Overview - ASTM International


Overview - ASTM International

Moisture Analysis

and Condensation

Control in Building


Heinz R. Trechsel, Editor

ASTM Stock Number: MNL40


RO. Box C700

100 Ban" Harbor Drive

West Conshohocken, PA 19428-2959

Printed in the U.S.A.

Library of Congress Cataloging-in-Publication Data

Moisture analysis and condensation control in building envelopes/Heinz R. Trechsel, editor.

p. cm.--(MNL; 40)

"ASTM stock number: MNL40."

Includes bibliographical references and index.

ISBN 0-8031-2089-3

1. Waterproofing. 2. Dampness in buildings. 3. Exterior walls. I. Trechsel,

Heinz R. II. ASTM manual series; MNL40.

TH9031.M635 2001

693.8'92--dc21 2001022577



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Printed in Philadelphia, PA



THIS PUBLICATION, Moisture Analysis and Condensation Control in Building Envelopes,

was sponsored by Committee C16 on Thermal Insulation and Committee E06 on Per-

formance of Buildings. The editor was Heinz R. Trechsel. This is Manual 40 in ASTM's

manual series.


Preface vii

Biographies of the Authors xv

Glossary--by Mark Albers xx

Chapter 1--Moisture Primer

by Heinz R. Trechsel 1

Chapter 2--Weather Data

by Anton TenWolde and Donald G. CoUiver 16

Chapter 3--Hygrothermal Properties of Building Materials

by M. K. Kumaran 29

Chapter 4--Failure Criteria

by Hannu Viitanen and Mikael SaIonvaara 66

Chapter 5--Overview of Hygrothermal (HAM) Analysis Methods

by John Straube and Eric Burnett 81

Chapter 6--Advanced Numerical Models for Hygrothermal Research

by Achilles N. Karagiozis 90

Chapter 7--Manual Analysis Tools

by Anton TenWolde 107

Chapter 8--MOIST: A Numerical Method for Design

by Doug Butch and George Tsongas 116

Chapter 9--A Hygrothermal Design Tool for Architects and Engineers


by H. M. Kuenzel, A. N. Karagiozis, and A. H. Holm 136

Chapter 10--A Look to the Future

by Carsten Rode 152

Appendix 1--Computer Models 161

Appendix 2--Installation Instructions 185

Index 189


by Heinz R. Trechsel I


IN ASTM MANUAL MNL 18, Moisture Control in Buildings, 2 Mark Bomberg and Cliff

Shirtliffe, in their chapter "A Conceptual System of Moisture Performance Analysis,"

make the case for a rigorous design approach that "should involve computer-based

analysis of moisture flow, air leakage, and temperature distribution in building ele-

ments and systems." In the Preface to the same manual, I state that one objective of

Manual 18 is to help establish moisture control in buildings as a separate and essential

part of building technology.

In 1996, the Building Environment and Thermal Envelope Council (BETEC) 3 con-

ducted a Symposium on Moisture Engineering. The symposium presented an overview

of the current state-of-the-art of moisture analysis and had a wide participation of

building design practitioners. The consensus of the participants was that moisture

analysis was now practical as a design tool, and that it should be given preference over

the simple application of the prescriptive rules. However, it was also the consensus

that the architect/engineer community was not ready to fully embrace the analytical

approach. Thus, both the building research and the broader building design commu-

nity recognized the need for moisture analysis and for a better understanding of cur-

rently available moisture analysis methods.

The concerns for moisture control in buildings have increased significantly since the

early 1980s. One sign of the increased concern is the number of research papers on

moisture control presented at the DOE/ASHRAE/BETEC conferences on "Thermal

Performance of Exterior Envelopes of Buildings" from 8 in 1982 to 17 in 1992 and to

27 directly related to moisture in 1998. Another measure is that the Building Environ-

ment and Thermal Envelope Council held four conferences/symposia from 1991

through 1999, and only two between 1982 and 1990.

In response to these developments ASTM Committees C16 on Thermal Insulation

and E06 on Performance of Buildings have agreed to co-sponsor the preparation and

publication of this new manual to expand and elaborate on the relevant chapters of

MNL 18: Chapter 2, "Modeling Heat, Air, and Moisture Transport through Building

Materials and Components," and Chapter 11, "Design Tools." The objective of this man-

ual, then, is to familiarize the wider building design community with typical moisture

analysis methods and models and to provide essential technical background for un-

derstanding and applying moisture analysis.



In 1948, the U.S. Housing and Home Finance Agency (a forerunner of the current

Federal Housing Administration) held a meeting attended by representatives of build-

1H. R. Trechsel Associates, Arlington, VA; Trechsel is also an architect for Engineering Field

Activity Chesapeake, Naval Facilities Engineering Command, Washington, DC. The opinions ex-

pressed herein are those of the author and do not necessarily reflect those of any Government


2 Manual on Moisture Control in Buildings, ASTM MNL 18, Heinz R. Trechsel, Editor, Philadelphia,

t 994.

3The Building Environment and Thermal Envelope Council is a Council of the National Institute

of Building Sciences, Washington, DC.


ing research organizations, home builders, trade associations, and mortgage finance

experts on the issue of condensation control in dwelling construction. 4 The focus of

the meeting was on vapor diffusion in one- and two-family frame dwellings in cold

weather climates. The consensus and result of that meeting was the Prescriptive Rule

to place a vapor barrier (now called a vapor retarder) on the warm side of the thermal

insulation in cold climates. The meeting also established that a vapor barrier (retarder)

means a membrane or coating with a water vapor permeance of one Perm or less. One

Perm is 1 g/h'ft2"in.Hg (57 ng/s'm2-pa). The rule was promulgated through the FHA

Minimum Property Standards? It still is referenced unchanged in some construction


The 1948 rule was based on the assumption that diffusion through envelope mate-

rials and systems is the governing mechanism of moisture transport leading to con-

densation in and eventual degradation of the building envelope. Since 1948, and par-

ticularly since about 1975, research conducted in this country and abroad has brought

recognition that infiltration of humid air into building wall cavities and the leakage of

rainwater are significant, in many cases governing mechanisms of moisture transport.

Accordingly, the original simple rule with a limited scope has been expanded to include

air infiltration and rainwater leakage, and to cover other climates and building and

construction types. The current, expanded prescriptive rules can be summarized as


9 install a vapor retarder on the inside of the insulation in cold climates,

9 install a vapor retarder on the outside of the insulation in warm climates,

9 prevent or reduce air infiltration,

9 prevent or reduce rainwater leakage, and

9 pressurize or depressurize the building so as to prevent warm, moist air from en-

tering the building envelope.

The current expanded rules have greatly increased the validity and usefulness of the

prescriptive rules. However, the rules still do not fully recognize the complexities of

the movement of moisture and heat in building envelopes. For example:

9 The emphasis on either including or deleting a separate vapor retarder is misplaced,

and the contribution of the hygrothermal properties of other envelope materials on

the moisture flow are not considered. In fact, incorrectly placed vapor retarders may

increase, rather than decrease, the potential for moisture distress in building enve-


9 Climate as the only determining factor is inadequate to establish whether a vapor

retarder should or should not be installed. Indoor relative humidity and the

moisture-related properties of all envelope layers must also be considered.

