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NBS SPECIAL PUBLICATION 659

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

Low-Sloped Roofing

Research Plan
NATIONAL BUREAU OF STANDARDS

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

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

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

the Institute for Computer Sciences and Technology.

THE NATIONAL MEASUREMENT LABORATORY provides the national system of

physical and chemical and materials measurement; coordinates the system with measurement

systems of other nations and furnishes essential services leading to accurate and uniform

physical and chemical measurement throughout the Nation's scientific community, industry,

and commerce; conducts materials research leading to improved methods of measurement,

standards, and data on the properties of materials needed by industry, commerce, educational

institutions, and Government; provides advisory and research services to other Government

agencies; develops, produces, and distributes Standard Reference Materials; and provides

calibration services. The Laboratory consists of the following centers:

Absolute Physical Quantities^ — Radiation Research — Chemical Physics —

Analytical Chemistry — Materials Science

THE NATIONAL ENGINEERING LABORATORY provides technology and technical ser- vices to the public and private sectors to address national needs and to solve national problems; conducts research in engineering and applied science in support of these efforts; builds and maintains competence in the necessary disciplines required to carry out this research and technical service; develops engineering data and measurement capabilities;

provides engineering measurement traceability services; develops test methods and proposes

engineering standards and code changes; develops and proposes new engineering practices;

and develops and improves mechanisms to transfer results of its research to the ultimate user. The Laboratory consists of the following centers:

Applied Mathematics — Electronics and Electrical Engineering^ — Manufacturing

Engineering — Building Technology — Fire Research — Chemical Engineering^

THE INSTITUTE FOR COMPUTER SCIENCES AND TECHNOLOGY conducts

research and provides scientific and technical services to aid Federal agencies in the selection, acquisition, application, and use of computer technology to improve effectiveness and

economy in Government operations in accordance with Public Law 89-306 (40 U.S.C. 759), relevant Executive Orders, and other directives; carries out this mission by managing the Federal Information Processing Standards Program, developing Federal ADP standards

guidelines, and managing Federal participation in ADP voluntary standardization activities; provides scientific and technological advisory services and assistance to Federal agencies; and

provides the technical foundation for computer-related policies of the Federal Government.

The Institute consists of the following centers:

Programming Science and Technology — Computer Systems Engineering.

'Headquarters and Laboratories at Gaithersburg, MD, unless otherwise noted; mailing address Washington, DC 20234. 'Some divisions within the center are located at Boulder, CO 80303.
OF STANDARDS Low-Sloped Roofing

Research Plan "

^

^

William C. Cullen*

Walter J. Rossiter, Jr.**

Robert G. Mathey**

James R. Clifton**

*William C. Cullen Associates, Inc. Potomac, MD 20854

**Building Materials Division

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

Washington, DC 20234

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

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Issued July 1983
Library of Congress Catalog Card Number: 83-600551

National Bureau of Standards Special Publication 659

Natl. Bur. Stand. (U.S.), Spec. Publ. 659, 40 pages (July 1983)

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WASHINGTON: 1983

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ABSTRACT

This report presents a long-range plan for roofing research. The plan was

developed in response to a need for roofing research addressing major materials

problems and changes in low-sloped roofing materials technology. The intent of

the plan is to establish the technical basis for developing standards and minimum levels of performance to assist in the selection of cost-effective and

durable roofing materials. Four major areas of needed research are identified:

(1) low-sloped roofing systems, (2) roofing membranes including single-ply and

built-up, (3) thermal insulation for roofing systems, and (4) condition assessment and repair of roofs. Within each research area, a goal is given as well

as a number of objectives to achieve the goal. A recommended approach to

accomplish each objective is also given.

Key words: low-sloped roofing; mathematical modeling; membranes; repair;

research plan; roofs; standards', thermal insulations.

iii
ACKNOWLEDGMENTS

During the preparation of this research plan for low-sloped roofing comments

and suggestions concerning its contents were requested from a number of knowledgeable individuals within the roofing community. The authors gratefully

acknowledge and express their sincere thanks and appreciation to those individuals who gave their time in reviewing a draft of the plan and making valuable

commefits and suggestions. All comments and suggestions received from these

members of the roofing community were considered in preparing the plan for

publication. The authors express their thanks and appreciation to: Robert L.

Alumbaugh, Naval Civil Engineering Laboratory, Port Hueneme , CA; Jean Boulin,

U.S. Department of Energy, Washington, DC; Carl G. Cash, Simpson, Gumpertz and

Heger, Inc., Cambridge, MA; Hubert Coon, Urethane Foam Contractors Association,

Dayton, OH; George E. Courville, Oak Ridge National Laboratory, Oak Ridge, TN;

Richard L. Fricklas, Roofing Industry Educational Institute, Englewood , CO;

Myer J. Rosenfield, U.S. Army Corps of Engineers, Construction Engineering

Research Laboratory, Champaign, IL; Fred Good, National Roofing Contractors

Association, Chicago, IL; C. W. Griffin, Denville, NJ; Harry R. Marien, U.S.

Air Force Civil Engineering Center, Tyndall AFB , FL; Richard D. Snyder, Asphalt

Roofing Manufacturers Association, Rockville, MD; and Wayne Tobiasson, U.S.

Army Corps of Engineers, Cold Regions Research and Engineering Laboratory,

Hanover, NH.

Special thanks and appreciation are extended to Geoffrey J. C. Frohnsdorff,

Chief of the Buildings Materials Division, for his many valuable comments and

suggestions concerning this plan and his encouragement throughout its preparation. The authors also thank their colleagues in the Building Materials Division including Lawrence I. Knab, Larry W. Masters, and David Waksman for their

reviews and constructive comments. The suggestions of Daniel Gross of the NBS

Center for Fire Research were also appreciated. The authors also express their

thanks to Mary Ramsburg of the Center for Building Technology for her

contributions of typing and editing the report.

iv
EXECUTIVE SUMMARY

This document presents a proposed long-range plan for research to provide the

technical bases for standards for low-sloped roofing materials and systems. It

is aimed at the development of needed measurement technology and largely

addresses materials research. The plan was developed in response to a need for

standard methods for evaluating the performance of new materials used in lowsloped roofing and for standards to provide the bases for their selection.

A need also exists to develop the technical basis to evaluate methods for roof

condition assessment and repair.

The United States inventory of low-sloped roofing is in the range of 25 to

30 X 109 ft2 (2.3 to 2.8 x 109 m2). Each year about 3 x 109 ft2 (0.3 x 109 ni2)

of low-sloped roofing is applied, divided somewhat equally between new roofing

and reroofing of existing buildings. The annual costs for low-sloped roofing

exceeds 10 billion dollars. The early failure rate (major and costly problems)

for these types of roofs is considerably higher than for any other major component of a building. While roofing systems account for approximately 2 to

5 percent of the total cost of new buildings, they give rise to about 50 percent

of building construction lawsuits.

A major change taking place in roofing membrane technology is the use of

single-ply membranes as an alternative to built-up membranes. Over 100 singleply membrane products by some 60 manufacturers are currently available. Con- sensus standards and minimum levels of performance for single-ply membranes

have not been developed in the United States. A technical basis for their

development is needed. Research in this area is given high priority.

Significant changes are also occurring in conventional bituminous built-up

membrane technology. For example, the built-up roofing industry is experiencing

an increase in the use of glass fiber mats (currently about 40 percent of

total) as well as a gain in the use of polymer fiber reinforcements. Little

data are available on the long-term performance of these new reinforcements

used in built-up membranes. A technical basis for the development of standards

for bituminous built-up membranes is needed.

Because of the wide variety of roofing materials and systems that are presently

available and their variable in-service performance, including premature

failure, criteria and appropriate test methods need to be developed to assist

in the selection of materials and systems and in the prediction of their

performance in service. The program goal is to develop the technical bases for

increasing the performance and durability of low-sloped roofing materials and

systems through the application of science and technology leading to the

development of test methods and selection criteria suitable for incorporation

in standards. Achievement of this goal will take many years and require the

cooperation of roofing researchers from government, university, and industrial

organizations

The plan proposes that major research efforts be concentrated in the following

categories

V
• Theoretical analysis of roofing system performance and the development of

models for predicting performance.

