NATIONAL BUREAU OF STANDARDS REPORT

7831

SOLAR HEATING, EMISSIVE COOLING, AND THERMAL MOVEMENT

AND THEIR EFFECT ON THE PERFORMANCE OF A BUILT-UP ROOF

by

William C. Cullen

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

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Documents, Government Printiiig Office, Washington 25, D.C.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1004-12-10447 30 March 1963 7831

SOLAR HEATING, EMISSIVE COOLING, AND THERMAL MOVEMENT

AND THEIR EFFECT ON THE PERFORMANCE OF A BUILT-UP ROOF

Sponsored by

Office of the Chief of Engineers

Department of the Air Force

Bureau of Yards and Docks

IMPORTANT NOTICE NATIONAL BUREAU OF S for use within the Government

and review. For this reason, I whole or in part, is not autt Bureau of Standards, Washin

the Report has been specifics

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

ress accounting documents intended

is subjected to additional evaluation

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

I copies for its own use.

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

SOLAR HEATING, EMISSIVE COOLING, AND THERMAL MOVEMENT

AND THEIR EFFECT ON THE PERFORMANCE OF A BUILT-UP ROOF

1.

INTRODUCTION

In military construction, a large percentage of the roof area is protected with built-up roof systems. The built-up system may be a relatively simple system or it may consist of a number of components as:

1. Roof deck

2. Vapor barrier

3. Insulation

4. Waterproof membrane

5. Protecting surface

Each of these components may involve many materials exhibiting many

different properties, the combination of which may result in a complex

roof system. It follows that as the complexity of a roof system increases

the problems involving performance and maintenance qlso increases and to

solve these problems, the properties of the system components must be

known o Obviously, it is impracticable to list, determine and evaluate

the properties of each specific material intended for use in a roof system

but, still, criteria are needed to differentiate between a material which

will perform as intended and one that will not. In this connection and

at the request of agencies of the Defense Department, a program was

conducted under Project 10447, Performance of Roofings, Tri-Service

Engineering Investigations of Building Construction and Equipment, NBS,

to study some fundamental factors involved in the performance of a built-up roof system.

Three factors which we believe to be primary contributing factors in

many premature roof failures are:

1. Solar Heating

2. Emissive Cooling

3 . Thermal Movement

- 2 -

Our experience in both the laboratory and in the field has established

that the high temperatures attained by a roof surface, rapid changes in

temperature, and thermal movements resulting from solar heating and

emissive cooling are contributing factors in common built-up roof failures as

1. Blistering

2. Wrinkling and buckling with the resultant cracking

3. Splitting and membrane ruptures

4. Slippages

5. Flashing failures

6. Chemical degradation of bitumen

7. Physical deterioration of bitumen

The purpose of this report is to present typical data on solar heating

and emissive cooling which were obtained during summer and winter exposures

and to relate this data to the properties of components of a roof system.

The properties include the mass, heat capacity and density of the substrate

to which the membrane is applied and to the reflective and emissive characteristics of the protecting surface. Another purpose is to furnish

data on thermal expansive and contractive characteristics of a composite

built-up membrane and to relate these characteristics to built-up roof

performance.

2. SOLAR HEATING AND EMISSIVE COOLING

The greatest known source of energy is the sun and this energy is

transmitted to the earth in wave form as infrared, ultraviolet and

visible radiation. Roofs, per se, are exposed to solar radiation and

the energy accompanying it. The law of conservation of energy demands

that the radiant energy impinging on a roof surface must be quantitatively

accounted for by three factors:

1. Reflection

2. Transmission

3. Absorption

For the purpose of this report, we shall deal primarily with the absorbed,

infrared energy that is converted to heat energy which in turn results

in the heating of the components of a roof system. It may be of interest

to note that Billington (l)—/ reported that the solar intensity (amount

of energy falling on a plane surface perpendicular to the rays) outside

the earths atmosphere is about 420 BTU/sq, ft. /hr. A good deal of this

energy is absorbed by the atmosphere and the maximum recorded at the

earth’s surface is about 320 BTU/sq. ft. /hr. The effect of solar

radiation on building components was recognized by Beckett (2) as early

as 1935 when he warned that there is a very real danger of structural

failure due to expansive movements resulting from heating of the slab

by sunshine.

