AlllDO TTEbflT

NAT'L NST OF STANDARDS & TECH R.I.C.

A1 11 00992689

/NBS building science series

i TA435 .U58^55;1974 C.I NBS-PUB-C 1974 NBS BUILDING SCIENCE SERIES 55

U.S. DEPARTMENT OF COMMERCE / National Bureau of Standards

Preliminary Performance

Criteria for Bituminous

IMembrane Roofing
The Building Science Series

The Building Scienoc Series disseminates technical information developed at the National Bureau of Standards 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. These publications, similar in style and content to the NBS Building Materials and Structures Reports (1938-59),

are directed tovi-ard the manufacturing, design, construction, and research segments of the building industry, standards organizations, and officials responsible for building codes. The material for this Series originates principally in the Center for Building Technology of the NBS Institute

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please contact the Scientific and Professional Liaison Section, Center for Building Technology, Institute for Applied Technology, National Bureau of Standards, Washington, D.C. 20234.

mailing list announcement on last l)agej
or BTANDABDH

L'RKART

APR 2 0 1976

7"/=> ^35"

/7o, 5 5

Preliminary Performance Criteria

for Bituminous Membrane Roofing

... C,

Robert G, Mathey and

William C. CuUen

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

U.S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretory

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts, Direcfor

Issued November 1974
Library of Congress Catalog Card Number: 74-600167

National Bureau of Standards Building Science Series 55

Nat. Bur. Stand. (U.S.), Bldg. Sci. Sen 55, 19 pages (Nov. 1974)

CODEN: BSSNBV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1974

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (Order by SD Catalog No. C13.29/2:55). Price 65 cents.
Contents

I'axe SI Conversion Units 1

1. Introduction 1 2. Bituminous membrane roofing in the United States 2

3. Performance approach 2

4. Performance attributes 3

5. Laboratory research program 4

5.1. Results of laboratory test 5

5.1.1. Tensile strength 5

5.1.2. Thermal expansion 6

5.1.3. Flexural strength 7

5.1.4. Tensile fatigue strength 7

5.1.5. Flexural fatigue strength 7

5.1.6. Shear strength (punching) 8

5.1.7. Impact resistance 9

5.2. Planned performance tests 9

6. Recommended performance criteria 9

6.1. Performance format 10

6.1.1. Tensile strength 10

6.1.2. Thermal expansion 10

6.1.3. Thermal movement 10

6.1.4. Flexural strength 10

6.1.5. Tensile fatigue strength 10

6.1.6. Flexural fatigue strength 10

6.1.7. Punching shear strength 10

6.1.8. Impact resistance 11

6.1.9. Wind resistance 11

6.1.10. Fire resistance 11

7. Summary and conclusions 11

8. References 12

III

Preliminary Performance Criteria for Bituminous Membrane Roofmg

Robert G. Mathey and William C. Cullen

This report is the first in a series of publications on performance criteria for built-up roof membranes. The development of a performance approach to bituminous built-up roof membranes is de- scribed and preliminary performance criteria are recommended. A number of test methods have been

developed iri order to obtain data to evaluate roofing membranes against the recommended criteria. Twenty attributes that effect the performance of roof membranes under service conditions are

identified and laboratory tests are described for measuring the engineering properties of the membrane

that pertain to many of these attributes. A level of performance is recommended for nine of the identified performance attributes.

Key words: Bituminous roof membranes; performance attributes; performance criteria; physical and

engineering properties; test methods.

SI Conversion Units

In view of present accepted practice in the United

States of America in the roofing technology area, common U.S. units of measurement have been

used throughout this paper. In recognition of the

position of the USA as a signatory to the General

Conference of Weights and Measures, which gave

official status to the International System of Units

(SI) in 1960, we assist the readers interested in making use of the coherent system of SI units by

giving conversion factors applicable to U.S. units

used in this paper. Length

1 in = 0.0254* meter

1 ft = 0.3048* meter

Area

1 in2 = 6.4516* X 10 meter^

1 ft2 = 0.09290 meter

2

Force

1 lb (lbf) = 4.448 newton

Stress

1 psi = 6895 newton/meterFrequency

1 cycle per second 1* hertz

* Exactly

1. Introduction

The maiority of low-slope roof constructions in the United States consist of bituminous built-up

roof systems. This term is used to describe roofs in which the waterproofing membrane is installed in layers of reinforcing felts which are adhered to- gether with a bituminous material. The membrane

is generally installed over insulation and is sometimes applied directly to the roof deck.

In the United States, the desired properties and

characteristics of bituminous membrane built-up

roofs have been traditionally described by prescriptive types of specifications for the individual materials which comprise the roofing membrane. The per- formance of the bituminous membrane itself has

been considered only from a practical viewpoint,

that is, observation of its durability under in- service conditions. The specification of materials

imposes constraints on the design of roofing systems,

manufacture of roofing products and the apphcation

of roofing materials. Poor performance of roofs has often been attributed to these constraints on the

design, manufacture and application process. Prescriptive specifications inhibit new product development and the introduction of innovative systems

for membrane roofing. The intent of this investi- gation has been the development of a performance

approach to the evaluation of bituminous membrane

roofing which is believed to be needed to overcome

the traditional road blocks that prescriptive specifications of roofing materials present.

This research at the National Bureau of Standards was carried out to identify and describe quantitatively the attributes which would be required of

bituminous membrane roofing to assure their

adequate performance in the varied climates of

the United States. This paper presents the results of that research and preliminary performance cri- teria for bituminous membrane roofing.

