laktjii iruiji (lit Libiary.

iiiMiiiilii^MI
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 10^ BMS3 Suitability of Fiber Insulating Lath as a Plaster Base 15^ BMS4 Accelerated Aging of Fiber Building Boards 10^ BMSo Structural Properties of Six Masonry 'Wail Constructions . 15^ BMS6 Survev of Roofing Materials in' the Southeastern States Ibi

BMS7 Water Permeability of Masonry Walls* * 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 lOi

BMSIO Structural Properties of One of the "Keystone Beam Steel Floor" Constructions Sponsored by the H. H. Robertson Co 10

i

BMSll Structural Properties of the Curren Fabrihome Corporation's "Fabrihome " C'oustruc- tions for Walls and Partitions lOp

BMSI2 Structural Properties of "Steelox" Constructions for Walls, Partitions, Floors, and Roofs

Sponsored by Steel Buildings, Inc 15<i 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 106 BMS16 Structural Properties of a "Tilecrete" Floor Construction Sponsored by Tilecrete Floors, Inc 106 BMS17 Sound Insulation of Wall and Floor Constructions 206 Supplement to BMS17, Sound Insulation of Wall and Floor Constructions. _ 56 BMS18 Structural Properties of "Pre-fab" Constructions for Walls, Partitions, and Floors Sponsored by the Harnischfeger Corporation 106 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 106 BMS21 Structural Properties of a Concrete-Block Cavity-Wall Construction Sponsored by the National Concrete Masonry Association . 106 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 - lOfi BMS24 Structural Properties of a Reinforced-Brick Wall Construction and a Brick-Tile CavityWall Construction Sponsored by the Structural Clay Products Institute 15^ BMS25 Structural Properties of Conventional Wood-Frame Constructions for Walls, Partitions,

Floors, and Roofs. 156 BMS26 Structural Properties of "Nelson Pre-Cast Concrete Foundation" Wall Construction

Sponsored by the Nelson Cement Stone Co., Inc 106 BMS27 Structural Properties of "Bender Steel Home" Wall Construction Sponsored by the Bender Body Co 106 BMS28 Backflow Prevention in Over-Rim Water Supplies 106 BMS29 Survey of Roofing Materials in the Northeastern States 106 BMS30 Structural Properties of a Wood-Frame Wall Construction Sponsored by the Douglas

Fir Plywood Association 106 BMS31 Structural Properties of "Insulite" Wall and "Insulite" Partition Constructions Sponsored by The Insulite Co 15ji

* Out of print. [List continued on cover page ni]
UNITED STATES DEPARTMENT OF COMMERCE . Henry A. Wallace, Secretary

NATIONAL BUREAU OF STANDARDS . E. U. Condon, Director

BUILDING MATERIALS

and STRUCTURES

REPORT BMS io6

Laboratory Observations of Condensation

in Wall Specimens

by

RICHARD S. DILL

and

HERMAN V. COTTONY

ISSUED AUGUST 2, 1946

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

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Foreword

The importance of the relation between the permeability of vapor

barriers and the heat-transfer characteristics of building Avails has

been emphasized by the increased use of insulating materials in

dwelling houses and other buildings. This increase is traceable to the

growing realization on the part of the public of the benefits to be

attained by using these materials to improve comfort conditions in

summer and to conserve heat in winter.

The installation of insulating materials in a building, how^ever,

is accompanied by a hazard in the form of possible damage to the

structure by moisture resulting from condensation of water vapor

within a wall, ceiling, or other building element. Condensation may

destroy the efficiency of insulation and shorten its life; it may also cause rot in timbers.

In the investigation covered by this report the effects of con- densation on several specimen walls were observed in the laboratory

with the objective of finding ways of preventing moisture damage.

Eight different arrangements of insulation and vapor seal were

tested, and the observations and conclusions are reported in this paper.

E. U. Condon, Director.

[II]
Laboratory Observation of Condensation in Wall Specimens

by RICHARD s, DILL and Herman v. cottony

CONTENTS

Foreword

I. Introduction

II. Apparatus

III. Test speeinien

IV. Test methods and conditions.

Page

II11

Page

IV. Test methods and conditions—Cont.

1. Methods

2. Conditions

V. Procedure and observatidns

VI. Conclusions

VII. References

ABSTRACT

Water-vapor migration' and condensation in walls were investigated by means of a laboratory apparatus

whereby a specimen wall was exposed to cold air on one side and to warm, humidified air on the other

side. The wall was insulated and protected against

water-vapor condensation in various ways for purposes

of observation. The test conditions were a little more

severe than those ordinarily expected anywhere in the

continental United States. The observed relation between vapor pressure and

condensatiiin and the observed effects of vapor barriers are described and discussed. In this investigation, it was found that condensation occurred within a heavily insulated wall, but that

conditions conducive to condensation within the wall

structure could be avoided by the use of an effective vapor barrier or by ventilating the interior of the wall with cold air.

