•'•a. 3941-^

U. S. DEPARTMENT OF COMMERCE
The program of research on building materials and structures, carried on by the

National Bureau of Standards, was undertaken with the assistance of the Central Housing Committee, an informal organization of governmental agencies concerned with

housing construction and finance, which is cooperating in the investigations through a committee of principal technicians.

CENTKAL HOUSING COMMITTEE

ON RESEARCH, DESIGN, AND CONSTRUCTION

A. C. Shire, Chairman.

United States Housing Authority.

Howard P. Vermilya, Vice Chairman.

Federal Housing Administration.

Sterling R. March, Secretary.

Pierre Blouke,

Federal Home Loan Bank Board.

Hugh L. Dryden,

National Bureau of Standards.

Louis A. Simon,

Public Buildings Administration.

Luther M. Leisenring,

Construction Division (War).

Edward A. Poynton,

OjB&ce of Indian Affairs.

John S. Donovan,

Farm Security Administration.

George W. Trayer,

Forest Service (F. P. Laboratory).

Joseph M. DallaValle,

Public Health Service.

George E. Knox,

Yards and Docks (Navy).

William R. Talbott,

Veterans' Administration.

Wallace Ashby,

Bureau of Agricultural Chemistry and Engineering.

NATIONAL BUREAU OF STANDARDS

STAFF COMMITTEE ON ADMINISTRATION AND COORDINATION

Hugh L. Dryden, Chairman,

Mechanics and Sound.

Phaon H. Bates, Gustav E. F. Lundell,

Clay and Silicate Products. Chemistry.

HoBART C. Dickinson, Addams S. McAllister,

Heat and Power. Codes and Specifications.

Warren E. Emley, Henry S. Rawdon,

Organic and Fibrous Materials. Metallurgy.

The Forest Products Laboratory of the Forest Service is cooperating with both

committees on investigations of wood constructions.

[For list of BMS publications and directions for purchasing, see cover page in]
UNITED STATES DEPARTMENT OF COMMERCE • Harry L. Hopkins, Secretary

NATIONAL BUREAU OF STANDARDS • Lyman J. Briggs, Director

BUILDING MATERIALS

and STRUCTURES

REPORT BMS63

Moisture Condensation in Building Walls

hy

HAROLD W. WOOLLEY

ISSUED DECEMBER 14, 1940

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

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

UNITED STATES GOVERNMENT PRINTING OFFICE • WASHINGTON • I94O

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

This paper was prepared as a result of numerous requests for information on moisture condensation in insulated walls, which will occur under certain conditions. It discusses these conditions in a general way and makes available to architects, builders,

and others information concerning factors which control the humidity in walls. Available data relative to certain types of wall have been collected so that estimates can be made concerning the probability of moisture condensation in walls of dwellings

if the factors governing such condensation, including design, structural materials, construction details, and moisture conditions inside and outside of the building are known.

The Forest Products Laboratory has made extensive studies of this problem in relation to frame construction, and their reports, given in the list of references at the end

of this paper, may be consulted for specific experimental data.

Lyman J. Briggs, Director,

[n]
Moisture Condensation in Building Walls

BY HAROLD W. WOOLLEY

CONTENTS

Page

Foreword ii

I. Introduction 1 II. General principles involved in condensation. 1

Page

III. Means of preventing condensation 11 IV. Conclusions 13

V. References 13

ABSTRACT

Moisture condensation in insulated walls will occur under certain conditions. This paper discusses these conditions in a general way and makes available to architects, builders, and others, information concerning factors which control humidity in walls. These

factors are presented so as to make possible estimates

of the probability of moisture condensation in walls of dwellings if the factors governing it such as design, structural materials, construction details, and moisture

conditions inside and outside the building, are known.

I. INTRODUCTION

In recent years difficulties resulting from

condensation of moisture, particularly within

insulated walls of dwelling houses, have re- ceived considerable attention. When such

condensation occurs to a sufficient degree,

damage to the building structure or decorations may result. No definite statistics are available to indicate to what extent condensation is producing damaging results. However, a

large number of cases of condensation have

been reported, particularly in new houses in the colder parts of the country. Condensation

problems are most frequent in houses of modern

tight construction, with weather stripping,

storm sash, insulation, and the newer types of heating systems that provide some means of

humidification.

The principles involved in the condensation

of moisture in building walls, though comparatively simple, are not understood by the aver- age layman and not always by ai'chitects and

builders. A general discussion of the principles of moisture condensation is therefore in- cluded in this paper, which may be helpful to

both the buying public and the builder. Tlie

discussion is based not so much on definite

tests made at the National Bureau of Standards

as on well-(>stablished facts derived from various

sources.

II. GENERAL PRINCIPLES INVOLVED

IN CONDENSATION

Atmospheric air always contains moisture.

Generally the moisture is not seen because it is in the form of an invisible vapor. It can easUy

be made visible as liquid water by cooling the

air. Thus in the summer water condenses as dew on the outside of a pitcher of cold water.

If the condensation occurs below the fi'eezing

point, it is expected to be in the form of frost. The freezing coils of a refrigerator acquire such

a deposit continually. Condensation of moisture is so common an occurrence that the principles governing it should be known to everyone.A definite volume of air held at a fixed temperature can contain permanently no more than

a definite amount of water in the form of vapoi-.

This limiting quantity of water per given

volume is termed "moisture content at saturation." If the air contains a greater proportion

of moisture than this at the particular temperature, the water will start condensing on the

surfaces of the container or even on the dust

particles in the air which then fall out in a fine mist. The ratio of the actual moisture

content to the saturation moisture content for the particular temperature is termed "relative

humidity." It is customarily expressed in

percent.

2R10U°—40 [1]
The concentration of water vapor may also be stated by giving its pressure. If water

vapor is present, part of the atmospheric

pressm-e is maintained by the water vapor and

the remainder of the pressure by the other constituents of the atmosphere. At a particular

temperature and at saturation the water vapor

exerts a definite pressure. Data on pressure

and density of saturated water vapor will be

found in table 1. If the pressure of the water

vapor at a particular temperature is less than

the tabulated value the air is not saturated.

The ratio of the actual pressure of the water

vapor to the saturation pressure of water vapor

for the particular temperature is also termed

relative humidity. Its value when defined

thus is essentially the same as that given

previously. Throughout this paper, use is made of the last-named "relative humidity."

Table 1.

