Astm stp 1498 2011

Journal of Testing and Evaluation
Selected Technical Papers
STP 1498

Condensation
in Exterior
Building Wall
Systems
JTE Guest Editors:
Bruce Kaskel
Robert J. Kudder


Journal of Testing and Evaluation
Selected Technical Papers STP1498
Condensation in Exterior Building
Wall Systems

JTE Guest Editors:
Bruce S. Kaskel
Robert J. Kudder

ASTM International
100 Barr Harbor Drive
PO Box C700
West Conshohocken, PA 19428-2959

Printed in the U.S.A.

ASTM Stock #: STP1498

Library of Congress Cataloging-in-Publication Data
Condensation in exterior building wall systems / JAI guest editors, Bruce S. Kaskel,
Robert J. Kudder.
p. cm. -- (Journal of testing and evaluation selected technical papers; STP1498)
Includes bibliographical reference and index.
ISBN: 978-0-8031-4471-2 (alk. paper)
1. Dampness in buildings. 2. Exterior walls--Protection. 3. Waterproofing. I. Kaskel,
Bruce S. II. Kudder, Robert J., 1945TH9031.C663 2001
2011006935
693.8’93--dc22
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Printed in Baltimore, MD
May, 2011


Foreword
THIS COMPILATION OF THE JOURNAL of TESTING and EVALUATION
(JTE), STP1498, on Condensation in Exterior Building Wall Systems
contains only the papers published in JTE that were presented at a
symposium in San Antonio, TX, October 10–11, 2010 and sponsored by
ASTM Committee E06 on Performance of Buildings.
The Symposium Co-Chairmen and JTE Guest Editors are Bruce S.
Kaskel, Wiss, Janney, Elstner, Associates, Inc., Chicago, IL and Robert J.
Kudder, Raths, Raths & Johnson, Inc., Willowbrook, IL.

Contents
Overview

........................................................................

Insulation Draws Water
W. B. Rose

...........................................................

vii
1

Testing/Analysis
Laboratory Tests of Window-Wall Interface Details to Evaluate the Risk of Condensation
on Windows
W. Maref, N. Van De Bossche, M. Armstrong, M. A. Lacasse,
H. Elmahdy, and R. Glazer
31

...............................................
.............................................
Moisture Damage in Vented Air Space of Exterior Walls of Wooden Houses
T. Umeno and S. Hokoi. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Drying Characteristics of Spray-Applied Cellulose Fiber Insulation
M. Pazera and M. Salonvaara

Moisture Measurements and Condensation Potential in Wood Frame Walls in a
Hot-Humid Climate
T. A. Weston and L. C. Minnich

...........................................

59
80

94

A Review of ASHRAE Standard 160—Criteria for Moisture Control Design Analysis in
Buildings
A. TenWolde

119

Moisture Response of Sheathing Board in Conventional and Rain-Screen Wall Systems
with Shiplap Cladding
F. Tariku and H. Ge

131

Investigation of the Condensation Potential Between Wood Windows and Sill Pans in a
Warm, Humid Climate
G. P. Stamatiades, III

148

..........................................................
.....................................................
...................................................
Case Studies

Interior Metal Components and the Thermal Performance of Window Frames
S. K. Flock and G. D. Hall

169

Controlling Condensation Through the Use of Active and Passive Glazing Systems
A. A. Dunlap, P. G. Johnson, and C. A. Songer

187

................................................
................................
Case Study of Mechanical Control of Condensation in Exterior Walls
C. M. Morgan, L. M. McGowan, and L. D. Flick. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

226

Considerations for Controlling Condensation in High-Humidity Buildings: Lessons
Learned
S. M. O’Brien and A. K. Patel

247

Fenestration Condensation Resistance: Computer Simulation and In Situ
Performance
E. Ordner

269

Improving the Condensation Resistance of Fenestration by Considering Total Building
Enclosure and Mechanical System Interaction
P. E. Nelson and P. E. Totten

286

.............................................

............................................................
.............................................


Condensation Problems in Precast Concrete Cladding Systems in Cold Climates
T. A. Gorrell

..........................................................
Author Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Subject Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

299
315
317


Overview
This STP represents the peer-reviewed papers first presented at the October
10–11, 2010 symposium on Condensation in Exterior Wall Systems in San
Antonio, Texas, sponsored by ASTM E06 Building Performance, Subcommittee E06.55 Exterior Wall Systems. The symposium and this STP represent the continued efforts of this subcommittee to exchange state-of-the-art
knowledge through symposia on topics related to the performance of exterior wall systems. Past symposia of this subcommittee include water leakage, repair and retrofit, faỗade inspection and maintenance, and performance of exterior wall systems. Condensation in walls is a timely topic for
ASTM E06 to address. Advancements in building sustainability, energy efficiency, and new wall systems have progressed significantly in recent years,