1
2. Bituminous Membrane Roofing in

the United States

Since the turn of the twentieth century, bituminous

buih-up roofing membranes have been used in the

United States to protect buildings, their contents and

occupants from the weather. In general, these

membranes have provided satisfactory service, but

in many instances, they have been the source of

problems for the manufacturer, designer, applier

and the user. The problems have been attributed,

in part, to such obvious causes as poor design, in- adequate specifications and improper workmanship.

Certainly these factors can be controlled to some

extent by education which would insure the use of

proper specifications and by construction inspection

which will insure good workmanship. Information

concerning adequate specifications and proper construction practices is available at the current state- of-the-art of bituminous roofing technology in the

United States. However, for various and sundry

reasons this information is sometimes ignored and

often not known by those who design, apply and use

roof systems.

The most common type of bituminous membranes

consist of two to five plies or layers of felt or fabric

which is saturated or impregnated and sometimes

coated with a bituminous material during manufacture. The felts may be composed of felted organic

materials, asbestos fibers or fibrous glass. The

bituminous material used as saturant and coating

may be either a petroleum asphalt or coal tar

pitch. In practice, the felts are adhered together

with petroleum asphalt or coal tar pitch during

application on the roof. Frequently, the membrane

is surfaced with gravel or slag which is embedded in hot bitumen.

The felts and bitumen which comprise the bi- tuminous built-up membrane are described by

prescriptive specifications issued by manufacturers,

the Federal Government or recognized standardmaking bodies such as the American Society for Testing and Materials. Roofing felts must satisfy

certain physical requirements such as the nature of

the felt including its weight, percent saturation,

flexibility and tensile strength. Roofing bitumens

(asphalt and coal tar pitch) are frequently described

by empirical characteristics such as softening point,

penetration and ductility.

The application specification defines the kind and

number of plies or layers of felt as well as the type

and amount of bitumen to be used between the plies.

This is the bituminous built-up membrane specifica- tion currently used in the United States. In spite of over 70 years use, nowhere are the required properties of a membrane identified or specified quantitatively. In fact, criteria for the built-up membrane

do not exist even though there are about 30 million

squares ' of bituminous built-up roofing applied

each year in the United States alone. The conse- quences of the unavailability of criteria are considerable and expensive as evidenced by the premature

failures of many new types of roof membranes which

should not have been marketed. Further, the lack

of criteria probably represents the largest single

constraint to the introduction of new and innovative

systems into the roofing industry. The consequences

become manifest when modifications of conventional

systems or new membrane systems are introduced.

Invariably, unforeseen problems arise causing failure of the membrane necessitating its replacement. The

problems could be substantially reduced and per- haps eliminated if criteria for acceptable bituminous

membranes were developed and made available to guide the developer or innovator. The development

of adequate criteria for membrane roofing will represent a great step forward in elevating the art of roofing to a scientific basis. The research reported in this paper was restricted

to the development of criteria and test methods for bituminous built-up membrane roofing. Since the

roof membrane is used in conjunction with one or more components of the total roof assembly (such

as the structural deck, vapor barrier and insulation)

the contribution of the various components, acting

alone or in concert with others, to the performance

of the roof membrane, must be dealt with. Therefore,

the forces attributed to these interactions and those

generated by the ambient environment have been

taken into consideration when levels were defined

for criteria for the bituminous built-up membrane.

For a comprehensive discussion of the built-up

roofing system, including the four interacting components, the reader is referred to a treatise on the

subject prepared by Griffin [1].

^

' One square equals one hundred square feet.

^ Figures in bracltets refer to literature references given in section 8.

3. Performance Approach

The major research goal is the development of

performance criteria which contains quantitative

definitions of a roof membrane's overall ability to perform under service conditions. In order to establish valid and acceptable criteria, the past perform- ance of roof membranes which have served satis- factorily must be used as a point of reference or

basis for developing the criteria. An important intent of the performance approach is to provide a basis for evaluating roofing membranes with reasonable assurance that the membrane wiU perform

satisfactorily over its intended use as well as, the

ambient exposure climate of the roofing membrane.

In depth consideration of weather conditions was

not considered in the development of the pre- liminary performance criteria. The value of any

2
criterion may be set according to climate, roof

design and expected life of the building.

The performance statements presented in this report consist of a requirement which is qualitative in nature and describes what the membrane is to accomplish. This is followed by a criterion or

criteria which expresses quantitatively, the ac- ceptable levels for adequate performance. An

evaluative technique or test method is then refer- enced or described by which compliance with the

stated criteria can be tested. Finally, a commentary

is helpful in providing an explanation of the reason

for, and the intent of, the staled criteria. The successful implementation of the perform- ance approach to the design, manufacture, and

installation of bituminous membrane roofing will represent a significant achievement in the application of bituminous roofing technology. In addition to providing guidance for the development of better

and more economical bituminous membranes, the

performance approach will pave the way for both new products and innovative systems which are

so badly needed by the roofing industry.

4. Performance Attributes

Observations made during field surveys of bitumi- nous built-up roofing throughout the fifty states in the U.S.A. and territories of Puerto Rico and Guam

over many years have led to the identification of

certain problems associated with the behavior of bituminous built-up membrane roofing systems. The

severity of the problems ranged from minor, such as small adhesion problems, to catastrophic such as severe membrane splitting and costly membrane

slippage. Blistering, wrinkling, and wrinkle cracking

of the membrane were among the more common

defects observed. Although frequently these defects were not evidenced by the immediate failure of the waterproofing systems, they resulted in shortening the expected life of 20 or more years of a built-up roof by a significant amount. Thermal

splitting or cracking of the membrane, slippage

between plies of the felt and wind blow-offs occurred

less frequently, but generally resulted in costly

and immediate repairs or sometimes in the removal

and replacement of the complete roof system. In the course of the field surveys, good performing

membranes were compared to those that deteriorated more rapidly than expected and the reasons

for the performance were explored. Samples of roof

membranes were brought into the laboratory, where

they were examined and their properties were measured and related to field behavior.