Pressure and density of water vapor

at saturution

[Saturation vapor pressure for water, p, in pounds per square inch. Sat- uration vapor density tor water, d, in grains » per cubic foot]

Tempera- ture P d Tempera- ture P d

°F °F

-15 0. 008230 0. 2182 25 0. 06405 1. .558 -14 . 009704 . 2303 26 . 06710 1. 629 -13 . 009201 .2430 27 . 07034 1.704 -12 . 009725 .2562 28 . 07368 1.781 -11 . 010276 .2702 29 . 07717 1.862 -10 . 010865 .2845 30 . 08080 1.946 -9 . 011464 .3001 31 . 08458 2. 033 -8 . 012101 .3158 32 . 08856 2. 124 -7 . 012775 .3327 33 . 09230 2. 203 -6 . 013483 . 3505 34 . 09610 2. 288 -5 . 014226 .3692 35 . 1000 2. 376 -4 . 015006 .3883 36 .1041 2. 469 -3 . 015825 .4086 37 . 1083 2. 563 -2 . 016685 .4299 38 . 1126 2. 660 -1 . 017586 . 4521 39 . 1171 2. 700

0 . 018533 .4750 40 . 1217 2.863

1 . 01953 .500 41 . 1265 2. 970

2 .02057 .525 42 . 1315 3. 081

3 . 02166 .552 43 . 1367 3. 196 4 . 02281 . 580 44 . 1420 3.315

5 . 02401 .609 45 . 1475 3. 436

6 . 02527 .640 46 . 1532 3. 562

7 . 02658 .672 47 . 1591 3. 692

8 . 02796 .705 48 . 1652 3. 826

9 . 02941 .740 49 . 1716 3.964

10 . 03092 .776 50 . 1780 4. 106

11 . 03251 .814 51 . 1848 4. 255

12 . 03418 .854 52 . 1918 4.407

13 . 03590 .896 53 . 1989 4. 661

14 . 03772 .939 54 . 2063 4. 722

15 . 03961 .984 55 .2140 4.889

16 . 04160 1.031 56 .2219 5.060

17 . 04369 1.081 57 . 2300 5.234

18 . 04586 1. 132 58 .2384 5. 415

19 . 04812 1. 185 59 .2471 5.602

20 . 05048 1.242 60 .2561 5. 795

21 . 05296 1. 299 61 .2654 5. 993 22' . 05555 1.361 62 .2749 6. 196 23 . 05826 1.423 63 .2848 6.407

24 . 06111 1.489 64 .2949 6. 622

Table 1.Pressure and density of water vapor

at saturation—Continued

Temperature P d Tempera- ture P d

F F

65 0. 3054 6. 846 78 0.4744 10.38

66 . 3162 7. 074 79 . 4903 10. 71

67 . 3273 7. 308 68 . 3388 7. 571 80 . 5067 11. 04

69 .3506 7.798 81 .5236 11.39

82 . 5409 11. 75

70 .3628 8. 055 83 !5588 12! 11 71 .3754 8. 319 84 .6772 12. 49 72 .3883 8.588

73 .4016 8. 867 85 .6960 12.87 74 .4153 9. 163 86 .6153 13. 27

87 .6352 13. 67 75 .4296 9.448 88 .6555 14.08

76 .4440 9.749 89 .6765 14. 51 77 .4690 10.06

» 7,000 grains equals 1 pound. When a given mixture of air and water vapor

is cooled without loss of moisture, a temperature is eventually reached where the air becomes

saturated with water vapor and condensation can occur. The temperature then existing is called the dew point. At any given dew point,

water vapor is always exerting a pressure corre- sponding thereto.

The air in the hollow spaces or pores in building walls always contains water vapor. Under

certain conditions the temperature of portions

of the wall may be below the dew point of the

air in contact with them, and condensation will occur. While at first it might appear that any water

not in vapor form in the wall would be ordinary

liquid water, the facts are not quite so simple.

Many building materials are able to absorb

water to a moderate extent without undergoing great changes. Wood will absorb water

up to from 20 to 30 percent by weight at rela- tive humidities near 100 percent. Beyond

some such point further water absorbed is retained as free liquid water. Other similar

materials differ in the moisture content at which

fui'ther absorbed water is only mechanically

held.

Water has several effects on building materials. As is very well known, some materials,

such as wood, expand with increasing moisture

content. If conditions of greatly varying

humidity occur in ditt'erent parts of the cross section of a single framing member there will be some tendency for the wood to warp. High

humidity favors decay of wood. Some other

materials are adversely affected by continued

[2]
exposure to liqiiitl water. Water promotes

corrosion of metals, and even some mineral

insulating materials show permanent change in the course of time when in contact with water. The insulating value of materials in general is greatly decreased by the presence of free water. Droplets of water tend to bridge gaps between

separate solid portions of ordinary insulating

materials and increase the transfer of heat.

The distillation of moistvire from place to place

in the wall can also increase heat transfer since

heat must be added to evaporate the moisture

and then is released again in the colder region

where the moisture may happen to condense.

Normally this effect will be important mainly

when the temperature indoors is increasing.

Moisture condensed in the walls may not

remain in its first location. It is even possible

for it to migrate and succeed in making the

plaster and wallpaper damp and discolored.

When that symptom appears in late winter or

spring, and unless the trouble is caused by leaks,

it is very probable that condensation in the

wall is responsible. In such a case the following explanation should be to the point.

If different gases mix without stirring, the

movement of the one gas into the other follows a simple law of diffusion. If one gas is of rela- tively low concentration, its rate of diffusion

into the other is closely proportional to its pressm-e difference per unit distance. The law

is found to hold fairly well for the diffusion of

moisture, even through many solid materials.

There are exceptions, but in this discussion

they will be largely ignored. Data in regard

to diffusion of water vapor through various

materials will be found in table 2. In this has

been used as a unit

Table 2.Permeability of various materials to water vapor

Tablk 2.