I. INTRODUCTION

Tl\e theoretical aspects of condensation in

huiklino- walls have been treated previously in

Building Materials and Structures Report

BMkS63, Moisture Condensation in Building

^^^llls, and a survey of the humidities orditiarily maintained in houses in winter is covered

in Building Materials and Structures Report

BMS56, A Survey of Humidities in Residences.

In addition, BMS63 contains a compilation of

available data on the vapor permeability of

various materials that are or may be commonly

used in building construction. Upon examination, the data may show inconsistencies that

would make conclusions based on them misleading. During the work covered by this paper

the conditions within a wall structure, with

special reference to dampness (water or ice

deposits) and vapor pressure were observed by means of a laboratory apparatus constructed

for the purpose. The wall was insulated in

various ways and provided with several differ- ent means of preventing condensation of water

vapor.

II. APPARATUS

Details of the apparatus constructed for this

work are illustrated in figure 1. The apparatus

consists essentially of a cold box cooled by a refrigerating coil, and a hot box heated elec- trically and enclosing a trough, or vat, con- taining a salt solution by means of which the

humidity in the hot box is controlled. A wall

specimen, installed for test in the position

sliown, is exposed to warm, humidified air on

one side and to relatively cold air on the other.

A sheet-copper diaphragm in the cold box

located between the specimen wall and the cool- ing coil, serves to arrest and collect, for observation and weighing, the water that has passed

through the wall in vapor form. The boxes are insulated wnth cork to minimize heat exchanges

except through the specimen. The hot box is lined with sheet copper inside the cork to prevent vapor exchanges through its walls. Temperatures in both boxes were automatically controlled. In the cold box, the supply

of refrigerant (carbon dioxide) to the cooling

coil was manually set slightly higher than nec- essary to maintain the desired condition. Electric heating coils with thermostatic switches

[1]
Sheet cop,->eri lining

Siding —

Sheathing

Paper

SheafhingInsulation - Plaster —

and lath

Air space

of the Hot

Box. Simulated

indoor

conditions

Hot Box

'Mill f 1-1 ?tF=

COe Refrigerating Coil

' Pefalning Compartment

.Outdoor conditions

Cold Box

Copper Wall -Rubber sealing gaskets

Figure 1.Lonr/itudinal section of test apparatus.

were used to offset the slightly excessive cool- ing effect and to afford sufficiently precise control. The heaters in the hot box were controlled

by mercury-in-glass thermoregulators operating throiigh relays.

Small electric fans were used in both boxes

to set the air gently in motion and thus promote

uniformity of temperature and luunidity

tliroughout the interior of each box.

A. saturated solution of calcium chloride

hexaliydrate was used in the humidifying pan

to maintain the selected humidity in the box.

The humidity in the hot box was measured

by means of a dew-point hygrometer, a modification of a device described in Scientific Paper

S500[l].^ A metal mirror in the device was

cooled by a stream of cold air until dew formed

on the surface; the temperature of the mirror

when this occurred was observed by means of a thermocouple. This temperature, being the dew

point of the air to which the mirror is exposed,

is an indication of the humidity in the box.

The permeabilities of materials used as vapor

barriers were determined by the official method

of the Technical Association of the Pulp and

Paper Industry. This method involves a test at 23° C with one face of the material exposed

to dry air and the other to air at 50-percent

relative humidity. The results are usually ex- pressed in grams (of water vapoi- transferred)

per square meter dui'ing 24 hours.

III. TEST SPECIMEN

For the purpose of this work a si^ecimen or

panel, simulating ordinary frame-wall construction, was tested with eight dilTerent

arrangements of insulation and vapor seal as indicated in table 1.

Table 1.

Compovents of test specimens

Tests

Insulation

Material

Shredded

bark. do Aluminum

foil. Rock wool - _

Wood-fiber

blanket. Rock wool .

.

do

.doThickness

Ventilation

sys in-, 3% in-.

1 sheet m inTwo 1- in. 3H in-. 3% in-.

SVs in-.

None--

do- do Holes top and bot- tom. None

-do- -do-

-doVapor barrier

None.

