increasing wall insulation in many houses is

likely to be insignificant in terms of decreasing or increasing actual ACR,

depending largely on how the house is operated by its occupants during the

year.

Note that no simple summation of AHR and ACR to compute total space heating and

cooling requirements is provided. Such a total would be relatively meaningless

since it does not correspond to the actual purchased energy needed to satisfy

these total requirements, due to differences in furnace and air conditioner

efficiencies. Nor would such a total recognize the difference in price (nor resource energy requirements) if different energy types were used for heating

and cooling (e.g., natural gas and electricity, respectively). The combined

effects of both AHR and ACR are best quantified in terms of present-value,

life-cycle dollar expenditures for energy used in space conditioning.^

Thermal insulation materials are generally of relatively low density (0.75 to

3.5 Ib/ft-^ for most rigid foam and mineral wool insulating materials) compared

to masonry materials. Variations in insulation density in this range will not

have a significant effect on wall performance, given equal thermal resistance.

Thus the AHR and ACR corresponding to other insulation types than the rigid

foam insulation modeled can also be interpolated using the data in table 11,

provided that the thermal resistance is known and its relative placement in

the wall is the same.

Because the weight of the 8-in concrete block walls (38.3 Ib/ft^ of wall area)

is nearly identical to the weight of brick veneer walls (4-in face brick on wood-frame walls), the AHR and ACR shown in table 11 will be appropriate to use for brick veneer walls as well.

4.1.2 Solar Absorptance Variations

The solar absorptance (a) of the exterior wall surface can have a significant effect on the thermal performance of walls. In general, one would expect that darker colored walls, having a higher solar absorptance,

would lose less heat during the heating season and gain more heat during the

cooling season than lighter colored walls. These expectations are borne out

in the results of the additional thermal analysis of 8-in block walls with an

a of 0.25 and 0.75, corresponding to a very light and a moderately dark colored

wall, respectively. (Appendix C provides a short guide to the correspondence

between surface color and solar absorptance.)

Table 12 provides the calculated AHR and ACR for the prototype house with

exterior walls having an a of 0.25 for 8 of the 11 locations examined in

This will be discussed further in section 5.

37
Table 12. Annual Heating and Cooling Requirements for Prototype House:

8-in Block Walls, a = 0.25

Annual Space Heating and

Cooling^ Requirements

(million Btu)

Overall Wall R-value in

U-value Furring Space

Location Btu/(ft2)(h)(°F) (ft2)(h)(°F)/Btu AHR ACR"'" ACR" acrT

Albuquerque 0.2417 0.96 23.01 8.27 3.37 11.64

0.0693 11.25 10.59 8.33 5.34 13.66

Atlanta A O A 1 7 U. Z^i

/

u. yb 1 "7 /. r\ 1 / . 4U O "7 "7 O. / / C {LI. 1 C /.I 15.41

0. 0693 11.25 9. 50 9. 02 r\ 1 "7 9.17 18.19

Indianapolis 0.2417 0.96 42.22 5.87 3.87 9.73

0.0693 11.25 23.57 6.01 5.81 11.82

Jacksonville 0.2417 0.96 3.73 20.80 10.28 31.08

0.0693 11.25 1.51 20.71 12.72 33.43

Madison 0.2417 0.96 49.76 2.90 1.81 4.71

0.0693 11.25 26.68 3.14 3.76 6.90

Phoenix 0.2417 0.96 4.31 34.56 k.ll 39.28

0.0693 11.25 1.75 31.32 6.73 38.06

Tampa 0.2417 0.96 0.89 23.46 13.17 36.62

0.0693 11.25 0.28 23.29 16.01 39.30

Washington, D,C. 0.2417 0.96 22.24 10.10 4.53 14.63

0. 1443 3.75 15.31 9.90 5.34 15.24

0.0693 11.25 10.13 9.81 6.32 16.12

a ACRT = ACR"*" + ACR-.

38
this report. Table 13 provides the calculated AHR and ACR corresponding to an

a of 0.75 for the same eight locations. Annual cooling requirements for the

prototype house with walls having an a of 0.25 and a U-value of approximately

0.10 Btu/ (f t^) (h) ( °F) on the average are decreased by 3 percent from that

of the a = 0.5 base case. The AHR are on the average increased by 2 percent.

The ACR for the same house with walls having an a of 0.75 and a U-value of

approximately 0.10 Btu/ (f t^ ) (h) ( °F) on the average are increased by 3 percent from that of the a = 0.5 base case and the AHR are decreased by 2 percent. Figure 4 shows the effect of solar absorptance on AHR and ACR for

the prototype house with 8-in block walls in the Washington, D C climate.

Variations in AHR and ACR that are attributable to differences in solar

absorptance could be important if they resulted in a significant change in the

expected energy savings due to the increased use of insulation. As would be

expected, the data in tables 12 and 13 show that the reductions in AHR due to

insulating the walls will be less for the darker colored walls (a = 0.75) and

more for the lighter colored walls (a = 0.25). On the average, the reductions in AHR due to insulating an 8-in block wall with R-11.25 insulation

are increased by 7 percent for the lighter wall and reduced by 7 percent

on the darker wall, with smaller effects in the colder climates and larger

effects in those climates with milder winters. When the lighter color wall

is insulated as shown in table 12, ACR"^ increase in four of the locations

(Albuquerque, Atlanta, Indianapolis, and Madison), although insignificantly.

Reductions in ACR"^ in the remaining locations also tend to be insignificant,

except in Phoenix. When the darker wall is insulated, as shown in table 13,

ACR"*" decrease in all cases. ACR"^ for the lighter wall tend to increase

slightly more than for the medium- colored wall as insulation is added, while

for the darker wall, ACR^ increase less. However, it is unlikely that these

changes will have an effect on the optimal insulation level except in

borderline cases. This will be discussed further in section 5.

While the effects of color will not likely affect the optimal level of

insulation, careful consideration of wall color can improve the overall thermal

performance of exterior walls in climates dominated by either space heating or space cooling requirements. However, if annual heating and cooling requirements are of the same order of magnitude, the seasonal effects of wall color

tend to be offsetting.

4.1.3 Concrete Density Variations

As seen in table 1, the use of lightweight concrete (80 Ib/ft-^) instead of

medium-weight concrete (100 Ib/ft^) will reduce the weight of the 8-in block

wall from 38.3 Ib/ft^ to 31.0 Ib/ft^ of wall area.l Likewise, the use of

heavyweight concrete (120 Ib/ft-^) will increase the weight of the 8-block wall

to 45.5 Ib/ft^ of wall area. Since the weight of the wall is expected to

affect its thermal performance, several simulations were run for the prototype

All wall weights are approximate, depending on the ratio of empty core to

solid volume.

39
Table 13. Annual Heating and Cooling Requirements for Prototype House:

8-in Block Walls, a = 0.75

Annual Space Heating and

Cooling^ Requirements

(million Btu)

Location

Overall Wall

U-value

Btu/(ft2)(h)(°F)

R-value in

Furring Space

(ft2)(h)(°F)/Btu AHR ACR+ ACR~ acrT

Albuquerque 0.2417

0.0693

0.96

11.25

20.83

10.08

9.86

8.77

4.57

5.88

14.42

14.65

Atlanta 0.2417

0.0693

0.96

11.25

16.24

9.22

9.97

9.35

8.26

9.81

18.23

19. 16

Indianapolis 0.2417

0.0693

0.96

11.25

40.48

23. 12

6.77

6.26

4,85

6.26

11.62

12.52

Jacksonville 0.2417

0. 0693

0.96

11.25

3.28

1.43

22.51

21.17

11.84

13.35

34.35

34.52

Madison 0.2417

0.0693

0.96

11.25

47.68

26. 15

3.44

3.28

2.63

4. 18

6.07

7.46

Phoenix 0.2417

0.0693 , 0.96

11.25

3.60

1.60

38.31

32.40

6.51

7.46

44.81

39.87

Tampa 0.2417

0.0693

0.96

11.25

0.33

0.27

24.04

23.73

15.79

16.56

39.83

40.29

Washington, D,C 0.2417

0.1443

0.0693

0.96

3.75

11.25

20.82

14.55

9.81

11.30

10.61

10.14

5.40

6.03

6.72

16.70

16.64

16.87

a ACrT = ACR+ + ACR".

40
41
m

house in the Washington, D.C., climate with each of these three walls at three

different U-values. The results of these simulations are shown in table 14.

Because the U-value of the wall is increased as higher density concrete blocks

are used, the effect of weight alone on thermal performance is masked. In

order to consider the effects of weight alone, the AHR and ACR are interpolated

to common U-values of 0.1 and 0.25 Btu/( f t^) ( h)

( °F) in table 15. Here it can

be seen that these moderate changes in wall weight have very small effects on space heating and cooling requirements and no significant effect on the change

in AHR or ACR due to the use of additional insulation.

While the effect of mass alone on heat transfer through these three walls is

insignificant, the effects of concrete density on overall wall U-values and

the resulting effects on AHR are quite significant, especially for the uninsulated wall. The house with the heavier uninsulated wall (45.5 Ib/ft^) and

higher wall U-value (0.42 Btu/( f t^) ( h)

( °F) ) has AHR that are 27 percent greater

than the lighter uninsulated wall (31.0 Ib/ft^) with the lower U-value (0.31

Btu/(f t2)(h)(°F)). The house with heavier walls insulated to R-11.25 has AHR

that are only 3 percent greater than the house with lighter walls insulated

to the same level. These differences are almost entirely attributable to the

differences in wall U-value rather than wall weight. As a result, variations

in weight alone for the 8-in block walls are not examined in other locations.

However, the effects of changes in U-value on AHR and ACR can be calculated

by interpolation for other density values in this same range using the data

calculated for the 100 Ib/ft^ 8-in block walls.

This analysis of relatively moderate weight differences for masonry walls

implies that the use of stucco as an exterior surface material will not have

any significant impact on the thermal performance of walls other than in terms

of a change in U-value. For this reason, stucco exteriors have not been

explicitly analyzed in this report.

4.1.4 8-in Block Walls (Insulated Cores)

Table 16 lists the AHR and ACR for the 8-in block wall (a = 0.5, concrete

density = 100 Ib/ft^) with the cores empty (U = 0.2417 Btu/ (f t^ ) (h) ( °F) ) and

filled with poured insulation having an R-value per inch of 2.7 (ft2)(h)

(°F)/Btu (U = 0.1116 Btu/(ft2)(h)(°F)). (This is the approximate R-value

per inch of perlite insulation.) AHR and ACR were calculated for all 11

locations listed in table 10. Figure 5 shows graphically the results of this

analysis for the Washington, D.C.^ climate and contrasts these results with

those of the 8-in block wall with uninsulated cores. Figures B.l through

B.ll in appendix B show the corresponding results for all 11 locations.

Comparision of the two wall types shows that for the same wall U-value the

wall with insulated cores has slightly lower AHR and ACR. This is due to

the fact that the relative placement of insulation in the wall has been

changed. Both AHR and ACR"*" are reduced with the pouring of insulation in

the cores in all locations.

