/O, oo

NATIONAL BUREAU OF STANDARDS REPORT

by

William C. Cullen

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards is a principal focal point in the Federal Government for assuring

maximum application qf the physical and engineering sciences to the advancement of technology in industry and commerce. Its responsibilities include development and maintenance of the national stand- ards of measurement, and the provisions of means for making measurements consistent with those standards; determination of physical constants and properties of materials; development of methods

for testing materials, mechanisms, and structures, and making such tests as may be necessary, particularly for government agencies; cooperation in the establishment of standard practices for incorporation in codes and specifications; advisory service to government agencies on scientific and technical problems; invention and development of devices to serve special needs of the Government; assistance

to industry, business, and consumers in the development and acceptance of commercial standards and

simplified trade practice recommendations; administration of programs in cooperation with United

States business groups and standards organizations for the development of international standards of

practice; and maintenance of a clearinghouse for the collection and dissemination of scientific, technical, and engineering information. The scope of the Bureau’s activities is suggested in the following

listing of its four Institutes and their organizational units. Institute for Basic Standards. Electricity. Metrology. Heat. Radiation Physics. Mechanics. Applied Mathematics. Atomic Physics. Physical Chemistry. Laboratory Astrophysics.'"' Radio Standards Laboratory: Radio Standards Physics; Radio Standards Engineering.** Office of Standard Ref- erence Data. Institute for Materials Research. Analytical Chemistry. Polymers. Metallurgy. Inorganic Materials. Reactor Radiations. Cryogenics.* * Office of Standard Reference Materials. Central Radio Propagation Laboratory.** Ionosphere Research and Propagation. Troposphere

and Space Telecommunications. Radio Systems. Upper Atmosphere and Space Physics.

Institute for Applied Technology. Textiles and Apparel Technology Center. Building Research.

Industrial Equipment. Information Technology. Performance Test Development. Instrumentation.

Transport Systems. Office of Technical Services. Office of Weights and Measures. Office of Engineering Standards. Office of Industrial Services.

* NBS Group, Joint Institute for Laboratory Astrophysics at the University of Colorado. ** Located at Boulder, Colorado.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1004-12-10447 20 May 1964 3352

PERFORMANCE OF ROOFINGS ON GUAM, M.I. AND OKINAWA, R.I.

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

IMPORTANT NOTICE NATIONAL BUREAU OF

for use within the Governmen

and review. For this reason, whole or in part, is not autl Bureau of Standards, Washii] the Report has been specifica

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST) on October 9, 2015.

gress accounting documents intended

is subjected to additional evaluation

ure listing of this Report, either in the Office of the Director, National by the Government agency for which

il copies for its own use.

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

CONTENTS

Page

1 . INTRODUCTION 1

2. G&JAM, MARIANA ISLANDS 1

2.1 Climatological Data 1 2.2 Roofing Systems and Their Performance 2 2.2.1 Bituminous Built-up Roofs 2 2.2.2 Exposed Concrete Roofs 3

2.2.3 Miscellaneous Roofing Systems 4

2.2.4 Non-Military Roofings 5

3. OKINAWA, RYUKYU ISLANDS 5 3.1 Climatological Data 5 3.2 Roofing Systems and Their Performance 6

3.2.1 Bituminous Built-up Roofs 6 3.2.2 Exposed Concrete Roofs 7 3.2.3 Non-Military Roofings 8

4. CONCLUSIONS AND DISCUSSION 8

4.1 Built-up Roofs 9

4.2 Exposed Concrete Decks 10

4.3 Miscellaneous Roofing Systems 11

4.4 Maintenance 11

4.5 Cost Data 12

5. ACKNOWLEDGMENTS 12

PERFORMANCE OF ROOFINGS ON GUAM, M.I. AND OKINAWA, R.I.

1 . INTRODUCTION

The National Bureau of Standards was requested by the Bureau of Yards and

Docks, U. S. Navy; the Directorate of Civil Engineering, U. S. Air Force;

and the Corps of Engineers, U. S. Army; to provide technical assistance

in a program to obtain performance data on roofing systems exposed in

tropical areas. The study was precipitated by the many premature failures

of roofings on both Guam and Okinawa^ resul ting in abnormally high maintenance and replacement costs. A survey of roofing systems on Guam and

Okinawa was conducted as a task under Project 10447, Performance of Roofings,

of the Tri-Service Engineering Investigation of Building Construction and

Equipment during April 6 to April 19, 1964 to develop data to assist those

charged with design, construction and maintenance responsibilities.

