NATIONAL BUREAU OF STANDARDS REPORT

6966

REPORT ON THE PERFORMANCE OF GLASS FIBER BASE BUILT-UP ROOFS

by

William C. Cullen

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U. S. DEPARTMENT QF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

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NATIONAL BUREAU OF STANDARDS REPORT

NIBS PROJECT MBS REPORT

1004-40-10441 30 September 1960 6966

REPORT ON THE PERFORMANCE OF GLASS FIBER BASE BUILT-UP ROOFS

by

William C. Cullen

Organic Building Materials Section

Building Research Division

Sponsored by

Office of the Chief of Engineers

Department of the Air Force

Bureau of Yards and Docks

NATIONAL BUREAU OF STANDAF

intended for use within the Govern

to additional evaluation and review,

listing of this Report, either in whol

the Office of the Director, National however, by the Government agency

to reproduce additional copies for its

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

own use.

accounting documents

ublished it is subjected

ction, or open-literature

ibtained In writing from

?rmission is not needed,

d if that agency wishes

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

REPORT ON THE PERFORMANCE OF GLASS FIBER-BASE BUILT-UP ROOFS

1 . INTRODUCTION

Asphalt built-up roofing has been used for over 30 years as a covering

for roofs of low slope. This type of roofing can be applied to both nailable and non-nailable decks and consists of alternate layers of asphalt

and a reinforcing medium. The reinforcing medium most commonly used is

a 15-pound asphalt-saturated organic base felt, although, in some cases,

an asphalt-saturated asbestos felt is employed. Other materials have

been proposed for use as the reinforcing medium from time to time and some

of these have been used to replace the conventional felts in a built-up

roof. Aluminum foil, burlap cotton fabric, and glass membranes in various

forms are among the materials which have been used or suggested for use. Asphalt-saturated glass fiber roofing felt, which is probably the most common in use next to the organic and asbestos felts, has been employed

as a roofing felt for approximately 10 years. This felt is described by

Interim Federal Specification SS-R-00620, "Roofing Felt, Glass, Fiber,

Asphalt-Saturated, Uncoated".

The various construction agencies of the United States Government

became interested in this concept of built-up roofing and, in fact, many

have accepted it for use on a ply-for-ply basis with the conventional

organic base felt roof. As a result of this interest, the National Bureau

of Standards was requested to study the performance of glass base built-up

roofs as part of the Tri-Service Building Materials Investigations Program

sponsored by the Office of the Chief of Engineers, U. S. Army; the Bureau

of Yards and Docks, U. S. Navy; and the Office of Civil Engineering, U.S.

Air Force.

This report gives the results of field studies of 33 glass fiber-base

built-up roofs carried out in 1956 and in 1960. The field studies included

roof inspections in 15 cities located in 8 states. In addition, the

results of a limited laboratory investigation as well as the results of

a letter survey are included.

Sections 2 and 3 of this report state the conclusions and suggestions,

respectively, which have been drawn from the study, while Appendices I,

II, and III describe in detail the respective phases of the study.
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2.

SUMMARY AND CONCLUSIONS

2 . 1 Field Studies

1. Generally the examinations made of 33 glass fiber-base built-up

roofs up to 6-1/2 years of age indicated that good performance was obtained

from this type of roof.

2. No correlation was established between the observed performance

of the roof and the number of plies of felt in the membrane. This con- clusion was anticipated prior to the study, due to the relatively short

term exposure of glass fiber-base roofs.

3. There was no evidence that blistering or buckling of the felts

had taken place on the roofs examined. This condition indicated the

excellent adhesion between the asphalt and the glass felts and the non- hydroscopic nature of the glass felt.

4. The field survey indicated that the performance of glass-base

built-up roofs in the Eastern United States was approximately equal to

their performance in the Western United States where they have a longer

history.

5. Mineral-surfaced roofs (gravel or slag) appeared to give better

service than their non-surfaced counterparts.