Permeability vaporof various malerialis to water -Continued

Material Thickness

Permeability

to moisture

(P)

Vapor

resistance (.UP)

BABBITT [8]

Grains sqfthr (Iblsq in.) Inches sgft hr (Ib/sq in.) Grains Fiberboard _ _ _ _ _ 0. 492 60.6 0. 0168 Fiberboard, 1 surface asphalt,

rolled . . . „ .492 8.0 .125 Fiberboard, 1 surface asphalt, dipped-- .63 17.3 .0578

Material Thickness

Permeability

to moisture (P) BABBITT (8J—Continued

Fiberboard, laminated, 2 samples cemented together with asphalts Fiberboard, laminated, 6 layers with 5 layers of as- phalt. Fib('rboanl Fiberboard, same reduced in thickness Do

Do

Do

Wood, spruce. Do

Do

DoDo

Do

Wood, pine Do

Do

Do. Do

Wood (pine) A

Wood (pine) A, 1 coat of Al

paint Wood (pine) A, 2 coats of Al

paint Wood (pine) A, 3 coats of Al

paint Wood (pine) B

Wood (pine) B, 1 coat of Al

paint Wood (pine) B, 2 coats of Al

paint Wood (pine) B, 3 coats of Al

paint Kraft paper, 1 sheet Kraft paper, 2 sheets Kraft paper, 3 sheets _ Kraft paper, 4 sheets Kraft paper, 5 sheets Kraft paper, 5 sheets Kraft paper, 5 sheets Kraft paper, 7 sheets Kraft paper, 7 sheets Kraft paper, 8 sheets Kraft paper, 8 sheets rubber,

hydroBlack vulcanized hardness 40 Plasticized rubber

chloride 30-30-30 paper A

30-30-30 paper B . Duplex Scutan 6-6, asphalt between 2 sheets of kraft.. Scutan 0-14 (kraft infused with asphalt on 1 surface) A

Scutan 0-14 B

Scutan 14 (kraft infused with

asphalt on surfaces) A

Scutan 14 B

Black building paper, black shiny paper infused with

asphalt

-Asphalt felt, 15-lb. felt building paper with soft dull appearance

Pressed corkboard A

Pressed corkboard B

Plaster Plasterboard, plaster between

sheets of heavy paper Masonite Presdwood, tempered Masonite Presdwood

Masonite Presdwood, 5 thick- nesses Masonite Presdwood, 7 thicknesses

Graim

Inches sq ft hr (Ib/sq in.)

. 985 2, 74

.527

1.06

0.803

..599 .405

.201

. 563

. 480 .405

.323 .232

.161

.80 .645

.496

. 315

. 169

. 508

. 00394

.0791

. 00158

.0071

.0071

.0071

.0071

.0071

.0071

.0173

.0319

.905 .985

1. 34

0.37

. 13 .13

0.23

37.0

43.4

56.4

74.5

133.3 3.48

4. 03

3. 94

4.93

7.24

10. 35 1.88

2. 52

3. 45

5. 55

9. 65

6. 47

3.42

0.92

.71

3. 85

1.95

1.53

168.

107.

sqft hr (Ib/sqin.)

80. . 0125

63.6 .0157

53.5 .0187 65.3 .0153

61.6 .0162

45.5 .0220 38.3 .0261 38.3 .0261 33.1 .0302

0.185 5.4

.382 2.62

1.83 0. 546

1.79 . 558

0.946 1.06

8.6 0. 116 15.97 .0626

13.9 .0719

15.8 . 0633

0.376 2.66

13.5 0. 0741

4. 75 .211 5.42 . 184

27.

1

.0369

70.2 .0142

9. 76 .102

21. 7 .0461

6.25 . 16

4.9 .204

[3]
Table 2.

Permeability of various materials to water vapor—Continued

Table 2.Permeability of various materials to water vapor—Continued

Thickness

Permeability Vapor

Material to moisture resistance (P) (1/P) TEESDALE (11]

Foil-surfaced reflective insulation, double-faced

Roll roofing— smooth, 40 to 65

lb/roll 108 sq ft Asphalt impregnated and

surface-coated sheathing

paper, glossy, 50 lb and 35

lb/500 sq ft Duplex or laminated papers,

30-30-30 ._. Duplex or laminated papers,

30-60-30 Duplex papers, reinforced Duplex paper, coated with

metal oxides Insulation backup paper,

treated Gypsum lath with Al-foil backing

Plaster, wood lath

Plaster, 3 coats of lead and oil. Plaster, 3 coats of flat wall

paint

Plaster, 2 coats of Al paint

Plaster, fiberboard or gypsum

lath

Slater's felt Plywood, H-in., Douglas fir, soy bean glue, plain Plywood, 2 coats of asphalt

paint Plywood, 2 coats of Al paint,. Plywood, H in., 5-ply Douglas fir Plywood, li in., 3-ply Douglas fir, artificial resin glue Plywood, H in., 5-ply Douglas fir, artificial resin glue___ Insulating lath and sheathiug, board type

Insulating sheathing, surface- coated Compressed fiber board,

Insulating cork blocks, 1 in._. Blanket insulation between

coated papers, yz and 1 in,_ Mineral wool, unprotected,

4 in

Inches Grains \sqfthr (Ib/sg in.) sgfthr (Ib/sqin.)

0. 172 to 0. 263

. 263 to . 348

. 433 to 1. 57

. 348 to 4. 19

2. 80 to 5. 24

1. 05 to 1. 75

1. 396 to 4. 19

1. 05 to 2. 63

1. 75 to 6. 97

0. 173 to 0. 785

22.

4

7. 5 to 7. 84

8. 72 2.35

40.2 to 41.

9

10. 5 to 52. 4

8. 72 to 13.

1

0. 87

2. 63

5.43 to 5.59

8. 72 to 13.

1

5.69 to 6.85

52.3 to 69.

8

6.17 to 8.88

10.3 12.6

3.90 to 4.07

59.2

Grains

5. 82 to 3. 8

3.8 to 2.87

2. 31 to 0. 637

2.87 to .239

0.357 to .191

.952 .716

.952

.572

5. 78

0. 133

.0249 .0952

to .572

to .239

to .381

to . 144

to 1. 27

n. 0446

to .127

.115 .425

to .0239

to .0191

. 115 to . 0764

. 184

.115

.179

.0191

1. 16 0.38

to .179

to .0761

to .146

to .0143

.256 to

.097 .0794

.246

.0169 FOREST PRODUCTS LABORATORY

paint, Kraft paperPlastered wall, i plasterboard lath Plastered wall, no paint, wood lath

Slater's felt, best type Duplex paper

Plastered wall, 2 coats of Al

paint, wood lath .^sphalt-coatedpaper,351b/500 sq ft roll Asphalt-coated paper,501b/500 sq ft roll Metal-coated paper

112. 0. 00893

41.7 .024

22.2 .045

10.1 .099 2.78 .36

2.43 .411

2.08 .481

1.04 .962 0.174 5.75 INTERNATIONAL CRITICAL TABLES

Still air, 3% in 70.9

257

0. 0141

Still air, 1 in . 00389 WRAY [3]

1 coat of Al paint on wood.

Bakelite resin varnish

1 coat of Al paint on wood,

glycerol phthalate varnish

2 coats of ordinary paint, lin- seed oil .

