Astm mnl 40 2001

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 an

Moisture Analysis and Condensation Control in Building Envelopes

Heinz R Trechsel, Editor

Library of Congress Cataloging-in-Publication Data

Moisture analysis a n d c o n d e n s a t i o n c o n t r o l i n b u i l d i n g e n v e l o p e s / H e i n z R Trechsel, editor

p c m - - ( M N L ; 40)

"ASTM stock n u m b e r : MNL40."

I n c l u d e s b i b l i o g r a p h i c a l references a n d index

ISBN 0-8031-2089-3

1 Waterproofing 2 D a m p n e s s i n buildings 3 Exterior walls I Trechsel,

H e i n z R II ASTM m a n u a l series; MNL40

TH9031.M635 2001

CIP

Copyright 9 2001 AMERICAN SOCIETY FOR TESTING AND MATERIALS, West Conshohocken,

PA All rights reserved This material may not be reproduced or copied, in whole or in part, in any printed, mechanical, electronic, film, or other distribution and storage media, without the written consent of the publisher

P h o t o c o p y R i g h t s

A u t h o r i z a t i o n to p h o t o c o p y i t e m s for internal, personal, or e d u c a t i o n a l c l a s s r o o m use, or

t h e internal, p e r s o n a l , or e d u c a t i o n a l c l a s s r o o m u s e of specific clients, is granted by the American Society for Testing a n d Materials (ASTM) provided that the a p p r o p r i a t e f e e is paid to t h e Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923; Tel: 978-

750-8400; online: http://www.copyright.com/

NOTE: This manual does not purport to address all of the safety concerns, if any, associated with its use It is the responsibility of the user of this manual to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use

Printed in Philadelphia, PA

2001

Contents

Chapter 1 Moisture Primer

Chapter 2 Weather Data

Chapter 3 Hygrothermal Properties of Building Materials

Chapter 4 Failure Criteria

Chapter 5 Overview of Hygrothermal (HAM) Analysis Methods

Chapter 6 Advanced Numerical Models for Hygrothermal Research

Chapter 7 - - M a n u a l Analysis Tools

Chapter 8 MOIST: A Numerical Method for Design

Chapter 9 A Hygrothermal Design Tool for Architects and Engineers

(WUFI ORNL/IBD)

Chapter 10 A Look to the Future

A p p e n d i x 1 - - C o m p u t e r Models 161

A p p e n d i x 2 Installation Instructions 185

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

t 994

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

of Building Sciences, Washington, DC

v i i i M A N U A L O N M O I S T U R E A N A L Y S I S I N B U I L D I N G S

ing r e s e a r c h o r g a n i z a t i o n s , h o m e b u i l d e r s , t r a d e a s s o c i a t i o n s , a n d m o r t g a g e finance

e x p e r t s o n the issue o f c o n d e n s a t i o n c o n t r o l in d w e l l i n g c o n s t r u c t i o n 4 The focus of the m e e t i n g was o n v a p o r d i f f u s i o n in one- a n d t w o - f a m i l y f r a m e dwellings in cold

w e a t h e r climates The c o n s e n s u s a n d r e s u l t of t h a t m e e t i n g was the P r e s c r i p t i v e Rule

to p l a c e a v a p o r b a r r i e r ( n o w c a l l e d a v a p o r r e t a r d e r ) o n the w a r m side of the t h e r m a l

i n s u l a t i o n in c o l d climates The m e e t i n g also e s t a b l i s h e d t h a t a v a p o r b a r r i e r ( r e t a r d e r )

m e a n s a m e m b r a n e o r c o a t i n g w i t h a w a t e r v a p o r p e r m e a n c e of one P e r m o r less One

P e r m is 1 g/h'ft2"in.Hg (57 ng/s'm2-pa) The rule w a s p r o m u l g a t e d t h r o u g h t h e FHA

M i n i m u m P r o p e r t y S t a n d a r d s ? It still is r e f e r e n c e d u n c h a n g e d in s o m e c o n s t r u c t i o n

d o c u m e n t s The 1948 rule was b a s e d on the a s s u m p t i o n t h a t d i f f u s i o n t h r o u g h envelope m a t e - rials a n d s y s t e m s is the g o v e r n i n g m e c h a n i s m of m o i s t u r e t r a n s p o r t l e a d i n g to con-

d e n s a t i o n in a n d e v e n t u a l d e g r a d a t i o n of t h e b u i l d i n g envelope Since 1948, a n d par-

t i c u l a r l y since a b o u t 1975, r e s e a r c h c o n d u c t e d in this c o u n t r y a n d a b r o a d h a s b r o u g h t

r e c o g n i t i o n t h a t infiltration of h u m i d a i r into b u i l d i n g wall cavities a n d t h e l e a k a g e of

r a i n w a t e r a r e significant, in m a n y cases g o v e r n i n g m e c h a n i s m s of m o i s t u r e t r a n s p o r t Accordingly, t h e o r i g i n a l s i m p l e rule w i t h a l i m i t e d s c o p e h a s b e e n e x p a n d e d to i n c l u d e

a i r i n f i l t r a t i o n a n d r a i n w a t e r leakage, a n d to c o v e r o t h e r c l i m a t e s a n d b u i l d i n g a n d

c o n s t r u c t i o n types The current, e x p a n d e d p r e s c r i p t i v e rules c a n be s u m m a r i z e d as follows:

9 install a v a p o r r e t a r d e r o n the i n s i d e of the i n s u l a t i o n in c o l d climates,

9 install a v a p o r r e t a r d e r o n the o u t s i d e of the i n s u l a t i o n in w a r m climates,

9 p r e v e n t o r r e d u c e a i r infiltration,

9 p r e v e n t o r r e d u c e r a i n w a t e r leakage, a n d

9 p r e s s u r i z e o r d e p r e s s u r i z e the b u i l d i n g so as to p r e v e n t w a r m , m o i s t a i r f r o m en-

t e r i n g the b u i l d i n g envelope

The c u r r e n t e x p a n d e d rules have g r e a t l y i n c r e a s e d the v a l i d i t y a n d u s e f u l n e s s of the

p r e s c r i p t i v e rules However, the rules still do n o t fully r e c o g n i z e the c o m p l e x i t i e s of the m o v e m e n t of m o i s t u r e a n d h e a t in b u i l d i n g envelopes F o r e x a m p l e :

9 The e m p h a s i s o n e i t h e r i n c l u d i n g o r d e l e t i n g a s e p a r a t e v a p o r r e t a r d e r is m i s p l a c e d ,

a n d t h e c o n t r i b u t i o n of t h e h y g r o t h e r m a l p r o p e r t i e s of o t h e r e n v e l o p e m a t e r i a l s on the m o i s t u r e flow a r e n o t c o n s i d e r e d I n fact, i n c o r r e c t l y p l a c e d v a p o r r e t a r d e r s m a y increase, r a t h e r t h a n decrease, the p o t e n t i a l for m o i s t u r e d i s t r e s s in b u i l d i n g enve- lopes

9 Climate as the o n l y d e t e r m i n i n g f a c t o r is i n a d e q u a t e to e s t a b l i s h w h e t h e r a v a p o r

r e t a r d e r s h o u l d o r s h o u l d n o t b e installed I n d o o r relative h u m i d i t y a n d the

m o i s t u r e - r e l a t e d p r o p e r t i e s of all e n v e l o p e layers m u s t also be c o n s i d e r e d

9 The two c l i m a t e c a t e g o r i e s "cold" a n d "warm" have never b e e n a d e q u a t e l y o r con-

s i s t e n t l y defined, a n d large a r e a s of the c o n t i g u o u s U n i t e d S t a t e s do n o t fall u n d e r

e i t h e r c o l d o r w a r m climates, h o w e v e r defined F o r example, ASHRAE, 6 in 1993,

u s e d c o n d e n s a t i o n zones b a s e d o n d e s i g n t e m p e r a t u r e s F o r c o l d weather, L s t i b u r e k 7 suggests 4000 H e a t i n g Degree Days o r m o r e , a n d t h e U.S D e p a r t m e n t o f A g r i c u l t u r e s uses a n a v e r a g e J a n u a r y t e m p e r a t u r e of 35~ o r less F o r w a r m climates, A S H R A E 9

e s t a b l i s h e d c r i t e r i a b a s e d on t h e n u m b e r of h o u r s t h a t t h e w e t b u l b t e m p e r a t u r e exceeds c e r t a i n levels, O d o m 1~ suggests average m o n t h l y l a t e n t l o a d g r e a t e r t h a n

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 edition)

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

PREFACE ix

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

18

ANALYTICAL M E T H O D S A N D M O D E L S A N D

T H E I R LIMITATIONS

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, m u c h 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

x M A N U A L O N M O I S T U R E A N A L Y S I S I N B U I L D I N G S

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:

W e a t h e r 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

C O N C L U S I O N S

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

Acknowledgments

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 appreciation

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

Davis McElroy Peter E Nelson Carsten Rode William B Rose Walter J Rossiter Jacques Rousseau Erwin L Schaffer