60-lb asphalt-saturated kraft. None except alumi- num foil. None.

None except coverini!' on blankets. None. Two-plv untreated

kraft. Two-ply asphalt-sat- urated kraft.

The test panel, the construction of which is shown in figure 2, was made of conventional

materials. The frame was 2- by 4-in. Douglas

fir, the inside face was plaster on metal lath,

and the outside face was shiplap siding on

sheathing, with sheathing paper (60-lb satuI'ated kraft) between. Tlie slieathing was No. 2 white pine and the siding was Douglas fii'. None of the parts was painted. The panel was

fastened together with wood screws, instead

of nails, to facilitate assembling and dis- mantling.

Three wooden plugs, each 2 in. in diameter, were fitted into holes bored for the purpose in the sheathing, as shown in figure 2. These plugs

served to indicate changes in moisture content

of the sheathing, as they formed a part of the

* Figures in brackets indicate the literature references at end of this paper. [2]
FiGUBE 2.—Test panel constnietion.

aheulhing that could be removed and weighed

"when desired.

IV. TEST METHODS AND CONDITIONS

1. IVIethods

Prior to each test, the perimeter of the panel was coated with paraffin to prevent gain or loss of moisture through the edges.

Copper-constantan thermocouples in con- junction with a suitable potentiometer were

used for all temperature measuiements.

There were five thermocouples on each inside

and outside surface of the sheathing, siding,

and plaster. On each of these surfaces, one of

the five thermocouples was located in the middle

of the panel. Two of the others were on the

horizontal and two were on the vertical center

line ; each was 5 in. from the edge of the panel.

Five thermocouples were similarly placed in

the cold box in a plane about 2 in. from the

panel for measuring the air temperature. Four

thermocouples were used to measure the air

temperature of the hot box.

Electric hygrometers were used for observing

the humidity in the stud space. These devices are described in Research Paper E.P1102 [2],

and a sketch of one is shown in the present

paper as iigure o. The device is a glass tube

-Bifilar Windings

Figure 3.

Eleetrii- Injgrometer.

wound with two coils of wire, the turns of

which alternate. The turns do not touch, but are connected electrically only by a hygroscopic film applied after winding. The re- sistance of this, film changes with the humidity

of the air to which the device is exposed

and is used to indicate the humidity. During

use, the temperature of each hygrometer was

measured by means of a thermocouple attached

to it. In order to calibrate this kind of hygrometer, saturated salt solutions which establish

3]'
known relative humidities in enclosures above

them were used. Since the hygrometers were

not considered stable, they were calibrated

before and after each run. The results of some

typical calibration tests are shown in figure 4.

ur\, -O!

for

'ec fr/c-a/

= 5

- Cr :|

Aiygroi s

D-l

\

0 -.^ C-l V

Ql0

^S

-in

= u

o \

M—

-V- -V

-A—

K 'O

opo'oo, y

mil

\

20 30 40 50 60 70 SO

Relafive Humidify in Percerrt

l'"i(jUKE 4.

Calihnilivii fvuTcs of (icclric lnj(/rijiii(ii:rs.

Improved and more stable instruments have

since been perfected and are described in National Bureau of Standards Research Paper

RP12(i5 [3].

The instrument shown in figure 3 consists of

two hygrometers in the same frame. An

alternating-current ohmmeter was used to measure the resistance of the hygroscopic film. During the tests with the fill insulation, three

of the electric dual-coil hygrometers described

above were placed in the stud space of the

specimen wall. They were located approximately on the vertical center line of the specimen at points 1 foot from the top, 1 foot from

the bottom, and halfway between. The hygrometers were enclosed in wire cages, which pre- vented contact between their elements and the

insulation.

During the tests with blanket insulation,

the three instruments were arranged vertically

as described above, but they were in the air

si^ace on the cold side of the insulation.

During the tests with reflective insulation,

only two insti'uments were used. One was

located on each side of the insulating sheet

approximately in the middle of the air space.

2. Conditions

It was desired to exjDose the test panel to severe conditions during these tests. The conditions were 70° F and 30-percent relative

humidity on the warm side and —5° F on the

cold side. No attempt was made to control the

humidity on the cold side. Presumably it was

governed by the temperature of the coppei'

wall located near the test panel on the cold side,

which would control the dew point in the sur- rounding air. Figure 5, a chart similar to one based on a survey described in BMS56, shows that less than 15 percent of the humidified houses sur0) o

L

CI01

o

0)o

io

Ct InI

Unhumidifled homes

Humidified homes

EL i

Indoor relaiive humidiiLj — percent

FiGUKE 5.