9 The two climate categories "cold" and "warm" have never been adequately or con-

sistently defined, and large areas of the contiguous United States do not fall under

either cold or warm climates, however defined. For example, ASHRAE, 6 in 1993,

used condensation zones based on design temperatures. For cold weather, Lstiburek 7

suggests 4000 Heating Degree Days or more, and the U.S. Department of Agriculture s

uses an average January temperature of 35~ or less. For warm climates, ASHRAE 9

established criteria based on the number of hours that the wet bulb temperature

exceeds certain levels, Odom 1~ suggests average monthly latent load greater than

4Conference on Condensation Control in Dwelling Construction, Housing and Home Finance

Agency, May 17 and 18, 1948.

SHUD Minimum Property Standards for One- and Two-Family Dwellings, 4900.1, 1980 (latest


6ASHRAE, Handbook of Fundamentals, American Society of Heating, Refrigerating, and Air-

Conditioning Engineers, Atlanta, 1993.

7Lstiburek, J. and Carmody, J., "Moisture Control for New Residential Buildings," Moisture Con-

trol in Buildings, MNL 18, H. R. Trechsel, Ed., American Society for Testing and Materials, Phil-

adelphia, 1994.

SAnderson, L. O. and Sherwood, G. E., "Condensation Problems in Your House: Prevention and

Solutions," Agriculture Information Bulletin No. 373, U.S. Department of Agriculture, Forest Ser-

vice, Madison, 1974.

9ASHRAE, Handbook of Fundamentals, American Society of Heating, Refrigerating, and Air-

Conditioning Engineers, Atlanta, 1997.

~00dom, J. D. and DuBose, G., "Preventing Indoor Air Quality Problems in Hot, Humid Climates:

Design and Construction Guidelines," CH2M HILL and Disney Development Corporation, Or-

lando, 1996.

average monthly sensible load for any month during the cooling season, and Lsti-

burek 11 suggests defining warm climate as one receiving more than 20 in. (500 mm)

of annual precipitation and having the monthly average outdoor temperature re-

maining above 45~ (7~

Over the last 20 years or so, building researchers have tried to refine the definitions

of cold and warm climates. Except for the efforts of Odom and Lstiburek (for which

the jury is still out), not much progress has been made. In the meantime, much pro-

gress has been made in the development of analytical methods to predict surface rel-

ative humidities, moisture content, and even the durability performance of building

envelope materials.

The above suggests that the prescriptive rules alone will not assure that building

envelopes are free of moisture problems. Accordingly, and consistent with the consen-

sus of the 1996 BETEC Symposium participants, we must look to job specific moisture

analysis methods and models for the solution to reduce or eliminate moisture prob-

lems in building envelopes. This does not mean that the traditional prescriptive rules

should be ignored or that they should be violated without cause. They should, however,

be used as starting points, as first approximations, to be refined and verified by mois-

ture analysis. This, then, is analogous to the practice in structural design, where, for

example, depth-to-span ratios are used as first approximations, to be refined by anal-

ysis. Which is, very much simplified, what Bomberg and Shirtliffe advocate in Manual




The progress made in the development of computer-based analysis methods, or models

since the publication of MNL 18 in 1994, has been spectacular. At last count, there

exist now well over 30 models that analyze the performance of building envelopes

based on historical weather data, and new and improved models are being developed

as this manual goes to press. The models vary from simplified models useable by

building practitioners on personal computers to sophisticated models that require spe-

cially trained experts and that run only on mainframe computers.

The simpler models may or may not include the effect of moisture intrusion due to

air and water infiltration. The more sophisticated models are excellent tools for build-

ing researchers and, as a rule, include the effects of rainwater leakage and air infiltra-

tion. As mentioned above, air infiltration and water leakage are significant causes of

moisture distress in building envelopes. This would seem to imply that only models

that include these two factors are useful to the designer. However, this is not neces-

sarily so for the following reasons:

9 The input data for air infiltration and water leakage are unreliable. Infiltration and

leakage performance data for various joint configurations and for entire systems are

generally unknown. Also, much of the performance of joints depends on field work-

manship and quality control over which the designer seldom has significant control.

9 Air infiltration and rainwater leakage, unlike diffusion, occur at distinct leakage sites.

These are seldom evenly distributed over the entire building envelope. Accordingly,

the effect of air and water leaks are bound to be localized with the locations un-

known at the design stage.

9 Both air and water leaks are transitional in nature, with durations measured in

hours, days, or weeks. Rainwater leakage depends on wind direction, and rainfalls

one day may not fall again during the next day or week. Air infiltration depends on

wind direction. Moist air moves into the envelope one day; the next day dry air may

enter the envelope and wetting turns to drying. In contrast, diffusion mechanisms

operate generally on a longer time horizon, frequently for weeks, months, or over

an entire season.

Although models that include air infiltration and rainwater leakage are excellent

research tools, models that do not include these transport mechanisms are still most

1, Lstiburek, J., "Builder's Guide for Hot-Humid Climates," Westford, 2000.



useful for the designer/practitioner provided that their limitations are recognized and

proper precautions are taken to reduce or eliminate air infiltration and water leakage.

The use of moisture analysis alone does not guarantee moisture-resistant buildings.

Careful detailing of joints and the use and proper application of sealants and other

materials are necessary. The issues of field installation and field quality control, men-

tioned above, must be addressed adequately by the designer and specification writer.

For example, for more complex and innovative systems, specifying quality control spe-

cialists for inspecting and monitoring the installation of envelope systems in Section

01450 and specifying that application only be performed by installers trained and ap-

proved or licensed by the manufacturer will go a long way towards reducing moisture

problems in service. Also important are operation and maintenance, both for the en-

velope and for the mechanical equipment. Face-sealed joints need to be inspected and

repaired at regular intervals. If pressurization or depressurization are part of the strat-

egy to reduce the potential for moisture distress, documentation of proper fan settings

is critical. However, these concerns are outside the scope of this manual and will not

be discussed further.

Moisture analysis is still an evolving art and science. While great advances have been

made in the development of reliable and easy-to-use models and methods, some input

data needed for all the models are still limited:

Weather Data

Appropriately formatted data are available only for a restricted number of cities. How-

ever, it is generally possible to conduct the analysis for several cities surrounding the

building location and to determine the correctness of the assumptions with great con-

fidence. Also, the data currently available were developed for determining heating and

cooling load calculations; their appropriateness for moisture calculations has been

questioned. Chapter 2 of this manual provides new weather data specifically developed

for moisture calculations.

Material Data

Data on the hygrothermal properties of materials are available only for a limited num-

ber of generic materials. A major effort is currently under way by ASHRAE and by the

International Energy Agency to develop the necessary extensive material database.

Some of the most recent material data are included in Chapter 3 of this manual.

Failure Criteria

Reliable failure criteria data are available only for wood and wood products, and even

for these the significant parameter of length of exposure has not been studied to the

desirable degree. Chapter 4 of this manual discusses these criteria.

Despite these concerns about the application of moisture models, designs based on

rigorous analysis are bound to be far more moisture resistant than designs based on

the application of prescriptive rules alone. The authors of this manual hope that it will

encourage building practitioners and students to conduct moisture analysis as an in-

tegral part of the design process. The more widespread use of moisture analysis to

develop building envelope designs will then in turn provide an added incentive for

model developers to improve their models, for producers to develop the necessary data

for their materials, and for researchers to establish new databases on weather data

better suited for moisture calculations.