1/ Numbers in parenthesis refer to literature references at the end

of this report.
' !

'
- 3 -

The effect of solar heating also contributes to the degradation of the

waterproofing bitumen since this process is essentially a photo-oxidative

reaction which is accelerated by heat.

Another concept, not as well known as solar heating, but equally as important to roof temperatures is emissive cooling which, in effect, is

the reradiation of energy from the roof surface to the sky. The emission

of radiation is not confined to luminous bodies as generally believed.

The radiation from a material at moderate temperatures is entirely in

the form of long-wave radiation which cannot be seen but can be detected

by its cooling effect on the material. Consequently the outgoing

radiation has a significant influence on roof surface temperature.

The emissivity of a perfectly black body is unity and it has been

reported (1) that most building materials have an emissivity of approximately 0.9 which is independent of the color or texture of the surface.

Metallic bodies, however, have low emissivities at ordinary temperatures,

and, therefore, will tend to remain at somewhat higher temperatures than

their non-metallic counterparts.

It becomes readily apparent that solar heating and emissive cooling

contribute substantially to the magnitude of the thermal cycle of a built-up roof system. Assuming a clear day, the roof surface temperature

begins to rise under exposure to the morning sun and it reaches its

maximum about noon and then declines as the sun declines until night

falls. If the night is clear and still, the heat loss from the roof

surface to the sky will result in a sub-cooling of the roof surface.

The magnitude and rate of the temperature increase or decrease will

depend on the following factors:

1. Intensity of solar radiation

2. Ambient air temperature

3. Clearity of the atmosphere

4. Wind velocity

5. Reflectance of the roof surface

6. Emissivity of the roof surface

7. Thermal properties of the roof system

The effects of wind velocity has been discussed by Hendry and Page ( 3 )«

Their computations indicated that the maximum roof temperature on a still day was 30°F higher than on a day with a 12mph wind and l6°F

higher than on a day with a 4mph wind.
'7 * .
- 4 -

Data which were reported by Cullen and Appleton (4) showed that roof

membranes insulated from the roof deck attained higher and lower

temperatures than non-insulated membranes and underwent greater

temperature fluctuations when exposed to varying weather conditions.

In order to study, the influence of other factors, such as the substrate and surface treatments on solar heating and emissive cooling,

a program of experimental work was planned and carried out.

2.1 Experimental Design

The laboratory experiments were designed to determine the effect of

both the thermal properties of the membrane substrate and the color and

character of the membrane surface on temperature and temperature fluctuations

of a built-up roof subjected to solar heating and emissive cooling.

Twenty, 18 in. x 18 in. , built-up roof system specimens were constructed

in the laboratory employing three different substrates and five different

protective surfaces. Conventional 4 ply asphalt-saturated organic felt

built-up membranes were applied to ten l/2” plywood decks and ten 2”

dense concrete decks. Two inches of expanded polyurethane insulation

was placed between the deck and the membrane on ten of the specimens.

One of five protective surfaces was then applied to each specimen.

Each specimen was instrumented with copper-constantan thermocouples

at selected locations and temperatures recorded simultaneously 24 hours

a day. Figure 1 is a schematic diagram of two smooth surfaced specimens

on concrete decks.

The specimens were exposed on the roof of the Industrial Building,

National Bureau of Standards, Washington, D. C., in a horizontal position

on a platform about 3 feet above the roof surface. Each specimen was

supported on face bricks about 3 inches above the platform. This arrangement provided for the free circulation of air beneath a large portion of

each experimental slab. Figure 2 shows a general view of the exposures

while Figure 3 is a close up of a typical specimen.