Humidity in residences indicated hy survey. Data obtained between 0 a.m. and .5 p.m. when outside temperature was below 20° F. [4]
veyed luid interior relative humidities above 30

percent when the outdoor temperature was less than 20° F. This is construed to mean that,

whereas the test conditions probably occur

occasionally in houses in the United States, they

are more severe than average, even for the cold

regions of the country.

V. PEOCEDURE AND OBSERVATIONS

During tests A and B, the stud spaces of the

pimel were filled with 3%-in. shredded redwood bark insulating material. During tests A,

no vapor barrier was used, while during tests B a barrier of 60-lb asphalt-saturated kraft

paper was placed directly behind the plaster.

Tliere was no ventilation in either case. The

l)anel arrangement, including the position of

the vapor barrier used during tests B, and the

"\'ai)or pressure and temperature gradients for

tests A and B are shown in figure 6.

Sheafhing

Sheafbing paper

Siding

0.6O Deal point vapor pressure curve

Plaster on

metal latti

Moisture barriers (Panel S'only)

Panel "B- 0.2IS Observed vapor pressures

Panel "A

FiGUKic 6.Panel arrangement during tests A and B.

The vapor pressure and temperature gradients

prevailing throughout both tests are also plotted in fig-ure 6.

The vapor barrier for tests B consisted of a

single sheet of asphalt-saturated paper, without

joints, located in each stud space. The barrier was sealed by turning the edges fiat against the

studs or frame at all points and joining them

to the wood with Scotch tape around the edgps.

It was thought that this kind of joint would be

superior to any that could be conveniently

made by means of nails and wood, but experience during this work showed the need for

developing a more satisfactory method of jointing.

From the data summary sheet, table 2, it will

be noted that condensation occurred on the

sheathing in both tests A and B, and that more

occurred in the sheathing during tests B than

during tests A, even though a moisture barrier was used only during tests B. This condensation appeared as frost. It was scraped from the

sheathing and weighed, and a small amount

that melted while the apparatus was being

opened w^as mopped up with absorbent cotton and weighed. The sum of the weights of this

water and of the frost is reported on the data

sheet as "water condensed on sheathing."

The frost gathered from the sheathing after

tests B was obtained from areas near the cor- ners of the panels. It is presumable that the

vapor seal was weakest at its corners, and tlie indication is that leaks existed there, I'esulting

in a heavy deposition of water on the sheathing

nearby. It is likely also that the wood of the

sheathing, near the corners, became saturated

early during the test, so that vapor which con- densed later was deposited as frost on the

surface of the wood. This probably explains

wliy more frost was gathered after tests B

than after tests A, as during tests A the sheathing never became saturated. Such frost as did

form during tests A was distributed evenly over

the surface of the sheathing.

The effects of the vapor barrier, as shown by

tests B, were lower vapor pressure in the stud

space, less water evaporated in the hot box, and

less water absorbed by the wood, as indicated

by the weights of the plugs. These and other

data are shown numerically in the data sum- mary sheet, table 2.
Table 2.

Data summary sheet—migration of water vapor tlirouyh wall

Data in columns numbered 1 and 2 represent two tests under similar conditions.

Tests A Tests B Tests C Tests D Tests E Tests F Tests Q Tests H

Test conditions and results

1 2 1 2 1 2 1 2 1 2 \ 2 1 2 1 2

Conditions: Hot-box temperature- --deg. F__ 69.4 69.3 69.2 69.4 69.0 68.9 69.0 69.3 69.4 69.2 69.4 69.2 69. 3 69. 2 69. 1 Hot-box relative humidity 29. 4 29.9 30.3 29. 7 29.3 29.4 29.3 29. 0 29.9 28. 0 28. 3 29. 4 30.0 30. 8 34. 2 Hot-box water vapor pressure

in Hg-_ 0. 212 0. 215 0. 217 0. 214 0.208 0. 208 0. 208 0. 208 0. 216 0. 201 0. 204 0. 211 0. 215 0. 221 0. 244 Permeability of vapor barrier

