Reference NBS

canons

NATL INST OF STAND & TECH

NBSIR 76-987

Effect of Insulation on the

Surface Temperature of Roof

Membranes

Walter J. Rossiter, Jr. Robert G. Mathey

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

February 1976

Final

U S DEPARTMENT OF COMMERCE

' QC JIONAL BUREAU Of STANOAROS

100

.U56

76-987

1976

•AtlOHAI. BUmBAl) or aTAMDAROS

LIBKAJtT MAY 1 3 1981

NBSIR 76-987 r^u^ Qc-loo

EFFECT OF INSULATION ON THE

SURFACE TEMPERATURE OF ROOF

MEMBRANES ^

Walter J. Rossiter, Jr. Robert G. Mathey

Center for Building Technology

Institute for Building Technology

National Bureau of Standards

Washington, D. C. 20234

February 1976

Final

U.S. DEPARTMENT OF COMMERCE, Elliot L. Richardson, Swcrefry

James A. Baker, III, Under Secretary

Or. Betsy Ancker-Johnson, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler. Acting Director

TABLE OF CONTENTS

Page

ABSTRACT 1

1. INTRODUCTION 1

2. BACKGROUND 2

3. HEAT TRANSFER THROUGH FLAT ROOFING SYSTEMS 2

4. DISCUSSION 12

5. SUMMARY AND CONCLUSIONS 15

6. REFERENCES 16

I

I

111

Effect of Insulation on the Surface Temperature of Roof Membranes

by

Walter J. Rossiter, Jr.

Robert G. Mathey

ABSTRACT

The surface temperatures of black, gray and white roofs were calculated for various

thicknesses of insulation located between the membrane and roof deck. The calculations

were performed using a steady-state heat balance equation to illustrate the increase in

roof surface temperatures due to solar radiation.

The calculations indicate that the first increment, about 1 inch (25 mm) ,—^ of

insulation causes a significant rise in the roof surface temperature due to solar radiation.

Increasing the amount of insulation above this first increment to greater thicknesses does

not appreciably increase the roof surface temperature.

Keywords: Built-up roofing; insulation; performance; radiative cooling; roofing; solar

heating; surface temperature.

1 . INTRODUCTION I

It has been reported that increased ^mounts of insulation between the roof deck and

the membrane will shorten roof life [1-3]— . The concern is that roofs with greater

amounts of insulation will be subjected to greater extremes in temperature. The reasons

stated for lessening roof life were accelerated aging due to higher roof temperatures in

the summer and larger contractive forces caused by thermal shock in the winter. Earlier

research at the National Bureau of Standards (NBS)[4] showed that bituminous membranes

placed over insulation develop higher temperatures on sunny days than membranes placed

directly on the deck. On clear nights membranes over insulation can be considerably colder

than those that are not insulated. This may have significance in the winter when ambient

temperatures are low.

Increased amounts of insulation (lower U-values) are now specified for roofs in many

cases because of the need for energy consei~vation. Buildings are among the largest energy

consumers in the United States and use approximately one-third of the total consumption [5].

Much of this energy can be conserved by decreasing the energy consumption of buildings. One

of the important methods of accomplishing this is by increasing the amount of insulation.

It is noted that approximately 70% of currently constructed low-sloped roofs are insulated [6].

Research is needed to determine the effect of insulation on roof performance. At present, criteria are not available to evaluate the performance of roofing systems which

contain increased amounts of insulation necessary to obtain lower U-values. Many factors

regarding insulation should be considered in evaluating roof performance. These factors

include mechanical properties such as impact resistance, compressive strength, punching

shear resistance, cohesive strength and flexural strength; dimensional stability including

warping and length changes; coefficient of thermal expansion; moisture effects including

1/ Numbers in parentheses are in units of the metric system, formally called the

International System of Units (SI)

2/ Numbers in brackets refer to references in Section 6.
absorption and permeability; adhesion between roofing components; durability; installation

procedures; f lammability ; and thermal conductivity.