while the consequential changes in wall moisture behavior resulting from
these advancements are less well understood.
Although the topic of condensation, per se, is not addressed in this subcommittees prior symposia, it has been a related topic in much of the work of
this subcommittee and the ASTM E06 committee at large. Numerous previous papers, available through ASTM, have addressed this topic. Seminal
manuals and prior symposia presented by ASTM E06, and ASTM committee
C16 on Thermal Insulation, chaired solely or in part by Heinz Treschel,
serve as background to our current work. A sampling of those volumes includes:
MNL 40 Moisture Analysis & Condensation Control in Building Envelopes - Treschel, ed. 2001;
MNL 18 Moisture Control in Buildings - Treschel, ed. 1994; and
STP 1039 Water Vapor Transmission Through building Materials and
Systems Treschel and Bomberg, eds. 1987.
Manual MNL 40 described some of the now-established computer simulations for condensation control such as WUFI (ORNL/IBP). Given the now
nine years time since that work was published, E06 believed that the stateof-the-art had advanced and that practical experiences have been gained
from the use of analytical products that were presented in the 2001 manual.
This symposium provided the opportunity for leading scientists and practitioners to again advance the body of knowledge on the topic of condensation
in exterior wall systems.
Beyond ASTM, organizations such as ASHRAE have offered longstanding input on the issue of condensation control. Other organizations have
grown more recently, such as BETEC; and USGBC along with their LEED
certification system. These organizations are interested, directly or peripherally, in the issue of condensation. They too have offered recent workshops
on the topic of condensation. Code writing organizations such as IBC, in
their energy code IECC, as well as their under-development green code,
vii


IgCC, are actively codifying issues related to condensation control, which
were brought to light in prior ASTM publications and in the work of these
other organizations. E06 believed in presenting this symposium, that these
current papers on condensation could have a similar impact in future building codes.
This STP is organized, in the same presentation as the October 2010 symposium, into two parts:
Testing/Analysis 7 papers that concentrate on testing/analysis of materials and mock-ups to predict and prevent condensation in common exterior

wall systems and
Case Studies 7 papers that document condensation problems found in the
real-world and their solutions.
In addition, there is one keynote paper by William Rose, which presents
the history that has lead to the present state-of-the-art and some of the erroneous concepts that have advanced to today. This paper sets the tone that
common-place thinking does not well serve the industry, and when it comes
to the on-going discussion of condensation control, new ideas, and concepts,
the consistent application of the principles of physics and the use of appropriate analytical techniques need to be embraced.
Although not included in this STP, the symposium attendees also benefited from a first-day tutorial session offered by Wagdy Anis and Robert
Kudder on condensation. This primer provided the science of condensation
formation and present technologies used to control its formation. For those
without this background, this tutorial served as necessary background for
the technical presentations.
An ASTM symposium and STP are a team-effort, which warrants the recognition of those who spend much time and energy in their success. First,
recognition goes to the many unnamed reviewers who, solely to better the
industry, spent many hours reviewing and re-reviewing the submitted papers. ASTM and JTE efforts were spearheaded by Dorothy Fitzpatrick and
Susan Reilly, respectively, with able assistance by Hannah Sparks and
Christine Urso. Upon Dorothy’s retirement, Mary Mikolajewski ably
stepped in. Finally, special recognition goes to WJE staffer, Amber Stokes,
who assisted the Editors keep to the ambitious review and symposium
schedule, and the numerous email correspondences necessary to pull this all
together.
Bruce S. Kaskel
Wiss, Janney, Elstner Associates, Inc.
10 S. LaSalle Street, Chicago, IL
Robert J. Kudder
Raths, Raths & Johnson, Inc.
835 Midway Drive, Willowbrook, IL

viii

Reprinted from JTE, Vol. 39, No. 1
doi:10.1520/JTE102972
Available online at www.astm.org/JTE

William B. Rose1

Insulation Draws Water
ABSTRACT: In the late 1930s, an architect and two researchers created a
version of hygrothermal building science for the United States that focused
on moisture conditions in exterior materials during cold weather. The version
they created was partial, and it was biased: It highlighted the importance of
vapor transport, while it obscured the importance of temperature impact.
They based their argument on the prevention of “condensation,” yet they
failed to provide a definition of condensation sufficient for use as a performance measure or criterion. They produced prescriptive recommendations
that later became code requirements, and these prescriptions embodied the
incomplete and biased nature of their analysis. They supported their argument with a flawed and misleading analogy. They and their followers left a
legacy of consumer fear of ill-defined moisture effects in buildings and of
designers assigning excessive importance to prescriptive measures. Their
version provides inadequate preparation for the anticipated re-insulation of
millions of U.S. buildings in the years to come. This paper will provide a short
description of the hygrothermal issues involved. It will trace the development
of the condensation version by Rogers, Teesdale, and Rowley and the efforts
that followed up to 1952. It will explain the legacy and impact of this approach related to existing building re-insulation and professional practice in
design and architecture. It will propose a framework for reviewing the link
between moisture control prescriptive requirements and performance outcomes.