• Development of minimum levels of performance for roofing systems, membranes,

and thermal insulation,

• Characterization of failure mechanisms of roof membranes and systems as a basis for understanding roofing performance and for advancement of roofing

technology.

• The advancement of the in-situ condition assessment and repair of roofs by

the application of measurement technology.

Four major areas for research for low-sloped roofing are covered in the plan,

namely: (1) low-sloped roofing systems, (2) roofing membranes, (3) thermal

insulations used in roofing systems, and (4) condition assessment and repair.

Each of these areas contains elements of the major research effort outlined

above. A possible flow scheme for conducting the proposed research is presented (see figure 2 in report). This flow scheme shows the relations between

the proposed major activities and goals for the four research areas.

vi
TABLE OF CONTENTS

Page

ABSTRACT iii

ACKNOWLEDGMENTS Iv

EXECUTIVE SUMMARY v

1. INTRODUCTION 1

1.1 Need for Roofing Research 1 1.2 Purpose of Plan 2

2. ROOFING TRENDS 4

3. PROGRAM GOAL STATEMENT 6

4. OUTLINE OF RESEARCH IN THE LONG-RANGE PLAN 7

5. RESEARCH AREAS 11

5.1 Low-Sloped Roofing Systems 11

5.2 Roofing Membranes 14

5.2.1 Single-Ply Roofing Membranes 14

5.2.2 Bituminous Built-Up Roofing Membranes 20

5.3 Thermal Insulation Used in Roofing Sytems 23

5.4 Condition Assessment and Repair of Roofs . 26

6. RESEARCH SCHEME AND CONCLUDING REMARKS 29

7. REFERENCES 31

vii

1. INTRODUCTION

A long-range research plan for low-sloped roofing has been developed and is

presented in this report. The major thrust of the plan is directed towards

materials and systems research, and the application of measurement technology

to roofing research.

Roofing research plans have been prepared by the U.S. Department of Energy

(DOE) and the U.S. Army Corps of Engineers (COE). The DOE plan was concerned

primarily with improving the thermal performance of roofing systems. A purpose

of the COE plan was to foster coordination and avoid duplication of roofing

research programs being carried out by Federal agencies. The DOE and COE plans were considered in the preparation of the present plan. The three plans

complement each other.

1.1 NEED FOR ROOFING RESEARCH

The long-range plan presented here was developed in response to a need for

roofing research addressing major roofing material problems and changes in lowsloped roofing materials technology. The need for research on low-sloped

roofing also was identified in the report, "Summary of a Workshop on Low-Slope

Roofing" [1], by the National Academy of Science's Advisory Board on the Built

Environment. The DOE National Program Plan [2] for energy conservation in

buildings also identified needed roofing research for materials and systems.

The United States inventory of industrial and commercial roofing (low-sloped)

is in the range of 25 to 30 x 109 ft2 (2.3 to 2.8 x 109 m2). Each year about

3 X 109 ft2 (0.3 X 109 m2) of roofing is applied, divided about equally between

new roofing and re-covering of existing roofs [3] . The annual costs for this

roofing exceeds 10 billion dollars. The early failure rate for these types of

roofs is considerably higher than for any other major element of a building.

While roof systems account for approximately 2 to 5 percent of the total cost

of buildings, they give rise to about 50 percent of building construction

lawsuits [4]. Many of the failures are amenable to technological solutions

which could result in significant cost savings.

A major change taking place in low-sloped roofing technology is the substitution

of single-ply membranes for conventional built-up membranes. In 1975, singleply membranes comprised about 2 percent of the membrane market, but it is

forecast that these membranes will command over 30 percent of the commercial

roofing market by 1985 [5]. Over 100 single-ply membrane products from about

60 manufacturers are currently available [6]. Consensus standards and minimum

levels of performance for single-ply membranes have not been developed in the

United States and a technical basis for their development is needed. Standards

are needed to provide a reliable basis for the selection of cost effective

durable materials. Research for single-ply membranes, therefore, is given

high priority in the research plan.

Significant changes are also occurring in bituminous built-up membrane

technology. For example, the built-up roofing industry is using more glass

fiber mats as well as polyester and other polymeric reinforcements. Glass fiber

1
mats may account for about 40 percent of the reinforcements used in built-up

membranes [7]. In spite of over a century of use, voluntary consensus standards for completed built-up bituminous membranes do not exist. Such standards

should be developed and research is needed to provide the technical basis for

their development.

With the influx of the single-ply membrane materials into the roofing market

and the changes occurring in bituminous roofing technology, a need exists for

reliable durability test procedures to predict the long-term performance of

these materials. ASTM Standard E 632, "Standard Practice for Developing ShortTerm Accelerated Tests to Aid Prediction of the Service Life of Building

Components and Materials," has been established to aid the complicated development of durability tests for any building material. The approach given in ASTM

E632 outlines a rational approach which could assist the development of durability test procedures for single-ply and other roofing materials. Reliable

durability data are essential for determining the life-cycle costs of roofing

membrane materials.

Although the plan emphasizes needs for materials research for low-sloped

roofing, it also recognizes that there are four essential elements to assuring

the quality of good roof performance: (1) sound design, (2) quality materials,

(3) good workmanship, and (4) good maintenance.

Steep roofing, e.g., residential roofing, is not covered by this research plan

as significantly fewer problems are encountered with this type compared to

low-sloped roofing. Some changes are taking place in the technology of roofing

shingles. For example, fibrous glass in felted form is replacing traditional

organic felts in the manufacture of shingles. Although such changes may

necessitate some modifications in the ASTM standards for shingles, these changes

are unlikely to require the level of research needed to establish standards

for new membrane materials for low-sloped roofing.

1.2 PURPOSE OF PLAN

An important purpose of developing the long-range plan was to define areas of

needed applied and fundamental research for low-sloped roofing. The plan

stresses research which should contribute to significant improvements in the

quality and performance of low-sloped roofing materials and systems. The intent

is to establish the technical bases for developing standards and performance

levels which will form the basis for the selection of cost-effective and durable

roofing materials.

The plan presented here is broad and quite extensive. The achievement of its

goals and objectives will take many years, requiring the joint efforts of all

segments of the roofing community including industry, government, educational

institutions, and standards-setting bodies. The plan recognizes and provides

for the transfer of the results of roofing research from researchers to

professional engineers, architects, designers, roofing contractors, roofing

mechanics and building owners. The results of the research would be available

to ASTM Committees and others which have responsibility for the development of

standards for building materials and roofing system performance including C16

2
on Thermal Insulations, D8 on Roofing, Waterproofing, and Bituminous Materials,

E6 on Performance of Building Construction, and G3 on Durability of Nonmetallic

Materials. The research results would also be available to international

organizations such as CIB* and RILEM** which recently formed a joint committee

on single-layer roofing.

* CIB —^£onseil international du B^atiment pour la Recherche d 'Etude et la

Documentation.

* RILEM—^Reunion International des Laboratoires d'Essais et de Recherches

sur les Materiaux et les Constructions.

3
2. ROOFING TRE,NDS

The long-range plan for roofing research is based on predictions of

technological developments and trends in the roofing industry over the next

decade. The predictions are based on published market surveys, information

from trade associations (for example, National Roofing Contractors Association,

Asphalt Roofing Manufacturers Association, Urethane Foam Contractors Association, and Single-Ply Roofing Institute), and projections based on the history

of the roofing industry. Predictions regarding materials used in low-sloped

roofs are:

• Low-sloped roofing construction will continue at an annual rate of about

3 X 10^ ft2 (0.3 X 10^ m2) per year at an applied cost of over 10 billion

dollars. This dollar figure is expected to increase in the future.

• Application of new roofing and reroofing or re-covering work will each

continue to account for about 50 percent of the total market during the

coming decade.

• Problems with low-sloped roofing systems requiring costly maintenance,

repair, and replacement by owners will continue at about the same relatively

high rate [8] during the decade.