42
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43
Table 15. Calculation of AHR and ACR for Prototype House in Washington,

D.C.^ Interpolated to Same U-Values: 8-in Block Walls, Three

Concrete Densities

Annual Space Heating and

Cooling Requirements

(million Btu)

U-value

(Btu/(ft2)(h)(°F))

Concrete

Density

(Ib/ft^)

Wall

Weight

(lb/ft2) AHR ACR+ acrT

0.25 80 31.0 22.17 10.98 15.84

0.25 100 38.3 22.09 10.75 15.68

0.25 120 45.5 21.98 10.76 15.86

0.10 80 31.0 12.00 10.12 16.27

0.10 100 38.3 11.97 10.09 16.22

0.10 120 45.5 11.99 10.08 16.27

44
Table 16. Annual Heating and Cooling Requirements for Prototype House:

8-in Block Walls, Insulation in Cores^

Annual Space Heating and

Cooling" Requirements

(million Btu)

Overal 1 Wal

1

R ~ V d _L1 1Ll1 pC inJ.1L U-value Core

Location Btu/(ft2)(h)(°F) (ft2)(h)(°F)/Btu AHR ACR+ ACR~ acr'^

Albuquerque 0.2417 0.96 23.01 8.27 3.37 11.64

0.0693 11.25 10. 59 8. 33 5. 34 13. 66

Atlanta 0.2417 0.96 17.40 8.77 6.64 15.41

0.0693 11.25 9.50 9.02 9. 17 18. 19

Indianapolis 0.2417 0.96 42.22 5.87 3.87 9.73

0.0693 11.25 23.57 6.01 5.81 11.82

Jacksonville 0.2417 0.96 3.73 20.80 10.28 31.08

0.0693 11.25 1.51 20. 71 12. 72 33.43

Madison 0.2417 0.96 49.76 2.90 1.81 4.71

0.0693 11.25 26.68 3. 14 3.7b 6. 90

Phoenix 0.2417 0.96 4.31 34.56 4.72 39.28

0.0693 11.25 1.75 31.32 6.73 38.06

Tampa 0.2417 0.96 0.89 23.46 13.17 36.62

0.0693 11.25 0.28 23.29 16.01 39. 30

Washington, D,C. 0.2417 0.96 22.24 10. 10 4.53 14.63

0. 1443 3.75 15.31 9. 90 5.34 15.24

0.0693 11.25 10. 13 9.81 6.32 16.12

^ Perlite insulation in cores, R-value per inch = 2.7 (f t^X h)

( °F)/Btu.

b ACrT = ACR"*" + ACR".

45
46
4.2 INSULATION IN BRICK AND BLOCK WALLS

The construction detail of the brick and block wall modeled is provided in

table 2, At 61.7 Ib/ff^ of wall area it has considerably more thermal mass than the 8-in block wall and thus somewhat improved thermal performance for any

given overall U-value can be expected. In addition, the U-value of the uninsulated brick and block wa 11 (0.20 Btu/(ft2)(h)(°F)) is somewhat lower than that

of the basic uninsulated 8-in block wall (0.24 Btu/ (f t^) (h) ( °F) )

.

Two basic approaches to insulating the brick and block wall are considered

here: insulation on the inside wall surface, covered with 0.5-in gypsum wallboard, and insulation in the cavity (i.e., between the brick and the block).

It can be expected that the insulation in the cavity will perform better than

insulation on the inside wall surface, since the insulation is moved toward the

outside of the wall. Due to time and resource constraints, computer runs were

made for only 8 of the 11 locations shown in table 10 (Albany, Jackson, and

Salt Lake City were not included ),

4.2.1 Insulation on Inside Surface

Table 17 shows the AHR and ACR of the prototype house with brick and block

walls insulated on the inside wall surface for eight locations. This same data

is shown graphically for Washington, D.C.^in figure 6 and for all eight locations in figures B.12 through B.19 in appendix B. The results of the thermal

analysis of the basic 8-ln block wall are included in these figures so that the

thermal performance of the two wall types of different weights can be compared

at equivalent U-values. In general, the thermal performance of the brick and

block wall insulated on the inside surface is slightly better than that of the

8-ln block wall when insulated to the same overall U-value. While it appears

that the effect of wall weight on AHR and ACR diminishes as the wall U-value

decreases, it should be noted that this is due largely to the decreased importance of the wall in establishing the overall AHR and ACR. If the thermal performance of the wall alone is considered, the effect of wall weight in terms of

reducing heat loss through the wall over the heating season tends to remain

relatively constant as the U-value is changed. •'•

Except in the case of Phoenix, the changes in ACR"*" due to increased insulation

are insignificant. ACR*^ for the brick and block wall house tend to increase

slightly more than for the 8-in block wall as the wall U-value decreases.

Again, ACR"^ include cooling loads outside the normal air conditioning season.

It should be noted that the proportion of total heating or cooling

requirements due to heat transfer through the walls of the house modeled in

this report is not representative of a typical house since no floor losses

are calculated.

47
Table 17. Annual Heating and Cooling Requirements for Prototype House:

Brick and Block Walls, Insulation on Inside Surface

Annual Space Heating and

Cooling^ Requirements

(million Btu)

Location

Overall Wall

U-value

D«-,, 1 { f t-1\ ( \ f Btu/ (.rt^AnA v )

R-value in

Furring Space^

Ktt^ V )

1

Btu A UD AnK ACK ACR ACR^

Albuquerque 0.2007

U. i Zoo

0.0654

0.96

11.25

18.95

it. Uo

10.00

8.23

ft 9 o. ZD 8.34

4.35

A Q

1

t. y 1 5.69

12.58

11 1 A 14.03

Atlanta 0.2007

U. 1 ZoD

0.0654

0.96

J . / J 11.25

14.79

11 7 n 9.10

8.81

ft Q9 0. 7Z

9.05

8.08

ft ft A 9.63

16.89

1 7 7A 1 / . / O 18.68

Indianapolis 0.2007

U. i Zt>D 0.0654

0.96

J. / J 11.25

37.04

0 Q "^9 zy. jz

22.89

5.92

J. yj

6.03

4.76

^ 1A 6.12

10.67

1 1 ICS 12. 16

Jacksonville 0.2007

0. 1286

0.0654

0.96

3.75

11.25

2.76

1.95

1.37

20.76

20.73

20.75

11.78

12.43

13.20

32.54

33.16

33.95

Madison 0.2007

0.1286

0.0654

0.96

3.75

11.25

43.34

34.04

25.84

2.93

3.03

3.15

2.43

3.09

4.02

5.36

6.11

7.17

Phoenix 0.2007

0.1286

0.0654

0.96

3.75

11.25

2.97

2.14

1.54

34.37

32.85

31.51

6.09

6.59

7.22

40.46

39.43

38.73

Tampa 0.2007

0.1286

0.0654

0.96

3.75

11.25

0.60

0.39

0.25

23.35

23.31

23.32

14.78

15.61

16.48

38. 13

38.92

39.80

Washington, D.C» 0.2007

0. 1286

0.0654

0.96

3.75

11.25

18.66

13.78

9.65

10.11

9.93

9.84

5.45

5.98

6.64

15.56

15.91

16.49

^ ACrT = ACR"*" + ACR".

b Air space (0.75 in) has an R-value of approximately 0.96 (f t^) (h)

(

"F) /Btu.

Insulation density in furring space is 2.2 Ib/ft-^ with an R-value per inch of

5.0 (ft2)(h)(''F)/Btu.

48
49
4.2.2 Insulation in Cavity

Table 18 shows the results of the NBSLD analysis of the prototype house with

brick and block walls insulated in the cavity space in eight geographic locations. This data is plotted in figure 6 for Washington, D.C. Figures B.12

through B.19 in appendix B display this data for the other locations, in

addition to the data for the brick and block walls insulated on the inside

surface.

At a U-value of approximately 0.20 Btu/ (f t^ ) (h) ( °F) the two walls are identical, since this is the uninsulated case. However, as insulation levels

are increased, the cavity-insulated wall outperforms the wall insulated on the

inside surface, in terms of reducing AHR, even when adjusted to the same U-value. (The U-value of the insulated cavity wall is slightly lower than

that for the wall insulated on the inside surface as modeled here because the

inside air space was eliminated in the NBSLD analysis of all walls insulated

on the inside surface.) At an overall U-value of 0.065 Btu/(f t2)(h)(°F)3 the

house with the cavity-insulated walls has AHR that range from 1 percent less

in the cold climates to 30 percent less in very mild winter climates than the

house with the Insulation on the Inside wall surface. At the same U-value,

the house with the cavity-insulated walls has ACR"*" and ACR*^ that range from

2 percent less in the warmest climates to 7 percent less in the mildest

summer climates than the house with insulation on the inside wall surface.

Decreases in ACR"*" due to increased wall insulation tend to be insignificant

except in Phoenix, while ACr''^ tend to increase less than in the previous case where insulation was added to the inside surface.

4.3 THERMAL ANALYSIS OF WOOD-FRAME WALLS

Construction details of a 2 x 4-in, 24-in-on-center, wood-frame wall are

provided in table 3. As can be seen, this is an exteraely lightweight wall

(approximately 6 Ib/ft^) relative to the two different masonry walls examined

previous ly (38 and 62 Ib/ft^). This lightweight wall will have neglible heat

storage characteristics relative to those heavier walls and thus it is expected

that its thermal performance would be somewhat lower for equivalent U-values.

Table 19 shows the results of the thermal analysis for the uninsulated wall and

2 levels of insulation (R-11, R-18) in 11 locations. (Stud dimensions are increased to 2 x 6-in for the R-18 wall, 24 in on center.) This same data is

shown graphically in figure 7 for Washington, D.C, and in figures B.l through

B.ll in appendix B for all 11 cities so that it can be easily contrasted with

the 8-in block wall data. As observed previously, the weight of the wall does

have some observable effect on its thermal performance, in that at any given

U-value the AHR, ACR"^, and ACR*^ for the wood-frame wall are higher than for

the masonry wall. Note that the reduction in ACR"^ tends to be significantly

greater for the wood-frame wall than for the masonry walls. When cooling loads

are calculated only for the months of April through October, ACR''^ tend to

decrease as insulation levels increase in Jackson, Jacksonville, Phoenix, and

Tampa. If the months of May through September are considered, Albuquerque and

50
Table 18. Annual Heating and Cooling Requirements for Prototype House:

Brick and Block Walls, Insulation in Cavity

Annual Space Heating and

Cooling^ Requirements

(million Btu)

Location

Overall Wall

U-value

Btu/(ft2)(h)(°F)

R-value in

Cavityb

(ft2)(h)(°F)/Btu AHR ACR+ ACR" acrT

Albuquerque 0.2007

0.1145

0.0615

0.96

3.75

11.25

18.95

12.86

9. 23

8.23

8.18

8. 11

4.35

4.89

5.39

12.58

13.07

13. 50

Atlanta 0.2007

0. 1145

0.0615

0.96

3.75

1 1.25

14.79

10.84

8. 15

8.81

8.75

8.81

8.08

8.85

9.42

16.89

17.59

18.22

Indianapolis 0.2007

0.1145

0.0615

0.96

3.75

11. 25

37.04

27.92

22. 28

5.92

5.84

5.89

4.76

5.35

5. 92

10.67

11.19

11.80

Jacksonville 0.2007

0. 1145

0.0615

0.96

3.75

11.25

2.76

1.59

1.02

20.76

20.38

20.29

11.78

12.42

12.96

32.54

32.80

33.24

Madison 0.2007

0.1145

0.0615

0.96

3.75

11.25

43.34

32.05

25.06

2.93

2.95

3.03

2.43

3.03

3.70

5.36

5.98

6.72

Phoenix 0.2007

0. 1145

0.0615

0.96

3.75

11.25

2.97

1.73

1.12

34.37

32.14

30.89

6.09

6.40

6.73

40.46

38.54

37.62

Tampa 0.2007

0. 1145

0.0615

0.96

3.75

11.25

0.60

0.29

0.17

23.35

22.96

22.86

14.78

15.70

16.40

38. 13

38.66

39.27

Washington, D.C« 0.2007

0. 1145

0.0615

0.96

3.75

11.25

18.66

12.73

9.21

10.11

9.76

9.67

5.45

6.02

6.51

15.56

15.78

16.18

a ACrT = ACR+ + ACR".

