NBSIR 73-140

Fire Endurance Test of Plywood-Faced

Exterior Walls for Single Family Housing

B. C. Son

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

March 1973

Final Report

Prepared for Office of Research and Technology

Department of Housing and Urban Development

Washington, D. C. 20410
i

\

iV
NBSIR 73-140

FIRE ENDURANCE TEST OF PLYWOOD-FACED

EXTERIOR WALLS FOR SINGLE FAMILY HOUSING

B. C. Son

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

March 1973

Final Report

Prepared for Office of Research and Technology

Department of Housing and Urban Development

Washington, D. C. 20410

U. S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts, Director

FIRE ENDURANCE TEST OF PLYWOOD-FAGED

EXTERIOR WALLS FOR SINGLE FAMILY HOUSING

by

B. C. Son

Building Fires and Safety Section

Center for Building Technology

ABSTRACT

As a part of the testing and evaluation activities in Operation

BREAKTHROUGH, a standard fire test conforming to ASTM E 119 was performed

at the National Bureau of Standards on a wall assembly where half represented a nonbearing single exterior wall (as found in single family

detached housing) and the other half represented a nonbearing double wall

assembly for an interdwelling separation which would occur at the interface of two parallel adjacent modules. Each wall contained a layer of

gypsum board as an interior (room) surface and a layer of plywood as an

exterior surface, and was framed with nominal 2 x 4 in. wood studs on

16 in. centers. No structural load was applied during the test.

The fire endurance of the single wall was 43 min. The initial mode

of failure was by excessive average temperature rise on the unexposed

surface of the wall.

Although the test results of the interdwelling wall were inconclusive,

its fire endurance was considered to be 1 hr 02 min. This fire endurance

was based on visual observation during the test and was the time when the

gypsum board on the unexposed side was observed to separate from the

wood studs.

Key Words : Fire endurance; Fire test; Housing systems; Interdwelling

wall; Operation BREAKTHROUGH; Single wall

i
TABLE OF CONTENTS

Page

ABSTRACT i

1.0 INTRODUCTION 1

2.0 CONSTRUCTION 1

3.0 INSTRUMENTATION 2

4.0 TEST PROCEDURE 3

5.0 TEST EVALUATION 4

6.0 TEST RESULTS 4

6.1 SINGLE WALL 5

6.2 DOUBLE WALL 5

7.0 DISCUSSION 6

REFERENCE 9

APPENDIX I, Log of Test 10

APPENDIX II, SI Conversion Units 11

ii
1.0 INTRODUCTION

Several modular systems proposed for the Operation BREAKTHROUGH

Program were constructed such that the sides of adjacent modules formed

an interdwelling double wall which was required to be a fire barrier.

Since information was not available on the fire resistance of double

wall constructions as compared directly with single wall construction

it was necessary to perform fire endurance tests. In the test assembly,

the interdwelling double wall was composed of the following sequence of

materials: Gypsum board or plaster, wood or steel studs, plywood, air

spaces, plywood, wood or steel studs, gypsum or plaster. The gypsum

board or plaster forms the interior or room side of the module, while

the plywood forms the exterior side.

A standard fire test was performed on a combined single and double

wall configuration, in which one-half of the assembly represented a

modular double wall and the other half a conventional (single) wall to

determine the difference in fire endurance between them. The fire

exposure followed the requirements of the Standard Methods of Fire Tests

of Building Construction and Materials, ASTM E 119—' .

2.0 CONSTRUCTION

The first wall, which was 8 ft high x 16 ft wide, was mounted into

a wall test frame in the NBS panel furnace. A second wall, which was

8 ft high X 8 ft wide, was added on the unexposed side at the south

end of the test frame, parallel to the first wall, forming a double wall

section with a 2-3/4 inch air space between the two walls. Each wall

1/ Standard Methods of Fire Tests of Building Construction and Materials,

American Society for Testing and Materials Designation E 119-70, available

at 1916 Race Street, Philadelphia, Pa. 19103

1
assembly consisted of a single layer of 5/8 inch Type X gypsum board as

an interior (room) surface and a single layer of 1/2 inch grade A-C

plywood as an exterior surface nailed to 2 x 4 inch (nominal) wood studs

on 16 inch centers . On the double wall section the gypsum board sides

faced the furnace and the testing room, while the plywood sides faced

the air space. Nominal 2x4 fire stops were placed in two stud spaces

of the first panel and in one stud space of the second panel at the midheight of the assembly . See Figure 1 for the details of the framing and

closures between the wall panels.

