19

U. S. DEPARTMENT OF COMMERCE

BUILDING

MATERIALS

AND

STRUCTURES

REPORT BMS93

Accumulation of Moisture in

Walls of Frame Construction

During Winter Exposure

- by

CHARLES G. WEBER

and ROBERT C. REICHEL

s5

NATIONAL

BUREAU OF STANDARDS
BUILDING MATERIALS AND STRUCTURES REPORTS

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BMSl Research on Building Materials and Structures for Use in Low-Cost Housing 10^ BMS2 Methods of Determining the Structural Properties of Low-Cost House Constructions lOji BMS3 Suitability of Fiber Insulating Lath as a Plaster Base 10)4 BMS4 Accelerated Aging of Fiber Building Boards 10^ BMS5 Structural Properties of Six Masonry Wall Constructions '. 15ji BMS6 Survey of Roofing Materials in the Southeastern States 15ji BMS7 Water Permeability of Masonry Walls 10(4 BMS8 Methods of Investigation of Surface Treatment for Corrosion Protection of Steel 10^ BMS9 Structural Properties of the Insulated Steel Construction Co.'s "Frameless-Steel" Constructions for Walls, Partitions, Floors, and Roofs 10^ BMSIO Structural Properties of One of the "Keystone Beam Steel Floor" Constructions Sponsored by the H. H. Robertson Co 10^ BMSll Structural Properties of the Curren Fabrihome Corporation's "Fabrihome" Constructions for Walls and Partitions 10^ BMS12 Structural Properties of "Steelox" Constructions for Walls, Partitions, Floors, and Roofs

Sponsored by Steel Buildings, Inc 15^ BMS13 Properties of Some Fiber Building Boards of Current Manufacture 10^ BMS14 Indentation and Recovery of Low-Cost Floor Coverings 10^ BMS15 Structural Properties of "Wheeling Long-Span Steel Floor" Construction Sponsored by

the Wheeling Corrugating Co 10^ BMS16 Structural Properties of a "Tilecrete" Floor Construction Sponsored by Tilecrete Floors, Inc 10^ BMS17 Sound Insulation of WaU and Floor Constructions 10^ Supplement to BMS 17, Sound Insulation of Wall and Floor Constructions 5^ BMS18 Structural Properties of "Pre-fab" Constructions for WaUs, Partitions, and Floors Sponsored by the Harnischfeger Corporation 10^ BMS19 Preparation and Revision of Building Codes 15^ BMS20 Structural Properties of "Twachtman" Constructions for Walls and Floors Sponsored

by Connecticut Pre-Cast Buildings Corporation 10^ BMS21 Structural Properties of a Concrete-Block Cavity-Wall Construction Sponsored by the National Concrete Masonry Association 10^ BMS22 Structural Properties of "Dun-Ti-Stone" Wall Construction Sponsored by the W. E. Dunn Manufacturing Co 10^ BMS23 Structural Properties of a Brick Cavity-Wall Construction Sponsored by the Brick

Manufacturers Association of New York, Inc 10^ BMS24 Structural Properties of a Reinforced-Brick Wall Construction and a Brick-Tile CavityWall Construction Sponsored by the Structural Clay Products Institute 10^ BMS25 Structural Properties of Conventional Wood-Frame Constructions for Walls, Partitions,

Floors, and Roofs 15)i BMS26 Structural Properties of "Nelson Pre-Cast Concrete Foundation" Wall Construction

Sponsored by the Nelson Cement Stone Co., Inc 10^ BMS27 Structural Properties of "Bender Steel Home" Wall Construction Sponsored by the Bender Body Co 10^ BMS28 Backflow Prevention in Over-Rim Water Supplies 10^ BMS29 Survey of Roofing Materials in the Northeastern States 10)fc BMS30 Structural Properties of a Wood-Frame Wall Construction Sponsored by the Douglas

Fir Plywood Association lOi

BMS31 Structural Properties of "Insulite" Wall and "Insulite" Partition Constructions Sponsored by The Insulite Co 15)6

[List continued on cover page ni]
UNITED STATES DEPARTMENT OF COMMERCE • J

esse H. Jones, Secretary

NATIONAL BUREAU OF STANDARDS • Lyman J. Briggs, Director

BUILDING MATERIALS

and STRUCTURES

REPORT BMS93

Accumulation of Moisture in Walls of Frame

Construction During Winter Exposure

by

CHARLES G. WEBER and ROBERT C. REICHEL

ISSUED NOVEMBER 4, 1942

The National Bureau of Standards is a fact-finding organization;

it does not "approve" any particular material or method of construction. The technical findings in this series of reports are to be construed accordingly.