^ Air space (0.75 in) has an R-value of approximately 0.96 (f t^) (h) (°F) /Btu.

Insulation density in cavity is 2.2 Ib/ft-^ with an R-value per inch of

5.0 (ft2)(h)(°F)/Btu.

51
Table 19. Annual Heating and Cooling Requirements for Prototype House: Wood-Frame Walls

Annual Space Heating and

Cooling^ Requirements

(million Btu)

Overall Wall R*~value in

U-value Stud Space''

Location Btu/(ft2)(h)(°F) (f t2)(h)(°F)/Btu AHR ACR"*" ACR" acrT

Albany 0.2130 0.94 48.27 3.62 3.63 7.25

0.0781 11.00 31.35 3.33 4.64 7.97 0.0543 18.00 28. 24 3. 27 4.94 8. 22

Albuquerque 0.2130 0.94 20.52 10.10 4.42 14.52

0.0781 11.00 11.11 9.02 5.45 14.48

0.05A3 18.00 9.43 8.79 5.82 14.61

Atlanta 0.2130 0.94 16.04 10.33 7.56 17.89

0.0781 11.00 9.92 9.55 9.15 18.69

0.0543 18.00 8.81 9.39 9.57 18. 96

Indianapolis 0.2130 0.94 38.63 6.88 4.57 11.45

0.0781 11.00 24.40 6.38 5.82 12.20

0.0543 18.00 21.81 6.27 6.20 12.47

Jackson 0.2130 0.94 12.03 20.78 7.76 28.54

0.0781 11.00 7.11 19.10 9,18 28.28

0.0543 18.00 6.22 18. 76 9.53 28. 29

Jacksonville 0.2130 0.94 3.65 23.12 10.72 33.84

0.0781 11.00 1.70 21.48 12.62 34. 10 0.0543 18.00 1.38 21.18 13.07 34.25

Madison 0.2130 0.94 45.44 3.67 2.71 6.38

0.0781 11.00 27.72 3.38 3.88 7.27

0.0543 18.00 24. 51 3. 32 4.25 7. 57

Phoenix 0.2130 0.94 4.39 37. 56 6.06 43. 62 0.0781 11.00 2.01 32.80 6.87 39.67

0.0543 18.00 1.61 31.86 7.17 39.03

Salt Lake City 0.2130 . 0.94 37.28 9.24 3.02 12.26

0.0781 11.00 22.59 8.19 3.79 11.98

0.0543 18.00 19.91 7.99 4.02 12.01

Tampa 0.2130 0.94 0.86 25.61 13.42 39.03

0.0781 11.00 0.33 24.04 15.79 39.83

Washington, D.C. 0.2130 0.94 19.82 11.32 4.94 16.27

0.1515 3.00 15.64 10.88 5.37 16.25

0.0781 11.00 10.65 10.31 6.26 16.57

0.0710 13.00 10. 17 10.25 6.36 16.61

0.0543 18.00 9.04 10.10 6.64 16.73

^ ACrT = ACR+ + ACR".

Air space (3.5 in) has an R-value of approximately 0.94 (f t^ ) (h) ( °F) /Btu.

Mineral wool insulation density in stud space is approximately 0.65 Ib/ft^.

52

Salt Lake City also show this decrease. In the remaining cities even during

the months of May through September, ACR''^ tend to increase slightly as walls

are better insulated.

4.4 REDUCTIONS IN AHR AND ACR

4.4.1 Generalized Data Analysis

The AHR and ACR corresponding to a range of U-values for each wall type have

been reported for a prototypical 1176 ft^ single-story house in 11 locations

(8 locations for brick and block walls). However, in an economic analysis

of insulation usage, it is the change in AHR and ACR due to a change in insulation resistance that is the most relevant aspect of the thermal analysis. The

reductions in AHR and ACR, converted to purchased energy savings and ultimately

to present-value dollar savings over the life of the house, must be sufficient

to justify the increased investment in insulation. In addition, the reductions

in AHR (and ACR where relevant) will be more generally useful if they are expressed in terms of Btu per square foot of wall area and can be estimated

for other climates as well.

For each geographic location examined, table 20 shows the reduction in AHR,

per square foot of net wall area, due to a reduction in the wall U-value of

0.10 Btu/ (f t^) (h) (°F) for each of the basic walls and insulation variations

considered .

'^ For the 8-in block walls with poured insulation in cores, this

represents a reduction in U-value from 0.21 to 0.11 Btu/ ( f t^) (h) ( °F ) . For the

other columns shown, the reductions in AHR/ft^ are due to a reduction in

U-value from 0.15 to 0.05 Btu/( f t^) ( h)

( °F) , based on interpolated AHR values

at those points, except as follows. For Jacksonville, Phoenix, and Tampa, the

0.10 Btu/(f t2)(h)( °F) reduction in U-value represents the interval between the

U-values of 0.20 and 0.10 Btu/ (f t^) (h) ( °F) . This somewhat higher interval was selected because it better represents the reduction in AHR in geographic

regions with less than 500 HDD base 55 °F and is the interval where the U-value

for an optimally insulated masonry wall is most likely to occur in those

regions. However, the reductions in AHR for changes in U-value outside these

intervals are not significantly different because of the underlying linear

relationship between AHR and U-value. A 0.10 Btu/( f t^) ( h)

( °F) reduction in

U-value is reported because it is easily used to scale the reduction in AHR/ft^

for reductions in U-value other than 0.10 Btu/(f t2)(h) ( °F) . Thus, to estimate

the reduction in AHR per square foot for any given reduction in U-value for a given wall type, insulation variation, and geographic location, simply multiply

the appropriate AAHR factor from table 20 by the reduction in U-value and

divide by 0.1. For example, a 0.05 Btu/ ( f t^) (h) ( °F ) reduction in the U-value

of an 8-in block wall, insulated on the inside surface, in Albany, yields 6.43

X 103 Btu/ft2 ((12.86)(0. 05)/0. 1) reduction in AHR.

Note that the differences between the AAHR/ft^ per AU of 0.10 Btu/ (f t^) (h) ( °F)

for each wall type are insignificantly different in the coldest climates but

All walls have an exterior solar absorptance of 0.5.

54
Table 20. Change in AHR/ft^ of Wall Area Normalized to

AU = 0.1 Btu/(ft2)(h)(°F)

AAHR (103 Btu/ft2)

8-in Block Wall Brick & Block Wall^ Insula- Insula- Insula- Insula- Woodtion tion tion tion In Frame

Location HDD^^op HDD^^op Inside^ In Core^ Inside Cavity Wall^

Albany "7 1 1 O

/ 1 io 4638 12. 86 12 .78 NAC NA 13 04

Albuquerque A 0 Q"7 240o 6

.

53 1 . 30 6. 70 7. 18 7 . 1 9

Atlanta 2959 1370 4. 37 4 .78 4. 27 4. 60 4 .70

Indianapolis COO/' 37 19 10. 84 10 .81 10. 76 10. 91 10. 94

Jackson 2352 1025 3. 40 3 .78 NA NA 3 .77

Jacksonville 1239 327 1. 20 1 .50 1. 09 1. 36 1. 48

Madison 7311 4765 13. 46 13 .43 13. 33 13. 53 13 .60

Phoenix 1571 404 1. 34 1 .73 1. 12 1. 44 1. 81

(AACRT)d (1. 77) (2 .82) (1. 34) (2. 15) (2 .93)

(AACR+)d (2. 66) (3 .41) (2. 12) (2. 55) (3 .53)

Salt Lake City 6216 3928 11. 04 11 .17 NA NA 11 .31

Tampa 459 57 0. 32 0 .41 0. 28 0. 35 0. 40

Washington, D, C« 4162 2185 6. 79 7 .09 6. 77 6. 91 6 98

a 0.10 Btu/(ft2)(h)(°F) reduction in U-value from 0.15 to 0.05 Btu/(f t2)(h)( °F)

except for Jacksonville, Phoenix and Tampa, where it is from 0.20 to 0.10

Btu/(ft2)(h)(°F).

^ 0.10 Btu/(ft2)(h)(°F) reduction in U-value from 0.21 to 0.11 Btu/ (f t2 ) (h) ( °F)

in all locations.

^ NA means AHR data base was not calculated.

^ Reduction in Annual Cooling Requirements (AACR) is only significant in

Phoenix. AACr'^ is calculated with windows closed at all times; AACR"*" is for

cooling only when tg >^ 78°F.

55
vary by as much as 60 percent in the mildest climates. However, in no case

does this variation exceed 700 Btu/ft^ of wall area per year.

In general, a reduction in wall U-value has a small and somewhat ambiguous

effect on cooling requirements depending on the extent to which natural ventilation is used, except in the case of Phoenix. Assuming that limited natural

ventilation is used throughout the year, the actual reduction in cooling

requirements is likely to be negligible in most cases, again with the exception

of Phoenix. As a result, the reductions in ACR"*" and ACRT are reported only for

that location in table 20,

4.4.2 Correlation with Climate Data

In order to develop a general relationship between the AAHR data shown in

table 20 and the Test Reference Year climate data used in computing the AAHR, a number of linear regressions were computed using heating degree day (HDD) data

from the TRY data records. Several degree day bases were tried in order to

determine which base gave the best results. The highest coefficients of determination (R^) were obtained for HDD base 55°F (HDD^^) in all cases. The resulting equations, adjusted to include the change in U-value, are given in table 21,

These equations predict the reduction in AHR within 10 percent in all locations

except Tampa. In Tampa, the predicted reduction tends to be 23 to 50 percent

too high; however the absolute error is insignificant due to the very low AHR

in that region.

It is interesting to note that the slopes of all five regression equations in

table 21 are, for all practical purposes. Identical, and that any significant

variation is found only in the intercept term. This suggests that any advantage that one wall type or insulation method has over another (in terms of

reducing annual heating requirements) is constant in absolute terms, regardless

of geographic location. In the milder heating climates this absolute advantage

may be relatively large, while in the colder climates this absolute advantage

is dwarfed by the variable term in the regression equation.

A HDD55 map of the United States, based on long-term weather observations, is

shown in figure 8. Using this map and the appropriate regression equation, the

approximate AAHR/ft^ of wall area can be found for any given AU, for each of

the wall types and insulation methods examined.