Since the 8 ft height of the specimen was less than the 10 ft height

of the test frame, a filler designed to have sufficient fire endurance

and rigidity during the test was placed at the bottom of the specimen.

The filler was made up of 2 x 12 lumber and protected on the fireexposed side with two layers of 5/8 inch Type X gypsum board and sprayed

with fire protective vermiculite plaster on metal lath. The unexposed

side was covered with a single layer of 5/8 inch Type X gypsum board'.

3.0 INSTRUMENTATION

The instrumentation consisted of 32 thermocouples, a deflection

indicator, and pressure measuring device. The thermocouples, ChromelAlumel (Type K) , were installed as follows: 8 thermocouples in the stud

space with a fire stop and the adjacent stud space of the first panel;

8 surface thermocouples and 4 thermocouples on the plywood board

(unexposed surface of the first wall); 4 thermocouples in the air space

between the two wall panels; 4 thermocouples in the stud space with a

fire stop and the adjacent stud space of the second panel: and 4 surface

2
thermocouples on the unexposed surface of the second wall. The surface

thermocouples were placed under standard 6x5 in. felted asbestos pads.

Figure 1 shows the locations of thermocouples . The photograph in

Figure 2 shows the unexposed surface of the specimen and the connections

of the thermocouples.

The deflection indicator consisted of a wire which was strung

horizontally across the center height of the specimen. At the start of

the test the wire was 3-1/4 in. from the double wall surface and 8-1/4 in

from the single wall surface. The variation of the distance from the

wire to the wall surfaces was measured at the center of each wall

periodically by means of a ruled measuring device during the test.

The pressure measurement within the furnace was made with a disk

type probe connected to a differential pressure transducer with tubing.

The probe consisted of 1/8 in. inside diameter stainless steel tubing

attached to the edge of a 1-1/8 in. diameter metal disk having rounded

edge and connected to a small hole in the center of the disk. The disk

was positioned so that the hole was normal to the upward flow of gas.

4.0 TEST PROCEDURE

The furnace temperature was measured by 12 thermocouples which

were equally distributed within the furnace. These thermocouples were

enclosed in sealed, standard weight, 1/2 in. diameter black iron pipe.

The furnace temperature, which was constrained to follow the standard

ASTM E 119 temperature-time curve by manual control of the gas flow to

the burners, is shown in Figure 3. The temperatures of the thermocouple

were printed out at 2 minute intervals on a data logger from which they

were punched onto cards for processing and plotting by computer.
Since the assembly represented nonbearing construction, no

structural load was applied. The details of the wall furnace with

typical wall assembly in place are shown in Figure 4.

The test was run with the furnace neutral pressure point located

at one-third height above the bottom of the specimen.

5.0 TEST EVALUATION

The fire endurance of a nonbearing construction is the time required

to reach the first occurrence of any one of the criteria of failure, which

are as follows

:

a. The assembly shall have maintained its integrity during the

fire endurance test without passage of flame or gases hot

enough to ignite cotton waste, for a period equal to that for

which classification is desired.

b. Transmission of heat through the assembly during the fire

endurance test shall not have been such as to raise the average

temperature on its unexposed surface more than 250°F (139°C),

or 325°F (181°C) at one point above its initial temperature.

A test shall be regarded as successful if the above conditions are met.

6.0 TEST RESULTS

A log of the test observation is given in Appendix I. The fire

endurance of the single wall was 43 min and that of the interdwelling

double wall was considered to be 1 hr 2 min.