The conduct of the survey consisted of "on the roof" observations of typical

roofing systems protecting structures on Army, Navy, Marine, and Air Force

installations. Personal contacts were made with roofing contractors and

military and civilian engineers experienced with construction performance

and maintenance of roofings.

This report includes our observations of the performance of roofing systems

on Guam and Okinawa, as well as our opinions and suggestions relating to

past and predicted performance of specific roofing systems.

Another purpose of the investigation was to provide technical assistance

to agencies of the Defense Department in connection with an evaluation

program of new roofing systems on Guam Island as proposed by the committee

members of Task 30 of Project 32. The importance of this phase appears

sufficiently significant as to warrant a, separate report which will be

submitted in the near future.

2. GUAM, MARIANA ISLANDS

2.1 Climatological Data

The climate of Guam is uniformly warm and humid throughout the year. Temperatures during the day are typically in the middle or high 80'

s

and nighttime

temperatures fall to the low 70'

s

or high 60' s. The relative humidity com- monly ranges from 65 - 75% in the afternoon to 85 - 100% at night.

The mean annual rainfall ranges from about 80 inches along the coast of the

western side of the southern half of the island to about 95 inches on the

windward (East) side.

2

The dominant winds are the trade winds which blow from east or northeast with common wind speeds of 15 - 25 mph during the dry season. Occasionally there are typhoons and these bring not only tremendous

rain% but violent winds. For example, during typhoon "Karen" on

11 November 1962 the sustained winds were measured at 180 mph with

gusts up to 207 mph. It was interesting to note that the U. S. Weather

Bureau states that the chances of having a typhoon pass close to Guam

in any particular year are 1 in 3 while the chances of having a typhoon

move directly across Guam are only 1 in 8.

2.2 Roofing Systems and Their Performance

2.2.1 Bituminous Built-Up Roofs

Asphalt built-up roofs have been used to protect permanent military

structures on Guam since the end of World War II. The roof decks of

these buildings generally consisted of either the waffle type pre-cast

concrete slabs or the conventional poured-in-place slabs, with both

types having little or no slope.

Prior to 1954, the built-up membrane consisted of multiple plies of an asphal t- saturated asbestos felt using an abnormally high softening point

asphalt (200 to 240°F) as the plying cement. For the most part the mem- branes were applied over a vegetabl e~ fiber insulation board and were surfaced with an aluminum coating. This type of roofing system gave poor

service since they required extensive maintenance and failed within a few

years. An extensive investigation of roofings on Guam by the author in

1954 attributed the deficiencies as evidenced by blistering, crackings

and general deterioration, to excessive moisture in the deck and insulation, to the use of insulation resulting in high roof temperatures, and

to the use of the high softening point asphalt. Figure 1 illustrates

typical weathering pattern of roof surface as observed in 1954, while

Figure 2 illustrates the difference in weathering of roofing insulated

from the deck and that applied directly on the concrete. As a direct

result of the investigation the smooth surfaced roofs were replaced

with coral- surf aced asphalt built-up roofs applied with a 170 - 190°F

softening point asphalt directly to the concrete deck.

Our observations during the April 1964 inspections indicated that the

coral- surfaced, bituminous built-up roofings have given satisfactory

service after as long as 10 years exposure, and they have by far out

performed their smooth-surfaced counterparts. Although asphalt has

been the bitumen predominately used and has served well, an experimental roof at the Naval Communication Center using coal -tar-pitch as the bitumen has also performed well after 10 years exposure as illustrated

in Figure 3. Figures 4, 5 and 6 illustrate the condition of typical coral-

FIGURE

3.

COAL-TAR-PITCH

BUILT-UP

ROOF

FIGURE

4.

CORALSURFACED

BUILT-UP

AFTER

10

YEARS

EXPOSURE

ON

GUAM„

ROOF,

OROTE

POWER

PLANT,

GUAM.