As a result of these long-term observations, some

twenty attributes have been identified which are believed to have significant impact on the total performance of the roofing system under in-service

conditions. It is important to note here that a maximum value of the level of performance for any one

attribute is not necessary to quantify performance

adequately. Rather, a balance of values among the

several attributes is more desirable, so long as they

remain within levels of acceptable performance.

The following attributes which were identified

for laboratory study:

1. Tensile Strength — The membrane is not ex- pected to perform as a structural member, but it must have sufficient strength to resist stresses caused by internal and external forces imposed on

it during use.

2. Thermal Expansion — Roofing membranes are exposed to rather large and often rapid temperature changes. The thermal expansion coefficient should not be so large as to cause deleterious

effects on the membrane under service conditions.

3. Flexural Strength — As stated in the case of

tensile strength, the membrane is not expected to perform as a structural member. However, it must

have sufficient flexural strength to resist forces such

as those caused by wind, moving wheel loads, foot

traffic, thermal and moisture movement and other

forces causing bending of the membrane, particularly during cold weather.

4. Tensile Fatigue Strength — Repeated stresses caused by thermal, moisture and building move- ment should be resisted by the membrane. The

strength of the membrane should not be significantly reduced by the application of repeated forces.

5. Flexure Fatigue Strength — Repeated stresses caused by wind uplift forces, vibrations, wheel loads,

foot traffic and the like should be resisted by the

membrane. The strength of the membrane should

not be significantly reduced when subjected to re- peated forces causing bending of the membrane.

6. Shear Strength — The membrane should withstand vertical punching shear forces from antici- pated foot traffic and the other effects. Horizontal

shear forces caused by different stress levels in the

felts should not affect the integrity of the membrane.

7. Impact Resistance — Falling objects such as

hailstones, tree limbs, tools, and the like, should be

resisted by the membrane without causing penetrations or breaks in it. 8. Notch Tensile Strength — The tensile strength

of the membrane should not be significantly reduced

by stress concentration caused by imperfections or

slightly damaged areas in the felts. At low temperatures, bituminous membranes have properties of

brittle materials.

9. Moisture Effects on Strength — Moisture in the

membrane resulting from the use of wet materials

or the penetration by water or water vapor into the

membrane can result in excessively high stresses

in the membrane. These stresses caused by wetting

and drying combined with thermal and other stresses must not exceed the strength of the membrane.

Furthermore, appreciable loss in strength of the

membrane may be attributed in some cases to the

presence of moisture in the roofing system.

3
10. Creep — Membranes are often subjected to stress over long periods of time as a result of internal

forces caused by thermal, moisture and building

movement along with externally applied forces. The membrane should be able to withstand sustained

stress without significant permanent deformation.

11. Ply Adhesion — Composite action of the membrane depends on sufficient adhesion of felts to each

other by means of the between-ply bitumen. Blister

formation can be reduced by eliminating voids

bewteen plies where moisture can accumulate.

12. Abrasion Resistance — The membrane should

withstand anticipated wearing away from windblown elements, traffic and other objects dragged

across the roof.

13. Tear Resistance — The membrane should

resist tearing or ripping when subjected to antici- pated external and internal forces.

14. Pliability— For anticipated climatic conditions, the membrane should withstand, without

rupture, repeated bending caused by forces imposed

during service. Forces resulting from vibration,

wind uplift, thermal, moisture and building move- ment can cause bending of the membrane. Pliability differs from flexural strength and flexural fatigue strength in that the flexibility of the membrane is of concern and not its strength or load

carrying capacity. In general, the pliability of the

membrane at the lowest anticipated temperature

should be considered.

15. Permeability— The penetration of water or water vapor from either outside or inside should be

prevented. Penetration of water vapor can result

in condensation, decrease in insulation efficiency

and other adverse effects, such as differential movement, deflection and rot of other system components.

16. Moisture Expansion — Not only can moisture cause a significant decrease in membrane strength

and induce high stress in the membrane, but it can also cause an increase in length of the membrane. This length increase is generally not reversi- ble and ridging results.

17. Weather Resistance — The membrane should

withstand anticipated climatic conditions, such as

solar radiation, moisture, pollutants, and the like without adverse effects on the performance of the

roof system when exposed for its expected service

life.

18. Wind Uplift Resistance — The membrane

should withstand anticipated wind forces without

adverse effects.

19. Fire Resistance — The membrane should pro- vide a specified resistance against combustibility

and flame spread.

20. Fungus Attack Resistance — Any appreciable

reduction in performance or appearance resulting

from decay should be prevented during the expected

service life of the membrane.

5. Laboratory Research Program

The twenty performance attributes identified

above were included in the plans of an experimental

program which was aimed at developing test methods, measurement techniques and meaningful

limits of acceptability of built-up roof membranes.

A literature survey was conducted to determine the

state-of-the-art of bituminous roofing technology

and most importantly, to identify current tests for measuring performance of built-up roof membranes.