4
6.1 SINGLE WALL

The failure of the single wall due to an average temperature rise

of 139°C above its initial temperature on the unexposed surface was

observed at 43 min (see Figure 5) . Flame penetration was observed at the

top of the vertical joint separating the single and double wall portion

of the assembly at 47 min and the gas supply to the furnace was discontinued. At this time the air temperature in the stud space of the first

wall was over 600°C (1112 °F) and increasing rapidly. Direct flame-through

of the plywood surface of the first wall occurred at 51 min. Figures 6

and 7 show the location of the flame-through just before and after the

instant of the flame-through. In Figure 6, gray smoke is visible at top

of the double wall portion.

6.2 DOUBLE WALL

The average temperature rise of the unexposed surface of the double

wall at 43 min was 15 °C (27 °F) . The average unexposed surface temperature rise and average temperature rise vs. time across the double wall

are shown in Figure 8. A comparison of the average temperature rises of

three groups of thermocouples on the unexposed surface of the first wall

is shown in Figure 5. The three groups of thermocouples consisted of

(1) 4 surface thermocouples under pads on the double wall side; (2) 4

thermocouples without pads on the double wall side; (3) 4 surface

thermocouples under pads on the single wall side.

Figure 9, taken at 55 min of test time, shows burning of the single

wall portion. Some flame and gray smoke are visible at top of the double

wall portion. Flame penetration had taken place at the top of the double

5
wall portion, but had not yet penetrated to the unexposed surface of the

double wall. The failure time of the double wall portion was estimated

to be 1 hr 02 min when the unexposed gypsum board was losing contact

with the wood studs. Figure 10, taken at approximately 1 hr 15 min of

test time, shows the exposed side of the assembly after it was moved

from the furnace while water was being applied from a fog nozzle.

7.0 DISCUSSION

The fire endurance of the single wall was 43 min by temperature

failure

.

During the test when the flame penetration, shown in Figure 7,

occurred at 47 min of test time, the gas supply to the burners was discontinued and thermocouples were disconnected; however, the combustion

of the assembly continued. Figure 9 shows the complete burning of the

single wall, while the double wall was still providing a barrier to

flame penetration.

In order to estimate the fire endurance of the double wall it was

assumed that the fuel contribution from, the plywood burning in the wall

was approximately the same order as the heat produced by continued

furnace operation. The fire endurance time was based on the time when

the gypsum board on the unexposed side of the double wall separated

from the studs. This occurred at approximately 1 hr 02 min of test

time.

The fire endurance of the double wall was significantly less than

twice the fire endurance of a single wall, that is, 62 min vs. 86 rain.

This result is in agreement with three different loaded doubla wall

6
tests subsequently performed under Operation BREAKTHROUGH. The results

of these four tests and the constructions of these other specimens are

shown in Table I and Table II below.

Table I

Comparison of Fire Endurances in Double Wall Tests

Test

Single Wall

(min)

Measured

Fire Endurance

Time

Twice Single

Wall (min)

Fire Endurance

Time

Double Wall

(min)

Measured

Fire Endurance

Time

Difference %

j Twice

Double /Measured

Wall / Single

/ Wall

Singledouble wall

43 86 62 28

T2 53 106 72 33

T3 69 138 102 26

Bl 42 84 73

1

13

Average 25

Note: In Table I above, the average difference in fire endurance between

twice single wall and double wall is 25%. This only applies when

the quality of each wall in a double wall configuration is nearly

the same, and generally when the facing surfaces in the air space

are composed of incombustible materials. (In another test of a double wall with steel studs, in which the facing walls were of

plywood, failure of the second wall occurred within 2 minutes

after the first wall failed.)

7
Table II

Construction of Double Wall Specimens —~——I

i Wall j Construction

_ T2 Paper honeycomb core with polyester/glass fiber skins and

' a sheet of gypsum board glued to each side.

l .T3 Similar to T2 with an additional layer of gypsum board on

the exposed surface and unexposed surface of the double

wall assembly.

Bl . Steel studs with one layer of gypsum board on each face.

Since the flame-through occurred at the top of the vertical joint

of the assembly and then spread downward, the intended comparison of

the two adjacent stud spaces with and without fire stop could not be

clearly obtained.