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

M a r k A A l b e r s

Mark A Albers is the

principal scientist and

manager of the Ther-

mal Technology Labo-

ratories at the Johns

M a n v i l l e T e c h n i c a l

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

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

genic insulations and radiative enhancement of glass fibers

D o u g B u t c h

Doug Burch currently

is an engineering con-

sultant with his com-

pany, Heat & Moisture

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

E r i c E E B u r n e t t

Eric E R Burnett is

a structural engineer with specialist compe- tence in the broad areas of building sci- ence and technology, building performance,

a n d s t r u c t u r a l c o n crete He has extensive

e x p e r i e n c e o f t h e 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-

x v

x v i M A N U A L O N M O I S T U R E A N A L Y S I S I N B U I L D I N G S

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 b i t u m e n membranes,

FRP and PVC structural elements, masonry (brick veneer/

steel stud, tie systems, durability, etc.) A n u m b e r 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 n u m b e r of building systems

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

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 n u m e r o u s ASH-

RAE committees, the Education and Technology Councils,

and currently serves as Society Treasurer

Andreas Hagen Holm

Andreas Hagen H o l m

is Senior Research En- gineer and head of the modeling group within the hygrothermal divi- sion of the Fraunhofer-

I n s t i t u t B a u p h y s i k (IBP) He finished Ex-

p e r i m e n t a l P h y s i c s with a Diploma (M.Sc.)

f r o m t h e T e c h n i c a l University of Munich,

G e r m a n y M o s t r e - cently, he has been in- volved mainly in the

d e v e l o p m e n t o f t h e 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 p h e n o m e n a 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

giozis is a Senior Re- search Engineer and the Hygrothermal Pro- ject Manager at the

O a k R i d g e N a t i o n a l

L a b o r a t o r y , B u i l d i n g

T e c h n o l o g y C e n t e r (USA) He received a Bachelor's degree and

a Master's degree in Mechanical Engineer- ing at UNB (CAN), a

ploma in Environmen- tal and Applied Fluid Dynamics at the yon

K a r m a n 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-

B I O G R A P H I E S OF THE A U T H O R S xvii

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

contracts Having ac-

quired specific knowl-

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 C o n s t r u c t i o n , the

N a t i o n a l R e s e a r c h Council of Canada Dr

Kumaran has an M.Sc

in P u r e C h e m i s t r y 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 R o d e

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." B o t h degrees were awarded by the Technical University of Denmark He was a guest researcher with

t h e O a k R i d g e N a - 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

xviii M A N U A L O N M O I S T U R E A N A L Y S I S I N B U I L D I N G S

Mikael Salonvaara

HaiTi Mikael Salon-

vaara is a research sci-

entist in the Building

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,

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

M o i s t u r e C o n t r o l in

B u i l d i n g s Team, lo-

c a t e d in t h e E n g i - neered Wood Products

a n d S t r u c t u r e s Re- search Work Unit The team's mission is to ex- tend the service life of

w o o d p r o d u c t s 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 o f 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

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-

d i a l m e a s u r e s , a n d

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

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

H a n n u 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

R e s e a r c h I n s t i t u t e 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

Glossary

by Mark Albers 1

2DHAV a two-dimensional model by Janssens that allows

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

terials

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 k g / m 3 In inch-

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

a b s o r p t i o n 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 i s o t h e r m - - t h e 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 p e r m e a n c e , (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

conditions

air retarder a material or system that adequately impedes

airflow under specified conditions

building e n v e l o p e - - t h e 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

water

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 s a t u r a t i o n - - s e e capillary saturation moisture con- tent

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 structure

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 t r a n s f e r - - s e e capillary conduction

capillary t r a n s p o r t c o e f f i c i e n t - - s e e liquid transport coef- ficient

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 Canada

C W E E D S - - t h e 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 o f airflow r a t e - - s e e air flux

density of heat flow r a t e - - s e e heat flux

density of moisture flow r a t e - - s e e moisture flux

density of vapor flow r a t e - - s e e 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

x x

G L O S S A R Y xxi

be 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

d e s o r p t i o n - - t h e process of removing sorbed water by the

reverse of adsorption or absorption

d e s o r p t i o n i s o t h e r m - - t h e 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

when cooled without addition of moisture or change of pres-

sure; any further cooling causing condensation

Dew Point M e t h o d - - 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

D I M - - a two-dimensional model by Grunewald that calcu-

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

materials

dry-bulb t e m p e r a t u r e - - t h e temperature read from a dry-

bulb thermometer

E M P T I E D - - a n 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

e q u i l i b r i u m moisture content (EMC) the balance of ma-

terial moisture content (MC) with ambient air humidity at

steady state

fiber saturation point ( F S P ) - - t h e moisture content at

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

cell walls are still saturated with water

Fick's L a w - - t h e 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 s a t u r a t i o n - - s e e capillary saturation

F R E T - - a two-dimensional simulation program for FREez-

ing-Thawing processes by Matsumoto, Hokoi, and Hatano

F S E C - - 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 D i a g r a m - - o n e 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

g r a i n - - t h e normal unit of weight used for small amounts of water at 1/7000 of a pound (0.0648 grams)

H A M - - c o m b i n e d 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 a n d HEAT3 Swedish two- and three-dimensional dynamic heat transfer analysis models that are commercially available

HEATING 7 2 - - a heat transfer model program developed at Oak Ridge National Laboratory (ORNL) which can be used

to solve steady-state a n d / o r transient heat conduction prob- lems in one-, two-, or three-dimensional Cartesian, cylindri- cal, or spherical coordinates (Oak Ridge, TN 37831)

H M T R A - - a Heat and Mass TRAnsfer two dimensional model by Gawin and Schrefler including soils, high temper- atures, and material damage effects

h u m i d i t y r a t i o - - t h e 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

librium of water at rest

h y g r o s c o p i c - - a t t r a c t i n g or absorbing moisture from the air

hygroscopic r a n g e - - t h e 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

h y g r o t h e r m a l a n a l y s i s - - t h e study of a system involving coupled heat and moisture transfer

IEA Annex 2 4 - - p a r t 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 D i a g r a m - - a simple one-dimensional steady-state moisture model introduced in 1976 using vapor diffusion only to predict condensation

xxii MANUAL ON M O I S T U R E ANALYSIS I N B U I L D I N G S

L A T E N I T E - - 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 t r a n s p o r t 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

m a x i m u m 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

m a x i m u m water c o n t e n t - - s e e 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)

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

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

pendicular to the direction of the transport

moisture l o a d - - t h e amount of moisture added to an envi-

ronment fi'om various sources

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

of suction gradient in the direction of the flow Suction in-

cludes capillarity, gravity, and external pressure

moisture storage f u n c t i o n - - t h e function describing the re- lationship between the ambient relative humidity and the absorbed moisture, composed of sorption isotherms (up to

- 9 5 % RH), and suction isotherms (above - 9 5 % 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 t h r e s h o l d - - t h e conditions under which a ma- terial or assembly will cease to perform as intended

p e r m - - t h e 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 c o e f f i c i e n t - - s e e vapor permeance

porosity the ratio, usually expressed as a percentage, of the volume of a material's pores to its total volume

psychrometric c h a r t - - 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 h u m i d i t y - - t h e 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

r e p - - t h e 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 a i r - - m o i s t 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 c u r v e - - t h e psychrometric curve through differ- ent temperatures and pressures that represents the dew point or 100% RH

saturation p o i n t - - t h e point at a given temperature and pressure where the air is saturated with moisture and the relative humidity is 100%

equilibrium with a plane surface of water

S H A M - - a Simplified Hygrothermal Analysis Method that extends EMPTIED's model with guidance on things like driv- ing rain and solar radiation

sorption isotherm the r e l a t i o n s h i p b e t w e e n the v a p o r

p r e s s u r e (or m o r e often relative humidity, RH) of t h e sur-

specific humidity the r a t i o of the m a s s of w a t e r v a p o r to

the t o t a l m a s s of t h e d r y air I n i n c h - p o u n d units, specific

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

(Btu'in'fl 2"h I'F 1) the t i m e r a t e of s t e a d y state h e a t flow

(ft2"F-J's 1) the r a t i o b e t w e e n the t h e r m a l m o i s t u r e per-

m e a b i l i t y a n d t h e d r y density

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

9 F - l - s - ~ ) - - t h e r a t i o b e t w e e n the m o i s t u r e flux a n d the m a g -

T M Y 2 - - a n u p d a t e d set of TMY d a t a for 239 US cities w h i c h

is a v a i l a b l e f r o m t h e N a t i o n a l R e n e w a b l e E n e r g y L a b o r a t o r y (NREL)

