NEW NIST PUBLICATION

October 18» 1988

NBSIR 88-3829

Technical and Economic Analysis of

CFC-Blown Insulations and Substitutes

for Residential and Commercial

Construction

Stephen R. Petersen

Applied Economics Group

Mathematical Analysis Division

Center for Computing and Applied Mathematics

A. Hunter Fanney

Heat Transfer Group

Building Environment Division

Center for Building Technology

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Gaithersburg, MD 20899

July 1988

Sponsored by

Building Systems Division

Office of the Assistant Secretary for Conservation

and Renewable Energy

ILSo Department of Energy

Washington, DC 20234

NBSIR 88-3829

TECHNICAL AND ECONOMIC ANALYSIS OF

CFC-BLOWN INSULATIONS AND SUBSTITUTES

FOR RESIDENTIAL AND COMMERCIAL

CONSTRUCTION

Stephen R. Petersen

Applied Economics Group

Mathematical Analysis Division

Center for Computing and Applied Mathematics

A. Hunter Fanney

Heat Transfer Group

Building Environment Division

Center for Building Technology

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Gaithersburg, MD 20899

July 1988

Sponsored by

Building Systems Division

Office of the Assistant Secretary for Conservation

and Renewable Energy

U.S. Department of Energy

Washington, DC 20234

U.S. DEPARTMENT OF COMMERCE, C. William Verity, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Abstract

Rigid foam insulations blown with chloroflourocarbons (CFC's) are among the

most thermally efficient materials available for insulating walls and roofs of

buildings. While they are more expensive than traditional insulating

materials, their usage where space constraints dictate a more efficient

insulator have become commonplace. Increasing concern about the effect of

CFC's released to the atmosphere may result in restrictions on the

availability of these insulation materials. This report evaluates the thermal

performance and economics of rigid foam insulating materials containing CFC's

and alternative insulation materials that contain little or no CFC

Residential walls (wood-frame and masonry), commercial wall systems (frame,

masonry, and curtain wall) and commercial low-slope roof systems are examined

in a wide range of climates in the United States to determine the cost

effectiveness of rigid foam insulation materials. Economic substitutes for

insulation materials containing CFC exist; however, they are not compatible

with all types of wall/window and roof systems and thus may make some wall and

roof systems impractical.

iii
Acknowledgments

The authors acknowledge the assistance of all those who helped in preparing

and reviewing this report. Douglas Burch and Betty Licitra provided valuable

assistance by conducting the finite difference analysis for the commercial

walls systems. Douglas Burch, Dr. James Hill, Rosalie Ruegg, Bob Mathey, and

Walter Rossiter, (all of NBS) , Kathy Wolfgram and Bill Strzepek (Dow Chemical,

U.S.A.), George Courville and Jeff Christian (ORNL) , Bill Gerkin (formerly of

DOE) , and Terry Statt (DOE) all provided helpful comments during the

preparation of this report. Laurene Linserunayer and Flora Parsons helped

prepare the final manuscript.

iv
CONTENTS

Page

ABSTRACT iii

ACKNOWLEDGMENTS iv

CONTENTS v

1. INTRODUCTION ......... . . 1

2. INSULATED SHEATHING FOR RESIDENTIAL WALLS 3

2.1 Wood-Frame Walls ........ 3

2.1.1 Base-Case WaLl System 5

2.1.2 Insulated Wall Sheathings and Estimated Costs 5

2.1.3 2 x 6 in. Wood-Frame Wails 8

2.1.4 Economic Thickness of Insulating Sheathing 9

2.1.5 Implications for CFC Substitutes for Wood-Frame Walls . . 12

2.1.6 Potential Impact of ASHRAE Standard 90.2 15

2.2 Rigid Foam Insulation in Residential Masonry Wall Construction . 17

2.2.1 Economic Thickness of Insulation . 18

2.2.2 Implications for CFC Substitutes for Residential Masonry

Walls 19

3. EXTERIOR WALLS FOR COMMERCIAL AND HIGH-RISE RESIDENTIAL BUILDINGS . . 23

3.1 The High Cost of Lost Space 25

3.2 Simulation Procedures and Methods of Economic Analysis 26

3.3 Insulation Analysis by Wall Type 28

3.3.1

Concrete -Masonry Walls 28

3. 3. 1.1 Brick and Block Cavity Walls: 28

3. 3. 1.2 Concrete Block Walls- -Exterior Insulation: ... 29

3.3. 1.3 Concrete Block Walls- -Interior Insulation: ... 31

3. 3. 1.4 Wood and Steel Stud Wall Systems: 31

3. 3. 1.5 Curtain Wall Systems: 32

3.4 Conclusions for Commercial/High-Rise Wall Systems 35

v
CONTENTS CONTINUED

Page

4. LOW- SLOPE ROOF SYSTEMS FOR COMMERCIAL BUILDING APPLICATIONS ..... 37

4.1 Alternatives Examined ..................... 37

4.2 Economic Thickness of Insulation ................ 41

4.3 Implications for CFC Substitutes in Commercial Roof Systems . . 44

4.4 Potential Impact of ASHRAE Standard 90.1 ...... . 44

5. SUMMARY 47

APPENDIX A. ............................. . A

APPENDIX B. ......... . .............. B-l

APPENDIX C .............. C-l

vi
LIST OF TABLES

Page

Table 2-1. Insulating Sheathing for Exterior Walls in New Housing Units . 4

Table 2-2. Thermal Transmittances (U) for Exterior Wood-frame Walls ... 7

Table 2-3. Economic Thickness for Insulating Sheathing (inches) .... 11

Table 2-4. Housing Completions in 1986 by Region and Heating System Type 13

Table 2-5. Energy Penalty for Substituting 0.5 in. EPS (R-2.2) for 0.5

in. Polyisocyanurate (R-3.6) or 0.5 in. Extruded Polystyrene

(R-2.5) 14

Table 2-6. Exterior Wall U-Values for 8-Inch Block with Rigid Foam

Insulation 20

Table 2-7. Economic Thickness for Rigid Foam Insulation in Masonry Walls

--Interior Insulation .................... 21

Table 2-8. Economic Thickness for Rigid Foam Insulation in Masonry Walls

--Exterior Insulation ..... 22

Table 3-1. Approximate Thickness Limitations on Plastic Foam Insulation

Consistent With 6000 Btu/ft^ Fuel Content 25

Table 3-2. Approximate Economic R-values for Brick-and-Block Cavity

Walls in Commercial Buildings 30

Table 3-3. Economic R-values for Foam Sheathing in Wood and Steel Stud

Walls 33

Table 3-4. Economic Thicknesses of Composite Foam-Core Curtain Wall

Panel Insulation 34

Table 4-1. Insulation Conductivity and Thicknesses .... 39

Table 4-2. Installed Insulation and Annual Maintenance Costs 39

Table 4-3. Optimal R-Values for BUR Insulation Based on 20-Year LCC ... 42

Table 4-4. Optimal R-Values for BUR Insulation Based on Cash Flow

Analysis at End of Second Year 43

Table 4-5. Energy Penalty for Substitution of 2 in. EPS (R-7.7) for

2 in. Polyisocyanurate (R-11.8) per 1000 ft^ of Roof Area . . 45

Table 4-6. Minimum R-Values and Corresponding Insulation Thicknesses for

Commercial Roof Deck Systems 45

Appendix B-l Residential Analysis B-l

Appendix B-2 Commercial Analysis B-l

Appendix C-l Installed Insulation Costs and U-Values Used in Analysis. . . C-l

Appendix C-2 Residential Wood-Frame Walls, Without' Extension Jam Costs . . C-2

Appendix C-3 Insulation in Masonry Walls .......... C-3

Appendix C-4 Built-Up Roof Insulation C-4

LIST OF FIGURES

Figure 2-1. Proposed U-Value Requirements for Wood-Frame Walls in SingleFamily Houses 16

Figure 4-1. ORNL Installed Insulation Costs for Built-Up Roofs 40

vii
.

.

.

*

*
1 . INTRODUCTION

Two of the most efficient insulating products used in new building

construction today are polyurethane (including polyisocyanurate) and extruded

polystyrene rigid foam insulation. These materials provide a cost-effective

means for improving the thermal performance of buildings over a wide range of

climates, especially when there are practical or economic limitations to

insulation thickness in wall and roof systems. Both of these materials are

manufactured with chemicals that contain chloroflourocarbons (CFC's), which

contribute substantially to their superior insulating properties. However,

CFC's have been implicated as a significant source of atmospheric ozone

depletion, and thus their manufacture and/or end use may be curtailed by the

Federal Government.

The purpose of this report is to investigate the suitability, cost

effectiveness, and potential energy consequences of alternative insulation

materials which require lower levels or no CFC's in their manufacture. Three

specific building components commonly insulated with CFC-blown rigid foam

sheathings are being investigated by NBS: residential wall systems (both woodframe and masonry), commercial wall systems, and commercial low-slope roof

systems. Each of these building components is evaluated over a wide range of

climatic conditions and heating/cooling systems types.

The insulation substitutes investigated in this report are expanded

polystyrene (EPS) and fiberglass, neither of which contains CFC's. These

materials are in fact less costly than polyurethane (and its common form,

polyisocyanurate) and extruded polystyrene. However, because they are less

efficient insulators, they require greater thicknesses to achieve the same

level of overall thermal performance in walls and roofs. Thus the key to the

economic analysis of substitutes for CFC-blown insulations is not the cost of

the insulation materials themselves but rather the cost of modifying the

building components (i.e., walls and roofs) in order to accommodate the

thicker insulation.

The general investigative approach used in preparing this report was to

identify the current usage of rigid foam insulation in specific building

components, identify substitute materials, identify constraints that might

make the use of substitutes more costly, and then Calculate economic

thicknesses for both the CFC-blown insulations and their substitutes in a wide

range of climates. Where the economic thickness for the substitute (i.e., the

maximum amount that is economically justified on a life-cycle basis) has a

lower thermal resistance (R-value) than the economic thickness for the CFCblown material, the annual energy penalty is calculated, both in Btu terms and

their present-value dollar equivalent (i.e., the discounted value of increased

energy purchases over the study period)

The construction cost data used in this report were derived from a number of

sources. Where possible, cost data for residential construction was taken

directly from ASHRAE Research Project 494-RP, "An Economic Data Base in

Support of SPC 90.2: Costs of Residential Energy, Thermal Envelope and HVAC

Equipment," prepared by the NAHB National Research Center (1986) in support of

the draft ASHRAE 90.2 standard "Energy Efficiency Design of New Low-Rise

1
Residential Buildings." Rigid foam sheathing prices were obtained from at

least six sources; ultimately the prices suggested by the Dow Chemical Co.

were used, as they provided the most comprehensive and consistent set of price

data found. Costs of extension jambs for wood- frame windows came directly

from the NAHB National Research Center. All residential construction costs

were adjusted to include 25 percent builder overhead and profit. The prices

of insulated sheathing provided by Dow Chemical Co. for residential wall

systems were also used as the basis for evaluating the costs of insulating

commercial wall systems. Costs surveys for commercial buildings (e.g., Means

and Dodge) were also consulted, but found to be unrealistically high for

insulated sheathing costs.

Cost data for insulating low-slope roof systems were taken directly from

ORNL/TM-9904 , "Economic Analyses of Insulation Materials Used In Low-Slope,

Built-Up Roof Systems," by George Courville and J.O. Kolb at Oak Ridge

National Laboratory (1984). That study represents a comprehensive technical

and economic analysis of alternative insulating materials suitable for use on

steel roof decks. The cost data and analysis in that study represent the

consensus of a wide range of roofing experts from government and industry, and

could not be duplicated without major funding and time commitment.

The regional energy costs and life-cycle cost procedures used in this report

were based on Federal Energy Management Program guidelines, as outlined in NBS

Handbook 135, Life-Cvcle Cost Manual for the Federal Energy Management

Program . (1987).

Estimates of annual energy savings due to the use of insulation in residential

wood- frame and masonry walls were based on thermal performance equations

developed in support of the ASHRAE Standard 90.2 research program. Estimates

of energy savings for commercial walls systems were based on parametric

analyses using the ASHRAE "Envelope System Performance Compliance Program"

developed in support of ASHRAE Standard 90.1. Corresponding energy estimates

for built-up roof systems were taken directly from the ORNL report. Estimates

of HVAC equipment efficiencies were taken directly from the corresponding

ASHRAE and ORNL sources in order to maintain as much consistency as possible

with these sources

Because the energy prices used in this study are regional, rather than sitespecific, the resulting economic thicknesses or R-values of insulation

reported here should be regarded as representative of the general climatic

location rather than the specific city used in analysis.

2
2. INSULATED SHEATHING FOR RESIDENTIAL WALLS

2.1 Wood-Frame Walls

Three types of rigid foam sheathing for insulating exterior walls are

typically used in the United States: polyurethane (mostly of the

polyisocyanurate variety) , extruded polystyrene and expanded polystyrene

(EPS) . In residential wood-frame construction these insulating sheathings

typically range in thickness from 0.5 to 1.0 inch, usually replacing noninsulating sheathings which range from 0.125 to 0.5 inches in thickness.

Rigid foam sheathing currently represents about 25-30 percent of the wall

sheathing market on a square foot basis for single-family housing^, although

major manufacturers claim that the number of new houses built with these

materials is between 40 and 50 percent^. In fact, the economic analysis

conducted in this section concludes that insulating sheathing used in

conjunction with wood-frame walls and R-13 fiber glass is generally cost

effective on a life-cycle-cost basis in most regions of the continental United

States except southern Florida and the southern California coast.

Most of the conventional (referred to in this report as "non- insulating"

)

sheathing used with wood-frame walls in the United States is 0.5 inch plywood

or fiberboard, and 0.125 inch aluminum- foil- faced hard board, with the latter

growing increasingly common. In general, these non- insulating sheathings have

better structural characteristics than the rigid foam sheathings. As a

result, corner bracing or plywood sheathing at the corners is often required

when rigid foam sheathings are substituted for the non- insulating sheathings

in wood- frame construction.

Table 2-1 shows the thermal conductivity (k-value) of each of the three

insulating sheathings types examined, along with the corresponding thermal

resistance (R-value) per inch and the estimated price per square foot for one

inch of thickness (uninstalled) and per unit of thermal resistance (R) . Data

are shown for two different densities of EPS: the 1.0 lb per cubic foot is

most commonly available, but the 1.5 lbs per cubic foot sheathing is also

available and can be manufactured using the same equipment by simply using

more feedstock (beads) . None of these three sheathing types has an advantage

from a structural standpoint and all can perform adequately from a moisture

migration standpoint in above-ground applications. While EPS is typically a

more fragile sheathing product than the other foam sheathings, and more

susceptible to ultraviolet degradation while exposed, it is available with

foil and/or vinyl facings to make it less vulnerable to damage.

^ LSI Systems, Inc., "Survey of Builder Usage of Building Materials for

the Construction of New Houses: Sheathing," Crofton, Md, August 1986.

o^Because rigid foam sheathing is not typically installed at corners or on

walls adjacent to unheated areas (e.g., garages and roof gables), the ratio of

rigid foam to total sheathing in houses insulated with rigid foam sheathing is

likely to be considerably less than 1.0, explaining some of the discrepancy

between these estimates.

3
Table 2-1. Insulating Sheathing for Exterior Walls in New Housing Units

Polyurethane Polystyrene

(Polyiso- Exj>anded Extruded

cvanurate) 1.0 lbs/ft:5 1.5 lbs/ft-3 k-value (Btu-inch/h-ftz -F) a 0.1389 0.2597 0.2398 0.2000

R per inch 7.2 3.85 4.17 5.00

typical cost per sq.ft.^:

per R $0,046 $0,031 $0,038 $0,052

per inch $0.33 $0.12 $0.16 $0.26

a Based on ASHRAE Handbook Of Fundamentals . 1985.

k These costs are representative of builder costs for the sheathing material

only, at 1 inch thickness. Costs vary by region, local supply conditions,

and volume of purchase.