6. Adequate service was obtained on roofs with slopes from dead-level

up to about 5 in. per foot.

7. It is our strong opinion that good service from a given built-up

roof depends more on the initial workmanship and subsequent maintenance

than on the materials which are used. This conclusion is not entirely

a product of this investigat ion, but is based, rather, on considerable

field experience.

2.2 Laboratory Studies

2.2.1 Examination of Specimens Gut Out from Actual Roofs -

1 . The age of the roofs from which the cut-outs were taken varied

from those under construction up to 6-1/2 years old.

2. Frequently, the number of plies determined in the laboratory

analysis was either more or less than reported to the observer in the

field survey. Of the eight cut-out specimens, two were 2-ply, three were 3-ply, two were 4-ply, and one was 5-ply.

3. The average weight of the asphalt per mopping was, with two ex- ceptions, less than the 30 pounds per 100 sq. ft. generally specified for

this type of roofing. Of the seven specimens examined, three had 15 pounds

or less per mopping, two had 20 to 25 pounds, and the remaining two had

30 and 47 pounds, respectively.

4. The analysis of the specimens indicated two types of binder were

employed in the manufacture of the glass felt depending on the age of the

roof. The glass felt using the phenolic binder (most recent specimens)

appeared to be of higher strength than those extracted from the older

roofs and consequently in better condition.

5. No correlation could be established between the tensile breaking

strength and elongation and the number of plies, the weight of bitumen

between plies, and the age of the roof from which the specimen was taken.

6. Excellent adhesion between the glass felt and the asphalt was evident on all 8 specimens confirming the observations made during the

field survey about the lack of blistering and buckling.

2.2.2 Laboratory Tests -

1. The built-up roof specimens prepared with glass-base felts in

the laboratory appeared to be more resistant in both the accelerated

weathering tests and the outdoor exposure test than those prepared with

asphalt-saturated organic-base felts.

2. Specimens of glass felt and built-up membranes prepared with

glass felt indicated less tendency to absorb and retain moisture than

their counterparts prepared with organic-base felts.

3. Conventional felts and built-up membranes constructed with

these felts exhibited greater tensile strength than the glass felt

specimens. However, in regard to the elongation properties, the glass

specimens performed slightly better.

2.3 General Conclusions

From the results of the laboratory tests, the replies of the letter

survey and the observed behavior of some 33 roofs in the field, it can be

concluded that glass-base felt built-up roofs will provide at least equal

service as those constructed with organic-base felts, provided that the

materials meet applicable specifications as to quality and quantity and,

most important, that the workmanship is in accordance with good roofing

practice

.
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.

.
4

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3. SUGGESTIONS

In the event that built-up roofs constructed with glass-base felts

are accepted for use, the following suggestions are offered as a guide to

insure that quality roofs are obtained. The suggestions are based not

only on the information obtained during this investigation, but also on considerable field experience.

1 . The built-up roof constructed with glass-base felts should be

specified on the basis of either one or both of the following:

(a) A ply-for-ply basis with the conventional organic base felt

roof requiring not less than 25 pounds of asphalt per 100

sq. ft. of roof area between each layer of felt.

(b) The total amount of bitumen (mopping + surfacing asphalt)

should be equal to or greater than that required for a com- parable organic base felt roof now specified. The amount

of asphalt between the layers of felt should in any case be

not less than 25 pounds per 100 sq. ft. of roof area.

2. A membrane of not less than 3 plies of felt should be specified,

i.e., not less than two moppings of bitumen in addition to the surfacing

asphalt

.

3.

A requirement be provided to make mandatory the faking of cutouts in order to insure that provisions described in 1 and 2 above are carried out.

4. ACKNOWLEDGMENT

The author acknowledges the assistance, counsel, and guidance provided

by Dr. H. R. Snoke, former Chief of the Organic Building Materials Section,

Building Research Division, National Bureau of Standards, in this study.

