NBSIR 73-190

Acoustical Evaluation of a Single

Family Attached Steel Frame

Modular Housing System Constructed

on an Operation Breakthrough Prototype

Site

Thomas L. Quindry

Applied Acoustics and lllufnination Section Center for Building Technology (Building Research Division)

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

April 1973

Final Report

Prepared for Office of Research and Technology

Department of Housing and Urban Development

Washington, D. C. 20410

NBSIR 73-190

ACOUSTICAL EVALUATION OF A SINGLE

FAMILY ATTACHED STEEL FRAME

MODULAR HOUSING SYSTEM CONSTRUCTED

ON AN OPERATION BREAKTHROUGH PROTOTYPE

SITE

Thomas L. Quindry

Applied Acoustics and Illumination Section

Center for Building Technology (Building Research Division)

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

April 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

ACOUSTICAL EVALUATION OF A SINGLE FAMILY ATTACHED

STEEL-FRAME MODULAR HOUSING SYSTEM CONSTRUCTED

ON AN OPERATION BREAKTHROUGH PROTOTYPE SITE

By

Thomas L. Qulndry

Applied Acoustics and Illumination Section

Building Research Division

ABSTRACT

The acoustical performance of a single family attached steelframe modular housing system was tested on an Operation BREAKTHROUGH

prototype site.

Test results are given concerning the noise isolation of interdwelling walls, the noise isolation of intra-dwelling walls and

floor-ceiling assemblies.

Key Words: Acoustics; noise isolation class; Operation BREAKTHROUGH

i
TABLE OF CONTENTS

Page

ABSTRACT i

1. INTRODUCTION 1

2. OBJECTIVE 1

3. TEST PROCEDURE 2

4. DESCRIPTION OF HOUSING SYSTEM 4

5. TEST RESULTS 5

5.1 Noise Isolation of Inter-Dwelling Walls 5

5.2 Noise Isolation of Intra-Dwelling Walls and

Floor-Ceiling 6

6. DISCUSSION 6

TABLE 1 8

TABLE 2 9

il
1. INTRODUCTION

Drawings and specifications for the housing systems being demonstrated as a part of the Operation BREAKTHROUGH Program were reviewed in

order to determine the acoustical performance of the dwelling units.

Any potential deficiencies in acoustic performance were noted such that

appropriate action could be taken prior to manufacture and site installation of the housing units.

Poor workmanship, however, can negate even the best planned acoustical improvement. The many unknowns associated with workmanship,

possible damage to the housing modules during shipment, assembly of

the housing modules on the building site, and even the modular concept

of construction typical of many of the Operation BREAKTHROUGH housing

systems, emphasized the importance of acoustical performance testing.

More builders than ever before are now at least aware that acoustic

quality in buildings is becoming an essential consumer requirement. A

great deal of information can ultimately be drawn from the acoustical

performance testing of Operation BREAKTHROUGH housing.

2. OBJECTIVE

The objective of this work was to obtain information regarding the

inter- and intra-dwelling noise isolation provided by this particular

prototype housing system constructed within the Operation BREAKTHROUGH

Program on one of the prototype sites, and to provide this information

as a data base for possible comparison with the acoustical performance

of conventional housing.

1
3. TEST PROCEDURE

All tests were performed in accordance with the methods outlined

in the appropriate standards. The pertinent tests include:

- Appendix Al of ASTM E 336-71, "Recommended Practice for the

Measurement of Airborne Sound Insulation in Buildings."

ASTM E 413-70T, "Tentative Classification for Determination

of Sound Transmission Class." (This test method is used

for the determination of Noise Isolation Class.)

ASTM C 423-66, "Standard Method of Test for Sound Absorption

of Acoustical Materials in Reverberation Rooms," Section

9.1, for measurement of decay rate procedure.

ANSI SI. 2-1962, "ANSI Standard Method for the Physical Measurement of Sound."

All measuremens were carried out using the NBS Mobile Acoustical

Laboratory—'^. A complete list of the equipment utilized for these

measurements is given in Table 1.

Airborne noise reductions were measured using 1/ 3-octave bands of

2/ pink random noise— to excite the speaker systems. A multiplex system

which scanned the outputs of the microphones was used for simultaneous

spatial averaging in both the source and receiving rooms. The output

of the multiplexer was passed through a 1/3-octaVe band-pass filter set

and then the measuring system. -

A total of six microphones, in a modified spherical array as shown

on Figure 1, was used in all rooms. The distribution of sound in the

source room was improved by the addition of an 8 ft x 11 ft honeycomb

1/— Winzer, George E. , National Bureau of Standards Mobile Acoustical

Laboratory, Sound and Vibration, May 1970.