• Single-ply roofing will command at least 30 percent of the low-sloped roofing

market in 1985 with an application of over 1 X 109 ft2 (0.1 x 109 m2) at an installed cost of about 3 billion dollars. Although the amount of single-ply

materials used will steadily increase, the number of products is expected

to decline during the decade.

• Serious problems may result in using single-ply materials if test methods,

criteria, standards, and quality assurance programs are not developed to

provide a reliable basis for material selection.

• The use of conventional multi-ply bituminous built-up roofing will decline

to about 60-70 percent of the market by 1985.

• The bituminous built-up roofing industry will experience a large increase

in the use of glass fiber mats as well as a modest gain in the use of

polyester and other polymer fiber reinforcements.

• The use of the more thermally efficient roof insulations (for example,

expanded polystyrene and polyurethane foams) will increase, while the use

of the more conventional board type insulations (fibrous glass and mineral

board) will decrease.

• Computer-aided design (CAD) will become increasingly important in the design

and construction of roofing systems. The recent advances in computer science

and technology have resulted in significant advances in the understanding of

the performance of building materials and systems and will help increase the

understanding of the performance of roofing systems.

4
The Influences of economic and social issues on roofing trends also were

considered, including:

9 The need to conserve energy and to find substitutes for materials which may

be in short supply will lead to the development of new materials for roofing

use.

• Increased rehabilitation of buildings will result in the need for reliable

methods, including non-destructive evaluation, to predict the condition of

roofing materials, and to evaluate the remaining service life of in-place

materials.

• Increased costs of labor may necessitate the use of less labor-intensive

techniques for roofing installation.

5
3. PROGRAM GOAL STATEMENT

To develop the technical bases for increasing the performance and durability of

low-sloped roofing materials and systems through the application of science and

technology leading to the development of test methods and selection criteria

suitable for incorporation in standards.

6
4. OUTLINE OF RESEARCH IN THE LONG-RANGE PLAN

The long-range plan covers four research areas for low-sloped roofing:

1. Low-sloped roofing systems

2. Roofing membranes

a. Single-ply roofing membrances

b. Built-up roofing membranes

3. Thermal insulations used in roofing systems

4. Condition assessment and repair

Under each research area a goal has been stated. Following the goal statement,

a brief narrative is generally provided to indicate the problems to be solved , the research approach , the products , the implementation of the research results

and the impact in the roofing industry. The narrative is followed by a set

of objectives for tasks to be performed in meeting the goal. A brief rationale

is given for each objective followed by recommendations for the required

research. A summary of the goals for each of the four research areas is given

in table 1.

As presented in the following sections of the report, each of the four research

areas is intended to stand alone with limited cross-referencing between them.

As a consequence, some parallelisms exist between the research suggested in

each of the four areas. The thrusts of the research efforts are concentrated

in the following categories.

• Theoretical analysis of roofing system performance and the development

of models for predicitng performance.

• Development of minimum levels of performance for roofing systems,

membranes, and thermal insulation.

• Characterization of failure mechanisms of roof membranes and systems

as a basis for understanding roofing performance and for advancement of

roofing technology.

• The advancement of in-situ condition assessment and repair of roofs

by the application of measurement technology.

A conception of the efforts which may be required in developing minimum

levels of performance for roofing systems, membranes, and thermal insulation

qan be obtained from examining table 2. Performance attributes (characteristics) are listed for systems, membranes, and thermal insulations as reported

in two NBS publications: Building Science Series 55 on bituminous membranes

[9], and Technical Note 972 dealing with single-ply membranes [10]. The closed

circles in table 2 indicate attributes for which preliminary minimum levels of

performance have been suggested. It is evident that preliminary levels of

performance are lacking for the majority of the performance attributes for

both single-ply and bituminous membrane roofing. Also, no performance attributes pertaining to thermal insulation were listed in these NBS reports. In

examining table 2, questions may be raised such as whether the list of suggested

7
Table 1. Areas of Needed Research and Goals

Area of Needed Research Goal

1. Low-Sloped Roofing Systems To develop an Improved understanding of the

factors controlling the performance of roofing

systems using material science and engineering

mechanics concepts; and to develop relationships between properties of the roofing

materials and performance of the roofing

systems

2. Roofing Membranes < -

Single-Ply Roofing

Membranes

To develop a technical basis for establishing

standards and minimum performance levels for

single-ply roofing membranes.

Bituminous Built-Up

Roofing Membranes

To advance the state-of-the-art of bituminous

roofing membrane technology by developing

methods for determining minimum performance

levels and developing improved methods for

evaluating and predicting the performance of

these membranes.

Thermal Insulation Used

In Roofing Systems

To develop a technical basis for establishing

minimum performance levels for roofing

insulation materials considering the thermal

and mechanical performance and design of

insulated roofing systems.

Condition Assessment and

Repair of Roofs

To develop a technical basis for roof condition

assessment and for the evaluation of repair

techniques

8
Table 2. Suggested Performance Attributes for Single-Ply and Bituminous Membranes.

Reference Suggested Minimum Levels

Which Lists of Performance**

Attributes*

Suggested Performance Attribute BSS 55 TN 972 Single-Ply Built-up

Roofing Systems

Wind (Uplift) Resistance / • • Fire (Flame; Resistance / // • • Punching Shear / / • • Impact (Hail) Resistance / / • • Durability (Weather Resistance) •

Roofing Membranes

Tensile Strength / • Flexural Strength • Thermal Expansion / • Thermal Shock Resistance / • Tensile Fatigue Strength / / • Flexural Fatigue Strength / / • Ultimate Elongation / Moisture Effects on Strength / /

Moisture Expansion / /

Permeability / /

Notch Tensile Strength /

Creep / /

Ply Adhesion / /

Abrasion Resistance / /

Tear Resistance / /

/ Pliability / /

Seam Strength / • Fungus Attack Resistance / / • Chemical Resistance / • Color Stability/Reflectivity /

Roofing Thermal Insulations

(No performance attributes

listed in cited publications)

* The check-mark indicates that the performance attribute was listed in NBS

Building Science Series (BSS) 55 on bituminous membranes [9] or NBS Technical

Note (TN) 972 on single-ply membranes [10].

** The Closed Circles Indicate Those Attributes for Which Preliminary Minimum

Levels of Performance Have Been Suggested.

1 9
attributes for each of the categories (systems, membranes, and insulation) is

complete or excessive, what data and analyses are needed to recommend performance levels where none exist, and does a theoretical basis exist to support

the previously suggested minimum levels of performance. One reason for the

development of this research plan was to address such questions on roofing

performance.

10
5. RESEARCH AREAS

5.1 LOW-SLOPED ROOFING SYSTEMS

Goal ; To develop an improved understanding of the factors controlling the

performance of roofing systems using material science and engineering mechanics

concepts; and to develop relationships between properties of the roofing

materials and the performance of the roofing system.

Comments ; The roofing system can be treated in terms of the individual

components of which it is composed. However, in its simplest form, this

approach does not consider the effects of interactions between components on

the ultimate performance of the system. Study of the entire system is necessary

to provide insights into the interactions which are important to system performance. The typical low-sloped roofing system has three major interacting

components: structural deck, thermal insulation, and waterproofing membrane.

Vapor flow retarders, when used, and roof flashings, must also be considered in

studying the system as a whole. The distribution of attachments and

penetrations and their effect on system performance should also be considered.

Of major concern to the roofing community is the technical complexity of the

modern roofing system [11]. The proliferation of materials and design combinations involving decks, thermal insulations, and membranes often creates unexpected adverse interactions between these components resulting in unacceptable

performance of the roofing system. It is not practical to conduct extensive

laboratory and field tests in order to predict the performance of each combination which may be assembled in service. A technical approach to overcoming

these problems is the use of validated mathematical modeling to predict performance of selected combinations of materials and designs in a roofing system

[12]. Modeling would facilitate the acceptance of new materials and innovative

designs. Once a model has been developed, it is essential that the validity

of the model be verified by testing roofing specimens under known conditions

and by field tests on actual roofs.