1.22

1.22

3. 48

2.26

0.82

.82

.287

.445

1 eoat of Al paint on wood,

ester gum varnish

Material Thickness

Permeability Vapor

to moisture i resistance (P) (VP) HERRMANN [4]

Hydrocarbon wax

Thiokol Gutta percha Hard rubber Para gutta Polystyrene Asphalt sealing compound.

Phenol fiber Soft vulcanized rubber Benzyl cellulose Bakelite Waterproof cellulose film. _ Cellulose acetate

Grains sgfthr (Ib/sg in.) Inches sg ft hr (Ib/sg in.) Grains

b 1 0. 000052 1.9 XW*

b 1 . 00014 7.1 X10 3 b 1 . 00035 2.86X10 3 b 1 . 00035 2.86X10 3

"> 1 . 00042 2.38X10 3 b 1 . 00087 1.15X10 3 1>1 . 00087 1. 15X10 3 b 1 . 00148 676

b 1 .00157 637

b 1 . 00226 442

b 1 .0035 286

b 1 .062 16.1

b 1 .12 8.3 MILLER [7]

Plaster base and plaster, H

Vapor barrier (Kimberly

Clark Corp. data)

Fir sheathing, % in Waterproof paper

Pine lap siding Paint film Celotex, ?4 in Brick masonry, 4 in

30 0.033

1. 65 .61 6 .167

100 .01 10 .1.14

25. 5 .0392

2.2 .454 MARTLEY [2]

Wood, Scot pine, per inch 21.4 0.0467 WRAY

Wood, western yellow pine, Kin 1.8 0.556

1

» Figures in brackets indicate the literature references at the end of this paper.

k Data recalculated on basis of 1-inch thickness.

of permeability to moisture the number of

grains per hour passing through 1 sq ft of the

actual thickness specified when the vapor pres- sures at the two surfaces differ by 1 Ib/sq in. The reciprocal of this permeability has also been listed and has been called the vapor resist- ance. The number of grains of moisture pass- ing through 1 sq ft in 1 hour with 1-lb/sq in. pressure difference =permeability = 1 /vapor re- sistance.

If winter air is brought into a house from the

outdoors and is heated without addition of moisture, the resulting warm air will contain

the same proportion of moisture as before, and

therefore the pressure of the contained water

vapor will be the same, but the relative humidity

will be lower than that of the air outside. This

is true because the warm air ' can contain more

moisture than it could when cold. If the difiuStrictly, the space contains the moisture.

[4]
sion of the water vapor through the walls is proportional to the vapor-pressure difference

between inside and outside, there will be no net passage of moisture, since this difference is zero. In such a case there would be no tendency

for air in any part of the wall to have a relative

humidity greater than the value outdoors. In

fact all parts would be subject to lower rela- tive humidities, since the air would be warmer

than the air out of doors.

Actually, in an occupied house moisture is always being added to the air, so that the vapor

pressure is higher inside the house than outside.

The water vapor penetrates the plaster or other

interior finish and passes on through the rest

of the wall to the outside. Accordingly, the

vapor pressure within the walls will be higher

than that outside, although less than that within

the interior of the house. The manner in which

the vapor pressure falls olf from tiie liigii value

inside the house to the low value outside the

house, together with the temperature distribution across the wall, detcu-mines the relative

humidity at all points within the wall. In an ordinary frame wall condensation is more likely to occur on the inner surface of the

sheathing than elsewhere, except when sheathing papers highly resistant to water vapor are employed, in which case condensation may first appear on the sheathing paper. In other types

of hollow walls condensation tends to occur in corresponding regions.

Differences in vapor pressure through dif- ferent parts of the wall from inside to outside

distribute themselves in proportion to the vapor

resistance of the respective parts. That is, the

fraction of the total vapor-pressure drop from

inside to outside occurring between the air inCQ

_l

uid

D

I/) CO

UJd

Cl

a>O

CL<

>

.35 - \ .

1\

\

.30

\

:

.... \

\ \

^ \.

.25

\l-

- \-\

.20

.15

.10

.OS

0

70

30

20

lOu.2

LU

so

g

U

40 olD

I-<

LUa

ai

Figure 1.-

Nature of the temperature, corresponding saturation vapor pressure, and actual vapor pressure distributions in an uninsulated brick wall.

Wall composed of A, plaster on metal lath; B, air space between furring strips; and C, brick, exposed to 70° F and 30-percent relative humidity

indoors and 10° F and 80-percent relative humidity outdoors.

[5]
doors and some chosen point within the wall is the same as that fraction of the total vapor

resistance of the wall occurring between the

air indoors and the chosen point.

In this it is analogous to heat flow, in which

differences in temperature through different

parts of the wall from inside to outside are proportional to the thermal resistance of these

parts. In other words, the fraction of the total temperature drop from inside to outside in- cluded between the indoor air and the chosen

point is the same as that fraction of the total resistance to heat flow included between the

indoor air and the same chosen point.

From these facts one can calculate the vapor

pressure and temperature at any point in the

wall and estimate whether the calculated vapor

pressure is safely below saturation vapor pres- sure for the calculated temperature. As an

explanation of this the following examples are

given.

1. A brick wall composed of metal lath and

plaster, air space between furring strips, com- mon and face brick is exposed to 70° F and 30-

percent relative humidity indoors and 10° F

and 80-percent relative humidity outdoors. A

section of this wall is pictured in figure 1 with

curves showing the nature of vapor-pressure

and temperature distributions within the wall. To determine whether condensation will occur on the inner sui-face of the brick, data on vapor

resistance and thermal resistance of the various

parts of the wall are examined.^

The following vapor resistances are taken,

starting with the indoor side of the wall

:

Air to surface of plaster not over 0.001 Metal lath and plaster (data for wood lath and

plaster) .04.5 Air space not over .014 Brick (doubling the figure for 4-in. masonry) .9 Surface of face brick to outside air Negligible.

The sum of the first thi'ee is 0.060, and the

total for the entire wall is 0.960. The vaporresistance fraction is therefore equal to 0.060/

.960, or about 0.0625. This means that about

one-sixteenth of the vapor resistance of the wall

is comprised between the air of the room and

the inner surface of the brick.

Units of vapor resistance and thermal resistance have been omitted

in much of the discussion following. The units are hr sq ft (Ib/sq in.)/ grain, and hr sq ft deg F/btu.