One objective of this manual is to provide the necessary technical background for the

practitioner to understand and apply moisture analysis. In addition, two models are

discussed in detail to familiarize the practitioner with the conduct of typical computer-

based analysis. The selection of the two models is based on ready availability and on

ease of operation. The two models are included on a CD ROM disk enclosed in the

pocket at the end of the manual. Also included on the disk are two programs to convert

various properties of air. Based on the information provided, the reader should be able

to start his or her own hands-on training in moisture analysis.

Heinz R. Trechsel




THIS MANUAL IS NOT THE WORK of a single person. It is the result of cooperation be-

tween the authors of individual chapters, a small army of reviewers, staff support

people, and the editor, all working together.

Thus, my utmost thanks to the authors who prepared their chapters. Each one is a

leading expert in his field, and the chapters are at the forefront of the current state-

of-the-art in moisture analysis. Next, I want to thank the reviewers, who generously

gave of their time and whose comments and suggestions improved the individual chap-

ters and the utility of the manual. The names of the reviewers are listed below. My

appreciation also goes to the executive committees of the two sponsoring ASTM Com-

mittees, C16 on Thermal Insulation and E06 on Performance of Buildings.

Aside from the technical inputs mentioned above, the manual would not have been

born without the untiring support of ASTM's staff: Kathleen Dernoga and Monica

Siperko, who shepherded the preparation of the Manual through all its phases and

provided much needed administrative support; and David Jones, who capably edited

the final drafts of the individual chapters. To all of them my most sincere thanks and


Our special thanks also to Mr. Rob Davidson of the Trane Company and to Dr. Car-

sten Rode of the Technical University of Denmark for their permissions to reproduce

the conversion programs. Also to Dr. James E. Hill, Deputy Director of the Building

and Fire Research Laboratory at the National Institute of Standards and Technology

in Gaithersburg, Maryland, to Prof. Dr. -Ing. habil. Dr. h.c. mult. Dr. E.h. mult. Karl

Gertis, of the Fraunhofer Institute ftir Bauphysik in Holzkirchen, Germany, and to Dr.

Andre Desjarlais of Oak Ridge National Laboratory at Oak Ridge, Tennessee, for their

permission to reproduce the two moisture analysis programs. I'm also much indebted

to Mr. Christopher Meyers of the Engineering Field Activity Chesapeake, Naval Facil-

ities Engineering Command for coordinating the four programs and preparing a user

friendly interface for the CD-ROM.

Finally, but by no means least, I was encourged by two good friends to prepare this

manual long before the first word was ever written. Ev Shuman of Pennsylvania State

University and Reese P. Achenbach, formerly Chief of the Building Environment Di-

vision at the National Institute of Standards and Technology, assisted me in formulat-

ing the initial plan for the manual. Both are no longer among us. However, their sug-

gestions have, to a large degree, shaped the manual you hold in your hands. My thanks

to them.

List of Reviewers

Michael Aoki-Kramer

Rollin L. Baumgardner

Mark T. Bomberg

Pierre M. Busque

David E Cook

George E. Courville

William R. Farkas

Lixing Gu

Kielsgaard (Kurt) Hansen

Hartwig M. Kuenzel

Peter Lagus

Davis McElroy

Peter E. Nelson

Carsten Rode

William B. Rose

Walter J. Rossiter

Jacques Rousseau

Erwin L. Schaffer

Heinz R. Trechsel


Max H. Sherman

George E. Stern

William R. Strzepek

Heinz R. Trechsel

Martha G. Van Geem

Thomas J. Wallace

Iain S. Walker

David W. Yarbrough

Biographies of the Authors

Mark A. Albers

Mark A. Albers is the

principal scientist and

manager of the Ther-

mal Technology Labo-

ratories at the Johns

Manville Technical

Center near Denver, CO.

He has two B.S. in En-

gineering degrees, an

M.S. in Physics, and

the coursework for a

Ph.D. in Physics from

the Colorado School of

Mines. His interests

have involved theoreti-

cal modeling and ex-

perimental research in

thermal insulations and systems from cryogenic to refrac-

tory temperatures. More recently his research concerns

building physics and hygrothermal modeling. He has pub-

lished in the areas of vacuum and cryogenic thermal testing

as well as thermal radiation modeling in insulations. Mark

is chairman of ASTM C16.94 on Thermal Insulation Termi-

nology and is active in ASTM C16.30 on Thermal Measure-

ments. He is on the editorial board of the Journal of Thermal

Envelope & Building Science and is a member of the Ameri-

can Physical Society. His patents are in the areas of cryo-

genic insulations and radiative enhancement of glass fibers.

Doug Butch

Doug Burch currently

is an engineering con-

sultant with his com-

pany, Heat & Moisture

Analysis, Inc. He is

currently developing a

public-domain, two-

dimensional, heat and

moisture transfer

model. Mr. Butch

worked previously at

the National Institute

of Standards and Tech-

nology (NIST) for 28

years. While at NIST,

he served as project

leader on a wide range

of research projects in-

cluding: (1) measuring and predicting the effect of thermal


mass on the space heating and cooling loads of buildings;

(2) measuring the steady-state and dynamic heat transfer in

walls in a calibrated hot box; (3) conducting infrared ther-

mographic surveys of buildings to locate thermal anomalies

and quantify heat loss; (4) measuring the heat and moisture

properties of building materials; (5) measuring space heating

and cooling loads for buildings; and (6) conducting full-scale

experiments to measure the heat and moisture transfer in

attics and walls. Before retiring from NIST, Mr. Burch de-

veloped the public-domain, one-dimensional, heat and mois-

ture transfer model called MOIST (Release 3.0). Mr. Burch

has published 100 papers and reports in the technical liter-

ature. He received a B.S. in Electrical Engineering from the

Virginia Polytechnic Institute and State University in 1965.

Additionally, Mr. Burch received a M.S. in Mechanical En-

gineering from the University of Maryland in 1970.

Eric E E Burnett

Eric E R Burnett is

a structural engineer

with specialist compe-

tence in the broad

areas of building sci-

ence and technology,

building performance,

and structural con

crete. He has extensive

experience of the

building industry, hav-

ing been involved in

the design and con-

struction of buildings

on three continents.

He has worked with

and consulted a num-

ber of R and D agen-

cies in the United States, Canada, and elsewhere. Dr. Burnett

is currently the Bernard and Henrietta Hankin Chair at the

Pennsylvania State University. He is cross-appointed to the

Departments of Civil and Environmental Engineering and

Architectural Engineering. He is also the Director of the

Pennsylvania Housing Research Center. Both as an educator

and a researcher, Dr. Burnett was associated with the Uni-

versity of Waterloo for more than 25 years. He was Director

of the Building Engineering Group, as well as a Professor of

Civil Engineering. As senior Consultant and Technical Direc-

tor for Building Science and Rehabilitation Group, he was

involved with Trow Consulting Engineers Ltd. For more than

ten years. Dr. Burnett's current research interests are di-


rected at the performance of building enclosures, i.e., wall

systems, roofs, etc., and the integration of structural and

control (heat, air, moisture) functions. Recent projects have

involved reinforced polymer modified bitumen membranes,

FRP and PVC structural elements, masonry (brick veneer/

steel stud, tie systems, durability, etc.). A number of projects

have been directed at the wetting and drying mechanisms in

wall systems using a full-scale test facility. He has been in-

volved in the development of a number of building systems

in particular housing.