2/ Pink random noise is a quantity (e.g., sound pressure) whose amplitude probability is a normal (Gaussian) distribution curve aad whose

frequency spectrum slopes at minus 3 dB per octave.
reflecting ipanel placed at an angle such that its top edge was resting

across the entire wall that was opposite the primary test wallTemporal averages of soimd pressure levels were ol)tained using a

true root-means-square voltmeter in order to obtain less statistical

error in sound pressure levels than can be obtained with the graphic

level recorder recommended in ASTM E 336-71. A differential amplifier

was used with two true r.m.s. voltmeters to obtain the differences in

the r.m.s. sound pressure levels of the random noise between the source

and the receiving room. Airborne noise reduction determination averaging times of 100 seconds for tests at frequencies from 125 through 400

Hz and 30 seconds for tests at frequencies from 500 to 4000 Hz

were used in order to achieve a statistical error (due to temporal

averaging) of less than +0-^ dB (at a confidence level of 95 percent).

The imcertainty in measured soxmd pressure levels, due to random

and systematic imcertainties associated with the overall data acquistition system, is estimated (95 percent confidence level) to be less than

+1 dB for relative sound pressure levels (measured to determine airborne

noise reductions) over a range of band-center frequencies from 100 to

4000 Hz. ASTM E 336-71 specifies that for suitable accuracy in determining the average soimd pressure levels in the source and receiving

rooms, the rooms should be large enough that there are at least 10 normal

modes per measurement bandwidth. The lower limit of frequency for which

this would occur using 1/3-octave bands was: 220 Hz for the bathroom,

150 Hz for the back bedroom and 140 Hz for the living room.

3
For the airborne noise reduction measurements the background noise

in the receiving room was at least 10 dB below the transmitted signal.

The evaluation sound absorption of the receiving rooms was determined

by the reverberation decay method described in ASTM C 423-66.

During the field measurements the temperature was nominally 68°F

and the relative humidity 43%.

; . ... , ^; -/Y^ 4.. DESCRIPTION OF HOUSING SYSTEM

The housing unit tested ±s classified as a single family attached

housing system. Four modules are placed longitudinally, two on top of

two, to form three living units. The lower two modules are anchored

to a concrete foundation wall which forms a full basement. The upper

modules rest on, and are structurally connected to, the lower modules.

Each adjacent dwelling unit is identical in layout and orientation

with a typical floor plan shown in Figure 1. The units were unfurnished

except for floor coverings and kitchen equipment. The living room,

stairway to the second floor, bedrooms and second floor hall were

carpeted with the remaining areas covered with vinyl asbestos tile

finish flooring. , ,

The party wall shown in Figure 2 is constructed of two layers of

1/2-inch gypsum drywall placed on each side of 1-1/2 inch x 3-1/2 inch

X 18 Ga steel channel shaped studs spaced 24 inches on center. The

studs are supported continuously top and bottom by 2 x 4 (nominal) wood

plates and 1 inch x 3-1/2 inch x 20 Ga steel channel. Four-inch thick

friction fit fiberglass insulation is placed between the studs. The

wall is supported on a continuous 3/4-inch plywood floor which is

common to both units.

4
The floor assembly for both the first and second floor as shovm in

Figure 2 consists of 1-3/4 inch x 7-1/4 inch x 18 Ga steel channel

shaped joists spaced 24 inches on centers to which is attached 3/4-inch

plywood subfloor. The ceiling assembly consists of 2 x 4 (nominal) inch

wood joists spaced 16 inches on center with 1/2-inch gypsum drywall as

the finish ceiling. The f loor/ceiling space between the second floor

and first floor party walls consists of: two 2x4 (nominal) inch wood

joists, 2x8 (nominal) inch wood joist, 1-3/4 inch x 7-1/4 inch x 18 Ga

steel channel, and 5/8-inch gypsum drywall.

The walls between modules within a given dwelling unit consist of

double 1-1/2 inch x 2-1/2 inch x 18 Ga steel channel shaped studs placed

with the webs parallel to the wall at 24 inches on centers with 1/2-inch

gypsum dr37wall on the outer surfaces as shown in Figure 3. The floor

is not continuous under these walls.

Interior doors are of a hollow core wood construction and undercut

approximately 3/4 to 1 inch.