The survey indicated that many new tests needed

to be developed to measure the performance of

built-up roofing, however, for some of the attributes,

such as wind uplift resistance and fire resistance,

available tests were considered adequate at this time. It is noted that a committee sponsored by the

Building Research Advisory Board of the U.S. National Academy of Science, which was chaired

by Wilham C. CuUen, developed a fist of perform- ance characteristics similar to those developed in

this investigation [2]. In the overall planning of the research program,

emphasis was placed on smaU and large scale tests as well as on field studies. The small scale tests, however, comprised the major portion of the research

program. The large scale tests were intended to supplement the small scale tests and to provide

data on stresses and deformations that occur or develop during service conditions due to thermal

and moisture changes. The large scale tests have

not been conducted, however, future plans call for carrying out these tests. Field studies have been

limited to the inspection of roof problems and recom- mendations or suggestions for their solution. The

recommendations were based, in part, on laboratory

tests of the field samples of roofing and the data were included in some of the small scale tests. Most

data from the small scale tests, however, were

derived from laboratory prepared samples.

Table 1. Materials used in preparation oftest specimens

Membrane ASTM

designation Materials designation

Bitumens:

Asphalt D312.TypeI

Coal-tar pitch D450,TypeA

Reinforcing felt: A Coal-tar saturated organic D227

felt B Asphalt saturated organic D226, 15 lb type

felt C Asphalt saturated asbestos D250, 15 lb type feh D Asphalt impregnated glass D2178,TypeI

mat E« Asphalt impregnated glass New product mat

^This type of asphalt impregnated glass mat was recently developed and therefore was not included in all the laboratory tests.

4
The small scale tests were carried out primarily on four types of 4-ply membrane, however, other

types of membranes were also included in the test program. The materials used in the preparation of

the membrane test specimens which were included

in all the various tests are identified in table 1. AH of the various laboratory tests were carried out using 4-ply membranes designated as A, B, C, and

D and some of the tests included membrane E. Limited tests were conducted using other types of

membranes including both laboratory prepared and

field specimens. Data are reported on the five types of membrane given in table 1. When applicable, the test specimens conformed

to standard size specimens such as those described

in ASTM D-2523 [3]. Prior to fabrication of the small

scale specimens, the moisture content of the felt was determined and properties of the bitumens

ascertained. The thickness of the between-ply

bitumen was controlled and measured for each

specimen.

5.1. Results of Laboratory Tests

Laboratory tests were conducted to measure the

performance of roofing with regard to the first seven attributes listed in section 4. The attributes are essentially mechanical properties of the memTABLE 2. Tensile strength of membranes

Type of membrane

Membrane

designation Tensile strength, lb/in

73 30 T 0°F -30 °F

'pb L T L T L T

Organic felt and coal tar A 126 62 395 217 468 265 410 237

Organic felt and asphalt B 141 60 396 186 506 267 592 283

Asbestos felt and asphalt C 120 36 301 123 448 182 479 165

Glass felt (Type I) and asphalt D 86 70 190 161 175 144 184 123

Glass felt (new product) and asphalt E 202 . 159 510 408 448 365 372 301

^ L denotes longitudinal or machine direction of felts. T denotes transverse or cross machine direction of felts.

TABLE 3. Load-strain modulus of membranes

Type of membrane

Membrane

designation

Load-strain modulus X 10'» lb/in

73 30 T 0°F -30 T

L^ L T L T L T

Organic felt and coal tar A 2.1 0.6 7.9 9.9 6.7 7.4 10.6 7.7

Organic felt and asphalt B 2.7 1.1 4.1 1.6 5.7 3.6 9.1 6.8

Asbestos felt and asphalt C 3.3 1.2 4.4 2.3 8.0 5.5 9.8 8.4

Glass felt (Type I) and asphalt D 1.3 1.2 1.4 1.3 3.0 2.6 1.5 1.0

Glass felt (new product) and asphalt E 2.5 2.2

1 2.7 2.2 2.8 2.2 2.6 2.4

" L denotes longitudinal or machine direction of felts. T denotes transverse or cross machine direction of felts.

brane which include tensile strength, thermal ex- pansion, flexural strength, shear strength, fatigue

strength, and impact resistance. Preliminary per- formance criteria, including the seven attributes

listed above and wind uplift resistance and fire resistance are presented in section 6. A brief description follows for each of the completed laboratory tests along with some typical data.

5.1.1. Tensile Strength

Tension tests were conducted on 4-ply specimens

by the procedure described in ASTM Standard

D-2523 modified to meet the needs of the research.

Specimens were elongated at a rate of 0.08 in/min. Tests were carried out at 73, 30, 0, and — 30 °F in both the machine direction and cross-machine

direction of the felts. An extensometer with a 2-in gage length was attached to the specimen at midlength and load strain data were continuously

recorded until failure occurred. The tensile strength

and load strain modulus were considered in the pre- liminary performance criteria in section 6. The

tensile strength and load strain modulus of the membranes are given in tables 2 and 3, respectively for the five different types of membranes. The values in the tables represent the average of 3 tests.

5
5.1.2. Thermal Expansion

Four tests were investigated to measure thermal

contraction or expansion of roof membrane samples.

These tests included using a continuous recording

extensometer; using quartz rods to support test specimens and make length change determinations; use of thermal mechanical analyzer; and by means

of mechanical measurements using a Whittemore

extensometer. A Whittemore extensometer is described in ASTM Standard C426 [4]. The Whitte- more extensometer gave unquestionably the best

results. It is relatively simple to use, gage points can be set rather easily, it gives accurate reproducible results and a fairly large number of specimens

can be tested at one time. The data were also reproducible for field specimens and results of

tests of comparable field and laboratory prepared

specimens gave favorable agreement.