UNITED STATES GOVERNMENT PRINTING OFFICE • WASHINGTON • 194 2

FOR SALE BV THE SUPERINTENDENT OF DOCUMENTS, WASHINGTON, D. C. • PRICE lO CENTS
Foreword

This report presents data on the actual accumulation of moisture in full-height sections of the north outside wall of a frame house

during winter weather. Seven different constructions were included,

and wood sheathing and fiber sheathing were used in direct comparison. The results appear to be of practical interest in modern house

design.

Lyman J. Bbiggs, Director.

[n]
Accumulation of Moisture in Walls of Frame Construction

During Winter Exposure

by CHARLES G. WEBER and ROBERT C. REICHEL

CONTENTS

Page Page Foreword ii IV. Performance of test walls . 4

I. Introduction 1 V. Summary and conclusions 5

II. Description of wall sections tested 2 yj References 5

III. Testing procedure 2

ABSTRACT

The condensation and accumulation of moisture in outside walls of frame construction were observed during winter weather in Washington, D. C. Seven dif- ferent constructions were exposed simultaneously as adjacent full-height sections of the north wall of a frame structure. The humidity and temperature of the inside air were controlled to produce an average

vapor-pressure drop across the waU of approximately

0.2 pound per square inch. Use of a good vapor barrier on the warm side of the waU prevented condensation. In every instance where no vapor barrier was used on the warm side of the wall, condensation occurred

within the wall. The use of a vapor barrier on the

cold side of the waU increased the accumulation of moisture. The performance of walls of standard wood

construction was not basically different from those

containing fiber sheathing boards.

I. INTRODUCTION

The accumulation of moisture within the

outside walls of houses during winter w^eather

has received much attention recently. It is not a new problem, but rather an old one

that has come to the front most emphatically

since the practice of humidif cation in homes

has become widespread. Newly developed

methods of adding moisture to the aii- by

so-called air-conditioning heating units have

produced conditions that are conducive to the condensation of moisture within walls

unless adequate measures are taken to prevent vapor from entering from the warm sides. The pi-oblem of condensation has also become more acute with the widespread use of insulation even without deliberate humidification.

Considerable investigative work has been

done on the problem in general, and numerous

articles have been published on the subject.

Woolley U] ^ discussed the theory of condensation in walls, and Teesdale [2J and Rowley

[3, 4J published excellent data on vapor trans- mission of materials, condensation of moisture

in various types of walls, and on methods of

preventing condensation. However, there have

been instances of luiexplained condensation ut walls, some of which have been attributed to the use of the lelatively new material, fiber sheathing.

This investigation was made for the purpose

of obtaming some basic information on the

accumulation of moisture m the outside walls

of frame construction, using fiber sheathing

and wood sheathing m direct comparison. To

accomplish this, full-scale wall sections of

various constmctions were placed in the north

wall of a test house on the Bm-eau groimds.

Their performance was observed during winter

weather while relatively high humidity and

temperature were maintained withm the

structure.

I Numbers in brackets indicate the literature references at tlie ejifi of this paper.

482576°—42 [1]
II. DESCKIPTION OF WALL SECTIONS

TESTED

Seven wall sections were tested, each repre- senting a specific type of frame construction.

The constructions of the various sections were

as foUows:

Section A, shown in figure 1, consisted of 2- hj 4 -inch studding with K-inch insulation

wallboard nailed to the inside and 2^^2-inch fiber sheathing board naUed to the outside. The

section A except that no vapor barrier was

included.

Section D was the same as section C except

that an asphalt duplex sheathing paper of

good quality was placed on the outside of the

sheathing, under the siding.

Section E was exactly like section D except

that ordinary sheathing of southern yellow

pine wood was used instead of the fiber sheathing boards.

^/x" loioiK^ioyi 50AR.0

16" (IV?R.E55 SltlIIO<|

Figure 1.Section of test panel A.

outside of the sheathing was covered with 10- inch cypress siding lapped 3 inches. The siding was painted on the outside with one coat of

primer and two coats of outside white paint.

A vapor barrier consisting of a 2 -ounce copper

foil bonded with asphalt to a backing of kraft

paper was placed immediately under the wallboard on the inside of the studding, with aU

joints lapped 4 inches.

Section B was the same as section A except

that the copper-foil vapor barrier was on the

outside of the stud space, under the sheathing.

Section C was of the same construction as

Section F differed from section E only in that a vapor barrier of copper foil paper was

placed against the inside surface of the sheathing.

Section G was the same as section F except

that the copper foil barrier was placed on the

warm side of the air space, between the wallboard and the studs, as in section A.

