NATL INST OF STAND & TECH

A111D7 sio=m

NBS

C. 2

NBS BUILDING SCIENCE SERIES 123

The Effect of Moisture

on the Thermal Conductance

of Roofing Systems

U.S. DEPARTMENT OF COMMERCE • NATIONAL BUREAU OF STANDARDS -"^
NATIONAL BUREAU OF STANDARDS

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NBS BUILDING SCIENCE SERIES 123 JUN 1 9 1980

I flC>i OjCC'C'/rc.

The Effect of Moisture ^^^^^

on the Thermal Conductance

of Roofing Systems /^^

Lawrence I. Knab

David R. Jenkins

Robert G. Mathey

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

Washington, D.C. 20234

Prepared for

Department of Energy

Architectural and Engineering

Systems Branch

Buildings Division Office of Buildings and Community Systems

Washington, D.C. 20585

U.S. DEPARTMENT OF COMMERCE, Philip M. Klutznick, Secretary

Luther H. Hodges, Jr., Deputy Secretary

Jordan J. Baruch, Assistant Secretary for Productivity, Technology, and Innovation

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Issued April 1980
Library of Congress Catalog Card Number: 80-600031

National Bureau of Standards Building Science Series 123

Nat. Bur. Stand. (U.S.), Bldg. Sci. Ser. 123, 46 pages (Apr. 1980)

CODEN: BSSNBV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1980

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

Price $3.50

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

This investigation was done under Oak Ridge National Laboratory subcontract no. DE-A105-780R06113 and the U.S. Department of Energy and is

part of the National Program for Building Thermal Envelope Systems and

Insulating Materials.

Cover: There are an estimated 25

billion square feet of built-up

roofing in the United States.
TABLE OF CONTENTS

Page

LIST OF TABLES v LIST OF FIGURES vi

ABSTRACT viii

CONVERSION FACTORS TO METRIC (SI) UNITS ix

1. BACKGROUND 1

2. SPECIMENS 3

3. MOISTURE INTRODUCTION AND MEASUREMENT 7

4. THERMAL CONDUCTANCE TEST PROCEDURE, EQUIPMENT AND

MEASUREMENT 11

5. TEST RESULTS AND ANALYSIS 15

5.1 Thermal Conductance of "Room Dry" Specimens 15

5.2 Moisture Gain and Distribution 16

5.3 Thermal Conductance of "Wet" BUR System Specimens 18

6. SUMMARY AND CONCLUSIONS 21

7. REFERENCES 25

TABLES 27

FIGURES 32
LIST OF TABLES

Page

Table 1 Properties of Roofing System Components 27

Table 2 Thickness, Density and "Room Dry" Thermal Conductance

Results for Individual BUR System Specimens 28

Table 3 Summary of Thermal Conductance Results for "Room Dry"

Conditions 29

Table 4 Insulation Moisture Content for Cores and BUR System

Specimens and Conditions of Specimens Before Coring .. 30

Table 5 Curve Fit Coefficients for Cr, and Ct^/Ct. 31

V
LIST OF FIGURES

Page

Figure 1 BUR System Specimen Composition 32

Figure 2 BUR System Specimen, Wooden Supporting Frame and the

Environmental Conditions Used to Induce Moisture 32

Figure 3 Insiilated Wooden Chambers Used to Induce Moisture in

the BUR System Specimens 33

Figure 4 Heat-Flow Meter Apparatus Used to Conduct Thermal

Conductance Tests 34

Figure 5 Moisture Gain in BUR System Specimens 35

Figure 6 Moisture Distributions by Coring for 2 in Polystyrene,

BUR System Specimen No. 37 36

Figure 7 Moisture Distributions by Coring for 1 in Perllte

Board, BUR System Specimen No. 13 37

Figure 8 Thermal Conductance vs Moisture Content for Glass

Fiber BUR System Specimens 38

Figure 9 Thermal Conductance vs Moisture Content for Perllte

Board BUR System Specimens 39

Figure 10 Thermal Conductance vs Moisture Content for Flberboard

BUR System Specimens 40

Figure 11 Thermal Conductance vs Moisture Content for Polyurethane BUR System Specimens 41

Figure 12 Thermal Conductance vs Moisture Content for Polystyrene BUR System Specimens 42

Figure 13 Thermal Conductance vs Moisture Content for all BUR

System Specimens Containing 1 in Insulation (Figs. 8

to 12) 43

Figure 14 Thermal Conductance vs Moisture Content for all BUR

System Specimens Containing 2 in Insulation (Figs. 8

to 12) 44

Figure 15 Ratio of "Wet" to "Room Dry" Thermal Conductance vs Moisture Content for all BUR System Specimens Containing 1 in Insulation 45

vl
LIST OF FIGURES

Page

Figure 16 Ratio of "Wet" to "Room Dry" Thermal Conductance vs Moisture Content for all BUR System Specimens Containing 2 in Insulation 46

vli
The Effect of Moisture on the Thermal

Conductance of Roofing Systems

by

Lawrence I. Knab*, David R. Jenkins**, and Robert G. Mathey*

ABSTRACT

The results of laboratory tests are presented describing the effect of

the moisture content on the thermal conductance of roofing systems con- taining insulation. Roofing systems, consisting of five types of rigidboard roof insulations with attached four-ply bituminous built-up

membrane, were tested. Moisture was induced into the roofing system

specimens by maintaining a constant water vapor pressure difference

across them. Moisture gain in the insulation varied depending on the

type and thickness of the insulation.

A procedure was developed, using a heat -flow meter apparatus (ASTM C 518

type), to carry out thermal conductance tests on roofing specimens con- taining moisture. More than 200 tests were performed over a wide range

of moisture contents. The approximate moisture distribution in the

insulation was determined from core samples.

Relationships between the thermal conductance and moisture content are presented. The relationships show that the presence of moisture in

roofing systems can cause significant increases in thermal conductance,

depending on the type and thickness of the insulation.

Key words: Built-up roofing, insulation, moisture, roofing, thermal

conductance, thermal conductivity, thermal resistance.

* Center for Building Technology

National Bureau of Standards

Washington, D.C.

** Professor of Engineering, University of Central Florida, Orlando,

Florida, on assignment to the National Bureau of Standards under

provisions of the Intergovernmental Personnel Act.

viii
Since the roofing industry generally uses conventional U.S. units, the

following table is provided for converting to metric units.