The lengths of test specimens as described in ASTM Standard D-2523 over a 5-in gage length were measured at 73, 30, 0, and —30 °F. The coeffi- cients of thermal expansion for three temperature

ranges for the membranes are shown in figure 1. The

average values presented in figure 1 are listed in table 4. The test method for measurement of thermal

expansion developed at the National Bureau of

Standards has been accepted as a proposal by

ASTM and is published as proposed test for "Coefficient of Linear Thermal Expansion of Roofing and Waterproofing Membranes" in the 1974

Book of ASTM Standards, Part 15 [5]. Values of the coefficient of expansion, tensile strength and load strain modulus can be used to calculate the thermal shock factor. Cullen and

Boone [6] reported on thermal-shock resistance for built-up membranes in 1967. Based on modification

and extension of their earlier work, it is proposed

that the thermal shock factor can be calculated as follows

:

TSFP

Ma

20xl0"6

10

O

u.

li. UJo

10

20

30

40

50

73 toSCF

Orientation Membrone T L O

A A 0 0

SOtoOop Oto-30''F

o°0

^ O A A

•••

A

I 70 50 30 10 -10 TEMPERATURE RANGE, "F

-30

Figure 1. Coefficients of thermal expansion for membranes for

three temperature ranges.

where,

TSF is the thermal shock factor

P is the tensile strength at 0 °F

M is the load strain modulus at 0°F

a is the coefficient of expansion for the temperature range 0 to —30 °F. Values of the thermal shock factor for five types

of membranes are given in table 5. The thermal

shock factor was computed using values of tensile strength, load strain modulus and coefficient of

thermal expansion from table 2, 3, and 4,

respectively.

Table 4. Coefficients of thermal expansion for roof membranes

Type of membrane Membrane

designation

Coefficient of thermal expansion °F ' temperature range ^

73 to 30 °F 30 to 0 T 0 to --30 T

L" L T L T

Organic felt and coal tar A -3.3 4.4 22.3 36.0 19.3 29.5

Organic felt and asphalt B -3.4 -6.6 2.7 12.6 13.9 37.4

Asbestos felt and asphalt C 2.3 9.2 4.8 18.1 19.5 37.5

Glass felt (Type I) and asphalt D -7.1 -5.3 8.9 10.1 35.1 46.4

Glass felt (new product) and asphalt E -7.3 3.9 -4.2 10.7 29.0 39.0

"Values in table to be multiplied by 10-".

''L denotes longitudinal or machine direction of felts. "^T denotes transverse or cross machine direction of felts.

6
5.1.3. Flexural Strength

Flexural tests were carried out on five types of

four-ply membrane samples at 73 and 0°F. The test specimens were of the type described in ASTM

Standard D-2523. Built-up roofing membranes

have essentially no stiffness, especially at room

temperature. It was therefore necessary to have the

ends of the specimen fixed for the flexural tests. A

support frame was designed and fabricated which

allowed the ends of the specimen to rotate at the

supports. The load was applied by means of IV2- in diam half round steel bar at the midspan of the

specimen. Flexural strength and maximum deflection of the membrane specimens are given in table 6 and table 7, respectively. These data repre- sent the average value of three specimens tested for each type of membrane at each temperature.

Table 5. Thermal shock factors for roof membranes Type of membrane Membrane

designation

Thermal shock factor, °F

L"

Organic felt and coal

tar A 360 120

Organic felt and

asphalt B 640 200

Asbestos felt and

asphalt

C 290 90

Glass felt (Type I) and asphalt

D 170 120

Glass felt (new

product) and asphalt E 550 420

°L denotes longitudinal or machine direction of felts. *T denotes transverse or cross machine direction of felts.

Table 6. Flexural strength of membrane specimen

Type of membrane Membrane

designation

Maximum load at midspan, lb

73 °F 0 °F

L T L T

Organic felt and

coal tar A 73 44 141 39

Organic felt and

asphalt B 48 33 143 43

Asbestos felt and

asphalt

C 45 17 97 17

Glass felt (Type I) and asphaltD 39 23 26 24

Glass felt (new

product) and asphalt E 164 126 159 132

Table 7. Maximum deflection of membrane specimens

Type of membrane Membrane

designation

Maximum deflection at midspan, in

73 T OT

L T L T

Organic felt and coal

tar A 1.3 1.7 0.7 0.6

Organic felt and

asphalt B 1.2 1.0 0.8 0.6

Asbestos felt and

asphalt

C 1.3 1.2 0.6 0.7

Glass felt (Type I) and asphaltD 1.7 1.2 0.7 0.6

Glass felt (new

product) and asphalt E 1.6 1.4 0.7 0.8

5.1.4. Tensile Fatigue Strength

Tensile fatigue strength tests were carried out on

four types of built-up roof membrane samples at 73 and 0 °F. The samples were of the type described

in ASTM Standard D-2523. The felts in the sample

membrane were oriented in the cross machine or transverse direction. Three sets of specimens of

each type of membrane, were tested to failure. The

rate of load application was 10 cycles per second

(cps) for specimens tested at 73 °F and 15 cps for specimens tested at 0 °F. Data for tension fatigue

tests at 73 °F are shown graphically in figure 2. The

rate of load application has an effect on the number

of cycles the specimens can withstand prior to

failure. A major consideration in the selection of the

load rate was the length of time to conduct the test. The maximum forces applied to the three sets were approximately 80, 60, and 40 percent of the

tensile strength of the membranes, respectively.