T O O L B O X - - a p u b l i c d o m a i n c o m p u t e r p r o g r a m o n t h e psy-

c h r o m e t r i c c h a r t s a n d t h e r m o d y n a m i c p r o p e r t i e s of m o i s t air

tortuosity factor the ill-defined d e g r e e of b e i n g t o r t u o u s

o r full of twists, turns, curves, o r w i n d i n g s r e l a t i n g to t h e

m i c r o s c o p i c i n t e r s t i c e s of a m a t e r i a l

transport coefficient the p r o p o r t i o n a l i t y c o n s t a n t in a dif-

f u s i o n e q u a t i o n , w h i c h t a k e n t i m e s the g r a d i e n t , gives t h e

t r a n s p o r t flux o r flow density

T R A T M O - - t h e T R a n s i e n t Analysis code for T h e r m a l a n d

e x p r e s s e d in m e t r i c u n i t s (s)

vapor diffusion thickness, (m), ( f t ) - - t h e p r o d u c t of a spec-

i m e n t h i c k n e s s a n d the v a p o r r e s i s t a n c e f a c t o r of the m a t e - rial

x x i v MANUAL ON M O I S T U R E A N A L Y S I S I N B U I L D I N G S

v a p o r 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

v a p o r p e r m e a b i l i t y , (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)

v a p o r p e r m e a n c e (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/

s.m2-pa)

v a p o r p r e s s u r e , (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)

v a p o r r e s i s t a n c e a n d r e s i s t i v i t y - - t h e 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

v a p o r r e s i s t a n c e 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)

v a p o r resistivity see vapor resistance and resistivity

v a p o r r e t a r d e r - - a material or system that adequately im-

pedes the transmission of water vapor under specified con-

ditions

v o l u m e t r i c h e a t c a p a c i t y , (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

v o l u m e t r i c m o i s t u r e c a p a c i t y , (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

w a t e r a b s o r p t i o n coefficient see absorption coefficient

w a t e r v a p o r content see v a p o r c o n c e n t r a t i o n

w a t e r v a p o r diffusion see vapor diffusion

w a t e r v a p o r d i f f u s i o n coefficient see vapor diffusion co- efficient

w a t e r v a p o r d i f f u s i o n resistance see vapor resistance

w a t e r v a p o r permeability see vapor permeability

w a t e r v a p o r permeance see vapor permeance

w a t e r v a p o r pressure see vapor pressure

w a t e r v a p o r resistance see vapor resistance,

w a t e r v a p o r resistivity see vapor resistivity

wet-bulb see wet-bulb temperature

w e t - b u l b t e m p e r a t u r e - - t h e temperature read from a wet- bulb thermometer resulting from the cooling due to evapo- ration from its surface

W U F I - - 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

W U F I / O R N L / I B P - - 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)

W U F I Z - - a two-dimensional version of the WUFI computer model

WYEC the Weather Year for Energy Calculations data con- sists of one year of hourly weather data produced by ASH- RAE

WYEC2 the revised and improved WYEC data for 52 lo- cations in the US and 6 locations in Canada

d e p t h are r e f e r r e d to s u c h excellent p u b l i c a t i o n s as the

ASHRAE Handbook off Fundamentals [1], ASTM MNL 18,

Moisture Control in Buildings [2], a n d o t h e r s cited as refer-

dries, c o m m e r c i a l kitchens, a n d p r o d u c t i o n processes Tem-

p e r a t u r e affects the m o i s t u r e c o n t e n t in air, as air a b s o r b s

m o r e m o i s t u r e w h e n it is w a r m t h a n w h e n it is cold Air

p r e s s u r e also affects the a b i l i t y of a i r to c o n t a i n m o i s t u r e ,

a l t h o u g h for b u i l d i n g a p p l i c a t i o n s this effect can be i g n o r e d

vapor; conversely, b y l o w e r i n g t h e t e m p e r a t u r e , w e c a n de-

1H R Trechsel Associates, Arlington, VA; Trechsel is also an archi-

tect for the Engineering Field Activity Chesapeake, Naval Facilities

Engineering Command, Washington, DC All opinions expressed are

his own and do not necessarily reflect those of any Government

At t h a t point, the a i r r e a c h e s its s a t u r a t i o n point, a n d t h e

t e m p e r a t u r e at w h i c h this o c c u r s is called the d e w p o i n t of the air If the t e m p e r a t u r e of s u c h s a t u r a t e d a i r is lowered, the a i r will no l o n g e r b e a b l e to c o n t a i n its m o i s t u r e I n t h e

a t m o s p h e r e , the excessive m o i s t u r e c o n d e n s e s in the f o r m

of w a t e r d r o p l e t s to f o r m c l o u d s a n d e v e n t u a l l y rain W i t h i n

b u i l d i n g s a n d w i t h i n b u i l d i n g envelopes, the excessive m o i s -

t u r e c o n d e n s e s o n a n y s u r f a c e t h a t is at a t e m p e r a t u r e b e l o w the d e w - p o i n t t e m p e r a t u r e

Since the p r o p e n s i t y of a given m i x t u r e of d r y a i r a n d wa- ter v a p o r to c o n d e n s a t i o n is a f u n c t i o n of b o t h t h e m o i s t u r e

c o n t e n t of the air a n d its t e m p e r a t u r e , the t e r m relative hu- midity is used The relative h u m i d i t y of a p a r t i c u l a r s a m p l e

of air is the r a t i o of t h e m o i s t u r e c o n t e n t of the a i r a n d t h e

m o i s t u r e c o n t e n t of t h a t air at s a t u r a t i o n Accordingly, if a given s a m p l e of air c o n t a i n s x kg of m o i s t u r e p e r kg of air,

The following definitions of t e r m s a p p l y to w a t e r v a p o r as

c o n t a i n e d in air The first t h r e e t e r m s d e s c r i b e r a t i o s of w a t e r

t e r v a p o r p e r k i l o g r a m (kg) of d r y air (Using the p o u n d

p e r p o u n d units in the i n c h / p o u n d s y s t e m h a s the a d v a n -

tages t h a t the r a t i o is n o n - d i m e n s i o n a l a n d will be the

s a m e for the SI a n d i n c h / p o u n d systems)

in SI units), the n u m e r i c a l values a r e the s a m e for inch-

p o u n d a n d for SI units However, s o m e t a b l e s a n d c h a r t s

s h o w i n c h / p o u n d units as g r a i n s p e r p o u n d a n d m e t r i c

units as g r a m s p e r k i l o g r a m

9 Relative h u m i d i t y - - t h e ratio, at a specific t e m p e r a t u r e , o f

the m o i s t u r e c o n t e n t of t h e a i r s a m p l e if it were at satu-

r a t i o n , a n d the a c t u a l m o i s t u r e c o n t e n t of the a i r s a m p l e

It is given as a p e r c e n t a g e

9 Water vapor p r e s s u r e - - t h e p a r t i a l p r e s s u r e e x e r t e d b y the

v a p o r at a given t e m p e r a t u r e , also s t a t e d as the c o m p o n e n t

o f a t m o s p h e r i c p r e s s u r e c o n t r i b u t e d b y the p r e s e n c e of

w a t e r vapor I n i n c h / p o u n d units, v a p o r p r e s s u r e is given

m o s t f r e q u e n t l y in i n c h e s of m e r c u r y (in.Hg); in SI u n i t s

w a t e r v a p o r p r e s s u r e is given in Pascals (Pa)

9 Water vapor permeance o r permeance c o e ~ c i e n t - - t h e t i m e

r a t e of w a t e r v a p o r t r a n s m i s s i o n t h r o u g h u n i t a r e a of flat

p r o d u c t i n d u c e d b y u n i t w a t e r v a p o r p r e s s u r e difference

b e t w e e n its two surfaces I n i n c h / p o u n d units, p e r m e a n c e

is given in the u n i t "perm," w h e r e 1 p e r m equals a t r a n s -

b e t w e e n its two surfaces I n i n c h / p o u n d units, p e r m e a b i l -

ity is given in g r a i n s of w a t e r p e r h o u r for e a c h s q u a r e foot

9 Water vapor resistance and r e s i s t i v i t y - - t h e r e c i p r o c a l s of

p e r m e a n c e a n d p e r m e a b i l i t y The a d v a n t a g e of the use o f

r e s i s t a n c e a n d resistivity is t h a t in a n a s s e m b l y o r s a n d -

w i c h of a c o n s t r u c t i o n , the r e s i s t a n c e s a n d resistivities o f

the i n d i v i d u a l l a y e r s c a n be a d d e d to a r r i v e at the resist-

a n c e o r resistivity of a n assembly, while p e r m e a n c e s a n d

I n SI units, the h u m i d i t y r a t i o is given in g r a m s o f m o i s t u r e

p e r kg of d r y air, a n d the values given in the t a b l e c a n be

c o n v e r t e d into SI h u m i d i t y r a t i o s by m u l t i p l y i n g t h e m b y

1 0 0 0

Table 2 was p r e p a r e d to p r o v i d e a n i l l u s t r a t i o n of the effect

of t e m p e r a t u r e , relative h u m i d i t y , a n d a l t i t u d e (elevation

a b o v e sea level) on the d e n s i t y o r w e i g h t o f air The t a b l e

s h o w s the e l e v a t i o n b o t h in feet a n d in m e t r e s , a n d t h e vol-

Table 3 p r o v i d e s a n e x a m p l e of the m a s s of a i r a n d the

a m o u n t of m o i s t u r e t h a t m i g h t be c o n t a i n e d in a typical b e d -

r o o m , s m a l l r e s i d e n c e , a n d c l a s s r o o m , b a s e d o n t h r e e as-

s u m e d relative h u m i d i t y levels The i n d o o r t e m p e r a t u r e is

u n i f o r m l y a s s u m e d to be 70~ (2 I~ a n d the a l t i t u d e is sea level The t a b l e also i l l u s t r a t e s t h a t the a c t u a l m o i s t u r e con-

t e n t is d i r e c t l y p r o p o r t i o n a l to the relative humidity As

s h o w n below, the l o w e r i n g of the R H level w i t h i n b u i l d i n g

e n v i r o n m e n t s is the single m o s t effective m e a n s of r e d u c i n g the p r o p e n s i t y for m o i s t u r e p r o b l e m s in buildings However,

t h e r e a r e b o t h p r a c t i c a l l i m i t s to the d e g r e e the R H c a n be lowered, as well as p h y s i o l o g i c a l l i m i t s to b o t h low a n d h i g h