The assistance of the Owens-Corning Fiberglas Corporation in furnishing

the lists of roofs of known history and in making the inspections is also

acknowledged

.

5

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APPENDIX I.

FIELD SURVEY

1 . INTRODUCTION

The purpose of the field survey was to evaluate the performance

characteristics of built-up roofs constructed with glass fiber base

felts in lieu of the conventional organic or asbestos base felts. It was realized, of course, that many factors other than the type of reinforcing membrane must be considered in evaluating the performance of a built-up roof and that serious failures may occur that axe in no way

related to the type and character of the base felt employed. For example,

it is our opinion that more premature roof failures are caused by faulty

workmanship than by inferior materials going into the roof. Proper and

timely maintenance is also of great importance in determining the service

of any built-up roof.

Built-up roofs constructed with glass fiber felts have been under

observation by personnel of National Bureau of Standards since 1956. In

August of that year, in connection with another project on built-up

roofing, 10 fiber glass roofs were inspected on the West Coast. In addition, annual inspections have been conducted on built-up roofs in the

Baltimore, Maryland, and Washington, D. C. areas since 1956. In 1960, at

the request of agencies of the Defense Department, additional roofs were

inspected throughout the country, including a reexamination of some of the

roofs observed in 1956.

Since the observations and conclusions drawn from the field survey

are based on the behavior of the roofs inspected, it should be stressed

that all of the roofs examined were less than 7 years of age. One roof

(Zellerbock Paper Co., Seattle, Washington) was reported to be 9 years

old when it was inspected in 1956. However, it was also reported that

this roof was not applied with the materials or by the method now

recommended by the manufacturer.

2. SELECTION AND INSPECTION OF ROOFS

In order to obtain glass base built-up roofs of known history for the

inspections during the field survey, it was necessary to rely upon a manufacturer of this type of roofing material. In 1956, in compliance with a National Bureau of Standards request, the Owens -Corning Fiberglas Corporation

submitted a list of 63 roofs located in 5 West Coast states 0 In 1959,

again at the request of this Bureau, the same manufacturer supplied a number of lists of built-up roofs located in various areas throughout the

country. The actual roofs to be inspected were selected by lot from these

lists

.
,

*

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6

All roof inspections were made in company with representatives of

the manufacturer and frequently with the owner or manager of the building.

In order to secure the greatest possible uniformity in the roof

inspections, a check list was developed and used during the examination

of each roof. This check list included a history of the roof, as well

as the elements which are important in the performance of a built-up

roof. A copy of this check list is presented in Figure 1.

In order to obtain the maximum information about a given built-up

roof, permission was asked and granted to remove a 24-in. by 12-in.

cut-out specimen from one out of each four roofs examined. The roofs

from which the cut-out specimens were taken were also selected by lot

prior to the inspections in the area. The areas from, which the cut-out

was made was selected by the National Bureau of Standards observer. Figure

2 shows the removal of a cut-out specimen, while Figure 3 shows the roof

area after the specimen was removed. The specimens were shipped to the

National Bureau of Standards for analysis and the results of the laboratory

examinations of these specimens are reported in Appendix II.

3. .AREAS INCLUDED IN THE FIELD STUDY

Critical inspections were made on approximately 33 roofs in 15

cities located in 3 States and the District of Columbia. The areas and

the number of roofs examined in each area are shown in Table 1

.

TABLE 1. Areas Where Roof Inspections Were Made

Area No. of Inspections

1

.

Seattle, Washington 3

2. Tacoma, Washington 1 3. San Francisco, California 2 4. Los Angeles, California 5 5. Phoenix, Arizona 2

6. Albuquerque, New Mexico 1 7. Edwards Air Force Base, California 2

8. Richmond -Nor folk, Virginia 5 9. Baltimore, Maryland 2 10. Washington, D. C. 5

11. Hagerstown, Maryland 1 12. Martinsburg, West Virginia 1 13. Greencastle, Pennsylvania 1 14. Philadelphia, Pennsylvania 2

FIGURE 1 . ROOF INSPECTION CHECK LIST

1

.