This paper shows that increasing the amount of insulation over that normally used in an insulated built-up roofing system will not cause a significant increase or decrease in the

roof membrane temperature. Calculations and illustrations are presented as examples that

give membrane temperatures for thicknesses of insulation ranging from zero to five inches

(0 to 127 mm)

2 . BACKGROUND

In a 1963 National Bureau of Standards Technical Note, Cullen reported temperature

data on some built-up roofing systems which were exposed to solar heating and radiative

cooling [4] . Solar heating is the process whereby the temperature of a surface rises above

ambient air temperature as the surface absorbs solar radiation. Radiative cooling is the

process whereby the temperature of a surface drops below ambient air temperature as the

surface exchanges long-wave radiation with the cold night sky. Cullen 's data showed that

in the summer built-up roofing membranes set on insulation may be as much as SOT (44°C)

hotter than ambient air temperature. He also reported that during a winter night a membrane

placed over insulation may be 20°F (11°C) cooler than ambient air. The magnitude of the

solar heating or radiative cooling was considered dependent upon a number of factors including mass, density and thermal properties of the substrate under the membrane, the

absorptance or emissivlty of the membrane surface, and atmospheric conditions. The paper

did not discuss the magnitude of solar heating or radiative cooling as a function of t-he amount of insulation or of the U-value of the test specimen.

The information presented in this NBS Technical Note [4] may be subject to some misinterpretation regarding the magnitude of temperature extremes of membranes placed

over greater amounts of insulation. The temperature of the membrane is affected by the

thickness of the insulation up to a certain point. Beyond this thickness the effect on surface temperature is insignificant. This is demonstrated herein by examining the

physical process which occurs when a roof is exposed to solar radiation. Temperatures of

building exterior surfaces exposed to solar radiation have been discussed in the

literature [7-9].

3. HEAT TRANSFER THROUGH FLAT ROOFING SYSTEMS

Heat transfer concepts, as defined by the ASHRAE Handbook of Fundamentals [10], are given in table 1. These concepts are also defined and discussed in a roofing trade

publication [11] . The important term to be considered in this discussion is the U-value

or overall coefficient of heat transmission (thermal transmittance)

There are two ways of increasing the thermal efficiency (lowering the U-value) of a roofing system. One method is to use a more efficient insulation (lower k-f actor) , and

the other is to increase the thickness of the insulation. Using presently available roof

insulation the k-f actor is limited and therefore a roof with a low U-value, for example

0.05 to 0.10 Btu/h ft^ °F (0.28 to 0.57 W/m^K) , cannot be achieved with the thickness of

insulation normally used. This leads to the only remaining option for lowering the

U-value; namely, increasing the thickness of the insulation. A list of k-factors for the

most common roofing insulations is given in table 2.

Figure 1 shows schematically the physical processes which occur when a roof is

exposed to sunlight (radiant energy). A portion of the sunlight incident on the roof is

absorbed, part is reflected. As some of the sunlight or radiant energy is absorbed, the

temperature of the roof surface rises. This energy is dissipated by three processes,

conduction, convection and re-radiation. The better the roof is able to dissipate the

energy through these three processes, the less the temperature of the roof surface will

rise. Adding insulation to the roof reduces the amount of heat dissipated by conduction.

Consequently, a roof membrane over insulation will be hotter than if it were placed

directly on a deck. As the amount of heat dissipated through conduction is reduced, the

heat dissipated through convection is increased. Therefore, the temperature of the

membrane will not continue to increase significantly as more insulation is added to the

roof.

2
Table 1. Heat Transfer Concepts

Symbol Concept Definition Units

thermal conductivity Timp rate of heat flow through a homogeneous material under steadystate conditions through unit area, per unit temperature gradiant.

Btu/h ft °F/in

thermal conductance Time rate of heat flow through a material for any thickness. C = k/n where n = thickness expressed

in inches or meters.

Btu/h ft

(W/m^K)

thermal resistance The reciprocal of the thermal

conductance, R = 1/C.

'F h ft /Btu

(m^K/W)

overall coefficient

of heat transmission

(thermal transmit tance)

The reciprocal of the summation

of the resistance of each material

in a wall, roof, floor or ceiling

plus the surface conductance on both sides. U = 1/R ^ , total

Btu/h ft

(W/m^K)

1/ SI units in parenthesis

3
Table 2. Thermal Conductivities of Roof Insulations

Insulation Density Thermal Conductivity, k—

Ib/ft^

(kg/m ) -

Btu/h ft^ "F/in

(W/mK)

3/ Foamed urethane— 1.5-2.5 0.16

(24-40) (0.9)

3/ Glass fiberboard— 4-9 0.25

(64-144) (1.4)

3/ Extruded polystyrene— 1.8 0.25

(29) (1.4)

4/

' Cork board— 6.5-8 0.28

(104-128) (1.6)

3/ Mineral fiberboard— 16-17 0.34

(256-272) (1.9)

Wood fiberboard—'' 15-22 0.36

(240-352) (2.0)

Perlite aggregate board—'' 11 0.38

(176) (2.2)

3/ Cellular glass- 9 0.40

(144) (2.3)

Lightweight concrete.