AGE:

10

YEARS

„
)
3

jsurfaced built-up roofs on the Orote Power Plant, the U. S. Naval

Hospital, and the Fleet Laundry which have served very satisfactorily

after 10, 8, and 7 years, respectively. However, it was observed that

each of these roofs required immediate preventive maintenance as exemplified by the area shown in Figure 7. Figure 8 shows the gradation of the

manufactured coral aggregate and the excellent coverage obtained with

this material on the hospital roof. Similar service was obtained from

surfaced built-up roofs observed on the Commissary Building and the CE

Shops Building at Anderson Air Force Base.

The good performance of these roofings was attributed to the use of

mineral surfacing, to the elimination of insulation from the top of the

deck, and to the use of a softer asphalt.

It should be pointed out that the use of surfacing aggregate for builtup roofs has not had universal acceptance on Guam due to its reported

vulnerability to blow off during high winds and the damage caused by

flying gravel. Although this criticism may be justified to some extent,

especially during typhoons, we cannot agree in toto with the opinion

that this shortcoming is sufficient to limit its use.

In way of summary, we believe that the coral- surfaced bituminous builtup roofing has given the better performance among the organic roofings

employed on Guam Island from both a service and maintenance standpoint.

However, we observed that many such roofs are in need of immediate preventive maintenance to insure continued good service. The need for

periodic inspections and timely maintenance cannot be overemphasized.

2.2.2 Exposed Concrete Roofs

Since the early 1950's many engineering personnel have advocated the use of the exposed concrete deck as the weather surface due to the poor

performance of most organic roofing systems. A distinction must be made

here between the pre-cast and the poured- in-place decks.

The use of the pre-cast roof decks as the weather surface has resulted in

both success and failure. For example, a prematurely failed built-up

roof was removed from the Orote Power Plant in 1953 and the inter-panel

joints between slabs were treated with a fatty-acid-pitch base sealant.

Unfortunately, this material failed within six months due to a separation

from the concrete causing severe leakage which required the immediate

reapplication of a multiple-ply roof membrane. As a matter of interest,

this roofing is still performing satisfactorily as described in paragraph

2.2.1. On the other hand? a weather-resistant and leakproof roof was obtained on the Bachelors Officers Quarters, Naval Communication Station,

Finegayen, on which the inter-panel joints were treated with a hot-poured
'

(
FIGURE

7.

EXPOSED

FELTS

WHICH

INDICATE

FIGURE

8.

EXCELLENT

COVERAGE

PROVIDED

NEED

FOR

PREVENTIVE

MAINTENANCE.

OROTE

BY

MANUFACTURED

CORAL

AGGREGATE.

POWER

PLANT.

4

joint sealer (Federal Specification SS-S-164) approximately three years

ago. It was reported that extreme care was exercised to prepare the

concrete surface at the joint in order to obtain good adhesion. The

satisfactory results are illustrated in Figures 9 and 10, which show

both a general and close-up view, respectively. An examination of the

interior revealed no water penetration despite the ponding water shown

in Figure 9.

The poured-in-place slabs have two advantages over their pre-cast counterparts in that they have fewer joints to treat and are of greater thickness. Consequently, they have performed very satisfactorily as exposed

decks for at least 10 years on Guam Island. Observations of typical

slabs indicated no leakage or seepage had occurred except where structural

or shrinkage cracks were evident. Figures 11 and 12 illustrate typical

poured-in-place slabs which have given maintenance-free service on structures at the Naval Communication Station, Finegayen. The dark

appearance of the roof on the house shown in Figure 12 resulted from

a biological growth which is common to warm and humid areas.

2.2.3 Miscellaneous Roofing Systems

The multiple-ply built-up roof and the exposed concrete decks have been

the predominately-used roofings on Guam. However, a number of less con- ventional systems were also observed during the survey. These systems

have been used on both an experimental and practical basis. Those used

on an experimental basis will be fully treated in a future report and

the performance of those used practically are reported herein.

A roof covering, consisting of a mopping of hot asphalt at 30 to 50 lb.

per square in., which is embedded with a single ply of fiberglass base

sheet and coated with a white vinyl emulsion paint, has been employed

on a number of roofs at Anderson Air Force Base. For example, in one case it was used to replace built-up roofing that was severely damaged

during typhoon "Karen" on the Meehan Theater and Building 21000. In

another case it was used to protect a poured-in-place deck which developed small cracks due to the vibrations produced by jet aircraft.