56
Table 21. Regression Equations for Five Wall Insulation Variations

(1) 8-in Block Wall - Insulation Inside (r2 = 0.997):

AAHRdO^ Btu/ft^) = AU(3.70 + 0.0274 HDD55) (4-1)

(2) 8-ln Block Wall - Insulation in Cores (R^ = 0.996):

AAHR(10^ Btu/ft^) = AU(7 .78 + 0.0267 HDD33) (4-2)

(3) Brick and Block Wall - Insulation Inside (r2 = 0.997):

AAHR(10^ Btu/ft^) = AU(2.04 + 0.0280 HDD53) (4-3)

(4) Brick and Block Wall - Cavity Insulation in Cavity (R^ = 0.997):

AAHR(10-^ Btu/ft^) = AU(4.57 + 0.0280 HDD35) (4-4)

(5) Wood-Frame Wall (R^ = 0.998):

AAHRdO^ Btu/ft^) = AU(7 .13 + 0.0271 HDD33) (4-5)

57

5. ECONOMIC ANALYSIS OF WALL INSULATION

In section 4 the reductions in annual heating and cooling requirements due to

insulating the exterior walls of a single-story house were calculated and cor- related with wall type, insulation method, and geographic location. In this

section, the calculation of corresponding reductions in life-cycle energy

costs will be discussed. Conditions for determining optimal insulation levels

for each wall type will be outlined. Finally, guidelines for optimal insulation levels will be developed, based on a number of localized variables.

59
5.1 CALCULATING THE PRESENT DOLLAR VALUE OF ENERGY SAVINGS

In order to determine the extent to which wall insulation is cost effective

on a life-cycle basis, changes in annual heating and cooling requirements

due to the increased use of insulation must be evaluated on a present-value,

life-cycle dollar basis. Incremental reductions in life-cycle heating and

cooling costs can then be compared with incremental increases in wall con- struction costs in order to determine the economically optimal insulation

level for a given wall design.^

Before the dollar value of changes in wall insulation levels can be

determined, it is necessary to convert changes in AHR and ACR^ ( AAHR and

AACR) to corresponding changes in annual metered heating and cooling energy

requirements (AAMHR and AAMCR). Determination of AMIHR and AAMCR requires that

the seasonal efficiencies of the heating (nn) ^^'^ cooling (nc) system be known.

The seasonal efficiency of each is defined here as the total energy output to

the conditioned space divided by the total energy input to the equipment summed over the hours in which a heating or cooling load occurs.-^ Thus, changes in

metered energy requirements are simply equivalent to the changes in space heating and cooling requirements divided by the seasonal efficiencies of the

heating and cooling equipment, respectively:

AAMHR = AAHR/t^, and (5-1)

AAMCR = AACR/r^. (5-2)

Changes in annual heating and cooling costs ( AAHC and AACC, respectively) are calculated as the change in annual metered requirements for heating and cooling

energy multiplied by their respective prices (Py and Pc) in equivalent units:

AAHC = ( AAMHR )(Ph), and (5-3)

AACC = (AAMCR) (Pc). (5-4)

Criteria for optimization is discussed in the following subsection.

AACR here refers to the effective change in annual cooling requirements,

i.e., the AACR that would be calculated if the actual operating procedures

with regard to natural ventilation were known. The analysis in section 4

above showed that, except in Phoenix, AACR due to wall insulation is likely

to be insignificant. However, a general methodology for evaluating dollar

savings which can include cooling energy savings is shown here.

By restricting seasonal efficiency calculations to actual heating or cooling

hours, the energy used in a standing gas pilot light during non-load hours is

not considered. In effect, equipment efficiencies should be evaluated as though they had an electronic ignition system when used to evaluate the

energy savings due to shell modifications.

60
The present value of the sum of annual energy savings over the expected useful

life of the insulation can be easily calculated once the appropriate uniform

present worth factors are known. Since energy costs are expected to increase

over time rather than remain constant, a modified uniform present worth factor

(UPW*) must be calculated based on the expected useful life of the insulation

(L), the projected annual rate of increase in energy prices (E), and the discount rate (D), which represents the time value of money, i.e., the rate of

return on the best alternative investment opportunity available to the homeowner. If E is constant over the life of the insulation, the UPW* can be

found as follows:^

UPW* = + E lfl - f l + ^ if D E, and ^^-^

)

D - E 1 + D

UPW* = L if D = E. (5-6)

If different energy types are used for heating and cooling, it is possible that

different rates of energy price increase will be projected for each, and as a result, the UPW* may be different for heating energy and cooling energy.

Reductions in present-value, life-cycle heating costs and cooling costs

(ALCHC, ALCCC, respectively) can then be calculated as:

ALCHC = (AAHC)(UPwJJ) , and (5-7)

ALCCC = (ALCC)(UPwJ) . (5-8)

The total reductions in present-value, life-cycle energy costs (ALCEC) can now be calculated as:

ALCEC = ALCHC + ALCCC. (5-9)

In summary form,

ALCEC = (AAHR](p^J(iiPw*) + ( AACRj

(p^ j [uPW*) • (5-10)

rijj H nc C

•'• If E is not constant, the UPW* must be evaluated for each of the n time

intervals, corresponding to the different values of E and summed together.

This can be evaluated as follows:

UPW* = I [ n (-—J) ] (-— U - (7— ) 1=1 j=0 1 + D D - Ei 1 + D

where n = number of time intervals,

Tj = length of interval j (Tq = 0), and

Ej = rate of price increase in interval j (Eq = 0).

61
When the differences in equipment efficiencies, unit energy costs, and rates

of energy price increase are considered, one can see why the simple summation

of AAHR and AACR is meaningless from both an energy and economic standpoint.

5. 2 CRITERIA FOR ECONOMIC OPTIMIZATION

The primary purpose of this report is to determine the economically optimal

level of insulation for a given wall type in a variety of climates and for a variety of energy costs. The economically optimal insulation level is defined

as that level which has the greatest cumulative net savings in any given

installation; i.e. present-value, life-cycle savings less present-value, lifecycle costs. In order for any increase in the use of insulation to increase

cumulative net savings, the incremental savings attributable to that change

must be greater than or equal to its incremental cost. For this reason,

accurate calculation of the change in energy requirements (and life-cycle

energy costs) due to additional wall insulation is more important than finding

the total energy requirements (and life-cycle energy costs) for the building.

These optimality criteria are shown graphically in figure 9. In the upper

part of that figure (a), cumulative present-value life-cycle savings are shown

as a function of the level of insulation used (in terms of thermal resistance)

in the wall. Also shown is the cumulative installed cost of that insulation.

Note that at any point between the origin and insulation level R', cumulative

savings are greater than cumulative costs. However, cumulative net savings,

also shown in the upper part of figure 9, are maximized at insulation level

R. Thus R is the optimal insulation resistance level, in that any alternative

level will result in lower net savings over the useful life of the insulation.

This same result can also be found by examining incremental savings and costs, as shown in the lower part of figure 9 (b). Here, incremental savings and

incremental costs (the additional savings and costs attributable to each additional increment of thermal resistance) are shown as a function of insulation

resistance. Incremental savings decrease as the overall resistance level is

increased because of the reciprocal relationship between thermal resistance

and thermal conductivity (i.e., U = l/R).-*^ Incremental costs for the first

few units of resistance (e.g., up to R-11 for mineral wool insulation in woodframe walls) tend to decrease because installation costs are somewhat fixed

and are applied to the first unit. However, beyond some point, incremental

costs per resistance unit begin to increase as wall modifications are needed

to accomodate more insulation, or as more thermally efficient, but more expensive, insulation materials (e.g., rigid foam) are substituted for less efficient materials. The intersection of the incremental savings and cost curves

Here R refers to the overall thermal resistance of the wall, which includes

not only the insulation but the other materials and air resistance values.

Note that this reciprocal relationship means that as R increases at a constant rate, U decreases at a decreasing rate.

62
R THERMAL RESISTANCE R'

I Incremental savings

I R THERMAL RESISTANCE R'

Figure 9. Economic optimization criteria for insulation.

63
occurs at the optimal resistance level, R. Any increase in R would incur

additional costs greater than additional savings, thereby decreasing cumulative

net savings. Any decrease in R would give up resistance units which contribute

greater savings than costs, also decreasing cumulative net savings. Thus, the

level of thermal resistance at which incremental savings just equals incremental costs maximizes cumulative net savings and is therefore the economically

optimal insulation level.

However, because insulation materials are not generally available in a continuous range of resistance values, it is not likely that the point where

incremental savings just equals incremental costs is practical. In this case, an alternative criterion requires that insulation resistance be increased as long as the additional savings attributable to each available increment are

at least as great as the cost of that increment. When no further increase in

the overall insulation resistance can generate incremental savings greater

than or equal to incremental costs, the optimal Insulation resistance level

has been reached. No alternative resistance level will have higher cumulative

net savings.

This incremental approach to economic optimization is quite useful in the

analysis of thermal insulation because changes in savings and costs due to

increases in thermal resistance are usually more accurately estimated than

total savings and costs. For this reason, the incremental approach is used

in this report.

5.3 CALCULATION OF OPTIMAL INSULATION LEVELS: EXAMPLES

In this subsection, the methodology for determining the optimal insulation

resistance for a given wall type and climate location is demonstrated. The

first and second examples are based directly on the reductions in annual heating requirements (AAHR) reported in table 20, That is, AAHR are calculated

by adjusting those given for AU =0.1 Btu/ (f t^) (h) ( °F) to correspond to the

actual AU achieved. The third example is based on the equations in table 21

which relate the reduction in annual heating requirements to heating degree

days (base 55 °F, HDD55).

This criterion is sometimes expressed as

MS = MC

where MS = marginal (i.e. incremental) savings,

MC = marginal (i.e. incremental) costs.

Second order conditions for the criterion require that MS - MC be decreasing

in the region of optimal insulation resistance. In addition, cumulative

savings must be greater than cumulative costs at this point or the optimal

insulation resistance is 0 (i.e., no insulation). For more information on

this subject, see S. R. Petersen, Retrofitting Existing Housing for Energy

Conservation; An Economic Analysis .

64
Example /i^l : 8-in Block Wall in Albuquerque

A house is to be built in Albuquerque with 8-in block walls having an area of

1000 square feet net of windows. Unless a greater resistance value can be

justified on a life-cycle cost basis, foil-backed gypsum board (approximately

R-3) will be the only means of insulation used. However, if more insulation

is cost justified, 2 x 3-in framing will be used along with mineral wool insulation. The alternative insulation resistance levels, U-values, and costs

(from table 4), as well as corresponding reductions in AHR (based on table 20) are shown in table 22. A natural gas furnace with a seasonal efficiency

(hh) of 70 percent is assumed for heating. Natural gas prices are expected

to be $0,30 per therm ($3.00 per million Btu) and are expected to increase in

real terms (i.e., adjusted to remove the effects of inflation) at 5 percent

per year.^ Cooling savings are not expected to be significant.

Since the useful life of the insulation is expected to be at least as long as the typical mortgage life, a 30-year life will be assumed in the analysis. A

real discount rate of 4 percent is used in the example to represent the time

value of money to a homeowner. This represents a minimum acceptable after- tax

rate of return for a long-term investment, adjusted to remove the effects of

inflation. (In fact this is quite high for most homeowners who are able to

make long-terra investments. However for homeowners who keep outstanding

nominal 18 percent credit card balances, a 4 percent real discount rate may

be more realistic given recent inflation rates. ^) Thus the modified uniform

present worth factor (UPW ) is computed, using equation 5-5 as:

[_L05)(1 - (1^)^^) = 34.92. ^-0.01^^ 4.04^ ^

Using equation 5-10, the incremental reduction in life-cycle energy costs

(ALCEC) for each additional level of resistance shown in table 22 can be

computed. For example,

ALCEC for R-3 is computed as:

ALCEC = f 5.22 million Btu ] ($3. OO/miUion Btu)(34.92) = $781

0.70

These price data are for example purposes only. Current DoE price projections by region can be found in Sitzer, Moden, and Don Vito, Historical and

Forecasted Energy Prices by DoE Region and Fuel Type for Three Microeconomic

Scenarios , DoE/EIA-0184/15 (Washington, D.C.: U.S. Department of Energy,

July 1979)

For example, for a homeowner in the 25 percent tax bracket (combined Federal

and State), an 18 percent interest rate would be reduced to an effective

rate of 13.5 percent ( (1-0. 25 ) (0. 18 ) ) . At an average inflation rate of

10 percent this would equal a real interest rate of approximately 3.5

percent.