Building 2. Location

3. Year applied 4. Manuf. & Spec.

5. Deck 6. Slope

7. Insulation 8. Surfacing

9. Bonded 10. Roof area

1 1 . Other remarks

GENERAL

1 . Appearance 2. Water tightness

3. Repaired areas 4. Other

FELTS

1 . Blisters 2. Cracks

3. Fi smooths 4. Buckled

5. Edges curled 6

.

De laminations

7. Condition of exposed felts

8. Condition at flashings

9. Condition at bends

10. Other observations

BITUMEN

1

2

3

4

5

6

Top pouring or surfacing _____ Between plies ___________

Water standing or dry ______

Alligatoring, cracking, etc.

Water-soluble products

Condition

7 Other observations

FIGURE 2. REMOVAL OF A CUT-OUT SPECIMEN.

FIGURE 3. AFTER REMOVAL OF SPECIMEN

- 7

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4.

OBSERVATIONS

The roofs selected for examination were applied to many types of

roof decks on slopes ranging from dead-level up to 5 inches per foot.

Smooth roofs as well as those protected with several types of mineral

surfacing were also examined. In addition, the inspections included

roof coverings on both insulated and non-insulated decks. The following

types of decks were representative of those on which glass fiber built-up

roofings were applied:

1 . Insulated steel

2. Sheet rock

3. Gypsum, poured and precast

4. Concrete, insulated and non-insulated

5. Wood

6. Corrugated galvanized.

The performance of the glass-base built-up roofs on each of the above

decks appeared to be satisfactory with one exception. The roof applied

directly to the corrugated metal deck on a roof in the Los Angeles area

was in poor condition as shown in Figure 4. The application of any

type of built-up roof directly to a corrugated metal deck is, of course,

not in accordance with good roofing practice and is to be condemned.

It is significant that blistering or separation between the plies of

the glass-base built-up roofs was not detected in a single instance. In

addition, the absence of wrinkling or buckling of the glass felts even

after direct exposure to the weather for a week or more was noted. In a few cases, fishmouthing was observed along the edge of the felts as shown

in Figure 5. However, it is felt that this deficiency is not inherently

present in the felt, but rather in the quality of the workmanship.

In still other cases, defects such as alligatoring, cracking,

excessive flow of bitumen, etc., were observed in the surfacing asphalt

as shown in Figures 6, 7, and 8. These defects, of course, are not

significant in relation to the performance of the reinforcing medium.

Actual cracking of the glass felt was observed on one roof, as shown

in Figure 9. However, a similar type failure was also observed on an asphalt-saturated, asbestos-felt roof on an adjacent bay on the same roof.

The reinspection of the roofs after periods of up to 4 years exposure

revealed no apparent change other than may normally be expected in any

built-up roof. This observation was not unexpected, sin't!rtt the proponents

of this system claim a life of 20 years and unless a roof is failing

prematurely, no significant change should occur after such a relatively

short period of exposure.
’* '

'
FIGURE 4 BUILT-UP ROOF APPLIED TO CORRUGATED METAL DECK

FIGURE 5. FISHMOUTH ON A SMOOTH, BUILT-UP ROOF



8

Concerning the merits of the one ply less approach for glass fiber

base built-up roofs, it was not possible to correlate the expected

durability of a given roof with the number of plies of the reinforcing

medium, although roofs of 2, 3, 4, and even 5 plies were observed. For

example, one roof which appeared to be in excellent condition after 6

years exposure proved to be only a 2-ply membrane, while other roofs of

the same age were in poor condition and were reported to be of 3-ply

construction.

The observations made during this study confirmed the conclusions

drawn from previous roof surveys that four major factors determine the

useful life of any built-up roof. They are: 1) well designed and well

constructed roof deck; 2) good quality of roofing materials; 3) adequate maintenance; and 4) good workmanship during application. Not the

least of these is good workmanship.

