NATIONAL BUREAU OF STANDARDS REPORT

8616

PERFORMANCE CHARACTERISTICS OF EXTERIOR WALLS

Progress Report for Period July 1 = December 31 s 1964

by

James V. Ryan

Report to

Housing and Home Finance Agency

Federal Housing Administration

Washington, D„ C„

II. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

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

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

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

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

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

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

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

listing of its four Institutes and their organizational units. Institute for Basic Standards. Electricity. Metrology. Heat. Radiation Physics. Mechanics. Applied Mathematics. Atomic Physics. Physical Chemistry. Laboratory Astrophysics.* Radio Standards Laboratory: Radio Standards Physics; Radio Standards Engineering.** Office of Standard Ref- erence Data. Institute for Materials Research. Analytical Chemistry. Polymers. Metallurgy. Inorganic Mate»

rials. Reactor Radiations. Cryogenics.** Office of Standard Reference Materials. Central Radio Propagation Laboratory.** Ionosphere Research and Propagation. Troposphere

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

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

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

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

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

NBS PROJECT NBS REPORT

42100-12-4210405 January 6, 1965 8616

PERFORMANCE CHARACTERISTICS OF EXTERIOR WALLS

Progress Report for Period July 1 - December 31, 1964

by

James V. Ryan

Building Research Division

to

Housing and Home Finance Agency

Federal Housing Administration

Washington, D. C„

NATIONAL BUREAU OF S

for use within the Government, and review. For this reason, tl whole or in part, is not authi Bureau of Standards, Washinf

the Report has been specificall

IMPORTANT NOTICE

Approved for public release by the

Director ot the National Institute of

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

ess accounting documents intended

s subjected to additional evaluation

e listing of this Report, either in he Office of the Director, National

y the Government agency for which

copies for its own use.

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

PERFORMANCE CHARACTERISTICS OF EXTERIOR WALLS

Progress Report for Period July 1 - December 31, 1964

by

J . V . Ryan

Building Research Division

1 . INTRODUCTION

The objectives of this project are to adopt or develop test methods

and techniques for the measurement of the performance characteristics of

exterior walls, and to provide representative values of those characteristics for typical walls. In the past, studies of building components

have dwelt with one or a very few characteristics. This project is designed to study all the characteristics subject to measurement and to

provide a basis for decisions as to which characteristics are of significance and what level of performance should be expected of a system

intended for use as exterior walls. For this study, interest was confined to wall characteristics and systems as applicable to residential

(houses or apartment buildings) construction.

2. PROJECT PLAN

The plan of the project called for (1) an analysis of the functions

of exterior walls in order to develop a list of all characteristics and

the selection of those subject to physical measurement, (2) review of

existing test methods having potential applicability, (3) testing of

representative samples by these methods, (4) development of additional

test methods and apparatus as needed, (5) measurement of the performance

characteristics of samples of representative wall systems by all the

various methods, and (6) where possible, suggest limiting values for

each of the significant wall performance characteristics subject to

physical measurement.

3.

ACTIVITIES

The activity described as (1) in the preceding section was completed

except for any review that may be indicated as results are obtained in

the rest of the study. Work was started under items (2), (3), and (4),

in various Technical Sections of the Building Research Division.

2 3.1

Structural Stability and Water Permeability 3.1.1

Racking Test

Although ASTM Test Method E72 describes a standard racking test

procedure, it is believed that a more realistic test procedure is

desirable. Recent NBS studies of quarter scale models of masonry

walls indicated that there is a significant increase in the racking

strength when the upper and lower boundaries of a wall are subjected

to relatively small vertical loads; such vertical forces would exist

along the horizontal boundaries of load bearing walls.

A racking frame will be assembled and suitable spring-loaded

yokes for applying the boundary forces will be fabricated.

3.1.2 Cracking Due to Static Loads

Cracking resulting from application of transverse loads (wind

load test) and racking loads will be studied as a function of applied

load, lateral deflections, and distortion under load. Cracks will

have to be classified into several categories, such as cracks causing

leakage, cracks which may be objectionable from standpoint of appearance, and cracks which may impair the structural integrity of the wall.