65
Table 22. Example #1: Albuquerque - 8-in Block Walls (1000 ft^)

Insulated on Inside Surface

Description U-value^

(Btu/(ft2)(h)(°F))

AU Z\AHRt»

(million Btu)

Cost^

(1000 ft2)

Base Wall 0.242

R-3 (foil-backed wallboard) 0. 162 0.080 5.22 $ 100

R-11 (mineral wool) 0.074 0.088 5.75 750

R-13 (mineral wool) 0.066 0.008 0.52 800

R-19 (mineral wool) 0.046 0.020 1.31 1000

^ Based on table 4.

b Calculated from table 20 (AAHR = (6530 Btu/ f t2 ) ( 1 000 f t2) (aU )/0. 1 ) .

Table 23. Example #1. Incremental Life-Cycle Savings and Costs

Description ALCEC^ ACost Cumulative Net Savings

R-3 $781 $100 $681

R-11 861 650 892

R-13 78 50 920

R-19 196 200 916

^ Based on natural gas price of $3.00 per million Btu, a UPW* of

34.92, and a heating efficiency of 70 percent.

66
The ALCEC for each incremental level of resistance shown in table 22 has

been calculated and displayed in table 23, along with the corresponding

incremental cost and cumulative net savings of those resistance levels.

Where incremental savings are greater than incremental costs, cumulative net

savings increase. When incremental savings are less than incremental costs,

cumulative net savings decrease. The R-13 insulation level has the greatest

cumulative net savings, $920, and is therefore the economically optimal level

of insulation resistance for the 8-in block walls in this example for

Albuquerque.

Example #2: Brick and Block Wall in Phoenix

In this example, a house with 1000 square feet of wall area is to be built

with brick and block and insulated in the cavity. Reductions in both annual

heating requirements and annual cooling requirements are expected. A gas

furnace with a seasonal efficiency of 70 percent will be used for heating.

A central air conditioner with a seasonal efficiency of 2.5 will be used for

cooling. In general, the air conditioner will be used only when the outdoor

temperature exceeds 78 °F. Natural gas is expected to cost $0.35 per therm

($3.50 per million Btu) and to increase at an annual real rate of 5 percent. Electricity is expected to cost $0.05 per kWh ($14.65 per million Btu)

and to increase at a real rate of 2 percent per year. A 30-year useful

life and 4 percent real discount rate is assumed. As computed in example

#1, the UPW* factor for gas is 34.92. The UPW* factor for electricity is

calculated as:

UPW* = fil^^ fl - r^^l 1 = 22.52

I0.O2J I I1.O4J J

Table 24 shows the alternative insulation resistance levels considered, the

wall U-values, and the corresponding insulation costs based on table 5. In

addition, table 24 shows the corresponding AAHR and AACR based on table

20. The ALCEC for the R-4 insulation is calculated, using equation 5-10,

as

:

ALCEC = ri-30 million BtuV^;-^. SO /rn-i 1 1 1 Btu)(34.92)

0.70

+ ( 2.30 million Btu

] (5^14. 65/million Btu)(22.52) = $531.

2.5

Table 25 shows the ALCEC for each resistance level examined in table 24,

along with the incremental cost and cumulative net savings for each level.

In this example, the R-4 insulation has the highest cumulative net savings

($21) and thus is optimal. The cumulative net savings for resistance levels

higher than R-4 are negative in this example.

67
Table 24. Example #2: Phoenix - Brick and Block Walls (1000 ft^)

Insulated in Cavity

Description U-value^ AU AAHR^ AACR^ Cost^

(Btu/(ft2)(h)(°F) (million Btu) (million Btu) (1000 ft^)

Base Wall 0.201

R-4 0.111 0.090 1.30 2.30 $ 510

R-6 0.091 0.020 0.29 0.51 $ 660

R-9 0.071 0.020 0.29 0.51 9 y uu

R-12 0.059 0.012 0. 17 0.31 $1 iJU

Based on table 5.

Calculated from table 20 (AAHR

AACR

= (1440 Btu/ft2)(1000 f t2)(AU)/0.1;

= (2550 Btu/ft2)(1000 f t^) (AU ) /O. 1 )

.

Table 2 5. Example #2 Incremental Life-Cycle Savings and Costs

Description ALCEC^ ACost Cumulative Net Savings

R-4 $531 $510 $ 21

R-6 118 150 -11

R-9 118 240 -133

R-12 71 230 -292

^ Based on natural gas price of $3.50 per million Btu, a UPW*

of 34.92, and efficiency of 70 percent for heating; electricity price of $14.65 per million Btu, a UPW* of 22.52, and

efficiency of 2.5 for cooling.

68
Example //3: Wood-Frame Wall in 6000 HDD-^s Climate

A house is to be built in Rapid City, S.D. (6000 HDD55) with wood-frame walls

to be insulated with mineral wool insulation. The house has 1000 square feet

of wall area net of windows. Table 26 shows the alternative levels of insulation resistance to be considered, including the corresponding reductions in

AHR for wood-frame walls in a 6000 HDD55 climate, based on equation 4-5 in

table 21. An electric resistance furnace with a seasonal efficiency (nn) of

100 percent will be used for heating. Electricity for heating is assumed to

have an incremental cost of $0,042 per kWh ($12.31 per million Btu), with an annual real rate of increase projected to be approximately 2 percent. Cooling

savings are expected to be insignificant. Again a 4 percent real discount

rate and a 30-year useful life is assumed in the example. Thus the UPW* is

the same as in example #2, 22.52.

The reduction in life-cycle energy costs is calculated for R-3 using equation

5-10 and the AAHR data in table 26:

ALCEC = [ 10.35 million Btu 1 ($12. 31/million Btu)(22.52) = $2869 . 1.00

The ALCEC for each incremental level of resistance shown in table 26 has been

calculated and displayed in table 27, along with the corresponding incremental

cost and cumulative net savings for each. In this example, the R-18 mineral

wool plus R-5 rigid foam sheathing is the economically optimal insulation level

of those alternatives considered. Since the incremental savings are considerably higher than incremental costs at this point, more insulated sheathing may

still be cost effective beyond the R-5 assumed.

If the wood-frame wall is to be covered with brick veneer instead of

lightweight siding, the reduction in AHR and corresponding ALCEC should be

based on equation 4-1, since these walls perform much the same as 8-in block

walls insulated on the inside. This will have little effect on the optimal

level of insulation, however, except in the very mildest climates. The insulation cost data will be the same for all wood-frame walls regardless of siding

used.

69
Table 26. Example #3: Wood-Frame Walls (1000 ff^) in 6000 HDDcc Climate

Description U-value^

(Btu/(ft2)(h)(°F))

AU AAHRb

(million Btu)

Costa

(1000 ft2)

Base Wall 0.213

R-3 (foil-backed wallboard) 0. 152 0.061 10.35 $100

R-11 (mineral wool) 0.078 0.074 12.56 300

R-13 (mineral wool) 0.071 0.007 1.19 350

R-18 (mineral wool) 0.055 0.016 2. 72 700

R-18 mineral wool and R-5 0.045 0.009 1.70 900

rigid foam sheathing

a Based on table 6.

Calculated using equation 4-5 for wood-frame walls in table 21:

AAHR (10^ Btu/ft2) = AU(7. 13 + (0. 0271 )(6000) )

.

Table 27. Example #3: Incremental Life-Cycle Savings and Costs

Description ALCECa ACost Cumulative Net Savings

R-3 $2869 $100 $2769

R-11 3482 200 6051

R-13 330 50 6331

R-18 754 350 6735

R-23 471 200 7006

a Based on electricity at $12.31 per million Btu, a UPW* of

22.52, and a heating efficiency of 100 percent.

Facing page: Framing the inside of masonry

walls with 2 X 3-in studs and insulating

with mineral wool was found to be a more cost-effective method than using rigid foam.

70
1! 6. INDEX NUMBER SYSTEM TO DETERMINE OPTIMAL INSULATION LEVELS

In order to provide a flexible methodology for determining optimal Insulation

levels for each wall type examined, based on the insulation specifications and

costs listed in section 2, an index number system is developed here. This

index system allows the user to vary energy prices, equipment efficiencies,

lifetimes, discount rates, projections of annual energy price increases, heating degree days, and insulation costs in order to determine the optimal insulation level for a given wall type and a given insulation type. This index

number system is based on reductions in space heating requirements only and

is therefore appropriate only where changes in air conditioning requirements

due to an increased level of wall insulation are assumed to be insignificant.

71
As noted in section 4, this assumption is reasonable if natural ventilation

is frequently used when the outdoor temperature is lower than the thermostat

setpoint (78°F in this report). In Phoenix and other regions where reductions

in cooling requirements are known to be significant, the calculation procedure

shown in the previous section should be used instead.

The index number system is based on the economic criteria for optimality,

requiring that incremental life-cycle savings from additional insulation be

at least as large as incremental costs (reference equation 5-10 with AACR = 0)

That is:

> AK , (6-1)

where AAHRj^ = the incremental reduction in annual heating requirements per

unit of net wall area due to the i^'^ level of insulation relative to

the (i-l)th level,

= price of purchased energy in same units as AAHR,

n = seasonal efficiency of heating equipment,

H

UPW|^ = modified uniform present worth factor, and

AK^ = the incremental cost of the i^'^ level of insulation relative

to the (i-l)t^ level per unit of net wall area.

Equation 6-1 can be transposed to:

(Ph](UP%)

, (6-2)

n

" AAHR,-

' H

or

I > AK,

AAHR^

(6-3)

where

I = (PhKTMh) (6-4)

n H

If I, the index number, is greater than or equal to AKj[/AAHRj^, the "breakpoint'

ratio for the ith level of insulation, that level of insulation is cost

justified.

In general, this breakpoint ratio should increase for each additional level of

insulation considered. (If the ratio for a succeeding increment of insulation

resistance is lower than that for the preceding increment, the two increments

72
should be combined and a new ratio computed.) Then the insulation level with

the highest breakpoint ratio which does not exceed this index number (I) is

the optimal insulation level.

The index number, 1, can be calculated as the product of UPWpj and

Tables 28 and 29 can be used to find the appropriate UPW* and price per mij^lion

Btu output from the furnance, P^^^' ^respectively . Table 28 gives the UPW

for several discount rates at the intersection of the "expected useful lifetime" column and the "rate of energy price increase" row. Table 29 gives the

price per million Btu output for selected energy types and seasonal furnace

efficiencies. Part A gives the price per million Btu, as metered at the building boundary, for a range of unit prices for natural gas, fuel oil, and electricity. Part B gives the price per million Btu output at the intersection of

the "price per million Btu (metered)" column and "furnace efficiency" row. The

following example shows how the index number can be calculated using tables 28

and 29.