III. TESTING PROCEDURE

The performance of the various sections was

observed for a period of 14 days in midwinter.

During this time the humidity and temperature

inside the house were controlled. The air

[2]
temperature on the inside, or warm side of the

wall, at approximately the breathing level, was 75° F during the day, and it was allowed

to drop to 60° F during the night, the mean

for the test period being 71° F. A mean rela- tive humidity of approximately 70 percent was maintained. The average outdoor temperature for the period was 28° F. Hence, the

wall at approximately breathing level and at

10 inches above tlie floor level. Temperatures

were measured with the use of Ciu'omel-Alumel

thermocouples and a suitable potentiometer.

Moisture data were obtained by checking the

weights of specimens of photographic blotting

paper of known relative-humidity-moisturecontent relationship. The location of the

o

PC

-VMl

''/z iNSULeiTioNsoPtnn

zs"

10 cYPn&ss siDiA/a

Figure 2.

Details of construction of test walls, showing locations where moisture and temperature determinations were made.

apparent average drop in vapor pressure across the walls from the inside to the outside was

about 0.2 pound per square inch. This corre- sponds to the drop across walls m a colder

climate with an inside humidity of approximately 50 percent, at 72° F, and outside

temperatures of zero or below.

Data on the performance of the wall sections were obtained by making daily temperature

and moisture determinations across each section.

The readings were taken across each section of

thermocouples {t) and of the moisture samples

(m) with respect to the cross section of the

walls, and the method of construction to permit access to the moisture samples are shown in figure 2. The arrangement permitted

the removal of the moisture specimens for weighing with a muiimum of disturbance and,

of course," temperature determinations were made without disturbing the wall. At the end

of the 14-day period, the sections were opened

and wet areas noted by inspection.

[3]
IV. PERFOEMANCE OF TEST WALLS

Comparative average temperature distri- butions through the wall sections containing

fiber sheathing boards and those containing

wood sheathing are showTi in figure 3. The

spread between the two distributions across the air space between the studding represents

"r 80—

6o~

JO—

30—

Figure 3.

Comparative temperature distributions through walls constructed ivith insulation sheathing

and with wood sheathing.

Table 1.

Accumulation of moisture within test walls after H days' exposure *

Wall

section Kind of sheathing Moisture-barrier location

Relative humidity

of air in stud

space

Moisture

content

of sheathing

Moisture

content

of siding

Condensation

observed

A Fiber On warm side, under the wall board, on inside of studding

Percent

55 100

93 100 100

100

81

Percent

8.7

8.3

14.9 16.0

60.1

6.1

6.4

j

Percent

8.0

7.1

167.5

7.7 7.0

6.6

6.4

None. On inside of vapor

barrier. On sheathing. Do.

Do. On inside of vapor

barrier. None.

B ...do Between studding and sheathing

C_ ...do None --- D

E

...do Wood. On cold side, under siding, on outside of sheathing do - F ...do On both sides of sheathing G ...do On warm side, under the wallboard, and on cold side, under

siding.

a The average inside ccmditions were 71° F and 70-percent relative humidity, and the mean outside temperature was 28° F.

the beneficial effects of the higher insulation

value of the fiber sheathing over that of the

wood sheathing.

The average moisture conditions within the

individual wall sections, and the observed con- densation at the end of the 14 days' exposure,

are sho^vn in table 1.

[4]
There was no evidence of condensation or accumulation of moisture in section A, which

had a vapor barrier on the warm side of the

wall and none on the cold side. Hence, the

performance of this section was considered

completely satisfactory.

There was no condensation in wall section

G. However, the humidity of the air within

the stud space increased to 81 percent. It wUl

be noted that the vapor barrier on the warm

side of this wall was exactly like that used in

section A. However, section 6 had a barrier

of asphalt-duplex paper on the cold side of the

wall, under the siding. The rise in the humidity of the air within the wall during the test indicates that, even with the best available

barrier on the warm side of a wall, the use of a vapor barrier on the cold side, also, may cause some accumulation of moisture withiji the wall. The moisture doubtless enters the wall by

leakage through the joints of the inside vapor

barrier, as it is practically impossible to form a perfect seal over the entire wall, even when

an impervious material is used.

Condensation of moisture occurred ui all of

the experimental wall sections except A. and

G. Thus, actual condensation took place in every instance where no vapor barriei- was used on the warm side of the wall. In all instances

where condensation did occur, the accumulation of moisture was greatest at the bottom of

the walls, near the sUls. The accumulation of moisture in this portion of a waU will in all probability result eventually in the decay of

the siU and of the lower ends of the studding.