The prices shown in table 2-1 for the four rigid foam sheathing products are

representative of builder costs at the national level. These prices vary

regionally and may vary significantly with the volume of purchase and the

degree of competition among suppliers and producers in a given market. While

the price per R of extruded polystyrene sheathing tends to be slightly higher

than that of polyisocyanurate , competitive pressures in some locations will

often bring the prices of these two sheathing types closer together, so that

the selection of one over the other will often be based more on perceived

product differences and availability than price difference, per se.

Two important relationships can be derived from table 2-1: (1) Polyurethane

insulation provides the most insulation effect for a given thickness, making

it the most thermally efficient of the three, while its price per unit of

thermal resistance is approximately 25 percent more per resistance unit (R)

than that of EPS, and (2) EPS has the lowest insulation efficiency of the

three; however, it also has the lowest price, both per unit of thermal

resistance and per unit thickness, at either of the densities shown.

Therefore, if the design objective is to insulate a wail of a given thickness

to the greatest degree possible, polyurethane would likely be the insulating

sheathing of choice. On the other hand, when space is not a constraint, and

there are no costs related to increasing the wall thickness to accommodate

more insulation, the lower density EPS sheathing is likely to be the most

cost-effective insulating sheathing.

These latter observations are crucial to establishing the cost penalties

related to the use of substitute insulation materials, such as EPS or fiber

glass, for CFC-blown insulation materials. That is, any cost penalties must

be based on increased energy consumption or the cost of expanding the wall

thickness to accommodate more insulation, since the substitute materials

themselves cost less than the CFC-blown materials.

4
Options to accommodate more insulation in wood frame walls can take two

distinct paths: (1) use of insulating sheathing at various thicknesses, or (2)

use of 2x6 in. framing, in place of 2x4 in. framing, in order to accommodate

more fiber glass insulation (usually R-19 batts) , with or without the use of

insulated sheathing. Superinsulation techniques (e.g., double walls with more

than 6 inches of fiber glass insulation sandwiched in the resulting cavity)

can be used to insulate wood-frame walls beyond these levels. However, these

are not representative of common construction practice in the United States

and will not be examined in this report.

2.1.1 Base-Case Wall System

In this report, 0.5 in. conventional fiberboard sheathing over a 2x4 in. woodframe wall with R-13 fiber glass insulation will be used as the primary

reference point for calculating the cost of adding insulated sheathing to

wood-frame walls. R-13 is the maximum amount of fiber glass insulation that

can be installed in a conventional 2 x 4 in. wood- frame wall. R-13 fiber

glass is used in the base case wall rather than the more typical R-ll because

its additional cost (approximately $0.06 per sq.ft, relative to R-ll) is

generally less than the cost of an equivalent (R-2) amount of insulated

sheathing product. Moreover, the R-13 fiber glass requires no additional

space and therefore does not increase the overall thickness of the wall.

The use of fiberboard sheathing in the base case will result in conservative

estimates of the energy savings from the substitution of insulating sheathing

products. While fiberboard sheathing has been the traditional sheathing

product used with wood- frame construction, it has been losing some of its

share of the market to 0.125 in. aluminum foil-faced board, which has somewhat

lower insulating properties . The savings from insulating sheathings are

somewhat greater when substituted for foil-faced board rather than for the

fiberboard. However, the economic thickness of insulated sheathing will not

change significantly as a function of the choice of the base-case sheathing.

2.1.2 Insulated Wall Sheathings and Estimated Costs

Table 2-2 shows the U-values for walls systems having either typical 0.5 in.

fiberboard sheathing or rigid foam insulating sheathing at several

thicknesses. Heat loss and gain through the opaqud portion of exterior walls

are assumed to be proportional to these U-values for any given wall type.

One -half inch is the conventional sheathing thickness for which most basic

wood- frame window and door systems are designed. Insulated sheathing is

assumed to replace fiberboard sheathing. To accommodate sheathing thicker

than 0.5 inch, window and door jambs must be expanded. (While some wood- frame

windows can be extended slightly further without requiring extension jambs,

the implications of this thickness constraint are the same. That is,

extension jambs will be required to accommodate less efficient sheathings,

e.g., EPS, in order maintain the same thermal performance as the most

efficient of the CFC-blown insulations, e.g., polyisocyanurate .

)

The cost of expanding a wood- frame wall to accommodate thicker sheathing is

primarily related to extending the window and door jambs so that they will

5
remain flush with the inside wall surface. For wood- frame windows the cost of

jamb extensions can be substantial. Jamb extensions provided by the window

manufacturer for an average size wood-frame window typically cost $12-$25,

depending on the thickness. The average house has 14 windows^ and 2 wooden

doors, so that the total cost for any increase in sheathing thickness up to

1.5 inches total is estimated at $200 [16x12, rounded], plus builder overhead

and profit. For thicknesses between 1.5 and 2.5 inches, a total cost of

approximately $300 [16x19, rounded], plus builder overhead and profit, is

estimated for this same house. (The cost of wood window and door jamb

extensions are typically based on their thickness, rounded up to the next

inch .

)

For metal windows, however, there is likely to be no cost penalty for jamb

extensions, because the inside window openings (sometimes referred to as

"returns") are typically finished with gypsum board, which can be extended an

inch or two at no appreciable incremental cost in terms of either material or

labor. The door frames will still likely require jamb extensions at a similar

cost to those of windows, for a total of approximately $25 (up to one inch),

plus builder overhead and profit. For houses with metal windows, only this

smaller $25 cost will be assumed.

A cost credit can be attributed to the use of EPS sheathing substituted for

polyisocyanurate or extruded polystyrene since its cost per R is significantly

lower. The builder cost for 0.5 inch polyisocyanurate (R-3.7) is

approximately $200 per 1000 sq. ft.^ EPS with the same R-value (approximately

0.86 inches) has a cost of approximately $155. In an average 1650 sq.ft,

single-family house-* the gross exterior wall area ranges from 1300-1900

sq.ft., depending on the configuration and number of stories. Assuming a

gross wall area of 1600 sq. ft.

,

the material savings from substituting EPS

for polyisocyanurate would be approximately $72 [ ($200- 155)xl . 6 ]

,

not

including builder overhead and profit. The material cost for 0.5 in. extruded

polystyrene (R-2.5) is approximately $170 per 1000 sq. ft., while R-2.5 EPS

(0.6 in.) costs approximately $125 per 1000 sq. ft., for a savings of

approximately $72 [ (170-125)xl . 6]

,

the same as that for EPS substituted for

polyisocyanurate

.

^LSI Systems, Inc., "Survey of Builder Usage of Building Materials for

the Construction of New Houses: Windows," Crofton, Md, August 1986.

^All costs per square foot for residential construction used in this

report are based on gross wall area rather than net wall area as this is

common cost-estimating practice. However, the heat loss/gain calculations are

based on opaque wall area only. In comparing costs of insulation versus energy

costs, an assumption of 15 percent window and door area is assumed.

^The median floor area of new single-family houses sold in the United

States in 1986 was 1650 sq. ft. Approximately half of all new houses are one

story and half two or more stories. Source :U.S. Departments of Commerce and

Housing and Urban Development joint publication "Characteristics of New

Housing: 1986," Construction Reports C25-86-13, Washington, D.C.,June 1987.

6
Table 2-2. Thermal Transmittances (U) for Exterior Wood-Frame Walls

(Btu/ft^-h-F)

Thermal Transmittance (U)

Wall construction/ Conventional Rigid Foam Sheathing

Fiber glass blanket plus Fiberboard Polyurethane Pp.iy stvrene

sheathine thickness Sheathing ('Polvisocvanurate') Expanded13 Extruded

2x4 wall (16 in. centers)/

R-13 fbrgls + 0.5 in. 0.0710 0.0603 0.0669 0.0650

R-13 fbrgls +1.0 in. n/a 0.0490 0.0582 0.0553

R-13 fbrgls + 1.5 in. n/a 0.0415 0.0515 0.0483

2x6 wall (24 in. centers)/

R-19 fbrgls + 0.5 in. 0.0524 0.0464 0.0502 0.0491

a Wood frame wall U-values are based on 2x4 in. studs (R=4.38) with 15 percent

frame- to-wall area ratio or 2x6 in. (R=6.88) studs with 12 percent frame- to-wall

area ratio. Other assumptions include the use of 0.5 in. gypsum wallboard

(R=0.45), 0.5 in. asphalt- impregnated fiberboard sheathing (R=1.32), and 0.5 in.

wood bevel lapped siding (R=0.81), outside surface R=0.17, inside surface R=0.68.

U-values are for opaque wall areas only. The fiberboard sheathing is replaced by

the thermal sheathing in these calculations. All U-values shown here are based on

parallel heat transfer calculation methods.

b 1.5 lbs/ft3 EPS

Because the foam sheathing is added to the outside of the house, no inside

space is lost and thus there is no cost penalty for lost space.

Theoretically, slightly more siding will be needed at each corner of the

house. However, for one or two inches this cost is likely to be trivial,

since it would not likely require the ordering of additional materials.

Thus the cost of substituting EPS sheathing for 0.5 in. polyisocyanurate or

extruded polystyrene sheathing, at a thickness sufficient to maintain

equivalent thermal performance, can either increase or decrease construction

costs, depending on the type of window and door systems used. Where metal

windows are used, a potential materials cost savings of $72, plus 25 percent

builder overhead and profit, could result in a total savings of approximately

$90 for a typical single-family house. In houses with wood-frame windows, the

materials cost could increase by $128 per house [ $ 200 - $ 7 2 ]

plus 25 percent

builder overhead and profit, for a total increase of approximately $160.

Once the wood extension jambs have been added to windows and doors, no

additional jamb cost is assumed for sheathing thicker than 0.5 inches, until

1.5 inches is reached. Thus EPS (1.5 lb/ft 3 density) can be substituted for

0.625 or 0.75 in. polyisocyanurate or extruded polystyrene sheathing,

maintaining the same R-value at little or no increase in wall -expans ion costs,

7
and at some savings in terms of material costs.

2.1.3 2x6 in. Wood-Frame Walls

The second design option that is evaluated in this section is the substitution

of 2x6 in. framing, R-19 fiber glass batts , and conventional sheathing for 2x4

in. framing with R-13 fiber glass and 0.5 in. polyisocyanurate sheathing.

Structurally, 24 in. stud centers can be used with the 2x6 wall instead of the

16 in. centers used with the 2x4 framing, although 0.625 in. gypsum board (in

place of 0.5 in.) may be needed to maintain the rigidity of the inside wall

surface. The 2x6 wall described here is approximately equivalent to the 2x4

wall in terms of its overall thermal transmittance (U) . (Any difference in

U-value is more likely to be due to construction anomalies than theoretical

differences.) However, the construction cost and value of lost interior space

for the former is considerably greater than that for the latter.

The additional framing and fiber glass costs, plus the substitution of

conventional fiberboard sheathing for the thermal sheathing results in a net

construction cost increase of approximately $.10 per sq. ft. of gross wall

area, or $160 for the average 1650 sq.ft, house with 1600 sq. ft. of exterior

walls. Two important adjustments must be made to this cost: (1) the cost of

window and door jamb adjustments and (2) the cost of the foregone interior

space due to the extension of the wall inward instead of outward.

(1) Because the wall thickness is increased by a full two inches, the cost of

the jamb extensions for wood windows and doors will be approximately $20 per

unit. Again assuming 14 windows and two wood doors in an average size house,

this amounts to $320 per house. However, if metal windows are used and the

window frames are finished with drywall, this cost will be inconsequential.

Then only the cost of extending the door jambs will be considered, at an

estimated total of $40 for two doors.

(2) Since the exterior walls are two inches thicker, every six linear feet of

wall occupies one square foot of interior space. The cost of extending the

walls of the house to maintain equivalent indoor space can serve as a

reasonable proxy for the cost of this foregone area. A detailed cost analysis

of the additional foundation, flooring, wall, and roof costs suggests that the

incremental cost of unfinished floor space is approximately $7.00 per sq. ft.,

including 25 percent builder overhead and profit. ^ (The average cost per

square foot for a new house is not a good proxy for this cost, since the end

walls, interior finishing costs, windows and doors, wiring, plumbing, etc.,

remain unchanged.) This is equivalent to approximately $0.12 [ (7/1 . 25)/(6x8)

]

per square foot of gross wall area before overhead and profit (to make this

compatible with the other cost estimates) , or approximately $200 for the 1600

sq. ft. of exterior wall area in the average house.

Thus the total cost estimate of 2x6 in. wood frame walls with R-19 fiber glass

^Petersen, S.R., Economics and Energy Conservation in the Design of New

Single-Family Housing . NBSIR 81-2380, National Bureau of Standards,

Gaithersburg, Md, August 1981, page 44.

8
insulation and 0.5 fiberboard sheathing substituted for 2x4 walls with R-13

and 0.5 in. polyisocyanurate sheathing is estimated at $680 if wood windows

are used and $400 if metal windows are used. Adjusted for 25 percent builder

overhead and profit, these estimates are $850 and $500, respectively.

2.1.4 Economic Thickness of Insulating Sheathing

Economic thicknesses of rigid foam sheathing used in place of fiberboard

sheathing are shown for three heating system types and 12 cities in table 2-3.

These thicknesses are shown in inches rather than thermal equivalents

(R-values) so that the reader will see how jamb extension costs affect the

determination of economic thickness. Economic thicknesses were calculated

both with and without jamb extension costs; where the latter differ from the

former they are shown in parentheses. Climate factors and the DOE region for

each of these cities are shown in Appendix A. The various thicknesses of

insulation evaluated and corresponding costs and wall U-values are shown in

tables C-l through C-3 of Appendix C.

The economic sheathing thickness is defined here as that thickness with the

greatest net present-value savings, i.e., the present value of energy savings,

in dollars, over a specified time horizon, less the installed insulation cost.

Energy savings were calculated for both space heating and cooling, using the

PEAR regression coefficients for wood-frame walls^. (Cooling savings are

relatively small except in Dallas, Orlando, and Phoenix.) The present value

(i.e., discounted value) of these energy savings over 25 years were then

calculated using regional DOE energy price forecasts (in 1987 constant

dollars) for natural gas and electricity and a seven percent real (i.e., net

of general inflation) discount rate.® These prices and the corresponding

uniform present worth factors used in this analysis are shown in Appendix B.

One alternative economic criteria to the life-cycle cost approach is the "twoyears- to-positive-cash-flow" approach used as a benchmark in the development

of the ASHRAE 90.2 Residential Energy Standard. In this alternative approach,

the annual energy savings are compared with the increase in annual mortgage

costs, on an after-tax basis, as of the end of the second year. (The second

year is used because income tax savings may not be realized until that time.

The conservation features are assumed to be financed over thirty years at nine

^PEAR (Program for Energy Analysis of Residences) is a microcomputer

program developed at Lawrence Berkeley Laboratory for the Department of

Energy. The regression equations used here were derived from this PEAR

program to support the development of the draft ASHRAE 90.2 Residential Energy

Standard. Thus the savings calculated here are compatible with the energy

savings estimated in this draft standard.

O

These are general data requirements for use in energy conservation

studies for DOE. DOE rules for the analysis of energy conservation

investments in Federal buildings do not allow the use of a study period longer

than 25 years. However, the use of a seven percent discount rate with a study

period longer than 25 years would have no practical affect on the results of

this analysis.