2.1.1 Properties of Substrate

Three different materials were selected and employed as substrates

for the experimental specimens. It is believed that these materials

represent the extremes of built-up roof substrates used in service.

Table 1 lists the selected materials together with their approximate

densities and specific heats.
.

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INSULATED SPECIMEN

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ASPHALT SURFACE

4 PLY MEMBRANE

THERMOCOUPLE

CONCRETE DECK

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NON-INSULATED SPECIMEN

FIG. I

FIGURE 3 0 TYPICAL SPECIMEN
* . •
- 5

-

TABLE 1.

PROPERTIES OF SUBSTRATE

Material Density Specific Heat

lbs /ft3

g cal/gram

Concrete 140 .21 to .25

Plywood 40 .42

Expanded Polyurethane 2 .40

2.1.2 Properties of Protecting Surfaces

Fife commonly used surfaces were selected for use in the experimental

work. It is our opinion that these surfaces represent the extremes

of those used in service. Table 2 lists the materials used together

with their significant properties.

TABLE 2.

PROPERTIES OF SURFACINGS

Material Color Weight Used Solar Reflectance

lbs/ 100 ft2

Asphalt Black 25 .5 to .10

Crushed Stone Dark Grey 400 .20 to .30

Scoria Maroon 150 .20 to .30

Marble Chips White 200 .50 to .60

Polyvinyl White Thin film (002") .85 to .95

Fluoride

2.2 Experimental Results

2.2.1 Solar Heating

The influence of the membrane base on the temperature and temperature

changes produced by the solar heating of a black, smooth- surfaced

roof membrane is shown in the time-temperature curves in Figure 4.

The maximum temperatures attained by the membranes over concrete,

wood and insulation on a summer day in August 1962 were 120°F, 145°F,

and 165°F, repectively. In respect to tempe rature fluctuations it is

interesting to note that between the hours of 500 pm (1730) and

6:00 pm (1800), the temperatures of the membranes over concrete, wood

and insulation declined 15 °F , 30°F, and 45°F, respectively. The

degree of temperature change between a membrane placed over insulation

and a similar one placed over concrete is vividly illustrated in

Figure 5® The temperatures were measured on a day which included sunshine, clouds, and heavy rains.

One might infer from this information that all insulated roof membranes

are subjected to greater extremes in both temperatures and temperature

variations. This is true if other factors are similar, however,

other variables come into play which limit these extremes to a lesser

or greater extent. For example, Figure 6 shows the effect of surface

color on the thermal cycle of a black and a white smooth-surfaced

built-up roof membrane placed over insulation. A comparison of curve 1 with curve 2 indicates a decline of 40°F for the black and only 15°F for

the white between noon (1200). and 1:00 pm (1300) and then as the

surfaces were again exposed to sunshine, the black surfaced membrane

registered a gain of 90°F while the white surfaced membrane was limited

to a 25°F rise between the 1:00 pm (1300) and 3? 00 pm (1500).

The influence of other surfaces as crushed stone and marble chips

on the thermal cycles of membranes placed over insulation and over

concrete are illustrated in Figure 7® These results again confirm

our theory that the higher the coefficient of solar reflectance of

the roof surface the smaller the temperature difference between the

insulated and non-insulated membranes.

Figure 8 illustrates the effect of the protecting surface on the

temperature and temperature changes of membranes placed over insulation.

Although these curves represent specimens placed over insulated concrete

decks similar curves were obtained on the specimens placed over insulated

wood decks. These observations indicate that the type or kind of deck

is not related to roof temperature when an efficient insulation is used.

For convenience, the maximum temperatures which were recorded at 1:30 pm

(1330) by membranes protected with the selected surfaces are listed in

Table 3®
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AUGUST

1962

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TABLE 3.