One may similarly examine the data on thermal resistance, or insulating value, for the

separate parts of the wall, as given in table 3. The following are taken as thermal resistances:

Table 3. -- Thermal resistance of various materials

Materials Thermal

resistance

hr sq ft deg F

Btu

Yellow pine or fir, 2^52 in. thick __. 0. 98 Yellow pine lap siding . _ - .78 Wood lath and plaster . .40 Metal lath and plaster. . . _ .23 Mineral wool, per in 3. 70 Stucco __ . . 0.08

Brick, common 4-in .80 Brick, face 4-in. . . . . .44 Fiberboard, per in ... _ ... 3.0 Plasterboard H-in 0. 35

Surface film, still air.. .61 Surface film, 15 mph .. ... .17 Surface film, rough stucco, 15 mph. ... .11 Air space more than 54 in. across not lined with re- .91

flector ..

Air to surface of plaster 0. 61 Metal lath and plaster . 23

1%-in. air space . 91 Common brick .80

Face brick . 44

Surface of face brick to outside air .17

The sum of the first three thermal resistances is 1.75, and the total thermal resistance of the

wall is 3.16. The thermal-resistance fraction

is therefore equal to 1.75/3.16, or 0.554. This means that about 55 percent of the thermal

resistance of the wall is comprised between the

air of the room and the inner surface of the

brick.

These fractions will now be applied. For the

water vapor there is indoors a vapor pressure of 30 percent of 0.3628 Ib/sq in., or 0.109 Ib/sq in. Outdoors there is a vapor pressure of 80 percent

of 0.03092 Ib/sq in., or 0.02474 Ib/sq in. The

drop in vapor pressure through the wall is 0.109

Ib/sq in. minus 0.025 Ib/sq in., or 0.084 Ib/sq in. Multiplying this drop by the vapor-resistance

fraction 0.0625, one obtains 0.00525 Ib/sq in. to be subtracted from the 0.109 Ib/sq in. indoors.

The result, 0.104 Ib/sq in., is the vapor pressure

adjacent to the inner surface of the brick—cor- responding to a "dew-point" temperature of

36° F. The same procedure may be continued in

regard to temperature. The temperature in-

[6]
doors is 70° F. The temperature outdoors is 10° F. The drop in temperature through the

wall is then 60°. Multiplying this drop by the

thermal-resistance fraction, 0.554, one gets

33.24° as the drop in temperature between the

air of the room and the inner surface of the

brick. Subtracting the 33.24° from 70°, the

indoor temperature, one obtains 36.76° as the

temperature of the innei' surface of the brick

which is higher than the above-noted "dewpoint" temperature.

This temperature and the vapor pressure for the same point are compared with the figures

given in table 1 for saturation pressures. One

finds for the temperature calculated a saturation

pressure of 0.107 Ib/sq in. Since the actual

vapor pressure as calculated (0.104 Ib/sq in.) is less than this, it is not indicated that condensation will occm" on the inner surface of the brick

in this particular wall for the particular conditions of temperature and relative humidity

quoted.

2. As a second example the same wall is considered, except that for the air space will be

substituted a fill of insulating material adding

negligible vapor resistance. The following

values of vapor resistances and thermal resist- ances are based on tables 2 and 3

:

Vapor Thermal

resistance resistance Air to surface of plaster 0. 001 0. 61 Lath and plaster . 045 . 23

Insulation (1%-in. mineral wool) . 014 6. 01 Brick

.9

1. 24

Surface to air 0 0. 17 The vapor-resistance fraction is as before,

0.0625, and the thermal-resistance fraction is 6.85/8.26, or 0.83. The use of these, with the

total vapor pressure and temperature drops

calculated before, gives for the inner surface of the brick a temperature of 20.2° F, and, as

before, a vapor pressure of water of 0.104 Ib/sq.

in. and a corresponding "dew-point" temperature of 36° F. Table 1 indicates that for the

temperature 20.2° F a vapor pressure of only

0.05098 Ib/sq in. can occur without condensation. It is thus seen that under these conditions of temperature and humidity water will be condensing against the inner surface of the

brick—the temperature being below the abovenoted "dew-point" value.

Similar calculations may easily be mnde loi- any wall, if data are available for its constituent

parts. As table 2 shows, data are not abundant

on all construction materials. For types of

wall construction which have been considered,

the r(^sults are somewhat similar to those just

obtained for the brick wall. In practically all hollow walls, the possibility of condensation on

the cold side of the hollow space is the critical point, since condensation is generally more;

likely to occur there than in neighboring regions.

A summary of calculations for different walls

for several indoor humidities and outdoor

temperatures is given in table 4. In interpreting the results given here, it is necessary to recall the warning that since the data were obviously very uncertain the results are

also very uncertain.

If the figures are to be used in building design, an ample factor of safety should be included,

although the figures seem likely to be in error

in such a direction that a factor of safety is already present. An important reason for this

is that in all this discussion the air leakage into

the wall from the outside has been disregarded.

Its effect is to reduce the tendency for condensation, but by an amount which natm-ally can- not be estimated without definite data as to the

amount of air leakage occurring.

Most of table 4 should be clear from the dis- cussion already given. To clarify the method

for calculating the last thi'ee columns, the

following example gives a calculation of the

vapor resistance which must be added to the

warm side of the wall to just barely prevent

condensation. The case considered is that of the brick wall with 1% in. of insulation and

exposed to 30° F and 80-percent relative

humidity outside and 70° F and 40-percent

relative humidity indoors. It is assumed that

the vapor resistance of lath and plaster and in- sulation in the wall is 0.06 hi" sq ft (Ib/sq in.)/

grain and the vapor resistance of the remaining

outer part of the wall is 0.9 hr sq ft (Ib/sq in.)/

grain. The temperature at the inner surface

of the brick, according to the previous explanation is found to be 70° F-0.83 (70° F-30°

F) = 70° F-0.83 (40° F) =70° F-33.2° F=

36.8° F.

[7]
Table 4.