KEYWORDS: condensation, moisture control, insulation

Condensation
In 1901, in the course of the design of the Minnesota State Capitol Building, the
architect Cass Gilbert was in discussion with Mr. Guastavino, a highly regarded
supplier of ceiling tiles, and a Mr. Butler, the contractor. Gilbert’s notes indicate

Manuscript received January 21, 2010; accepted for publication June 14, 2010; published
online August 2010.
1
Research Architect, Univ. of Illinois at Urbana-Champaign, Champaign, IL 61820.
Cite as: Rose, W. B., ‘‘Insulation Draws Water,’’ J. Test. Eval., Vol. 39, No. 1. doi:10.1520/
JTE102972.
Copyright © 2011 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West
Conshohocken, PA 19428-2959.
1


2 JTE • STP 1498 ON EXTERIOR BUILDING WALL SYSTEMS

I urged that great difficulty might be encountered in condensation, in
which Mr. Butler agreed, and that this condensation would drip and injure the work below it or form as ice and cause the upper work to heave.
Mr. Guastavino said he had considered this. I had several times, during
the conversation, mentioned the danger from condensation. I then proposed that…we should abandon the idea of an opening in the center of
this inner bell with a canopy over it, and should make it a continuous
vault of Mr. Guastavino’s material, and asked Mr. Butler if he were willing
to go forward on this basis, and if he had any doubts as to Mr. Guastavino’s material for the inner bell. He said he had no doubts about it and was
willing to go forward with it 关1兴.
This architectural conversation occurred more than 3 decades prior to the
appearance of building condensation as an issue of concern in the technical
engineering literature. Mr. Gilbert grasped, in a general sense, the conditions
under which frosting, melting, and paint peeling might occur and how these

conditions are associated with air flow through openings and with chilled surfaces. Condensation, in the sense of this discussion, was a visceral concern for
the architect, and it represented a range of possible phenomena rather than a
specific phenomenon. Mr. Gilbert did not need a scientific understanding of
condensation; he had a practical problem, which was resolved by practical
assurance from experienced collaborators. The appearance of “condensation”
as a vaguely defined worry about buildings predates by several decades the
appearance of technical studies related to condensation.

Insulation Draws Water
When insulation was introduced into wood frame houses in the late 1920s and
early 1930s, the paint began to peel. House painters often refused to paint
insulated houses 关2兴. The painters developed a pithy expression to describe
what happens: “Insulation draws moisture.” The residential paint-peeling problem was assigned in 1929 to F. L. Browne, a chemist with the U.S. Forest
Products Laboratory in Madison, Wisconsin. He recognized that the paintpeeling problem was occasional and was associated with two types of “abnormal conditions.”
共1兲 Type A—Rainwater seeping through leaky joints left by poor carpentry
work or faulty design
共2兲 Type B—Moisture originating within the building and carried by air
circulating within the hollow outside walls. When moisture laden air
comes in contact with surfaces at sufficiently lower temperature, water
condenses 关3兴.
Browne’s finding that bulk water effects were the cause of most problems
共Type A兲 bears repeating in every discussion of the subject. Regarding Type B
conditions, he notes that “sufficiently low temperature” is a precondition for
condensation. He suggests that the source of the moisture was from the interior
and air circulation was the transport mechanism.
Does insulation draw water? The Forest Products Laboratory 关4兴 had developed the wood sorption isotherm several years earlier 共see Fig. 1兲. It shows a


ROSE, doi:10.1520/JTE102972 3

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FIG. 1—Wood sorption isotherm from Ref 4.

somewhat-linear relationship between the equilibrium moisture content in
wood and relative humidity 共RH兲 of air that surrounds the wood for temperatures above freezing. Figure 2 shows the same data as in Fig. 2 but plotted as
lines of constant wood moisture content on a psychrometric chart. This representation allows temperature control and vapor control to be viewed independently.
RH 共ratio vp/svp of vapor pressure, vp, to saturation vapor pressure, svp兲
can be raised in two ways of course—by increasing the vapor pressure 共numerator兲 or by lowering the temperature 共denominator兲. So at the same vapor
pressure, a cold piece of wood will be wetter than a warm piece of wood. We

FIG. 2—Lines of constant wood moisture content plotted on a psychrometric chart.
Horizontal arrows show the impact of change in temperature; vertical arrows show the
impact of change in vapor.


4 JTE • STP 1498 ON EXTERIOR BUILDING WALL SYSTEMS

may expect that upon adding insulation to a wall, the exterior materials during
Winter will get cold, and by virtue of being cold, they will get wet. How wet is
a matter for analysis of course. Also, freezing events in exterior materials will
be more common and more severe. Insulation “draws” cold, and cold draws
wetness. So one cannot quarrel with the painters’ claim that insulation draws
moisture, at least on physical grounds. Insulated buildings in cold climates
have wetter cladding and sheathing materials than similar uninsulated buildings.