These results do not indicate that condensation or accumulation of moisture is essentially

different in waUs constructed with fiber sheathing than in those containing wood sheathing.

Wood sheathing is more absorbent than the

fiberboard, and the absorption of moisture

from the warm side by wood sheathing might

delay to some extent actual condensation.

However, the moisture will probably do as much

or more harm when absorbed by the sheathing

as it would if it actually formed on its surface. No effects of condensation or accumulation on the outside paint were noted, and it is assumed that the test period was of too short

duration for such effects. It may be assumed

that an accumulation of moisture such as was

noted in wall section C wiU eventually result

m failure of the paint.

V. SUMMA.RY AND CONCLUSIONS

For walls of a frame house exposed to moderate winter weather in Washington, D. C,

while moderately high humidity was maintained on the inside, a good vapor barrier on the warm

side of the walls prevented condensation of

moisture. The addition of a moisture-proof

sheathing paper to the cold side of a wall tended

to cause an accumulation of moisture between

the walls even when an excellent barrier was

used on the warm side. There was no essential difference in this respect between the performance of waUs of

standard wood-frame construction and those

sheathed with fiberboards. It is indicated,

however, that a vapor seal should not be used on the cold side of outside walls if the inside air of a house is to be humidified. Hence, a sheathing that is highly impervious to vapor

may tend to cause an accumulation of moisture.

It is essential that the moisture barrier on the

warm side of the wall be continuous and unbroken, especially between floor levels, and at plumbing and electrical outlets, and other openings. Joints in the membrane serving as the

vapor barrier should be over studs or over

headers provided for the purpose. A lap of 2 inches or more is recommended for all joints. VI. REFERENCES

[1] H. W. Woolley, Moisture condensation in building

walls, NBS Buildins Materials and Structures Report BMS63 (1940). lOfi.

[2] L. V. Teesdale, Condensation in walls and attics, U. S. Department of Agriculture, Forest Service, Forest Products Laboratory, R1157.

[3] F. S. Rowley, A. B. Algren, and C. E. Lund,

Methods of moisture control and their application

to building construction, University of Minnesota Bui. 17.

f4J F. S. Rowley, A. B. Algren, and C. E. Lund, Condensation of moisture and its relation to building construction and operation, University of Minnesota Bui. 18. Washington, August 5, 1942.

BUILDING MATERIALS AND STRUCTURES REPORTS

[Continued from cover page ii] BMS32 Structural Properties of Two Brick-Concrete-Block Wall Constructions and a Concrete- Block Wall Construction Sponsored by the National Concrete Masonry Association _ 10^ BMS33 Plastic Calking Materials 10^ BMS34 Performance Test of Floor Coverings for Use in Low-Cost Housing: Part 1 10^ BMS35 Stability of Sheathing Papers as Determined by Accelerated Aging 10^ BMS36 Structural Properties of Wood-Frame Wall, Partition, Floor, and Roof Constructions

with "Red Stripe" Lath Sponsored by The Weston Paper and Manufacturing Co.- 10^ BMS37 Structural Properties of "Palisade Homes" Constructions for WaUs, Partitions, and

Floors, Sponsored by Palisade Homes 10^ BMS38 Structural Properties of Two "Dunstone" Wall Constructions Sponsored by the W. E. Dunn Manufacturing Co 10^ BMS39 Structural Properties of a Wall Construction of "Pfeifer Units" Sponsored by the Wisconsin Units Co 10^ BMS40 Structural Properties of a Wall Construction of "Knap Concrete Wall Units" Sponsored

by Knap America, Inc 10^ BMS41 Effect of Heating and Cooling on the Permeability of Masonry WaUs 10^ BMS42 Structural Properties of Wood-Frame Wall and Partition Constructions with "Celotex"

Insulating Boards Sponsored by The Celotex Corporation 15^ BMS43 Performance Test of Floor Coverings for Use in Low-Cost Housing: Part 2 10^ BMS44 Surface Treatment of Steel Prior to Painting lOji BMS45 Air Infiltration Through Windows 10^ BMS46 Structural Properties of "Scot-Bilt" Prefabricated Sheet-Steel Constructions for WaUs,

Floors, and Roofs Sponsored by The Globe-Wernicke Co 10^ BMS47 Structural Properties of Prefabricated Wood-Frame Constructions for Walls, Partitions,

and Floors Sponsored by American Houses, Inc 10^ BMS48 Structural Properties of "Precision-Built" Frame Wall and Partition Constructions