Donald G. CoUiver

Donald G. Colliver is

an Associate Professor

in the Biosystems and

Agricultural Engineer-

ing Department at the

University of Kentucky

in Lexington, Ky. He

has conducted exten-

sive research in energy

usage in residences, air

infiltration and venti-

lation, and the analysis

of climatological data

for determination of

design weather condi-

tions. Much of the

weather data research

has been done in sup-

port of research pro-

jects determining the

short-term extreme pe-

riods of temperature

and humidity and also in developing the tables of design

weather conditions in the ASHRAE Handbook--

Fundamentals. He has written numerous papers, articles,

and Handbook chapters and developed several weather anal-

ysis design tools that use historical data on CD-ROMs. Dr.

Colliver is a Registered Professional Engineer in the Com-

monwealth of Kentucky and an ASHRAE Fellow and Distin-

guished Service Award recipient. He has led numerous ASH-

RAE committees, the Education and Technology Councils,

and currently serves as Society Treasurer.

Andreas Hagen Holm

Andreas Hagen Holm

is Senior Research En-

gineer and head of the

modeling group within

the hygrothermal divi-

sion of the Fraunhofer-

Institut Bauphysik

(IBP). He finished Ex-

perimental Physics

with a Diploma (M.Sc.)

from the Technical

University of Munich,

Germany. Most re-

cently, he has been in-

volved mainly in the

development of the

computer code WUFI

and WUFI2D and its application for sensitivity and stochas-

tic analysis. He also worked on the combined effect of tem-

perature and humidity on the deterioration process of in-

sulation materials in EIFS, studied the phenomena of

moisture transport in concrete, and developed a new mea-

surement technique for detecting the salt and water distri-

butions in building material samples.

Achilles Karagiozis

Achilles Nick Kara-

giozis is a Senior Re-

search Engineer and

the Hygrothermal Pro-

ject Manager at the

Oak Ridge National

Laboratory, Building

Technology Center

(USA). He received a

Bachelor's degree and

a Master's degree in

Mechanical Engineer-

ing at UNB (CAN), a

second Master's Di-

ploma in Environmen-

tal and Applied Fluid

Dynamics at the yon

Karman Institute in

Fluid Dynamics (Bel-

gium), and a Ph.D. in

Mechanical Engineer-

ing at the University of

Waterloo (CAN). He has multi-disciplinary knowledge that

spans several important technical fields in building science.

Dr. Karagiozis is internationally considered a leader in build-

ing envelope thermal and moisture analysis. At NRCC (1991-

1999) Dr. Karagiozis was responsible for NRC's long-term

hygrothermal performance analysis of complex building sys-

tems. At NRCC he developed the LATENITE hygrothermal

model with Mr. Salonvaara (VTT) and was responsible for

the development of the WEATHER-SMART model, the

LATENITE hygrothermal pre- and post processor (LPPM)

model, and the LATENITE material property database sys-

tem model. At the Oak Ridge National LaboratolT (USA) he

has been developing the next generation of software simu-

lation packages for hygrothermal-durability analysis. In col-

laboration with Dr. Kuenzel and Mr. Holms (IBR Germany),

he co-developed the WUFI-ORNL/IBP model, a state-of-the-

art educational and application tool for architects and en-

gineers. At ORNL he developed MOISTURE-EXPERT, a

leading edge hygrothermal research model. Dr. Karagiozis is

actively participating in International Energy Agency Annex

24 (1992-1996), BETEC, CIB W40, ASHRAE T.C. 4.4, and

T.C. 4.2, ASTM E06 on Building Performance. He is also an

Adjunct Professor at the University of Waterloo and is col-

laborating with world-renown institutes (IBP and VTT) in

the area of hygrothermal-durability analysis. He is currently

involved in holistic building analysis, experimental hygroth-

ermal field monitoring, Stucco clad and EIFS performance,

crawlspace hygrothermal performance, and is developing

guidelines for performance of walls, roofs, and basements.

He has over 70 scientific publications in journals and trade


Hartwig Michael Kuenzel

Hartwig Michael

Kuenzel is head of the

hygrothermal division

of the Fraunhofer-

Institut Bauphysik

(IBP), the largest re-

search establishment

in Germany for build-

ing physics funded

mainly by industrial

contracts Having ac-

quired specific knowl-

edge in CFD modeling

at the University of Er-

langen, he concen-

trated on transient

heat and moisture

transfer in building

materials and compo-

nents since entering the IBP in 1987. The computer code

WUFI was developed during his Ph.D. thesis, defended at the

civil engineering faculty of the University of Stuttgart in

1994. In the same year he became Research Director at IBP

for hygrothermal modeling, laboratory, and field testing. He

has been active in many international projects (IEA Annex

14 &24), standard committees (ASHRAE, CEN), and contin-

uous education seminars. Dr. Kuenzel has published over

100 scientific articles in trade journals and text books. He is

chairing a European CEN working group that will produce

a standard for the application of heat and moisture simula-

tion tools in building practice.


Mavinkal K. Kumaran

Mavinkal K. Kumaran

(Kumar) is a Senior

Research Officer and a

Group Leader at the

Institute for Research

in Construction, the

National Research

Council of Canada. Dr.

Kumaran has an M.Sc.

in Pure Chemistry

from Kerala Univer-

sity, India (1967) and a Ph.D. in Thermodynamics from Uni-

versity College London, UK (1976). In 1967 he began his ca-

reer as a lecturer in chemistry. He joined NRC as a Research

Associate in the Division of Chemistry in 1981 and continued

to contribute to the field of thermodynamics of liquids and

liquid mixtures. He joined the Institute for Research in Con-

struction in 1984 and developed an internationally recog-

nized research group on hygrothermal analyses of buiIding

envelope materials and components. He has been leading

that group's activities since 1986. In recognition of his con-

tributions to building science and technology, he was

awarded a senior fellowship by the Japan Society for Pro-

motion of Science in 1992, and another senior fellowship by

the Kajima Foundation, Japan in 1996.

Carsten Rode

Carsten Rode earned a

Master of Science de-

gree in Civil Engineer-

ing in 1987. He ob-

tained a Ph.D. in the

same subject in 1990,

writing a thesis enti-

tled "Combined Heat

and Moisture Transfer

in Building Construc-

tions." Both degrees

were awarded by the

Technical University of

Denmark. He was a

guest researcher with

the Oak Ridge Na-

tional Laboratory in

1989. He is author of the program MATCH for combined

heat and moisture transfer in building constructions, which

is among the first such transient programs made available to

users outside the research community. He was senior re-

searcher with the Danish Building Research Institute from

1992-1996 and has been Associate Professor with the Tech-

nical University of Denmark since 1996. He has been a par-

ticipant in various international research projects, e.g., IEA

Annex 24 on Heat, Air and Moisture Transfer in Insulated

Envelope Parts, and the EU project COMBINE on Computer

Models for the Building Industry in Europe.


Mikael Salonvaara

HaiTi Mikael Salon-

vaara is a research sci-

entist in the Building

Physics and Indoor

Climate group at VTT

Building Technology,

which is one of the

nine research insti-

tutes of the Technical

Research Centre of

Finland. He finished

his Master's thesis at

Lappeenranta Univer-

sity of Technology in

1988 while already

working at VTT Build-

ing Technology in Es-

poo, Finland. The re-

sult of his thesis was

the two-dimensional heat, air, and moisture transfer model

TRATMO2. He worked for over two years (Nov. 1993-Jan.