The availability of mathematical models to all segments of the roofing industry

will be a large step toward providing an improved technical basis for evaluating roofing performance and for establishing minimum levels of performance

for important materials properties. Mathematical models can be a valuable tool

in assisting the manufacturing segment and the design profession in specifying

and assembling compatible material combinations for use in decks, insulations

and membranes. Another important use of mathematical models will be in

computer-aided design [13].

5.1.1 Objective 1 —Identification of Failure Modes

Objective : To obtain and analyze information on the in-service performance and

failure modes of low-sloped roofing systems.

Comments : Analysis of information on in-service performance and field failures

of roofing systems and materials will form, in part, the basis for the development of models described in the following objective and for the development of

11
simulative accelerated durability tests. It is anticipated that the needed

data will be obtained from organizations such as the National Roofing

Contractors Association (NRCA) and the newly established University of Maryland

Architecture and Engineering Performance Information Center (AEPIC).

Recommended Approach ;

• Analyze data obtained from industry associations (NRCA, AEPIC), contacts

with technical experts, and by field inspections; relate problems to causes,

for example, is it a material durability problem or a design problem?

» Identify probable failure mechanisms; for example, is failure due to

deterioration of a single material or to incompatibility between or among

roofing components, or the constituents of a composite material?

& Document relations between failure mechanisms and premature problem

manifestations.

5.1.2 Objective 2—Development of Mathematical Models

Objective : To develop mathematical models which describe essential aspects of

total roofing system performance and simulate interactions between and among

the various components of the low-sloped roofing system.

Comments ; To provide many years of satisfactory service, a roofing system must

be capable of withstanding the environmental and service stresses to which it

will be subjected. Examples of such stresses include temperature, moisture,

UV radiation, wind, hail (impact), foot traffic, and building movement.

Empirical testing of systems comprised of any of the many available roofing

materials, particularly the multitude of newer ones entering the market, does

not provide adequate information for prediction of performance. Such testing

is costly and time consuming and incapable of evaluating all materials in all

roofing designs. Moreover, empirical testing of new materials may discourage

their use because of the expense involved in testing. In principle, mathematical modeling offers a much more cost-effective and broadly-applicable approach

to understanding the ability of a roof system to resist the stresses impressed

upon it and the ability of the individual components to interact compatibly.

Modeling also provides a means of identifying important performance properties

and establishing minimum levels of performance for those properties.

Although some mathematical modeling of roofing performance has been

accomplished, the models do not, in general, deal with total system performance

[12]. Models describing total system performance should be developed. Total

system models should be structured so as to be easily understood and readily

modified by developing and linking together well-documented submodels describing

specific aspects of roofing performance.

Recommended Approach ;

9 Define satisfactory roofing performance and modes of failure of roofing

systems to be described by mathematical modeling; identify environmental

12
and mechanical stresses which affect system performance and the specific

modes of failure.

• Develop mathematical relationships (submodels) between specific failure

mechanisms and measurable properties of the roofing materials in order to

describe the ability of the roofing system to resist failure,

o Where possible, use available data for comparison with the results of the

submodels; revise the submodel as necessary to achieve agreement between

the submodel results and available test data,

• Combine submodels to develop a model for predicting the roofing system

performance,

• Develop relationships which can be used in computer-aided designs for roofs,

and provide recommendations for system design and materials selection based

on results of the modeling.

• Develop relationships for calculating minimum performance levels for

materials and systems based on roof design.

5.1.3 Objective 3 —Validation and Revision of Mathematical Models

Objective ; To compare the results from the models with the results of

labqratory and field testing, and where necessary, revise the models.

Comments ; A mathematical model gains credibility after validation against the

results of laboratory and field testing. A large gap may exist between the

performance predicted from a theoretically developed model and what actually

occurs on the roof. As an intermediate validation, a model can be tested under

simulated service conditions in the laboratory. It is envisioned that relatively large (for example, 10 x 10 ft or 3 x 3 m) specimens of complete roofing

systems may be necessary for model validation in the laboratory. The next step

is to move from the laboratory to the field; these studies could be carried on either concurrently or sequentially. The models can also be tested by measuring

the performance of real systems under known weather conditions. The results of

the simulations may be used to revise the models whenever necessary.

Recommended Approach ;

• Conduct laboratory tests using large specimens exposed under controlled and

cyclic environmental conditions in appropriate test chambers; where

necessary, develop appropriate test apparatus and instrumentation.

• Conduct appropriate field tests of roofs; characterize the service

environment, building movements, and the changes in roofing performance.

• Compare theoretical results predicted by the models with those of the

laboratory and field tests and revise the models as necessary.

13
» Prepare and publish papers and reports which document the models and

demonstrate the usefulness of the modeling approach to roofing designers.

5.2 ROOFING MEMBRANES

This section presents needed research for both single-ply and bituminous

built-up membranes. They comprise over 95 percent of the waterproofing membranes for low-sloped roofing systems. Ideally, performance standards should

be developed applicable to all types of membranes for low-sloped roofing.

Although the research needs for the two types of membranes are presented

separately, the intent of the proposed research is to provide the basis for

the establishment of standards applicable to all membranes.

In typical roofing design, the waterproofing membrane is placed on the

insulation. In contrast, for protected membrane roofing, the membrane is

placed below the insulation. In this case, the insulation provides protection

to the membrane from the effects of weather. The research proposed for

membranes will consider both types of roofing design.

5.2.1 Single-Ply Roofing Membranes

Goal : To develop a technical basis for establishing standards and minimum

performance levels for single-ply roofing membranes.

Comments: Since the mid-1970s, a rapid increase in the use of sheet-applied

single-ply membranes has occurred. In 1982, there were over 100 sheet-applied

single-ply roofing products manufactured and distributed by about 60 manufacturers in the U.S. A number of these products were from various European

countries as well as from Australia, Canada, and Japan.

Unlike the more traditional roofing materials, sufficient information is not

available to indicate the reliability of single-ply membranes to perform adequately under the broad extremes of U.S. climatic conditions in buildings

constructed using U.S. building practices. Long-term field performance experience in the U.S. is also lacking for most of the materials. Serious premature

failures have occurred with some products. To avoid an increase in the incidence of premature failures, meaningful standards need to be developed and

accepted to aid materials selection. Fear of failure could become a barrier

to the use of new materials for which standards do not exist. Establishment of

meaningful standards and test methods would provide a sound basis for material

selection. This requires the development of the technical basis for the needed

standards

.

The emphasis will be on laboratory research directed toward identifying failure

modes and mechanisms, measurement methods for characterizing classes of singleply membranes (particularly with regard to performance properties used in

mathematical models), as well as the development of test methods and methods

for the determination of performance levels for incorporation into voluntary

consensus standards. : . ?

14
Field studies are also needed to identify failure mechanisms and the level of

performance under characterized service environments. Failure mechanisms also

may be identified in collaborative studies with industry associations such as the NRCA. Also, it is expected that data on failures can be obtained from the

AEPIC performance data described in Objective 1 under Roofing Systems

(section 5.1.1).

5.2.1.1 Objective 1 —Definition of Performance Attributes

Objective: To define performance attributes of single-ply roofing membranes

based on existing information such as field performance, research results,

test methods, and standards.

Comments ; An important first step in developing standards and minimum levels

of performance for single-ply membranes is to identify the properties and performance attributes which the membrane must have and retain in order to provide

a watertight component of the roofing system for the intended service life of

the roof. Since the widespread and rapidly-growing use of single-ply materials

has occurred, much information has been generated around the world by organizations such as research laboratories, government agencies, standards-setting

bodies, and trade associations. This information should be assembled and

collated to help define preliminary performance attributes. Such a study

would also provide a basis for setting priorities for conducting research

needed to support the development of standards for single-ply materials. In

addition the study would help identify failure mechanisms of single-ply membranes. Thus, it could be used, in part, as the basis for mathematical models

for membrane and system performance.

Recommended Approach ;

• Obtain available domestic and foreign standards from such standards bodies

as ASTM (US), DIN (Germany), AFNOR (France), BSI (UK), CGSB (Canada), and

others.

» Review these documents and other literature for applicable information on specified performance levels, measurement methods, environmental factors,

accelerated weathering techniques, and mathematical modeling procedures

which may apply to the measurement of properties and the prediction of

performance of single-ply membranes.