CO^fVERSION FACTORS TO METRIC (SI) UNITS

Physical

Quant i ty

To Convert

From To Multiply By

Length ft m 3.05 X 10"^

Area ft2 m2 9.29 X 10"2

Volume ft3 m3 2.83 X

10"2

Temperature Fahrenheit Celsius T(, = (Tp-32)/1.8

Temp. Diff. Fahrenheit Kelvin K = (ATp)/1.8

Density Ibm/f t^ kg/m^ 1.602 X

10"*"^

Thermal

Transmi t tance

(or Conductance) Btu/h.ft^.'F W/m^.K 5.68

Thermal Resistance h.ft2.°F/Btu m^.K/W 0.176

Heat Flow Btu/h W 2.93 X 10"^

Mass per Unit Area Ibm/ft^ kg/m2 4.88

ix
Facing Page: The heat loss through

roofing system can be

significant portion of

the overall heat loss

a building.
1 . BACKGROUND

The roofing system is often a major component in the heat transmission

through the envelope of a building. Most low-slope roofing in the

United States consists of rigid board thermal insulation with an attached built-up bituminous membrane. The thermal resistance of this

type of roofing depends on factors such as the type and thickness of

insulation, the number and size of roof penetrations, the spacing of

insulation joints, the number of metal fasteners penetrating through

1
the insulation, and the amount and distribution of moisture in the

roofing system. Small amounts of moisture in some insulations can significantly increase their thermal conductance.

A number of researchers have studied the effect of moisture content

on the thermal conductivity of insulation. Dechow and Epstein [1]*

reported the results for their own laboratory study, together with

the results of five other empirical studies [2,3,4,5,6], all of which

were performed to determine the effect of moisture on the thermal

conductivity of various insulations. Dechow and Epstein also presented

empirical relationships between thermal conductivity and the moisture

content for polyurethane foam, polyisocyanurate, low and high density

expanded polystyrene, and glass fiber insulations. For these relationships, the thermal conductivity increased with increasing moisture content and the change in thermal conductivity per unit change in moisture

(slope) was either constant or increased with respect to moisture

content

.

Cammerer [7], in a comprehensive review published in 1957, dealt at

length with the effect of moisture distribution on the measurement of

thermal conductivity and on the change in moisture distribution during

the measurement period. He considered a number of building materials.

In a more recent, review, Tye [8] also considered the effect on thermal

conductivity of moisture transmission in damp materials. Tye noted that

the geometric arrangement of the moisture is a critical factor and that

several processes of heat transfer need to be considered. Tye developed

a number of models which may be useful in predicting the behavior of

porous composite materials, such as roofing insulation.

Recently, Tobiasson and Ricard [9] presented laboratory results for

moisture gain and its effect on the thermal resistance of some commonly

used roof insulations. Powell and Robinson [10] investigated the effect

of moisture on heat transfer through insulated concrete deck roof con- structions with attached built-up bituminous membranes. No other

studies to date, however, were available in the open literature on roofing systems containing insulation with a built-up roofing (BUR)

membrane. Moreover, the effect of the amount and distribution of the

moisture on the thermal conductance of roofing systems containing

insulation has not been investigated.

This paper presents the test results of a laboratory program, sponsored

by the Department of Energy (DOE), to determine the effect of the moisture content on the thermal conductance of roofing systems consisting of

insulation and a BUR membrane. The study presented herein was performed

in conjunction with another laboratory investigation, sponsored by the

Department of the Air Force, to evaluate various techniques for nondestructively determining moisture content and its distribution in roofs.

Facing Page: Specimen being fabricated - hot asphalt being "mopped" on.

Numbers in brackets refer to the references at the end of this report.

2
2. SPECIMENS

Thermal conductance tests were performed on "room dry" roofing insulation boards, BUR membranes, and insulation boards with attached BUR

membranes (BUR systems). The "room dry" roofing test specimens were

stored at room conditions at approximately 70**? and 50% relative

humidity (RH) . The moisture contents of the insulation board and roofing felts were determined gravimetrically after oven drying. Thermal

conductance tests ("wet") were also conducted on a set of BUR system

specimens in which moisture was introduced into the specimens. All

specimens were nominally 2 by 2 ft in area. Five types of rigid board

3
roof insulations, in 1 and 2 in nominal thicknesses, were included in

the study; they were glass fiber, perlite board, fiberboard, expanded

polystyrene, and foamed polyurethane. The BUR system specimens were

fabricated by a roofing contractor under the supervision of National

Bureau of Standards' personnel. The BUR membranes consisted of four

plies of type 15 asphalt saturated, organic felts (Type I - ASTM

D 226-77 [11]). The felts were applied to the insulation boards in

sandwich fashion by hot mopping with type III asphalt (ASTM D 312-77

[12]). Figure 1 shows a schematic of the composition of a BUR system

specimen.

Table 1 gives the average measured properties for the insulation, felt,

and asphalt used in the fabrication of the test specimens. The glass

fiber board had an asphaltic facing sheet over which the BUR membrane

was applied. In this study, the facing was considered as part of the

membrane. The polyurethane board originally had asphaltic facing sheets

on both sides. In order to increase the rate of moisture absorption,

the asphaltic facing sheets were removed from both sides with a band saw to provide the required 1 and 2 in thicknesses. The thickness of

the boards before cutting was 2.25 in for the 1 in specimens and 3.25 in

for the 2 in specimens. The batch from which the 1 in thick specimens

were cut was probably different from the batch from which the 2 in

specimens were cut. This is supported by the difference in density

(table 1) and visual difference; i.e. the 2 in thick boards appeared

less uniform in texture than the 1 in thick boards.

Table 2 identifies the individual BUR system specimens for which "room

dry" and subsequent "wet" thermal conductance tests were performed.

The table gives average measured values for total specimen thickness,

membrane thickness, and membrane weight per unit area in specimens

which had been taken apart after completing the conductance tests.

The insulation thickness was taken as the difference between the total

specimen and the membrane thicknesses. In some cases, as noted in

table 2, the thickness of the specimen could not be measured because

the insulation had deformed. Therefore, the total specimen thickness

had to be estimated using the measured membrane thickness and values

of insulation thickness given in table 1. Some melting and consequent

reduction in the thickness of the polystyrene insulation occurred during

application of the hot asphalt and roofing felts.

The four membranes of the glass fiber BUR system specimens (nos. 3, 53,

7 and 57 in table 2) had an average thickness of 0.40 in and an average

weight per unit area of 2.05 Ib/ft^. These four membranes were grouped

separately since the facing sheet on the glass fiber insulation was con- sidered as part of the membrane. The remaining 15 BUR system specimens

in table 2 had an average membrane thickness of 0.35 in and an average

4
weight per unit area of 1.76 lb/ft . The corresponding coefficients of

variation (GOV)* for the 15 measurements were 8.4 and 10.0 percent,

respectively for the thickness and weight per unit area.