Sponsored by the Homasote Co 10{5

BMS49 Metallic Roofing for Low-Cost House Construction 10^ BMS50 Stability of Fiber Building Boards as Determined by Accelerated Aging 10^ BMS51 Structural Properties of "Tilecrete Type A" Floor Construction Sponsored by the THecrete Co 10^ BMS52 Effect of Ceiling Insulation Upon Summer Comfort 10^ BMS53 Structural Properties of a WaU Construction of "Munlock Dry Wall Brick" Sponsored

BMS54 Effect of Soot on the Rating of an Oil-Fired Heating Boiler 10^

by the Munlock Engineering Co 10^ BMS55 Effects of Wetting and Drying on the Permeability of Masonry WaUs 10^ BMS56 A Survey of Humidites in Residences 10^ BMS57 Roofing in the United States—Results of a Questionnaire 10^ BMS58 Strength of Soft-Soldered Joints in Copper Tubing _. 10^ BMS59 Properties of AdhesiVes for Floor Coverings 10^ BMS60 Strength, Absorption, and Resistance to Laboratory Freezing and Thawing of Building

Bricks Produced in the United States 15|S

BMS61 Structural Properties of Two Nonreinforced Monolithic Concrete Wall Constructions. _ lOji BMS62 Structural Properties of a Precast Joist Concrete Floor Construction Sponsored by the Portland Cement Association 10^ BMS63 Moisture Condensation in Building Walls 10^ BMS64 Solar Heating of Various Surfaces 10^ BMS65 Methods of Estimating Loads in Plumbing Systems 10^ BMS66 Plumbing Manual 20^ BMS67 Structural Properties of "Mu-Steel" Prefabricated Sheet-Steel Constructions for Walls,

Partitions, Floor, and Roofs Sponsored by Herman A. Mugler 15^ BMS68 Performance Test for Floor Coverings for Use in Low-Cost Housing: Part 3 15^ BMS69 Stability of Fiber Sheathing Boards as Determined by Accelerated Aging lOfi BMS70 Asphalt-Prepared RoU Roofings and Shingles 15f5 BMS71 Fire Tests of Wood- and Metal-Framed Partitions 20

BMS72 Structural Properties of "Precision-Built, Jr." Prefabricated Wood-Frame WaU Construction Sponsored by the Homasote Co 10^ BMS73 Indentation Characteristics of Floor Coverings 10^ BMS74 Structural and Heat-Transfer Properties of "U. S. S. Panelbilt" Prefabricated SheetSteel Constructions for Walls, Partitions, and Roofs Sponsored by the Tennessee

Coal, Iron & Railroad Co 15^ BMS75 Survey of Roofing Materials in the North Central States 15^ BMS76 Effect of Outdoor Exposure on the Water PermeabiUty of Masonry Walls 15^ BMS'77 Properties and Performance of Fiber TUe Boards 10^

, BMS78 Structural, Heat-Transfer, and Water-PermeabUity Properties of Five Earth-WaU

Constructions 20^ BMS79 Water-Distributing Systems for Buildings 15fi BMS80 Performance Test of Floor Coverings for Use in Low-Cost Housing: Part 4 15^ BMS81 Field Inspectors' Check List for Building Constructions (cloth cover, 5x7^ inches) 20^S BMS82 Water Permeability of WaUs Built of Masonry Units 20^

[List continued on cover page iv]
BUILDING MATERIALS AND STRUCTURES REPORTS

[Continued from cover page iii] BMS83 Strength of Sleeve Joints in Copper Tubing Made With Various Lead-Base Solders 100 BMS84 Survey of Roofing Materials in the South Central States 15^ BMS85 Dimensional Changes of Floor Coverings with Changes in Relative Humidity and

Temperature lOfS BMS86 Structural, Heat-Transfer, and Water-Permeability Properties of "Speedbrik" Wall

Construction Sponsored by the General Shale Products Corporation 15j5 BMS87 A Method for Developing Specifications for Building Construction—Report of Subcommittee on Specifications of the Central Housing Committee on Research, Design,

and Construction 10^ BMS88 Recommended Building Code Requirements for New Dwelling Construction with Special

Reference to War Housing 15^ BMS89 Structural Properties of "Precision-Built, Jr." (Second Construction) Prefabricated Wood-Frame Wall Construction Sponsored by the Homasote Co 15^ BMS90 Structural Properties of "PHC" Prefabricated Wood-Frame Constructions for Walls,

Floors, and Roofs Sponsored by the PHC Housing Corporation 150 BMS91 A Glossary of Housing Terms 150 BMS92 Fire-Resistance Classifications of Building Constructions 250

BMS93 Accumulation of Moisture in Walls of Frame Construction During Winter Exposure 100