Illustrative calculations concerning vapor barriers

Wall type

Inner

part

Frame wall; Uninsulated

354 in. of insulation

1 in. of insulation in middle of space

2 in. of insulation in middle of space Frame and stucco: Uninsulated

3^6 in. of insulation

1 in. of insulation

2 in. of insulation

Brick veneer: Uninsulated ---

'i^i in. of insulation

1 in. of insulation

2 in. of insulation

Brick, solid 8 in., furred, metal lath, and

plaster: Uninsulated 1% in. of insulation

1.92

14. 41

6. 53

10. 23

1.92

14. 41

6. 53

10. 23

1.92

14. 41

6. 53

10. 23

1. 75

6. 85

•esist- Thermal-resistance

fraction

(to chosen

point: Cold side

of insulation, or hollow

space, if present

Vapor resistance ^ Vaporance

fraction

(to chosen

point)

Necessary increase in inner vapor

resistance to prevent condensation

at the chosen point

Total Inner

part Total

30° F. 80%

outside;

70° F. 40%

inside

10° F. 80%

outside;

70° F. 30%

inside

-10°F.S0%,

outside:

70° F. 20%

inside

3. 85 0. 50 0.06 0. 460 0. 13 0 0 0

16. 34 .88 .06 .460 . 13 .47 1.28 2.24

8. 46 .77 .06 .460 .13 .14 0.48 0.83

12. 16 .84 .06 .460 . 13 .32 .90 1.54

3.09 .62 .06 .305 . 197 0 0 0. 06

15. 58 .93 .06 .305 . 197 .43 1.24 2.30

7.70 .85 .06 . 305 . 197 . 19 0. 58 1. 01

11. 40 . 90 .06 .305 . 197 .32 .92 1! 65

3. 87 .50 .06 .71 .0845 0 n 0

16. 36 .88 .06 .71 . 0845 .80 2.11 3. 67 8.48 .77 .06 .71 .0845 .27 0. 82 1.38

12. 18 .84 .06 .71 .0845 .56 1.49 2. .14

3. 16 .654 .06 .96 .0625 0 0 0.05 8.26 .83 .06 .96 . 0625 .73 1. 92 3. 24

« hr sq ft deg F/Btu.

t hr sq ft (lb/in. 2)/grain. The vapor pressure at this inner brick surface

must not be higher than the saturation vapor

pressure for 36.8° F, as given by table 1, namely 0.1075 Ib/sq in. The vapor pressure on the outside of the wall is found to be 0.80

times 0.0808 Ib/sq in., or 0.06464 Ib/sq in. The vapor pressure indoors is 0.40 times 0.3628,

or 0.1451 Ib/sq in. The drop in vapor pres- sure across the outer part of the wall is 0.1075

Ib/sq in. minus 0.0646 Ib/sq in., or 0.0429

Ib/sq in. The drop in vapor pressure across the inner

side of the wall is 0.1451 Ib/sq in. minus 0.1075

Ib/sq in, or 0.0376 Ib/sq in. Since the vapor

resistance of the various parts are proportional

to the corresponding vapor pressure drops, the

vapor resistance on the inner side needs to be

0.0376/0.0429 times as great as the vapor re- sistance of the outer side. This gives 0.0376/-

0.0429 times 0.9 hr sq ft (Ib/sq in.)/grain=0.79

hr sq ft (Ib/sq in.)/grain as the inner vapor

resistance desired. Since this wall was supposed to have an inner vapor resistance of 0.060 hr sq ft (Ib/sq in.)/gTain originally, it is

necessary to add a barrier having as vapor re- sistance the difference of these, or 0.73 hi- sq ft (Ib/sq in.)/grain. One might now search table 2

for possible barriers having vapor resistances of

this magnitude or greater and having negligible

thermal resistance.

The graphs in figures 2, 3, and 4 may be con- venient for rapid judgment as to the adequacy

of a given moisture barrier for a given wall. The outdoor relative humidity is here assumed

to be 80 percent and the indoor temperature

70° F for each case. These are considered more

or less typical of winter conditions occurring

in many parts of the country with snow throughout the winter. If thermal-resistance fractions

and vapor-resistance fractions are laid out

along their corresponding axes, the point thus

located by intersection of the horizontal and

vertical lines indicates the indoor relative

humidity at which trouble might occur under

the conditions quoted for the separate charts,

namely for outdoor temperatures of 30°, 10°,

and — 10° F, respectively.

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zg

\-

u

<

Ll

liJ u

2

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H

(O

10

UJ0^

UJI

h

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- _

1 - / p

/ /

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Figure 2.

Indoor

O .1 .2 ,3 .4- .5 .6 .7 .6 .9 I.O VAPOR RESISTANCE FRACTION

humidity able to cause condensation at a given point in a wall, as drier inim.d by the elative thermal-resistance fraction and the vapor-resistance fraction.

(Fraction of thermal resistance on warm side of the point and fraction of vapor resistance on warm side of the point in question.) Curves A, 30%; B, 40%; C, 50%; D, 60%; and E, 70% indoor relative humidity.

Conditions: 30° F outdoors; 70° F indoors; and 80-percent relative humidity outdoors.

For example, any combination of thermalresistance fraction and vapor-resistance fraction represented by a point on or below the 40-

percent line represents a type of wall in which

condensation will not occur unless the indoor

humidity exceeds 40 percent. The region below the 40-percent line therefore represents

combinations of thermal and vapor resistances

in which relative humidities up to 40 percent are

safe. The region above the line represents

combinations in which humidities as high as 40

percent should be avoided.

Thus one may consider the case of a wall the

thermal-resistance fraction of which is 0.50 and

the vapor-resistance fraction 0.13. Figure 2 shows that a relative humidity of about 54

percent or more indoors could lead to condensation when the outdoor temperature is 30° F. Figure 3 indicates about 38 percent for a temperature of 10° F, and figure 4 indicates about

26 percent for an outdoor temperature of —10°

F. These results would doubtless be considerably altered if the ventilation of the wall by

air leakage could be allowed for. Figures 2, 3, and 4 can be used for determining the moisture-condensation conditions

at a selected spot in insulated walls of many

types, through which heat is transferred by

conduction or its equivalent, provided the heattransfer resistance and the vapor-transfer re- sistance fractions are known. It cannot be

directly utilized in connection with walls having appreciable ventilating spaces. When studying any thermal-conduction type

of wall, full consideration must be given to the

actual space distribution within the wail of both the thermal and the vapor-transfer re- sistances. Critical points are to be looked for where there is space concentration of vaportransfer resistance on the cold side of any space

concentration of thermal resistance.

Without regard in any respect to the actual

space distribution of the thermal and vaportransfer resistances, if the space distribution of

[9]
o

u_

UlU

Z

(JO U)

LU

<

a:

LUX

I.O

.9

.8

.7

.6

.5A

.3

.2

.1

/

,-

-' /

B

L>

-t;

.1 .2 .3 A .5 .6 .7 .6 VAPOR. RESISTANCE FRACTION

1.0

Figure 3.Indoor relative humidity able to cause condensation at a given point in a wall, as determined by the thermal-resistance fraction and the vapor-resistance fraction.

(Fraction of thermal reisistance on warm side of the point and fraction of vapor resistance on warm side of the point in question.) Curves A, 10%; B, 20%; C, 30%, i), 40%; and E. 50% indoor relative humidity.