(if used) (g/m2)/24 hr" . . . 3. 82 3. 82 8.87 8. 87 1. 16 1. 16 . 78 . 78 Temperature of sheathingdegF.. 11. 5 11.3 11.5 12. 0 18. 3 7.3 6. 5 8. 5 8. 7 10.8 10.2 7. 5 7. 4 6. 5 10. 6 Dew-point vapor pressure

in Hg-- 0. 065 0. 064 0. 065 0. 067 0. 094 0. 052 0. 051 0. 055 0. 055 0. 062 0. 060 0. 052 0. 052 0. 051 0. 061

f . 030 ' .039 1 Vapor pressure in stud space / . 146 . 037 .046 [Below Below f Below Below Below ] in Hg_- .064 .048 .028 .043 I .062 1 Below Below 0.019 > .062 . 061<

0. 020 0. 018 0. 016 |0. Oil)

l*'0. 012 *0. 012

j

0.018

Cold-air terapi'iaturc... deK K.. -B. 8 -7. 1 -5.

1

-5.

1

-7. 1 -6.8 -5.9 —6. 5 -0. 7 -6. 7 -7.3 -7. 6 -7. 5 -7.3 —5. .''i Estimated water vapor pressure m cold air in Hg. 0. 008 0. 006 0. 008 0.008 0. 005 0. 005 0. 007 0. OOR 0. 007 0.007 0. 007 0. 005 0. 005 0. 005 Length of tost hr^. 99. 7 99.0 99.7 99.5 118. 1 99. 7 97.0 99.9 97. 7 99.

0

97.7 99.2 99.

1

99. 2 98.8 98. 5 Water evaporated in hot box

Grains-. 2, 020 1. 840 170 754 2, 200 1, 900 1, 740 2, 160 1. 190 1. 150 2, 110 1. 700 1, 140 1,090 1,190 538 Water condensed on sheathing Grains . 29 29 93 159 . None None Trace None None None 34 155 131 225 31 12 Water oondenseif on sheathing paper - Grains. . None None None None .-do . ..do - None ..do .. ..do -- .do .- None None None None None None

Water condensed on siding Grains . 1.5 Trace Trace 4.6 ..do - ..do ..do - ..do -- -.do - ..do .. ..do -do . ..do -- ..do -. ..do Do.

Water condensed on copper wall Grains.. 216 262 217 312 177 244 1,790 1, 630 55 117 80 283 131 182 174 270 Gain of moisture bv insulation % by wt.. 1.0 0.4 0.1 0.0 0.

1

0.1 0.0 0.1 0.0 0.0 Gain of moisture by wood % by wt._ 0. 76 . 76 .43 .48 0. 48 0. 57 .46 .46 0.0 0.03 .98 .97 0.28 0.20 .08 .31

Values determined by the Paper Section of the National Bureau of Standards by the official method of The Technical Association of the Pulp and Paper Industry.

^ Upper value is for top of panel, center is for the middle, and lower is for the bottom of panel.

During tests C, aluminum-foil insulation was

used. The material was paper, faced on both

.sides ATith aluminum foil. It was secured in the

stud space midway betAveen the sheathing and

the plaster. The joint, consisting of the turned

edge secured to the wood by Scotch tape, was

used in this case also. There was no vapor

barrier in the panel other than the insulating

sheet itself and no ventilation.

The panel arrangement and the observed

vapor pressure and temperature gradients for

tests C are shown in figure 7. The vapor pres- sure indicated that condensation should not

occur, and none was observed when the wall was

dismantled. HoAvever, some moisture did pass

through the wall and condense on the copper

sheet on the cold side, as shoAvn in table

It is probable that the seal between the insulating sheet and the wood framing was imperfect.

The effect of ventilating the insulated space was studied in tests D. The stud space Avas

filled with rock wool and no vapor barrier Avas used. The arrangement of the test panel and

the vapor pressure and temperature gradients

are shown in figure 8. Holes were bored through

the outside face of the panel to provide ventilation. A 1-in. hole Avas bored through sheathing and siding opposite each of the tAvo outer stud spaces at top and bottom, about a foot

from the top and the same distance from the

bottom. To ventilate the center stud si)ace, the

upper and loAver moisture-gain measuring plugs

Avere removed during this test. A trace of moisture Avas found on the sheathing after the first of the tAvo tests under this

condition Avas made; after the second test, no

moisure was found in the panel. The vaporpressure curves plotted in figure 8 indicate that

the conditions necessary for condensation Avere avoided by a small margin. Furthermore, the

Avater-vapor pressure in the stud space Avas very

loAv near the A^entilating openings and higher

near the middle of the panel.