9
percent interest, with no down payment. The marginal tax bracket is assumed to

be 30 percent, combined Federal and state.) No discounting or projecting of

energy costs beyond the second year is required in this approach. If the

savings are greater than the increased mortgage cost (after taxes) by the end

of the second year, the investment is assumed to be cost justified from a

homeowner standpoint.

This second economic criterion for cost effectiveness may appear more

attractive to many homeowners than one based on a 25 year life-cycle cost

analysis. In this analysis both criteria give almost identical results in

terms of determining optimal sheathing thicknesses. (However, this

relationship will not always hold in performing engineering-economic analyses,

and therefore two-years-to-positive-cash-flow should not be used as general

test for determining cost effectiveness.) In a few cases, where an additional

increment of sheathing thickness was justified on the two-years- to-positivecash-flow basis but had a small net loss on a life-cycle cost basis, that

increment was included in the table of economic thicknesses.

The results in table 2-3 are quite useful in the analysis of EPS as a

substitute for polyisocyanurate and extruded polystyrene sheathings. When

natural gas is used as a heating fuel, and jamb extension costs for wood

windows and doors are on the order of those discussed above, the economic

level of sheathing does not exceed 0.5 inches in any of the 12 cities. If the

0.5 in. EPS is substituted for the more thermally efficient sheathings, there

will be an energy penalty as well as a construction cost savings.

When a heat pump is used for heating, economic thicknesses of sheathing exceed

0.5 inches only in the coldest two cities (Boston and Minneapolis). In these

two locations, the use of EPS at a thickness thermally equivalent to the 0.5

to 1.0 inches of polyisocyanurate or extruded polystyrene typically used will

be cost effective. However, heat pumps do not have a large market share in

these locations, and thus the number of houses in this category will be small.

In the other 10 locations, only the 0.5 inch EPS can be economically

justified.

10
Table 2-3. Economic Thickness for Insulating Sheathing (inches)

(For Wood-Frame Walls with R-13 Fiber Glass Insulation)

HEATING SYSTEM3

/

SHEATHING TYPE BOSTON WASHINGTON ATLANTA ORLANDO MINNEAP :KANS CITY

NATURAL GAS/

Polyisocyanurate 0.5(1 .0) D 0.5 0.5 0.0 0. 5(1.0) 0.5

EPS 0.5(1. 5) 0. 5(1.0) 0.5(0.87° )0 .

0.5(1. 5) 0. 5(1.0)

Extruded Polys

0. 5(1.0) 0.5 0.5 0.0 0. 5(1.0) 0.5

HEAT PUMP/

Polyisocyanurate 1.5(1. 5) 0.5 0.5 0.0 1.5(1. 5) 0. 5(1.0)

EPS 1. 5(2.0) 0.5(1. 5) 0.5(0.87) 0.5 2.0 0.5(1. 5)

Extruded Polys. 1.5(1. 5) 0.5 0.5 0.0 1.5 0. 5(1.0)

ELECTRIC/

Polyisocyanurate 1. 5(2.0) 0.5(1. 5) 0.5 0.0 1. 5(2.0) 1.5

EPS 2.5 1. 5(2.0) 0.5(1. 5) 0.5 2.5 1. 5(2.0)

Extruded Polys. 1. 5(2.0) 1.5 0. 5(1.0) 0.5 1. 5(2.0) 1.5

DALLAS/FW DENVER PHOENIX SEATTLE OAKLAND LOS ANGELES

NATURAL GAS/

Polyisocyanurate 0.5 0.5 0.5 0.5 0.0 0.0

EPS 0.5 0. 5(1.0) 0.5(0.87) 0.5(0.87) 0.5 0.5

Extruded Polys. 0.5 0.5 0.5 0.5 0.5 0.0

HEAT PUMP/

Polyisocyanurate 0. 5(1.0) 0.5 0.5 0.5 0.5 0.0

EPS 0.5(0.87) 0. 5(2.0) 0.5(0.87) 0.5(0.87) 0.5(0.87) 0.5

Extruded Polys. 0.5 0. 5(1.0) 0.5 0.5 0.5 0.0

ELECTRIC/

Polyisocyanurate 0.5 1.5 0.5 0.5 0.5 0.5

EPS 0.5(1. 5) 2. 0(2. 5) 0. 5(1.0) 0.5(1. 5) 0.5(1. 5) 0.5

Extruded Polys. 0.5 1.5 0.5 0.5 0. 5(1.0) 0.5

aElectric air conditioning assumed in all cases.

^Values in parentheses represent levels computed without jamb extension costs if diffe

than value calculated with jamb extension costs.

c 0.87 inches of EPS is approximate thermal equivalent of 0.5 inches of polyisocyanurat

11
When electric resistance heating is used, economic thicknesses exceed 0.5

inches in Washington, D.C., Kansas City, and Denver as well as Boston and

Minneapolis. Levels of EPS which are thermally equivalent to the typical 0.5

to 1.0 inches of polyisocyanurate and extruded polystyrene can be justified

over a wider area when electric heat is used. However, electric resistance

heat is more prevalent in the moderate climates than in these colder climates,

so that again the relative number of houses in this heating category will be

small

.

Table 2-4 shows the current number of housing completions in the United States

by region and heating system type. It is apparent that the vast majority of

new houses fall into those categories where costly extension jambs make the

use of sheathing thicknesses greater than 0.5 inches economically unjustified.

The energy penalties corresponding to the use of 0.5 in. EPS as a substitute

for the same thickness of polyisocyanurate or extruded polystyrene are shown

in table 2-5. These penalties were calculated for a 1650 sq. ft. house with

1360 sq. ft. of net (opaque) wall area, equivalent to 1600 sq. ft. of gross

wall area with 15 percent windows and doors. Also included in table 2-5 are

the present-value dollar equivalents of these energy penalties over 25 years,

discounted at seven percent (net of general inflation)

.

If no jamb extension costs are incurred when using sheathing thicker than 0.5

inches, the economic thickness of EPS sheathing is greater than 0.5 inches in

most cases. As a result, EPS equivalents of the polyisocyanurate or extruded

polystyrene sheathings are cost effective for the typical 0.5 to 1.0 in

thickness. No energy penalty or dollar cost will be incurred if the thermal

equivalent is used. However, some builders accustomed to using 0.5 sheathing

may be reluctant to switch to the greater thicknesses required.

2.1.5 Implications for CFC Substitutes for Wood-frame Walls

The use of rigid foam sheathing of at least 0.5 in. thickness, in place of

conventional (non- insulating) sheathing, appears to be cost effective in

almost every region of the United States, with the possible exceptions of

southern Florida and the southern California coast. However, at present, only

40 to 50 percent of all new houses are constructed with this product. Because

the long-term energy savings attributable to this product are substantial,

especially in the northern climates and in electrically heated houses, its

usage should be encouraged from an energy conservation standpoint. Studies

conducted in this country and abroad, however, suggest that CFC agents

currently used to expand rigid foam insulation may damage the earth's ozone

layer, and that the usage of these agents should be curtailed. This would

require either new blowing agents for polyurethane and extruded polystyrene

products, or the increased usage of EPS, which does not contain CFC's.

No non-CFC chemical substitutes for blowing agents currently used in the

manufacture of polyurethane sheathing are currently available. There is some

potential for reducing the amount of CFC used per unit volume of foam, or

using a less environmentally harmful CFC agent, without significantly

affecting the thermal conductivity of the foam. The resulting product would

be more costly. However, a modest increase in the installed cost would not

12
significantly affect the economic thicknesses of this material shown in

table 2-3.

A chemical substitute for the CFC blowing agent used in the manufacture of

extruded polystyrene has been identified which promises the same or better

thermal performance without negative side effects at a slight increase in endproduct cost. However, this chemical is not currently available in quantity,

and toxicity testing has not been completed. Ten years may be required before

complete replacement of current CFC-based blowing agent could be

accomplished.^ Again, the economic thicknesses would not likely differ

substantially from those shown in table 2-3.

Table 2-4. Housing Completions in 1986 by Region and Heating System Type

Single-Family Housing

(Thousands of units')

Census Region

Heating System Northeast Midwest South West

Natural Gas 80 132 153 162

Oil 47 0 0 0

Heat Pump 28 15 231 47

Electric Resist. 30 15 104 27

Multi-Family Housing

(Thousands o f Buildings')

Census Region

Heating System Northeast Midwest South West

Natural Gas 6 5 5 14

Oil 0 0 0 0

Heat Pump 1 1 12 4

Electric Resist. 8 10 17 19

^"Regulatory Impact Analysis: Protection of Stratospheric Ozone,

Volume III: Addenda to the Regulatory Impact Analysis Document, Part IB: Rigid

Foam - Polystyrene and Miscellaneous Foam," Radian Corporation, August 1987.

13
Table 2-5. Energy Penalty for Substituting 0.5 in. EPS (R-2.2) for 0.5 in.

Polyisocyanurate (R-3.6) or 0.5 in. Extruded Polystyrene (R-2.5)

(1600 sq.ft. Single-Family Detached House with 1360 sq.ft. Opaque Wall Area)

HEATING SYSTEM/ MILLION BTU/YR AND PRESENT VALUE DOLLARS OVER 25 YEARS—

BASE SHEATHING

NATURAL GAS/

BOSTON WASHINGTON ATLANTA ORLANDO MINNEAP

.

KANSAS CTY

Polyisocyanurate 1.62 1.35 0.86 0.15 2.25 1.46

$225 $121 $77 $13 $195 $121

Extruded Polys. 0.47 0.39 0.25 0.04 0.65 0.42

HEAT PUMP/

$65 $35 $22 $4 $56 $35

Polyisocyanurate 0.64 0.51 0.29 0.05 1.03 0.56

$199 $111 $56 $9 $238 $127

Extruded Polys. 0.18 0.15 0.08 0.01 0.30 0.16

ELECTRIC/

$57 $32 $16 $2 $6 $37

Polyisocyanurate 1.10 0.92 0.58 0.10 1.53 0.99

$342 $202 $112 $19 $355 $226

Extruded Polys. 0.32 0.26 0.17 0.03 0 . 44 0.29

COOLING SYSTEM:

ELECTRIC AC

$99 $58 $32 $6 $102 $65

Polyisocyanurate 0.02 0.03 0.04 0.10 0.03 0.05

$6 $8 $8 $19 $6 $11

Extruded Polys. 0.01 0.01 0.01 0.03 0.01 0.01

$2 $2 $2 $5 $2 $3

NATURAL GAS/

DALLAS/FW DENVER PHOENIX SEATTLE OAKLAND LOS ANGELES

Polyisocyanurate 0.66 1.70 0.39 1.48 0.82 0.42

$51 $126 $31 $139 $65 $33

Extruded Polys. 0.19 0.49 0.11 0.43 0.24 0.12

HEAT PUMP/

$15 $36 $9 $40 $19 $10

Polyisocyanurate 0.22 0.68 0.12 0.57 0.28 0.13

$53 $151 $27 $72 $61 $29

Extruded Polys. 0.06 0.20 0.04 ' 0.16 0.08 0.04

ELECTRIC/

$15 $43 $8 $21 $18 $8

Polyisocyanurate 0.45 1.16 0.26 1.00 0.56 0.28

$109 $255 $58 $128 $123 $63

Extruded Polys. 0.13 0.33 0.08 0.29 0.16 0.08

COOLING SYSTEM:

ELECTRIC AC

$31 $73 $17 $37 $35 $18

Polyisocyanurate 0.10 0.03 0.20 0.01 0.00 0.00

$25 $6 $45 $1 $0 $0

Extruded Polys. 0.03 0.00 0.06 0.00 0.00 0.00

$7 $2 $13 $0 $0 $0

aPresent values based on DOE energy price proj ections over 25 years , discounted

at 7% (real)

.

14
It is difficult to estimate the aggregate energy and economic impact of the

substitution of EPS sheathing for CFC-blown materials. This is because the

economic choice of thermally equivalent sheathing thicknesses is governed to a

large extent by the choice of wood- or metal-framed windows. If the costs

associated with extending the jambs of windows and doors are small, there is

no cost to the substitution of EPS for the CFC-blown products; in fact there

may be a material cost savings. When wood- framed windows are used, however,

the cost of extending the jambs to accommodate the increased thickness of

sheathing can be significant (on the order of $160, net, per house). If the

increased thickness is not installed, the energy penalty can be substantial,

as shown in table 2-5. In general, if the present value of the energy penalty

is shown to be higher than the cost of the increased insulation thickness, the

increased thickness is considered to be cost effective, and vice versa.

2.1.6 Potential Impact of ASHRAE Standard 90.2

Figure 2-1 shows the U- value requirements for above -grade wood- frame walls as

proposed in the draft ASHRAE Standard 90.2, "Energy Efficiency Design of New

Low-rise Residential Buildings." When adopted, this new standard would

require a maximum U-value for wood- frame walls of 0.065 (Btu/ft^-h-F) almost

uniformly across the contiguous United States, with the exception of the

Atlantic coastal areas below Charleston, SC, the Gulf coast, and parts of

southern Arizona and southern California. Compliance would require the

equivalent of R-13 fiber glass insulation plus an insulating sheathing, either

0.375 in. polyisocyanurate , 0.5 in. extruded polystyrene, or 0.75 in. EPS. In

the coldest regions of the country (e.g., northern Minnesota and parts of

Alaska) the U-value requirement is 0.043 (Btu/ft^-h-F)

This requirement

could be met by utilizing R-13 fiber glass insulation plus an insulating

sheathing of either 1.5 in. polyisocyanurate, 2.0 in. extruded polystyrene, or

2.5 in. EPS. Alternatively, a U-value of 0.043 could be attained by

constructing 2x6 walls with R-19 fiber glass insulation and 0.75 in.

polyisocyanurate, 1.0 in. extruded polystyrene, or 1.25 in. EPS sheathing.

The ASHRAE standard has served as the basis for the CABO Model Energy Code

used by the three major building code authorities (ICBO, BOCA, and SBCCI)

The Model Energy Code, in turn, is the basis of the energy conservation

requirements referenced in the building codes of the majority of states, with

the exceptions typically adopting even more stringent standards.

The draft ASHRAE Standard 90.2 is likely to be approved by CARO in 1988. The

wall performance requirements of this standard will likely minimize the energy

impact of a change in the availability of specific insulating sheathings,

since they can be achieved by alternative material specifications. If this

standard is adopted as presently drafted, there will likely be a substantial

increase in the amount of insulating sheathing used in the U.S., some of which

would likely be manufactured using CFC's. If the production of CFC-blown

rigid foam insulation is curtailed, this standard will expand the market for

substitute insulating materials significantly.

15
mww>w

xsjo

Figure 2-1. Proposed U-Value Requirements for Wood- Frame Wall in

Single-Family Houses (Draft ASHRAE Standards 90.2).

16
2.2 Rigid Foam Insulation in Residential Masonry Wall Construction

New houses with concrete -masonry exterior walls are built primarily in the

South and Southwest regions of the United States. These walls are typically

constructed of eight inch concrete block, sometimes covered with stucco, or,

less often, four inch block and four inch brick (referred to here as cavity

wall construction). In general, placing insulation on the exterior of a

masonry wall, or even in the air space in a cavity wall, improves the energyrelated performance of these walls several percentage points more than the

same amount of insulation placed on the inside of the wall.^® This is because

insulation on the exterior surface emphasizes the mass effect of these walls

while insulation on the interior surface in effect isolates the mass from the

conditioned space. However, insulation on the outside surface requires a

protective covering, such as stucco, which increases the effective cost of

this technique (unless the wall was to be covered even without insulation)

The space available for the placement of insulation in conventional masonry

wall construction is considerably more constrained than in wood-frame walls.