Perlite aggregated'

20-40 0.70-1.15

(320-641) (4.0-6.5)

Lightweight concrete, . Vermiculite aggregate20-40 0.70-1.15

(320-641) (4.0-6.5)

1^1 Tabulated values are for a mean temperature of 75''F (24''C).

2^/ SI units in parenthesis.

y Values from the ASHRAE Handbook of Fundamentals, 1972 edition [12].

4^/ Values from the ASHRAE Handbook of Fundamentals, 1967 edition [13].

V Values from the Manual of Built-Up Roof Systems [14].

4
<s§- s

tu 2

CO oc CO

LU °b

cj 3 £ CO

-J< 2»- ^ o

UJ

Q ^

£2 3

if) 5
I

The absorptance of radiant energy and dissipation of heat energy can be expressed

mathematically. The law of conservation of energy states that energy can neither be

created nor destroyed. Thus, for a steady-state condition all the sunlight energy absorbed

by the roof must be dissipated by conduction, convection and re-radiation, as given in the

following equation.

Absorbed Energy = Heat Losses (Conduction + Convection + Re-radiation)

This is called a heat balance equation. For a steady-state condition, it is mathematically

expressed as follows [15]

al = U (t - t.) + h (t - t ) + eAR (1)

s i O S o where

a = absorptance of the roof for solar radiation

2 2

I = total solar radiation incident on the roof, Btu/h ft (W/m )

U = coefficient of heat transmission of the roof, not including outside surface

2 2 conductance, Btu/h ft °F (W/m K)

tg = surface temperature, °F (°C)

t^ = inside air temperature, °F (°C)

h^ = coefficient of heat transfer by convection and long-wave length radiation to the

1/ 2 2 surroundings (not including the sky) at the outer surface,— Btu/h ft "F (W/m K)

t^ = outside air temperature, "F (°C)

e = hemispherical emittance of the surface

1/ 2 2 AR = the net long-wave radiation to the sky,— Btu/h ft (W/m )

The above equation includes the two terms which are of interest to this discussion,

namely, the U-value and the surface temperature. After selecting values for the other

parameters, the surface temperature of the roof was calculated as a function of the U-value.

Table 3 lists three sets of values for the parameters in equation (1) which were used in

the calculations. These values represent environmental conditions on a hot, sunny, summer day where the outside air temperature is 95°F (35°C), the inside air temperature is 72*F

(22*'C) and the wind is 5-10 miles per hour (2-4 m/s) at the roof level. Each set differs

from the others only in the value of the absorptance of the roof surface. Values of

absorptance correspond to black, gray and white surfaces.

A simple roof structure, chosen as a basis for the calculation of roof surface

temperatures in this paper, is shown in figure 2. The roof consists of a metal deck, insulation and a built-up roofing membrane. The thickness and k-f actor of the roof Insulation were varied. The total thermal resistance of this roof, Rj-q^. •)» as shown in figure 2, is

1.25 h ft^ "F/Btu (0.22 m^ K/W) plus the thermal resistance of the insulation, R^.

\otal = 1-25 + (2)

Using equation (2) and the relationship U = l/^total' U-value of this roof was calculated as a function of the thickness of the insulation. Tables 4, 5 and 6 give

U-values of the roof for k-factors of the insulations of 0.17, 0.24 and 0.36

Btu/h ft^ "F/in (0.024, 0.035 and 0.052 W/m K) respectively.

IT The definitions of h^ and AR differ from those given in the ASHRAE Handbook of

Fundamentals [15]. These definitions were changed in this paper for editorial

clarification.