Compai'isons of the temperature differences

through the plaster during tests D with those

that occurred during tests F indicate that the

ventilation Avas responsible for additional heat

loss through the panel of approximately 10

[6]
Computed dew

po'ini vapor pressures

aaisObservBd vapor- pressures

Double faced

Aluminum foil insulaiton

-0.70

0.60

r0.50

-OAO

aso

~O.IO

FiGTJKE 7.

Panel arrangement during tests ('.

percent. The temperature differences for tests D, F-1, and F-2 were 1.5, 1.4, and 1.3 degrees F,

respectively.

During tests E, the stud places were insulated

with shredded-wood-fiber blankets composed of

wood fibers enclosed in asphalt-impregnated

crepe-paper envelopes. Each blanket was 15 in. wide and approximately 1 in. thick and was

cut from a roll to a length equal to the height

of the panel. They were placed in double thick- ness in the stud space of the panel with air

spaces on the plaster and on the sheathing-side

approximately equal. There was no vapor barrier other than the envelope of the blankets and

no ventilation.

The arrangement of the wall and the vapor

pressure and temperature gradients for tests E

are shown in figure 9. No condensation was

observed after either of the two tests. The rela- tively small quantity of water evaporated in the hot box, gained by the plugs in the sheathing and condensed on the copper diaphragm on

the cold side, indicates that the blankets were

effective in retarding the passage of water

vapor through the wall. The fact is not established, however, that the wood fiber did not

absorb some moisture during the test. It probably would be necessary to conduct a test of

considerably more than 100 hours' duration

to determine what happened in this respect.

It will be noted fj'om the data summary sheet,

table 2, tliut the vapor permeability of the paper

forming the vapor barrier was comparatively

high.

For tests, F, G, and H, the stud spaces were

filled with rock-wool insulating material. No

vapor barrier was used during tests F. During

tests G, 2-ply untreated kraft paper with a layer

of asphalt between the plies was used as a moisture barrier. In tests H, 2-ply asphaltsaturated kraft paper with a layer of asphalt

between the plies was used as a moisture barrier.

There was no ventilation.

The arrangement of the panel and the observed vapor pressure and temjierature gradients for tests F, G, and H are shown on

Compufed deai poinf vapor pressures

Range ofobsen

vapor pressure.

O.IO

Figure 8.Panel arrangement during tests D.
Compufed deai- poinf vapor pressures

O.ZI2-0—

Observed and—

esiimafed vapor

pressures

barriefs ofthe

ihsulaiion baifs

OJ32(?)-:--T-y '

I ' ^<005SX

-0.70

-0.60

-0.50

-0.40

-0.30

-o.eo

-O.IO

FiGUKE 9.

Panel arrangement during tests E.

figure 10. The curves indicate that condensation

should occur only under the conditions of tests F, when no barrier was used. Nevertheless,

condensation also occurred during tests G and

H; but this can again be attributed to defects

in the seal around the edges of the vapor barrier

where it joined the wood, because the frost

formed only in the corner. The frost that

collected after tests F was evenly distributed over the inner surface of the sheathing.

The data indicate that frost should form

under the condition of tests F. The observed

vapor pressure in the stud space averaged 0.062

and 0.061 in. of mercury during the two tests, and the dew-point vapor pressure corresponding to the observed temperatures are also 0.062

and 0.061 in. of mercury. The figures check- more closely than would be expected from the

estimated precision of the apparatus and test method.

The chief effects of the vapor barriers used in

tests G and H were the decrease in amount of

water necessarily evaporated in the hot box and

the lower vapor pressure in the stud space. The difference in the permeabilities of the

treated and untreated sisal kraft papers used

in tests G and H was not sufficient to make a clearly discernible difference in the observed

vapor pressures in the stud spaces.

VI. CONCLUSIONS

The results of the experiments performed

with this apparatus indicate that its use is a

practicable means of testing wall constructions

for condensation under selected conditions of

temperature and humidity on the warm and

cold sides of the walls. The means for sealing

the joint between a paper or metal-foil vapor

barrier and framing should be better than the

Scotch drafting tape used in this experiment.

The failure of this joint during the tests suggests the possibility that vapor barriers in

actual use permit the passage of a considerable

amount of vapor around their edges.

-Moisfure barrier

(Panels G & H)

63.4

0.70

Compufed deuj

point vapor pressures

Observed

Vapor pressures

-QSO

- -0.40

~0.30

-O.SO

tOJO

FiGTXEE 10.