Fiberglass blankets can only be used if the wall is framed out on the inside;

this involves considerable expense not only from the cost of the otherwise

unnecessary framing but from the lost interior space as well. As a result, if

any insulation is used at all it is most likely to be rigid foam sheathing,

which has a much higher thermal efficiency per inch than the fiberglass

insulation typically used in wood frame construction. However, rigid foam

insulations, especially the most efficient types blown with CFC's, have a much

higher cost per unit of resistance than fiberglass. As a result, the economic

level of insulation, in terms of overall R-value, is significantly lower for

masonry walls than for wood frame walls. (Economic insulation levels for

masonry walls are discussed further below.)

Two approaches to insulating masonry walls are investigated further in this

study: (1) rigid foam insulation on the interior surface, covered with

wallboard; and (2) rigid foam insulation on the exterior wall, covered with

stucco. In both cases, a reflective 0.75 -inch air space adjacent to the

wallboard is assumed (i.e., at least one surface has a foil face). Cavity

wall construction (brick exterior, cavity, and concrete clock interior) is not

explicitly treated here. However, the economic level of insulation for cavity

wall construction would be nearly identical to that of case (1).

The steady- state U-values of an eight- inch block wall, insulated to several

levels of thermal resistance using polyisocyanurate , EPS, and extruded

polystyrene sheathing, are shown in table 2-6. These U-values are essentially

identical whether the sheathing is inside or outside, since the stucco has no

significant insulating effect and an equivalent air space is assumed in both

cases. (U-values do not reflect the mass effect of the wall; however, the

equations used to estimate the energy savings from insulation are sensitive to

1 0

-‘-'•'Petersen, S.R., Barnes, K.A. , and Peavy, B.A., Determining CostEffective Insulation Levels for Masonry and Wood-Frame Walls in New Single

Family Housing . NBS Building Science Series 134, U.S. Department of Commerce,

National Bureau of Standards, Gaithersburg, MD, 1981.

17
the placement of the insulation.)

2.2.1 Economic Thickness of Insulation

The prices for rigid foam sheathing used in this analysis of masonry walls are

the same as those used in section 2 for wood- frame walls. However, unlike the

wood-frame wall analysis, no conventional sheathing (e.g., fiberboard) is

replaced by the insulated sheathing. Thus the net cost of the first 0.5

inches of foam sheathing is significantly higher in the masonry wall analysis

than in the wood frame analysis. No allowance for window and door extension

jambs is made in the masonry wall analysis, since the window and door returns

are assumed to be fabricated from gypsum board at no significant increase in

cost over the non- insulated wall cost. (Metal windows are typically used in

masonry construction. Wood- framed windows must be substantially modified to

fit a 9.25 inch or greater overall wall thickness.)

If the insulation is applied to the interior wall surface, an adjustment

should be made to account for the lost floor space, as was done for 2x6 in.

wood-frame wall. A slightly higher cost adjustment factor, $8.25 per square

foot of net floor area (including builder overhead and profit)

,

is used

because extending masonry walls is more expensive than extending wood- frame

walls. This is equivalent to approximately $0.07 [ (8 . 25/1 . 25)/(8xl2)

]

per

inch of additional wall thickness per square foot of gross wall area before

profit and overhead, or approximately $80 per inch of increased wall thickness

for a one-story 1200 square masonry foot house. (Masonry houses tend to be

smaller than average in size, thus a smaller house is used in this example

than the median 1650 square foot house used in the wood-frame analysis.)

When insulation is applied to the outside wall, no interior space is lost, and

as a result no adjustment is made to the insulation cost. Moreover, the cost

of the exterior finish is not included here, based on the assumption that it

would have been added with or without the insulation. (If the finish would be

used only with insulation, then its cost must be added to the insulation cost

in the economic analysis. This is likely to make exterior insulation less

cost effective than interior insulation.) While fastener costs can be

expected to increase as thicker insulation is used, either outside or inside,

these costs are relatively low and are not likely to affect the economic level

of insulation significantly.

The same methodology for calculating energy savings and their present value in

dollar terms used for wood- frame walls was used to calculate the optimal

insulation levels for masonry walls. The estimating equations used to

determine energy savings for masonry walls result in somewhat higher savings

than those used for wood-frame walls, however, reflecting the mass effect of

the masonry walls. The various thicknesses of insulation evaluated are shown

in table 3 of Appendix C, along with their corresponding costs and U-values

.

Table 2-7 shows the economic levels of rigid foam insulation applied to the

inside wall for five Southern and Southwestern locations, with three different

heating system types. Table 2-8 shows the corresponding estimates

of economic insulation thickness for exterior applications. These

calculations were made at 0.25 inch intervals of thickness, rather than in

18
terms of resistance, since sheathing is sold by thickness, not R-value.

Corresponding resistance values are shown in table 2-6 . Economic levels tend

to be higher for exterior sheathing applications (table 2-8) than for interior

applications (table 2-7) because exterior insulation improves the mass effect

of the walls and no penalty for loss of inside space is incurred. Including

the cost of the protective coating would not change these economic levels,

since its cost does not vary with insulation thickness.

In general, the economic level of insulation in masonry walls is low compared

to that of wood-frame walls in the same climate, especially for houses heated

with gas or a heat pump. The R-values corresponding to these economic

thicknesses run from zero in the mildest climates to a high of only R-8.3,

although an additional R-3 reflective foil surface on either the wallboard or

the insulation is cost effective in all cases. These relatively low R-values

are not due to the thermal performance of masonry walls, per se, but rather to

the higher cost of insulating them. Note also that only building locations in

the South and Southwest are shown in these tables; substantially more

insulation would be cost effective in northern climates where this type of

construction is less frequently used.

2.2.2 Implications for CFC Substitutes for Residential Masonry Walls

High-efficiency rigid foams are generally the insulation of choice from a

practical and economic standpoint when constructing masonry walls for new

houses because of inherent space limitations. If the insulation is installed

on the inside wall surface, covered with wallboard, or in a wall cavity, any

space occupied by the insulation reduces the interior living space by a

corresponding amount. Exterior insulation may be preferred, both from a

thermal performance basis and because it does not intrude into the interior

space. However, it must be covered with a protective finish, which adds

considerably to its initial cost and possibly to maintenance costs as well. As

a result, interior insulation is usually the more cost effective alternative.

The substitution of EPS for polyisocyanurate or extruded polystyrene rigid

foam insulation to near-equivalent R-values appears to be cost effective in

most of the applications shown in tables 2-7 and 2-8. While the EPS does

require more space than the latter materials, the resulting insulation

thicknesses are quite low relative to the overall thickness of these walls, at

least in these mild climates. Even when the adjustment for the cost of

foregone interior space is made, the substitution of EPS for polyisocyanurate

or extruded polystyrene is unlikely to increase initial construction costs

significantly. Framing out the interior wall and insulating with fiberglass

does not appear to be a cost-effective substitute for rigid foams when the

cost of the foregone interior space is considered.

19
Table 2-6. Exterior Wall U-Values for 8-Inch Block with Rigid Foam

Insulation3 (Btu/ft^-hr-F)

No insulation, non reflective air space (0.75 in.): 0.2799

No insulation, reflective air space (0.75 in.): 0.1928

Rigid Foam Sheathing—

Insulation Thickness Polyurethane Polystyrene

Inches ('Dolvisocvanurate') Exnanded Extruded

R U R U R U

0.5 3.6 0.1129 2.09 0.1365 2.5 0.1291

0.75 5.4 0.0937 3.13 0.1193 3.75 0.1111

1.0 7.2 0.0801 4.17 0.1060 5.0 0.0974

1.25 9.0 0.0700 5.21 0.0954 6.25 0.0868

1.5 10.8 0.0622 6.26 0.0867 7.5 0.0782

1.75 12.6 0.0559 7.30 0.0795 8.75 0.0712

2.0 14.4 0.0507 8.34 0.0734 10.0 0.0654

aMasonry wall U-values are based on nominal. 1x2 in. (actual 0.75x1 .5 in.

)

furring strips (R-0.94) with 12 percent frame-to -wall area ratio

.

An

emissivity of 0.03 is assumed for foil-faced sheathings or wall board. All Uvalues shown are based on the parallel heat transfer calculation method.

^R-values shown are for the insulation only; U-values are for the total wall,

including the surface conductances.

These conclusions are based on masonry wall construction in the South and

Southwest where this is most common; in northern climates the substitution of

EPS or other insulating materials at the same level of thermal performance as

the CFC-blown insulations would be less acceptable from a practical and

economic standpoint.

20
Table 2-7. Economic Thickness for Rigid Foam Insulation in Masonry Walls - Interior Insulation3

HEATING SYSTEM^/ Economic Thickness in Inches

SHEATHING TYPE ATLANTA ORLANDO DALLAS/FW PHOENIX LOS ANGELES

NATURAL GAS/

Polyisocyanurate 0.75

EPS 1.0

EXTRUDED POLYS. 0.75

HEAT PUMP/

Polyisocyanurate 0.75

EPS 1.25

EXTRUDED POLYS. 0.75

ELECTRIC/

Polyisocyanurate 1.25

EPS 2.0

EXTRUDED POLYS. 1.5

0.0 0.5 0.0 0.0

0.0 0.75 0.0 0.0

0.0 0.0 0.0 0.0

0.0 0.75 0.0 0.0

0.0 0.75 0.0 0.0

0.0 0.75 0.0 0.0

0.0 1.0 0.75 0.75

0.0 1.75 1.25 1.25

0.0 1.5 0.75 0.75

aReflective air space assumed in all cases, including zero insulation.

^Electric air conditioning . assumed in all cases.
Table 2-8. Economic Thickness for Rigid Foam Insulation in Masonry Walls - Exterior Insulation3

HEATING SYSTEMb

/ Economic Thickness in Inches

SHEATHING TYPE ATLANTA 1ORLANDO DALLAS/FW PHOENIX LOS ANGELES

NATURAL GAS/

Polyisocyanurate 0.75 0.0 0.75 0.0 0.0

EPS 1.75 0.0 1.25 0.0 0.0

EXTRUDED POLYS. 0.75 0.0 0.75 0.0 0.0

HEAT PUMP/

Polyisocyanurate 0.75 0.0 0.75 0.75 0.75

EPS 1.75 0.0 1.50 0.75 0.75

EXTRUDED POLYS. 1.25 0.0 0.75 0.0 0.0

ELECTRIC/

Polyisocyanurate 1.5 0.0 1.5 1.0 1.0

EPS 2.0 0.0 2.0 1.75 2.0

EXTRUDED POLYS. 2.0 0.0 2.0 1.0 1.25

aReflective air space assumed in all cases, including zero insulation.

^Electric air conditioning assumed in all cases.

22
3. EXTERIOR WALLS FOR COMMERCIAL AND HIGH-RISE RESIDENTIAL BUILDINGS

In this section, typical insulation practices for the exterior walls of

commercial buildings will be examined, and the substitutability of non-CFC

blown insulations (particularly expanded polystyrene, EPS) for CFC-blown

insulations will be addressed both from an economic and building code

standpoint. For the purposes of this report, the exterior walls of commercial

and high-rise residential buildings are divided into three primary categories:

concrete -masonry walls; wood or steel studs (load or non- load bearing, with

wood, stucco, metal, or brick exterior finish); and non- load-bearing curtain

walls, including composite foam-core panels and flat panels (often of

honeycombed metal, concrete, or stone) which are attached directly to the

superstructure. Rigid foam materials are widely used to insulate all of these

wall system types. Polyisocyanurate , extruded polystyrene, and expanded

polystyrene (EPS) are all used in concrete-masonry and stud wall systems.

Composite foam-core panels are typically manufactured with polyurethane or

. polyisocyanurate foam, although some manufactured panels covered with a

stucco-type finish are insulated with expanded polystyrene (EPS) . Fiberglass

batts or boards, foamed-in-place polyurethane, and sprayed cellulosic

insulation, are most commonly used on the interior side of flat-panel curtain

wall systems.

In general, economic R-values for wall insulation in commercial and high-rise

residential buildings will be somewhat lower than in single-family dwellings

for a number of reasons: (1) heating and cooling loads in commercial

buildings tend to be dominated by internal heat gains, so that the energy

savings potential of exterior wall insulation is significantly smaller than in

a single-family dwelling; (2) interior space generally has a much higher

rental value for commercial buildings, so that increasing the wall thickness

inward to accommodate insulation is often economically unattractive; (3)

exterior walls in commercial buildings have a large (often greater than 50

percent) ratio of glass to gross wall area, making thicker wall systems less

effective relative to the lost floor space and making window selection a more

critical design variable; (4) income tax rules favor operating costs which

can be written off in the year of occurrence (e.g., energy), rather than

capital costs (e.g., insulation) which must be depreciated over a long period

of time (currently 31.5 years); and (5) mortgages for commercial buildings are

usually limited to 15 years, which increases the positive cash flow

requirements in the earlier years of the building's life. Furthermore, design

aesthetics may be the most important consideration in choosing an exterior

wall system, and the choice of the wall system itself will often determine the

type and amount of insulation that can be economically used.

Aesthetics and energy considerations are not the only driving forces in

exterior wall design; fire safety and related building code provisions must be

considered as well. The three major model building codes in the United States

have specific provisions for limiting the amount of plastic foam insulation on

the exterior side of walls in multistory buildings in order for the wall to be

23
considered non-combustible-^ . The Uniform Building Code and Standard Building

Code limit the amount of plastic foam insulation, by its potential fuel

contribution, to 6000 Btu/sq ft of exterior wall area. The Basic Building

Code limits the thickness of plastic foam insulation to four inches of

thickness, regardless of the foam type or its fuel content. A multistory

flame test may also be required for some wall systems, further restricting the

choice of insulation materials. Polyurethane and polyisocyanurate are

considered to be " thermoset" materials; that is, they have a tendency to char

when exposed to flame, but do not loose their shape. Expanded and extruded

polystyrenes are "thermoplastic" materials, which melt and burn when exposed

to high heat or flame.

Table 3-1 shows the approximate limit on thickness imposed by a limit on

potential fuel contribution of 6000 Btu/ft^ , along with the corresponding Rvalue, for the most common types of foam plastic insulation. It is apparent

that polyurethane and polyisocyanurate can be installed at significantly

greater thicknesses (with significantly greater total R-values) than are

permissible for the polystyrene insulation materials under these same code

provisions. While foam insulation in thicknesses greater than two inches is

not common in conventional construction at this time, these thickness

constraints could impose restrictions on exterior wall design as insulation

standards for new buildings are upgraded over time if the availability of

polyurethane and polyisocyanurate insulations (both containing CFC's) is

curtailed.

Other important considerations in selecting an insulation material for

exterior wall applications are (1) the dimensional stability of the material,

(2) thermal conductivity (time rate of heat transmission per unit thickness

per unit area), (3) moisture permeability, (4) its ability to fit snugly into

irregular cavities, and (5) in certain applications, its adherence to other

surfaces. In some applications, such as use with some stucco or similar

textured coatings, some "give" on the part of the insulation is desirable,

while in composite panels, rigidity is important. Low conductivity is

especially important for applications which may reduce inside usable space,

since commercial office space tends to have a high cost per square foot of

usable area in terms of the rent that it commands. Low conductivity may also

be important if it allows a given level of thermal performance to be achieved

without violating building code restrictions on the walls fuel content or

thickness. The ability of the insulation to seal and insulate irregular

shapes is important in curtain wall systems which are mounted on metal bracing

on the outside of the building superstructure. Adhesion properties are

important in this latter application and in the manufacture of composite foamcore panels for use in curtain wall construction.

^This restriction on fuel contribution is related to the containment of

flame spread on the exterior of the building, not in the interior spaces. In

general, exterior walls containing plastic foam insulation must be covered on

the inside by a thermal barrier of 0.5 in. gypsum wallboard or equivalent.