R H levels in b u i l d i n g s for h u m a n o c c u p a n c i e s

W h i l e the i n f o r m a t i o n in Tables 1, 2, a n d 3 a n d in s i m i l a r tables a v a i l a b l e in the l i t e r a t u r e is useful in i l l u s t r a t i n g t h e

m a g n i t u d e of the v a r i o u s factors involved in m o i s t u r e con- trol in buildings, t a b u l a r i n f o r m a t i o n is of l i m i t e d value to the designer, w h o n e e d s to u n d e r s t a n d the overall r e l a t i o n -

TABLE 1 Humidity ratio as a function of temperature and relative humidity (in pound of moisture per pound of dry air or kilogram of moisture per kilogram of dry air)

Relative Humidity

0~ ( - 18~ 0.0002 0.0004 0.0006 0.0008 20~ (-7~ 0.0005 0.0011 0.0016 0.0021

60~ (16~ 0.0027 0.0055 0.0082 0.0110 80~ (27~ 0.0054 0.0109 0.0165 0.0223 100~ (38~ 0.0102 0.0208 0.0318 0.0431

b y ASHRAE F i g u r e 1 is the c h a r t r e p r o d u c e d f r o m the

ASI-IRAE Handbook of Fundamentals [3] A l t h o u g h A S H R A E

p u b l i s h e s five charts, o n l y c h a r t n u m b e r 1 is r e l e v a n t for

m o s t b u i l d i n g designers It a p p l i e s to sea level a n d d r y - b u l b

chart, it is difficult to r e a d at t h e scale u s e d h e r e in Fig 1

Accordingly, to b e t t e r i l l u s t r a t e the m e a n i n g a n d significance

of the i n f o r m a t i o n c o n t a i n e d , w e have p r e p a r e d a s i m p l i f i e d

f o r m a t of t h a t c h a r t in Fig 2 However, for analysis, t h e orig-

inal A S H R A E chart, o r s i m i l a r c h a r t s p r o d u c e d b y HVAC

m a n u f a c t u r e r s , s h o u l d be used

The p s y c h r o m e t r i c c h a r t s p r o v i d e d on t h e x-axis the dry-

b u l b t e m p e r a t u r e a n d o n t h e y-axis t h e m o i s t u r e content

The steep d i a g o n a l lines r e p r e s e n t the v o l u m e of d r y a i r for

u n i t mass, a n d t h e low slope d i a g o n a l s r e p r e s e n t the wet-

b u l b t e m p e r a t u r e s The c u r v e d lines r e p r e s e n t t h e lines of equal relative humidity, a n d the last curve to t h e left r e p r e - sents 100% R H o r s a t u r a t i o n

t e r s e c t i o n w i t h t h e last c u r v e d line on t h e left, w h i c h r e p r e - sents 100% relative h u m i d i t y o r s a t u r a t i o n The value is t h e

d e w - p o i n t t e m p e r a t u r e of the a i r / v a p o r m i x t u r e (15~ in t h e

e x a m p l e ) A l t h o u g h the c h a r t is in SI units, t h e p r o c e d u r e

w o u l d b e exactly t h e s a m e for a n i n c h / p o u n d chart, e x c e p t

t h a t the t e m p e r a t u r e s for d r y - b u l b a n d for d e w p o i n t w o u l d

b e in ~

Problem 2, Fig 4: Given a r e t h e d r y - b u l b t e m p e r a t u r e of 35~

a n d t h e d e w - p o i n t t e m p e r a t u r e of 20~ F i n d the relative hu- midity

Solution: F i n d the d e w - p o i n t t e m p e r a t u r e on t h e s a t u r a t i o n

o r d e w - p o i n t curve (20~ in t h e e x a m p l e ) a n d m o v e h o r i z o n - tally u n t i l the i n t e r s e c t i o n w i t h the n e a r vertical over t h e dry-

b u l b t e m p e r a t u r e (35~ in the example) By e x a m i n i n g the

l o c a t i o n of the closest i n t e r s e c t i o n w i t h t h e c u r v e d R H lines, the R H of the a i r a n d v a p o r m i x t u r e c a n b e e s t i m a t e d as 43%

Problem 3, Fig 5: Given are the d r y - b u l b t e m p e r a t u r e of 10~

a n d the relative h u m i d i t y as 50% F i n d t h e h u m i d i t y ratio

3 0 ~

10 ' / ,_ "-_.71 ,

/ / " _ / ~@'/ " , ".~" I / / 7 - , , @ ' / ">~ I

/ " {

- - -

0oC 10~C 20~ 30 ~ 4 0 0 C 5 0 ~

DRY eULB TEMPERATURE

FIG 2 ~ i m p l i f i e d psychrometric chart based on ASHRAE Chart shown on Fig 1

~ - - ~ - I-'iT: ,~.~ 2,,L-h -, ~.,.-'~"~"""~, -'C'~ 4 ' ": '" -~"rl"T/~'%1-~ ,.'-.-gC3 ~I T" I-3, -I" L.I ,"~" :LI N" ~ 1 "

-_1 ~ ' L r - l ' ~ 1 - I ~ 1 " 1 Y ' I 1"4~I',,,I " 4 _ t l ' l I - ' L ' ~ i ] ' N - 4 I I%'J i g ' l l iP'~,~i"".d'~ I ~ - i ~ l - ' J - I ' - 1 [ ' - J ~ , ~ J ' I , P - J P - I 1 " ' 4 - I l t ~ ' t ~ l - I I ' - I ] l ~ - i i ' - E " ~ " l - _ l \ l " 1 - I I~'~]L I 1

" " - - - 30~ D R Y BULB

FIG 3 Calculation of dew-point temperature based on dry-bulb temperature and relative humidity

Solution: Find the dry-bulb temperature on the horizontal

dry-bulb line (10~ in the example) and move up the near

vertical line to its intersection with the 50% RH curve From

that intersection, move horizontally to the right to the hu-

midity ratio scale The humidity ratio is 4 g of moisture per

kilogram of dry air

Problem 4, Fig 6: Given is the dew point of 5~ Find the humidity ratio

Solution: Find the dew-point temperature on the dew-point

or saturation curve (or 100% relative humidity curve) (5~

in the example) From that point move horizontally to the right until its intersection with the humidity ratio scale, The

humidity ratio in the example is 5.5 g of moisture per kilo-

gram of dry air

Problem 5, Fig 7." Given are the dry-bulb temperature of 35~

and the wet-bulb temperature of 25~ Find the relative hu-

midity, dew-point, and humidity ratio

Solution: Find the dry-bulb temperature on the horizontal

line (35~ in the example) and move up the near vertical line

to its intersection with the diagonal wet-bulb temperature

line of 25~ The relative humidity is the nearest relative hu-

midity curve (45% in the example) If desired, the dew point

temperature can then be determined by moving horizontally

to the left to the saturation curve The dew-point is 2 I~ in

the example To determine the humidity ratio, move from

the intersection of the dry-bulb and the wet-bulb tempera-

ture to the right and find the humidity ratio as 16 g of moist

air per kilogram of dry air

While the use of psychrometric charts is simple, it must

be noted that calculations based on the charts are approxi-

mate only However, for purposes of moisture analysis, the

results are generally sufficiently accurate

Also available are the ASHRAE published tables on the

thermodynamic properties of moist air [4] These allow in

general greater accuracy, but are less convenient to use for

the envelope design professional

In addition, there are several computer programs on the

market that simplify the calculations Two of these programs

are included on the CD Rom in the back cover pocket

One of the programs, developed by the Trane Company, is

one module out of a broader program developed for solving

many thermodynamic tasks It is based on i n c h / p o u n d units

as used in the United States

The other program was developed by Carsten Rode and allows the use of both metric (SI) units of measurements and

M O I S T U R E S O U R C E S

In cold climates, condensation control in buildings is con- cerned mainly with indoor moisture sources In air- conditioned buildings in warm and humid climates, infil- trating warm and humid air is the primary concern In all climates, special consideration must be given to indoor moisture sources such as indoor swimming pools and spas, commercial laundries and kitchens, and moisture-producing industrial processes must be considered on a case-by-case basis Except as noted, the following is summarized and ab- stracted from Christian [5] For consistency, all values of moisture were converted to pounds (lb) for the i n c h / p o u n d system and to kilograms (kg) for the SI system

I n d o o r S o u r c e s

People

All buildings designed for h u m a n occupancies must ac- count for the body moisture generated by people The mois-

ture release f r o m respiration a n d perspiration depends on

the activity level and air t e m p e r a t u r e E h r h o r n a n d Gertis

[6] estimate the following ranges of moisture release for

three activity ranges at 68~ (20~

Commercial and Institutional

Based on the above data and a s s u m i n g light to m e d i u m activity levels for schools, offices, a n d light industrial occu- pancies, a daily per capital moisture source of approximately

2 2 l b / d a y (1 kg/day) per 8 h shift seems a reasonable as~

s u m p t i o n

8 MANUAL ON MOISTURE ANALYSIS I N BUILDINGS

lS g/kg HUMIDITY RATIO

Indoor firewood storage

420 to 705 lb (190 to 320 kg) over six m o n t h s of storage

Cloth drying indoors, n o t v e n t e d

4.8 to 6.44 l b / l o a d (2.2 to 2.92 k g / l o a d )