Our observations indicated that this system has performed adequately

during its one year exposure. The apparent high solar reflectance of

the white emulsion contributed to the relatively cool roof temperatures

which were experienced. There was some evidence that the emulsion

coating was susceptible to attack by fungus, especially in shaded areas where water collects and stands. The performance of this system must

be considered satisfactory to date. Nevertheless, we believe it is

difficult to project its future performance based on such a short-time

exposure. It is questionable whether the experience to date is sufficient to warrant its extended use on Guam.
1

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The performance of another unconventional roofing system used to protect

over 1000 units of Capehart Housing at Anderson Air Force Base has not

been quite so successful. Originally an aluminum coating was specified

to protect the poured-in-place decks for reflectance and aesthetic purposes

only. However, cracking sufficient to cause leakage, developed in the

slabs which required additional waterproofing of the slab. As an economy

measure a roof covering of hot asphalt (35 - 50 lb /sq) surfaced with

an aluminum coating was used.

A critical examination of several roofs revealed severe blistering of

the asphalt and cracking and alligatoring of the aluminum coating after

about 5 years exposure. In addition, engineering personnel reported

that over 30 complaints of leakage have been recently received from

residents of the area.

It was obvious to even those uninitiated in roofing performance that

this system was not sound. It not only failed in its primary function

to waterproof the roof declq but now presents a costly task to remove and

replace. A multiple-ply bituminous built-up roof appears to offer the

only logical system.

2.2,4 Non-Military Roofings

It was interesting to note that a large percentage of civilian structures

were roofed with corrugated galvanized steel roofing which has apparently

served well on sloping decks and has required little maintenance. However,

the corrugated metal roofings were particularly vulnerable to high winds

and, it was reported, that many such roofs were severely damaged or destroyed completely during typhoon "Karen".

3. OKINAWA, RYUKYU ISLANDS

3.1 Climatological Data

The Ryukyu Islands are located within the temperate zone. Nevertheless,

the warm Japanese current provides a mild climate. The yearly temperature

averages 72°F with a high of about 89°F during the summer and a low of

61°F during the winter. The relative humidity is high and varies from a low of 617c during the winter to a high of 89% in the summer, with an average of 76%.

The rainfall is quite heavy with a yearly average of 82 inches. The summer months have the heaviest rainfall, although a minimum of 4 inches falls

even in the driest months.

Okinawa, like Guam, is subject to relatively high winds and occasionally

there are typhoons which are not only accompanied by very heavy rains,, but

also by violent winds.

- 6 -

3.2 Roofing Systems and Their Performance

3.2.1 Bituminous Built-Up Roofs

Smooth-surfaced, asphalt built-up roofs have been used to some extent on Okinawa to protect both pre-cast and poured-in-place concrete roof decks.

The roof areas covered with such systems varied from 12 squares for a single family dwelling to over 2000 squares for large warehouses (as illustrated in Figures 1 3 & 14) and had roof slopes from flat to one inch per foot.

Coal-tar-pitch has not been used to any extent for roofing on Okinawa.

Surfaced, built-up roofs have been used only to a very limited extent

due to the vulnerability of the gravel surfacing to blow off during

relatively high winds frequently experienced on the island. In many

cases, an aluminum coating has been used in lieu of mineral surfacing to

protect the bitumen and to provide for solar reflectance. The use of

insulation between the membrane and the deck has also seen only limited

application since reflective coatings have provided the necessary thermal

characteristics of the roofing systems.

We have also included under this category a somewhat unconventional

system consisting of two plies of a glass mat - asphalt emulsion which

was surfaced with a ply of woven glass fabric coated with an aluminum

coating. This roof was used to protect ranch type homes in the Sukiran

Area which were completed in 1953.

The performance of the conventional smooth-surfaced asphalt built-up

roofing on Okinawa appeared to be somewhat less satisfactory than that

which would be normally expected of similar roof coverings in the continental United States. On the other hand, we believe they have performed

better than similar roofs have on Guam Island. The severe and premature

weathering of the surface protection appeared to be the most serious

deficiency which will result in early failure if timely and adequate

maintenance are not provided. This condition is illustrated in Figures

15 and 16 which are photographs taken of an Engineering Warehouse in

the Machinate Service Area after only 2 years exposure. Figures 17 and

18 illustrate typical weathering of an aluminum-surfaced asphalt built-up

roof on a Type C home in the Sukiran Housing Area after about 10 years

exposure. Although these examples were typical of the surface deterioration which occurred, it was interesting to observe that the asphalt was

soft and pliable, even in areas where water collected and stood, and

appeared to be of good quality.