Panel arrangement during tests P. a, and H. [8]
The results of tests A indicate that condensation can be expected in a frame wall insulated

with ^% in. of fibrous material if the air on the

^Yarm side is maintained at 70° F and 30-percent relative humidity and the air on the other

side is maintained at approximately 0° F. The

results of tests B show that conditions con- ducive to condensation in a wall insulated as

in tests A can be avoided by means of a vapor

barrier with a permeability of 3.8 grams or less per square meter per 2-i hours when exposed at 23° C to dry air on one side and 50-percent

relative humidity on the other. Most commercial sheathing papers of better grade have a permeability lower than the above value, and

therefore can be used effectively as vapor barriers. Asphalt-impregnated paper used as en- velopes for insulating blankets was effective

in preventing condensation, as shown in tests E. During these tests, 1-inch blankets were

installed in double thickness in the middle of

the stud space. The blankets consisted of

shredded wood fiber enclosed in asphalted

paper. A single sheet of metal-foil insulation

in the middle of the stud spaces will prevent

condensation in the wall under conditions of

the above severity, provided the seal at the

edges, where the foil is fastened to the studs

and frame, is vaporproof. The tests indicated

the importance of a good edge seal for paper

vapor barriers both for test specimens and

in actual use.

Washington, August 14, TJ45.

VII. REFEKENCES

[1] R. .T. Kennedy, A method of deterniinint,' the dew

points of fuel-air mixtures, BS Sci. Ptip. 20, 47

(1925) 8500.

[2] F. W. Dunmore, An electric liygrometer and its application to radio meteorography, J. Research

NliS 20, 723 (1938) RP1102.

[3] F. W. Dunmore, An improved electric hygrometer,

J. Research NBS 23, 715 (1939) RP1265.

ADDITIONAL REFERENCES

H. J. Barre, The relation of wall construction to moisture accumulation in fill-type insulation, Research Bulletin 271. Iowa State College of Agr. and

Mech. Arts.

L. V. Teesdale, Condensation problems in modern buildings, R 1196, U. S. Department of Agr., Forest Service, Forest Products Laboratory, Madison, Wis.

L. V. Teesdale, Condensation problems in farm buildings, R 1186. U. S. Department of Agr., Forest Service, Forest Products Laboratory, Madison, Wis.

F. T. Carson, Permeability of membranes to water vapor

with special reference to packaging materials, NBS

Misc. Pub. M127 (19.37). F. L. Brown, Some causes of blistering and peeling of paint on house siding, R 6. U. S. Department of Agr., Forest Service, Forest Products Laboratory, Madison,

Wis.

F. B. Rowley, A. B. Algren, and C. B. Lund, Condensation within walls, Heating, Piping, Air Conditioning 10, 49 (1938). M. Heinig, L. V. Teesdale, and C. E. Curran, Comparative resistance to vapor transmission of commercial building papers. Technical Association

Papers, Series XXII No. 1 (1939).

U. S. GOVERNMENT PRINTING 0 F F I CE—I 946—696496

[9]

BUILDING MATERIALS AND STRUCTURES REPORTS

[Continued from cover page ii] BMS32 Structural Properties of Two Bric-Concrete-Block Wall Constructions and a Concrete- Block Wall Construction Sponsored by the National Concrete Masonry Association. 15 ^ BMS33 Plastic Calking Materials 15>i 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 — _ 10^5 BMS36 Structaral 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 Walls, 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;4 BMS39 Structural Properties of a Wall Construction of "Pfeifer Units" Sponsored by the Wisconsin Units Co - lOjS BMS40 Structural Properties of a Wall Construction of "Knap Concrete Wall Units" Sponsored

by Knap America, Inc lOi

BMS41 Effect of Heating and Cooling on the Permeability of Masonry Walls* * BMS42 Structural Properties of Wood-Frame Wall and Partition Constructions with "Celotex"

Insulating Boards Sponsored by The Celotex Corporation 15 i BMS43 Performance Test of Floor Coverings for Use in Low-Cost Housing: Part 2 10^ BMS44 Surface Treatment of Steel Prior to Painting 10(4 BMS45 Air Infiltration Through Windows 15^ 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 10j5 BMS48 Structural Properties of "Precision-Built" Frame Wall and Partition Constructions

Sponsored by the Homasote Co 15«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

Tilecrete Cfo 10?; BMS52 Effect of Ceiling Insulation Upon Summer Comfort 10^ BMS53 Structural Properties of a Masonry Wall Construction of "Munlock Dry Wall Brick"

Sponsored by the Munlock Engineering Co 10^ BMS54 Effect of Soot on the Rating of an Oil-Fired Heating Boiler lOp