© Obtain data on materials properties and documentation on in-service

performance, as well as laboratory information on alleged failure mechanisms

and their relationship to field performance.

9 Conduct a workshop on defining performance attributes for single-ply

membranes

.

9 Review existing test procedures for determining membrane attributes and

provide recommendations for needed test method development.

9 Prepare report on applicable attributes.

15
5.2.1.2 Objective 2—Characterization of Failure Mechanisms

Objective ; To identify and characterize mechanisms involved in premature

failures experienced in single-ply membranes and seams under service conditions.

Comments ; Elastomeric, plastomeric and modified bituminous materials which are used in single-ply membranes undergo chemical, physical, and mechanical property

changes when exposed to degradation factors such as UV radiation, moisture,

temperature, and mechanical stress. The rates of change depend on the intensity

of the exposure and the synergism among the factors. An end result is that

changes occur which decrease the membrane's ability to perform its essential

function of keeping the roof watertight. For example, seams in membranes may

open. Characterization of bonded seams and identification of their failure

mechanisms is particularly important, since seams have been the source of

many premature failures of single-ply membranes [14]. A basic knowledge of

failure mechanisms which occur in the three classes of single-ply membranes

will greatly assist in improving performance through design guidelines, and

material design. Further, this knowledge will contribute to the development

of test methods and minimum levels of performance. It is important to note

that unacceptable performance may be due not only to poor resistance to the

service environment, but also to material flaws already present or introduced

at the time of installation.

Recommended Approach ;

* Develop hypotheses of failure modes based on an analysis of the data on failed (exposed) and control (unexposed) specimens.

® Characterize seam interfaces and identify modes of failures for bonded seams.

9 Characterize original and failed specimens mechanically, chemically, and

microstructurally to determine mechanisms of degradation and the extent of

changes which occurred during exposure.

® Characterize failed membranes in terras of failure patterns (for example,

tearing, puncturing, splitting) including shape, orientation, and density

of microcracks or microtears. -

9 Field expose membrane samples with seams to well-characterized service

environments in statistically-designed experiments.

• Expose samples having seams to accelerated environmental testing procedures

employing various realistic combinations of radiation, moisture, temperature,

and mechanical stress. The procedure described in ASTM E 632 will be

followed.

« Measure changes which occur and analyze data with respect to degradation

mechanisms and the rates of the degradation processes.

o Develop analytical relationships consistent with the degradation mechanisms

and the rates of degradation.

16
• Prepare report on research findings.

5.2.1.3 Objective 3—Methods for Characterizing Membrane Properties

Objective ; To develop methods for characterizing the important properties of

single-ply membrane materials and seams.

Comments : As mentioned, there are over ICQ products currently available in the

marketplace being promoted as useful for single-ply roof membranes. A first

step in setting forth technical information and data on the performance characteristics of these materials is to develop methods for characterizing the pertinent chemical, physical, and mechanical properties which are critical to the

performance of these materials under in-service conditions. Mathematical model

ing of system performance (section 5.1.2) could be used as a means of

identifying the important properties which should be measured.

Recommended Approach ;

• Identify those properties which are critical to the long-term performance of

single-ply membranes under service conditions. Develop mathematical models

describing performance under service conditions to identify those properties

required for acceptable performance.

• Develop, as necessary, techniques for measuring the mechanical, physical,

and chemical properties identified above.

• Prepare report describing test methods for characterizing the properties of

materials important to their performance in a roofing system.

• Submit draft standard test methods for characterizing single-ply membranes

and seams to standards-writing organizations such as ASTM.

5.2.1.4 Objective 4—Evaluation of Service Life

Objective ; To develop methods and measurement techniques to evaluate and

predict the service lives of single-ply roofing membranes and seams.

Comments : On-the-roof experience has suggested that failure at seams has been

a major problem with single-ply membranes. It must be remembered that the

roofing membrane is the waterproofing component of the roofing system. Therefore, in evaluating or predicting a membrane's service life, not only should

its material properties be included, but also integrity of the entire membrane

must be considered. To ensure this integrity over the service life of the roof

seams located where sheets overlap either in the field of the roof, or at the

perimeter and other projection flashings must remain watertight over the ser- vice life of the membrane. Therefore, test methods based on adhesion theory

should be developed to predict the field performance of seams as well as methods for the prediction of the durability of the materials themselves.

Obviously a roofing membrane should retain its critical properties above a certain level over the life of the roof. To predict service life, accelerated

17
weathering tests are required which realistically simulate exposure environments. The methodology given in ASTM E 632 should be followed in developing

the accelerated weathering tests. Figure 1 presents a flow chart of the

recommended procedures given in ASTM E 632 for developing predictive service

life tests. The test results could be used in demonstrating the application

of the reliability approach in making service-life predictions.

Recommended Approach ;

• Apply theories of adhesion of polymeric materials to understanding factors

controlling the performance of seams of single-ply membranes.

• Apply principles and procedures described in ASTM E 632 to service life

prediction of single-ply membranes including seams.

9 Modify existing test methods and develop new test methods as required for use in service life predictions.

« Identify or develop accelerated weathering apparatus and environmental

simulation chambers as needed for testing.

9 Conduct test program using selected samples with bonded seams of the three

classes of single-ply membrane materials.

9 Develop mathematical models based on the application of ASTM E 632 to

relate deterioration rates of membranes and seams to their properties.

9 Demonstrate the prediction of the service life of single-ply membranes and seams using statistically-designed experiments.

9 Prepare draft test methods on the prediction of membrane and seam service

life for submittal to ASTM and other standard and specification writing

groups.

5.2.1.5 Objective 5 —Minimum Levels of Performance

Objective : To develop methods for determining or calculating minimum levels of

performance for single-ply membranes and seams based on the roofing design.

Comments ; In the application of the performance concept to any building

material or system, a critical factor is the identification, in quantitative

terms, of minimum acceptable levels of performance. It would be desirable that one set of performance levels might suffice for all single-ply membranes and

all designs. Considering the demand imposed by different roof designs and

exposures, this does not appear to be possible. The type of membrane and

roofing design should be considered as well as its service environment and

the method of membrane application, i.e., loose-laid, fully adhered, or partially adhered. Next, the minimum performance levels of seams must be

identified. The minimum performance levels should apply not only to initial

performance, but to performance over the expected lifetime of the roof.

18
PART 1 - PROBLEM DEFINITION

Define 1n-use performance

requirements and criteria

Characterize the component or material r

Identify critical per- formance characteristics

and properties that can serve as degradation

indicators

Identify the expected type

and range of degradation

factors including those related to weathering,

biological, stress,

incompati bi 1 i ty and

use factors

Postulate how degradation

characteristic of in- use performance can be induced by accelerated

aging tests

Identify possible degra- dation mechanisms

Define performance

requirements for predictive service

life tests

PART 2 - PRE-TESTING

Design and perform preliminary accelerated aging

tests to demonstrate rapid failures caused by individ- ually applied extreme degra- dation factors and to con- firm degradation mechanisms

PART 3 TESTING

I Design and perform

predictive service

life tests using the degradation factors of importance to determine

the dependence of the

rate of degradation on exposure conditions

10 Design and perform long- term tests under service conditions J

Compare types of degra- dation obtained by both in-service and predictive

service life tests 7C 12 <

QUESTION: Are the changes

induced by predictive^

service life tests repre-" sentative of those observed in-service?

No

PART 4 - INTERPRETATION AND REPORTING OF DATA

13

14

15

16

Develop mathematical models of degradation

and compare rates of change in predictive service life tests with

those from in-service

tests

Establish performance cri- teria for predictive

service life tests

Predict service life under expected in- service conditions

Report

the data

Figure 1. Recommended procedure given in ASTM E 632 for developing

predictive service life tests

19
Recommended Approach;

• Determine the performance history under service conditions of the various

classes of single-ply membranes from literature and field surveys.

• Relate failure modes and mechanisms identified in section 5.1.3, (Objective

3) to performance history.

• Identify critical attributes and their relation to failure modes and field

performance history.