A rating was assigned to each roof on the completion of the inspection. The rating was based on the overall appearance, the defects which

were noted, and adequacy of service reported by owner. The ratings were

as follows:

A number of roofs were not rated as they were new or under construc5. RATINGS

Good

Fair

Poor

Excellent 3

17

3

2

tion.

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APPENDIX II.

LABORATORY STUDY

1

.

INTRODUCTION

A limited laboratory investigation was carried out to supplement the

information obtained during the field survey. Some of the physical

characteristics of the glass-base felts as well as of built-up specimens

prepared with these felts were compared with the characteristics of

similar specimens prepared with the conventional organic-base felt. The

specimens were prepared in the laboratory and subjected to the following

tests :

1 . Accelerated Weathering

2. Outdoor Exposure

3. Water Absorption

4. Tensile Strength and Elongation.

In addition, the specimens which were cut out of the actual roofs

during the field survey were examined in the laboratory to determine

their composition and physical characteristics.

2. LABORATORY TESTS

2.1 Accelerated Weathering

Duplicate specimens, 6-in. by 2-3/4-in., of 3-ply glass-base and 3-ply

organic-base built-up roofs were prepared in the laboratory and exposed in

a carbon arc type accelerated weathering apparatus for 500 hours. This

test was carried out in accordance with ASTM Designation: E42-57, Type A.

There was no apparent change noted in the specimens prepared with the

glass-base felt after 500 hours exposure. However, the organic-base felt

specimens indicated a separation as large as 1/8 in. along each edge between the first and second plies of felt. The results of this test indicated the specimens prepared with the glass-fiber felts were more stable

under the conditions of test than those prepared with the conventional

felts

.
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,* .

\
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2.2 Outdoor Exposure

Specimens of both types of felt, as well as built-up specimens which

were prepared in the laboratory, were exposed outdoors on the roof of the

Industrial Building, National Bureau of Standards. The 5- by 5-in. speci- mens were exposed on a dead-level deck during July and August 1960.

The effect of the outdoor exposure on the specimens was similar to

that observed in the simulated service test described in Section 2.2

above. The specimens prepared with the organic felts appeared to be

less stable than the glass-fiber specimens and a separation between the

plies of these specimens was also observed after a few weeks exposure.

2.3 Water Absorption

The water-absorption tests were conducted on specimens of both types

of felts as well as on built-up specimens prepared with both the glassfiber and organic-base felts. The tests were conducted in accordance with

ASTM Designation: D57Q-57T. for a period of 120 hours.

The results of the tests are reported in Table 2 and are expressed

in grams of water absorbed and percent of water absorbed in relation to

the dry weight of the specimens after 120 hours immersion.

2.4

Tensile Properties

The tensile properties of built-up specimens prepared in the

laboratory were determined essentially in accordance with the method

described in ASTM Designation: D638-58T. Specifically, the specimens were tested on an Instron Testing Machine with an initial jaw separation

of 4 inches. The results of the tensile tests expressed in pounds of

force required to rupture the specimen and the percentage elongation of

the sample prior to rupture are reported in Table 3.

3. RESULTS OF LABORATORY EXAMINATION OF ACTUAL

ROOF SPECIMENS

The cut-out samples of the actual roofs obtained during the field

survey were examined in the laboratory to determine the character of the

specimen as well as the number of plies of felt in the reinforcing mem- brane and the approximate weight of bitumen used as the adhesive between

the plies of felt. The information which was obtained in the laboratory

analysis, together with the name, location, and reported age of the roof

from which the sample was taken are reported in Table 4.
•

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TABLE 2. Results of Water-Absorption Tests.