The specimens were loaded in tension-tension so

that the smaller force was 10 percent of the larger

applied fatigue force. A preliminary analysis of data of tensile fatigue

tests at 0 °F indicated that the specimens tested at 80 percent of their tensile strength failed at considerably fewer number of cycles of force than when

tested at room temperature. The specimens tested

at 60 and 40 percent of their tensile strength failed

in general at considerably more cycles of force at 0 °F than when tested at 73 °F.

5.1.5. Flexural Fatigue Strength

The same four types of membranes as described

in the tensile fatigue tests were tested in flexural fatigue at 73 and 0 °F. Test specimens were the

type described in ASTM Standard D-2523. The

felts in the test specimens were oriented in the cross machine or transverse direction. The specimens

7
lOOp

f goesI

80

Ico

uj 70

-1Z 60 —

UJH

u. 50- o

IT^ 30- o

S 20

00

Membrane A

Symbol O

All membranes were

oriented in the tronsverse

direction

i„il •A.

0 ia0°°^.3DAOO

A 0crb O OD

I I I I II 100,000 i.ooopoo lopoojooo

Figure 2.

10 100 1000 10,000 NUMBER OF CYCLES OF LOAD

Tensile fatigue strength of built-up roofing membranes tested at 73 °F.

were tested in the same manner as in the flexural

tests, except the specimens were subjected to repeated cycles of loading. The loading was controlled by the amplitude of the midspan deflection.

The deflection amplitudes were 0.2, 0.15, and 0.125

in with the rates of loading 2, 3, and 4 cps, respectively for specimens tested at 73 °F. The decision was made to control the amplitude of the midspan

deflection of the specimen as compared to controlling the load. Regardless of whether the force or amplitude was controlled, the other would vary

during the test. The data given in figure 3 shows the relationships

between the midspan deflection and the number of

cycles of load causing failure for specimens tested

at 73 °F. A preliminary analysis of data of flexural

fatigue tests at 0 °F indicated that specimens failed

at considerably less cycles offeree than when tested

at room temperature except the organic felt-coal tar membranes tested at amplitudes of force of

0.20 and 0.12 in.

5.1.6. Shear Strength (punching)

Tests were carried out to determine the punching

shear resistance of four types of built-up, four-ply

membranes placed over five types of insulation. The punching shear tests were conducted at both

73 and 0 °F. The five types of insulation included

foam glass, wood fiber, perlite board, fiberglass

and plastic foam. The compressive strengths of the

insulations were determined in order to compare

0 22

0.20

^ 018

z"o

O

LiJ 0.16

u.Q

0.14

0.12

0 10,

Membrane Symbol

o % 00

All membranes were oriented

in the transverse direction

^ O O ^ Q 0 0

OOO^

J I -I I

I I I I I I _] I I

I I I I I I 100 1000 "10,000 100,000 i,ooopoo NUMBER OF CYCLES OF LOAD Figure 3. Flexural fatigue strength of built-up roofing membranes tested at 73 °F.

8
the punching shear strength of the membranes

placed over the five types of insulation. Three different diameter steel probes were used

in the tests. The diameters were Vi, ^/4, and 1 in. The test specimen (membrane over insulation) was

placed over a simulated steel deck so that the 8 X 12 inch specimen spanned a 2%-inch flute opening.

The force was applied at midspan of the unsupported

length of the specimen. Data from the •'y4-in probe

tests are shown in figure 4. Results of the tests at 0 °F gave, in general, high shear strengths and

smaller corresponding indentation depth. Tests using the Va-in diam probe gave more

scatter and ranj;e of data than when the "A in diam probe was used. The 1-in diam probe gave

data which was more uniform with very little scatter and range compared to data from the % in probe

tests.

5.1.7. Impact Resistance

Five types of four-ply, built-up roof membranes

placed over five types of insulation were tested to

determine their resistance to impact. Ice spheres,

simulated hailstones, were impacted on the face

of the test specimens to simulate hail. The diameter

of the ice spheres used in the tests were 1, 1 Vi,

1 V2, 1^/4, 2, and 2 V2 in. The speed of the ice spheres corresponded to the speed at which hail- stones hit the ground. It was found, in general,

that 1 V2-in diam ice spheres traveling at 112 feet per second (ft/s) did not damage the membranes.

Damage was observed in the membranes when

larger size ice spheres were used.

5.2. Planned Performance Tests

It is planned to carry out the development of performance tests for the attributes listed in section

4 for which tests are not available. Upon completion

of these additional tests, the performance criteria in section 6 will be expanded to include the results of the needed laboratory studies. It is expected that as information is developed relating to performance

of built-up roofing, the levels of performance will also be revised and updated.

1400

1200

1000

800

600

400

200

•P

O Tested at TS^F •Tested at 0°F 3/4 inch diameter probe used for tests

0 01 0 2 0 3 0 4 05 06

INDENTATION DEPTH, in Figure 4. Punching shear strength of built-up roof membranes and corresponding

indentation depth.

6. Recommended Performance

Criteria

The recommended performance criteria are considered preliminary and will be revised or updated when additional information becomes

available. Obviously, some of the performance

tests and corresponding criteria may not be needed

and may be deleted after reviewing the completed

performance criteria. As an example, both the

tensile strength and flexural strength may not be

needed in the criteria. Since both are essentially related to the membranes tensile strength properties. Experience may prove that both impact resist- ance and shear strength can be combined into one

criterion.