24
Table 3-1. Approximate Thickness Limitations on Plastic Foam Insulation

Consistent with 6000 Btu/ft^ Fuel Content

Insulation Fuel Content3 Typical Density Allowable Approximate

Type (Btu/pound) (pounds/ft^) Thickness R-value

(Inches)

Polyurethane 10,000 1.5 4.8 30

Polyisocyanurate 10,000 2.0 3.6 26

Extruded Polystyr<ene 17,000 2.0 2.1 11

Expanded Polystyr<ene 17,000 1.0 4.2 16

1.5 2.8 12

Approximate fuel content; actual fuel content, may vary by manufacturer.

3.1 The High Cost of Lost Space

The high thermal performance of CFC-blown foam insulations is particularly

beneficial in commercial buildings if the thicker walls needed to accommodate

insulation intrude into the usable area. The relatively high rental cost of

interior office space ($5.00 to $50.00 per year per square foot of usable

area, and even higher for premium locations in some major cities) imposes a

significant penalty for every inch of wall intrusion. For each 12 feet of

running exterior wall on each floor, one inch of increased wall thickness

translates to one foot of lost floor space. Using a 25 year life, a five

percent inflation rate, and a 12 percent nominal discount rate, the present

value of the rent paid for each square foot of usable area is approximately

$120 per $10 of annual rent. This is equivalent to two dollars per inch

thickness per square foot of opaque wall area per $10 of annual rent, assuming

ten foot high walls per story and 50 percent window to wall area. (The uniform

present worth factor is equal to 12.01; each 12 running feet of exterior wall

are assumed to have 120 square feet of gross wall Area, or 60 square feet of

opaque wall area, per story. Any cost attributable to the insulation must be

allocated to the opaque wall area, not to the window area.)

In assessing the cost of lost interior space in commercial buildings, it is

assumed in this report that the rentable floor space is of prime consideration

in the design of the building. If the exterior walls can be extended outward

to accommodate thicker insulation without changing the foundations and

superstructure, the impact of insulation thickness on rentable area is likely

to be negligible. If the exterior wall system has a large interior space for

wall supports, wiring, and/or HVAC pipes and ducts, insulation thickness may

also be irrelevant from a cost standpoint as well. However, whenever there is

a direct tradeoff between insulation thickness and rentable floor area (i.e,

the insulation intrudes inward from the wall supports) , the rental value of

the lost floor area must be included in the true cost of the insulation.

25
When rentable space must be given up to accommodate wall insulation, the most

thermally efficient foam insulations (polyurethane and polyisocyanurate) will

generally be the insulation material of choice from an economic standpoint.

If these insulation materials are not available, requiring that a less

efficient insulation material be substituted, design economics will generally

dictate that the wall thickness remain unchanged and the thermal performance

be reduced accordingly.

Energy conservation provisions in existing building codes and in the proposed

ASHRAE 90.1 energy efficiency standards for commercial buildings typically

require a specified minimum energy performance for exterior walls. These

provisions may override design decisions based on purely economic criteria in

some cases. However, these provisions are usually stated in terms of thermal

performance of the overall wall, including both window and opaque wall areas.

If high efficiency insulation materials (i.e., rigid foams blown with CPC’s)

were not available, adjustments to the exterior wall design to comply with

these standards would more likely to be made to the size and U-value of the

windows than to the thickness of the opaque wall area if this required the

wall to intrude into the occupied space. While this cost may be significant,

especially in terms of design freedom, it is likely to vary widely in response

to site-specific considerations and is not estimated in this report.

3.2 Simulation Procedures and Methods of Economic Analysis

The heating and cooling loads for a representative commercial building were

computed using the Envelope System Performance Compliance Calculation

Program^ developed to support the proposed ASHRAE Standard 90.1. The

computations are based on a building module consisting of a single story of a

multistory building with a square floor plan. The module consists of four

perimeter zones of identical geometry surrounding an interior zone. The floor

and ceiling are modeled as adiabatic surfaces (i.e., having no heat loss or

gain), which is a realistic assumption for multistory buildings. The walls at

each end of the four perimeter zones are also modeled as adiabatic surfaces.

The four perimeter zones were oriented to four cardinal points of the compass.

Each exterior wall is 100 feet in length and has a height of 12 feet resulting

in an exterior wall area of 1200 ft^. Fenestration comprises 27 percent of

the total wall area on the north, east, and south walls while accounting for

32 percent on the west wall. Shading coefficient and visible transmittance

values of 0.48 and 0.36, respectively, were used in the computer simulations.

The glazing U-value which includes the mullion factors was maintained at

0,8 Btu/hft^F for the analysis. The equipment and lighting loads were assumed

to be 0.5 watts/ft^ and 1.73 watts/ft^ respectively.

Parametric runs were conducted for each city by varying the opaque wall

U-value for each wall system considered in this analysis. The resulting data

was used to generate curves of heating and cooling loads for this building in

each city as a function of its opaque wall U-value. Sensitivity analyses were

performed in which changes in glazing area and internal heat gains were made

^Envelope System Performance Compliance Calculation Program, Version 1.0,

DOE Report No. CE-0166, November 1986.

26
to this representative building. It was found that while total space heating

and cooling loads change significantly with these two variables, changes in

the space heating and cooling loads which are directly attributable to

reductions in the U-value of the opaque wall changed very little.

Changes in space heating and cooling loads were converted to corresponding

changes in annual energy consumption using steady- state estimates of heating

and cooling system performance. A seasonal efficiency of 70 percent was used

for natural gas heating and 95 percent for electric resistance heating; a

seasonal COP of 2.0 was used for air conditioning. Electric heat pump HSPFs

(heating season performance factors) range from 5.1 to 7.7, depending on the

severity of the winter climate^. Corresponding reductions in electricity

consumption by air-handling equipment were not estimated, but are assumed to

be small. It should be noted that energy savings due to changes in wall

insulation levels are sensitive to equipment efficiency, and that equipment

efficiency varies widely from building to building, depending on the type of

equipment, its age, and how well it has been maintained.

Energy prices and projected rates of increase over time used in the economic

analysis were based on regional projections by the U.S. Department of Energy,

as published by the National Bureau of Standards^. These factors are shown

in Appendix B. Life-cycle cost guidelines consistent with both NBS Handbook

135, Life-Cycle Costing Manual for the Federal Energy Management Program and

ASTM Standard Practice E-917, "Measuring Life-Cycle Costs of Buildings and

Building Systems" were used to compute economic levels of insulation. The

economic level of insulation is defined here as that level with the lowest

total present-value life-cycle cost, including initial costs, operating and

maintenance costs, resale value, and tax considerations. A twelve percent

nominal after-tax discount rate was used to convert future savings to present

value^. A study period of 25 years and a straight-line depreciation period

of 31.5 years were used in the analysis. Half of the real value of the

insulation is assumed to remain at the end of the 25 year study period;

however, when this value is discounted to present value it is relatively

insignificant in comparison to its initial cost.

Insulation costs used to compute economic levels are the same per-square- foot

costs used in section 2 for residential analysis, except that costs for

commercial wall insulation are applied directly to the opaque wall area while

1LJ3 HSPFs used are as follows: Phoenix 7.38, Los Angeles 7.34, San Francisco

6.74, Denver 5.77, Orlando 7.67, Atlanta 6.80, Boston 5.88, Minneapolis 5.10,

Fort Worth 7.04, Seattle 6.05, Washington 6.41, Kansas City 6.07.

l^Lippiatt and Ruegg, Energy Prices and Discount Factors for Life-Cvcle

Cost Analysis . NBSIR 85-3273-2, U.S. Department of Commerce, National Bureau

of Standards, Gaithersburg MD, 1987.

A twelve percent nominal discount rate is approximately equivalent to a

seven percent real discount rate plus a five percent rate of general

inflation. The seven percent real discount rate is used in analysis of energy

conservation investments in Federal buildings.

27
costs for residential wall insulation are applied to the gross wall area. It

should be recognized that installed insulation costs can vary significantly

from installer to installer depending on a number of factors, including union

or non-union status, location, timing, job size and other site-specific

characteristics

.

It should also be noted that the life-cycle cost criteria for determining the

economic level of insulation used in this report may be considered unrealistic

by many building owners more concerned with year-to-year cash flows than long

term economics. As a result, the economic R-values shown in this section

should be considered only as design benchmarks for assessing the

substitutability of insulation materials and not as design guidelines for new

buildings

.

3.3 Insulation Analysis by Wall Type

In this subsection, common uses of insulation materials in exterior commercial

and high-rise residential walls systems are explored and economic thicknesses

estimated for a wide range of locations and fuel prices. The substitution of

non-CFC-blown insulations for CFC-blown foams in these same applications is

investigated.

3.3.1 Concrete-Masonry Walls

Concrete -masonry walls can be insulated on the outside or inside surfaces, in

the cores of concrete blocks, or in the cavity of a composite brick and block

wall. Rigid foam insulation is the most common material for this purpose,

although some loose-fill materials (e.g., perlite) are sometimes used to fill

cavities and molded plastic inserts (or more loose-fill insulation) are

sometimes placed in core sections. The three rigid foam sheathings discussed

in section 2 for residential wall construction are most typical for insulating

masonry walls in commercial buildings: polyurethane (including

polyisocyanurate) , extruded polystyrene, and expanded polystyrene (EPS). The

analysis of concrete -masonry walls will be limited to these three materials in

the cavity of a brick and block cavity walls and on the outside surface of

concrete block walls. The use of insulation in the cores of concrete blocks

will not be evaluated for two reasons: the insulation materials used in cores

does not generally contain CFCs ; and, more importantly, the insulation of

cores has serious shortcomings from a thermal performance standpoint because

of the thermal bridging effects of the solid portions of the concrete blocks.

As a result, this insulation technique should only be used to supplement rigid

foam insulation.

3. 3. 1.1 Brick and Block Cavity Walls:

In commercial buildings cavity wall construction typically consists of eight

inch concrete block, an air space (cavity) , and four- inch face brick. The

cavity can be expanded to accommodate up to four inches of insulation. The

rigid foam insulations shown in table 3-1 are all satisfactory for this

application. Since they are protected from fire on both the inside and

outside they are not subject to the thickness constraints shown in this table.

In general, the major economic considerations in selecting among insulation

28
types and in determining economic thickness are based on the cost of the

insulation per resistance unit and an assessment of wall expansion costs. If

the cavity can be expanded to accommodate thicker insulation by moving the

face brick outward at minimal cost, the substitution of EPS for a rigid foam

insulation blown with CFC to the same level of overall thermal performance

will have little impact on the construction cost or energy cost of the

building. If the inside surface of the wall must be moved inward to

accommodate the increased thickness of insulation required to maintain thermal

performance, the added cost, in terms of lost interior space, will likely

discourage the additional insulation, resulting in a significant energy

penalty over the life of the building.

Economic levels of rigid foam insulation in a brick and block cavity wall were

calculated for a commercial office building in twelve locations in the United

States. DOE regional energy price projections for both electricity and

natural gas were used in a life-cycle cost analysis. A study period of 25

years and a real (net of general inflation) after-tax discount rate of seven

percent were used in the analysis. Results are shown in table 3-2 for three

different heating systems in each location: electric heating, natural gas, and

heat pump; electric air conditioning was assumed in all buildings. These

results are reported for rigid foam insulation in general, without identifying

the particular insulation type, as the costs and results (in terms of economic

R-values) are similar for all three types examined. The corresponding

insulation thicknesses range from 0 to 2 inches for polyisocyanurate , 0 to

approximately 3.5 inches for EPS, and 0 to 3 inches for extruded polystyrene.

In general, the economic levels of insulation shown in table 3-2 are quite low

compared to those for residential walls. This result is primarily due to the

relatively small energy savings attributable to the insulation of commercial

wall systems in comparison to residential construction. Not only do heating

savings tend to be smaller in the former, but insulation actually tends to

increase cooling loads in commercial buildings with brick and block cavity

walls (except in Phoenix) , offsetting some or all of the savings in the

heating mode

As a result of this analysis, it is estimated that there is no economic or

energy penalty incurred in switching from polyisocyanurate or extruded

polystyrene to EPS for brick and block cavity walls.

3. 3. 1.2 Concrete Block Walls- -Exterior Insulation:

Rigid foam sheathing on the exterior surface is the most effective method of

insulating concrete block walls from a thermal performance standpoint, since

it helps realize the full potential of the thermal storage properties of such

walls. Insulation of the outside surface also has no effect on usable

interior space, unless the outside dimensions of the building are strictly

limited and the block walls must be moved inward to compensate for the

insulation. Exterior insulation does require that a protective coating be

applied. A stucco or similar coating is typically used. At a cost of $2.00

to $4.00 per square foot, this significantly reduces the cost effectiveness of

exterior insulation, unless this coating is to be applied for reasons other

than insulation protection (e.g,, for design aesthetics). All three types of

29
rigid foam insulation materials are used for this purpose, although the choice

is narrowed somewhat by the type of exterior coating used. Hard coatings,

being more rigid, require a more rigid foam sheathing such as extruded

polystyrene, while soft coatings tend to be more yielding, which is more

compatible with a less rigid foam sheathing such as EPS.

The economic R-values shown for brick and block cavity walls in table 3-2 are

approximately valid for concrete block walls with an exterior insulation and

finish system. (This does not imply that the walls perform equally well, but

only that the additional energy savings from additional increments of

insulation are similar in both walls.) EPS appears to be a viable substitute

for CFC-blown insulation materials in exterior wall insulation systems,

despite the requirement for thicker insulation, since the wall and window sill

expansion costs will likely be quite small. In fact, EPS is the most commonly

used rigid foam insulation in these applications. However, there have been

complaints about failures of the soft-coat exterior finish systems related to

water leakage and subsequent damage, which may require a more rigid standard

for EPS in these systems. And the manufacturers and installers of the hardcoat systems will be negatively impacted by the non-availability of extruded

polystyrene unless they are able to modify their product to improve its

compatibility with less-rigid foam sheathings.

Table 3-2. Approximate Economic R-values for Brick- and- Block

Cavity Walls in Commercial Buildings 3

Location HDD65 CDH74

Electric

Furnace

Natural

Gas

Heat

Pump

PHOENIX 1382 55998 R-4 R-3 R-3

LOS ANGELES 1494 01193 R-0 R-0 R-0

SAN FRANCISCO 3237 00835 R-4 R-0 R-0

DENVER 6083 07510 R-7 R-5 R-7

ORLANDO 0531 27247 R-0 R-0 R-0

ATLANTA 3069 11892 R-5 R-4 R-3

BOSTON 5775 05094 R- 14 R-7 R-10

MINNEAPOLIS 8059 06946 R- 14 R-10 R-12

FORT WORTH 2354 28048 R-5 R-0 R-3

SEATTLE 5280 01260 R-7 R-5 R-4

WASHINGTON DC 4228 09952 R- 10 R-5 R-5

KANSAS CITY 5201 13730 R- 12 R-5 R-7

aBased on a 25-year life-cycle cost analysis.

30
3. 3. 1.3 Concrete Block Walls- -Interior Insulation:

The economic R-values shown in table 3-2 are also reasonably representative

for rigid-foam insulation on the inside of concrete block walls, covered with

minimum half- inch gypsum board, but only when no cost is attributed to the

lost interior space. (Again, this does not imply that the walls perform

equally well.) In fact, this cost can be quite high, depending on the use of

the building, making the real cost of insulation prohibitively high in many

instances. In general, if insulation must be used on the inside surface, only

the most efficient insulation materials (e.g., polyisocyanurate) can be

justified. If those materials were no longer available, and EPS were to be

substituted, the insulation thickness required to achieve the same thermal

performance would increase by approximately 70 percent (assuming 1.5 lb

density EPS at R-4.17 per inch versus polyisocyanurate at R-7.2 per inch). In

most installations, it could be expected that the insulation thickness would

be held constant, with a corresponding reduction in thermal performance.