Swimming pools

C h r i s t i a n p r o v i d e s the f o r m u l a a n d n e c e s s a r y table to es-

t i m a t e the m o i s t u r e e v a p o r a t i o n f r o m s w i m m i n g pools This

e v a p o r a t i o n d e p e n d s o n the w a t e r t e m p e r a t u r e a n d the R H

a n d t e m p e r a t u r e o f t h e air

Indoor plants and aquariums

I n d o o r p l a n t s c a n also a d d significantly to the m o i s t u r e

l o a d o f a building A l m o s t all w a t e r u s e d to w a t e r p l a n t s en-

ters the air A s m a l l p l a n t m a y a d d o n l y 0.22 l b / d a y (0.1 kg

m o i s t u r e l o a d n e a r the u p p e r l i m i t for the i n t e n d e d occu- pancy F o r a m o r e d e t a i l e d analysis of i n d o o r m o i s t u r e sources, t h e r e a d e r is r e f e r r e d to C h r i s t i a n [5]

m a y release 22 lb (10 kg) o r m o r e p e r d a y d u r i n g the first winter, a n d 11 lb (5 kg) d u r i n g the s e c o n d y e a r [9] Thus,

c o n s t r u c t i o n m o i s t u r e , specifically in c o n c r e t e a n d m a s o n r y buildings, c a n be a s e r i o u s m o i s t u r e s o u r c e d u r i n g t h e first

y e a r s of occupancy, b u t it s h o u l d n o t be a l o n g - t e r m p r o b - lem However, d u r i n g the p r o c e s s of d r y i n g o u t of a c o n s t r u c - tion, s u c h m o i s t u r e c a n be significant, e s p e c i a l l y w i t h m o i s -

t u r e - r e t a r d i n g c o n s t r u c t i o n ( i n s t a l l a t i o n of v a p o r r e t a r d e r s )

a n d insufficient ventilation E a r l y o c c u p a n c y b e f o r e s u b s t a n - tial d r y i n g o u t s h o u l d t h e r e f o r e be avoided

If w a t e r in the f o r m of r a i n is a l l o w e d e n t r a n c e into the

b u i l d i n g o r into wall a n d r o o f c o n s t r u c t i o n s , this s o u r c e c a n over-whelm all i n t e r i o r o r o t h e r e x t e r i o r sources A single sig- nificant r a i n w a t e r l e a k h a s b e e n o b s e r v e d b y this a u t h o r to

ing w a r m weather, o n l y to c o n d e n s e o n interior, c o l d e r sur-

faces in walls of a i r - c o n d i t i o n e d buildings The first p r i o r i t y

be v e n t i l a t e d to the o u t d o o r s , in p r a c t i c e m u c h of it will find

its w a y into t h e s t r u c t u r e a b o v e t h r o u g h floor p e n e t r a t i o n s ,

ducts, a n d a c c e s s stairs It is o b v i o u s t h e n t h a t the d e s i g n e r

n e e d s to control, o r b e t t e r prevent, m o i s t u r e f r o m e n t e r i n g

b a s e m e n t s a n d crawl spaces The first of t h e p r e v e n t i v e m e a -

sures s h o u l d be to p r o v i d e a d e q u a t e slope o f the g r a d e a w a y

p r o x i m a t i o n s are p r o v i d e d in the ASHRAE Handbook of Fun-

damentals [9] a n d in ASTM M N L 18, C h a p t e r 8 [5], t h e de-

s i g n e r of a b u i l d i n g envelope will n o t be a b l e to p r e d i c t

a c c u r a t e l y o r even a p p r o x i m a t e l y the a s - b u i l t a i r l e a k a g e per-

f o r m a n c e of the envelope, specifically since he o r she often

h a s little c o n t r o l over field q u a l i t y c o n t r o l d u r i n g c o n s t r u c -

t i o n a n d has g e n e r a l l y no c o n t r o l over the o p e r a t i o n a n d

m a i n t e n a n c e of t h e building, all of w h i c h will l a r g e l y deter-

m i n e the air i n f i l t r a t i o n rate The d e s i g n e r should, however,

i n c l u d e in the specifications a d e q u a t e p r o v i s i o n s for field

q u a l i t y control, d e s i g n the wall to be i n h e r e n t l y r e s i s t a n t to

a i r infiltration, a n d detail the w a l l c o n s i s t e n t w i t h the q u a l i t y

of w o r k m a n s h i p to be specified a n d expected

B U I L D I N G MATERIALS

B u i l d i n g m a t e r i a l s c a n be affected b o t h b y m o i s t u r e a n d c a n

affect the m o i s t u r e p e r f o r m a n c e of a b u i l d i n g a n d its ele-

m e n t s The p r o p e r t i e s r e l e v a n t to m o i s t u r e analysis a r e dis-

c u s s e d in m o r e d e t a i l in C h a p t e r 3 o n M a t e r i a l s , a n d failure

c r i t e r i a a r e d i s c u s s e d in C h a p t e r 4 The following is a b r i e f

s u m m a r y of m o i s t u r e - r e l a t e d c o n c e r n s for b u i l d i n g m a t e r i - als

Terminology above P e r m e a n c e is a m e a s u r e of a specific

p r o d u c t ' s r a t e of w a t e r v a p o r t r a n s m i s s i o n , s u c h as a n

a s p h a l t - l a m i n a t e d kraft p a p e r o r a 3 / 4 in (19 m m ) t h i c k ex-

t r u d e d p o l y s t y r e n e b o a r d P e r m e a b i l i t y is a m e a s u r e of a m a - terial's r a t e of w a t e r v a p o r t r a n s m i s s i o n p e r u n i t thickness Thus, the p e r m e a n c e of t h e a b o v e - m e n t i o n e d 3 / 4 in ex-

t r u d e d p o l y s t y r e n e b o a r d is 0.9 p e r m (50 n g / s 9 m 2 9 Pa), b u t the p e r m e a b i l i t y of e x t r u d e d p o l y s t y r e n e m a t e r i a l is 1.2

p e r m p e r i n c h t h i c k n e s s (30 n g / s 9 m 9 Pa p e r m e t r e thick- ness) O t h e r useful t e r m s a r e w a t e r v a p o r r e s i s t a n c e a n d re- sistivity, w h i c h a r e t h e r e c i p r o c a l values of p e r m e a n c e a n d

p e r m e a b i l i t y The w a t e r v a p o r t r a n s m i s s i o n r a t e t h r o u g h m a t e r i a l is n o t

o n l y d e p e n d e n t o n t h a t p a r t i c u l a r m a t e r i a l a n d its thickness,

b u t also o n the v a p o r p r e s s u r e a c t i n g a c r o s s the m a t e r i a l or,

a s s u m i n g equal t e m p e r a t u r e , o n the relative h u m i d i t y o n

b o t h sides of the m a t e r i a l The m o s t f r e q u e n t l y u s e d test

m e t h o d is ASTM E 96, Test M e t h o d s for W a t e r V a p o r Trans-

m i s s i o n of Materials The test e s s e n t i a l l y consists of install- ing the m a t e r i a l in a d i s h (or cup), w h i c h c o n t a i n s e i t h e r a

d e s i c c a n t (Desiccant o r Dry-Cup m e t h o d ) o r c o n t a i n s w a t e r ( W a t e r o r Wet-Cup m e t h o d ) The d i s h is t h e n p l a c e d in a

c a b i n e t w i t h c o n t r o l l e d t e m p e r a t u r e a n d h u m i d i t y a n d is

w e i g h e d at r e g u l a r intervals W h e n the i n c r e a s e (Desiccant

m e t h o d ) o r d e c r e a s e ( W a t e r m e t h o d ) r e a c h e s a s t e a d y rate, the w a t e r v a p o r t r a n s m i s s i o n r a t e c a n be c a l c u l a t e d The re- sults of the two tests for s o m e m a t e r i a l s will differ signifi- cantly, as the w a t e r t r a n s m i s s i o n r a t e is d e p e n d e n t on the

m o i s t u r e c o n t e n t of the a i r o n b o t h sides of the s p e c i m e n The r e s u l t s of the tests, r e p o r t e d in C h a p t e r s 3 a n d 4 of MNL 18 [2], in g e n e r a l are b a s e d o n e i t h e r the D e s i c c a n t o r the W a t e r m e t h o d W h e r e the d e s i g n e r has a choice, the re- sults f r o m D e s i c c a n t tests s h o u l d be u s e d w h e r e relatively low relative h u m i d i t y will p r e d o m i n a t e , while results f r o m

W a t e r tests s h o u l d be u s e d in c o n d i t i o n s w h e r e h i g h relative

h u m i d i t i e s will p r e d o m i n a t e I n the past, d a t a for m o s t m a - terials w e r e a v a i l a b l e o n l y for e i t h e r the W a t e r m e t h o d o r the D e s i c c a n t m e t h o d T h a n k s to w o r k b y s u c h o r g a n i z a t i o n s

as the I n t e r n a t i o n a l E n e r g y Agency a n d v a r i o u s r e s e a r c h in- stitutions, d a t a for w a t e r v a p o r p e r m e a b i l i t y is n o w a v a i l a b l e for r a n g e s of relative h u m i d i t i e s a n d t e m p e r a t u r e s C h a p t e r