Example #4 ; Find the index number for wall insulation based on oil heat at

$0.84 per gallon, expected to increase at an annual rate of 4 percent (real) over the building life of 30 years. A real discount rate of 4 percent and

a seasonal efficiency of 70 percent are assumed.

Solution; Using table 28, a UPW of 30.0 is found. Using table 29, a cost of

$8.57 per million Btu output is found. By simple multiplication of the UPW*

and price per million Btu output, the index number is found to be approximately

257.

Breakpoint ratios for the insulation levels examined in this section have been

calculated for the 8-in block wall insulated on the inside surface in table 30,

the brick and block wall with insulation on the inside wall surface in table 31,

the brick and block wall with insulation in the cavity in table 32, and the woodframe wall in table 33. (Breakpoint ratios are not calculated for insulation

poured into the cores of 8-in block walls since this is more expensive than the

other alternatives examined.) These ratios are based on the insulation resistances and costs shown in tables 4 to 6 and the AAHR are based on the equations in table 21. Using these tables and the appropriate index number,

the optimal insulation level can be quickly determined for each wall type and

insulation type, as shown in the following example.

Example //5 ; Find the optimal level of rigid foam insulation in an 8-in block

wall for the 3000 HDD55 region, given an index number of 257.

Solution; Using the 3000 HDD55 row in table 30, the highest index number for

rigid foam insulation in the 8-in block wall not exceeding 257 is 243, corre- sponding to R-15 (approximately 2-in rigid foam plus 0.75-in reflective air

space). This wall has an overall (opaque area ) U-value of 0.055 Btu/(ft2)(h)

(°F).

Note in tables 30 and 31 that two columns are shown for R-13 mineral wool

insulation. The first column represents R-13 in an incremental fashion to R-11

(i.e., an increase of 2 resistance units). The second column represents R-13

73
Table 28. Modified Uniform Present Worth Factors (UPW*)

Rate of Fuel

Discount Rate Price Increase Useful Lifetime (years)

20 25 30 35 40

yj/o 9 S fl 'X^ n An n 2% 24.8 32.7 41.4 51.0 61.6

4% 31.0 43.3 58.3 76.6 98.8

o^ J

'^Q7* nU DO* £. ft'^ O ft J • o

lift 1 1 A/i n 8% 49.4 79.0 122.3 186.1 279.8

1 rw 0 J. U1 no 0 1 fin o

10"/ fin 7 1 /. Q Z / U. J

/i fi l '0 J. J0 Q 1

on JU J J

A®/ 1 O 1 3. J Z 3. U 17 A 2% 20.0 25.0 30.0 35.0 40.0

4% 24.7 32.5 41.1 50.6 61.1

(\7 \j /. i9 ft /J.J 8% 38.5 57.1 82.0 115.1 159.1

10% 48.5 77.1 118.7 179.5 268.

1

12% 61.5 104.9 174.0 284.5 460.8

20 25 30 35 40

0% 13.6 15.6 17.3 18.7 19.8

2% 16.4 19.6 22.5 25.2 27.5

4% 20.0 25.0 30.0 35.0 40.0

6% 24.6 32.3 40.9 50.2 60.5

8% 30.4 42.4 56.8 74.2 95.2

10% 38.0 56.2 80.3 112.2 154.5

12% 47.6 75.3 115.3 173.3 257.3

20 25 30 35 40

0% 11.5 12.8 13.8 14.5 15.0 2% 13.7 15.8 17.5 18.9 20.0

4% 16.5 19.7 22.6 25.3 27.7

6% 20.0 25.0 30.0 35.0 40.0

8% 24.5 32.2 40.6 49.9 60.1 10% 30.2 41.9 56.0 73.0 93.5

12% 37.5 55.3 78.7 109.6 150.2

20 25 30 35 40

0% 8.5 9.1 9.4 9.6 9.8 2% 9.9 10.8 11.4 11.8 12.

1

4% 11.7 13.1 14.1 14.9 15.5

6% 13.9 16.0 17.8 19.3 20.5

8% 16.6 19.9 22.9 25.6 28.1

10% 20.0 25.0 30.0 35.0 40.0

12% 24.3 31.9 40.1 49.2 59.1

74
Table 29. Unit Energy Prices (Metered) and Corresponding Price per

Million Btu Output from Furnace

A. Price per Million Btu Metered (Ph/hh) for Selected Fuel Types

Fuel Price

Type Unit Unit Energy Price

Gas $/ therm 0.20 0.30 0.40 0.50 0.60 0.80 1.00 1.20 1. 50 1.80

Oil $/gallon 0.28 0.42 0.56 0.70 0.84 1.12 1.40 1.68 2. 10 2.52

Elec. i/kWh 0.70 1.00 1.40 1.70 2.10 2.70 3.40 4. 10 5. 10 6. 10

$/Million Btu

(metered)

2.00 3.00 4.00 5.00 6.00 8.00 10.00 12.00 15. 00 18.00

B. Price per Million Btu Output for Selected Furnace Efficiencies

Price per Million Btu Metered (Ph/hvi)

2.00 3.00 4.00 5.00 6.00 8.00 10.00 12.00 15.00 18.00

Furnace

Efficiency^

0.6 3.33 5.00 6.67 8. 33 10.00 13.33 16.67 20.00 25.00 30.00

0.7 2.86 4.29 5.71 7. 14 8.57 11.43 14.29 17.14 21.43 25.71

0.8 2.56 3.75 5.00 6. 25 7.50 10.00 12.56 15.00 18.75 22.50

0.9 2.22 3.33 4.44 5. 56 6.67 8.89 11.11 13.33 16.67 20.00

1.0 2.00 3.00 4.00 5. 00 6.00 8.00 10.00 12.00 15.00 18.00

1.4 1.43 2.14 2.86 3. 57 4.49 5.71 7.14 8.57 10.71 12.86

1.6 1.25 1.88 2.50 3. 13 3.75 5.00 6.25 7.50 9.38 11.25

1.8 1.11 1.67 2.22 2. 78 3.33 4.44 5.56 6.67 8.33 10.00

2.0 1.00 1.50 2.00 2. 50 3.00 4.00 5.00 6.00 7.50 9.00

2.2 0.91 1.36 1.82 2. 27 2.73 3.64 4.55 5.45 6.82 8.18

^ Efficiencies greater than 1.0 are for heat pumps.

75
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79
incremental to R-3. In these two tables, the breakpoint ratios for R-13 incremental to R-11 are lower than for the R-11 level. This indicates that if R-11

is cost effective (including the cost of the 2 x 3-in framing), then R-13 will

be even more cost effective. As stated above, when a succeeding increment of

insulation resistance has a breakpoint ratio lower than that for the preceding

increment, the two increments should be combined and a new ratio computed. The

second column for R-13 insulation represents this combination of two increments

(R-3 to R-11 and R-11 to R-13).

Example #6 : Find the optimal level of thermal resistance for a brick and

block wall being insulated on the inside with mineral wool insulation in the

3000 HDD55 region, given an index number of 102.

Solution : Using table 31, R-11 insulation is not quite cost effective since

its breakpoint ratio is 105. However, the R-13 insulation, being slightly

more cost effective, is cost effective at the breakpoint ratio of 102. Since

no higher level is cost effective, R-13 is the optimal insulation level in

this case.

While this index number methodology provides a good basis for determining

optimal insulation levels, it should be recognized that the estimated AAHR

and AK (and, thus, the breakpoint ratio, AK/AAHR) are subject to considerable variation. Variations in AAHR may result from differences in the operational profile (e.g., no night thermostat setback), differences in local climatic factors, differences in exterior absorptance, and differences in the

overall design of the house. Factors which affect AK include regional variations in material and labor costs, the use of union or non-union labor, general inflation over time, the use or non-use of subcontractors, and overhead

and profit rates. As a result, for insulation levels with breakpoint ratios

that are quite close to the appropriate index number, some subjective considerations should be made as to whether the lower or higher level of Insulation at

that point is the more appropriate point to stop insulating. For example, for

exterior wall surfaces that are very light in color (and thus do not absorb as much solar radiation) the higher level of insulation may be cost effective,

while for dark surfaces the lower insulation level may be the maximum costeffective level. Similarly, if no night thermostat setback is used and the

house is heated throughout the winter, the AAHR will be greater and therefore

the higher insulation level will likely be cost effective.

Facing page: Additional research Is needed

to develop more cost-effective methods of

insulating masonry walls.

80
7. SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS FOR FURTHER RESEARCH

7 .1 SUMMARY

The purpose of this report is to determine economically optimal insulation

methods and resistance levels for both masonry and wood-frame walls in singlefamily housing. The economically optimal method and level of insulation has

the greatest present-value net savings (total savings less total costs) over

its expected life of all alternatives considered. Since net savings are determined in part by climate and projected energy costs, optimal insulation

methods and levels can be expected to vary with both geographic location and

the energy types used for space heating and cooling. In addition, since the

81
costs of insulating different wall types (e.g., masonry and wood-frame) may

vary significantly, and the effect of insulation in the different wall types

may vary as well, optimal insulation methods and resistance levels may vary by

wall type in many cases.

This report examines each of these key variables in order to determine optimal

insulation levels for exterior walls. Reductions in annual heating requirements (AHR) and annual cooling requirements (ACR) due to several levels of

thermal resistance are calculated for 3 basic wall types in 11 locations

for 8-in block and wood-frame walls, and in 8 locations for brick and block

walls. Generalized relationships between reductions in U-value and reductions

in AHR are developed and correlated with heating degree days (base 55°F).

Representative costs for the most common insulating methods are estimated over

a range of commonly available thermal resistances. A methodology is outlined

for determining the present value of the energy savings from the increased use

of insulation based on current energy prices, projected energy price escalation

rates, a discount rate, and useful insulation life. An index number system is

devised to aid the reader in determining optimal insulation levels for each

wall type with a minimum of computation required.

7. 2 CONCLUSIONS

A number of important conclusions have been reached in this study. It is

anticipated that some of these may have a significant impact on insulation

practices for new home construction if they are confirmed and accepted by the

home-building industry.

° Since the insulation of masonry walls is considerably more expensive

than the insulation in wood-frame walls, the economically optimal level

is considerably lower for the former than the latter. In much of the

Southern and Southwestern United States, no more than R-3 (reflective

air space) insulation is cost effective for masonry walls in gasheated houses, while R-11 or R-13 mineral wool insulation is cost

effective in similar houses with wood-frame walls in the same locations.

° Framing the inside of masonry walls with 2 x 3-in studs and insulating

with mineral wool is significantly less costly than the use of rigid

foam insulation, even after adjustment for lost interior space. When

mineral wool is used, the optimal insulation levels are generally

similar to those for wood-frame housing, except in the mildest heating

climates. In general, if mineral wool insulation is used, R-11 or R-13

is more cost effective than lower levels (e.g., R-5 or R-7) because

the extra cost is quite low relative to the extra benefits.

° Reductions in annual heating requirements due to insulating exterior

walls are similar for both wood-frame and masonry walls insulated on

the inside surface in regions with greater than 3000 heating degree

days (base 65°F). The reductions tend to be quite significant if the

other shell components (i.e., attic, windows, floors) are insulated

in a cost-effective manner. In regions with less than 3000 heating

degree days, the reductions tend to be relatively less for the insula82
tion in masonry walls than in wood-frame walls (given equivalent reductions in U-values). However, these differences are generally small in

absolute terms.