Each measured noise reduction was normalized to a reference re2 2 ceiving room absorption, , of 10 m (100 ft ) according to the following equation:

5. TEST RESULTS

5.1 Noise Isolation of Inter-Dwelling Walls

NR

n NR - (10 log^Q ~ )

where NR

o Normalized noise reduction

n NR Noise reduction before normalization

A Total sound absorption of the receiving space.

5
in the housing system that vjas tested, the partjwall on the first

floor which separated the living rooms> of two units included a stairway

of one of the units, thereby creating a buffer zone as shown in Figure 1.

Measurements of noise reduction and absorption were carried out on this

wall and also the inter-dwelling partition separating the bathroom and

back bedroom. The normalized noise reductions obtained are shown as a

function of frequency in Figures 4 and 5. The three-segmented solid

line represents the Noise Isolation Class (NIC) contour fitted to these

data according to the specified procedure in ASTM E 413-70T. The dotted

line points to the normalized NIC value. The normalized NIC values

obtained are given in Table 2.

5 . 2 Intra-Dwelling Walls and Floor-Ceiling

The results of measurements of the normalized noise reductions

between the front bedroom and the horizontally adjacent back bedroom

with both bedroom doors closed, the bathroom and the horizontally

adjacent back bedroom with both doors closed, and the front bedroom

and the vertically adjacent living room with the bedroom door closed are

given in Figures 6, 7, and 8 respectively. The NIC contours are fitted

to the data and the normalized NIC values are given in Table 2.

6. DISCUSSION

During the testing several observations were made. For instance,

the steel studs in the partition separating the front bedroom and the

stairway, as shown in Figure 1, vibrated noticeably when 1/3-octave band

pink noise at 125 Hz center frequency was generated in tlie front bedroom

6
through the H])eakers. In addition, by pushing on the plywood paneling

on this wall in the bedroom the rattling noise characteristics changed.

It appeared that the paaeling was loosely fastened to the <5tuds.

Subjective observations were made to try and determine the cause of

the lesser acoustical performance of the party wall separating the

bathroom and back bedroom of two units. The generated sound seemed to

have less attenuation through the party wall in the area of the shower

stall. According to available plans and specifications two layers of

gypsum drywall are supposed to cover the entire party wall in the bathroom including the area behind the shower stall. The NIC value obtained

from the measured data along with the subjective observations indicate

that a major sound flanking path occurs in the shower stall area. This

might indicate that one or both layers of gypsum drywall had not been

placed full length in the area behind the shower stall.

7
TABLE 1

Instrumentation*

1. Brllel & Kjaer 1402 Random Noise Generator

2. (3) Brljel & Kjaer Models 1612^ 5004 Band-Pass Filter Sets

3. JBL Speaker Systems

4. (2) Bruel & Kjaer 2606 Measuring Amplifier

5. (2) Briiel & Kjaer 215 RMS Converter & Log Amplifier

6. (2) Briiel & Kjaer 221 Microphone Energizer - Multiplixer

7. Bruel & Kjaer 2305 Graphic Level Recorder

8. (12) Brllel & Kjaer 4132 Gondensor Microphones

9. (12) Bruel & Kjaer 2619 FET Preamplifier

10. (2) Briiel & Kjaer 4220 Pistonphone

11. NBS Differential Amplifier

12. NBS Reverberation Time Measuring System

13. HP 5325 A Counter

Commerical instruments are identified in this report in order to

adequately specify the experimental procedure. In no case does such

identification imply recommendation or endorsement by the National

Bureau of Standards, nor does it imply that the equipment identified

is necessarily the best available for the purpose.
TABLE 2

The Measured Noise Isolation Characteristics of

the llousinj^ System

Partition

Source Room

Unit

Receive Room

Unit

Normal ized

NIC

Inter- dwelling

Wall

Living Room

13-SFA/03-15

Living Room

13-SFA/03-li|-

52

Inter-dwelling

Wall

Bathroom

13-SFA/03-13

Bedroom

(Back)

13-SFA/03-14

42

Intra-dwelling

Wall

Bedroom

(Front)

13-SFA/03-14

Bedroom

(Back)

13-SFA/03-14

41

Intra-dwell ing

Wall

Bathroom

13-SFA/03-14

Bedroom

(Back)

13-SFA/03-14

29

Intra-dwelling

Floor/Ceiling

Bedroom

(Front)

13-SFA/03-14

Living Room

13-SFA/03-14

40
X X

X

X X

X

X

Back

Bedroom

Both roomA o

Front

Bedroom

to3

o

2nd FLOOR

Inter- dwelling wall

Jntra- dwelling wair

Microphone

Positions (Typ)

Kitchen

Speaker Position (typ)

a' up

Living Room

X

<M®

o

o

3

o

St FLOOR

igure 1. Floor plan of housing system showing microphone and speaker

positions

.