3 of this m a n u a l p r o v i d e s s u c h n e w data

10 M A N U A L O N M O I S T U R E A N A L Y S I S I N B U I L D I N G S

Moisture Absorption

Many building materials have the ability to absorb moisture

In a well-designed building, moisture absorption in building

materials should not be of concern; however, excessive mois-

ture content of some building materials can lead to prema-

ture deterioration and even failure Serious decay in wood

occurs at and above fiber saturation of about 30% moisture

content and between 50~ (10~ and 100~ (38~ [10] High

moisture content in thermal insulation materials can de-

grade the thermal resistance of thermal insulating materials

failure Surface wetting (by liquid water or by condensation)

can lead to mold growth, rust on unprotected steel, and to

the deterioration of finishes Chapters 3 on Materials and 4

on Failure Criteria in this manual will elaborate on these

issues

D i m e n s i o n a l Changes in Wood

While wood is dimensionally stable at fiber saturation, it

changes dimensions as it gains and loses moisture below this

point In general such changes are not of catastrophic sig-

nificance in buildings; however, they can cause uneven set-

tlement, loosened connectors, warpage with attendant un-

sightliness, splitting of boards, and can, therefore, reduce the

ability to shed rainwater The greatest moisture-induced di-

mensional changes are in the direction of the annual growth

rings (tangential), about half as much across the rings (ra-

dial), and only slightly along the grain of the wood Readers

interested in greater details of moisture-related shrinkage of

wood and of other wood-related properties of wood are re-

ferred to Ref 10, from which the above was extracted

Vapor Retarders

To prevent excessive moisture movement into and through

building walls, vapor retarders (formerly called vapor bar-

riers) are frequently used These are mostly membrane-type

materials or, more rarely, paints with a low moisture trans-

mission rate ASTM C 755, Practice for Selection of Vapor

Retarders for Thermal Insulation, defines vapor retarders as

"materials or systems which adequately retard the transmis-

sion water vapor under specified conditions." It goes on to

state that "for practical purposes it is assumed that the per-

meance of an adequate retarder will not exceed 1 perm, al-

though at present this value may be adequate only for resi-

dential construction." Regardless of the qualification, the

1-perm value is currently accepted as the working definition

of a vapor retarder To be effective, vapor retarders should

also be essentially airtight to prevent the passage of moist

air

Air Retarders

While the purpose of vapor retarders is the prevention of

excessive diffusion into and through walls and wall elements,

the purpose of air retarders (AR) is to prevent excessive air

leakage into and through building walls and wall elements,

while being highly permeable to water vapor ASTM E 1677,

specifications for Air Retarder (AR) Material or System for

Low-Rise Framed Building Walls, does not specify a level of

required water vapor permeance However, materials are available in the 10 to 50 perm (570 to 2850 ng/s 9 m Pa) range and may be considered appropriate According to ASTM E 1677, the air leakage rate of an AR should not ex- ceed 0.06 cfm/ft 2 at 0.3 in of water (0.3 9 10 3/(s 9 m 2) at 75 Pa) when tested in accordance with ASTM Test Method for Determining the Rate of Air Leakage Through Exterior Win- dows, Curtain Walls, and Doors Under Specified Pressure Differences Across the Specimen (E 283) Alternatively to in- stalling a separate air retarder, other materials, such as in- terior gypsum board in cold climates, can provide an ade- quate air seal if the boards are properly caulked at the sill, head, and at all joints such as windows, doors, and at plumb- ing penetrations [12] Since airtightness of the AR is critical

to its performance, and, since the performance of seals is primarily a function of field workmanship, adequate provi- sions for quality control should be included in the building specifications so that the installed AR will meet the intent of ASTM E 1677 In cold climates, air retarders installed out- side of the insulation enhance the effectiveness of the insu- lation by preventing cold air from entering the wall cavity

C o m b i n e d Vapor Retarders and Air Retarder

A combination vapor retarder and air retarder system will prevent moisture movement both by diffusion and by mass transport The system can consist of a single element that is both air and water vapor resistant, or it can consist of two elements, a vapor retarder and an air barrier

A C C E P T A B L E M O I S T U R E L E V E L S

In buildings, there are three components that limit accept- able moisture levels: h u m a n health and comfort, the deteri- oration of a building's contents for example the storage of hygroscopic materials such as antiquities (in museums) or chemicals, and the need to safeguard the building's structure itself from moisture-related deterioration While for most buildings RH levels in the 30 to 50% should be acceptable, for specialized buildings other allowable RH and tempera- ture limits may need to be observed

H u m a n Health a n d Comfort

Within a fairly broad range, moisture in the air is of no great significance to h u m a n health and comfort In other words, humans are tolerant of a wide range of moisture and tem- perature conditions of the air ASHRAE suggests the indoor levels of temperature and moisture content for h u m a n oc- cupancies as shown in Fig 8 [13] As shown on that chart, during winter, the relative humidity level should not fall sig- nificantly below 30% and should not exceed 70% Other au- thorities recommend 40 to 60% [14]

As summarized by Burge, Su, and Spengler [15], several studies have indicated a significant association of home dampness a n d / o r mold and respiratory symptoms in chil- dren Although some of these studies showed conflicting re- sults, it appears that excessive RH levels such as higher than 75%, and any surface mold growth, should be avoided Sur- face mold can grow without the presence of liquid (con- densed) water, and high relative surface humidities alone can

IJJ

~- 50 I

25 2O

10

15 L E

cause mold growth The International Energy Agency has

determined that surface mold can grow at surface relative

humidities of 80% or higher [16]; other researchers have rec-

ommended that surface RH should not exceed 70% [12] Ac-

cordingly, health and comfort require that both the RH level

in the occupied spaces and the surface relative humidity be

controlled within the above suggested limits

Building Contents

Buildings containing antiquities and precious artworks have

their own moisture/temperature requirements In general,

somewhat higher levels of RH will be desirable Plender-

leight and Werner [17] recommend RH limits of a minimum

of 50% to a maximum of 65% within a temperature range

of 60 to 75~ (16 to 25~ except for picture galleries for

which a constant RH of 58 and 63~ (17~ is recommended

However, it appears that artifacts are more sensitive to rapid

changes in temperature and RH levels than to absolute val-

ues Because the recommended RH levels are above those

recommended for buildings in general, the storing and pre-

senting of important artifacts in climate-controlled cabinets

should be considered

For the storage of hygrostatic materials and for some in- dustrial processes, specialized temperature and RH levels may be required These must be known to the designer be- fore attempting to design the building envelope, but no gen- eral guidelines can be provided

Building Structure

The temperature and RH levels recommended for health and comfort of building occupants in general are acceptable for the building structure Also, the prevention of mold growth will also reduce the potential for premature deterioration of interior finishes Where significant and regular condensation

is allowed to form on steel constructions, corrosion could become a problem This is one reason that the thickness of any one part of structural steel sections as a rule should not

be less than 1/4 in thick, although thinner, cold-formed light-gage galvanized steel shapes are routinely used as sec- ondary elements, such as for supporting metal curtain walls

General R e c o m m e n d a t i o n s

Since most calculations of temperatures and relative humid- ities are based on design values and do not include local

12 M A N U A L O N M O I S T U R E A N A L Y S I S I N B U I L D I N G S

discontinuities in insulation, thermal bridges, and air and

rainwater leaks, it is recommended that designers use con-

servative estimates and allow indoor RH levels well within

the comfort zone, surface RH levels below the 70%, and

moisture content of wood structures not over 20%, unless

exacting field quality control mechanisms are in place and

unless maintenance and operations can be expected to meet

rigorous standards This may be more likely to be accom-

plished in major commercial and institutional buildings than

in one- and two-family dwellings

M O I S T U R E M O V E M E N T

Moisture in the form of water vapor moves from one place

to another either through mass transport, that is, by the

movement of moist air, or through diffusion The driving

force of mass transport is air pressure; the driving force of

diffusion is vapor pressure The movement of liquid water

can also result from wind pressure moving raindrops

through cracks and joints, but as a general rule follows grav-

ity forces

Mass Transport

Driving Force

The flow of water vapor as part of airflow follows the same

laws as the flow of air The driving force of airflow into and

across the building envelope is the air pressure difference

acting on the envelope When the air pressure within the

building is greater than the pressure outside the building,

the building is said to be under positive pressure If the pres-

sure indoors is lower than the pressure outside, the building

is said to be under negative pressure Note that the pressure

differential is not necessarily the same for the entire build-

ing; it can vary depending on orientation or building level,

both in magnitude and in direction, that is positive and neg-

ative Air pressures and resulting air movements within the

building can also be affected by interior partitions and shafts

(such as for elevators and stairs)

The practitioner is seldom required to establish either the

total pressure difference nor the resulting total air-leakage

rate However, building designers should be aware of the fac-

tors that affect the total driving forces and resulting air in-

filtration so that he or she can place the needed emphasis

on those design and detail parameters that primarily affect

the overall moisture resistance of the envelop

9 Wind pressure acts as a positive pressure on the windward

side of the building and as a negative pressure on the lee-

ward side of the building Since wind speed is a function

of height above ground, the wind pressure acting on a

building wall will also vary with height above ground

Wind pressure is lowest at ground level and increases with

building height It is generally largest near corners and in

high or unusually shaped buildings; only extensive analysis

and wind tunnel studies can reliably predict the pressure

distribution over the surface of the building envelope

Wind pressure also is affected by surrounding geographic

features, other nearby buildings, and by trees and shrub-

bery Windbreaks in the form of trees, bushes, and fences

can effectively lower wind impingement and resulting air infiltration from prevailing wind Both wind direction and wind speed can vary rapidly For a more detailed discus- sion of wind pressure as a result of airflow around build- ings, see ASHRAE [18]