• Analyze the data obtained from the test method development objective

(Objective 4, section 5.2.1.4) by modeling and other methods to develop a basis for determining or calculating minimum performance levels.

© Review conclusions with experts in private and public sectors.

• Publish methods for determining or calculating minimum performance levels

for the various classes of membranes with seams, considering the methods of

attachment, the service environment, and roofing design.

5.2.2 Bituminous Built-Up Roofing Membranes

Goal . To advance the state-of-the-art of bituminous roofing membrane technology

by developing methods for determining minimum performance levels and developing

improved methods for evaluating and predicting the performance of these

membranes

.

Comments ; For over a century the multi-ply bituminous roofing membranes have

been used as the principal waterproofing component of low-sloped roofing systems

in the U.S. Traditionally, the composite membrane has consisted of two to five

plies of reinforcing felts or fabric adhered to each other on the job-site with

a thermoplastic bituminous adhesive. The felts or fabrics are composed of a variety of bituminous impregnated fibers such as cellulose, asbestos, fibrous

glass, and more recently, polymeric fibers. The adhesive is either petroleum

asphalt or coal-tar bitumen. These components of the membrane are described

in prescriptive material specifications promulgated by ASTM and others. However, until 1974, in spite of over a century of use required performance

properties of the bituminous roofing membranes had not been developed. In

1974, NBS published a research report [9] suggesting preliminary performance

criteria for bituminous membrane roofing. Although this document was regarded

as a major step in advancing the state-of-the-art of roofing technology, it was a preliminary effort to describe membrane roofing in performance language.

Specifically, many of the performance levels were empirically determined and

did not consider different roofing designs. The research proposed in this

section builds on the past research to update the performance criteria of

bituminous membrane roofing, and to provide a fundamental basis for developing

the minimum levels of performance.

In most cases, the problems with bituminous built-up roofing are well known

[15]. Examples of such problems include blistering, splitting, ridging,

20
slippage, and ply-delamination. Many of these problems are undoubtedly amenable

to technological solutions, once the technological knowledge can be translated

into practical guidelines, specifications and standards for implementation by

manufacturers, specifiers, and applicators. The impact of using a scientific

and technological basis to attain increased performance can be large, since

the forecast for use of these membranes through the mid-1980s is of the order

of 2 X 109 ft2 (0.2 X 109 m2) each year.

5.2.2.1 Objective 1 —Characterization of Built-Up Membranes

Objective : To develop the technical basis for characterizing bituminous

built-up roofing membranes and to characterize their failure mechanisms.

Comments ; Roofing membranes are intended to have service lives of 25 years or more. Although the majority of built-up membranes perform satisfactorily, premature failures are coimnon. To better understand the performance of these

membranes, methods are needed for their characterization. Information is also

needed on the factors contributing to premature failures and on failure mechanisms of built-up membranes. This information will be valuable in making

service-life predictions of built-up membranes and in understanding their

performance.

Recommended Approach ;

• Develop methods to characterize built-up membranes with regard to

interactions between the bitumen and reinforcing fabric, and determine modes

of deformation, degradation, and stress build-up.

• Based on modes of in-service failures of built-up membranes, develop

relationships between their failures, materials properties, and environmental

service stresses including, for example, the effect of moisture.

• Characterize failed membranes in terms of failure patterns (for example,

tearing, puncture, splitting) including shape, orientation, and density of

microcracks or microtears.

• Develop relationships between environmental and mechanical stress and the

fracture mechanics properties of built-up membranes using accelerated

weathering techniques.

• Develop analytical models relating the failures of membranes to their

composition and microstructure under in-service environments and mechanical

stresses. Test the models against laboratory data.

• Develop accelerated durability tests which produce the same failure

processes that occur in the field. Prepare draft standards incorporating

these accelerated durability tests and submit them to ASTM.

21
5.2.2.2 Objective 2—Mnlmum Levels of Performance

Objective ; To analyze existing minimum levels of performance for bituminous

built-up roofing membranes and develop methods for determining performance

levels needed in current and future roofing designs.

Comments : Twenty attributes which a built-up membrane should possess have

been identified. Test methods and minimum acceptable performance levels for

nine of these attributes have been proposed. Although there has been a considerable improvement in the performance of built-up membranes, premature failures

continue to occur at an unacceptably high rate. A need exists to reexamine and

possibly modify existing minimum levels of performance and test methods for

bituminous membrane roofing. Further relationships need to be developed to

determine minimum performance levels for specific roofing designs.

Recommended Approach :

• Obtain data and information (for example, NCRA's Project Pin Point and AEPIC)

on problems with built-up roof membranes.

9 Analyze the test methods and minimum performance levels given in the NBS

preliminary performance criteria [9] with respect to their applicability to

current and future bituminous membrane technology and roofing designs.

9 Using the above-listed data and information, combined with the results of

the mathematical models developed in section 5.2.2.1 (Objective 1), identify

additional attributes for which minimum levels of performance needed to be

determined.

9 Identify test methods, modify existing methods if necessary, or develop new

ones to characterize the important properties of built-up membranes not

included in the NBS preliminary performance criteria [9].

9 Develop relationships to assist in determining minimum performance levels

for specific designs.

9 Submit newly developed test methods to ASTM for consideration as standard

test methods.

5.2.2.3 Objective 3 —Characterization of New Materials

Objective : To develop methods for characterizing new materials used in the

fabrication of bituminous built-up membranes.

Comments : During the past decade a number of materials have entered the

built-up roofing marketplace as replacements for the traditional reinforcing

felts or fabrics. Fibrous glass technology has resulted in felts being produced by three different processes, one wet and two dry. New light-weight

polyester based reinforcements have been introduced that are described as having desirable properties conducive to improved roofing membrane performance.

Changes have also occurred with asphalt materials which are being modified

22
with elastomers to improve their performance in bituminous membrane roofing.

Methods for characterizing these new materials are needed.

In addition, the roofing industry has begun to recognize the limited

applicability of empirical consistency tests such as softening point, penetration, and ductility to describe the rheological properties of roofing bitumens.

The measurement of viscosity would provide an improved method of specifying

roofing asphalts. Viscosity is a rheological property describing a fluid's

resistance to flow. For roofing bitumens, viscosity not only pertains to flow

but reflects indirectly the adhesive characteristics. These characteristics

in turn have been related to bituminous roofing membrane failures such as splitting, blistering, and sliding. Reliable test methods for both laboratory

and field use are needed for measuring the rheological properties of roofing

bitumens at application and service temperatures.

Recommended Approach :

• Analyze available information on material properties, application

specifications, and in-service performance of membranes constructed from

the new materials to identify needs for test methods for their

characterization.

• Develop measurement techniques needed for characterizing new materials and

develop the technical bases for needed test methods for measuring the

performance properties of new materials.

• Perform accelerated weathering studies to compare the service-life of roofs

constructed with new materials with those of traditional materials. The

methodology given in ASTM E 632 should be followed.

• Develop test methods for both laboratory and field use for determining

asphalt viscosity at application and service temperatures.

• Develop the technical basis for a new ASTM specification for classifying

roofing asphalts using fundamental rheological properties as the performance

requirements in lieu of the empirical measures of flow characteristics now

used.

5.3 THERMAL INSULATION USED IN ROOFING SYSTEMS

Goal . To develop a technical basis for establishing minimum performance levels

for roofing insulation materials considering the thermal and mechanical

performance and design of insulated roofing systems.

Comments ; The total proportion of low-sloped roofs which have thermal

insulation as a component is about 80 percent. There are many types and thick- nesses of insulation available in the marketplace. They vary from the cellulosic fiberboard types to more thermally efficient materials such as the

polymeric foams. Their use is not limited to new roofing as a considerable

amount is employed in improving the thermal efficiencies of existing roofs.

These insulations, in board form, are used in conjunction with both the

23
multi-ply bituminous built-up membranes and with the single-ply membranes.

In addition, polyurethane foam insulation is applied as a component of a sprayed-in-place roofing system.