Moderate to severe blistering was also observed on many of the built-up

roofs, which, no doubt, resulted from excessive moisture in some component of the roof system. Although this was a common deficiency, we

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believe that it did not substantially contribute to premature failures

Examples of this defect were observed at Fort Buckner as illustrated in

Figure 19 after 9 years exposure and on the built-up roof of the prototype barracks building (Figure 20) located at Camp Butler as evidenced by

the numerous repaired areas shown in Figure 21

Although our observations indicated that the smooth surfaced, built-up

roof performance was less than satisfactory we believe this roofing has

proven to be more effective than most other systems in obtaining a watertight system. Further, based on our observations on Guam, we believe

the performance of a built-up roof could be considerably improved by

the use of a mineral surfacing.

The performance of the glass mat - asphalt emulsion, etc., roofing system

appeared to be quite satisfactory on both sloping and flat roofs. Figure

22 illustrates a typical home protected with such a roof and Figure 23

shows the roofing after about 11 years exposure. 'This system required

periodic recoatings with the aluminum compound.

3.2.2 Exposed Concrete Roofs

Under this category we have included the concrete decks to which have

been applied non-reinf orced, organic compounds for waterproofing, thermal

reflectance or for aesthetic reasons.

The predominate type of roofing observed on permanent military structures

on Okinawa appeared to be the exposed pre-cast concrete deck. Although

a number of poured-in-place roofs were also observed. The waterproofing

of the latter type presented little difficulty and typical successful

roofs are shown in Figures 24 and 25. The roof illustrated in Figure 25 was coated with a vinyl emulsion for reflective purposes. A failed

built-up roofing on a 165 man barracks shown in Figure 26 was removed and

the poured-in-place deck was employed as the roof after the shrinkage

cracks were made watertight as shown in Figure 28. The treatment con- sisted of embedding fibrous glass strips in a bituminous plastic cement

and has proved to be quite effective.

In the case of the pre-cast roof decks, the successful treatment of interpanel joints and the frequent structural cracks in the relatively thin

waffle type slabs presented a rather difficult problem to those charged

with design and maintenance responsibilities. A case in point was a typical barracks building at Camp Hansen shown in Figure 27. The interpanel joints were treated with a bituminous material into which was em- bedded woven glass fabric and the entire roof surface, including the

taped joints, was surfaced with an aluminum coating. Leakage was re- ported to have occurred in these buildings and based on our observations,

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19.

BLISTERING

OBSERVED

ON

BUILT-UP

ROOF

ON

EXCHANGE

BUILDING,

FIGURE

20.

PROTOTYPE

BARRACKS

BUILDING

FORT

BUCKNER.

CAMP

BUTLER.

FIGURE

23.

ASPHALT

EMULSION-GLASS

FABRIC

ROOFING

AFTER

11

YEARS

EXPOSURE.

FIGURE

24.

POUREDIN-PLACE

CONCRETE

DECK

AFTER

3

YEARS

EXPOSURE.

- 8 -

we believe the failure of the taping system over the inter-panel joint,

as shown in Figure 29, was primarily responsible for the leakage. The

continuous movement between panels due to solar heating and radiative

cooling resulted in a stress concentration immediately over the joint,

thus causing a failure in the taped joint. The severe embrittlement of

the bituminous compound and glass reinforcing fabric due to weathering,

no doubt, contributed to the failures. Engineering personnel have recognized the limitations of methods used to treat inter-panel joints and were experimenting with a number of systems as shown in Figure 30.

The aluminum roof coating appeared to be in fair condition after about

3 years exposure. Slight blistering of the coating was evident and

there was some indication of erosion where the material was applied

relatively thin. The definite dulling of the coating indicated a loss

of solar reflectance. We would anticipate from our observations that

a recoating will be necessary in a year or two.