10
Attic

crawl space

1/2 Gypsum drywall

2x6 Wood Joists at I6"0.C.

3/4 Plywood Sub-Floor

INTERDWELLING WALL

Figure 2. Section through inter-dwelling wall and intra-dwelling floor-ceiling

assemblies.

II
l-l/2"x2-l/2'xl8Ga.

oor

INTRA-DWELLING WALL

gure 3. Section through intra-dwelling wall.

12
I

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60

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> pq <

HO

o

1 o

Q M

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N UQ M (/) M

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50

40

30

20

10 _

I 1 I 1 I I I I I t I I I I 125 250 500 IK 2K 4K

FREQUENCY, Hz

(NORMALIZED TO Ao = 10 METRIC SABINS)

Figure 4. Normalized 1/3-Octave Band Noise Reduction Between Two

Living Rooms Separated by an Inter-Dwelling Wall. Units

13-SFA/03-15 and 13-SFA/03-14 (includes stairway buffer

zone) (NIC - 52)

.

13
70

PQ%H

CJO

1 O

M § H 1—

CJ) t3 H Q

W Q

W

tS] w

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H-t M

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25

60

50

20

10

I I I 1 1 i I 1 i 1 I II f I 1 125 250 500 IK 2K 4K

FREQUENCY, Hz

(NORMALIZED TO Ao = 10 METRIC SABINS)

Figure 5. Normalized 1/3-Octave Band Noise Reduction Between a Bathroom and a Back Bedroom Separated by an Interl^y^'Z Dwelling Wall. Units 13-SFA/03-13 and 13-SFA/03-14

- (NIC - 42) .

14
<:

pqW

> PQ < X) HU

O 22

1 O

§ TI M C_) PC t3 H Q

W

O Pi W

N W M C/D iJ M

o

O

125 250 500 IK

FREQUENCY, Hz

(NORMALIZED TO Ao = 10 METRIC SARINS)

Figure 6. Normalized 1.3-Octave Band Noise Reduction Between the

Front Bedroom and a Back Bedroom Separated by an IntraDwelling Wall. Unit 13-SFA/03-14 (NIC - 41).

15
70

I

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' ' I ' ' I

PQW

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w

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ISo

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60

50

40

30 —

20

10 _

I 1 i I I i t 1 I I I 1 I I 125 250 500 IK 2K 4K

FREQUENCY, Hz

(NORMALIZED TO Ao = 10 METRIC SABINS)

Figure 7. Normalized 1/3-Octave Band Noise Reduction Between a Bathroom and a Back Bedroom Separated by an IntraDwelling Wall. Unit 13-SFA/03-14 (NIC - 29).

16
Figure 8. Normalized 1/3-Octave Band Noise Reduction Between a Front Bedroom and a Living Room Separated by an Intra

Dwelling Floor-Ceiling Assembly. Unit 13-SFA/03-14

(NIC - 40)

IT
1'

I
FORM NBS-114A (1-71) U.S. DEPT. OF CCMM. ] 1. PIJBIJC.ATION VR RFPORr NO.

BIBLIOGRAPHIC DATA jj^sxR 73-190

2. Gov t Accession

No.

4. TITLF AND SUBTITLE

Acoustical Evaluation of a Single Familv Attached Steel-Frame

Modular Housing ' System Construct. ': .; an Opcr;tLion

BREAKTHROUGH Prototvpe Si :.e

3. Recipient's Accessiun Nd.

5. Publication Date

6. Pertormin < TV

7. AUTHORvS)

Thomas L. Quindry

8. Performing Organization

NBSIR 73-190

10. Project/Task,' ork Unit .No. 4600A48

9. PERFORMLMG ORGAN IZATIO.N NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPART.MENT OF COMMERCE

WASHINGTON, D.C. 20234

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

12. Sponsoring Organization Name and Address

Office of Research and Technology

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.) The acoustical performance of a single family attached steel-frame modular housing

system was tested on an Operation BREAKTHROUGH prototype site.

Test results are given concerning the noise isolation of interdwelling walls, the

noise isolation of intradwelling walls and floor-ceiling assemblies.

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

Acoustics; noise isolation class; Operation BREAKTHROUGH

18. AVAILABILITY STATEMENT

IxX UNLIMITED.

I I FOR OFFICIAL DISTRIBUTION. DO NOT RELEASE

TO NTIS.

19. SECURITY CLASS

(THIS REPORT)

UNCLASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF PA

22, Price