Where energy standards require a specified thermal performance for exterior

walls, it is likely that a combination of window and wall design changes would

be met to comply with the standard, rather than simply increasing the

thickness of the insulation to maintain the same insulation R-value.

3. 3. 1.4 Wood and Steel Stud Wall Systems:

The exterior walls of both load- and non- load-bearing walls can be framed

with wood or steel studs. Stucco or similar coatings, wood, brick, or other

siding materials are typically used to cover the exterior surface. The cavity

between the studs is often insulated with R-ll or R-13 fiberglass batts

If

thermal performance beyond that typically achieved with the fiberglass batts

is desired, rigid foam insulated sheathing can be attached to the exterior

side of the studs, under the outer surface. In the case of the stucco -type

coatings, insulated sheathing is often used as the base on which the coating

is applied. All of the rigid foam insulations examined in this section are

appropriate for use with wood or steel stud systems. However, some types of

stucco-type coating systems are more compatible with certain types of

sheathing. For example, so-called "soft" coating systems (e.g., the Dryvit

system) require sheathing with a lower modulus of elasticity, such as EPS,

while harder coatings may require a more rigid sheathing, such as extruded

polystyrene

The costs of rigid foam insulation used as sheathing with wood and metal stud

wails is similar to those used for residential wood-frame walls in section 2.

Metal window and door systems are most prevalent in commercial and high-rise

residential buildings. Thus there is little additional cost in terms of the

window and door jamb expansion to accommodate the additional thickness of EPS

when substituted for the CFC-blown insulation materials. It is unlikely that

rigid foam insulation used to augment fiberglass insulation in the wall cavity

would approach a thickness prohibited by the fire -safety provisions of the

building codes.

Table 3-3 shows economic R-values of insulated sheathing used with stud wall

systems in commercial office buildings, assuming that R-13 fiberglass batts

are installed in the stud space. (Since fiberglass batts are generally less

31
costly per resistance unit than foam insulation, it is more economical to

start with the former.) These economic thicknesses are calculated using a 25-

year life-cycle cost analysis. In general, the insulated sheathing is only

cost effective in these applications in northern climates with electric heat.

Designers using a more stringent economic criteria (e.g., seven-year payback

or positive cash flow in early years) would find the foam sheathing to be

uneconomical in most applications (again, assuming that R-13 fiberglass is

used in the stud space.)

It should be noted that in the case of stucco-type exterior finish systems,

one- inch foam sheathing is typically required as the base for the exterior

coating. In the milder climatic regions, this exterior finish system may be

used without fiberglass batts . In such cases, a desired increase in

insulation would more likely be accomplished by adding fiberglass batts rather

than increasing the thickness of the foam sheathing.

It is concluded that for wood- and steel-stud wall systems, the substitution

of a non-CFC blown rigid foam insulation for a thermally equivalent CFC-blown

material would have little or no economic cost or energy penalty in terms of

building construction or operating costs. However, as noted above, some

buildings with a "soft" stucco- type finish system using EPS have had problems

with water damage. Consideration should also be given to the manufacturers

and installers of those exterior coating systems which require a more rigid

surface than that provided by EPS. A reduction in the availability of

extruded polystyrene would force these manufacturers to modify their coating

system or go out of business.

3.3. 1.5 Curtain Wall Systems:

Two types of curtain wall systems are considered for analysis is this report:

composite foam-core panels, in which the insulation is installed at the

factory, and flat panels, to which the insulation is attached after the panels

are installed.

Composite foam core panels with metal skins are typically manufactured with

polyurethane (or polyisocyanurate) foam. These panels are available in

several standard thicknesses, with two inch thickness being the most common.

Other thicknesses can be manufactured, although for some manufacturers this

may require that assembly lines be modified at substantial cost. For some

systems, a redesign of curved corner panels would also be required.

Compatible window systems are manufactured to be used with standard panel

thicknesses. However, these same window systems can be used with thicker

panels using modified sill adapters.

Manufacturers of the metal-skin composite panels state that polyurethane or

polyisocyanurate foams are the only viable candidates for this application for

several reasons. (1) These panels can be manufactured rapidly on an assembly

line where the chemicals are poured into the panel, expanding and adhering

firmly to both surfaces in less than a minute. The alternatives must be glued

to the inside surfaces and cured under pressure, greatly increasing the amount

of manufacturing time. (2) The polyurethane/polyisocyanurate

32
Table 3-3. Economic R-values for Foam Sheathing in Wood and Steel Stud Walls 3

(Assumes R-13 fiberglass batts in stud space)

Location HDD65 CDH74

PHOENIX 1382 55998

LOS ANGELES 1494 01193

SAN FRANCISCO 3237 00835

DENVER 6083 07510

ORLANDO 0531 27247

ATLANTA 3069 11892

BOSTON 5775 05094

MINNEAPOLIS 8059 06946

FORT WORTH 2354 28048

SEATTLE 5280 01260

WASHINGTON DC 4228 09952

KANSAS CITY 5201 13730

Electric Natural Heat

Furnace Gas Pump

R-0 R-0 R-0

R-0 R-0 R-0

R-0 R-0 R-0

R-6 R-0 R-0

R-0 R-0 R-0

R-0 R-0 R-0

R- 10 R-0 R-0

R- 12 R-0 R-6

R-0 R-0 R-0

R-0 R-0 R-0

R-0 R-0 R-0

R-0 R-0 R-0

aBased on 25-year life cycle cost analysis.

materials are the most thermally efficient foams suitable for this purpose and

result in high-efficiency panels at practical thicknesses. (3) Neither the

expanded nor extruded polystyrene products can satisfy the fire protection

provisions of the model building codes with regard to exterior flame spread

for multistory buildings. The polystyrene materials melt when exposed to heat

from a fire and the panels then offer little resistance to flames from below.

For these reasons, it is concluded that expanded polystyrene is not an

acceptable substitute for the polyurethane/polyisocyanurate materials

currently used in the manufacture of metal-skin composite foam-core panels.

New blowing agents for these latter materials are being investigated which

have lower or zero levels of CFC's, with some degradation in terms of thermal

performance (approximately 15 percent according to industry estimates) . This

loss in thermal performance could be compensated by making thicker panels, at

a relatively small increase in the overall manufacturing cost of the panel

(although some one-time costs related to the modification of the assembly line

may be significant). In the milder climates, it is more likely that the same

thicknesses will be maintained, with slightly reduced thermal performance,

since the additional cost of the thicker insulation will not be cost justified

in these installations. In the colder climates, some adjustment to thicker

insulation levels might be expected over time. However, even if these

alternate blowing agents and the resulting foams are found to be acceptable

environmentally, much additional research will be needed to demonstrate their

suitability from the standpoint of the fire-safety and adhesion properties

needed for these applications.

33
Table 3-4 shows estimates of economic thicknesses for composite foam-core

curtain wall panel insulation in 12 locations, by heating system type. These

estimates were calculated using the same energy costs and insulation costs

used in table 3-2. (This assumes the incremental cost per inch of

polyisocyanurate insulation is approximately $0.40 per square foot;

incremental costs of the composite panels will likely vary substantially from

manufacturer to manufacturer, depending on the set-up costs involved in

changing the product thickness.)

Table 3-4. Economic Thicknesses of Composite Foam-Core Curtain Wall Panel

Insulation3

Location HDD65

PHOENIX 1382

LOS ANGELES 1494

SAN FRANCISCO 3237

DENVER 6083

ORLANDO 0531

ATLANTA 3069

BOSTON 5775

MINNEAPOLIS 8059

FORT WORTH 2354

SEATTLE 5280

WASHINGTON DC 4228

KANSAS CITY 5201

ElectricFurnace

CDH74 Inches _R

55998 1.5 11

01193 0 0

00835 1.0 7

07510 2.0 14

27247 1.0 7

11892 1.5 11

05094 2.5 18

06946 2.5 18

28048 1.5 11

01260 1.5 11

09952 2.0 14

13730 2.0 14

Natural

Gas

Heat

Pump

Inches _R Inches JR

1.0 7 1.0 7

0 0 0 0

1.0 7 1.0 7

1.5 11 1.5 11

0 0 0 0

1.0 7 1.0 7

1.5 11 2.0 14

2.0 14 2.5 18

1.0 7 1.0 7

1.0 7 1.0 7

1.5 11 1.5 11

1.5 11 1.5 11

aPolyisocyanurate insulation (R-7 . 2/inch) , based on 25 year life-cycle cost

analysis

.

Flat curtain wall panels are typically insulated on the inside after they are

attached to the building. Installation of rigid foam insulation on the inside

surface of these wall systems is often impractical due to the irregular shapes

of the cavities that result from the interface of these panels with the

supporting members and window systems. Fiberglass boards and batts are most

frequently used for this purpose; sprayed cellulosic insulation is also used

in some installations. However, foamed- in-place polyurethane has a particular

advantage for this application, in that it completely fills the cavities,

while its superior adherence properties provide an improved seal against air

infiltration. Polyurethane has more than twice the thermal resistance per

inch of fiberglass batts, making a significantly higher levels of overall wall

34
performance achievable in a limited-depth wall cavity „ If the use of

polyurethane for these curtain wall applications were curtailed, it is likely

that the same thickness of fiberglass insulation would be used, but at a

considerable energy penalty.

Another approach to the insulation of manufactured composite panel systems is

to attach rigid foam sheathing to the outside surface of non- combustible board

stock and apply the same exterior stucco-type exterior finishing system used

with the wood- and steel-stud wall system. These panels can then be attached

to the superstructure of a building without the need for scaffolding. A noncombustible fire rating can be attained, even with EPS, if the exterior

coating system provides sufficient protection to the insulation. Economic

R-values similar to those shown in table 3-4 (but with approximately twice the

thickness) would be appropriate for this latter system.

3.4 Conclusions for Commercial/High-Rise Wall Systems

The choice of an exterior wall system for commercial buildings and high-rise

residential buildings is much wider than that for a typical single- family

residence. As with the latter, the choice of a wall system can have a

significant effect on the appropriate insulation type and its economic

thickness

For most masonry and stud wall systems, EPS, which contains no CFC agent, can

be used in place of CFC-blown rigid foam insulation with no economic or energy

penalty, provided that the exterior wall surface can be expanded outward at

little or no increase in construction cost in order to maintain the same level

of thermal performance. Exceptions to this conclusion are (1) concretemasonry walls with insulation installed on the interior surface, (2) hard-coat

exterior finish and insulation systems which require the more rigid surface

provided by extruded polystyrene, and (3) buildings for which the outside wall

dimensions are strictly limited at the building site. In general, the cost of

rental space in commercial buildings is so high that any intrusion into the

occupied space to maintain the thermal performance of the insulation will be

uneconomical

For some curtain wall systems, the choice of insulation material is determined

more by fire codes than by economics, per se. The polyisocyanurate or

polyurethane insulation currently used in metal-skinned foam-core panels

cannot be replaced with EPS in non-combustible wall construction. The

elimination of CFC-blown foam insulation would have a significant negative

impact on the design of many new commercial buildings and the industry

manufacturing this product.

In flat-panel curtain wall systems (e.g., metal, stone, and aggregate panels),

where the insulation is typically added to the inside surface after the panels

are attached to the building, fiberglass is the most commonly used insulation

material. Foamed- in-place polyurethane is also used in this latter

application with superior results, not only because of its improved thermal

performance but because it is able to seal the wall to reduce air

infiltration. While this latter insulation system is not as prevalent as

fiberglass, a reduction in the availability of CFCs for foam insulation will

35
have a negative impact here as well, primarily in terms of increased energy

usage. It is unlikely that fiberglass would be used at the thickness required

to achieve a level of thermal performance equivalent to foamed- in-place

polyurethane in such installations.

Curtain wall panels are also manufactured using EPS insulation with a

protective stucco- like coating on the outside. These panels could be

substituted for those containing CFC-blown insulation materials in some new

buildings where a stucco- like exterior is acceptable.

36
4. LOW- SLOPE ROOF SYSTEMS FOR COMMERCIAL BUILDING APPLICATIONS

4.1 Alternatives Examined

The energy data and economic analysis reported here are derived for the most

part on a recent Oak Ridge National Laboratory report entitled "Economic

Analyses of Insulation Materials Used in Low-Slope, Built-Up Roof Systems .16"

That report provides a comprehensive summary of currently marketed rigid-board

insulation materials for use below membranes of low-slope, above-deck, builtup roof systems on U.S. Air Force Facilities. The primary requirements of

that study were to compare, on a 20-year life-cycle cost (LCC) basis,

currently available insulation materials as alternatives to fiber glass

insulation, and to determine economically optimal levels for built-up roof

(BUR) systems on a LCC basis. Only insulation systems recommended by the

National Roofing Contractors Association were included in that study, and for

each insulation type, a system design was selected with a strong likelihood of

a long (approximately 20 year), trouble-free, life.

While the NBS analysis is based on ORNL data for built-up roofing systems,

similar conclusions can be drawn for other low-slope roof systems in which the

rigid insulation boardstock is covered by a protective membrane. However,

"protected-membrane" systems, in which the insulation is placed over a watertight membrane, usually require a water-resistant and durable rigid foam

insulation such as extruded polystyrene, which in turn is covered with ballast

to hold it in place. For this reason the results of this analysis cannot be

extrapolated to protected-membrane systems. However, these latter systems

make up only a small percentage of the total number of low-slope roofing

systems installed in the United States.

Calculations of heating and cooling energy requirements attributable to roofs

with a wide range of insulation values were performed at ORNL using the

DOE-2. 1A building energy analysis program for a 60,000 square foot building in

six cities. Differences in energy usage attributable to wet insulation over

part of the roof life and differences caused by the effect of aging on thermal

conductivity for gas -filled, closed cell foam insulations were incorporated

into the calculations. In addition, the transient heat transfer

characteristics of the various roof systems were considered in the ORNL

analysis. A sensitivity analysis with respect to roof area did not show any

significant variation in energy usage per square foot over a wide range of

roof sizes.

Seven different types of insulation were analyzed in the ORNL report for use

under BUR membranes: fiber glass, perlite, wood fiberboard, cellular glass,

expanded polystyrene (EPS) composite, polyisocyanurate composite, and

polyurethane composite. Extruded polystyrene was not analyzed because this

insulation type is not recommended for use under BUR membranes by the National

Roofing Contractors Association (NRCA) . A perlite composite underlayment and

1LOft Courville , G.E., and Kolb, J.O, "Economic Analyses of Insulation

Materials Used in Low-Slope, Built-Up Roof Systems," ORNL/TM-9004 , Oak Ridge

National Laboratory, Oak Ridge, TN, 1984.

37
fiberboard cover were assumed for all of the rigid foam insulations.

Table 4-1 summarizes the initial thermal conductivities and corresponding

insulation thicknesses for a range of design R-values for each of these

insulation types used. Note that the values used for unfaced polyurethane and

polyisocyanurate foams (k = 0.17 Btu-inch/ft^-h-F, or R-5.8 per inch) were

selected by the authors of the ORNL report to represent the average value for

the first year of use on the basis of work reported by Muhlenkamp and

Johnson 17

'

ORNL obtained price quotes for installing each of these seven insulation types

at several different thicknesses from 40 roofing contractors in 37 states.

Maintenance and inspection costs were estimated for each type of insulation

based on past U.S. Air Force experience. Energy prices were based on the then

current DOE energy prices. Insulation salvage values were calculated as a

percentage of their initial cost. An eight percent real discount rate was

used in the ORNL study to determine the present value of energy and

maintenance costs and salvage values so that a. total present-value life-cycle

cost could be determined for each installation.