Specimen

Dry

Weight

Water

Absorbed

Water

Absorbed

grams grams percent

Glass felt; asphalt-saturated 1.172 0.126 10.8

Organic felt, asphalt-saturated 2.176 0.954 43.8

Built-up, 3-ply glass 13.047 0.240 1.8

Built-up, 4-ply glass 14.691 0.239 1.6

Built-up, 3-ply organic 14.966 1.685 11.3

Built-up, 4-ply organic 17.946 2.040 11.4

TABLE 3. Results of Tensile Tests

Specimen Breaking Strength Elongation

lbs percent

Built-up, 3-ply glass 47 5.0

Built-up, 4-ply glass 91 8.3

Built-up, 3-ply organic 175 5.0

Built-up, 4-ply organic 194 3.3

12

TABLE 4. Results of Examination of Cut-Out Specimens.

Name of Structure Location Age

No. of

Plies

Average Weight

of Asphalt

Between Plies

lbs/ 100 ft 2

Rocket Storage Shed Andrews AFB, Md. 1 4 25

Corning Glass Martinsburg, W. Va. * 3 47

Robertshaw Fulton Los Angeles, Calif. 6 2 L20

Standard Oil El Segundo, Calif. 2 2

Housing Edwards AFB, Calif. 1 4 LI 5

Firestone Store Phoenix, Ariz. 6 3 LI 5

Roach and Mercer Richmond, Va. 1 5 15

Power Plant Hagerstown, Md

.

4 3 30

*Roof under construction when examined.

‘w'Impossible to calculate amount of mopping asphalt due to character

of specimen.
. >
13 -

APPENDIX III.

LETTER SURVEY

1 . INTRODUCTION

In order to supplement the data obtained during the field survey, a letter was prepared and distributed to a number of owners of glass-fiber

built-up roofs to develop information about the behavior and maintenance

requirements of this type of roofing. Those who received the letter were

selected by lot from the same list of 63 roofs described in Appendix II,

submitted to the National Bureau of Standards in 1956. Figure 10 is a copy of the letter which was distributed.

A summary of the results of the letter survey are presented in Table

2. RESULTS

5.

TABLE 5. Results of Letter Survey

Number of Letters Distributed

Number of Replies Received

Average Age of Roofs Reported On

Number Reporting:

20

12 *

5 yrs.

Very good service

Satisfactory service

Poor service

*0ne reply stated that they had not used glass-fiber roofing.

**This user also reported unsatisfactory service with other

types of built-up roofing.

USCOMM-NBS-DC

FIGURE 10. FORM LETTER FOR LETTER SURVEY

Gentlemen;

The National Bureau of Standards has undertaken, for the benefit

of other agencies of the Government, a study of the performance characteristics of the newer types of roofing materials. In this connection,

we are soliciting your assistance as a user of one of the new roofing

materials

.

It is our understanding that you have one or more buildings covered

with a built-up roof which employs glass-base felts in place of the

conventional organic or asbestos base felts. It would be most helpful

if you could furnish us with information regarding the age, performance,

and the maintenance required for such roofs in comparison with built-up

roofs of the conventional type. Any information we receive will, of

course, be considered as confidential.

Your cooperation will be appreciated greatly.

Very truly yours.

William C. Cullen, Chemist,

Organic Building Materials Section.

U.S. DEPARTMENT OF COMMERCE

Frederick H. Mueller, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director

THE NATIONAL BUREAU OF STANDARDS

The scope of activities of the National Bureau of Standards at its major laboratories in Washington, D.C., and

Boulder, Colo., is suggested in the following listing of the divisions and sections engaged in technical work. In

general, each section carries out specialized research, development, and engineering in the field indicated by its

title. A brief description of the activities, and of the resultant publications, appears on the inside of the front cover. WASHINGTON, D.C. ELECTRICITY, Resistance and Reactance. Electrochemistry. Electrical Instruments. Magnetic Measurements.

Dielectrics. METROLOGY. Photometry and Colorimetry. Refractometry. Photographic Research. Length. Engineering

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Instruments. Basic Instrumentation.

Office of Weights and Measures. BOULDER, COLO.

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