3.1.3 Dimensional Stability

Much of the cracking observed in structures is known to result

from the use of a variety of dissimilar materials in a single structure.

A procedure will be explored to measure possible distortion or warpage

in exterior wall panels consisting of dissimilar materials subjected

to severe thermal gradients.

3.1.4 Wind Load and Water Permeability Tests

The test chamber for these tests is completed and a sample wall

panel has been constructed and placed in the chamber. The sample wall

panel is a conventional wood frame with vinyl siding, 3/8-in. plywood

sheathing, 2-in„ fiber glass insulation, and 1/2-in. gypsum wall board.

As a result of a preliminary test with this wall, modifications are being made to the air-supply system to increase its capacity. When

these modifications are completed, a series of "shake down" tests will

be made using the wall system described above. The testing procedures

will be as outlined in the progress report for June 30, 1964.

- 3 -

3,2 Smoke Teat (Fire Performance)

The desirability and usefulness of a small-scale laboratory test

chamber for the evaluation of the smoke generation characteristics of

materials under simulated building fire conditions was outlined in the

previous progress report. During the past six months, the main effort

has been directed toward establishing test requirements and procedures

which would permit simple, reproducible and realistic smoke measurements.

The following specific activities were undertaken:

1. The construction of a new smoke chamber of larger volume

(7 times) and optical path length (3 times),

2. The design, construction and calibration of an air-cooled

radiometer for establishing reproducible conditions of

irradiance on the specimen surface, and

3. The evaluation of important test parameters such as the

type and duration of the specimen exposure, and the

orientation and length of the light path.

As a result of these tests, basic requirements for a suitable test method

have been established, and the current NBS smoke measuring method incorporates the following features:

1. The specimen is exposed on, and generates smoke from, one surface only,

2. The specimen receives a controlled radiant exposure

from an electrically powered furnace; hence no combustion air is required for, and no exhaust products

are formed by, the heat source,

3. The method is suitable for radiant ignition (no pilot)

or for pilot ignition (small gas pilot).

4. A sufficiently large chamber is used to prevent

premature consumption of air, even when the chamber

is entirely closed to prevent loss of smoke.

5. The photometer light path is vertical to reduce the

recorded effects of smoke pulsing and stratification.

- 4 -

6, The results are reported in terms of optical density

log-j^ par unit path length since

this is the most characteristic measure of smoke

quantity and comparative obscuring power.

Future work includes plans (a) to compare the response of a blue-* and

a red=sens itive vacuum phototube with that of a visually corrected

barrier layer cells, (b) to extend the measurements to a larger chamber,

if necessary, and (c) to perform tests on a wide variety of surface

finish materials with and without the use of a pilot flame.

During the past six months considerable progress has been made on developing design details and construction drawings for an apparatus

for conducting tests on air and vapor transfer through exterior wall

systems. A portion of the time was used in preparing a space adequate

for housing the apparatus and its supporting equipment. The apparatus

has been designed to provide two environmental chambers between which

test specimens of exterior wall systems will be fixed. In this manner,

the specimen will be exposed to spaces simulating those of both indoor

and outdoor conditions.

The air infiltration will be measured by metering the air supply

required to hold a constant pressure difference between the two spaces.

After calibration of the chambers for air leakage through their walls, an accurate measurement of air infiltration through the test specimen

can be made.

Instrumentation for measuring, and systems for producing and con- trolling, interior and exterior environmental conditions will be provided to study: (1) the presence of condensate at points within the

wall structure, and (2) the removal of moisture from the air that has

passed through the wall system as a means of determining the rate of

vapor transfer.

Items which have been most actively engaged in during the past six

months are:

1. Refinements in design of the apparatus:

3.3 Air and Water Vapor Traps fer

(a) Methods for prevention of air leakage and detailed

design of the. joints- between the test frame and

the two' environmental chambers.