This study will focus on only three of these insulation types -- fiber glass,

EPS composite, and polyisocyanurate composite -- since these are the most

thermally efficient materials for roof deck insulation, i.e., the insulation

types with the lowest k values. (Polyisocyanurate will be used in this

analysis to represent polyurethane composites as well, since the thermal

conductivity is the same for both, while the cost of the latter is slightly

higher than the former.) Table 4-2 shows the installed insulation costs and

annual maintenance and inspection costs used for these three insulation types.

The total installed cost per 100 sq. ft. is also shown graphically as a

function of R-value in figure 4-1. These initial costs include an adjustment

for energy equivalence over time (recognizing a slight increase in the thermal

conductivity of the polyisocyanurate foam as it ages over 20 years) , an

adjustment for long term durability (by the inclusion of a cover board for the

EPS and fiber glass insulations and a bottom board for the latter as well)

,

and an adjustment for the length of the required nailers. These costs do not

include any adjustment for rooftop HVAC equipment clearance; thus in retrofit

applications where limited clearance below existing equipment prevents the use

of the optimal R-value, the most thermally efficient insulation material

(i.e., polyurethane or polyisocyanurate) will generally be the economic

choice

.

^Muhlenkamp, S.P. and Johnson, S.E., "In-Place Thermal Aging of

Polyurethane Foam Roof Insulation," Paper No. 11, 7th Conference, Proceedings

of the NRCA-NBS Conferences on Roofing Technology . April 1983.

38
Table 4-1. Insulation Conductivity and Thicknesses 3

Insulation Type Initial Thermal Insulation Thickness; (inches)

Conductivity^ (k) R- 10 R- 15 R- 20 R-25 R- 30

(Btu-inch/ft—-h-F)

Fiber Glass 0.25 2.50 3.75 5.00 6.25 7.50

Perlite 0.36 3.60 5.40 7.20 9.00 10.80

Fiberboard 0.36 3.60 5.40 7.20 9.00 10.80

Cellular Glass 0.38 3.80 5.70 7.60 9.50 11.40

EPS Foam 0.26 2.60 3.90 5.20 6.50 7.80

Polyisocyanurate foam 0.17 1.70 2.55 3.40 4.25 5.10

Polyurethane foam 0.17 1.70 2.55 3.40 4.25 5.10

aSource : ORNL/TM- 9004

^For first year, dry condition.

Table 4-2. Installed Insulation and Annual Maintenance Costs 3

Installed Cost Annual Maint

Fiber Glass ($/100 ft2

) ($/100 ft2) R-10 158 10

R-20 268 0

R-30 378 10

EPS Composite

R-10 179 9

R-20 210 9

R-30 241 9

Polyisocyanurate composite

R-10 165 9

R-20 216 9

R-30 268 9

aSource : ORNL/TM-9004 . Note: all installation costs have been adjusted for

energy equivalence, longevity, and wood nailer costs. Costs have been

adjusted to 1987 dollars from 1984 dollars using a 12 percent cumulative

inflation factor.

39
Figure 4-1. ORNL Installed Insulation Costs for Built-Up Roofs

(per 100 ft^, 1983 dollars).

40
All insulation was assumed to be installed on an existing steel deck roof with

1/4 in.-per-foot minimum slope. A three-ply fiberglass membrane was assumed

to be installed over the insulation or cover board in all cases; however, the

cost of this membrane is not included in these installed insulation costs.

4.2 Economic Thickness of Insulation

In order to make the results of the ORNL study consistent with the methodology

used in other sections of this NBS report, their economic analyses have been

recomputed using current DOE energy price projections and a 7 percent real

discount rate. Optimal levels of insulation in each location for three

heating system types were recomputed for each of the six locations and three

heating system types. These results are shown in table 4-3.

The results reported in table 4-3 are consistent with the ORNL findings,

except that the optimal levels for built-up roof insulation tend to be

slightly lower now than in 1984. This is because current DOE projections of

energy price increases are somewhat less steep, than similar projections made

by DOE at the time that the original study was completed. In addition, a more

conservative insulation salvage value was used in the new analysis (50 percent

rather than the 90 percent used in the ORNL study). In general, because the

EPS composite has the lowest incremental cost per unit of R-value, its optimal

R-values are slightly higher than those computed for polyisocyanurate and

considerably higher than those for fiber glass insulation. For insulation

levels between R-10 and R-15, all three systems have similar life-cycle costs;

for levels above R-15, the two foam insulations have nearly identical lifecycle costs and are somewhat less than those for the fiber glass.

Table 4-3 shows optimal R-values for these same installations based on the

premise that insulation costs are financed over 15 years and that positive

cash flow must be reached by the end of the second year. Energy, maintenance,

and depreciation costs are all assumed to be tax deductible in this analysis.

While these optimal R-values are generally somewhat lower than those shown in

table 4-3, they are more indicative of the economic criteria that would be

used for many commercial and industrial applications. As a result, these

R-values will generally be closer to what is often installed in such buildings

than the levels determined using 20-year life-cycle costs.

1

In the ORNL study, it was assumed the insulation could be left in place

after roof membrane failure, with a new membrane over the top, since a

protective fiberboard cover was assumed to be installed with the insulation.

Note that the present value of this "salvage value" is quite small since it is

discounted over 20 years

41
Table 4-3. Optimal R-Values for BUR Insulation Based on 20-Year LCC

Insulation/ Location

_Heating Systema Minot

N.D.

Indianaolis INOrlando

FL

San Antonio TXPhoenix

AZ

Bakersfield CA

Fiber Glass

Natural gas R-15 R-15 R- 10 R-10 R-10 R-10

Heat Pump R-20 R-15 R- 10 R-10 R-10 R-10

Electric Furn. R-25 R-20 R- 10 R-15 R-15 R-15

EPS Composite

Natural gas R-30 R-25 R-15 R-20 R-20 R-20

Heat Pump >R-30 R-30 R-15 R-20 R-20 R-20

Electric Furn. >R-30 >R-3Q R-15 R-20 R-20 R-20

Polyisocyanurate

Natural gas

Composite

R-20 R-20 R- 10 R-15 R-15 R-15

Heat Pump R-30 R-30 R- 10 R-15 R-15 R-15

Electric Furn. >R-30 >R-30 R-10 R-20 R-20 R-25

aHeating system efficiencies used: natural gas=70 percent, electric

resistance=95 percent; heat pump HSPF: Minot=4. 7, Xndianapolis=5 . 9

,

0rlando=7 „ 7 , San Antonio=7 . 3 , Phoenix =7.4, Bakersfield = 7.1; Cooling

system SEER=6„8 in all locations.

42
Table 4-4. Optimal R-Values for BUR Insulation Based on Cash Flow Analysis

at End of Second Yeara

Insulation/ Location

heating System3 Minot

ND.

IndianaDolis INOrlando

FL

San Antonio TXPhoenix

AZ

Bakersfield CA

Fiber Glass d _ i n IS. 1 or less in all applications

EPS Composite

Natural gas R-15 R-15 R-10 R-10 R-10 R-10

Heat Pump R-20 R-15 R-10 R-10 R-15 R-15

Electric Furn. R-25 R-20 R-15 R-15 R-15 R-15

Polyisocyanurate

Natural gas

Composite

R-10 R-10 R-10 R-10 R-10 R-10

Heat Pump R-15 R-15 R-10 R-10 R-10 R-10

Electric Furn. R-20 R-15 R-10 R-10 R-15 R-15

aAssumes 15 year mortgage at 10 percent interest, depreciation over 31.5

years, energy and maintenance as deductible expenses, and marginal income tax

rate of 25 percent.

43
4.3 Implications for CFC Substitutes in Commercial Roof Systems

The implications of both the original ORNL research and this new NBS economic

analysis, with regard to substitutes for insulation materials blown with

CFC's, are the same: Both fiber glass and EPS composites are cost effective

substitutes for polyisocyanurate (and by implication, polyurethane) roof deck

insulation. However, both of these substitutes will require significantly

thicker insulation to achieve a given R-value . Thus the exception to this

conclusion lies in those retrofit applications where rooftop HVAC equipment

constrains the thickness of the insulation to a level lower than that required

to achieve the desired R-value. (For new buildings the clearance under HVAC

equipment can generally be increased at little or no additional cost if the

designer is aware of this constraint.) Table 4-5 shows the energy penalties

per 1000 ft^ of roof area that can be attributed to the substitution of EPS

(k=0.26) for polyisocyanurate (k=0.17) when the insulation thickness

constraint is 2 inches. These would be substantial losses, enough to justify

some modification of the clearances in many cases.

In general, the EPS/perlite composite will be a more economical choice as a

substitute for polyisocyanurate than fiber glass insulation because higher Rvalues can be economically justified. It should also be recognized that the

density of the EPS material can be increased above the 1.0 lbs/ft^ used in the

ORNL study to improve its thermal conductivity. An increase to 1.5 lbs/ft^

will reduce its thermal conductivity by eight percent, so that the thermal

performance equivalent to the polyisocyanurate board can be achieved with a 40

percent increase in thickness. This will lessen any energy penalty

attributable to the substitution of EPS for polyisocyanurate when thickness

constraints are present.

4.4 Potential Impact of ASHRAE Standard 90.1

The draft ASHRAE 90.1 standard for energy conservation in commercial building

design specifies an overall thermal transmittance (U) for a roof system to be

less than or equal to a specified value. This design value is computed by a

relationship which takes into account the heating and cooling degree days at a

base of 65F, and the cooling degree hours at a base of 80F. Table 4-6 shows

the equivalent R-value requirement for each of the six locations evaluated in

this section. In addition, table 4-6 shows the corresponding thickness for

the three types of insulation considered: fiber glass, EPS composite, and

polyisocyanurate composite.

The minimum R-values shown in table 4-6 compare reasonably well with the

optimal R-values shown in table 4-3 for the polyisocyanurate composite on the

roofs of buildings heated with natural gas, considering that the optimal

values were computed at R-5 intervals rather than continuously. The exception

here is for Phoenix, where the draft ASHRAE standard requires R-21.5, and the

economically optimal level for gas and heat pump is R-15 (although R-20 is

optimal with electric resistance)

.

44
Table 4-5. Energy Penalty for Substitution of 2 in. EPS (R-7.7) for 2 in.

Polyisocyanurate (R-11.8) per 1000 ft^ of Roof Area

Location: Minot Indiana Orlando San Anto- Phoenix BakersN.D. oolis IN FL nio TX AZ field CA

Energy Penalty in Million Btu/Yr

Annual heating load: 10.9 7.4 2.1 2.9 2.9 4.0

Annual cooling load: 0.4 0.8 1.8 2.8 3.1 2.0

Increased. Present-Value Cost of Energy over 20 Years

a

Natural gas $992 $815 $368 $545 $585 $591

Heat Pump $1570 $978 $322 $584 $570 $584

Electric Furn. $2270 $1720 $545 $949 $907 $1040

aAll energy cost calculations assume

efficiency assumptions in table 4-3

electric air

.)

conditioning. (See

Table 4-6. ]Minimum R-Values and Corresponding Insulation

Commercial Roof Deck Systems

Thicknesses for

Standard 90.1 Required Th i ckne s s ( inche s

)

Location Minimum R-Value Fiber Glass EPS Polyisocyanurate

Minot, N.D 22.8 5.7 5.9 3.9

Indianapolis 17.2 4.3 4.5 2.9

Orlando 13.1 3.3 3.4 2.2

San Antonio 15.7 3.9 4.1 2.7

Phoenix 21.5 5.4 5.6 3.7

Bakersfield, CA 16.3 4.1 4.2 2.8

45
These draft ASHRAE requirements could not be met economically with fiber glass

board. However, the optimal R- value for EPS composite, from an LCC

standpoint, is well above the ASHRAE requirements in all locations except for

Phoenix. The use of EPS composite in built-up roof systems provides a more

cost-effective means of achieving the minimum ASHRAE requirements, and in fact

makes it cost-effective, again from a LCC standpoint, to exceed the standard

in most of these locations.

46
5. SUMMARY

Substitutes for CFC-blown rigid foam insulations were evaluated for use in

three distinct building components: residential walls systems (both wood-frame

and masonry), commercial walls systems, and commercial low-slope roof systems.

It was found that the most suitable substitutes, expanded polystyrene (EPS)

and fiber glass, typically have a lower cost per resistance unit than most

commonly used CFC-blown foams (polyisocyanurate and extruded polystyrene) , but

that greater thicknesses of these substitutes are required to attain the same

thermal performance as the latter materials. As a result, any economic costs

attributable to such substitutions are related to expanding the walls and

roofs to accommodate the thicker insulation rather than to the materials

themselves

EPS rigid foam sheathing is the most suitable substitute for polyisocyanurate

or extruded polystyrene sheathings for wood-frame walls. The EPS specifically

evaluated has an R- value of 4.17 per in. at a density of 1.5 Ibs/'ft , and has

a protective facing to improve its handling characteristics and reduce

ultraviolet degradation while exposed. The costs of using a thicker EPS

sheathing than the polyisocyanurate or extruded polystyrene on wood- frame

walls was found to be determined primarily by the cost of extension jambs for

wood-framed windows and doors. For an average size (1650 ft^ of floor area)

house the net cost of adding wood extension jambs (after subtracting the

savings in material costs) to accommodate sheathing thicknesses greater than

0.5 in. is approximately $160. In new houses with metal windows no

significant cost for increasing the depth of the window jambs is expected,

since these extensions are typically gypsum board finish. In general it was

found that substituting 2x6 in. studs for 2x4 in. studs and insulated

sheathing, in order to accommodate an equivalent amount of fiber glass

insulation, is not a cost effective means of reducing the usage of CFC-blown

insulation.

The cost of increasing the thickness of an exterior masonry wall to

accommodate a thermally equivalent amount of EPS rigid foam insulation in

place of polyisocyanurate or extruded polystyrene on the inside surface or in

the wall cavity is primarily related to lost interior space. This cost is

approximately the same as the reduction in cost attributable to the usage of

EPS in place of the CFC-blown insulations, so that there is no significant net

increase in cost for using EPS. If the EPS insulation is installed on the

exterior wall, no wall expansion cost is expected. Insulation on the exterior

surface is actually more energy efficient than an equivalent amount on the

inside surface. However, insulation on the exterior surface must be covered

with a protective finish, which makes this an overall more costly alternative.

The choice of an exterior wall system for commercial buildings and high-rise

residential buildings is much wider than that for typical single -family

residence; as with the latter, the choice of a wall system can have a

significant effect on the appropriate insulation type and its economic

thickness. For most masonry and stud wall systems, EPS can be used in place

of CFC-blown rigid foam insulation with no economic or energy penalty,

provided that the exterior wall surface can be expanded outward at little or

no increase in construction cost in order to maintain the same level of

47
thermal performance. Exceptions to this conclusion are (1) concrete-masonry

walls with insulation installed on the interior surface, (2) hard-coat

exterior finish and insulation systems which require the more rigid surface

provided by extruded polystyrene, and (3) buildings for which the outside wall

dimensions are strictly limited at the building site. In general, the cost of

rental space in commercial buildings is so high that any intrusion into the

occupied space to maintain the thermal performance of the insulation will be

uneconomical

.

For some curtain wall systems, the choice of insulation material is determined

more by fire codes than by economics, per se. The polyisocyanurate or

polyurethane insulation currently used in metal-skinned foam-core panels

cannot be replaced with EPS in non- combustible wall construction. The

elimination of CFC-blown foam insulation would have a significant negative

impact on the design of many new commercial buildings and the industry

manufacturing this product.