Conditions: 10° F outdoors: 70° F indoors; and SO-percent relative humidity outdoors.

the thermal resistance is the same as (or approximately the same as) the space distribution

of the vapor-transfer resistance, the wall acts exactly (or approximately) as though it were composed of homogeneous insulating material.

In certain cases the walls may well be treated

as though made up of separate layers of homogeneous insulating materials. When this condition is reached (or approximated) one cannot

determine by mere superficial examination just

where and when condensation may take place

the below-dew-point temperatures may be

reached within the mass of the material, al- though not at either edge.

Consider, for example, the case where the wall

may properly be regarded as a single uniform

thick sheet having at its warm surface air of one temperature and relative humidity and at the cold surface air of another temperature and

relative humidity. There is in all parts of the

wall the same rate of passage of moisture if no

condensation is occurring and a steady state

has been established. The vapor-pressure drop

is then uniformly distributed across the material in the same manner as is the temperature

drop. This may be illustrated by figure 5 in

v/hich the temperatm-e is indicated at uniform

intervals along a horizontal axis. This may be

considered the direction across the layer of

material having uniform spacing of insulation

of uniform thermal resistance or at least uniform sections of the total thermal resistance of the material. The two surfaces of the material

are then located on this scale by their corre- sponding temperatures. Plotted vertically are the saturation pressures for water vapor cor- responding to all temperatures along the horizontal axis. If the actual vapor pressures at the two siu-faces are now plotted for their positions as indicated on the temperature scale, for example A and B, the vapor pressure at any point between will be indicated by the

distance vertically upward to the straight line between them. As examples, three cases have

[10]
O .1 .2 .3 .4 .5 .6 .7 .8 .9 I.O VAPOR RESISTANCE FRACTION

Figure 4.

Indoor relative humidity able to cause condensation at a given point in a wall, as determined by the thermal-resistance fraction and the vapor-resistance fraction.

(Fraction of thermal resistance on warm side of the point and fraction of vapor resistance on warm side of the point in question.) Curves .4, 50%; B, 10%; C, 20%; D, 30%; and E, 40% indoor relative humidity.

Conditions: —10° F outdoorx; 70° F indoors; and 80-percent relative humidity outdoors.

been shown, originating from having different

vapor pressures at the point A corresponding

to 25-, 50-, and 80-percent relative humidities.

In each case the vapor pressure at the point

C with temperature 40° F is indicated on the

vapor-pressure scale by the line upward from C

to the appropriate slanting line. Thus the

slanting line thi'ough D illustrates a case with

50-percent relative humidity at A in which the

vapor pressm-e at C is below the saturation

value, although the apparent tangency with the

saturation pressure curve near 20° F indicates

that condensation is in danger of occurring in a very limited region of the part at 20° F. The

slanting line through D' lies above the saturation curve for much of the wall and in particular

for the point C, indicating that for a relative

humidity of 80 percent at A condensation is to be expected throughout a considerable portion

of the wall. The third slanting line, passing

through D", lies entirely below the saturationpressm:e ciu-ve and indicates that condensation

will occiir at no point in the slab when the

relative humidity at A is 25 percent. These

calcidations, which are approximately correct,

may be useful in indicating possibilities of con- densation within the material of a wall with

similar spatial distribution of the heat and vaportransfer resistances, where seemingly there is no

specific critical condensation point.

III. MEANS OF PREVENTING

CONDENSATION

The methods by which condensation of

moisture in insulated walls may be avoided are becoming fairly well known. A little consideration of the principles already explained here

shows that possible remedies will include:

1. Lowering the indoor relative humidity,

either by lowering the rate at which water vapor

is added to the air in the house or by increasing

the ventilation of the house interior to the

outdoors.

fill
a

to

CD

UJD

d

Cl

o

a

<

>

1

1< ]

1

/

/

/ 1

1

11 I

,/ }f

1,

* ->

y

/

y t;

/

/

- / '

B c A

-20 -lO O lO 20 30 40 50 60 70 80

DEGREES F Figure 5.

Method of predicting vapor pressure conditions in a wall composed of a single slab of permeable material.

80-percent outside humidity (at B); D', line for 80-percent humidity inside (at A); D, line for 50-percent humidity inside (at A); D", line for 25-percent humidity inside (at .-1); straight lines, actual vapor pressures; and curve, saturation vapor pressures.

2. Increasing the vapor resistance on the

warm side of the insulation.

3. Lowering the vapor resistance on the cold

side of the insulation by venting to the outside

air or b}^ using less vapor-resistant outer wall

materials without diminishing protection against

driving rains. These will be considered in order.

1. The indoor relative humidity is likely to be kept at sufficiently moderate values to avoid

condensation on windows most of the time.

When use is made of single-glazed windows, the

mean relative humidity is then likely to be so low that trouble from condensation within walls

will not occur. However, when use is made of

double-glazed windows, or storm windows,

there may be condensation within the wall

without condensation on the glass, either inside or outside.

2. The addition of a vapor barrier on the

warm side of the wall insulation is an effective

procedure. High humidities frequently occur

temporarily, even in houses which would

scarcely be described as humidified. If the

inside relative humidity is kept high the vapor

barrier is of value because it furnishes the only

remaining way of effectively reducing the rate

at which moisture enters the wall. Naturally,

if a vapor barrier prevents part of the loss of

moisture through the walls, it will also reduce

the rate at which moisture must be supplied to maintain any chosen relative humidity. Any

water evaporated is, of course, removed largely

by normal ventilation.

3. The provision for adequate ventilation from

the interior of the wall to the outdoors or the use

of sheathing paper with smaller vapor resistance can be helpful. Unless the ventilation to out- doors is abundant, there is a tendency for the

beneficial effect of ventilation of the wall to be

limited to the vicinity of the openings to the

outside. The air space between the insulation

and sheathing should be so proportioned as to permit air circulation and thus allow water

vapor to seek natural outlets. It is, of course, obvious that the wall must be left capable of

[12]
shedding tiie rains, or even more water may

enter from the outside than would have

accumulated by condensation from the insifle. Tlie calculation of the resistance necessary

in a vapor barrier in order to prevent condensation in a particular wall has already been

discussed, and some results are given in table 4.

It will be noted that for conditions which do

not seem unusually severe the resistance which

must be added is such that the vapor resistance on the warm side of the insulation becomes

several times as great as that on the cold side. The metal foils and some of the asphalt papers

are effective vapor barriers.