The values of Individual membrane thicknesses In table 2 are the average

of 6 to 9 measurements. The coefficients of variation for each membrane

ranged from 4 to 14 percent, with the exception of specimen number 82,

which was 22 per cent.

The coefficient of variation Is the standard deviation divided by

the mean.

5
Facing Page: Ponded water can increase

the possibility of water

intrusion in the roofing

system.

6
3. MOISTURE INTRODUCTION AND MEASUREMENT

Thermal conductance tests were performed on BUR system specimens con- taining a wide range of moisture contents. Moisture was induced in the

2 X 2 ft specimens by controlling temperature and relative humidity

conditions on each side of the specimens. Specimens were placed on

the top of insulated wooden chambers, as shown in figures 2 and 3.

The inside of each of two large insulated chambers, 8 x 16 ft in area

was maintained at 100°F (+7"?) and 100% RH by means of four pools (each

about 25 ft^) containing heated water. The two insulated chambers were

in an environmental room which was maintained at SCF (+4°F) and 25%

7
I

(+5%) RH. Thus, the insulation (bottom) side of the specimens was subjected to lOO^F and 100% RH while the membrane (top) side of the specimens was subjected to 50°F and 25% RH. The calculated vapor pressure

difference was 1.84 in of Hg for the environmental conditions under

which the specimens were exposed. The intent of using this relatively

large vapor pressure difference was to induce moisture into the specimens at a rapid rate; usually, much lower vapor pressure differences

exist under actual field environmental conditions.

A wooden frame, approximately 2 x 2 ft, with a continuous wooden ledge

at the bottom was used to support the individual specimens (figure 2).

The ledge provided about a 1/2 in width of support at the bottom on all

four specimen edges. When additional support was needed, aluminum

angle, 1/2 in width, spanned the center of the wooden frame in both

directions. The edges of the specimens for all insulations except the

per lite boards were sealed with an impervious, vinyl, vapor-barrier

paint. A wax was used to seal the edges of the perlite board specimens.

Due to handling, some specimen edge seals cracked or fell off, but the

sides of the wooden frame (figure 2) tended to prevent moisture from

entering through the edges. Figure 2 shows a schematic of the BUR

system specimen, supporting frame, and the environmental conditions

used to induce moisture in the specimens.

Before the specimens were placed into chambers, they were weighed and

measured. When the specimens were removed from the chambers, the time was recorded and the specimens weighed; the difference in weight between

the "room dry" and "wet" condition was taken as the moisture gain. With

the exception of the specimens containing glass fiber insulation, the

surface of the insulation was wiped with paper towels to remove any free

or condensed surface water prior to weighing. In most cases, the specimens containing glass fiber insulation were turned on edge for several

minutes to drain water prior to weighing. The rate of gain of moisture

was determined from the exposure time in the chamber and the corresponding weight gain. When the specimen was returned to the chamber for

additional exposure and moisture gain, the time and weight were again

recorded. The exposure time ranged from about 10 to 100 days, depending

on the type of insulation. It is noted that there was interruption in

the introduction of moisture in some specimens because the desired moisture contents had been reached and because of maintenance of the laboratory facilities. Some specimens were stored in plastic bags at room temperature up to about three weeks before testing.

To estimate the vertical moisture distribution (from the cold to warm

side of the specimen) of the water in the insulation, 0.91 in diameter

cores were taken by hand using a cork-borer from several BUR system

specimens containing perlite board and polystyrene. The cores were

taken before and after the thermal conductance tests to determine if

the distribution of water had changed during the test. Cores were

generally not taken from the center 10 in square area, because this area was used as the heat flow monitoring section in the thermal

conductance tests. The resulting holes were plugged with a core of

8
polyurethane or polystyrene Insulation. The cores were cut into four

approximately equal length sections for the nominal 1 in insulations

and into eight sections for the 2 in insulations. The core sections were immediately placed into preweighed glass flasks with tight sealing

lids and weighed. After removing the lids and oven drying, the flasks were again weighed, to determine the moisture loss in each of the sections of insulation. These data provided an approximation of the moisture distribution. For higher moisture contents in the insulation and

particularly for the polystyrene insulation, it was impossible to avoid

some water loss during the coring and sectioning processes. None the

less, some definite trends for water distribution in the insulations

of the BUR system specimens were obtained.

9
Facing Page: Heat-flow meter apparat

used in thermal conductance tests.

10
4. THERMAL CONDUCTANCE TEST PROCEDURE, EQUIPMENT, AND MEASUREMENT

Measurements of thermal conductance of the "room dry" roofing insulation

boards, BUR membranes, and the "room dry" and "wet" BUR system specimens were made using an ASTM C 518 [13] type heat -flow meter apparatus*.

A Dynatech R-Matic heat-flow meter apparatus was used for these

tests. This does not imply a recommendation or endorsement by the

National Bureau of Standards.

11
The procedure used in this study differed from the ASTM C 518 procedure

mainly because the moisture levels in the specimens tested are not

considered in ASTM C 518 and the specimen surfaces (bituminous built-up

membranes) were not always flat.

The metering section consisted of a 10 in square, fully integrated, heat

flow meter which was built into the lower (hot) plate of the apparatus.

The hot and cold plate surface temperatures, the heat-flow meter output,

and the specimen thickness were digitally displayed on a front panel

meter (figure 4).

The following procedure was used to conduct the thermal conductance

tests

1. "Wet" specimens were removed from the chamber after exposure to moisture and wiped or drained to remove any free

water. The time and specimen weight were recorded.

2. The specimen was then wrapped in 0.0005 in thick PVC sheet

and placed in a 0.003 in thick polyethylene bag which was then stapled. This was done to prevent water leakage from

the specimen and damage to the heat -flow meter apparatus.

To be consistent, all specimens (including "room dry"

specimens) were wrapped as described.

3. The wrapped 2 x 2 ft specimen was then inserted in the

heat-flow meter apparatus (figure A). The specimen was placed horizontally in the apparatus with the membrane

side in contact with the upper (cold) plate, maintained

at about 50°F and the insulation side in contact with the

lower (hot) plate maintained at about 100°F. It is noted

that in about 8 percent of the "wet" conductance tests

performed on BUR specimens the lower plate temperature

ranged from 86 to 90°F. The lower plate temperature was about 85°F during the 6 "room dry" roofing membrane tests.