It was reported that similar roofing deficiencies prevailed at Camp Schawb*

but to a greater extent? after about 6 years exposure. The difference in

performance between Camp Hansen roofings and those on Camp Schawb were attributed to improved specifications and increased inspection during

appl ication

Our observations of the roofs on new permanent buildings at Camp Butler^

which were not occupied, revealed essentially the same treatment as that observed at Camp Hansen and in our opinion similar service can be

expected

3.2.3 Non-Military Roofings

It was of interest to the author to observe the roofings used on the

typical Ryukyuan homes. For the most part clay or concrete tile roofs

complete with their "Kara Shishi" , or Chinese Guardian Dogs, are traditional as shown in Figure 31. However, a number of thatched roofs were

often seen in the rural areas as illustrated in Figure 32. These roofings

have proven to be quite durable against the Okinawa weather. However, if

it is of any comfort to the military engineer, these roofs also leak, are also vulnerable to damage during high winds and also require periodic

ma intenance

4. CONCLUSIONS AND DISCUSSION

The intense solar radiation, the high temperatures^ and the very high

humidities experienced on Guam and Okinawa certainly accelerate the degradation of organic roofing materials. However, the small temperature

fluctuations which occur throughout the year on these islands are con- ducive to good roof performance in respect to physical deterioration

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THATCHED

ROOFS

OBSERVED

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SHISHI"

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CHINESE

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N

RURAL

AREAS.

GUARDIAN

DOG.

- 9

-

(thermal movement, etc,). Since our experience indicates that physical

deterioration of components of the roof system produce the more serious

consequences, we would expect better performance in Guam and Okinawa

than in areas experiencing larger temperature fluctuations *

It can be seen from the climatological data reported in paragraphs 2.1 and

3.1 that the climates of Guam and Okinawa are quite similar in respect to

temperature, humidity, rainfall, and wind velocity. The intensity of solar

radiation appears to be greater at Guam, but the thermal gradient to which

a roof is subjected is greater at Okinawa. Nevertheless, we believe

the climates are sufficiently similar as not to warrant radical changes

in the design, construction, or maintenance of roofing systems. Therefore, the following discussion refers to the performance of roofing on both Guam and Okinawa.

4. 1 Built-Up Roofs

For the past 10 years, the mineral-surfaced (coral) asphalt built-up

roofs have given satisfactory performance on Guam with little or no maintenance. Of course, a number of deficiencies occurred in these

systems, such as blistering, exposed felts due to weathering, and a loss of aggregate due to high winds, but none so serious as to affect

its end use. A number of such roofs weathered the tremendous winds of

typhoon "Karen" with little damage except the loss of loose surfacing.

We concluded that this type of roofing has served well both from a functional and economic standpoint on Guam and believe similar service

can be expected of surfaced built-up roofs on Okinawa.

Rather severe criticism has been made against the use of mineral surfacing

for built-up roofs due to the damage caused by flying gravel during high

winds. We have observed ample evidence that a roofing aggregate can be

made resistant to blow-offs by a process described as double-surfacing

and still perform its basic functions to permit the use of the waterproofing bitumen in large quantities and to protect the surfacing bitumen

from destructive ultraviolet radiation. Regardless of whether the

criticisms are justified or not, if a multiple-ply roof is required,

one must make the choice between a smooth and a surfaced built-up roof.

We know of no adequate substitutes for the aggregate sur facings.

The smooth-surfaced asphalt built-up roofs have not given adequate

service either on Guam in the past or currently on Okinawa. The

serious deficiencies observed were the premature weathering of the

surface and blistering which occurred beneath or within the membrane.

In addition, these systems required and do require more maintenance than

their surfaced counterparts.

" 10

In summary, we believe that the surfaced built-up roofings will render

the better service among the membrane type systems provided they are constructed of acceptable materials which are applied in accordance

with good roofing practices. The bitumen, whether coal- tar-pitch or asphalt, should be specified to conform to applicable Federal, Military,

or ASTM Specifications and of a softening point as low as practicable,

commensurate with the slope of the roof. The reinforcing medium should

consist of organic, asbestos, or glass felts treated with the appropriate

bitumen and conforming to applicable Federal or ASTM Specification. The

surfacing material should be manufactured of native materials (coral in

Guam, crushed stone in Okinawa) and conforming as nearly as possible to

the requirements of ASTM Designation D1863. We would also suggest that

the use of insulation be eliminated from between the roof deck and the

roof membrane.

4.2 Exposed Concrete Decks

The exposed concrete slabs have, per se, performed quite satisfactorily

as roofings in Guam and Okinawa. The poured- in-place type have not

presented the problems which have been encountered in the pre-cast types.