96) as a guest researcher at the Institute for Research in Con-

struction (National Research Council of Canada) where he

developed the new heat, air, and moisture transfer simula-

tion model LATENITE with Dr. Karagiozis. He continued the

model development at VTT Building Technology as the

leader of "Calculation Tools" team. His expertise is heat, air,

and moisture transfer in buildings and building envelope

parts, effects of moisture on durability and service life, and

on emissions from building materials. He has published over

60 scientific and technical publications on hygrothermal per-

formance of buildings. He is active in national and interna-

tional technical committees and projects dealing with build-

ing envelope performance and indoor air quality.

John Straube

John Straube is in-

volved in the areas of

building enclosure de-

sign, moisture physics,

and whole building

performance as a

consultant, researcher,

and educatol: He is a

faculty member in the

Department of Civil

Engineering and the

School of Architecture

at the University of

Waterloo, where he

teaches courses in

structural design and

building science to

both disciplines. Re-

search interests in-

clude driving rain

measurement and control, pressure moderation, ventilation

drying, and full-scale natural exposure performance moni-

toring of enclosure systems, and hygrothermal computer

modeling of all the above. He has a broad experience in the

building industry, having been involved in the design, con-

struction, repair, and restoration of buildings in Europe,

Asia, the Caribbean, United States, and Canada. As a struc-

tural engineer he has designed with wood, hot-rolled and

cold-formed steel, concrete, masonry (brick, concrete, aer-

ated autoclaved concrete, natural stone), aluminum, poly-

mer concrete, carbon and glass FRP, fiber-reinforced con-

crete and structural plastics (PVC, nylon). He has been a

consultant to many building product manufacturers and sev-

eral government agencies (NRCC/IRC, NRCan, CMHC,

DOE, ORNL, PHRC) and is familiar with building-related

codes (e.g., NBCC, CSA, NECB, ACI, DIN, etc.) and stan-

dards (e.g., CSA, CGSB, ASTM, AAMA, ASHRAE) as well as

the measurement and testing procedures of the performance

of buildings and their components.

Anton TenWolde

Anton TenWolde is a

research physicist at

the USDA--Forest Ser-

vice, Forest Products

Laboratory in Madi-

son, Wisconsin. He is

Team Leader for the

Moisture Control in

Buildings Team, lo-

cated in the Engi-

neered Wood Products

and Structures Re-

search Work Unit. The

team's mission is to ex-

tend the service life of

wood products in

buildings through im-

proved building design

and operation. He holds an M.S. (Ingenieur) in Applied

Physics from the Delft University of Technology, Delft, the

Netherlands (1973), and an M.S. in Environmental Manage-

ment from the University of Wisconsin, Madison, Wisconsin

(1975). TenWolde is an active member of ASHRAE. He

chaired the revision of the 1997 ASHRAE Handbook of Fun-

damentals chapters on moisture control in buildings and is

chairman of ASHRAE Standard 160P, Design Criteria for

Moisture Control in Buildings. He has authored or co-

authored more than 45 articles and reports on moisture con-

trol in buildings.

Heinz R. Trechsel

Heinz R. Trechsel is a

graduate architect of

the Swiss Federal In-

stitute of Technology

in Z(irich and is a reg-

istered architect in the

state of New York. As

an independent con-

sultant, he investigates

and consults on mois-

ture problems in build-

ings, develops reme-

dial measures, and

serves as a witness in

cases related to mois-

ture problems in build-

ings. Trechsel also is a

staff architect with the

Engineering Field Activity Chesapeake of the Naval Facilities

Engineering Command. He was previously employed by the

National Bureau of Standards (now National Institute of

Standards and Technology), the Applied Research Labora-

tory of the United States Steel Corporation, and various ar-

chitectural firms in New York and in Europe. He is a mem-

ber of ASTM Committee E06 on Performance of Buildings

since 1961 and was a member of Committees C16 on Insu-

lations and D20 on Plastics.

George Tsongas

George Tsongas is a

private consulting en-

gineer specializing in

building science and

moisture problems in

buildings. After 29

years he retired re-

cently from his faculty

position in the Me-

chanical Engineering

Department at Port-

land State University

in Oregon and is now a

Professor Emeritus.

He has directed a num-

ber of field studies for

the U.S. DOE of mois-

ture problems in the

walls of new and exist-

ing site-built and manu-


factured homes. He also has investigated indoor air quality

problems inside existing and new residences, as well as ven-

tilation and dehumidification moisture control strategies. In

addition, he has completed extensive computer modeling of

the moisture performance of residential roofs, walls, and in-

door spaces. He has worked with Doug Burch to modify the

MOIST computer program algorithms, and has provided

training for NIST on the use of the MOIST software. In ad-

dition, he routinely is an expert witness in legal cases in-

volved with residential moisture problems. In that capacity

he has inspected many thousands of dwelling units for sid-

ing, wall, roof, floor, and indoor moisture problems. He also

has completed a number of laboratory studies of the mois-

ture performance of different types of siding, as well as wall

moisture intrusion and migration mechanisms. He has about

70 technical publications that include his work. Dr. Tsongas

received four engineering degrees from Stanford University.

Hannu u

Hannu Viitanen was

born in 1951 in Turku,

Finland and graduated

with a Master's degree

in biology from the

University of Turku in

1980. He obtained a

Doctor's degree at

SLU, Uppsala, Swe-

den, in 1996. He has

been a senior research

scientist at VTT Build-

ing Technology since

1980. He has worked

as a visiting professor

at the Finnish Forest

Research Institute

from 1996-98. His thesis focused on the modeling of critical

conditions of mold growth and decay development in

wooden materials. He has more than 120 publications in the

field. His expertise is wood preservation, mold growth on

wood, and decay problems in buildings. He has been in-

volved in consultation and training concerning conservation

and reparation of buildings. He has been an active member

of the International Research Group on Wood Preservation

since 1988 and has been a national representative in COST

E2, Wood Durability, WG1 since 1994.


by Mark Albers 1

2DHAV--a two-dimensional model by Janssens that allows

complex airflow paths like cracks, gaps, and permeable ma-


absolute humidity, (kg.m-3),(lb.ft-3)--the ratio of the mass

of water vapor to the total volume of the air sample. In SI

units, absolute humidity is expressed as kg/m 3. In inch-

pound units, absolute humidity is expressed as lb/ft 3.

absorption coefficient, (kg'm 2"s-1/2), (lb'ft-2"s-~/2)--the co-

efficient that quantifies the water entry into a building ma-

terial due to absorption when its surface is just in contact

with liquid water. It is defined as the ratio between the

change of the amount of water entry across unit area of the

surface and the corresponding change in time expressed as

the square root. In the early part of an absorption process

this ratio remains constant and that constant value is des-

ignated as the water absorption coefficient.

adsorption isotherm--the relationship between the vapor

pressure (or more often relative humidity, RH) of the sur-

roundings and the moisture content in the material when

adsorbing moisture at constant temperature.

air flux, (kg.m-2.s 1), (lb.ff-2.s l)__th e mass of air trans-

ported in unit time across unit area of a plane that is per-

pendicular to the direction of the transport.

air permeability, (kg.m- 1-pa- l-s- 1), (lb.ft ~.in.Hg- l.s- i)--the

ratio between the air flux and the magnitude of the pressure

gradient in the direction of the airflow.

air permeance, (kg-m-2.Pa-l.s-1), (lb.ft-Z.in.Hg-~.s 1)--the

ratio between the air flux and the magnitude of the pressure

difference across the bounding surfaces, under steady state


air retarder--a material or system that adequately impedes

airflow under specified conditions.

building envelope--the surrounding building structures

such as walls, ceilings, and floors that separate the indoor

environment from the outdoor environment.

capillarity--the movement of moisture due to forces of sur-

face tension within small spaces depending on the porosity

and structure of a material. Also known as capillary action.