- 3

(b) Design of adequate observation ports and access

doors including construction drawings for shop

use,

(c) Remote instrumentation which must penetrate the

chamber walls.

2. Renovation of the space in Building 14, Room SB101, for

suitable housing of the apparatus,

3. Installation of an overhead monorail and trolley for

lifting and turning the frame and test specimens.

4. Construction of the frame in which the test specimens

are to be placed for testing. This arrangement for

holding the test wall consists of a heavy metal frame

member capable of supporting loads of several thousand

pounds with very little deflection of the frame. The

opening for the location of the specimen is 8 ft, 4 in,

wide by 9 ft, 6 in. high. The opening is adequate to

hold two 4-ft by 8-ft panels with joints at top and

bottom to simulate ceiling and floor joints. The frame

is supported from an overhead rail and trolley having

a swivel attachment. The overhead suspension and

attachments which have been installed allow the frame

and specimen to be rotated, thus it can be easily

removed from the apparatus, turned, and reinserted.

By reversing the specimen, the apparatus can be

simplified in that one chamber will provide heating

and the other will provide cooling for all tests, so the environment in each chamber need not be varied

over an unusually large range.

5. Construction of the chambers has just begun during the

last three weeks of December. Approximately all of the

materials and components, such as doors, windows, etc., are available or are on order. It is anticipated that

work on the construction of the two chambers will

continue through the months of January and February,

1965.

3.4 Weathering, Discoloration, Denting, etc.

Weathering of samples of Tedlar-coated aluminum siding and white,

gray, brown, and beige factory-painted aluminum siding in carbon and

6

xenon arc weatherometers was continued* The samples have been exposed

for 1,500 hours in the twin carbon arc machine and for 2,000 hours in

the xenon arc machine* Small color changes have occurred as measured

by a tristimulus colorimeter. A chemical colorimetric technique indicates a further degradation of the samples compared to 500 hours'

exposure. Weathering tests have been started on a Tedlar-coated wood

siding, a factory-painted galvanized steel siding, and a pigmented

plastic siding.

Work has been started on the cleanability of the sidings. A

slight modification of Federal Test Method Standard No. 141 is being

used. Cleanability of these sidings will be determined on both new samples and sampled aged in the weatherometers.

Samples of additional commercial products have been obtained.

These are Woodrock, a wood, asbestos fibers and cement product made

by National Gypsum; Colorlok, a siding consisting of a pigmented

polyester film bonded to Masonite board made by Masonite Corporation;

and a pigmented plastic siding made by Bird and Son. Data on denting,

cracking, abrasion resistance, weathering, etc. will be obtained on

these materials.

3.5 Heat Transfer

The objective is to devise and evaluate a practical method of

experimentally determining the transient thermal response parameters

of exterior walls, useful for walls of composite (non-homogeneous)

construction. It is feasible, in principle, to determine an effective

thermal diffusivity for a wall consisting of one solid homogeneous

material, but it is necessary to investigate whether a similar meaningful parameter can be established for non-homogeneous walls before

attempting to develop a test method for its measurement. The investigation is being made, at this stage, entirely by mathematical means.

At the end of FY 1964, it had been found that the thermal response

of a composite wall consisting of up to three layers of homogeneous

but different materials, when subjected to an abrupt but constant step

in temperature at one face, could not be represented by means of a simple or constant "effective dif fus ivity"“-in short, that this particular method was not feasible. In recognition of the fact that walls

normally are subjected to exterior temperature conditions which vary

slowly rather than abruptly, and also have a moderate thermal resistance

at the interior surface due to an air film, a tentative method was devised incorporating these conditions. The mathematical analytical

7

solution for the case of a three-layer composite wall (one layer can be an empty air space) has been completed, and coded for numerical

computation,. Six walls, representing a wide range of exterior wall

constructions, have been selected for study to determine if a meaningful response parameter is feasible. The effect of a variation in the

time period of the temperature cycle is also being investigated.

USCOMM-NBS -DC