Tyler Stewart Rogers
Rogers was an architect and one of the founders of the reference work Timesaver Standards for Architects. He wrote a seminal article on garages, as Americans were turning from carriage houses toward the use of the automobile. In a
1936 article 关5兴, he held the title of Director of Technical Service, though the
organization is not identified. In 1938, he was Director of Technical Publications for Owens Corning Fiberglass.
In November 1936, the opening salvo of the condensation paradigm was
provided in American Architect and Architecture, “Insulation: What we know
and ought to know about it,” by Rogers. His main intent was to present heat
transmission factors for building materials, which constituted “new information, never before presented to the architectural profession.” He cited the need
for better knowledge regarding properties, installation techniques, testing
methods, rating methods, and amounts needed. Then he began a discussion of
moisture.
The advent of air conditioning2 is opening up still another field for constructive research. Technicians know that when indoor relative humidities
are artificially controlled 共as they should be for comfort and health兲 there
is a theoretical dew point temperature somewhere within the exposed
walls or roof at which point air-borne moisture is condensed into water….
It is further known that vapor pressures tend to move this internal moisture toward the cold side of the wall.
These facts set up a number of speculations that cannot be answered
without further research. It seems important to know how much airborne moisture permeates building sections of different types…. It would
appear also that plaster, building paper or any other impervious curtain
on the warm side might be a sufficient barrier to prevent any measurable
accumulation of dampness…. Much research is being undertaken, more is

planned for 1937…. Progress is being made 关5兴.
Rogers was setting the stage for decades of understandings—and
distortions—to come, so his words should be reviewed carefully. The following
represent distortions contained in his writing.
• Although insulation was introduced about the same time as humidifica2

This includes Wintertime humidification.


ROSE, doi:10.1520/JTE102972 5

tion 共“air conditioning”兲, here Rogers associated wetness with humidification rather than with insulation. The moisture increase associated
with insulation itself was not discussed.
• “Dewpoints” have locations within the wall.
• The terms “condensed” and condensation can be applied in the absence
of definition. Rogers saw no need to distinguish condensation phenomena on sorptive and non-sorptive materials.
• Wetness on the outside requires a humidified interior as the moisture
source.
• Prescriptions 共“sufficient barrier to prevent measurable accumulation of
dampness”兲 may be suggested or offered prior to the completion, publication, and discussion of research.
Rogers then wrote “Preventing Condensation in Insulated Structures” for
the first issue of Architectural Record, March 1938 关6兴. It began
Architects, owners and research technicians have observed, in recent
years, a small but growing number of buildings in which dampness or
frost has developed in walls, roofs or attic spaces. Most of these were
insulated houses, a few were winter air-conditioned. The erroneous impression has spread that insulation “draws” water into the walls and
roofs….
Obviously, insulation is not at fault—at least not alone. Nor could winter
air-conditioning, creating comparatively high and sustained relative humidities for health, be charged with sole responsibility, for not all structures reporting dampness were equipped with humidifiers. The need for
research became apparent.

Rogers attributed the new problems to new conditions, including “humidification, reduced infiltration, weathertight construction, and efficient insulation,” and he stated that all four “are highly desirable in terms of health, comfort, and economy.” This framing of the problem meant that other means of
moisture control needed to be adopted.
In this article Rogers, provided no operational definition of condensation.
He stated, in fact, that the problem of condensation had been fully solved; this
was even before it was ever satisfactorily defined. His position was that these
new measures must and will be adopted. He proceeded to discuss measures
necessary to mitigate the wetness associated with adoption of the new elements. The measures he proposed were the vapor barrier and attic ventilation.
Rogers stated
Architects may avoid all technicalities in explaining this new vapor barrier principle by using some parallel situation such as that shown in figure
13. Here are two basins into which water is running at the same rate. The
basin at the left has an outlet larger than the supply. In this no water
3

Figure 3 in this paper.