6
Table 3. Parameters Used in the Heat Balance Equation for

Calculating the Surface Temperature as a Function

of U- value

Parameter Units Case I Case II Case III Black Surface Gray Surface White Surface

CL— 0.9 0.7 0.5

1-' Btu/h ft 300 300 300

(W/m^) (945) (945) (945)

"ICc)

72

(22)

72

(22)

72

(22)

h 1/

o Btu/h ft^ "F 4 4 4 (W/m^ K) (23) (23) (23)

t o

"F

("C)

95

(35)

95

(35)

95

(35)

0.9 0.9 0.9

Btu/h ft^ 20 20 20

(W/m^) (63) (63) (63)

1/ Values from reference [4], page 7.

2/ This value is typical for a horizontal surface on a sunny summer day at noontime

at 40" northern latitude.

3/ Value from the ASHRAE Handbook of Fundamentals [16]. This value represents a wind

velocity of 5-10 miles per hour (2-4 m/s) across the surface.

V Value from the CRC Handbook of Materials Science [17]. Value is for anon-metallic

surface.

5/ Value from ASHRAE Handbook of Fundamentals [15]. Value is for a horizontal surface.
8
Table 4. Calculated Surface Temperature of the Roof as a Function of the Thickness of the Insulation,

k = 0.17 (0.024)

Thickness of U-value—

Insulation Btu/h ft^ °F Surface Temperature of the Roof, "F ("Q

in (mm) (W/m^K) Case I, Black Case II, Gray Case III, White

0 0. 80 143 .131.118 .

(4.5) (62.1) (55.1) (48.2)

0.5 0.24 153.1 139.0 124 .

(13) (1.4) (67.3) (59.4) (51.6)

1.0 0.14 155.1 140.6 126.1

(25) (0.80) (68.4) (60.3) (52.3)

1.5 0. 10 155.9 141.3 126.6

(38) (0.57) (68.8) (60.7) (52.6)

2.0 0.077 156.4 141.7 126.9

/CI \ (51) (0.44) (69.1) (60.9) (52.7)

2.5 0.063 156.7 141.9 127.1

(64) (0.36) (69.3) (61.1) (52.8)

3.0 0.053 156.9 142.1 127.3

(76) (0.30) (69.4) (61.2) (52.9)

3.5 0.046 157.0 142.2 127.4

(89) (0.26) (69.4) (61.2) (53.0)

4.0 0.041 157.1 142.2 127.4

(102) (0.23) (69.5) (61.2) (53.0)

5.0 0.032 157.2 142.4 127.6

(127) (0.18) (69.6) (61.3) (53.1)

OO 0.0 158.0 143.0 128.0

(70.0) (61.7) (53.3)

y U-value of the hypothetical roof system shown in Figure 2. The U-value does not Include

the thermal resistance of the air at the outside surface of the roof.
Table 5. Calculated Surface Temperature of the Roof as a Function

of the Thickness of the Insulation, k = 0.24 (0.035)

Thickness of U-value—

Insulation Btu/h ft °F Surface Temperature of the Roof, °F (°C)

in (mm) (W/m^K) Case I, black Case II, Gray Case III, White

0 0.80 143.7 131.2 118.7

(4.5) (62.1) (55.1) (48.2)

0.5 0.30 152.0 138.0 124.1

(13) (1.7) (66.7) (58.9) (51.2)

1.0 0.18 154.3 139.9 125.6

(25)

i i : (1.0) (67.9) (59.9) (52.0)

1.5 ' r V 0.13 155.3 140.8 126.2

(38) (0.74) (68.5) (60.4) (52.3)

2.0 0.10 155.9 141.3 126. 6 (51) (0.57) (68.8) (60.7) (52.6)

2.5 0.086 156.2 141.5 126.8

(64) (0.49) (69.0) (60.8) (52.7)

3.0 0.072 156.5 141. 7 127.0

(76) (0.41) (69.2) (60.9) (52.8)

3.5 0.064 156.7 141.9 127.1

(89) (0.36)

''. (69.3) (61.1) (52.8)

4.0 0.055 156.8 142.0 127.2

(102) (0.31) . (69.3) (61.1) (52.9)

4.5 0.049 157.0 142.1 127.3

(114) (0.28) (69.4) (61.2) (52.9)

5.0 0.045 157.0 142.2 127.4

(127) (0.26) (69.4) (61.2) (53.0)

oo 0.0 158.0 143.0 128.0

(70.0) (61.7) (53.3)

1/ u-value of the hypothetical roof system shown in Figure 2. The U-value does not include

the thermal resistance of the air at the outside surface of the roof.