9 Stack effect in buildings is the result of temperature differ- ences between the building interior and the atmosphere During cold weather, heated air in the building is less dense and tends to rise This will cause a negative indoor pressure on the lower floors, and a positive pressure on the upper floors and on the roof, and will result in exfiltration

of indoor air at the top of the building and in infiltration

of outdoor air at the bottom of the building During warm weather in an air-conditioned building, the process is re- versed, with air infiltration taking place at the top of the building and exfiltration at the bottom As a general rule, the stack effect is greater during winter, since the temper- ature differences are greater For a detailed discussion of stack effect and of calculating methods to determine the resulting pressure differentials, see ASHRAE [18]

9 Mechanical ventilation acts on the entire building envelope

to either provide positive or negative pressure and results

in either a net outflow of inside air or a net inflow of out- side air, while wind pressure and stack effect result in equal amounts of air being infiltrated as being exfiltrated Mechanical systems that include fresh air intakes allow for adjustments to provide for either positive or negative in- door pressure depending on damper settings In residential buildings, combustion furnaces and boilers can cause air pressure difference and air movement, even in the absence

of mechanical ventilation fans

9 Combined driving forces: Although the three driving forces discussed above can be determined separately, the result- ing airflow rates can not simply be added up, but the total pressure differential must be established and the infiltra- tion must be determined on the basis of the leakage open- ings and the total pressure [18]

Air Leakage Sites

Of equal importance to the total air and moisture mass transport movement are the leakage sites, their size, effective leakage area (ELA), and, to a degree, their location It is un- derstood that the larger the opening, the greater the poten- tial air movement However, some types of openings produce different air leakage rates, depending on the direction of air- flow Based on a model developed by the Lawrence Berkeley Laboratory, ASHRAE [18] provides a table of typical effective air leakage areas (ELA) through building components at a nominal pressure difference of 0.016 in of water (4 Pa) Note that the leakage areas can be converted from the reference pressure to airflow rates at other pressures, using equations also given in ASHRAE [18] ASHRAE also presents a method for relating air infiltration rates to effective leakage area

Diffusion

Water vapor can move through materials by diffusion The driving force for such movement is the difference in water vapor pressure (as defined above) between the two sides of the material Water vapor pressure depends on the moisture content of the air and its temperature or its relative humid-

creasing, o r a b a t i n g wind; t h e d i r e c t i o n of the a i r m o v e m e n t

m a y c h a n g e w i t h i n t i m e f r a m e s of m i n u t e s to days Also, the

d i s t r i b u t i o n of l e a k i n g a i r w i t h i n t h e b u i l d i n g envelope is n o t

evenly d i s t r i b u t e d over the e n t i r e s u r f a c e of t h e wall o r roof,

b u t it is often r a n d o m l y c o n c e n t r a t e d in relatively few m a j o r

l e a k a g e sites It is for this r e a s o n t h a t the d e s i g n p r a c t i t i o n e r

m u s t develop t h e r m a l e n v e l o p e details to p r e c l u d e signifi-

c a n t a m o u n t s of m o i s t a i r into a n d t h r o u g h b u i l d i n g w a l l

a n d r o o f elements B e c a u s e of t h e r a n d o m a n d u n k n o w n lo-

c a t i o n of a i r leaks t h a t i n v a r i a b l y exist in b o t h n e w a n d ex-

isting b u i l d i n g envelopes, t h e analysis tools s u i t a b l e for t h e

d e s i g n e r do not, o r n o t always, i n c l u d e the effect of a i r leaks

Similarly, t h e tools c a n n o t r e l i a b l y a c c o u n t for w a t e r leaks

t h a t also a r e g e n e r a l l y l o c a t e d at i n d i v i d u a l , u n k n o w n leak-

age sites u n e v e n l y d i s t r i b u t e d o v e r the e n t i r e wall o r roof I n

o t h e r words, a i r t i g h t n e s s a n d r a i n w a t e r r e s i s t a n c e m u s t b e

d e s i g n e d i n t o walls a n d roofs Analysis s h o u l d n o t be r e l i e d

u p o n to j u d g e the a d e q u a c y of details to p r e v e n t a i r a n d wa-

ter l e a k a g e i n t o walls, roofs, a n d buildings

I n c o n t r a s t , v a p o r d i f f u s i o n acts evenly d i s t r i b u t e d over

large a r e a s of wall a n d roofs, and, while variable, b o t h w i t h

r e g a r d to d i r e c t i o n a n d quantity, it g e n e r a l l y acts over l o n g e r

p e r i o d s of d a y s to w h o l e seasons F u r t h e r m o r e , t h e a i r tight- ness, the specific a i r l e a k a g e sites, a n d the l o c a t i o n a n d ex-

t e n t of r a i n w a t e r leaks in a b u i l d i n g is s e l d o m , if ever, k n o w n

d u r i n g t h e d e s i g n stage (One e x c e p t i o n m i g h t be w h e r e a

b u i l d i n g a n d wall d e s i g n has b e e n extensively t e s t e d a n d where, b a s e d o n s u c h tests, close a p p r o x i m a t i o n s m i g h t be possible.) F o r all t h e s e r e a s o n s , the d e s i g n e r c a n c o n f i d e n t l y use m o i s t u r e m o d e l s s u c h as M O I S T ( C h a p t e r 8) a n d W U F I

r o o f s y s t e m s a n d w h i c h a r e excellent tools for i n v e s t i g a t i n g the effect of i n d i v i d u a l p e r f o r m a n c e p a r a m e t e r s M o s t o f

b u i l d i n g s a n d trees w i t h i n 30 ft (9 m) in m o s t d i r e c t i o n s Table 4 s h o w s the a s s u m p t i o n s a n d the c a l c u l a t e d h o u r l y

m o i s t u r e m o v e m e n t d u e to infiltration The t o t a l c a l c u l a t e d

m o i s t u r e m o v e m e n t r a t e d u e to a i r infiltration for t h e h o u s e

w o u l d be 2.8 lb ( l 2 kg) p e r hour

Table 5 s h o w s t h e c a l c u l a t e d m o i s t u r e m o v e m e n t t h a t

c o u l d o c c u r t h r o u g h diffusion The c a l c u l a t i o n s are b a s e d

TABLE 4 Calculated moisture infiltration rate due

to air infiltration

In./Lb Units SI Units Volume of house 9000 ft 3 2 5 5 m 3

Effective leakage area 107 in 2 0.07 m z

TABLE 5 Calculated moisture movement through building

As c a n be seen, in this e x a m p l e , the a m o u n t of m o i s t u r e

m o v e m e n t a c r o s s t h e b u i l d i n g envelope b y infiltration is ap-

p r o x i m a t e l y 25 t i m e s the a m o u n t of m o i s t u r e m o v e d b y dif-

fusion Of course, h a d the e n v e l o p e b e e n a s s u m e d to be less

p e r m e a b l e to w a t e r vapor, say o n l y 0.5 p e r m , t h e m o i s t u r e

m o v e m e n t b y d i f f u s i o n w o u l d b e even lower; conversely, h a d

t h e effective l e a k a g e b e e n smaller, the m o i s t u r e m o v e m e n t

b y m a s s t r a n s p o r t h a d b e e n lower This i l l u s t r a t e s the im-

p o r t a n c e of d e s i g n i n g a i r t i g h t n e s s into the envelope, of as-

to c a t a s t r o p h i c failures a n d t h u s c a n n o t b e ignored By con-

trast, m o i s t u r e m o v i n g b y d i f f u s i o n is m o r e likely to involve

t h e e n t i r e s u r f a c e o r m a j o r p a r t s of the t h e r m a l envelope,

a n d r e p a i r s , if necessary, m a y be m u c h m o r e costly a n d dis-

r u p t i v e t h a n r e p a i r s of a i r o r w a t e r leaks It is for all t h e s e

r e a s o n s that, in the a b s e n c e of r e l i a b l e m e t h o d s for a c c o u n t -

ing for a i r a n d w a t e r l e a k a g e sites, m o i s t u r e a n a l y s i s b a s e d

o n d i f f u s i o n a l o n e is still very useful to the d e s i g n e r for se-

lecting m a t e r i a l s so t h a t c o n d e n s a t i o n w i t h i n envelope con-

G r e a t Britain The r e a s o n for this d i s c r e p a n c y is n o t clear,

b u t it a p p e a r s to b e r e l a t e d to c l i m a t e a n d b u i l d i n g m a t e r i a l s

C a p i l l a r i t y refers to the m o v e m e n t of m o i s t u r e d u e to forces of s u r f a c e t e n s i o n w i t h i n s m a l l tubes Generally, t h e

n a r r o w e r the tube, t h e h i g h e r will be t h e rise a g a i n s t t h e force of gravity Accordingly, c a p i l l a r i t y in a m a t e r i a l de-

p e n d s o n t h e s t r u c t u r e of the m a t e r i a l Oliver e s t i m a t e s t h a t for a p o r e r a d i u s of 4 9 10 4 in (0.01 m m ) , a rise of 60 in (1.5 m) c a n be a n t i c i p a t e d , a n d for a p o r e r a d i u s of 44 9 10 -5

in (0.001 m m ) , a rise o f 4500 ft (1500 m) c a n be a n t i c i p a t e d

I n t y p i c a l m o i s t u r e analysis in the U n i t e d States, c a p i l l a r i t y

is neglected However, in a r e a s w h e r e r i s i n g d a m p is k n o w n

to b e a p r o b l e m , its effect s h o u l d be c o n s i d e r e d in d e s i g n b y specifying c a p i l l a r y b r e a k s b e l o w c o n c r e t e b a s e m e n t slabs

a n d t h e i n s t a l l a t i o n of d a m p p r o o f c o u r s e s in walls [20]