6 JTE • STP 1498 ON EXTERIOR BUILDING WALL SYSTEMS

FIG. 3—Flawed analogy comparing diffusion transport 共kinetic兲 to bulk flow 共dynamic兲
共from Ref 6兲.

accumulates. The one on the right has an outlet restricted in size to less
that that of the inflow. Here water accumulates until it spills over the
sides.
So with the wall sections shown below these basins. The room between is
indicated as being warm and humid. In the wall at the left there is a vapor
barrier not completely perfect in its stoppage of vapor movement. However, it checks most of the vapor, and what little remains can pass out
through the colder side of the wall with little difficulty. This wall shows no
accumulation of vapor.
This description is fundamentally flawed. The funnel and faucet analogy

describes a dynamic system where the faucet water feeds all of the materials
along its path. In kinetic moisture diffusion, the entire surrounding air and
materials provide moisture to the materials, not just a high source at a distance. Rogers said that by checking interior moisture at the warm side, the
“wall shows no accumulation of vapor.” However, vapor will accumulate in
materials that move to low temperature, and the capacity for barriers to mitigate that accumulation is limited. Rogers’ analogy is captivating—and misleading. Arguing that under diffusion “all of the water comes from the high vapor
pressure side” is equivalent to claiming that “all of the heat comes from the
high temperature side” under heat conduction.
The remainder of the article dealt with practical matters of placing vapor
barriers and providing attic ventilation. These included two pages from Timesaver Standards on Heat Transmission, listing coefficients of heat transmission
of common building materials, and two pages on Preventing Condensation in
Insulated Structures. These figures were widely reproduced in guidance literature that followed.


ROSE, doi:10.1520/JTE102972 7

FIG. 4—Larry V. Teesdale, U.S. Forest Products Laboratory.

L. V. Teesdale
The first of two researchers Rogers referenced was L. 共Larry兲 V. Teesdale of the
Forest Products Laboratory 共see Fig. 4兲. His paper, “Condensation in walls and
attics” 共1937兲 关7兴, began
Condensation or moisture accumulation within walls and in attics or roof
spaces has become a subject of considerable concern to many home owners and prospective builders, especially in the states north of the Ohio
River…. There have been so many cases in recent years that any prospective builder may hear about ice in attics, stained ceilings and side walls,
plaster becoming loose, ruined decorations, decayed side wall, roof, studs,
and sheathing, floors that have bulged up, outside paint failures, and numerous other manifestations of moisture resulting from condensation.
Obviously the question arises as to why we hear so much more about this
condition now than we used to just a few years ago. The answer is relatively simple. During the last few years there has been a marked tendency
on the part of the architects, builders and home owners to improve homes
both new and old with the idea of increasing the comfort of the occupants

and decreasing operating expenses. Prominent among these improvements are the increasing use of storm sash, insulation, weather strips,
calking around windows and doors, and other means of decreasing heat
loss and wind infiltration. Because of the tighter construction the normal
humidity or vapor pressure within a house so constructed is higher than
in houses less tightly constructed. In addition, as a health and comfort
measure the normal humidity is usually augmented by evaporating water
or some other means of winter air conditioning. Improvements that add
to comfort and health are worth while and should not be discouraged, but
it so happens that they introduce the unanticipated moisture problem just
described.


8 JTE • STP 1498 ON EXTERIOR BUILDING WALL SYSTEMS

In these opening paragraphs, Teesdale, like Rogers, emphasized how improvements have led to tighter envelopes and thereby to higher indoor vapor
pressures. Teesdale, again like Rogers, introduced the term condensation freely
and qualitatively without presenting a definition. The focus of his work was on
the moisture effect of added insulation, and he identified a moisture effect that
is independent of indoor vapor pressures, namely the wetting effect that comes
with colder material temperatures.
Comparing figures 1 and 24, it is at once evident that, within the stud
space, the temperature gradients are much steeper in figure 2 than in
figure 1, and that the respective sheathing temperatures are much lower
in figure 2 than in figure 1. This results from the addition of insulation in
figure 2. Because of the lower sheathing temperatures5 condensation will
occur on the sheathing with lower room humidities when insulation is
used than when it is not used. Conditions within the walls are actually
more complicated than the drawings and examples indicate, because they
are not static….
Now we come to one of the most baffling paragraphs in all of building

science.
There are a number of types and kinds of insulation on the market and
the potential buyer often hears that certain types “draw water” and become wet. This is not true. Such insulation, because of its efficiency in
reducing heat loss, lowers the temperatures within the wall and thus sets
up the condition that increases the amount of moisture that may accumulate. Once understanding the conditions that cause the moisture it is also
possible to provide means of prevention as discussed later.
A close look reveals that Teesdale contradicted himself here—compare the
phrases “become wet” and “moisture that may accumulate.” Insulation is efficient in reducing heat loss. So temperatures within the wall—actually the outer
materials—are lowered. Lowering those temperatures sets up the condition
that increases the amount of accumulated moisture in the cold materials. Teesdale’s objection to insulation “drawing water” cannot be an objection to the fact
of moisture accumulation; Teesdale agrees with that. Why then did he object to
the simplification that drawing water expresses? Is this an early example of
spin and counterspin regarding public opinion? Teesdale suggests an answer as
he moved toward a summary:
Moisture accumulation within a wall like those illustrated in figures 1 and
2 is affected by five factors:
共1兲
共2兲
共3兲
共4兲
4
5

Outside temperature and humidity.
Efficiency of the insulation.
Inside atmosphere 共temperature and humidity兲.
Resistance of the outer wall to vapor movement.