In the case of the pre-cast roofing slabs, the main area of concern is

the proper treatment of the inter-panel joints. Our observations indicated that the most effective and economical procedure was to treat the

joint with a reinforcing fabric embedded and coated with a suitable

bituminous material (we would suggest a plastic cement conforming to

Fed. Spec. SS-C-153), The use of a "bondbreaker’ ! consisting of a 2-in.

wide strip of paper, plastic sheeting, etc., placed directly over the

joint will eliminate a stress concentration at that point and prevent

the early failures now experienced.

Some have advocated the use of a sealant to secure watertight interjoints which have been used successfully to a limited extent on Guam

and Okinawa. In this connection, we have contacted Mr. Arthur Hockman,

the sealant expert of the National Bureau of Standards, who predicts

that an acceptable watertight joint can be obtained by this procedure.

However, he warns that proper surface treatment of the concrete is

mandatory to obtain the desired results. The surface must be absolutely

free from foreign matter and he suggests that it be lightly wiped with

an organic solvent such as toluene prior to the application of the

sealant. The sealant should be a polysulfide type conforming to Federal

Specification TT-S-0Q227a. Mr. Hockman further suggests that a

,f bondbreaker,! of polyethylene, aluminum foil, etc., be placed at the base of

the joint to insure a proper shape factor during extension of the sealant.

Our observations indicated that both pre-case and poured-in-place con- crete slabs develop cracks to some extent due to shrinkage, structural

or thermal movement, etc., and methods of repair must, be considered.

The maintenance engineer has two alternatives in such cases

1 „ Isolate and repair each individual crack,

2. Apply a membrane over the entire roof.

It is obvious that the former method should be used as long as it is

effective and economical,, Now the question arises, when does it become

uneconomical to isolate and repair the cracks „ This endpoint we cannot

define and would suggest that the opinion of the engineer responsible

for maintenance and repair should largely govern.

The use of organic coatings for solar reflectance and for aesthetic purposes has been quite satisfactory on both islands. However, their value

as a waterproofing medium is questionable. The acrylic and vinyl emulsions and aluminum coatings have been used predominately. It should be

stressed here that any organic surface coatings will require additional

applications every 3 to 5 years.

4.3 Miscellaneous Roofing Systems

In our opinion, the use of the unconventional roof systems as described

in this report are not suitable for use on permanent structures. This

statement is based on the poor performance of one system at Anderson

Air Force Base and on the maintenance which will be required for other

systems

In connection with some of the newer one-ply systems which have been

included in the Guam tests, such as;

a. polyisobutylene or asbestos felt,

b„ polyvinyl fluoride on asbestos felt,

c. sheet butyl roofing,

we believe they possess good possibilities for special applications on Guam and Okinawa at this time, but sufficient exposure data have not been

developed to recommend their extended use. The cost data from the Guam

tests also indicate they are not competitive with conventional systems

in the Pacific area.

4.4 Maintenance

We have observed on all installations a general need for roofing maintenance on all types of roofing systems. It was evident that the need for

periodic inspection and maintenance was not always recognized and further,

when it was, funds were not always available to implement the action.

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We strongly believe that failure to recognize and correct minor defects

and deterioration in its earliest stages are the greatest causes of premature roof failures and frequently result in costly repairs and re- placements. We further believe that funds which are made available

for inspection, maintenance, and repair programs will ultimately result

in enormous savings.

4.5 Cost Data

We attempted to obtain accurate cost data in respect to roofings during

the survey and based on information from numerous sources (some con- flicting reports), we have established the following factors:

Guam - 2 to 2-1/2 times average cost (California)

Okinawa - 1-1/2 to 2 times average cost (California).

5. ACKNOWLEDGMENTS

We acknowledge with thanks the excellent cooperation and the courtesies

extended to the author by both civilian and military personnel representing the Bureau of Yards and Docks, U„ S. Navy; the Corps of Engineers,

U. S. Army; and the Office of Civil Engineering, U. S. Air Force, in the

Pacific areas. The assistance of Messrs. Samuel Taam and James Bowman,

Pacific Division, Bureau of Yards and Docks; Messrs, Marv Bistodeau,

Oscar David, and Robert Taylor, Materials Testing Laboratory, OICC,

U. S. Navy, Guam; and Mr. Roy C. Schild, Chief, Design Branch, U„ S.

Army Engineer District, Okinawa, are worthy of special mention.

USCOMM-NBS-DC