Changes in annual cooling requirements due to increasing insulation

levels are not likely to be significant except in regions with

extremely hot summers like those in southern Arizona. In fact, cooling

requirements may increase if a house is kept tightly closed up, especially in the spring and fall. Small reductions in annual cooling

requirements may occur if air conditioning is only used when the outdoor temperature is warmer than the thermostat setpoint. Except in

regions with very mild heating climates, however, such savings do not

have a significant effect in selecting the optimal insulation level.

In climates typified by mild winters or summers, increased mass can significantly improve the thermal performance of exterior walls, in

terms of reducing annual heating or cooling requirements. However,

in these regions heating or cooling requirements tend to be relatively

small to begin with. As more severe climates are encountered, the

advantages of mass over lighter construction techniques are sharply

reduced

.

Insulation in the cavity of a brick and block wall generally performs

significantly better than the same insulation placed on the inside

surface of the wall. If the installed cost per resistance unit of

cavity insulation is the same as for insulation on the inside surface,

cavity insulation is generally more cost effective.

Insulation in the cores of 8-in concrete blocks is generally less cost

effective than an equivalent level (in terms of overall U-value) of

insulation installed on the inside wall surface, even though the former

is slightly more effective than the latter in reducing heat loss.

The color of the exterior surfaces of walls may have more effect on AHR and ACR than mass in those walls. However, unless the location of

the house is clearly dominated by either heating or cooling loads, the

advantages of color in one season will be offset by the disadvantages

of the same color in the opposite season.

7.3 RECOMMENDATIONS FOR FURTHER RESEARCH

The results of this report, in terms of identifying maximum cost-effective

levels of insulation in exterior walls for single-family housing, are based

largely on simulations of the thermal performance of walls in a single prototypical house. The primary advantage of simulation data is in being able to

hold all relevant factors constant except the one to be examined in a sensitivity analysis. However, it is important that the simulation algorithms be

adequately verified by actual measured data. While small scale validation

measurements have been successfully made for the NBSLD computer program,

additional measurement data are needed to demonstrate the sensitivity of the

algorithms to changes in thermal mass and insulation levels.

83
Research into more cost-effective methods of insulating masonry walls is

needed. Because of the high cost of insulating with rigid foam insulation,

the maximum economic level of rigid foam insulation is generally considerably

lower than that for mineral wool insulation. However, the mineral wool insulation is approximately twice as thick as the rigid foam, and may therefore

be less attractive to the builder and buyer. Placement of insulation near

the outside of the wall can significantly improve the thermal performance of

the wall but this is generally a more costly approach than insulating on the

inside, since a protective coating must be applied. Insulation systems

which can significantly reduce this cost are needed.

Expansion of this research to include data for multifamily housing and

commercial buildings will be of considerable benefit to the building community

At present, masonry wall construction is more prevalent in these buildings

than in single-family housing in most parts of the United States. As a result

the potential savings from improved insulation guidelines are likely to be

considerably greater as well.

84
REFERENCES

Arens, Edward A. and Carroll, William L., Geographical Variation in the Heating

and Cooling Requirements of a Typical Single-Family House, and Correlation of

these Requirements to Degree Days . BSS 116, National Bureau of

Standards, U.S. Department of Commerce, Washington, D.C., November 1978.

ASHRAE Handbook of Fundamentals , American Society of Heating, Refrigerating and

Air-Conditioning Engineers, Inc., New York, 1972.

"BIA Technical Notes on Brick Construction - 21," Brick Institute of America,

McLean, Va

.

Hastings, S. R., Three Proposed Typical House Designs for Energy Conservation

Research , NBSIR 77-1309, National Bureau of Standards, U.S. Department of

Commerce, Washington, D. C, 1977,

Kusuda, T., NBSLD, The Computer Program for Heating and Cooling Loads in

Buildings , BSS 69, National Bureau of Standards, U.S. Department of Commerce,

Washington, D.C», 1976.

Means Building Construction Cost Data, 1980 , Robert Snow Means Company, Inc.,

Duxbury, Mass., 197 9.

NAHB Research Foundation, Inc., "Annual Builder Practices Survey," Rockville,

Md.

Peavy, B., Burch, D. , Powell, F., and Hunt, C. M. , Comparision of Measured

and Computer-Predicted Thermal Performance of a Four Bedroom Wood-Frame

Townhouse , BSS 57, National Bureau of Standards, U.S. Department of Commerce,

Washington, D^C, 1973.

Peavy, B., Powell, F., and Burch, D. , Dynamic Thermal Performance of an Experimental Masonry Building , BSS 45, National Bureau of Standards, U.S.

Department of Commerce, Washington, D. C. , 1972,

Petersen, Stephen R., Retrofitting Existing Housing for Energy Conservation:

An Economic Analysis , BSS 64, National Bureau of Standards, U.S. Department

of Commerce, Washington, D«C*, December 1974.

Petersen, Stephen R. and Barnett, James P., Expanded NBSLD Output for Analysis

of Thermal Performance of Building Envelope Components , NBSIR 80-2076, National

Bureau of Standards, U.S. Department of Commerce, Washington, D,C. , July 1980.

Reagan, J. A. and Acklam, D. M. , "Solar Reflectivity of Common Roofing Materials and Its Influence on the Roof Heat Gain of Typical Southwestern Residences," Summer Attic and Whole-House Ventilation , NBS Special Publication 548,

National Bureau of Standards, U.S. Department of Commerce, Washington, D.C.,

July 1979 (proceedings of a workshop sponsored by the Department of Energy and

the Attic Ventilation Industry).

85
Roberts, Nail, Rogers, and Greenburg, "Comparison of Computer-Predicted Thermal

Loads with Measured Data from Three Occupied Townhouses," ASHRAE Transactions , Vol. 83, Part I, American Society of Heating, Refrigerating and Air-Conditioning

Engineers, Inc., New York, 197 8.

Sitzer, Moden, and Don Vito, Historical and Forecasted Energy Prices by DoE

Region and Fuel Type for Three Microeconomic Scenarios , DoE/EIA-0184/1 5, U.S.

Department of Energy, Washington, D.C,, July 1979.

Snell, J. E., Achenbach, P. R., and Petersen, S. R., "Energy Conservation in New

Housing Design," Science , Vol. 192, June 25, 1976.

Stamper, E. , "Weather Data," ASHRAE Journal , February 1977.

Tietsma, G. J. and Peavy, B. A., The Thermal Performance of a Two-Bedroom

Mobile Home , BSS 102, National Bureau of Standards, U.S. Department of

Commerce, Washington, D,C», 1978.

U.S. Department of Agriculture, Farmers Home Administration, "Thermal

Performance Standards," Washington, D.C., 1979.

U.S. Department of Energy, Office of Conservation and Solar Energy, Economic

Analysis, Energy Performance Standards for New Buildings , Doc. 9568.00,

Washington, D.C», November 1979.

U.S. Department of Housing and Urban Development, "Minimum Property Standards

for One- and Two-Family Dwellings," Washington, D»C., 1979.

86
APPENDIX A

GLOSSARY OF SELECTED TECHNICAL TERMS

annual cooling requirements - the total yearly output from the cooling system

into the conditioned space of a building needed to maintain the indoor

temperature specified.

annual heating requirements - the total yearly output from the heating system

into the conditioned space of a building needed to maintain the indoor

temperature specified.

core cross section - the cross section of a concrete masonry unit that

contains a hollow cell or a cell filled with an insulating material.

discount rate - the rate of interest reflecting the time value of money that

is used to convert benefits and costs occurring at different times to a common

time.

life-cycle cost - the total owning and operating costs of a building or building subsystem over its useful life, usually discounted to present value.

metered energy requirements - purchased energy as measured at the building

boundary, i.e., before heating or cooling equipment conversion efficiency is

considered

.

mineral wool insulation - inorganic fibrous insulating materials, available in

batt, blanket, rigid, and loose-fill form.

net savings - the savings attributable to a given alternative less the costs of

that alternative.

optimal insulation level - the level of insulation (best expressed in terms of

thermal resistance) which minimizes the life-cycle heating and cooling costs,

including the cost of insulation, attributable to a given building envelope

component

.

R- thermal resistance ( (f t^) (h) ( °F ) /Btu) ; the reciprocal of the heat transfer

coefficient of a building envelope component or a particular material within

the component.

response factor method - a method for calculating the thermal transmission

through a building envelope component which considers the ability of the

component to store heat and the amount of heat which has been stored in the

component in previous hours.

rigid foam insulation - organic cellular insulating materials in rectangular

dimensions, preformed to standard lengths, widths, and thicknesses.

A-1
solar absorptance - the ratio of the radiant flux from the Sun absorbed by a body to that incident to it.

specific heat - the ratio of the quantity of heat required to raise the

temperature of a body 1 °F to that required to raise the temperature of an equal mass of water 1 °F.

thermal mass - the weight of a given volume of material multiplied by its

specific heat.

thermal performance - for a building component, the ability to reduce heat

transmission which contributes to a heating or cooling load.

IJ - overall coefficient of heat transmission or thermal transmittance (air to

air) through a building envelope component, usually expressed in Btu/(ft^)(h)

( °F) where °F is fahrenheit degree temperature difference between air on the

inside and air on the outside of a building envelope component.

web cross section - the cross section of a concrete masonry unit that is solid

concrete

.

A-2
APPENDIX B

GRAPHICAL REPRESENTATIONS OF

ANNUAL HEATING AND COOLING REQUIREMENTS

FOR SELECTED CITIES

B-1
55

50

45

3

£

CO°

40

00

I—s 35

UJ§ 30

Zj

§ 25

i 20

I—5 15

^ 10

5

H

'- Heating

C = Cooling, total C+ = Cooling, to * 78 F

C- Cooling, to* 78 F 8" block wall, hollow cores

8" block wall, perlite filled Wood-frame wall

J \ L

.10 .15 .20 WALL U-VALUE, Btu/(°F'ft2-h)

c^c-

.05 .25

Figure B.l Albany, New York: Relationship Between Annual Heating and

Cooling Requirements and Wall U-value for an 1176 ft^ House

(8-in Block Walls and Wood-Frame Walls)

B-2
CO

COQ

CO

9£ 25 -

LU

OHE 20

o

o

CD

.10 .15 .20

WALL U-VALUE, Btu/( F ft^ h)

Figure B.2 Albuquerque, New Mexico: Relationship Between Annual Heating and

Cooling Requirements and Wall U-value for an 1176 ft^ House

(8-in Block. Walls and Wood-Frame Walls)

B-3
35

30

^ 25

H = Heating

C = Cooling, total C+ - Cooling, to * 78 F

C- Cooling, to -= 78 F 8" block wall, hollow cores

8" block wall, perlite filled Wood-frame wall

5 20

15

10

WALL U-VALUE, Btu ( F ft^ h)

Figure B.3 Atlanta, Georgia: Relationship Between Annual Heating and

Cooling Requirements and Wall U-value for an 1176 ft^ House

(8-in Block Walls and Wood-Frame Walls)

B-4
.05 .10 .15 .20 .25

WALL U-VALUE, Btu/rF ft^ • h)

Figure B.4 Indianapolis, Indiana: Relationship Between Annual Heating and

Cooling Requirements and Wall U-value for an 1176 ft^ House

(8-in Block Walls and Wood-Frame Walls)

B-5
35

30

^ 25

5 20

15

10

1

—

1 1 1 1

H

- Heating

C

C = Cooling, total —

C + = Cooling, to 2 78°F

C- = Cooling, to -= 78'