As explained previously, the flame penetration occurred at the top

of the vertical joint separating the single and double wall portions of

the assembly. Since the furnace burners were immediately shut down in

the interest of building safety, it was not possible to obtain a direct

comparison of the ultimate fire endurance of the two wall configurations.

For such a comparison, separate tests of single wall and double wall

configuration should be carried out.

8
REFERENCE

1. American Society for Testing and Materials, 1970

"Standard Methods of Fire Tests of Building Construction and

Materials ASTM Designation E 119-70," available from the American

Society for Testing and Materials, 1916 Race Street, Philadelphia,

Pennsylvania 19103.

9
APPENDIX I

Log of Test

Observation

Visual Observation

Time Observation

MlnrSec

0:00 Start test

2:00 Paper on gjrpsum board of the exposed surface burning

2:30 Paper burning completed

10:00 Slight amount of smoke appeared on the unexposed side

13:00 Joints in gypsum board of the exposed surface appear

to be opening slightly.

22:30 Beginning of smoke and flaming at joints on the

exposed surface

37:00 Strong flaming through joints on the exposed side

39:00 Second gypsum sheet from south on the exposed surface

buckling and its joint opening about 1 inch.

42:00 First joint from south opened about 4 inches.

44:00 Second gypsum sheet from south on the exposed surface

fell in.

47:00 Flame penetration at the top of the vertical joint of

the single-double wall assembly.

47 :30 Gas off

55:00 The unexposed surface (plywood) of single wall portion

burning completely.

62:00 The unexposed surface (gypsum board) of double wall

portion is separating from the studs.

10
APPENDIX II

SI Conversion Units

In view of present accepted practice in this country in this

technological area, connnon US units of measurement have been used

throughout this paper. In recognition of the position of the United

States as a signatory to the General Conference on Weights and

Measurements which gave official status to the metric SI system of

units in 1960, we assist readers interested in making use of the

coherent system of SI units by giving conversion factors applicable

to US units used in this paper.

Length

1 in. = 0,0254 meter

1 ft = 0.3048 meter

Mass

1 lb = 0.45 Kilograms

Stress

2

1 psf = 47.88 newton/meter2

1 psi = 0.332 newton/meter

1 plf = 13.49 newton/meter

Temperature

Temperature in °F = 9/5 (temperature in °C) + 32 °F

11
2"x2-3/4" Wood Closure

2 T/C in Air Space Between Two Wall Panels

TOP VIEW /— 2"x2-3/4" Wood Closure

2"x5"Wood Closure

First Pane^ '

Second PanelF=l

l/2"Plywood

T/C without pad

/ JK/ II _ x-in(

T

V

4 Surface T/C

X H X II _ II -Tl

5/8" Gypsum Board

T/C under pad

16'

40"-

-2' 16"

2x4 Wood Stud 16" Center

X 4fX

Stop

i

Front view of FIRST PANEL

U- 8' ».

•

X

N

I- iki 1 X

1 |i

•i 1

1 ' 1

1 '

1 1 1

1 X 1 X] 1

1

1 II 1 |re Sqop || 1

1 ! i

1 il II

1 >

1

1 i! ll

1

t—i

^

1 II |l 1

1 l| |l

1

1 A 1 ^ ll 1

1 !l 1

1 Ii 11 1

T/C Located in Space

Between Gypsum Plywood

Board

T/C Under 6"x6"

T/C without pad

ietween Two Panels or

)tud Spaces

Front view o f SECOND PANEL

Figure 1. Details of ""he construction and locations of thermocouples of the

specimen.