10
Table 6. Calculated Surface Temperature of the Roof as a Function

of the Thickness of the Insulation, k = 0.36 (0.052)

Thickness of U-value—

Insulation Btu/h ft^ "F Surface Temperature of the Roof. °F (°C)

in (mm) (W/m^K) Case I, Black Case II, Gray Case III, White

0 0.80 143.7 131.2 118.7

(4.5) (62.1) (55.1) (48.2)

0.5 0.38 150.5 136.8 123.1

(13) (2.2) (65.8) (58.2) (50.6)

1.0 0.25 152.9 138.8 124.7

(25) (1.4) (67.2) (59.3) (51.5)

1.5 0.18 154.3 139.9 125.6

(38) (1.0) (67.9) (59.9) (52.0)

2.0 0.15 154.9 140.4 126.0

(51) (0.85) (68.3) (60.2) (52.2)

2.5 0.12 155.5 140.9 126.4

(64) (0.68) (68.6) (60.5) (52.4)

3 .

0. 10 155.9 141.3 126.6

(76) (0.57) (68.8) (60.7) (52.6)

3.5 0.091 156.1 141.4 126.8

(89) (0.52) (68.9) (60.8) (52.7)

4.0 0.081 156.3 141.6 126.9

(102) (0.46) (69.1) (60.9) (52.7)

4.5 0.073 156.5 141.7 127.0

(114) (0.41) (69.2) (60.9) (52.8)

5.0 0.066 156.6 141.8 127 .1 (127) (0.37) (69.2) (61.0) (52.8)

oo 0.0 158.0 143 .

128.0

(70.0) (61.7) (53.3)

ll u-value of the hypothetical roof system shown in Figure 2. The U-value does not include

the thermal resistance of the air at the outside surface of the roof.

11
Substituting these U-values and the values of the parameters given in table 3 in the

heat balance equation (equation 1) , the surface temperatures of the roof were calculated as

a function of the thickness of the insulation. Tables 4, 5 and 6 show the results of these

calculations for black, gray and white roofs having insulation with various k-factors. The

results of these calculations are illustrated graphically in figure 3.

4. DISCUSSION

The surface temperature calculations outlined in the preceding section were based on heat transfer design values and some realistic values of parameters included in the heat

balance equation (equation 1) . It is emphasized that these values of surface temperature

were not determined experimentally. However, the calculated values can be used to illustrate the effect of increasing amounts of insulation on the temperature extremes of the

roofing membrane. The theoretical calculations of surface temperatures for steady-state

conditions were based on physical principles which are well established [15]

Three different colored roof surfaces were considered in the calculations. As expected,

the calculated values shown in figure 3 indicated that a black surface exposed to sunlight

becomes hotter than a gray surface and the gray surface is hotter than a white surface. In all three cases, even when there is no insulation in the roof system, the surface temperature

is greater than the selected ambient temperature of 95°F (35°C). If the roof is capable

of absorbing solar radiation, its surface will in general heat up.

It can also be seen in figure 3 that when insulation is added between the membrane and

the deck, the roof surface temperature rises. However, only the first inch (25 mm) or so of insulation causes a significant rise in the surface temperature. As an example, 1 inch

(25 mm) of insulation placed under the black surfaced roof causes an increase of about

ll^F (6°C). Additional insulation above this amount causes little increase in the surface

temperature. For the black surfaced roof, increasing the insulation thickness from 1 to

5 inches (25 to 127 mm) only results in an increase of the surface temperature of about 2 to 4°F (1 to 2°C) depending on the k-factor of the insulation.

The k-factor for a given thickness of the insulation had very little effect upon the

surface temperature, as shown in figure 3. As the k-factor decreases, the surface temperature approaches Its maximum temperature at a slightly faster rate.

Figure 3 is included to show the effect of the thickness of insulation on surface

temperatures because this is an important concern of the roofing industry. A measure of the

thermal efficiency of a roofing system is its U-value and not the thickness of insulation.