R E F E R E N C E S

[1] ASHRAE, Handbook of Fundamentals, American Society of Heating, Refrigerating, and Air-Conditioning Engineers, At- lanta, 1997

[2] ASTM, Moisture Control in Buildings, ASTM MNL 18, H R

Trechsel, Ed., American Society for Testing and Materials, West Conshohocken, 1994

[3] Psychrometric Charts, published by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers, At- lanta Figure 1 was reproduced from the ASHRAE Handbook of Fundamentals, Chapter 6, "Psychrometrics," Atlanta, 1997, p 6.15

[4] ASHRAE Handbook of Fundamentals, "Psychrometrics," Amer- ican Society of Heating, Refrigerating, and Air-Conditioning Engineers, Atlanta, 1997, pp 6.3-6.11

[5] Christian, J E., "Moisture Sources, Chapter 8, Moisture Control

in Buildings, ASTM MNL 18, American Society for Testing and Materials, West Conshohocken, PA, 1994, pp 176-182 [6] Ehrhorn, H and Gertis, K., "Minimal Thermal Insulation and Minimal Ventilation," Gesundheit Engineering, Vol 107, 1986 [Cited by Christian, above.]

[7] Rousseau, M Z., "Sources of Moisture and Its Migration through the Building Enclosure," ASTM Standardization News,

November 1984, pp 35-37

[8] Quirouette, R L., "Moisture Sources in Houses," Condensation and Ventilation in Houses, National Research Council of Can- ada, Division of Building Research Humidity, NRCC 23293, Ot- tawa, May 1984

[9] ASHRAE, Handbook of Fundamentals, "Ventilation and Infiltra- tion," Chapter 25, American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Atlanta, 1997, p 25.22

[10] Sherwood, G E., "Moisture Related Properties of Wood and the Effect of Moisture on Wood and Wood Products," Moisture Con- trol in Buildings, Chapter 5, ASTM MNL 18, American Society for Testing and Materials, West Conshohocken, PA, 1994, pp 176-182

[11] Langlais, C., Silberstein, A., Sandberg, R I., and Sherwood,

G E., "Effects of Moisture in the Thermal Performance of In- sulating Materials," Moisture Control in Buildings, Chapter 4, ASTM MNL 18, American Society for Testing and Materials, West Conshohocken, PA, 1994, pp 54-71

[12] Lstiburek, "Moisture Control for New Residential Buildings,"

Moisture Control in Buildings, Chapter 17, ASTM MNL 18,

C H A P T E R I - - M O I S T U R E P R I M E R 15

American Society for Testing and Materials, West Consho-

hocken, PA, 1994, pp 321-347

[13] ASHRAE, Handbook of Fundamentals, "Thermal Comfort,"

Chapter 6, American Society of Heating, Refl'igerating, and Air-

Conditioning Engineers, Atlanta, 1997, p 8.12

[14] Amrein, E and Martinelli, R., Witrmediimmung und Dampfdif-

Wohnungsbau, Bern, 1972, pp 28-33

[15] Burge, H A., Su, H J., and Spengler, J D., "Moisture, Organ-

isms, and Health Effects," Moisture Control in Buildings, Chap-

ter 6, ASTM MNL 18, American Society for Testing and Mate-

rials, West Conshohocken, PA, 1994, pp 84-90

[16] International Energy Agency, Guidelines and Practices, Vol 2, International Energy Agency, Annex XIV, Leuven, Belgium,

[19] TenWolde, A., "Design Tools," Moisture Control in Buildings,

Chapter 1 l, ASTM MNL 18, American Society for Testing and Materials, West Conshohocken, PA, 1994, pp 208-215

[20] Oliver, A C., Dampness in Buildings, Nichols Publishing, New York and London, 1988, pp 145-181

should be based on the specific climatic conditions that the

building experiences or will experience In Chapter 23,

"Thermal and Moisture Control in Insulated Assemblies

Applications," in the 1997 ASHRAE handbook [1], three cli-

mate types are delineated for the purposes of moisture con-

trol: heating, cooling, and mixed climates However, the

definitions of these climate types are somewhat arbitrary,

and they are used only to formulate a set of prescriptive and

generic moisture control strategies Neither the definition of

climate type nor the moisture control strategies in the 1997

ASHRAE handbook are supported by analyses of the per-

formance of buildings under design weather conditions and

under standard indoor moisture design loads At present, a

standard for such moisture design loads is under develop-

ment within ASHRAE (SPC 160P Design Criteria for Mois-

ture Control in Buildings) It will include criteria for mois-

ture design weather data but will not provide the actual

weather data Until such design weather data are available,

a moisture analysis has to be conducted with currently avail-

able weather data or design weather data generated by the

user

Building moisture analysis can provide specific informa-

tion on the expected moisture levels in specific building con-

structions during a specific period of time If the analysis is

done for design purposes, the input data should reflect de-

sign conditions for the interior as well as the exterior of the

building The kind of weather data needed for moisture anal-

ysis depends on the analytical tool used and the purpose of

the analysis Generally, building moisture analysis requires

more detailed weather data than building energy analysis or

air-conditioning equipment sizing and design In addition to

temperature, wind, and solar radiation data, the analysis re-

quires a measure of outdoor humidity (vapor pressure, wet-

bulb temperature, dew point temperature, or humidity ratio)

and often calls for precipitation data

S O U R C E S OF W E A T H E R DATA

Detailed historical hourly weather data are available from

the National Climatic Data Center (NCDC) The World Data

Center for Meteorology at the NCDC in Ashville, NC, can provide archived weather data from around the world The Surface Airways Meteorological and Solar Observing Net- work (SAMSON) data set contains historical hourly data for the United States, and the Canadian Weather Energy and Engineering Data Sets (CWEEDS) provide data for Canada Some of this information is available on the Word Wide Web Data sets have been derived from these historical data using statistical criteria that depend on the intended use of the data A brief description of some of these data sets follows Chapter 26, "Climatic Design Information," in the 1997

A S H R A E Handbook [1] provides weather information that is

useful for the design and sizing of heating, ventilating, air- conditioning, or dehumidification equipment These data help determine peak operating conditions for the equipment However, the weather conditions described occur only rarely The summer conditions given are exceeded only 0.4, 1, or 2% of the time, and the winter design conditions are based

on a 0.4 and 1% frequency (also referred to as 99.6 and 99% annual percentiles) The 1997 annual frequency data re- placed data at 1, 2.5, and 5% frequency for summer and 1 and 2.5% frequency for winter [1], which were included in

the ASTM Manual on Moisture Control in Buildings [2] Data

of such extremity would rarely be called for in moisture anal- ysis

ASHRAE has produced one year of hourly weather data known as Weather Year for Energy Calculations (WYEC) data [3] The data were recently revised, improved, and re- issued as WYEC Version 2, or WYEC2 data, for 52 locations

in the United States and 6 locations in Canada [4] The MOIST building moisture analysis computer program uses WYEC data [5] The WYEC data represent typical conditions from the viewpoint of building energy consumption and do not include precipitation

Typical Meteorological Year (TMY) data were produced for building energy analysis as well An updated set, TMY2, for

239 cities in the United States is available from the National Renewable Energy Laboratory [6] The Canadian Weather Year for Energy Calculations (CWEC) data were developed for 47 locations, using the TMY algorithm and software and

is available from Environment Canada The TMY data do not include precipitation

* The Forest Products Laboratory is maintained in cooperation with

the University of Wisconsin This chapter was written and prepared

by U.S Government employees on official time, and it is therefore

in the public domain and not subject to copyright

1Research physicist, USDA Forest Service, Forest Products Labo-

ratory, One Gifford Pinchot Drive, Madison, WI 53705-2398

2Associate professor, Biosystems and Agricultural Engineering De-

partment, University of Kentucky, Lexington, KY 40506-0276

C L I M A T E D E F I N I T I O N S F O R

M O I S T U R E C O N T R O L

Recommendations for moisture control strategies are usu- ally given by climate type For instance, the 1997 ASHRAE handbook provides recommendations for heating climates,

16

Copyright © 2001 by ASTM International www.astm.org

C H A P T E R 2 - - W E A T H E R DATA 17

T A B L E l a - - M e a n m o n t h l y d r y - b u l b a n d d e w - p o i n t t e m p e r a t u r e s (~ o v e r 30 y e a r s (1961-1990) for U n i t e d S t a t e s l o c a t i o n s State

January April July October Mean Mean Mean Mean Mean Mean Mean Mean WBAN Location DB DP DB DP DB DP DB DP

1 8 MANUAL ON M O I S T U R E A N A L Y S I S I N B U I L D I N G S

TABLE l a - - M e a n m o n t h l y d r y - b u l b a n d d e w - p o i n t t e m p e r a t u r e s (~ o v e r 30 y e a r s (1961-1990) for U n i t e d S t a t e s l o c a t i o n s (continued)

January April July October Mean Mean Mean Mean Mean Mean Mean Mean State WBAN Location DB DP DB DP DB DP DB DP