The insulations perform their major function of restricting heat flow in or out

of the building as long as they remain in a relatively dry condition. Moisture

accumulation in insulations is not the only manner by which insulations may

adversely affect roofing performance. Insulations can affect the level and

distribution of stresses in the roofing membrane. This, in turn, may shorten

membrane life or cause early failure if the system is designed improperly or applied incorrectly. The problems associated with insulated roofing systems

are well known [16] and the impact of these problems in terms of wasted energy

and premature failure of roofing systems are recognized by the roofing industry.

However, neither the mechanisms of failure nor the relation of insulation

properties to the observed problems have been adequately studied. The identification of failure mechanisms and the characterization of the important

properties of insulations are necessary for determining the influence of

thermal insulations on the roof system performance. Further, methods need to

be developed to assist in determining the minimum performance levels of

thermal insulation for specific roof designs.

5.3.1 Objective 1 —Characterization of Insulation Properties

Objective : To develop measurement techniques for characterizing the important

properties of roof insulation materials.

Comments ; Some of the insulation types which are currently available include:

1) fiberboard, 2) perlite, 3) fibrous glass, 4) foam glass, 5) polyurethane

foam, 6) expanded and extruded polystyrene, and 7) phenolic foams. Also, two or more of these materials are often laminated into what is referred to as com- posite board insulations. To understand and predict their performance both

thermally and mechanically, important properties must be characterized. This

objective is not only concerned with the identification and measurement of the

initial properties of insulation materials but also with the changes which

occur upon aging under service conditions.

Recommended Approach :

• Identify the important properties of thermal insulations which control their

performance and durability in roofing applications. They may be identified,

in part, based on the results from solving mathematical models for roofing

systems (section 5.1).

• Develop measurement techniques needed for characterizing the important

properties of thermal insulation, and the effect of moisture migration

through the roofing system on the insulation properties.

• Develop accelerated aging test methods and use them to determine the effects

of aging on the properties of the insulations including durability,

mechanical and thermal properties, and fire resistance.

24
• Prepare research reports on the methods for characterization of roof

insulation materials and submit the methods to ASTM for possible inclusion

in insulation standards.

5.3.2 Objective 2 —Minimum Levels of Performance

Objective : To develop the technical basis for establishing minimum levels of

performance for roof insulation materials based on roofing design.

Comments ; In spite of over 70 years use of thermal insulations in low-sloped

roof ing sys tems , insulation materials are specified only by prescriptive specifications. With the exception of thermal transmittance , performance levels are not given nor has a technical basis been developed for determining

performance levels based on roofing design.

Recommended Approach ;

• Analyze field performance data and information regarding roof failures

attributed in full or in part to roofing insulations; identify their major

properties and aging characteristics that play a role in failure processes.

o Develop accelerated durability tests which simulate failure mechanisms

occurring in service, and which would provide the basis for making realistic

service life predictions and assist in determining minimum levels of

performance.

• Develop relationships to assist in determining mimimum performance levels

for thermal insulation based on roof design.

• Prepare a report on methods for determining minimum performance levels

based on design.

5.3.3 Objective 3—Sprayed-in-Place Foam Insulation Roofing Systems

Objective ; To develop the technical basis for the development of test methods

for determining minimum levels of performance for sprayed-in-place foam

insulation roofing systems.

Comments : Sprayed-in-place polyurethane foam (SPUF) roofing systems have been

used for over 15 years as an alternative to the more traditional types of roofing systems used on low-sloped or sloping decks. The systems consist of a layer

of polyurethane foam insulation sprayed on a suitable substrate. A protective

coating (liquid-applied) is applied to the foam to provide weatherproof ing.

In 1973, NBS published suggested guidelines for the selection and use of these

systems [17]. A set of preliminary minimum levels of performance together

with appropriate test methods were also provided to identify acceptable

materials. Performance attributes for sprayed-in-place foam insulation roofing

included fire safety, wind resistance, water resistance, stress resistance,

impact resistance, dimensional stability, and coating durability. Over the

past decade, significant advances in the technology of polyurethane foam roofing

25
systems have occurred. Further, considerable research concerning system

performance and the protective coatings has been conducted by several laboratories. The results of these research activities should provide the starting

point for the determination of minimum levels of performance. It is anticipated

that industry associations such as the Urethane Foam Contractors Association

(UFCA) could provide information concerning performance and mechanisms of

failure in service. Minimum performance levels should consider the possibility

of the development of sprayed-in-place roofing systems incorporating insulation

other than polyurethane.

Recommended Approach ;

o Analyze existing information including the previously suggested minimum

performance levels and the results of previously conducted research as the

basis for determining revised levels of performance.

• Develop, as needed, measurement techniques for characterizing

sprayed-in-place polyurethane foam roofing systems.

o Identify and conduct laboratory and field research needed to provide

information necessary for the determination of minimum levels of performance.

• Develop accelerated aging procedures (using the practice given in ASTM E 632)

to predict the service life of protective coatings used in these systems.

9 Prepare a draft document containing minimum levels of performance and submit

it to ASTM for consideration as a standard for sprayed-in-place polyurethane

foam roofing systems.

5.4 CONDITION ASSESSMENT AND REPAIR OF ROOFS

Goal ; To develop a technical basis for roof condition assessment and for the

evaluation of repair techniques.

Comments : Determination of the condition of roofing materials and systems is

needed to make decisions on the need for repair, the type and extent of needed

repairs, and whether the roof should be replaced. Condition assessment of

roofs is based largely on visual inspections, which give little information on

the sub-surface condition of the roof. Further, it is difficult to locate

leaks in a membrane by visual examination. The increased use of non-destructive

evaluation (NDE) techniques should greatly improve the information obtained in

roofing inspections. A technical base, however, needs to be developed for

facilitating the interpretation of the results of NDE inspections.

Roofing repairs most often involve the membrane. Several years ago, guidelines

were prepared for the repair of built-up membranes [18]. However, significant

advances have since been made in materials which should be incorporated into

the guidelines. In addition, the repair of single-ply membranes needs to be

addressed. Guidelines for effective repairs should be based on an understanding

of the failure mechanisms and on the factors controlling the performance of

repair materials.

26
In the following two objectives, single-ply membranes and built-up membranes

are considered separately. It is anticipated that different methods will be

needed for repairing the various types of single-ply sheets and seams and

built-up membranes.

5.4.1 Objective 1 —Condition of Single-Ply Roofing Systems

Objective: To develop measurement techniques and guidelines for the diagnosis

of problems involving single-ply membranes and for evaluating maintenance and

repair methods applicable to these membranes and systems.

Comments ; As previously discussed, a wide variety of polymeric materials are being used for single-ply roofing membranes. Typically, roofing is exposed to

the most severe environment of any major building component and, consequently,

the roof usually requires a considerable amount of maintenance and repair.

Because many of the newer single-ply materials have had limited service histories , maintenance and repair techniques for these materials have not been

adequately developed. Maintenance and repair techniques suitable for bituminous

built-up membranes may not be applicable to single-ply membranes, and different

techniques may be needed for various types of single-ply membranes.

With millions of square feet of these materials being applied each year, already

applied, or to be applied, a great need exists to develop measurement techniques

for problem identification as well as for guidelines covering the maintenance

and repair of roofs. A technological basis needs to be developed to insure

that corrective measures perform as intended and do not cause additional

problems. Techniques also need to be developed for evaluating proposed and

existing maintenance and repair methods.

Recommended Approach ;

• Analyze diagnostic procedures including NDE techniques used for conventional

roofing to determine whether they apply to single-ply membranes, and develop

the technical basis for the selection, use, and interpretation of NDE methods

for the inspection single-ply membranes.

• Develop improved NDE methodologies, if needed, for evaluating the condition

of single-ply membranes.

o Develop measurement techniques to evaluate the effectiveness of methods for

repairing membrane problems such as splits, tears, and punctures.

• Develop NDE techniques to determine the quality of seams in single-ply

membranes.

a Develop the technical basis for guidelines covering the maintenance and

repair of single-ply membranes.

27
5.4.2 Objective 2—Condition of Built-Up Roofing Systems

Objective ; To develop the technical basis for guidelines for non-destructive

evaluations of the condition of weathered in-place built-up roofing membranes

and systems and for making repairs.