SURFACE EFFECT ON ROOF TEMPERATURE

Surface Max. temp. At

op From ambient

Black 166 8l°F

Crushed stone 148 63°F

Marble chip 118 33°F

White 93 8°F

Ambient 85

It has been established by this and other studies that insulation placed

between the deck and the membrane may lead to the accelerated deterioration

of the built-up roof. On the other hand, if insulation is omitted or

placed beneath the deck, it follows that the thermal movement in the

slab may be considerable due to solar heating and emissive cooling. The

question, therefore, arises as to the magnitude of the temperature

changes which occur in the insulated and uninsulated slab. Figure 9

indicates the extent of these changes by the time-temperature curves

for the membrane and roof slab temperatures as recorded in both insulated

and uninsulated specimens on a summer day in August 1962, Incidently,

Curve 2 coincides with the ambient temperature. It can only be concluded

that the temperature changes in an uninsulated slab were considerably

less than those which occur in an insulated membrane.

A snow cover appears to be an important factor in stabilizing temperatures

cf a roof membrane. We observed during winter exposures in December and

January 1963 when the specimens were covered with snow that no variation

was recorded in the temperatures of the ambient and roof membranes

regardless of the type of substrate and surface treatment employed.

2.2,2 Emissive Cooling

We have seen that the reradiation of energy from a roof surface often

results in a sub-cooling of the roof surface. The degree of sub-cooling

is dependent on a number of factors including the properties of the

substrate, the wind velocity and atmospheric conditions. Figure 10

serves to illustrate these points. The ambient temperature (Curve l)
.
AUGUST

1962

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and that of uninsulated specimen (Curve 2 & 3) and insulated specimen

(Curves 4 & 5) were obtained coincident with one another on a day when

the sky was cloudy until 1:00 am (0100 hours) when the cloud cover lifted.

This event was immediately reflected in the apparent temperatures of

the ambient and insulated and non-insulated specimens. The temperature

of the membrane placed on insulation was about 12°F cooler than those

placed over concrete and about 20°F cooler than the ambient. In each

case, we observed that the white surfaced membranes (Curves 3 & 5)

were slightly cooler than their black counterparts.

The emissive properties of most organic roofing materials, unlike their

solar heating characteristics, are for all practical purposed independent

of surface color or texture. A case in point is illustrated in Figure 11

where the marked effect of solar heating on the black specimen is clearly

indicated in comparison with the slight effect of emissivity on both

the black and white surfaced specimens. The time-temperature curves

identified as 1, 2 and 3 were recorded on 13 October 1962.

Again during the snow cover in December-January it was observed that

the temperatures of the ambient air and all the specimens were essentially

the same when the specimens were covered with snow.

2.3 Summary

In connection with solar heating and emissive cooling of roof surfaces,

the findings of this study may be summarized as follows:

1. Roof surfaces are heated by solar radiation. The degree of

heating is dependent upon:

a. Character of substrate (mass, density, specific lieat)

b. Properties of surface protection (color and texture)

c. Atmospheric conditions (wind velocity, rain, clouds,

haze, etc.)

d. Presence of a snow cover.

2. Roof surfaces may be sub-cooled by their emissive properties.

The magnitude of sub- cooling is dependent upon:

a. Character of substrate (mass, density, and specific heat)

b. Nature, -ef tb*e exposed material (metallic, organic)

c. Atmospheric conditions

d. Presence or absence of snow cover.

For all practical purposes the emissive cooling of organic building

materials is independent of color or texture of the surface.
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DAY

- 9 -

The data obtained in the experimental work indicated that a black, insulated roof membrane was subjected to a temperature change of about

180°F in a period of one year and in excess of 80°F in a period of

two hours when exposed in the Washington, D. C. area.

Obviously for other membranes, both insulated and non-insulated, these

extremes will be somewhat less depending on the base on which the

membrane is applied and on the color and texture of the protecting

surface. It is expected that these extremes will also vary to a lesser or greater extent for similar roof systems exposed in different

locations.