Capillary-active--the term attributed to a material that ab-

sorbs water by capillary forces when in contact with liquid


1Thermal Technology Laboratories, Johns Manville Technical

Center, Denver, CO.


capillary conduction--the movement or transport of liquid

water through capillaries or very small interstices by forces

of surface tension or capillary pressure differences.

capillary pressure--the pressure or adhesive force exerted

by water in an enclosed space as a result of surface tension

because of the relative attraction of the molecules of the wa-

ter for each other and for those of the surrounding solid.

capillary saturation--see capillary saturation moisture con-


capillary saturation moisture content--the completely

saturated equilibrium moisture content of a material when

subjected to 100% RH. This is lower than the maximum

moisture content, due to air pockets trapped in the pore


capillary suction stress--the force associated with the neg-

ative capillary pressure resulting from changes in water con-

tent that produces a liquid transport flux.

capillary transfer--see capillary conduction.

capillary transport coefficient--see liquid transport coef-


condensation--the act of water vapor changing to liquid

water, or the resulting water.

critical moisture content--the lowest moisture content

necessary to initiate moisture transport in the liquid phase.

Below this level is considered the hygroscopic range where

moisture is transported only in the vapor phase.

CWEC--Canadian Weather year for Energy Calculations

data developed for 47 locations, available from Environment


CWEEDS--the Canadian Weather Energy and Engineering

Data Sets provide weather data for Canada.

degree of saturation--the ratio between the material mois-

ture content and the maximum moisture content that can be

attained by the material.

density of airflow rate--see air flux.

density of heat flow rate--see heat flux.

density of moisture flow rate--see moisture flux.

density of vapor flow rate--see vapor flux.

density, (kg.m-3), (lb.ft 3)--the mass of a unit volume of the

dry material. For practical reasons, the phrase "dry material"

does not necessarily mean absolutely dry material. For each

class of material, such as stony, wooden, or plastic, it may

e necessary to adopt prescribed standard conditions; for ex-

ample, for wood this may correspond to drying at 105~ un-

til the change in mass is within 1% during two successive

daily weighings.

desorption--the process of removing sorbed water by the

reverse of adsorption or absorption.

desorption isotherm--the relationship between the vapor

pressure (or more often relative humidity, RH) of the sur-

roundings and the moisture content in the material when

desorbing or removing moisture at a constant temperature.

There is often very little difference between this curve and

the adsorption isotherm.

dew point--the temperature at which air becomes saturated

when cooled without addition of moisture or change of pres-

sure; any further cooling causing condensation.

Dew Point Method--a manual design tool used for evalu-

ating the probability of condensation within exterior enve-

lopes by comparing calculated to saturation vapor pressures.

diffusion resistance factor--the ratio of the resistance to

water vapor diffusion of a material, and the resistance of a

layer of air of equal thickness.

DIM--a two-dimensional model by Grunewald that calcu-

lates transient heat, air, salt, and moisture transfer in porous


dry-bulb--see dry-bulb temperature.

dry-bulb temperature--the temperature read from a dry-

bulb thermometer.

EMPTIED--an acronym for Envelope Moisture Perform-

ance Through Infiltration Exfiltration and Diffusion, EMP-

TIED is a computer program to estimate moisture accumu-

lation using vapor diffusion and air leakage. The program is

useful in wetter and cooler climates. Developed by Hande-

gord for Canada Mortgage and Housing Corporation

(CMHC), it is available free.

equilibrium moisture content (EMC)--the balance of ma-

terial moisture content (MC) with ambient air humidity at

steady state.

fiber saturation point (FSP)--the moisture content at

which all free water from cell cavities has been lost but when

cell walls are still saturated with water.

Fick's Law--the law that the rate of diffusion of either vapor

or water across a plane is proportional to the negative of the

gradient of the concentration of the diffusing substance in

the direction perpendicular to the plane.

FRAME 4.0--a two-dimensional steady-state heat transfer

model widely used in North America and especially useful

for windows and other lightweight assemblies.

free saturation--see capillary saturation.

free water saturation--see capillary saturation.

FRET--a two-dimensional simulation program for FREez-

ing-Thawing processes by Matsumoto, Hokoi, and Hatano.

FSEC--a commercially available computer model from the

Florida Solar Energy Center simulating whole building prob-


lems involving energy, airflow, moisture, contaminants, and

air distribution systems.

(;laser Diagram--one of the first one-dimensional moisture

models using vapor diffusion only with steady-state bound-

ary conditions to predict condensation. It was originally pub-

lished in 1958-59 as a graphical method.

grain--the normal unit of weight used for small amounts of

water at 1/7000 of a pound (0.0648 grams).

HAM--combined Heat, Air, and Moisture analysis.

heat flux, (W.m 2), (Btu.ft-2.h-1)__the quantity of heat trans-

ported in unit time across unit area of a plane that is per-

pendicular to the direction of the transport.

HEAT2 and HEAT3--Swedish two- and three-dimensional

dynamic heat transfer analysis models that are commercially


HEATING 7.2--a heat transfer model program developed at

Oak Ridge National Laboratory (ORNL) which can be used

to solve steady-state and/or transient heat conduction prob-

lems in one-, two-, or three-dimensional Cartesian, cylindri-

cal, or spherical coordinates. (Oak Ridge, TN 37831).

HMTRA--a Heat and Mass TRAnsfer two dimensional

model by Gawin and Schrefler including soils, high temper-

atures, and material damage effects.

humidity ratio--the ratio of the mass of water vapor to the

mass of dry air contained in a sample. In inch-pound units,

humidity ratio is expressed as grains of water vapor per

pound of dry air (one grain is equal to 1/7000 of a pound)

or as pounds of water vapor per pound of dry air. In SI units,

humidity ratio is expressed as grams (g) of water vapor per

kilogram (kg) of dry air. (Using the pound per pound units

in the inch-pound system has the advantage that the ratio is

nondimensional and will be the same for the SI and inch-

pound systems. In this case the ratio would also be called

the specific humidity.)

hydraulic conductivity, (kg.s l-m 1.Pa 1), (lb.s-l.ft 1.in '

Hg 1)--the time rate of steady state water flow through a

unit area of a material induced by a unit suction pressure

gradient in a direction perpendicular to that unit area.

hydrostatic--the physics concerning the pressure and equi-

librium of water at rest.

hygroscopic--attracting or absorbing moisture from the air.

hygroscopic range--the range of RH in a material where

the moisture is still only in an adsorbed state. This varies

with material but is usually up to about 98% RH.

hygrothermal analysis--the study of a system involving

coupled heat and moisture transfer.