Based on research conducted in this program,

as well as research conducted concurrently in other

investigations and previously at the National Bureau

of Standards and elsewhere, it is possible, even at this early stage, to state examples of criteria for roofing membranes. In order to place the perform- ance concept as it applies to roofing in perspective,

the authors felt it woUld be useful to incorporate

known data into the performance format. As a point

of departure, several examples are given. The values

are preliminary and should not be construed to be

final values. As results are obtained from perform- ance in-service experience and laboratory research,

9
the values will continue to be updated and adjusted

to reflect the developing state-of-the-art.

6.1. Performance Format

6.1.1. Tensile Strength

Requirement The roof membrane shall withstand, without rupture, the normal

stresses imposed from internal or external causes.

Criterion The tensile strength shall not be

less than 200 Ibjin in the weakest

direction of the membrane when

tested atO°F.

Test ASTM D-2523 testing load-strain

properties of roof membrane's.

Commentary This criterion is based on perform- ance in service. Certain membranes

exhibit anisotropic behavior. Therefore, the results of tests in the

weakest direction (usually trans- verse or "cross machine" direction)

should apply.

6.1.2. Thermal Expansion

Requirement The roofing membrane shall not

exhibit large movements when subjected to temperature change.

Criterion The linear expansion coefficient

shall not exceed 40 X 10-^1°F.

Test NBS test procedures (ASTM Pro- posed Method of Test for "Coefficient of Linear Thermal Expansion

of Roofing and Waterproofing Membranes," ASTM Annual Book of

Standards, Volumn 15, 1974).

Coefficient to be determined from

temperature range 0 to — 30 °F. Commentary Most roof membranes exhibit ani- sotropic properties regarding temperature change. Test should

usually be performed in the trans- verse or "cross machine" direction

since greater movement is generally

expected in this direction. Areas

which are not subject to cold

weather may estabUsh larger limits for the coefficient of linear ex- pansion.

6.1.3. Thermal Movement

Requirement The roof membrane shall withstand

the normal temperature changes of

its environment.

Criterion The thermal shock resistance factor should not be less than 100 °F.

Test NBS test procedures as described

in this paper. Commentary Areas which are not subject to large

and sudden temperature changes

may establish lower limits for the

thermal shock resistance factor.

6.1.4. Flexural Strength

Requirement The roof membrane shall withstand, without rupture, the normal

bending stresses imposed from

external causes.

Criterion The load capacity in flexure for a one-inch wide strip with fixed ends

and loaded at midspan (7-in span)

at 0 °F should be at least 30 lb. Test NBS test described in this paper. Commentary Certain membranes exhibit anisotropic behavior, the results of the

tests in the weakest direction (usually transverse or "cross machine")

should apply.

6.1.5. Tensile Fatigue Strength

Requirement The roof membrane shall withstand, without rupture, repeated

forces causing high and low levels of tensile stress in the membrane.

Criterion The roof membrane shall withstand

without rupture a minimum of

100,000 cycles of repeated force

(tension) of 20 lb when tested at 73 °F and a minimum of 100,000

cycles of repeated force (tension) of

100 lb when tested at 0 °F. Test NBS test described in this paper. Commentary Certain membranes exhibit anisotropic behavior, the results of the

tests in the weakest direction (usually transverse or "cross machine")

should apply.

6.1.6. Flexural Fatigue Strength

Requirement The roof membrane shall withstand,

without rupture, repeated forces

causing high and low levels of bending stress in the membrane.

Criterion The roof membrane shall withstand

without rupture a minimum of

10,000 cycles of force causing a

deflection of 0.125 in at midspan

(7-in span) of a one inch wide strip

with fixed ends tested at 73 °F. Test NBS test described in this paper. Commentary Certain membranes exhibit anisotropic behavior, the results of the

tests in the weakest direction (usually transverse or "cross machine")

should apply.

6.1.7. Punching Shear Strength

Requirement The membrane shall withstand,

without rupture, vertical punching

shear forces from foot traffic and

other eff^ects. Criterion The punching shear strength shall not be less than 250 psi (force/

probe area), when tested at 73 °F

using a ^U-in diam probe.

10
Test NBS test described in this paper. Commentary Membrane should be attached to the insulation when conducting the

test.

6.1.8. Impact Resistance

Requirement The roof nniembrane should withstand the impact from hailstones

and other falling objects.

Criterion The roofing membrane should be

able to withstand an impact of a

1 y^-in diam hailstone falling at a speed oi 112 ftjs without allowing

penetration of water.

Test NBS Hail Resistance Test, Building Science Series No. 23. Commentary The test does not approximate the

energy of large sharp objects, as

large icicles or tree limbs. Areas

which are not subject to hailstorm

or falling icicles could establish

lower limits for impact resistance.

6.1.9. Wind Resistance

Requirement The roof membrane shall withstand

anticipated wind loads without

damage.

Criterion The roof membrane should meet

the requirements of class {30), (60), or (90) according to Underwriters'

Laboratory Bulletin of Research

No. 54. Note, one class should be

selected depending on local wind

conditions. Test Underwriters' Laboratories test procedure described in UL Bulletin

ofResearchNo. 54, 1962. Commentary The above criterion is believed

adequate for most locations in the

United States. However, in high

wind areas, a more rigid criterion may be needed. Other tests such as those recommended by Factory

mutual and Owens-Corning Fiberglas Corporation may be suitable.

6.1.10. Fire Resistance

Requirement The roofing membrane should not be susceptible to ignition from

sparks and fire brands.

Criterion The intermittent flame, flame spread

and burning brand rating of the

membrane should be classified according to Underwriters' Laboratory Bulletin UL-790 as (A), (B),

or (C) as required by local codes.