Some of the flexible blanket and rigid board

types of insulatmg materials are now provided

with self-contained vapor barriers. When used on the warm side of the insulation a barrier is advantageous; on the cold side it is disadvantageous. When a moisture-repelling protective

sheet is used on the cold side, it is essential to have a sheet of considerably greater—usually

several times greater—vapor resistance on the

warm side. The blanket type of insulation can be in- stalled near the center of certain types of wall

space so as to leave a continuous air space for ventilation on the cold side. For old houses,

in which it is difficult to install barrier sheets next to the insulation, the use of two coats of

aluminum paint on the inside wall surface has

been recommended by some investigators. In insulated attics the situation is quite

different. For insulation on the attic floor,

ventilation with attic window louvres may take

care of many cases so as to avoid condensation

of moisture on the under side of the roof, but

in some cases vapor barriers are needed in addition to ventilation. If the insulation is placed

close to the roof, it becomes much more diffi- cult to ventilate the space between, and re- course to effective vapor barriers becomes

especially necessary. An additional factor is that some modern roofs, such as the metal and

built-up types, are made of materials with very

high vapor resistance. For these it becomes

much harder to get a vapor barrier on the

warm side with vapor resistance several times

as great as that of the roof. In such cases attempts to provide both adequate ventilation

and vapor barriers would appear necessary.

Further discussions of the prol>lem of cond(>nsation in insulated walls will be found in a number of the publications referred to at the

end of the paper.

IV. CONCLUSIONS

The available data on the moisture perm('al)ility of various building materials and the more modern types of structures are too meager and discordant to pei-mit any more

than a very rough estimate of the conditions

under which condensation will take place in insulated walls. It is possible, however, in the

case of many types of wall to calculate for any

given condition of humidity and temperature

the ratio between the moisture permeabilities

of the interior and exterior portions of the wall

which is necessary to prevent condensation.

For exterior and interior conditions of temperature and humidity which do not seem impossibly severe, it is necessary in a well-insulated

wall to have the vapor resistance of the warm

side of the wall several times as great as that on the cold side in order to prevent the possibility of condensation. The extent to which

air leakage into a wall from the outside is significantly advantageous is unknown, but

any such leakage will decrease the tendency for condensation.

V. REFERENCES

[1] S. T. C. Stillwell, The movement of moisture with

reference to timber seasoning. Forest Products

Research, Dept. Sci. Ind. Research, Great

Britain Tech. Papers No. 1 (1926).

[2] J. F. Martley, Moisture movement through wood;

the steady state. Forest Products Research,

Dept. Sci. Ind. Research, Great Britain Tech. Papers No. 2 (1926).

[3] R. I. Wray and A. R. Van Vorst, Permeability of paint films to moisture. Ind. Eng. Chem. 25,

842 (August 1933).

[4] R. L. Taylor, D. B. Herrmann, and A. R. Kemp,

Diffusion of water through insulating materials. Ind. Eng. Chem. 28, 1255 (November 1936).

[5] F. B. Rowley, A. B. Algren, and C. E. Lund, Condensation within walls. Heating, Piping, .A.ir Conditioning 10, 49 (January 1938).

[6] J. D. Babbitt, The permeability of building materials

to water vapor. Heating, Piping, Air Conditioning 10, 751 (November 1938).

[7] L. G. Miller, Calculating vapor and heat transfer through umlls. Heating and Ventilating 35, No.

11, 56 (November 1938).

[13]
[8] J. D. Babbitt, The diffusion of water vapour throxigh various building materials. Canadian J. Research 17, 15 (February 1939).

[9] L. V. Teesdale, Resistance of materials to vapor trans- mission. Heating, Piping, Air Conditioning 11, 213 (April 1939).

[10] F. B. Rowley, A. B. Algren, and C. E. Lund, Condensation of moisture and its relation to building

construction and operation. Heating, Piping, Air Conditioning 11, 41 (January 1939).

[11] L. V. Teesdale, How to overcome condensation in

building walls and attics. Heating and Ventilating 36, No. 4, 36 (April 1939).

[12] L. V. Teesdale, Condensation in walls and attics. R1157. U. S. Department of Agr., Forest

Service, Forest Products Laboratory, Madison,

Wis.

[13] L. V. Teesdale, Condensation problems in farm

buildings. R1186. U. S. Department of Agr., Forest Service, Forest Products Laboratory,

Madison, Wis.

[14] L. V. Teesdale, Condensation problems in modern

buildings. R1196. U. S. Department of Agr., Forest Service, Forest Products Laboratory,

Madison, Wis.

[15J J. D. Babbitt, The permeability of building papers

to water vapour. Canadian J. Research 18, 90 (May 1940).

[16] J. D. Babbitt, Observations on the permeability of hygroscopic materials to water vapour. I Observations at relative humidities less than 75%.

Canadian J. Research 18, 105 (June 1940).

Washington, August 9, 1940.

[14]

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Floors, Sponsored by Palisade Homes 10(4 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(4 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 Walls 10^ BMS42 Structural Properties of Wood-Frame Wall and Partition Constructions With "Celotex"

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

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 100 BMS48 Structural Properties of "Precision-Built" Frame Wall and Partition Constructions

Sponsored by the Homasote Co 100 BMS49 Metallic Roofing for Low-Cost House Construction 100 BMS50 Stability of Fiber Building Boards as Determined by Accelerated Aging 10(4 BMS51 Structural Properties of "Tilecrete Type A" Floor Construction Sponsored by the Tile- crete Co 100 BMS52 Effect of Ceiling Insulation Upon Summer Comfort 100 BMS53 Structural Properties of a Masonry WaU Construction of "Munlock Dry Wall Brick"

Sponsored by the Munlock Engineering Co 100 BMS54 Effect of Soot on the Rating of an Oil-Fired Heating Boiler 100 BMS55 Effects of Wetting and Drying on the Permeability of Masonry Walls 100 BMS56 A Survey of Humidities in Residences 100 BMS57 Roofing in the United States; Results of a Questionnaire 100 BMS58 Strength of Soft-Soldered Joints in Copper Tubing 100 BMS59 Properties of Adhesives for Floor Coverings 100 BMS60 Strength, Absorption, and Resistance to Laboratory Freezing and Thawing of Building

Bricks Produced in the United States 150 BMS61 Structural Properties of Two Nonreinforced Monolithic Concrete Wall Constructions 100 BMS62 Structural Properties of a Precast Joist Concrete Floor Construction Sponsored by the Portland Cement Association 100 BMS63 Moisture Condensation in Building Walls lO0t