Figure 4 shows the surface temperature of the black, gray and white roofs as a function of

the U-value in the range 0.0 to 0.38 Btu/h ft^ °F (0.0 to 2.2 W/m2K) . This is the range of

interest when discussing insulated roofs. Before the energy crisis and the need to conserve

energy, most insulated roofs had design U-values of about 0.15 to 0.20 Btu/h ft^ °F (0.85 to 1.1 W/m^K). Now, some specifications are requiring U-values as low as 0.05 Btu/h ft °F

(0.28 W/m^K) . Of course, a U-value of 0.0 (infinite thickness of insulation) is impossible

since it means that the roof transmits no heat. However, a U-value of 0.0 can be used to show theoretically the maximum temperature of the roof surface for a given environmental

condition (tables 4, 5 and 6).

Figure 4 shows that decreasing the U-value from 0.20 to 0.05 Btu/h ft^ °F (1.1 to 0.28 W/m'^K) has a minimum effect on the surface temperatures of the black, gray and white

roofs. For the black roof, the increase in surface temperature for this range of U-values

is only 3''F (2°C). For the other two roofs, it is even less.

The surface temperature calculations have been performed for a steady-state condition.

Under this condition the rate of energy absorbed by the roof is dissipated at an equal rate. Steady-state condition is in general never attained for heat transfer through a roof system.

Steady-state condition is approached when a low density insulation having a low heat capacity

is located between the membrane and the deck. The surface temperature calculations are more complicated for a non-steady-state condition, and are beyond the scope of this paper. In general, the surface temperature of a membrane will not be as high when it is placed on a high heat capacity material as compared to a low heat capacity material having the same U- value. There is a thermal lag as a high heat capacity material takes time to store thermal

energy.

12
0

THICKNESS OF INSULATION, mm

25 50 75 100 125 150

160

UJ

o

CO

no

100

BLACK ROOF

GRAY ROOF

WHITE ROOF

INSULATION k FACTOR

OI7 (0.024)

024 (0.035)

0.36 (0.052)

Outside ambient air temperature, 95" F ( 35**C)

J I I J L J L

0 12 3 4 5

THICKNESS OF INSULATION, in

70

65

60

55

50

45

40

35

O

o

LU

CC

D

<

LU

CL

LU

LUO

cr3

FIGURE 3. SURFACE TEMPERATURE OF THE ROOF MEMBRANE AS A FUNCTION

OF THE AMOUNT OF INSULATION FOR THE PARAMETERS GIVEN

IN TABLE 3.

13
Oo '3aniVd3di/^3i 30Vddns

o lo

^

ro cvj

do'3anivd3diM3i 30\/3ans

14
It is interesting to note Cullen [4] reported that roof surface temperatures attained

by black surfaced membranes over concrete and wood on a summer day in Washington, DC were

120 and 145 °F (49 and 63 °C) respectively. This difference in the maximum membrane temperatures of 25°F (14°C) indicates from the experimental results that the heat capacity of

uninsulated decks effects the surface temperature of applied membranes.

The heat balance equation (equation 1) can also be used to show the effect of radiative

cooling on the surface temperature as a function of the U-value. The magnitude of radiative

cooling is greatest on clear still nights when the roof is receiving negligible radiation

from the sky. Calculations of surface temperatures are not shown since they are similar to those for solar heating. In general, a membrane placed directly on a deck will not be as cold as one on insulation. However, increasing the thickness of insulation (decreasing

the U-value) above the amount normally used causes little decrease in the temperature of the

surface of the roof due to radiative cooling.

5. SUMMARY AND CONCLUSIONS

The surface temperatures of black, gray and white roofs were calculated for various

thicknesses of insulation located between the membrane and the deck. The calculations were performed using a steady-state heat balance equation to illustrate the increase in roof

surface temperature due to solar radiation. The values of the parameters used to solve this

equation represented environmental conditions of a hot, sunny, summer day where the outside

temperature was 95°F (35°C), the inside temperature was 72°F (22°C) and the wind was 5-10

miles per hour (2-4 m/s) at the roof level.

The calculations indicate that the first increment, about 1 inch (25 mm), of insulation

causes a significant rise in the roof surface temperature due to solar radiation. Increasing

the amount of insulation above this first increment to greater thicknesses does not appreciably increase the roof surface temperature.