By means of a vacuum pump or by gradually and gently com- pressing the specimen with the hot and cold plates, most

of the entrapped air was forced out of the bag. The

plates were then brought in contact with the insulation

or BUR system specimens by compressing them approximately

0.06 in after initial contact. It is noted that lack of

flatness in bitumen surfaces makes it possible to trap air

between the bitumen surface and the cold plate. The possibility of air layer could affect the thermal conductance

values. The temperatures of the plates in the heat -flow

meter apparatus (adjacent to the membrane and insulation

sides of the specimen) were about the same as the temperatures to which the specimens were exposed during introduction of moisture in the insulated chambers. This was done

deliberately to maintain the same rate of moisture migration during testing and moisture introduction.

12
4. The above conditions were maintained until essentially

steady-state heat flow occurred. Then the following data

were recorded: specimen thickness (distance between hot

and cold plates), hot and cold plate surface temperature,

and the heat flow. In this study, steady-state heat flow

was defined to occur when three successive thermal conductance readings were taken 20 minutes apart and agreed to

within 1 percent. This resulted in tests lasting from

about 2 to 5 hours.

In 93 percent of the thermal conductance tests reported,

the three successive readings agreed to within 1 percent

or less. In 6 percent of the tests reported, the three

successive readings agreed to within 1 to 2 percent and

for 1 percent of the tests, the readings agreed to within

2 to 4 percent. In most cases, the three successive readings were taken 20 minutes apart and, with the exception

of one test, all the readings were taken at least 17

minutes apart.

5. When the test was completed, the specimen was removed

from the apparatus, unwrapped, weighed, and the time

recorded before being returned to the chambers for

further moisture gain.

The mean temperature during the thermal conductance tests was about 75°F which was close to the temperature in the room in which the tests were conducted.

When steady-state heat flow is achieved, the thermal conductance of the

specimen is determined from the one dimensional Fourier heat transfer

equation:

q = C^AT. (1)

Noting that

q = SQ

and solving for C gives:

C SQ

AT

(2)

where: C = thermal conductance in Btu/(h*f f^* °F)

S = apparatus constant, having dimensions of Btu/(h«ft 'mV)

;

found [14] to be 4.05 for a specimen thickness of less

than or equal to 2.25 in and 4.03 for a specimen thickness

between 2.26 and 3.00 in. The apparatus constant was

13
determined, with an uncertainty of about 2 percent, using

a standard reference material. Calibration procedures are described in reference 14.

AT = temperature difference between hot and cold plates in °F

q = heat flow rate per unit area, Btu/h»ft

Q = signal from heat -flow meter in millivolts (mV)

The thermal resistance or R-value is calculated from:

R = ^

(3) SQ ^

^

/

Facing Page: Ridging and blistering of

built-up roof membranes

may be caused by moisture

in the roofing system.

14
5. TEST RESULTS AND ANALYSIS

5.1 THERMAL CONDUCTANCE OF "ROOM DRY" SPECIMENS

Table 3 gives average values of "room dry" thermal conductance, Cjj, and

their corresponding coefficients of variation (COV) for insulation and

BUR system specimens.

As shown in table 3, the COV values were relatively small, particularly

since the COV values included both the within specimen and between specimen variability. For the two cases in table 3 where the COV values

15
for Cjj for the insulation specimens could be computed, the GOV values

for the BUR system specimens were higher than those for the corresponding insulation specimens. This was probably due to the variability of

the membrane thickness (GOV ranged from about 4 to 14 percent) which

was present in the BUR system specimens but not in the insulation specimens. Table 2 shows the Gp values for individual BUR system specimens,

many of which subsequently had moisture induced in them. The values

from table 2 are the "room dry" reference values for the plots of

thermal conductance vs moisture content presented later.

Preliminary tests on "room dry" insulation board with and without

wrapping (0.0005 in PVC sheet and 0.003 in polyethylene bag) were con- ducted to determine the effect of the wrapping material. The procedure

for the preliminary tests differed from the procedure given earlier in

this report in that the time between readings was less. For the preliminary tests, the specimens were in the heat-flow meter apparatus for

at least two hours, and two or three readings were taken at least 15

minutes apart. The results showed that for the insulation tested (glass

fiber, 1 in; perlite board, 1 and 2 in; fiberboard, 1 and 2 in; polystyrene, 1 and 2 in; and polyurethane , 1 in) there was no appreciable

difference in thermal conductance for specimens with and without wrapping. It was also shown by calculation that the effect of the wrapping

material is not significant.

5.2. MOISTURE GAIN AND DISTRIBUTION

Figure 5 shows the insulation moisture content, Vp, in terms of the

elapsed time in the chambers for ten BUR system specimens, one for each

of the five insulation ^ypes and two insulation thicknesses studied.

The moisture content, Vp, in the specimen insulation is expressed as the percent. by volume of water in the insulation; Vp was based on the

average moisture gain for the entire specimen. The volume of insulation was detemined from the insulation thickness (table 2) and the overall

specimen dimensions (about 2 x 2 ft). The volume of water was determined from the weight gain of the specimen (62.4 lb = 1 ft^).

The lack of smoothness in the data plots in figure 5 for the glass

fiber specimens is attributed in part to their being drained prior to

being weighed. For equal exposure times (90 days), the 1 in polyurethane absorbed the largest amount of moisture (about 60%) while the 2 in

polyurethane absorbed the smallest (about 5%). It is also noted that

the rates of absorption of the 2 in polyurethane and 2 in polystyrene

were lower than the other specimens. Both 1 in perlite board and 1 in

fiberboard initially absorbed moisture very rapidly. The 2 in fiberboard specimen fell apart by delaminating, after absorbing about 18

percent moisture in a relatively short exposure period (17 days).

* Y

_ ^ Volume of moisture ^ ^ -^qq ^ Volume of insulation

16
In general it can be seen from figure 5 that specimens with 1 in

insulation absorbed moisture more rapidly and eventually absorbed

more moisture per unit volume for a given exposure time than did their

counterparts with 2 in insulation. Since the exposure conditions on the internal and external faces of the specimens were the same during

forced introduction of moisture, the differences in the response of the

1 in and 2 in specimens may be due to the lesser permeance of thicker

insulations or to the location of the plane of condensation. Other

factors which may be significant are the physical state of the water

introduced (vapor or liquid) and its distribution in the voids of the

insulation.

The response of the generally considered closed cell materials included

in this study suggests that some breakdown in cell structure occurred

due to moisture, that the cells were not initially completely closed, or that continuous moisture paths developed around and through the cells.

Large moisture gains in polyurethane foam and expanded polystyrene

insulations have been reported by other investigations [1,9].