3. THERMAL MOVEMENT OF COMPONENTS OF A ROOF SYSTEM

It is an established fact that with few exceptions the dimensions of

materials increase as the temperature of the material increases and

decrease as the temperature decreases. The relation between linear

change and temperature has been expressed as follows:

AL = A L0 At where:

AL = change in length

L

q = length at some reference temperature

At = temperature change

c*\ = proportionality constant which varies from

material to material and is identified as the coefficient of linear expansion.

Our experience in the field has indicated that many of the common

built-up roof failures can be directly or indirectly traced

to thermal movements within a specific component of the roof system

or by the differential movement among the components as the membrane,

insulation, deck and flashings. It is our opinion that the expansive

and contractive movements resulting from temperature change are of

paramount importance and, therefore, the extent of this movement

should be known.

The coefficients of linear expansion for many materials used in the

roof system has been determined and are reported in the literature.

Values for some materials are given in Table 4 where they are reported

in the usual term of inches per inch per degree F and in inches per

100 feet per 100 degrees F.

However, little published information is available for the coefficient

of linear expansion of a composite membrane consisting of alternate

layers of bitumen and felt. Therefore, a program was initiated to

measure this property of a number of composite membranes.
.

' '
TABLE 4

LINEAR EXPANSION OF MATERIALS USED AS COMPONENTS OF A ROOF SYSTEM

Material Coefficient of Linear Expansion

in. / in. • in. /lOO ft.

°F 100°F

Roof Decks

Steel 6.0 X lot .7

Concrete 5.0 X 10 i

.6

Wood 2.0 X lcr

6

.2

Plywood 3.5 X 10l6 A

Gypsum 8.0 X 10

0

1.0

Insulations

Foam glass 4.

6

X 10“°

10" 5

10“5

.6

Poly Styrene 3.0 X 3.6

Polyurethane 3.0 X 3.6

Flashing Metals r Aluminum 1.3 X 10-§ 1.6

Copper 9.5 X 10

6

1.1

Gal. Iron 6.7 X 10-5

10 5

.8

Lead 1.6 X 1.9
.
3.1 Experimental Design

Two types of samples were used in the experimental work, the first was

a sample taken from an actual roof while the remainder consisted of

samples prepared in the laboratory. Table 5 identifies the samples.

TABLE 5

Sample No. No. of Plies Description

1 5 asphalt-organic felt from

actual roof.

2* 4 asphalt - 15 lb. asphalt

sat. organic felt.

3* 4 coal tar pitch - 15 lb. coal

tar sat. organic felt.

4* 4 asphalt - 6 lb. asphalt

impregnated glass mat (felt).

3* 4 asphalt - 15 lb. asphalt

saturated asbestos felt.

* Approximately 20 pounds/100 sq.ft, of bitumen were used between the

plies and no surfacing was applied to the specimens.

Duplicate specimens, 12 in. x 2 in., were cut from the samples. Two

brass reference plugs were inserted into the specimen near each end

exactly 10 inches apart when measured at a temperature of ?3°F. The

specimens were placed unrestrained on a flat surface in the conditioning

chamber. A copper-constantan thermocouple was inserted into a control

specimen and the temperature of the chamber was reduced to -60°F.

The distance between the reference plugs on each specimen was measured

to the nearest ten thousandeth of an inch with a Whittemore Strain

Guage. The temperature in the chamber was gradually raised in increments

of about 10°F and after the specimens reached equilibrium the distance

between the reference plugs was measured. This procedure was repeated

for each specimen over the temperature range of -60°F to l60°F. The

coefficient of linear expansion were calculated by solving the following

equasion for ©C :
M
11

3.2 Results

The results of the experiments indicated that the linear change for

composite bituminous membranes was apparently not constant over the

temperature range to which exposed. The changing nature of this

coefficient is illustrated in Figure 12 where the length increase

of Sample 1 is plotted against the temperature. The calculated

coefficients of linear expansion expressed in./in./°F and in. /100ft./

100° F for the ranges indicated are also given. The length-temperature

curves for other built-up specimens exhibited similar characteristics although

their coefficients of linear expansion were somewhat less than those

of Sample 1. The calculated coefficients of linear expansion for the

various samples over three temperature ranges are given in Table 6.