F

c+ ~

8" block wall, hollow cores

8" block wall, perlite filled Wood-frame wall ^

—— -rX-^—

'

H —

1 1 1 1

C1 .05 • .10 .15 .20 .25

WALL U-VALUE, Btu ( F ft^ h)

Figure B.5 Jackson, Mississippi: Relationship Between Annual Heating and

Cooling Requirements and Wall U-value for an 1176 ft^ House

(8-in Block Walls and Wood-Frame Walls)

B-6
35

30

^ 25

5 20

15

10

H = Heating

C = Cooling, total C+ = Cooling, to > 78 F

C- Cooling, to< 78 F 8" block wall, hollow cores

8" block wall, perlite filled Wood-frame wall

WALL U-VALUE, Btu '( F ft^ h)

Figure B.6 Jacksonville, Florida: Relationship Between Annual Heating and

Cooling Requirements and Wall U-value for an 1176 ft^ House

(8-in Block Walls and Wood-Frame Walls)

B-7
55

50

45

OQ

CO°

40

00

s 35

i 30

CD

o

S 25

a

<c^ 20

_. 15

10

H ^ Heating ^ C = Cooling, total C+ = Cooling, to > 78 F

C- = Cooling, to -= 78 F 8" block wall, hollow cores

8" block wall, perlite filled Wood-frame wall

Figure B.7 Madison, Wisconsin: Relationship Between Annual Heating and

Cooling Requirements and Wall U-value for an 1176 ft2 House

(8-in Block Walls and Wood-Frame Walls)

B-8
H = Heating

C = Cooling, total C+ = Cooling, to * 78 F

C- -- Cooling, to-= 78°F

8" block wall, hollow cores

8" block wall, perlite filled Wood-frame wall

•C- _

.10 .15 WALL U-VALUE, Btu/( F ft^ • h)

25

Figure B.8 Phoenix, Arizona: Relationship Between Annual Heating and

Cooling Requirements and Wall U-value for an 1176 ft^ House

(8-in Block Walls and Wood-Frame Walls)

B-9
40

35

2 30

C0

25

20 -

15 -

C0

2 10 -

5 -

H = Heating

C Cooling, total C+ = Cooling, to 2 78°F

C- - Cooling, to< 78°F

8" block wall, hollow cores

8" block wall, perlite filled Wood-frame wall

-C

-C+

C-

.05 .10 .15 .20

WALL U-VALUE, Btu/(°F-ft2.h)

.25

Figure B.9 Salt Lake City, Utah: Relationship Between Annual Heating and

Cooling Requirements and Wall U-value for an 1176 ft^ House

(8-in Block Walls and Wood-Frame Walls)

B-10
45

40

35

30

25

20

15

10

5

H = Heating

C = Cooling, total C+ = Cooling, to ^ 78°F

C- ^ Cooling, to-= 78°F

8" block wall, hollow cores

8" block wall, perlite filled Wood-frame wall

•C-

.05 .10 .15 WALL U-VALUE, Btu /(°F-ft2 • h)

.20 .25

Figure B.IO Tampa, Florida: Relationship Between Annual Heating and

Cooling Requirements and Wall U-value for an 1176 ft^ House

(8-in Block Walls and Wood-Frame Walls)

B-11
35

03

CD 30

^ 25

=>aUJ

Q£

C3

E 20

oo

H = Heating

C = Cooling, total C+ = Cooling, to 2 li^f

C- Cooling, to-= 78°F

8" block wall, hollow cores

8" block wall, perlite filled Wood-frame wall

CD

15

10

.05 .10 .15 .20 .25

WALL U-VALUE, Btu ( F ft^-h)

Figure B.ll Washington, D.C. : Relationship Between Annual Heating and

Cooling Requirements and Wall U-va lue for an 1176 ft^ House

(8-in Block Walls and Wood-Frame Walls)

B-12
CO

CO

aUJ

Qc: o

u

<3

35

30

^ 25 -

5 20

15 -

10

H = Heating

C = Cooling, total C+ - Cooling, to ^ 78°F

C- = Cooling, to<= 78°F

8" block wall, insulation on inside Brick and block wall, insulation on inside Brick and block wall, insulation in cavity

5 c-

.05 .10 .15 WALL U-VALUE, Btu I F-ft^

.20 .25

Figure B.12 Albuquerque, New Mexico: Relationship Between Annual Heating

and Cooling Requirements and Wall U-value for an 1176 ft^ House

(8-in Block Walls and Brick and Block Walls)

B-13
CO

C/5

35

30

^ 25

aLU

OSCO

E 20

_Joo

o

i 15

10

5 -

H = Heating

C = Cooling, total C+ = Cooling, to > 78°F

C- = Cooling, to* 78°F

8" block wall, insulation on inside Brick and block wall, insulation on inside Brick and block wall, insulation in cavity

.10 .15 .20

WALL U-VALUE, Btu/CF ft^ • h)

25

Figure B.13 Atlanta, Georgia: Relationship Between Annual Heating and

Cooling Requirements and Wall U-value for an 1176 ft^ House

(8-in Block Walls and Brick and Block Walls)

B-14
45

40

35

30

25

20

15

10

5

H = Heating

C = Cooling, total C+ = Cooling, to > 78°F

C- = Cooling, to* 78°F

8" block wall, insulation on inside Brick and block wall, insulation on inside — Brick and block wall, insulation in cavity

•C _

•C-

.05 .10 .15 WALL U-VALUE. Btu ( F ft^ hl

.20 .25

Figure B.14 Indianapolis, Indiana: Relationship Between Annual Heating and

Cooling Requirements and Wall U-value for an 1176 ft^ House

(8-in Block Walls and Brick and Block Walls)

B-15
35

CO

CO

C/5 30

9E 25

H = Heating

C = Cooling, total C+ - Cooling, to i 78°F

C- = Cooling, to< 78°F

CD5 20

o

o

C+

^ 15

I I ^ 10

8" block wall, insulation on inside Brick and block wall, insulation on inside Brick and block wall, insulation in cavity

1

.10 .15 WALL U-VALUE, Btu/

C-

.05 .20 .25

Fft^-h)

Figure B.15 Jacksonville, Florida: Relationship Between Annual Heating and

Cooling Requirements and Wall U-value for an 1176 ft^ House

(8-in Block Walls and Brick and Block Walls)

B-16
Figure B.16 Madison, Wisconsin: Relationship Between Annual Heating and

Cooling Requirements and Wall U-value for an 1176 ft^ House

(8-in Block Walls and Brick and Block Walls)

B-17
H = Heating

C = Cooling, total C+ = Cooling, to * 78°F

C- = Cooling, to* 78°F

8" block wall, insulation on inside Brick and block wall, insulation on inside — Brick and block wall, insulation in cavity

WALL U-VALUE, Btu ("F ft^ • h)

Figure B.17 Phoenix, Arizona; Relationship Between Annual Heating and

Cooling Requirements and Wall U-value for an 1176 ft^ House

(8-in Block Walls and Brick and Block Walls)

B-18
H = Heating

C = Cooling, total C+ = Cooling, to ^ 78°F

C- = Cooling, to<= 78°F

C +

8" block wall, insulation on inside Brick and block wall, insulation on inside Brick and block wall, insulation in cavity

.05 .10 .15 WALL U-VALUE, Btu/rF ft^

.20 .25

Figure B.18 Tampa, Florida: Relationship Between Annual Heating and

Cooling Requirements and Wall U-value for an 1176 ft^ House

(8-in Block Walls and Brick and Block Walls)

B-19
35

CO

(/5 30

°£ 25

E 20

o

o

15

10

H = Heating

C = Cooling, total C+ - Cooling, to 2 78°F

C- = Cooling, to* 78°F

8" block wall, insulation on inside Brick and block wall, insulation on inside Brick and block wall, insulation in cavity

.05 .10 .15 WALL U-VALUE, Btu/( F ft^ • h)

.20 .25

Figure B.19 Washington, D.C« : Relationship Between Annual Heating and

Cooling Requirements and Wall U-value for an 1176 ft^ House

(8-in Block Walls and Brick and Block Walls)

B-20
APPENDIX C

SOLAR ABSORPTANCES OF WALLS BY COLORS

A. Concrete Masonry Unit

Plain or grey

Coral

Adobe Red

Buff

B. Brick

Brown

Light Red

Buff

Red

C. Painted Concrete Masonry Unit

Bone White

Navaho White

Pearl White

Sea Shell Beige

Desert Sand

D. Painted Wood Paneling

55-60 percent

66 percent

68 percent

69 percent

72 percent

62 percent

49 percent

65 percent

27 percent

28 percent

31 percent

45 percent

58 percent

Avocado Green

Sand Dune

Beige

85 percent

74 percent

60 percent

E. Stained Wood Paneling

Weathered Brown

Dark Brown

90 percent

87 percent

^ Source: J. A. Reagan and D. M. Acklara, "Solar Reflectivity of Coimnon Roofing

Materials and Its Influence on the Roof Heat Gain of Typical Southwestern

Residences," Summer Attic and Whole-House Ventilation , NBS SP 548

(Washington, D«C«: National Bureau of Standards, 1979).

C-1

ft U. S. GOVERNMENT PRINTINC OFFICE : 1981 352-978/9037
NBS-lUA (REV. 2-8C) U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO. NBS BSS 134

2. Performing Organ. Report No. 3. Publication Date August 1981

4. TITLE AND SUBTITLE

Determining Cost-Ef f ective Insulation Levels for Masonry and Wood-Frame

Walls in New Single-Family Housing

5, AUTHOR(S)

Stephen R. Petersen, Kimberly A, Barnes, Bradley A. Peavy

6. PERFORMING ORGANIZATION (If joint or other thon NBS. see instructions) 7. Contract/Grant No. NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE 8. Type of Report & Period Covered

WASHINGTON, D.C. 20234 Final

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City, State, ZIP)

Office of the Assistant Secretary for Conservation and Solar Applications

Department of Energy

Washington, DC 20545 ^

10. SUPPLEMENTARY NOTES

Library of Congress Catalog Card Number: 81-600083

Document describes a computer program; SF-185, FlPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most si gnificant information. If document includes a si gnificant

bibliography or literature survey, mention it here) Economically optimal insulation methods and resistance levels for three

different types of walls in a one-story, single-family residence are calculated

for a wide range of geographic locations, energy prices, heating and cooling

equipment efficiencies, and financial evaluation criteria. The three basic

wall types examined are 8-in concrete block walls, brick and block walls, and

wood-frame walls with lightweight siding. Changes in annual heating and cooling

requirements for an 1176 ft^ prototype house resulting from several different

insulation resistances in each wall type are calculated using the NBS Load

Determination program and Test Reference Year climate data for a number of

geographic locations. Changes in heating requirements are correlated with

heating degree days to provide estimates of energy savings in all geographic

regions of the continental United States. Cooling requirements are not found

to vary significantly with the thermal resistance of the walls under a typical

operating profile except in the southwestern desert. An index number system

is developed to quickly determine insulation levels based on the data generated

in the report.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

building design; building economics; energy conservation; exterior wall; HVAC

calculations; insulation; life-cycle cost analysis; masonry; mass.

13. AVAILABILITY

[X|] Unlimited 1^ For Official Distribution. Do Not Release to NTIS

[x] Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.

1231 Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

126

15. Price

$4.75

USCOMM-DC 6043-P80
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