In flat-panel curtain wall systems (e.g., metal, stone, and aggregate panels),

where the insulation is typically added to the inside surface after the panels

are attached to the building, fiberglass is the most commonly used insulation

material. Foamed- in-place polyurethane is also used in this latter

application with superior results, not only because of its improved thermal

performance but because it is able to seal the wall to reduce air

infiltration. While this latter insulation system is not as prevalent as

fiberglass, a reduction in the availability of CFCs for foam insulation will

have a negative impact here as well, primarily in terms of increased energy

usage. It is unlikely that fiberglass will be used at an equivalent level of

thermal performance for those installations currently using foamed- in-place

polyurethane

.

Curtain wall panels are also manufactured using EPS insulation with a

protective stucco- like coating on the outside. These panels could be

substituted for those containing CFC-blown insulation materials in some new

buildings where a stucco- like exterior is acceptable.

Both fiber glass board and EPS rigid foam were found to be cost-effective

substitutes for polyisocyanurate or polyurethane rigid foam in insulating

built-up roofs on commercial buildings. The exceptions, which are difficult

to quantify in terms of frequency of encounter, are those existing

installations where roof-top equipment has insufficient vertical clearance to

allow the use of a thicker insulation material. If the same thickness of EPS

or fiber glass is used instead of the more efficient polyisocyanurate or

polyurethane, the energy penalty will be significant.

48
Appendix A.

1. Wall Analysis:

2. Roof Analysis:

Climatic Data and DOE Regions for Locations Evaluated

CITY HDD65 CDH74 DOE REGION

BOSTON 5775 5094 1 WASHINGTON 4828 9952 3

ATLANTA 3069 11892 4

ORLANDO 531 27247 4

MINNEAPOLIS 8059 6946 5

KANSAS CITY 5201 13730 7

DALLAS/FT WORTH 2354 28048 6

DENVER 6083 7510 8

PHOENIX 1382 55998 9

SEATTLE/TACOMA 5280 1260 10

SF/OAKLAND 2922 342 9

LOS ANGELES 1494 1123 9

MINOT ND 9177 4584 8

INDIANAPOLIS IN 5620 7639 5

ORLANDO FL 531 27247 4

SAN ANTONIO TX 1578 30394 6

PHOENIX AZ 1382 55998 9

BAKERSFIELD CA 2194 28514 9

A,

'

. .
Appendix B. DOE Regional Price Projections and Uniform Present-Worth Factors^

Table B-l. Residential Analysis (Walls)

Energy prices (1987) and corresponding UPW based on 25 years and 7%

discount rate plus DOE energy price projections for residential sector:

REGION ELECTRICITY NAT GAS

PRICE UPW PRICE UPW

1 29.15 10.69 7.34 18.96

2 26.25 11.22 6.86 14.65

3 20.03 10.97 6.10 14.63

4 19.20 9.98 5.46 16.53

5 22.86 10.13 5.34 16.16

6 19.36 12.52 4.92 15.60

7 21.21 10.77 4.74 17.54

8 21.29 10.36 4.55 16.29

9 21.31 10.36 4.88 16.34

10 10.29 12.43 5.58 16.86

Avg . U . S20.54 10.75 5.50 15.78

Table B-2. Commercial Analysis (Roof and Walls)

Energy prices (1987) and corresponding UPW based on 20 years and 7%

discount rate plus DOE energy price projections for commercial sector:

REGION ELECTRICITY NAT GAS

PRICE UPW PRICE UPW

1 29.07 9.75 6.10 14.05

2 25.44 10.18 5.52 13.88

3 19.79 9.95 5.40 13.16

4 19.38 9.12 4.73 14.89

5 22.63 9.24 4.72 14.58

6 18.82 11.3 4.18 14.41

7 20.71 9.7 3.93 16.02

8 20.71 9.4 4.25 14.44

9 21.12 9.4 5.64 12.06

10 10.26 11.1 4.44 16.00

Avg . U . S

20.80 9.7 4.85 14.17

^Source: Lippiatt, B.C., and Ruegg, R.T., Energy Prices and Discount

Factors for Life-Cycle Cost Analysis . NBSIR 85-3273-2 (Rev. 6/87)

National

Bureau of Standards, Gaithersburg, MD, 1987

B-l

Appendix C. Installed Insulation Costs and U-Values Used in Analysis

The following tables contain the insulation R-values and corresponding Uvalues and installed costs used in to determine the economic thicknesses or

values for insulation in each building component evaluated in this report,

costs were adjusted to include 25 percent builder overhead and profit. All

costs are in 1987 dollars.

Table C-l. Residential Wood-frame Walls, With Extension Jamb Costs

WALL

NO.

WALL

U

SHEATHING

R

COST

/FT2 WALL DESCRIPTION

1 0.0781 1.320 $0.36 3.5” WALL WITH R-ll FIBERGLASS

2 0.0710 1.320 $0.43 3.5” WALL WITH R-13 FIBERGLASS

3 0.0538 1.320 $1.33 5.5" WALL WITH R-19 FIBERGLASS 16" CENTERS

4 0.0524 1.320 $1.05 5.5" WALL WITH R-19 FIBERGLASS 24" CENTERS

5 0.0603 3.600 $0.51 R- 13 + 0.5" POLYI SOCYANURATE

6 0.0490 7.200 $0.90 R- 13 + 1" POLYI SOCYANURATE

7 0.0415 10.800 $1.13 R- 13 + 1.5" POLYI SOCYANURATE

8 0.0669 2.090 $0.38 R- 13 + 0.5" EPS

21 0.0644 2.610 $0.56 R- 13 + 0.625 "EPS

24 0.0603 3.600 $0.60 R-13 + 0.86" EPS

9 0.0582 4.170 $0.65 R- 13 + 1" EPS

22 0.0546 5.210 $0.71 R-13 + 1.25" EPS

10 0.0515 6.255 $0.77 R-13 + 1.5" EPS

23 0.0488 7.300 $0.92 R-13 + 1.75" EPS

11 0.0463 8.340 $0.97 R-13 + 2" EPS

12 0.0650 2.500 $0.46 R-13 + 0.5" EXT. POLYS

13 0.0553 5.000 $0.81 R-13 + 1" EXT. POLYS

14 0.0483 7.500 $0.99 R-13 + 1.5" EXT. POLYS

15 0.0464 3.600 $1.13 R- 19 + 0.5" POLYI SOCYANURATE

16 0.0395 7.200 $1.45 R-19 + 1" POLYI SOCYANURATE

25 0.0488 2.610 $1.11 R-19 + 0.625 "EPS

17 0.0451 3.850 $1.16 R-19 + 1" EPS

26 0.0430 5.210 $1.26 R-19 + 1.25" EPS

18 0.0426 5.775 $1.29 R-19 + 1.50" EPS

27 0.0393 7.300 $1.47 R-19 + 1.75" EPS

19 0.0491 2.500 $1.08 R-19 + 0.5" EXT. POLYS

20 0.0434 5.000 $1.36 R-19 + 1" EXT. POLYS

C-l

RAll
Table C-2. Residential Wood-frame Walls, Without Extension Jamb Costs

WALL

NO.

WALL

U

SHEATHING

R

COST

/FT2 WALL DESCRIPTION

1 0.0781 1.320 $0.36 3.5" WALL WITH R-ll FIBERGLASS

2 0.0710 1.320 $0.43 3.5" WALL WITH R-13 FIBERGLASS

3 0.0538 1.320 $1.08 5.5" WALL WITH R-19 FIBERGLASS 16" CENTERS

4 0.0524 1.320 $0.79 5.5" WALL WITH R-19 FIBERGLASS 24" CENTERS

5 0.0603 3.600 $0.51 R-13 + 0.5" POLYI SOCYANURATE

6 0.0490 7.200 $0.74 R- 13 + 1" POLYI SOCYANURATE

7 0.0415 10.800 $0.97 R-13 + 1.5" POLYI SOCYANURATE

8 0.0669 2.090 $0.38 R- 13 + 0.5" EPS

21 0.0644 2.610 $0.40 R-13 + 0.625 "EPS

24 0.0603 3.600 $0.44 R-13 + 0.86" EPS

9 0.0582 4.170 $0.49 R-13 + 1" EPS

22 0.0546 5.210 $0.55 R-13 + 1.25" EPS

10 0.0515 6.255 $0.61 R-13 + 1.5" EPS

23 0.0488 7.300 $0.66 R-13 + 1.75" EPS

11 0.0463 8.340 $0.72 R-13 + 2" EPS

12 0.0650 2.500 $0.46 R-13 + 0.5" EXT. POLYS

13 0.0553 5.000 $0.64 R-13 + 1" EXT. POLYS

14 0.0483 7.500 $0.83 R-13 + 1.5" EXT. POLYS

15 0.0464 3.600 $0.87 R-19 + 0.5" POLYI SOCYANURATE

16 0.0395 7.200 $1.10 R- 19 + !" POLYI S OCYANURATE

25 0.0488 2.610 $0.77 R-19 + 0.625 "EPS

17 0.0451 3.850 $0.81 R-19 + !" EPS

26 0.0430 5.210 $0.92 R-19 4

* 1.25" EPS

18 0.0426 5.775 $0.95 R-19 + 1.50" EPS

27 0.0393 7.300 $1.03 R-19 + 1.75" EPS

19 0.0491 2.500 $0.95 R-19 + 0.5" EXT. POLYS

20 0.0434 5.000 $1.01 R-19 + !" EXT. POLYS

C-2
Table C-3. Insulation in Masonry Walls (residential)-*

WALL WALL SHEATH COST/FT^

NO. U R INTERIOR EXTERIOR WALL DESCRIPTION

1 0.2799 0.000 $0.00 $0.00

2 0.1928 0.000 $0.05 $0.05

3 0.1129 3.600 $0.48 $0.43

4 0.0937 5.400 $0.60 $0.52

5 0.0801 7.200 $0.76 $0.66

6 0.0700 9.000 $0.90 $0.77

7 0.0621 10.800 $1.04 $0.88

8 0.0559 12.600 $1.18 $1.00

9 0.1366 2.090 $0.35 $0.30

10 0.1194 3.130 $0.42 $0.34

11 0.1060 4.170 $0.52 $0.41

12 0.0954 5.210 $0.60 $0.47

13 0.0867 6.260 $0.68 $0.53

14 0.0795 7.300 $0.76 $0.58

15 0.0734 8.430 $0.85 $0.65

16 0.1291 2.500 $0.49 $0.44

17 0.1110 3.750 $0.58 $0.51

18 0.0974 5.000 $0.72 $0.62

19 0.0868 6.250 $0.84 $0.71

20 0.0782 7.500 $0.96 $0.80

21 0.0713 8.750 $1.08 $0.90

NON -REFLECTIVE AIRSPACE

3/4 IN REFLECTIVE AIR SPACE

0.5 IN POLYISOCYANURATE (FOIL FACING)

0.75 IN POLYISOCYANRURATE (FOIL FACING)

1.0

IN POLYISOCYANURATE (FOIL FACING)

1.25

IN POLYISOCYANURATE (FOIL FACED)

1.5

IN POLYISOCYANURATE (FOIL FACING)

1.75

IN POLYISOCYANURATE (FOIL FACING)

0.5 IN EPS (FOIL FACING)

0.75 IN EPS (FOIL FACING)

1.0 IN EPS (FOIL FACING)

1.25

IN- EPS (FOIL FACING)

1.5

IN EPS (FOIL FACING)

1.75

IN EPS (FOIL FACING)

2.0 IN EPS (FOIL FACING)

0.5 IN EXTRUDED POLYS (FOIL WALLBOARD)

0.75 IN EXTRUDED POLYS (FOIL WALLBOARD)

1.0 IN EXTRUDED POLYS (FOIL WALLBOARD)

1.25

IN EXTRUDED POLYS (FOIL)

1.5

IN EXTRUDED POLYS (FOIL WALLBOARD)

1.75

IN EXTRUDED POLYS (FOIL WALLBOARD)

1 Cost and U-value do not include exterior finish.

C-3
Table C-4. Built-up Roof Insulation

ROOF ROOF INSUL. COST

NO. U R /ft2 WALL DESCRIPTION

1 0.1000 10.0 $1.58 FIBERGLASS R-10

2 0.0667 15.0 $2.13 FIBERGLASS R-15

3 0.0500 20.0 $2.68 FIBERGLASS R-20

4 0.0400 25.0 $3.23 FIBERGLASS R-25

5 0.0333 30.0 $3.78 FIBERGLASS R-30

6 0.1000 10.0 $1.79 EPS COMPOSITE R-10

7 0.0667 15.0 $1.94 EPS COMPOSITE R-15

8 0.0500 20.0 $2.10 EPS COMPOSITE R-20

9 0 . 0400 25.0 $2.26 EPS COMPOSITE R-25

10 0.0333 30.0 $2.41 EPS COMPOSITE R-30

11 0.1000 10.0 $1.65 POLYISOCYANURATE R12 0.0667 15.0 $1.91 POLYI SOCYANURATE R13 0.0500 20.0 $2.16 POLYISOCYANURATE R14 0.0400 25.0 $2.42 POLYISOCYANURATE R15 0.0333 30.0 $2.68 POLYISOCYANURATE R16 0.0850 11.8 $1.74 POLYISOCYANURATE 2"

17 0.1300 7.7 $1.72 EPS COMPOSITE 2”

10

15

20

25

30
FORM NBS-1 14A (REV. 11-84)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See in struction s

)

1. PUBLICATION OR

REPORT NO.

HBSIR 88-3329

2. Performing Organ. Report No. 3. Publication Date

4. JULY 1988

TITLE AND SUBTITLE

Technical and Economic Analysis of CFC-Blown Insulations and Substitutes for

Residential and Commercial Construction 5.

AUTHOR(S)

Stephen R. Petersen and A. Hunter Fanney

6.

PERFORMING ORGANIZATION (If joint or other thanNBS. see instructions)

NATIONAL BUREAU OF STANDARDS

U.S. DEPARTMENT OF COMMERCE

GAITHERSBURG, MD 20899

7. Contract/Grant No.

8. Type of Report & Period Covered

9.

SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City . State , ZIP)

Building Systems Division

U « S. Department of Energy

Washington, D.C, 20585

10.

supplementary notes

~ J Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual summary of most si gnificant information. If document includes a significant

bi bliography or literature survey, mention it here)

Rigid foam insulations blown with chlorof lourocarbons (CFC’s) are among the most

thermally efficient materials available for insulating walls and roofs of buildings c While they are more expensive than more traditional insulating materials, their

usage where space constraints dictate a more efficient insulator have become

commonplace. Increasing concern about the effect of CFC*s released to the atmosphere

may result in restrictions on the availability of these insulation materials. This

report evaluates the thermal performance and economics of rigid foam insulating

materials containing CFC's and alternative insulation materials that contain little

or no CFC. Residential walls (wood-frame and masonry), commercial wall systems

(frame, masonry, and curtain wall) and commercial low-slope roof systems are

examined in a wide range of climates in the United States to determine the cost

effectiveness of rigid foam insulation materials. Economic substitutes for

insulation materials containing CFC exist; however,' they are not compatible

with all types of wall/window and roof systems and thus may make some wall and

roof systems impractical.

12.

KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) building economics; building energy performance; building envelope;

chloroflourocarbons; energy conservation; thermal insulation

13.

AVAILABILITY

[X] Unlimited

| | For Official Distribution. Do Not Release to NTIS

[~1 Order From Superintendent of Documents, U.S. Government Printing Office, Washington, DC

20402.

[X] Order From National Technical Information Service (NTIS), Springfield, VA 22161

14. NO. OF

PRINTED PAGES

62

15. Price

$13 ,95

USCOMM-DC 85-6006
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