12

1000_

950-

— I 1 1 1 r 1 1 1— 1 r- 0 5 10 15 20 25 30 35 40 45 50

TIME (MINUTES)

Figure 3. Average Furnace Temperature for Test Compared With Standard E119

14
SECTION LONGITUDINAL SECTION HALF ELEVATION

O I f J * J !0 IS' SCALE

FIGURE 4. DETAILS OF WALL-TESTING FURNACE,

A, PURNACE chamber; B, BURNERS; C , THERMOCOUPL E PROTECTION TUBES; D, PIT POR DEBRIS',

E, OBSERVATION WINDOWS; F. AIR INLETS; G, FLUE OUTLETS AND DAMPERS; H, FIREBRICK

FURNACE LINING! I. REINFORCED CONCRETE FURNACE-SHELL, K, GAS COCKS; L, CONTROL VALVE,

M, LADDERS AND PLATFORMS TO OBSERVATION WiNOOWSi N, MOVABLE FIREPROOFED TEST

frame; 0, LOADING BEAM, P, HYDRAULIC JACKS, Q.TEST WALL; R, ASBESTOS FELTED PADS

COVERING THERMOCOUPLES ON UNEXPOSED SURFACE OF TEST WAlL.

USCOMM-NBS-DC
12

3

© 4 ASTM T/CS on unexposed sur. of the 1st ^ 4 Bare T/CS on the unexp, sur. of the 1st wall at the double wall portio

. 4 ASTM T/CS on the unexp, surface

wall at the double wall porCior

the double w. of the single wall portion.

400.

o 300_

(jj o

cc3^-o:

flC UJ

CL. £ 200.

/3i

100_

^0 25

TIME irtlNUTES)

Figure 5. Comparison of Average Temperature Rises of 3 Groups of

Thermocouples

16

1,
Fig, 6 Location of the flame through just before the instant of the

flame through. Gray smoke may be noticed at top of the

double wall portion.
1000_

900_

1 O plenmum of First wall

^ ^ unexposed surface of First wa 1

1

+

X

800_

Air space between two walls

plenum of second wall

unexposed surface of second wall

See Figure 1 for the T/C locations

700_

o 600_

CD

UJo

bJ 500,

ZD

)—cr

a:UJ£ 400.

300_

200-

100_

10 15 20 25 30 35 45

TIME (MINUTES)

Figure 8. Average Temperature Rise Across Double Wall Panel For

Test

18
Fig., 9 Complete btLituiiii-g tu., wall while the uaexpost

of the double wall inta
Fig. ID Exposed side of the wail

assembly after it was removed

from the furnace.
FORM NBS-I I4A (1-71) U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. 2. Gov't Accession

Np.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Fire Endurance Test of Plywood-Faced Exterior Walls for

Single Family Housing

5. Publication Date

6. Performing Organization Code

7. AUTHOR(S)

Byung Chan Son

8. Performing Organization

NBSIR 7J-140

9. PERFORMING ORGANIZATION NAME AND ADDRESS

INAl lUINAL DUKtAU Ur olAINUAKUC)

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/ Work Unit No. 4600461

11. Contract/Grant No. IAA-H-16-70

12. Sponsoring Organization Name and Address

W^J-J_\.^C \^ J- O C a 1. CLl-IV^ ^ 11 LL\J JLKJ Department of Housing and Urban Development

Washington, D.C. 20410

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 significant information. If document includes a significant

bibliography or literature survey, mention it here.) As a part of the testing and evaluation activities in Operation BREAKTHROUGH, a standard fire test conforming to ASTM E 119 was performed at the National Bureau

of Standards on a wall assembly where half represented a nonbearing single exterior

wall (as found in single family detached housing) and the other half represented

a nonbearing double wall assembly for an interdwelling separation which would

occur at the interface of two parallel adjacent modules. Each wall contained a layer of gj^sum board as an interior (room) surface and a layer of plywood as an exterior surface, and was framed with nominal 2 x 4 in. wood studs on 16 in.

centers. No structural load was applied during the test.

The fire endurance of the single wall was 43 min. The initial mode of failure

was by excessive average temperature rise on the unexposed surface of the wall.

Although the test results of the interdwelling wall were inconclusive, its fire

endurance was considered to be 1 hr. 02 min. This fire endurance was based on visual observation during the test and was the time when the gypsum board on the

unexposed side was observed to separate from the wood studs.

17. KEY WORDS (Alphabetical order, separated by semicolons)

Fire endurance; Fire test; Housing systems; Interdwelling wall; Operation

BREAKTHROUGH; Single wall

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USCOMM-DC 66;-J4.P7l