Cores were taken before and immediately after the thermal conductance

tests to determine if the moisture distribution had changed. The

moisture content of the cores and corresponding specimens is given in

table 4 along with information regarding the sequence of coring relative

to the thermal conductance tests. Figure 6 shows moisture distributions

for three different moisture contents in 2 in polystyrene. The moisture

distribution for each of these three moisture contents did not appear to

be significantly different before and after testing. A similar trend is

shown in figure 7 for 1 in perlite board (cores 4B and 4A) . It is noted

that core 2AA (2 in polystyrene), which was taken two hours after the

thermal conductance test, had a moisture distribution similar to cores taken before and immediately after the test (cores 2B and 2A).

Some uncertainty in the reported moisture distributions may be attributed to the experimental technique of coring. The amount of water lost

while coring can be estimated by comparing the average moisture content

based on the core test with the that based on the entire BUR system specimen weight. Table 4 shows these two average moisture content values.

As can be seen, significant moisture was lost while coring the 2 in

polystyrene, particularly at larger moisture contents.

Distinct areas of visible free water, particularly for higher moisture

contents, were observed on the surface of the warm side of the glass

fiber insulation. It appeared that the lateral distribution of moisture

in these specimens varied considerably. As noted earlier, these specimens were drained prior to the thermal conductance tests; this also

contributed to the variability in the lateral moisture distribution.

17
5.3 THERMAL CONDUCTANCE of "WET" BUR SYSTEM SPECIMENS

Figures 8 to 12 show the thermal conductance, Cy, vs moisture content,

Vp, relationships for the BUR system specimens. The curves plotted in

figures 8 to 12 are either linear or quadratic best fit curves.

Quadratic curves were used when they exhibited a significant improvement

in fit as compared to the linear curves. In each figure, the upper

curve is for specimens containing 1 in insulation and the lower curve is

for 2 in insulation. Table 5 presents linear or quadratic coefficients

and the residual standard deviations for the best fit curves plotted in

figures 8 to 12. It is noted that the Cy and Vp scales differ in these

figures.

For specimens containing glass fiber insulation (figure 8) or 1 in polyurethane (figure 11) the Cy vs Vp curves are concave upward; the 2 in

polystyrene curve (figure 12) is only slightly concave upward. It is

noted that the small moisture gain of the 2 in polyurethane insulation

(figure 11) makes it difficult to comment on the C^ vs Vp trend for that

configuration. In contrast, the Cy vs Vp curves for specimens containing the other insulations are slightly concave downward (perlite - figure 9 or fiberboard - figure 10), or are linear (1 in polystyrene - figure 12). These differences are probably associated with different

moisture distributions in the various insulations and with the possibility of the existence of continuous moisture paths through the insulation

thickness

To compare the thermal conductances of the BUR system specimens con- taining different types of insulations, the data and best fit curves (figures 8 to 12) are shown collectively for the specimens containing

1 in insulation in figure 13 and 2 in insulation in figure 14. As

figures 13 and 14 indicate, Cy for all the BUR system specimens

increased with an increase in Vp, except for the specimen containing

2 in fiberboard. The slopes of the curves in figure 13 were not appreciably different except for specimens containing glass fiber insulation.

In general, all Cy vs Vp curves in figure 13 lie in a relatively narrow

band bounded by the perlite and polyurethane insulations. In figure 14,

the curves lie in an even narrower band than those in figure 13. Since

the conductance of the BUR system specimens is dependent on thickness,

it should be noted that the measured thicknesses of the nominal 1 and

2 in insulations differed from their nominal thickness (table 2).

Figures 15 and 16 are similar to Figures 13 and 14 and show the ratios

of the "wet" to "room dry" thermal conductance (Cy/Cp). The Cy/Cp ratio

gives the relative change in the thermal conductance by removing the

magnitude of the "room dry" thermal conductance from consideration. The

Cp values for the individual BUR system specimens (table 2) were used

when computing the Cy/C^ ratio. Table 5 shows the coefficients for the

best fit linear or quadratic curves for Crj/Cy, vs Vp.

18
The curves for C^/Cp vs Vp were close to each other over the entire

range of Vp for the BUR system specimens, except curves for specimens

containing 1 and 2 in glass fiber and 1 in polyurethane insulations

(figures 15 and 16). For example, at 20 percent moisture content,

specimens containing 1 and 2 in glass fiber insulation had values of

Cy/Cp of about 3 whereas C^/Cp for the other specimens (figures 15 and

16) ranged from about 1.5 to 2.4. Similarly at 40 percent moisture

content the specimen containing 1 in polyurethane had a Cy/C^ value

of about 4.5 compared to about 2.2 to 2.9 for the other specimens

(figure 15).

19
Facing Page: Moisture intrusion in

roofing systems can occur

during their construction.

20
6. SUMMARY AND CONCLUSIONS

Laboratory thermal conductance vs moisture content relationships are presented for roofing system specimens containing moisture. The specimens consisted of built-up bituminous membranes applied to rigid board

insulation. The following five types of insulations in 1 and 2 in

thicknesses were included in the study: glass fiber, perlite board,

fiberboard, polyurethane and expanded polystyrene.

The thermal conductance was measured on roofing specimens containing

a wide range of moisture contents in the insulations. Moisture was

21
introduced by imposing temperature and vapor pressure gradients across

the specimen thickness using large insulated chambers in an environmentally controlled laboratory. The moisture content and approximate distribution were determined from specimen weight gain and coring data.

Thermal conductance tests were conducted over relatively short time

periods, about 2 to 5 hours, using an ASTM C 518 type heat -flow meter

apparatus. A procedure was developed to test "wet" specimens and interpret the results for heterogenous roofing systems.

Linear and quadratic best fit curves are presented for thermal conductance vs moisture content (percent by volume of insulation) of roofing

specimens containing different insulations. The thermal conductance of

the roofing specimens in general increased with an increase in moisture

content for all insulations. The best fit curves for thermal conductance vs moisture content lie in relatively narrow bands for specimens

containing the 1 and 2 in insulations (figures 13 and 14).

For comparison, the thermal conductance data for individual specimens were normalized by dividing by the "room dry" thermal conductance value.

The normalized curves were relatively close to each other throughout the

entire moisture content range, with the exception of specimens containing glass fiber and 1 in polyurethane insulations (figures 15 and 16).

The amount and rate of gain of moisture varied considerably depending on

the insulation type and thickness. The moisture gain in about 100 days or less of exposure ranged from about 20 to 60 percent moisture content

by volume of insulation, for all specimens, including those containing

nominally closed cell insulations. A notable exception was the specimen

containing 2 in polyurethane which gained only about 5 percent moisture

in 90 days of exposure.