Test ASTM E-108. Underwriters' Laboratory Bulletin, UL-790 describes

test procedure and rating values. Commentary The ASTM test method with limits established by UL criterion are believed adequate for most loca- tions in the United States. This

criterion has been widely used by

the roofing industry and has gained

acceptance.

7. Summary and Conclusions

The major goal of the research was to develop

performance criteria which would contain quantitative definitions of the roof membranes overall performance under service conditions. Preliminary

performance criteria were recommended along with

tests to measure performance of roof membranes

for nine of the 20 attributes that were identified. These attributes have a significant impact on the

total performance of membrane roofing. The values

given are based on data obtained from the four, and

in some cases, five types of basic four ply membrane

specimens. From the authors experience, it is beUeved that four ply membranes constructed in a similar fashion as those described in this paper and

properly applied would perform adequately in any

area of the United States provided they comply with

the stated performance criteria in section 6. However, established performance criteria would not

require membranes to have a specific number of

plies.

The laboratory program was intended to develop

tests which are needed to measure performance of roof membranes. Some of the tests described are new, other are modifications of existing tests and

some are established tests which have satisfactorily

served the roofing industry in the past. The new

tests include flexural strength, tensile fatigue

strength, flexural fatigue strength, punching shear

strength and impact resistance. The tests that were

modified include tensile strength, thermal expansion

and thermal movement. Tests that were not changed

are those used by the roofing industry for wind

resistance and fire resistance.

Laboratory tests which need to be developed to complete the performance criteria include notch

tensile strength, moisture effects on strength, creep,

ply adhesion, abrasion resistance, tear resistance,

pliability, permeability, moisture expansion, weather

resistance, and fungus attack resistance. Research

is being continued in some of these areas. As performance criteria for membrane roofing

become more complete, it is expected that some of

the performance characteristics can be deleted or combined with others to reflect the current state-ofthe-art. It is also anticipated that additional perform- ance attributes may be needed and described quantitatively to make the performance criteria more

11
meaningful. Such needs should be studied carefully

with respect to one, two or three ply systems.

With the establishment of acceptable perform- ance criteria for membrane roofing at least two

benefits are readily apparent. First, the criteria would provide the basis for the evaluation of both

presently used roofing systems and innovative

membranes with regard to expected in-service

performance. Secondly, they can be used by manufacturers as a guide in the production of roofing

materials and, in particular, the development of new products for membrane roofing. In addition to these two benefits, performance criteria will enhance better and more economical service from

bituminous membranes. The development of adequate criteria for membrane roofing based on quantitative terms will provide an important step in elevat- ing the art of roofing to some resemblance of a

science.

The work described in this paper was jointly

sponsored by the Owens-Corning Fiberglas Corporation and the National Bureau of Standards. The

authors wish to acknowledge the financial support

of Owens-Corning Fiberglas Corporation in conducting the research described in this paper. In particular, they wish to express their sincere thanks to Miles E. Jacoby of the Owens-Corning Fiberglas

Corporation, Product Testing Laboratories, who

served as project coordinator for his valuable

technical and administrative assistance.

8. References

[1] Griffin, C. W., Jr., Manual of Built-Up Roof Systems, The

American Institute of Architects (McGraw-Hill Book Company, 1970).

[2] Study of Roof Systems and Constituent Material and Components Special Advisory Report No. 6, Technical Report

No. 25, Building Research Advisory Board, National Acad- emy of Sciences, National Research Council, 1964.

[3] Recommended Practice for Testing Load-Strain Properties

of Roof Membranes, ASTM Designation D-2523-70, Part 11, ASTM Annual Book of Standards, 1973.

[4] Standard Method of Test for Drying Shrinkage of Concrete

Block, ASTM Designation C-426-70, Part 12, ASTM Annual Book of Standards, 1974.

[5] Proposed Test for Coefficient of Linear Thermal Expansion of Roofing and Waterproofing Membranes, Part 15, ASTM

Annual Book of Standards, 1974.

[6] CuUen, William C. and Boone, Thomas H., Thermal-shock

resistance for built-up membranes, Nat. Bur. Stand. (U.S.), Bldg. Sci. Ser. 9, 18 pages (Aug. 1%7).

12
NBS-) 14A (REV. 7-73)

J. U.S. DEPT. OF COMM. 1. PUBLICATION OR RKPORT NO. 2. Gov't Accession BIBLIOGRAPHIC DATA No. SHEET NBS-BSS-55

3. Recipient's Accession No.

4, TITLE AND SUBTITLE

Preliminary Performance Criteria

for Bituminous Membrane Roofing

5. Publication Date November 1974

6. Performing Organization Code

7. AUTH0R{S) j^obert G. Mathey and William C. Cullen 8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No.

1 1. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Same as Number 9.

13. Type of Report & Period Covered Interinoi

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

Library of Congress Catalog Card Number: 74- 600167

16. ABSTRACT (A 200-word or less factual summary ol most si^ilicant information. If document includes a significant

bibliography or literature survey, mention it here.)

This report is the first in a series of publications on performance

criteria for built-up roof membranes. The development of a performance

approach to bituminous built-up roof membranes is described and

preliminary performance criteria are recommended. A number of test

methods have been developed in order to obtain data to evaluate roofing

membranes against the recommended criteria. Twenty attributes that

effect the performance of roof membranes under service conditions are

identified and laboratory tests are described for measuring the engineering properties of the membrane that pertain to many of these attributes.

A level of performance is recommended for nine of the identified performance attributes.

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

Bituminous roof membranes; performance attributes; performance criteria;

physical and engineering properties; test methods.

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