BMS55 Effects of Wetting and Drying on the Permeability of Masonry Walls 10^ BMS56 A Survey of Humidities in Residences lOi

BMS57 Roofing in the United States—Results of a Questionnaire * 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 156 BMS61 Structural Properties of Two Nonreinforced Monolithic Concrete Wall Constructions lOj^ BMS62 Structural Properties of a Precast Joist Concrete Floor Construction Sponsored by the Portland Cement Association 10 <^ BMS63 Moisture Condensation in Building Walls 106 BMS64 Solar Heating of Various Surfaces 10?i 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, Ploor, and Roofs Sponsored by Herman A. Mugler 15^ BMS68 Performance Test for Floor Coverings for Use in Low-Cost Housing: Part 3 15(i BMS69 Stability of Fiber Sheathing Boards as Determined by Accelerated Aging 10?i BMS70 Asphalt-Prepared Roll Roofings and Shingles 15(4 BMS71 Fire Tests of Wood- and Metal-Framed Partitions 20(5 BMS72 Structural Properties of "Precision-Built, Jr." Prefabricated Wood-Frame Wall Construction Sponsored by the Homasote Co 10c 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 156 BMS76 Effect of Outdoor Exposure on the Water PermeabiUty of Masonry Walls 15^ BMS77 Properties and Performance of Fiber Tile Boards 10(f BMS78 Structural, Heat-Transfer, and Water-Permeability Properties of Five Earth-Wall Constructions 20 BMS79 Water-Distributing Systems for Buildings 156 BMS80 Performance Test of Floor Coverings for TTse in Low-Cost Housing: Pact 4--1 15(4 BMS81 Field Inspectors' Check List for Building Constructions (cloth cover, 5 x 7]^ inches) 20)4

* Out of print. [List continued on cover page iv]
BUILDING MATERIALS AND STRUCTURES REPORTS

[Continued from cover page iii] BMS82 Water Permeability of Walls Built of Masonry Units 20^5 BMS83 Strength of Sleeve Joints in Copper Tubing Made With Various Lead-Base Solders 10^ BMS84 Survey of RooiSng Materials in the South Central States 15^ BMS85 Dimensional Changes of Floor Coverings with Changes in Relative Humidity and Temperature 10?f BMS86 Structural, Heat-Transfer, and Water-Permeability Properties of "Speedbrik" \^'all Construction Sponsored by the General Shale Products Corporation 15(5 BMS87 A Method for Developing Specifications for Building Construction—Report of Subcommittee on Specifications of the Central Housing Committee on Research, Design,

and Construction lOp

BMS88 Recommended Building Code Requirements for New Dwelling Construction with Special Reference to War Housing * BMS89 Structural Properties of "Precision-Built, Jr." (Second Construction) Prefabricated WoodFrame Wall Construction Sponsored by the Homasote Co 15jS BMS90 Structural Properties of "PHC" Prefabricated Wood-Frame Constructions for Walls,

Floors, and Roofs Sponsored by the PHC Housing Corporation 15 (5 BMS91 A Glossary of Housing Terms ISfi BMS92 Fire-Resistance Classifications of Building Constructions 25^

BMS93 Accumulation of Moisture in Walls of Frame Construction During Winter Exposure 10^ BMS94 Water Permeability and Weathering Resistance of Stucco-Faced, Gunite-Faced, and

"Knap Concrete-Unit" Walls lOs* BMS95 Tests of Cement-Water Paints and Other Waterproofings for Unit-Masonry Walls 15^ BMS96 Properties of a Porous Concrete of Cement and Uniform-Sized Gravel lOfi BMS97 Experimental Dry-Wall Construction with Fiber Insulating Board lOi

BMS98 Physical Properties of Terrazzo Aggregates 15^ BMS99 Structural and Heat-Transfer Properties of "Multiple Box-Girder Plywood Panels" for Walls, Floors, and Roofs 15(5 BMSlOO Relative Slipperiness of Floor and Deck Surfaces 10^ BMSlOl Strength and Resistance to Corrosion of Ties for Cavity Walls lOjt BMSi02 Painting Steel 10(5 BMS103 Measurements of Heat Losses from Slab Floors 10 ff BMS104 Structural Properties of Prefabricated Plywood Lightweight Constructions for Walls,

Partitions, Floors, and Roofs Sponsored by the Douglas Fir Plywood Association 25^

BMS105 Paint Manual $1.00

BMS106 Laboratory Observations of Condensation in Wall Specimens lOp *Out of print.