TABLE 6.

COEFFICIENT OF LINEAR EXPANSION OF BUILT-UP ROOF SPECIMENS

Sample

1

2

3

4

5

Description Coefficient of linear expansion

in. / in./°F

(cC )

-60°F to 0°F 0°F to 77°F 77°F to 154 °F

Asphalt -rag

Asphalt -rag

Coal tar-rag

Asphalt -glass

Asphalt4.1 x 10”^ 1.5 x 10“5

, 1.8 x 10 3.0 x

10~°

1.4 x 10“^ 7.5 x 10‘6

3.2 x 10“5 5.3 x 10“6

1.2 x 10“5

4.5 x 10“6

2.5 x 10*^

3.1 x 10"?

2.4 x 10

asbestos
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12 -

The results of the determinations revealed that the expansion and contraction of a built-up membrane due to changing temperatures is apparently

greater than for the other components generally used in a built-up

roof system. The data also indicated the changing nature of the linear

movement of a composite membrane depending on the temperature range to

which exposed. This phenomenon appears to hold true for both asphalt

and coal-tar pitch materials and for both organic and inorganic reinforcing felts.

The significance of the data appears obvious in that movements due to

thermal changes are most critical in the low temperature ranges as opposed to the minimal movement in the high temperature ranges.

Although the magnitude of the length change was unexpected, the changing

nature of the coefficient of linear expansion can be explained theoretically,

at least in part, by the visco -elastic behavior of roofing bitumens.

4. SUMMARY AND CONCLUSIONS

It is an accepted fact that many built-up roof systems are complex

systems made up of many components and that the materials comprising

the components of a roof system exhibit different movement rates when

subjected to temperature changes. As a result of the data obtained in

this study, we have established the following:

a. Built-up roof membranes may be subjected to large temperature

changes as a result of solar heating and emissive cooling,,

b. Built-up roof membranes apparently undergo greater thermal

movements than most other components of a roof system.

c. Thermal movement per degree change in temperature of a builtup membrane is not linear with temperature ana increases as the temperature is decreased.

When these concepts are considered collectively, it is readily apparent

that many of the failures which commonly occur in built-up roof systems

result directly or indirectly from solar heating, emissive cooling and

thermal movement.

Flashing failures at, the junction of a bituminous membrane with metal

base flashings, gravel stops and other metal appurtepances may be

caused or accelerated by their differences in emissivity and by their

different coefficients of linear expansion*
, .
- 13 -

Temperature and temperature changes are certainly factors to be considered

in the wrinkle cracking or buckling of roofing felts and in the formation

and subsequent growth of blisters beneath or between the plies of the

membrane especially if moisture is present in some component of the

roof system.

Solar heating is a most important factor when a slippage of roof membrane

occurs, assuming other pertinent factors are present.

In connection with the weathering of the roofing bitumen, it is a well-known fact that the chemical degradation of asphalt is accelerated

by increased temperatures. In addition, our experience indicates that

the physical deterioration of a weathered bitumen may be accelerated

by thermal shock due to rapid temperature changes.

Theoretically, solar heating, emissive cooling, and thermal movement

may also result in insulation problems such as breakage, cupping or

curling, if the following conditions are present: l) Insulation has

a high coefficient of linear expansion, 2) adhesion of insulation to

roof deck is poor and 3) large thermal gradient exists within the

insulation.

Reports from the field regarding splitting failures and membrane ruptures

indicated that thermal shock is a primary factor in many such failures.