IEA Annex 24--part of the International Energy Agency

which publishes documents ("Heat, Air and Moisture Trans-

fer in Insulated Envelope Parts") through the participation

of leading physicists and engineers working in this area from

around the world.

Kieper Diagram--a simple one-dimensional steady-state

moisture model introduced in 1976 using vapor diffusion

only to predict condensation.


LATENITE--a one-, two-, or three-dimensional computer

model developed by Karagiozis and Salonvaara. Likely the

most comprehensive heat air and moisture model available.

It is not available for general use.

liquid conduction coefficient, (m2"s-1), (ft2.s-l)--the pro-

portionality constant or transport property that taken times

the gradient of RH gives the resulting liquid flux.

liquid conductivity--see hydraulic conductivity.

liquid diffusivity--see liquid conduction coefficient or liq-

uid transport coefficient.

liquid transport coefficient, (m2-s-1), (ftE-s l)--the multi-

plier or proportionality constant in the diffusion equation

between the gradient of water content and the resulting liq-

uid transport flux.

liquid transport flux, (kg.m-2.s-l), (Ib.ft-2.s 1)--the amount

and rate of liquid movement through a given area or plane.

MATCH--a one-dimensional computer model by Carsten

Rode that is similar to MOIST and uses both sorption and

suction curves to define the moisture storage function. It is

commercially available.

maximum moisture content--the building material mois-

ture content that corresponds to the saturation state where

the open pores are completely filled with water. This is avail-

able only experimentally in a vacuum.

maximum water content--see maximum moisture content.

MDRY--a Moisture Design Reference Year weather data set

that reflects more severe weather conditions perhaps seen

one out of ten years.

MOIST a free public domain one-dimensional thermal and

moisture transfer model and computer program developed

by Burch while at the U.S. National Institute of Standards

and Technology (NIST).

moisture content (MC)--the moisture content of a building

material can be defined as either (i) the mass of moisture

per unit volume of the dry material [all building materials],

or (ii) the mass of moisture per unit mass of the dry material

[denser materials], or (iii) the volume of condensed moisture

per unit volume of the dry material [lighter materials].

moisture diffusivity, (m2.s 1), (ft2.s-l)__the moisture diffu-

sivity in the hygroscopic range is the ratio between vapor

permeability and volumetric moisture capacity. Outside that

range it is the ratio between moisture permeability and vol-

umetric moisture capacity.

moisture flux, (kg.m-2.s-1)--the mass of moisture trans-

ported in unit time across unit area of a plane that is per-

pendicular to the direction of the transport.

moisture load--the amount of moisture added to an envi-

ronment fi'om various sources.

moisture permeability, (kg-m-l-Pa-l-s-1), (lb-ft-l.in.Hg -~

9 s-~)--the ratio between the moisture flux and the magnitude

of suction gradient in the direction of the flow. Suction includes

capillarity, gravity, and external pressure.

moisture storage function--the function describing the re-

lationship between the ambient relative humidity and the

absorbed moisture, composed of sorption isotherms (up to

-95% RH), and suction isotherms (above -95% RH).

MOISTWALL--a one-dimensional computer model devel-

oped at the Forest Products Laboratory that is a numerical

version of the Kieper Diagram based on vapor diffusion only.

MOISTWALL2--a one-dimensional computer model with

the effect of airflow added to the original MOISTWALL

model vapor diffusion.

NCDC--the National Climatic Data Center, which is a source

of detailed hourly historical weather data.

open porosity, (m3.m-3), (ft3.ft-3)--the volume of pores per

unit volume of the material accessible for water vapor.

performance threshold--the conditions under which a ma-

terial or assembly will cease to perform as intended.

perm--the unit of vapor permeance, defined as the mass

rate of water vapor flow through one square foot of a ma-

terial or construction of one grain per hour induced by a

vapor pressure gradient between two surfaces of one inch of

mercury (or in other units that equal that flow rate).

permeance coefficient--see vapor permeance.

porosity--the ratio, usually expressed as a percentage, of the

volume of a material's pores to its total volume.

psychrometric chart--a graph where each point represents

a specific condition of an air and water vapor system with

regard to temperature, absolute humidity, relative humidity,

and wet-bulb temperature.

relative humidity--the ratio, at a specific temperature, of

the actual moisture content of the air sample, and the mois-

ture content of the air sample if it were at saturation. It is

given as a percentage.

rep--the unit of water vapor resistance equal to 1/perm.

RH--relative humidity.

SAMSON--the Surface Airways Meteorological and Solar

Observing Network, a source of historical hourly weather

data for the United States.

saturated air--moist air in a state of equilibrium with a

plane surface of pure water at the same temperature and

pressure, that is, air whose vapor pressure is the saturation

vapor pressure and whose relative humidity is 100%.

saturation curve--the psychrometric curve through differ-

ent temperatures and pressures that represents the dew

point or 100% RH.

saturation point--the point at a given temperature and

pressure where the air is saturated with moisture and the

relative humidity is 100%.

saturation vapor pressure--the vapor pressure that is in

equilibrium with a plane surface of water.

SHAM--a Simplified Hygrothermal Analysis Method that

extends EMPTIED's model with guidance on things like driv-

ing rain and solar radiation.

SIMPLE FULUV--a two-dimensional model by Okland de-

veloped to investigate convection in timber frame walls.

sling psychrometer--a device consisting of both a wet-bulb

and a dry-bulb thermometer on a handle allowing whirling

in the air in order to determine the moisture content or rel-

ative humidity of the air.

sorption--the general term used to encompass the processes

of adsorption, absorption, and desorption.

sorption curve--see sorption isotherm.

sorption isotherm--the relationship between the vapor

pressure (or more often relative humidity, RH) of the sur-

roundings and the moisture content in a material at a con-

stant temperature. Since the hysteresis between the adsorp-

tion and desorption isotherms is usually not very

pronounced, the adsorption isotherm or a mean isotherm is

often used.

specific heat capacity, (J'kg - I'K- 1), (Btu.lb - 1.F- ~ )--the heat

(energy) required to increase the temperature of a dry unit

mass of a material by 1 degree.

specific humidity--the ratio of the mass of water vapor to

the total mass of the dry air. In inch-pound units, specific

humidity is expressed as pounds of water vapor per pounds

of dry air. In SI units, specific humidity is expressed as

kilograms of water vapor per kilogram of dry air. Because

specific humidity is a ratio, and if both the mass of water

vapor and the mass of the dry air are measured in the same

units (pounds in inch-pound units, kilograms in SI units),

the numerical values are the same for inch-pound and for SI

units. However, some tables and charts show inch-pound

units as grains per pound and metric units as grams per kil-


specific moisture capacity, (kg.kg-l.pa-1), (lb.lb 1.in

.Hg 1)--the increase in the mass of moisture in a unit mass

of the material that follows a unit increase in vapor pressure

or suction.

stack effect--temperature and resulting pressure differ-

ences between a building exterior and interior that drives air

infiltration or exfiltration.

suction curve--see suction isotherm.

suction isotherm--the relationship between the capillary

suction pressure and the moisture content in a material at a

constant temperature.

TCCC2D--the Transient Coupled Convection and Conduc-

tion in 2D structures, an advanced model by Ojanen that also

predicts mold growth.