Comments : Each year in the United States about 1.5 x 10^ ft^ (0.14 x 10^ m^)

of low-sloped roofing are replaced or recovered. Since these are generally

older roofs, it may be assumed that most have built-up membranes. Proper and

routine maintenance and repair procedures could extend the life of a significant number of these roofs for many years with significant savings. In some

cases, the old roofing may be replaced needlessly. In others, old roofing is

left in place when it should have been removed. It is often covered with a new membrane which may fail prematurely because of inherent deficiencies in

the old roofing. The building owner, faced by major decisions with large

economic consequences, has little information on which the decision may be

based. Even an expert must often make decisions on the basis of assumptions

which are questionable.

There is a need to analyze existing data to determine the effectiveness of

conventional repair techniques. Where warranted, new data and methods should

be developed to assist the decision maker in deciding what procedures should

be followed to extend the life of the roofing system.

Recommended Approach ;

• Analyze the effectiveness of diagnostic procedures which are currently used

to ascertain the condition of weathered built-up roof membranes and systems.

These procedures include those for field visual examinations, as well as those for destructive and non-destructive methods of evaluation.

• Analyze laboratory testing techniques used to evaluate weathered membranes

and, if necessary, develop improved measurement techniques.

• Conduct an experimental laboratory study which simulates the conditions that occur when a weathered membrane is covered with a new membrane to examine

the effectiveness of this reroofing technique.

• Investigate the feasibility of using destructive and non-destructive

techniques for the evaluation of weathered membranes under simulated and

in-service conditions.

9 Develop the technical basis for reliably predicting the remaining service

life of bituminous membranes.

9 Develop test methods for evaluating the performance of repair techniques and

materials.

28
6. RESEARCH SCHEME AND CONCLUDING REMARKS

This report presents a research plan for low-sloped roofing materials and

systems. The proposed research is divided into four major areas: low-sloped

roofing systems, roofing membranes (single-ply and bituminous built-up), thermal

insulation for roofing systems, and condition assessment and repair of roofs.

The intent of the plan is to establish the technical bases for developing

standards and performance levels which may assist in the selection of costeffective and durable roofing materials and systems. The plan is broad and

many years may be needed to achieve the goals and objectives proposed, even with

collaboration among all segments of the roofing community. Figure 2 outlines a possible flow scheme for conducting of the proposed research, and shows

the relations between proposed major activities and goals for the four major

research areas. The time frame for the accomplishment of the goals and objectives will, of course, be dependent upon the available resources including

personnel, funds, and facilities including equipment.

As evident from figure 2, research on low-sloped roofing systems and membranes

including both single-ply and built-up bituminous is given highest priority.

There is a co-dependence of the research activities in these two areas. For

example, the development of models can facilitate in the development of standards for membranes because modeling provides means for identifying important

membrane performance properties and determining minimum levels of performance.

Values of materials properties of well-characterized membranes are needed for

performing modeling computations. In addition, to have credibility, models

must be validated by comparing theoretical or predicted results with experimental data. The research on low-sloped roofing systems and membranes would

be expected to extend a number of years, culminating in the development of a technical basis for making realistic predictions of the performance and service

lives of roofing materials and systems.

Research on thermal insulations is planned to begin later than that for roofing

systems and membranes. It is believed that, unless sufficient resources were available, the magnitude of the proposed research in the plan will not allow

an earlier starting time for the thermal insulation research. Nevertheless,

as indicated in figure 2, values of some material properties of thermal insulations will need to be determined for the development of mathematical models on roofing systems. Research on condition assessment and repair is also planned

to begin later than that for roofing systems and membranes. This research is

not strongly linked with the other activities and could be started earlier if resources were available.

29
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30
7. REFERENCES

1. Transactions of the Federal Construction Council for 1980-81, "Summary of

a Workshop on Low-Slope Roofing," Federal Construction Council, Advisory

Board on the Built Environment, Chapter 6, pp. 65-71.

2. The National Program Flan for the Thermal Performance of Building Envelope

Systems and Materials, Oak Ridge National Laboratory, ORNL/Sub-7973/1

,

March 1982, pp. 37-39.

3. Busching, H. W. , Mathey, R. G. , Rossiter, Jr., W. J., and Cullen, W. C.

,

"Effects of Moisture in Built-Up Roofing—A State-of-the-Art Literature

Survey," NBS Technical Note 965, July 1978, p. 2.

4. Appelhans, P., "Litigation Center Growth Continues," The Roofing Spec,

March 1980, p. 40.

5. The Roofing Spec, May 1982, p. 32.

6. The Roofing Spec, June 1982, pp. 32-39.

7. The Roofing Spec, May 1982, pp. 32-33.

8. The Roofing Spec, July 1981, p. 35.

9. Mathey, R. G. and Cullen, W. C, "Preliminary Performance Criteria for

Bituminous Membrane Roofing," NBS Building Science Series 55, November

1974, 12 pages.

10. Rossiter, Jr., W. J. and Mathey, R. G. , "Elastomeric Roofing: A Survey,"

NBS Technical Note 972, July 1978, 54 pages.

11. Griffin, C. W. , "Manual of Built-Up Roofing Systems," 2nd edition,

McGraw-Hill, New York, 1982, pp. 7-18.

12. Proceedings of the DoE-OBlNL Workshop on Mathematical Modeling of Roofs,

CONF-811179, Oak Ridge National Laboratory, 1981. 362 pages.

13. Abel, J. F. , McGuire, W. , and Ingraffea, A. R., "In the Vanguard of

Structural Engineering," Engineering: Cornell Quarterly, Winter 1980-

1981, pp. 23-36.

14. The Roofing Spec, May 1982, p. 30.

15. Griffin, C. W. , op. cit., pp. 279-335.

16. Ibid., pp. 53-93.

17. Cullen, W. C. and Rossiter, Jr., W. J., "Guidelines for Selection of

and Use of Foam Polyurethane Roofing Systems," NBS Technical Note 778,

May 1973, pp. 33-37.

31

^
"Maintenance and Repair of Roofs," Departments of the Airmy, the Navy, the

Air Force, and the Marine Corps, Hi 5-167, NVFAC MO-113, AFM 91-31, and

MCO P11014.9, Washington, D.C., 1974, 116 pages.

32
NBS-114A iREv. 2-8C) U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

NBS SP 659

2. Performing Organ. Report No. 3. Publication Date July 1983

4. TITLE AND SUBTITLE

Low- Sloped Roofing Research Plan

5. AUTHOR(S)

William C. Cullen, Walter J. Rossiter, Jr., Robert G. Mathey, James R. Clifton

6. PERFORMING ORGANIZATION (If joint or other than NBS. see instructions) 7. Contract/Grant No. NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE 8. Type of Report & Period Covered

WASHINGTON, D.C. 20234 Final

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State, ZIP)

10. SUPPLEMENTARY NOTES

Library of Congress Catalog Card Number 83-600551

I I Document describes a computer program; SF-185, FlPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bi bliography or literature survey, mention it here)

This feport presents a long-range plan for roofing research. The plan was

developed in response to a need for roofing research addressing major materials

problems and changes in low-sloped roofing materials technology. The intent of

the plan is to establish the technical basis for developing standards and minimum levels of performance to assist in the selection of cost-effective and

durable roofing materials. Four major areas of needed research are identified:

(1) low-sloped roofing systems, (2) roofing membranes including single-ply and

built-up, (3) thermal insulation for roofing systems, and (A) condition assessment and repair of roofs. Within each research area, a goal is given as well

as a number of objectives to achieve the goal. A recommended approach to

accomplish each objective is also given.

12. KEY WORDS fSix tc twelve entries; alphabeiica! order; capitalize only proper names; anc seporate key words by semicoions;

Low^sloped roofing; mathematical modeling; membranes; repair;

research plan; roofs; standards; thermal insulations.

13. AVAILABILITY

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'

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XX Order Frorr SuDermtendent of Documents, U.S. Governmer.i Printing Office, Vvashmgion, D.C. 20402.

[ Order From National Technical Information Service (NTiS), Springfield, VA. 2216 I

14. NO. OF

PRINTED PAGES

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