If this is correct, solar heating, emissive cooling, and thermal movement must certainly be considered. Sub- cooling of tha membrane due

to surface emissivity and the magnitude of linear change exhibited by

a bituminous membrane at low temperatures appears significant, especially

if the membrane is applied over insulation. This opinion is strengthened

by our observations in this study concerning the insulating value of a snow cover which tends to stabilize roof temperatures. This factor

accounts for, at least in part, the greater number of complaints involving

roof splitting and membrane rupture failures that are received during

extended cold spells with no snow cover.

In conclusion, we believe that the data obtained in the present program

has shed new light on the pertinent factors involved in many premature

failures in a built-up roofing system. Further, the information

obtained confirms many of our opinions formally based on field

experience alone.
! "
14 - 5.

PRACTICAL APPLICATION OF THE DATA

It is often quite difficult to convert the data which are obtained in

the laboratory directly to practical applications in the field.

Nevertheless, due to the critical need of information in roofing

practices, we feel that an interpretation of this data for use in the

field is not only justified but is necessary. We are aware, of course,

that others involved in the various phases of the roofing industry

may interpret some of the results differently.

The following statements are based on both the data obtained in this

study and on considerable field experience.

1. The use of insulation between the roof deck and membrane should be

avoided in extremely cold climates especially those with little snow

fall. If the use of insulation above the deck is necessary, and it

will be in many cases, the roof should be surfaced with a mineral

aggregate and adequate expansion joints should be installed to prevent

membrane failures.

2. Roof membranes placed over insulation should always be surfaced

with a mineral aggregate or a surface having a high solar reflectance

value. Criteria, other than solar reflectance, must also be considered

in the selection of a surfacing material as durability, hardness,

sieve gradation, and maintenance required.

3. The use of smooth, asphalt surfaced, built-up roofs should be

avoided, especially those which are insulated.

4. In connection with the prevention of membrane slippages on roofs

having slopes of 1 inch or more per foot, two factors should be considered:

1) the use of reflective surfacing materials to reduce temperature and

2) the placement of insulation beneath the roof deck.

5« The emergency application of a reflective coating to an existing

roof showing indications of slippage may prevent a costly failure.

6. Reflective surfaces may be applied to built-up membranes to reduce

interior temperature and to reduce air conditioning loads in a conditioned

structure.

7. Base flashings constructed of bituminous materials should be used

in conjunction with built-up roofings wherever possible.

8. When metallic flashings are tied into the bituminous membrane, a bituminous plastic cement should be employed between the metal and

bituminous membrane to compensate for the differential movement of the

two materials.
• a 5
- 15 -

6. ACKNOWLEDGEMENT

The author acknowledges with thanks the assistance of Mr. William H.

Appleton who constructed and instrumented the built-up roof specimens

and prepared the specimens for and made the measurements of the coefficients

of linear expansion of the roof membranes. The author also acknowledges

with appreciation the advise and encouragement given to him by Dr. W. W.

Walton, Chief of the Organic Building Materials Section, National Bureau

of Standards, and the members of the Tri-Service Committee.

7. REFERENCES

1. Billington, Neville S., J. of Inst, of Heating and Vent. Eng.

Vol. 19, 112 (June 1951).

2. Beckett, H. E., J. of Inst, of Heating and Vent. Eng., Vol. 3,

79 (1935-36).

3. Hendry, A. W. and J. K. Page, "Thermal Movements and Stresses in

Concrete Slabs in Relation to Tropical Conditions", International

Symposium on Concrete and Reinforced Concrete to Tropical Countries , r.i.l.e.m. , Haifa, Israel, (i960).

4. Cullen, W. C. and W. H* Appleton, "The Effects of Insu3a tion on

the Durability of a Smooth-Surfaced, Built-Up Roof", National

Bureau of Standards Report No. 7^70 o (March 30, 1962).

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