This paper deals only with the surface temperature of roofs containing various amounts

of insulation. As pointed out in the paper, the authors believe that research is needed to determine the effect of insulation on roof perfonnance . Criteria are needed to enable the

evaluation of the performance of roofing systems which contain increased amounts of insulation necessary to obtain lower U-values.

15
6 . REFERENCES

1. "NRCA Tells How to Stop Roof Problems Caused by New Insulation Guidelines", American

Roofer and Building Improvement Contractor, November-December 1974, p. 5.

2. "Energy Shortage Could Lessen Roof Life", Carolina Contacts, November-December 1974,

p. 15.

3. Rissmiller, Edwin, "Roof Temperature Change - Cause and Effect", Roof ing/Siding/lnsulation, April 1975, p. 22.

4. Cullen, William C, "Solar Heating, Radiative Cooling, and Thermal Movement - Their

Effects on Built-up Roofing", Nat. Bur. Stand. (U.S.), Tech. Note 231, 33 pages,

December 1963.

5. Seidel, Marquis R. , Plotkin, Steven E. and Reck, Robert 0., "Energy Conservation

Strategies", Environmental Protection Agency Report EPA-R5-7 3-021 , July 1973, p. 12.

6. "Project Pinpoint, The First Returns", The Roofing Spec, March 1975, p. 12.

7. Latta, J.K. and Garden, G.K. , "Temperature Gradients Through Building Envelopes",

Canadian Building Digest 36, National Research Council, Canada, UDC 697.133, December

1962.

8. Stephenson, D.G., "Extreme Temperatures at the Outer Surfaces of Buildings", Canadian

Building Digest 47, National Research Council, Canada, UDC 697.13, November 1963.

9. Garden, G.K., "Thermal Considerations in Roof Design", Canadian Building Digest 70,

National Research Council, Canada, UDC 69.024, October 1965.

10. ASHRAE Handbook of Fundamentals, American Society of Heating, Refrigerating and AirConditioning Engineers, Inc., New York, N.Y., 1972, p. 347.

11. "Thermal Factors - K, C, R, and U", American Roofer and Building Improvement Contractor,

January-February 1975, p. 18.

12. ASHRAE Handbook of Fundamentals, American Society of Heating, Refrigerating and AirCondltioning Engineers, Inc., New York, N.Y., 1972, Chapter 20, Table 3A, p. 361.

13. ASHRAE Handbook of Fundamentals, American Society of Heating, Refrigerating and AirConditioning Engineers, Inc., New York, N.Y., 1967, Chapter 26, Table 3, p. 431.

14. Griffin, C.W. , "Manual of Built-Up Roof Systems", The American Institute of Architects,

McGraw-Hill Book Company, New York, N.Y.,1970, p.59.

15. ASHRAE Handbook of Fundamentals, American Society of Heating, Refrigerating and AirConditioning Engineers, Inc., New York, N. Y. , 1972, p. 410.

16. Ibid., p. 348.

17. CRC Handbook of Materials Science, Volume I: General Properties, editor Charles T. Lynch, CRC Press, Inc., Cleveland, Ohio, 1974, Table A, p. 538.

use OMM NHS-t)i: 16
NBS-114A (REV. 7-73)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUHL1CAT10N OR REPORT NO.

NBSIR 76-987

2. Gov't Accession

No.

3. Recipient's A<icession No.

4, TITLE AND SUBTITLIi

Effect on Insulation on the Surface Temperature of Roof

Membranes

5. Publication Date February 1976

6. Performing Organization Code

7. AUTHOR(S) 8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No.

11. Contract/Grant No.

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

Same as 9

13. Type of Report & Period Covered

Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

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

bibliography or literature survey, mention it here.)

The surface temperatures of black, gray and white roofs were calculated for various thicknesses of insulation located between the membrane and roof deck. The calculations were m

performed using a steady-state heat balance equation to illustrate the increase roof surface temperatures due to solar radiation.

The calculations indicate that the first increment, about 1 inch (25 mm), of insulation

causes a significant rise in the roof surface temperature due to solar radiation. In- creasing the amount of insulation above this first increment to greater thicknesses does not appreciably increase the roof surface temperature.

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

surfart^^eiafLe'!""""'"' P««-^nce; radiative cooling; roofing; solar heating;

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UNCLASSIFIED

21. NO. OF PAGES

19

20. SECURITY CLASS

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22. Price

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