Figure 5 in this paper.
Emphasis added.

FIG. 5—Figures from Ref 7, showing theoretical temperature profiles in uninsulated and insulated assemblies.

ROSE, doi:10.1520/JTE102972 9


10 JTE • STP 1498 ON EXTERIOR BUILDING WALL SYSTEMS

FIG. 6—Figures from Ref 8, showing test data temperature profiles in uninsulated and
insulated assemblies, compared to theoretical 共Fig. 7兲.

共5兲 Resistance of the inside wall to vapor movement.
As the outside temperature and humidity cannot be controlled, and as
insulation adds to comfort, health and fuel economy, methods of prevention are limited to the three other factors….
Teesdale expressed here an insulation imperative. According to him, we
must insulate and, given that, we must accept the consequences of colder and
wetter exteriors,; we must settle for whatever moisture improvements are possible by manipulating indoor humidity and access of that humidity to the exterior materials—vapor barriers. Promoting the use of insulation is fine, of
course. What is not fine is that Teesdale appears to be willing to lend a voice
that “insulation does not draw water,” while demonstrating just the opposite,
very clearly and succinctly.
A few months later, an article without author attribution appeared in The
Architectural Forum, which contained language and drawings so similar to
Teesdale’s report that his authorship is unmistakable 关8兴. This article contained
much of the material from his previous report, but this time it included measured values, shown in profile charts, where his previous charts were only theoretical 共see Fig. 6兲. The article explained how these charts are made and interpreted.
…two words of caution with their interpretation are worth repeating here:
The first of these is that the theoretical dewpoints shown are in all cases
room dewpoints. This assumes that the vapor pressure within the stud
space will be the same as that within the house, a condition which will
never actually exist. Actually the vapor pressure and dewpoint within the

stud space will be somewhat lower than that within the house. How much
lower will depend on how much the inner and outer wall surfaces resist
the passage of vapor; if the inner surface passes vapor readily and the
outer surface is relatively impervious, the condition will be substantially
as shown; if, however, the surface is relatively impervious, or the outer


ROSE, doi:10.1520/JTE102972 11

part of the wall passes vapor easily, actual dewpoints will be lower than
those shown.
The second word of caution is in regard to the location of the dewpoints,
which are in some cases shown within the insulation. This is purely a
matter of diagrammatic convenience and does not mean that condensation will actually take place at this point. Actually, the moisture in such
cases will collect on the nearest cold surface—the inside of the wood
sheathing. This is because the condensation of moisture sets up a relative
“vapor vacuum” which draws4 vapor from the surrounding air. Whenever
condensation is actually taking place, the actual vapor pressure within the
stud space will be equal to that for saturated air at the temperature of the
inside of the sheathing, as indicated on the “test data” diagrams, and
condensation will be possible only at this point.
Bravo, Larry. Cold sheathing draws moisture; indeed it operates like a
vapor vacuum, sucking up vapor from the air that surrounds it. This is the one
instance of critical challenge to the developing paradigm, and it was buried in
an anonymous article, out of the mainstream. Note that the measured data
contains cavity vapor pressure values. The vapor pressure values do not correspond to vapor permeances of the inner and outer skins: For one thing, those
values are not known. For another, the permeances are presumed to be the
same in the two cases shown in Fig. 6, yet the measured vapor pressure in the
cavity is quite different. The explanation under the second word of caution
correctly explains the measured data. And this is the explanation that claims

that cold materials draw moisture.
Teesdale’s figures 共Fig. 6兲 merit close study. They show clearly that what
determines the actual vapor pressure in a cavity is the temperature of the
sheathing, far more than the vapor permeance values of the assembly materials. In his two examples, the material permeances are essentially the same,
while the cavity pressures differ greatly. This is consistent with how the American Society of Heating, Refrigerating and Air-Conditioning Engineers
共ASHRAE兲 profile method is conducted.6 That method requires that cavity
vapor pressure in excess of the saturation vapor pressure at the temperature of
the colder materials be set to a value equal to that saturation vapor pressure,
and net accumulation rates are then calculated. Many users who are not familiar with the method may simply find vapor pressure in excess of saturation
vapor pressure and suggest condensation occurs. This mistaken but widespread
approach has no support in ASHRAE Handbook Fundamentals 2009 关9兴 and is
inconsistent with physical findings including those of Teesdale.
Teesdale also pointed out, in the second word of caution, that language
referring to the “location of dewpoint” or “where you reach dewpoint” represents an interpretation of a graphic device and does not reflect a representation
of actual conditions. There is no “where” regarding dewpoints.
This article has a curious introduction 共clearly not by Teesdale, most likely
6
ASHRAE 2009 Handbook Fundamentals. Chapter 27, “Heat, Air and Moisture Control in
Building Assemblies—Examples,” Examples 9 and 10.