TCCD2--the Transient Coupled Convection and Diffusion 2

Dimensional model, an improvement built upon Kohonen's

model, mainly used for framed building walls.

THERM 2.0--a two-dimensional steady-state heat transfer

model widely used in North America and especially useful

for windows and other lightweight assemblies.

thermal conductivity, (W'm I'K 1), (Btu.ft-l.h-l.F 1) or

(Btu'in'fl 2"h I'F 1)--the time rate of steady state heat flow

through a unit area of a homogeneous material induced by


a unit temperature gradient in a direction perpendicular to

that unit area.

thermal diffusivity, (m2.s 1), (fti.s 1)__th e ratio between the

thermal conductivity and the volumetric heat capacity of the


thermal moisture diffusion coefficient, (mi.K I'S-1),

(ft2"F-J's 1)--the ratio between the thermal moisture per-

meability and the dry density.

thermal moisture permeability, (kg.m 1.K 1.s-1), (lb.ft 1

9 F-l-s-~)--the ratio between the moisture flux and the mag-

nitude of the temperature gradient in the direction of the

transport in the absence of any moisture content gradient.

thermal resistance, (K.m2.W 1), (F.fta.h.Btu 1)__th e quan-

tity determined by the steady state temperature difference

between two defined surfaces of a material or construction

that induces a unit heat flow rate through a unit area.

TMY--Typical Meteorological Year data produced for build-

ing energy analysis.

TMY2--an updated set of TMY data for 239 US cities which

is available from the National Renewable Energy Laboratory


TOOLBOX--a public domain computer program on the psy-

chrometric charts and thermodynamic properties of moist


tortuosity factor--the ill-defined degree of being tortuous

or full of twists, turns, curves, or windings relating to the

microscopic interstices of a material.

transport coefficient--the proportionality constant in a dif-

fusion equation, which taken times the gradient, gives the

transport flux or flow density.

TRATMO--the TRansient Analysis code for Thermal and

MOisture physical behaviors of constructions was developed

by Kohonen and was one of the first computerized building

enclosure models.

TRATMO2--TRansient Analysis of Thermal and MOisture

behavior of 2-D structures, by Salonvaara. This advanced

model considers convection and radiation in porous mate-


vapor concentration, (kg.m-3), (lb.ft-3)--the vapor content

in a given volume of air (or volume of air in the pores of a

building material), defined as the ratio between the mass of

water vapor in that volume, and the volume.

vapor diffusion--the movement of water vapor through ma-

terials and systems driven by the vapor pressure differences

or gradient.

vapor diffusion coefficient, (s)--the same as vapor per-

meability; however, permeability is usually expressed in Eng-

lish units (perm.in), while the diffusion coefficient is usually

expressed in metric units (s).

vapor diffusion thickness, (m), (ft)--the product of a spec-

imen thickness and the vapor resistance factor of the mate-



vapor flux, (kg.m-2.s 1), (lb.ft-2.s-l)__the mass of vapor

transported in unit time across unit area of a plane that is

perpendicular to the direction of the transport.

vapor permeability, (ng-s-l.m-l.pa-1), (gr.h-~'ft-l.in.Hg -1)

or (perm.in)--the time rate of water vapor transmission

through a unit area of fiat material of unit thickness induced

by a unit water vapor pressure difference between its two

surfaces. In inch-pound units, permeability is given in grains

of water per hour for each square foot of area divided by the

inches of mercury of vapor pressure difference per thickness

in feet (gr/h-ft.in.Hg). In SI units, permeability is given as

nanograms of water per second for each square meter of

area divided by the Pascals of vapor pressure difference per

thickness in meters (ng/s.m-Pa).

vapor permeance (ng.s-l-m-2-pa-l), (gr.h-l.fl-2.in.Hg -1) or

(perm)--the time rate of water vapor transmission through

unit area of flat material induced by unit water vapor pres-

sure difference between its two surfaces. In inch-pound

units, permeance is given in the unit "perm," where one

perm equals a transmission rate of one grain of water per

hour for each square foot of area per inch of mercury (gr/

h.ft2.in.Hg). (A grain is 1/7000 of a pound.) There is no direct

SI equivalent to the penn. However, one perm equals a flow

rate of 57 nanograms of water per second for each square

meter of area and each Pascal of vapor pressure (ng/


vapor pressure, (Pa), (in.Hg)--the partial pressure exerted

by the vapor at a given temperature, also stated as the com-

ponent of atmospheric pressure contributed by the presence

of water vapor. In inch-pound units, vapor pressure is given

most frequently in inches of mercury (in,Hg); in SI units wa-

ter vapor pressure is given in Pascals (Pa).

vapor resistance and resistivity--the reciprocals of per-

meance and permeability. The advantage of the use of re-

sistance and resistivity is that in an assembly or sandwich of

a construction the resistances and resistivities of the individ-

ual layers can be added to arrive at the resistance or resis-

tivity of an assembly, while permeances and permeabilities

can not be so added.

vapor resistance factor, (dimensionless)--the ratio between

the vapor permeability of stagnant air and that of the ma-

terial under identical thermodynamic conditions (same tem-

perature and pressure).

vapor resistivity--see vapor resistance and resistivity.

vapor retarder--a material or system that adequately im-

pedes the transmission of water vapor under specified con-


volumetric heat capacity, (J.m 3.K-1), (Btu'ft-3"F-l)--the

heat (energy) required to increase the temperature of a dry

unit volume of the material by one degree.

volumetric moisture capacity, (kg'm-3"pa-1), (lb-ft-3"in

.Hg-1)--the increase in the moisture content in a unit vol-

ume of the material that follows a unit increase in the vapor

pressure or suction. For the hygroscopic range, volumetric

moisture capacity can be calculated from the slope of the

sorption curve, and above critical moisture content it can be

calculated as the slope of the suction curve.

WALLDRY--a simple model of the drying of framed wall

assemblies using moisture transport by vapor diffusion only.

water absorption coefficient--see absorption coefficient.

water vapor content--see vapor concentration.

water vapor diffusion--see vapor diffusion.

water vapor diffusion coefficient--see vapor diffusion co-


water vapor diffusion resistance--see vapor resistance.

water vapor permeability--see vapor permeability.

water vapor permeance--see vapor permeance.

water vapor pressure--see vapor pressure.

water vapor resistance--see vapor resistance,

water vapor resistivity--see vapor resistivity.

wet-bulb--see wet-bulb temperature.

wet-bulb temperature--the temperature read from a wet-

bulb thermometer resulting from the cooling due to evapo-

ration from its surface.

WUFI--a one- or two-dimensional computer model devel-

oped by Hartwig Kuenzel at the Fraunhofer Institut fuer

Bauphysik. The model incorporates driving rain, has stable

calculations, is easy to use, is well validated with field data,

and is commercially available.

WUFI/ORNL/IBP--a one- or two-dimensional advanced

computer model originally developed by Kuenzel but ex-

tended in a joint research collaboration between Oak Ridge

National Laboratory (ORNL) and the Fraunhofer Institute

for Building Physics (IBP).

WUFIZ--a two-dimensional version of the WUFI computer


WYEC--the Weather Year for Energy Calculations data con-

sists of one year of hourly weather data produced by ASH-


WYEC2--the revised and improved WYEC data for 52 lo-

cations in the US and 6 locations in Canada.

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