The vertical moisture distribution in specimens containing 1 in perlite

and 2 in polystyrene insulations did not appear to change appreciably

during the thermal conductance tests (figures 6 and 7). Lateral movement of free water in glass fiber insulations precluded the determination of representative vertical moisture distributions.

The authors wish to recognize the helpful guidance and suggestions

in the use and calibration of the heat-flow meter apparatus by

Dr. M. C. I. Siu. The authors wish to thank Mr. Douglas M. Burch for

his advice and comments pertaining to thermal engineering. The authors

appreciate the long hours and the cooperation of Messrs. Michael Glover,

Jessie C. Hairston, James C. Owen, David K. Ward, and Nathaniel E.

Waters in the preparation of test specimens, conduct of tests, and collection of data. Mr. A. Phillip Cramp is recognized for his important

contribution, including the supervision of the fabrication of roofing

system specimens and the development of the coring method to determine

moisture distribution. Mr. Bernard J. Hunt is recognized for his design

of the environmental chamber used to introduce moisture in the test

22
specimens. Finally, Ms. Catherine A. Scarbrough and Mr. Nathaniel E

Waters deserve recognition for their roles In the reducing, computer

Izlng, and plotting of the data.

23

7. REFERENCES

1. Dechow, F. J. and Epstein, K. A., "Laboratory and Field Investigation of Moisture Absorption and Its Effect on Thermal Performance

of Various Insulations," Thermal Transmission Measurements of

Insulation , ASTM STP 660, R. P. Tye, Ed., American Society for

Testing and Materials, Philadelphia, PA, 1978, pp. 234-260.

2. Thorsen, S. H. , "Determination of the Expansion Coefficient, Water

Absorption, Moisture Diffusivity, as well as Thermal Conductivity

at Different Moisture Contents for Polystyrene and Urethane Cellular Plastics," Institute for Building Technology, Chalmers

Technical University, Goteborg, Sweden, August 1973.

3. Paljak, I., "Condensation in Slabs of Cellular Plastics," Materlaux

et Constructions , Vol. 6, No. 31, 1973, pg . 53.

4c Levy, M. M., "Moisture Vapor Transmission and Its Effect on Thermal

Efficiency of Foam Plastics," Journal of Cellular Plastics , January

1966, pp. 37-45.

5. Mittasch, H. , "Dependence of the Thermal Conductivity of Plastic

Foams on Their Moisture Content," Plaste und Kautschuk , Vol. 16,

No. 4, 1969, pg. 268.

6. Achtziger, J., "Measurement of the Thermal Conductivity of Plastic

Foams With Any Desired Moisture Content," Kunststoffe in Bau ., Vol. 23, 1971, pg. 3.

7. Cammerer, J. S., "The Influence of Humidity on the Thermal Conductivity Coefficients of Building Materials According to the International Literature," (Feuchtigkeitsregelung Durchfeuchtung Und

Warmeleitfahigkeit) , 37-60, 1957, Translated by D. A. Sinclair,

Ottawa, Canada, 1964.

8. Tye, R. P., Ed., "Heat Transmission in Damp Materials," Thermal

Conductivity Vol. 1, Academic Press, 1969, pg . 326.

9. Tobiasson, W., and Ricard, J., "Moisture Gain and its Thermal Consequence for Common Roof Insulations," Proceedings, 5th Conference

on Roofing Technology, NBS and NRCA, April 19-20, 1979.

10. Powell, F.J., and Robinson, H.E., "The Effect of Moisture on the

Heat Transfer Performance of Insulated Flat-Roof Constructions,"

National Bureau of Standards, Building Science Series 37, October

1971.

11. ASTM "Asphalt -Saturated Organic Felt Used in Roofing and Waterproofing," ANSI/ASTM D 226-77, Annual Book of ASTM Standards, Part

15, Philadelphia PA, 1978.

25
12. ASTM "Standard Specification for Asphalt Used in Roofing," ANSI/

ASTM D 312-71 (Reapproved 1977), Annual Book of ASTM Standards,

Part 15, Philadelphia PA, 1978.

13. ASTM "Standard Test Method for Steady State Thermal Transmission

Properties by Means of the Heat Flow Meter," ANSI/ASTM C 518-76,

Annual Book of ASTM Standards, Part 18, Philadelphia PA, 1978.

lA. Siu, M. C. I., "Fibrous Glass Board as a Standard Reference

Material for Thermal Resistance Measurement Systems," Proceedings

of DOE/ASTM 'Insulation Conference, Tampa, Florida, October 23-24,

1978.

26
>—

s

6.53 7.64 5.99 6.59 3.80 4.12

48.1 55.6 39.2 33.5

z

ire

Content

om

dry"'^ t

by

Volume

COV

(%)

60.7 48.0 18.5

'

17.6

2.96 2.10

160. 154.

20.8 38.1

Molsti

"ro

Percen

Average 0.0733 0.0348 0.222 0.295 1.32 1.41

0.00245 0.00128

0.101

0.0357 2.08

z

COV

(%) 00 in o ^ in CO r-.

Density

Average

(oven

dry)

9.56 8.17

10.4

9.47

16.4 15.2

1.30 1.13 1.59 1.86

.122^

Ib/ft^

about

62.4

z r>.r^^0'«0^ncn^o^00^0^ CM

j

:kness

(In) >

o

CJ

4.72 1.94 2.18 1.59 1.53

0.643 4.56 8.90

Thl(

Average 0.75 2.07 1

.02

2.06 1.00 2.00 0.99 1.99 0.97 2.16

0.035

iterlal ber

1

In^

Iber

2

In^

board

1

In

board

2

in

ird

1

in

ird

2

in

"ene

1

in

-ene

2

in

bene

1

in

bene

2

in

Felt,

ASTM

5 '

ASTM

[II

Glass

fJ

Glass

fi

Perllte Perlite

Fiberb02

Fiberboj Polystyi Polystyi

Polyuret Polyuret

Roofing

Type

]

Asphalt^ Type

:

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t-l CO •u 4-1 3 no

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0) •4-1 4-1 u i-C a; o 3 01 (0 at O > u •z Oi ^ X, <

fl3 £> to

27
Table 2. Thickness, Density and "Room Dry" Thermal Conductance Results^ for Individual BUR System Specimens

Spec

No.