12 JTE • STP 1498 ON EXTERIOR BUILDING WALL SYSTEMS

by Rogers兲 apparently written to address the concerns of the architecture audience.
Already validated by these reports7 are the following generalizations:
共1兲 Condensation is a thoroughly predictable, understandable phenomenon which need hold no terrors4 for the architect or builder who masters its fundamentals.
共2兲 It does not result from the use of any particular insulating material, nor
does it necessarily affect adversely one type of material more than another.
共3兲 Precautions against it are effective and relatively so inexpensive as to
seem desirable in any event.

Terrors? What should be apparent at this point is that there are two parallel
domains of the world of condensation: One, represented by Rogers and the
architects, which addresses visceral worries regarding a non-specific range of
moisture effects; the other represented by Teesdale and the emerging science/
engineering community, in which the puzzles offered by condensation phenomena provide a fascinating glimpse into physical processes calling out for explanation. As we will see, terrors come to play a role when vapor barriers are
marketed in 1950 using slogans such as “The Menace of Moisture” and “War
Against Water.”
There is a curious contrast between the statement here that
“Condensation…does not result from the use of any particular insulating material” and previous statements by both Rogers and Teesdale to the effect that
“some types and kinds” of insulation materials “draw water.” The “type or kind”
argument distracts from the more fundamental matter of insulation per se
leading to wetness conditions.

American Society of Heating and Ventilating Engineers „Now ASHRAE…
In 1937, Technical Advisory Committee IF-23—Insulation was formed at
American Society of Heating and Ventilating Engineers 共ASHVE兲. The first report of this committee was presented at the 1937 annual meeting 关10兴. That
report stated
The committee further gave consideration to the following questions concerning the usage of insulation, but deferred until a later date in making
recommendations concerning the need for study of any of the particular
subjects mentioned or concerning their order of importance.
共1兲 The effect of “regain moisture” on the conductivity of insulating materials. 共Quotes are from the original.兲
共2兲 The effect of condensed moisture on the conductivity of insulating materials in a structure.
The report then listed 19 other subjects, none of which deal with moisture.
What is of interest here is the explicit distinction between regain moisture and
7

Rogers was referring to the work of Teesdale and Rowley.


ROSE, doi:10.1520/JTE102972 13

“condensed moisture.” The exact definitions were not given and are not known
because the distinction dropped from use. But it is tantalizing to speculate as to
the intended distinction. Thermal wetting versus source humidity? Sorbed
moisture versus hard-surface condensation? Assuming these are distinct wetting processes and further assuming that vapor barriers restrict condensed
moisture, had this committee described a wetting process that does not lend
itself to vapor barrier control? We are unable to answer at this point.

Frank Rowley
As Professor of Mechanical Engineering at the University of Minnesota, Rowley
共Fig. 7兲 had worked with National Mineral Wool Association funding to determine values for thermal resistance of materials. His work and that of his coresearchers and students came from the laboratory and from theory.
In “A Theory Covering the Transfer of Vapor Through Materials,” ASHVE
July 1939 关11兴, he posited that
For convenience, it has often been assumed that the laws for vapor transmission are similar in form to those governing the flow of heat through
the walls of a building, and that coefficients of vapor transmittance may
be developed for materials or combinations of materials in the same manner as coefficients of heat transmission…. Before accepting a complete
analogy between the two problems an analysis should be made to determine those elements which are similar and those which may be
conflicting.
Note the argument given for assuming at the outset that vapor moves by
diffusion: For convenience. To Rowley’s credit, he did not consider that a sufficiently strong argument without further validation.
Rowley then sought to define condensation. He distinguished nonhygroscopic materials from hygroscopic. Defining condensation for nonhygroscopic materials was, of course, quite simple. Then he distinguished nonpermeable from permeable hygroscopic materials. For permeable materials, he
stated, without demonstration, that vapor transport would be by diffusion only,
and frost or ice may form as condensation within the material if, at any point,
dewpoint exceeds sensible temperature. His discussion of non-permeable hygroscopic materials introduced capillary transport. His discussion was long,
involved, and at times speculative. At no point in this discussion did he state
what constituted condensation. In other words, this effort to provide a theoretical underpinning for “preventing condensation” was unable to provide an operational definition of condensation for capillary materials 共e.g., wood,
masonry兲.8 As a consequence, there was no metric available to determine per8
ASHRAE Handbook Applications 2013, Chapter 43, “Building Envelopes,” contains this
approved wording: “Moisture condensation is the change in phase from vapor to liquid
water. Condensation occurs typically on materials such as glass or metal that are not

porous or hygroscopic and on capillary porous materials that are capillary saturated.
Use of the term ‘condensation’ to refer to change in phase between vapor and bound


14 JTE • STP 1498 ON EXTERIOR BUILDING WALL SYSTEMS

FIG. 7—Frank Rowley, professor of Mechanical Engineering, University of Minnesota.