Insulation

Type and Nominal Thickness (in)

Total Specimen Thickness

(in)

Insulation

Thickness

(In)

Membrane Thickness

(in)

Membrane Weight Per Unit Area

(Ib/ft^)

Thermal Conductance Cp

No. of Tests

Average Cp (Btu/h.ft2.°F)

3 Glass fiber 1 1

15<= 0 75'! 0 40^ 2 05^ 2 0 .266

53 Glass fiber 1 1 25 0 87 0 38^ 1 94^ X 0 . 250

7 Glass fiber 2 2 59 2 17 0 42^ 2 17^ 2 0.110

Glass fiber 2 2 60 2 20 0 40^ 2 05^ 2 0.110

13 Perllte board 1 1 37'= 1 02'' 0 35 1 90 - 0.341^

63 Per lite board 1 1 43 1 08 0 35 1 75 2 0.335

17 Perllte board 2 2 39C 2

06'' 0 33 1 63 1 0.177

67 Perllte board 2 2

35^^ 2

06'' 0 29 1 41 2 0.181

22 Flberboard 1 1 32'= 1 OO"* 0 32 1 57 2 0.340

28 Flberboard 2 2 38<= 2

00'' 0 38 1 98 2 0.176

33 Polystyrene 1 1 12 0 78 0 34 1 76 1 0.273

751'' Po lystyrene 1 ^ 1 fx Q 7 8 Q 38 ]^ 76 1 0.276

82*' Polystyrene 1 1 24 0 88 0 36 1 75 4 0.250

37 Polystyrene 2 2 38 2 02 0 36 1 83 0.131^

Po lys t yr ene 2 2 .29 1 89 0 40 2 06 1 0.132

87*' Polystyrene 2 2 .30 1 95 0 35 1 84 2 0.130

42 Polyurethane 1 1 .41 1 .09 0 32 1 65 2 0.157

48 Polyurethane 2 2 .31 2 .00 0 31 1 55 0.0795*

98'' Polyurethane 2 2 .25 1 .89 0 36 1 94 1 0.0726

Ml*^ Membrane 0 35 1 78 4 1.248

"2'^ Membrane 0 .40 2 15 2 1.40

^ Unless noted otherwise, specimens were used for "room dry" and subsequent "wet" thermal conductance tests.

^ Thermal conductance tests performed for "room dry" conditions only; note that for specimen no. 82, no moisture

was Induced; specimen no. 98 was soaked in water for 5 months rather than exposed to water vapor prior to thickness measurements.

*= Based on sum of Insulation thickness (estimated from table 1) and the membrane thickness.

'' Based on table 1

.

^ Includes an asphaltlc facing sheet. Estimates of the average density (d), thickness (t), and coefficients of variation (shown in parentheses) for 7 facing specimens are:

Asphaltlc facing on 1 inch glass fiber insulation: d" =43 Ib/ft^ (11%); t = 0.14 inch (9.9%)

Asphaltlc facing on 2 inch glass fiber insulation: d = 40 Ib/ft^ (3.1%); T = 0.13 inch (9.7%)

* Value based on table 3; "room dry" thermal conductance test not performed on this specimen.

8 Coefficient of variation was 1.7%.

^ Membrane only, tested at "room dry" conditions.

28
Table 3. Summary of Thermal Conductance Results for "Room Dry" Conditions

System

Insulation

Type and Nominal

Thickness (in)

No. of SpecimensTotal No.

of C[j Tests

Average Thermal

Conductance On (Btu/h'ft^-'F) C0V^(7.)

h Insulation Glass fiber'' 1 2 4 0.266 0.673

BUR'^ Glass fiber'' 1 3 5 0.256 3.39

Insulation Glass fiber 2 1 2 0.115

BUR Glass fiber 2 3 6 0.111 1.17

Insulation Perlite board 1 2 3 0.375

BUR Perlite board 1 3 8 0.341 1.64

Insulation Perliee board 2 1 2 0.184

BUR Perlite board 2 k 8 0.176 1.52

Insulation Fiberboard 1 1 2 0.364

BUR Fiberboard 1 3 7 0.330 3.94

Insulation Fiberboard 2 1 2 0.199

BUR Fiberboard 2 3 5 0.173 1.30

Insulation Polystyrene 1 1 2 0 . 266

BUR Polystyrene 1 3 6 0.258 4.96

Insulation Polystyrene 2 1 2 0.137

BUR Polystyrene 2 2 3 0.131

Insulation Polyurethane 1 1 2 0.166

BUR Polyurethane 1 2 7 0.168 4.41

Insulation Polyurethane 2 2 4 0.0741 7.72

BUR Polyurethane 2 2 5 0.0795 5.37

Coefficient of Variation.

Insulation (without built-up roofing membrane).

BUR system specimen (insulation with built-up roofing membrane).

Facing on glass fiber insulation in contact with cold plate of heat-flow meter apparatus.

29
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31
ASPHALT

FLOOD COAT

FOUR FELTS AND

INTERPLY ASPHALT

INSULATION

Figure 1 . BUR System Specimen Composition

COLD DRY (TOP) SIDE

SCF ; 25% RELATIVE HUMIDITY

4 PLY ROOFING

MEMBRANE

INSULATION

WOODEN FRAME

TO HOLD SPECIMEN

SPECIMEN EDGES REST

ON WOODEN LEDGE

100°F ; 100% RELATIVE HUMIDITY USED WHEN NEEDED TO SUPPORT

1 INCH THICK SPECIMENS

Figure 2. BUR System Specimen, Wooden Supporting Frame and the

Environmental Conditions Used to Induce Moisture

32
EXTRUDED POLYSTYRENE FACING

Detail View

50°F ; 25% RH OUTSIDE

16 FTOverall View

Figure 3. Insulated Wooden Chambers Used to Induce Moisture

in the BUR System Specimens

33

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J
NBS-114A (REV. 8-78)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. BSS 123

2. Gov't. Accession No,

4. TITLE AND SUBTITLE

The Effect of Moisture on the Thermal Conductance of

Roofing Systems

3. Recipient's Accession No.

5. Publication Date April 1980

6. Performing Organization Code

7. AUTHOR(S)

Lawrence I. Knab, David R. Jenkins, and Robert G. Mathey

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

10. Project /Task /Work Unit No.

IX. Contract/Grant No.

12. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS rsfreer, city, srafe, ziP)

Department of Energy

Office of Building and Community Systems

20 Mass. Avenue, N.W.

Washington, DC 20585

13. Type of Report <!< Period Covered Final

14, Sponsoring Agency Code

15. SUPPLEMENTARY NOTES Library of Congress Catalog Card Number: 80-600031

Also published in the proceedings of the DoE/ASHRAE Conference on the Thermal

Performance of the Exterior EnveloDes of Buildings,

I

I Document describes a computer program; SF-185, FIPS Software Summary, irattached.

16. ABSTRACT (A 200-word or less factual summary ot most significant information. If document includes a signi ficant bibliography or

literature survey, mention it here,) The results of laboratory tests are presented describing the effect of the moisture

content on the thermal conductance of roofing systems containing insulation. Roofing

systems, consisting of five types of rigid-board roof insulations with attached fourply bituminous built-up membrane, were tested. Moisture was induced into the roofing

system specimens by maintaining a constant water vapor pressure difference across them.

Moisture gain in the insulation varied depending on the type and thickness of the

insulation.

A procedure was developed, using a heat-flow meter apparatus (ASTM C 518 type), to carry

out thermal conductance tests on roofing specimens containing moisture. More than 200

tests were performed over a wide range of moisture contents. The approximate moisture

distribution in the insulation was determined from core samples.

Relationships between the thermal conductance and moisture content are presented. The

relationships show that the presence of moisture in roofing systems can cause significant increases in the thermal conductance, depending on the type and thickness of

the insulation.

17. KEY WORDS (six to twelve entries: alphabetical order; capitalize only the first letter of the first key word unless a proper nameseparated by semicolons)

Built-up roofing, insulation, moisture, roofing, thermal conductance, thermal

conductivity, thermal resistance.

18. AVAILABILITY [^Unlimited

i I For Official Distribution. Do Not Release to NTIS

[xJ Order From Sup. of Doc, U.S. Government Printing Office, Washington, DC

20402, Insert Stock Number And Sales Price.

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NBS TECHNICAL PUBLICATIONS

PERIODICALS

JOURNAL OF RESEARCH—The Journal of Research of the National Bureau of Standards reports NBS research and develop- ment in those disciplines of the physical and engineering sciences in which the Bureau is active. These include physics, chemistry,

engineering, mathematics, and computer sciences. Papers cover a broad range of subjects, with major emphasis on measurement

methodology and the basic technology underlying standardization. Also included from time to time are survey articles on topics

closely related to the Bureau's technical and scientific programs. As a special service to subscribers each issue contains complete

citations to all recent Bureau publications in both NBS and non- NBS media. Issued six times a year. Annual subscription: domestic

$17; foreign $21.25. Single copy, $3 domestic; $3.75 foreign. NOTE: The Journal was formerly published in two sections: Section A "Physics and Chemistry" and Section B "Mathematical

Sciences." DIMENSIONS/NBS—This monthly magazine is published to in- form scientists, engineers, business and industry leaders, teachers,

students, and consumers of the latest advances in science and

technology, with primary emphasis on work at NBS. The magazine

highlights and reviews such issues as energy research, fire protection, building technology, metric conversion, pollution abatement,

health and safety, and consumer product performance. In addition, it reports the results of Bureau programs in measurement

standards and techniques, properties of matter and materials, engineering standards and services, instrumentation, and

automatic data processing. Annual subscription: domestic $11;

foreign $13.75. NONPERIODICALS

Monographs—Major contributions to the technical literature on

various subjects related to the Bureau's scientific and technical activities. Handbooks—Recommended codes of engineering and industrial practice (including safety codes) developed in cooperation with in- terested industries, professional organizations, and regulatory

bodies. Special Publications—Include proceedings of conferences sponsored by NBS, NBS annual reports, and other special publications

appropriate to this grouping such as wail charts, pocket cards, and

bibliographies. Applied Mathematics Series—Mathematical tables, manuals, and

studies of special interest to physicists, engineers, chemists,

biologists, mathematicians, computer programmers, and others engaged in scientific and technical work.

National Standard Reference Data Series—Provides quantitative data on the physical and chemical properties of materials, compiled from the world's literature and critically evaluated. Developed under a worldwide program coordinated by NBS under

the authority of the National Standard Data Act (Public Law

90-396).

NOTE: The principal publication outlet for the foregoing data is the Journal of Physical and Chemical Reference Data (JPCRD)

published quarterly for NBS by the American Chemical Society

(ACS) and the American Institute of Physics (AIP). Subscriptions,

reprints, and supplements available from ACS, 1 155 Sixteenth St., NW, Washington, DC 20056.

Building Science Series—Disseminates technical information developed at the Bureau on building materials, components,

systems, and whole structures. The series presents research results,

test methods, and performance criteria related to the structural and

environmental functions and the durability and safety characteristics of building elements and systems.

Technical Notes—Studies or reports which are complete in themselves but restrictive in their treatment of a subject. Analogous to monographs but not so comprehensive in scope or definitive in treatment of the subject area. Often serve as a vehicle for final reports of work performed at NBS under the sponsorship of other government agencies.

Voluntary Product Standards—Developed under procedures

published by the Department of Commerce in Part 10, Title 15, of

the Code of Federal Regulations. The standards establish nationally recognized requirements for products, and provide all concerned interests with a basis for common understanding of the

characteristics of the products. NBS administers this program as a supplement to the activities of the private sector standardizing

organizations. Consumer Information Series—Practical information, based on NBS research and experience, covering areas of interest to the con- sumer. Easily understandable language and illustrations provide

useful background knowledge for shopping in today's tech- nological marketplace. Order the above NBS publications from: Superintendent of Documents. Government Printing Office. Washington, DC 20402. Order the following NBS publications—FIPS and NBSlR's—from

the National Technical Information Services, Springfield. VA 22161

.

Federal Information Processing Standards Publications (FIPS

PUB)—Publications in this series collectively constitute the Federal Information Processing Standards Register. The Register

serves as the official source of information in the Federal Govern- ment regarding standards issued oy NBS pursuant to the Federal Property and Administrative Services Act of 1949 as amended,

Public Law 89-306 (79 Stat. 1127), and as implemented by Executive Order 11717(38 FR 12315, dated May 11. 1973) and Part 6 of Title 15 CFR (Code of Federal Regulations).

NBS Interagency Reports (NBSIR)—A special series of interim or

final reports on work performed by NBS for outside sponsors

(both government and non-government). In general, initial dis- tribution is handled by the sponsor; public distribution is by the National Technical Information Services, Springfield, VA 22161,

in paper copy or microfiche form.

BIBLIOGRAPHIC SUBSCRIPTION SERVICES

The following current-awareness and literature-survey bibliographies are issued periodically by the Bureau:

Cryogenic Data Center Current Awareness Service. A literature sur- vey issued biweekly. Annual subscription: domestic $25; foreign

$30. Liquefied Natural Gas. A literature survey issued quarterly. Annual

subscription: $20.

Superconducting Devices and Materials. A literature survey issued

quarterly. Annual subscription: $30. Please send subscription or- ders and remittances for the preceding bibliographic services to the National Bureau of Standards, Cryogenic Data Center (736) Boulder, CO 80303.
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