formance outcomes of prescriptive measures for normal building materials.
Rowley and his colleagues conducted experiments of wall and attic construction in 1938 关12兴. They made use of a refrigerated room capable of reaching −20° F in which they placed test assemblies. They developed an ingenious
method of working around their inability to define condensation for capillary
materials. The assemblies were designed for rapid dismantling so that an aluminum plate, located at the inside of the sheathing, could be removed and
weighed to determine frost accumulation or condensation at that location.
Thus, the appearance of frost on an aluminum plate became a surrogate for
condensation on wood or masonry.
The interior space was maintained at 70° F and 40 % RH. The assemblies
were all 2 ⫻ 4 studs, metal lath and plaster at the interior, Ponderosa pine shiplap sheathing, building paper, and redwood siding, with 3 5/8 mineral wool
between studs. To summarize their test facility findings, see Table 1.
We may note the following from Rowley’s data.
• Accumulation is largely a product of sheathing temperature. Recall that
the inside of the sheathing temperature provided by Teesdale, with outdoor temperature of −20° F, was 1.6° F with insulation and 38.5° F
without insulation.
water in capillary or open porous materials is discouraged.”


No paint, no vapor barrier
2 coats “seal coat” paint
2 coats white flat paint
Glossy asphalt impregnated sheathing paper
30–30–30 duplex paper

Asphalt felt paper
Duplex crepe paper

10
Inside Surface
of Sheathing Temperature, °F
⫺0.2
22.8
0.8
23.6
⫺1.5
20.6
⫺2.0
20.5
⫺3.2
20.9
⫺2.2
21.3
⫺1.8
21.6

⫺19.5

⫺19.5
10
Condensation on Sheathing,
grams/ ft2 / 24 h
2.15
1.41
0.20

0.00
0.24
0.00
0.07
0.00
0.25
0.00
0.52
0.18
0.09
0.00

Outdoor Temperature, °F

TABLE 1—Temperature and frost accumulation 共condensation兲 results from Rowley 关12兴.

ROSE, doi:10.1520/JTE102972 15


16 JTE • STP 1498 ON EXTERIOR BUILDING WALL SYSTEMS

• Paint is an excellent “vapor barrier,” comparable to the protection provided by the papers available at the time.
• Since the sheathing is below freezing in this test, the test method—frost
on an aluminum plate at steady state—represents actual conditions
since moisture sorption would be inactive. Under actual conditions, a
warming spell would melt the frost and allow sorption.
• To gain a sense of the impact of sorption, we may calculate thus 1 ft2 of
3/4 in. thick Ponderosa pine weighs ⬃1.0 kg. The “safe” moisture range
may be from 10 % to 25 % moisture content, or 150 g accumulation
within that range. So, with no vapor protection, the safe duration of a

cold spell would be 70 days at −20° F 共150 g/2.15 g/sf/24 h兲. It should be
obvious that a painted wall can withstand a cold spell ten times longer.
• The conditions at the inside of the sheathing are not a strong indicator
of the wetness at the layer of wood beneath the paint. There was a shift
in the site of concern from the paint substrate to the inside of the
sheathing, with no justification provided.
These results were the only published measured results regarding the impact of vapor barriers and attic ventilation prior to the promulgation of vapor
barriers as a code requirement in 1942 共see Housing and Home Finance Agency
共HHFA兲 below兲. These measurements, under the steady-state conditions Rowley imposed, lent support to the prescriptive measures that were on the table—
vapor barriers and attic ventilation.
They could hardly do otherwise. The choice of −20° F for “outdoor” conditions would naturally highlight the occurrence of condensation, in the case
where even small amounts of moisture are diffused or leaked onto the test
plate. Rowley’s research was configured to find performance thresholds where
complying structures fall on the desirable side and non-complying structures
show condensation. A research design that was not constrained to the prescriptive measures suggested might well have been structured differently, and might
have reached other conclusions. The research appears to be post hoc; it appears
to rationalize a given set of design decisions rather than initiate design approaches that a fairer research design would suggest.
Furthermore, the vapor barrier research provided a clear demonstration of
the effectiveness of paint as a vapor barrier. If Rowley’s results are correct, and
we may assume they are, then the use of paint appears equal in performance to
the barrier materials he studied. This should have been cause to suspend the
vapor barrier momentum. Indeed, were not the troubled houses painted at the
interior? It did not.
Rowley’s co-researcher, Lund described their Minnesota research in 1952
关13兴, saying, “There have been many erroneous statements made that insulation
is one of the primary causes of structural condensation.” That is as close as the
University of Minnesota team came to saying that insulation “draws water.”

Housing and Home Finance Agency
Throughout the 1940s, the Housing and Home Finance Agency had carried

through its mandate to facilitate low-cost home construction during and after