Housing. The Impact of Economy and Technology

1092 Pages·1981·27.757 MB·English

by  Oktay Ural and Robert Krapfenbauer (Eds.)

PROCEEDINGS OF THE
INTERNATIONAL CONGRESS ON HOUSING
THE IMPACT OF ECONOMY AND TECHNOLOGY
NOVEMBER 1S18, 1981
VIENNA, AUSTRIA
PRESENTED BY:
International Association for Housing Science
P.O. Box 340254, Coral Gables, Florida 33114
IN COOPERATION WITH:
Florida International University, Miami, Florida
Technical Universities-Vienna, Graz, Innsbruck
Orgnisation Internationale des Experts, Paris
Academy of Applied Art, Department of Structural Science, Vienna
Pergamon Titles of Related Interest
Goodman et al. LOW COST HOUSING TECHNOLOGY:
An East-West Perspective
Ural ENERGY RESOURCES AND CONSERVATION
RELATED TO BUILT ENVIRONMENT
Ural HOUSING: Planning, Financing, Construction
Related Journals*
BUILDING AND ENVIRONMENT
COMPUTERS, ENVIRONMENT AND URBAN SYSTEMS
HABITAT INTERNATIONAL
TECHNOLOGY IN SOCIETY
UNDERGROUND SPACE
*Free specimen copies available upon request.
1
PERGAMON
ON URBAN AND REGIONAL AFFAIRS
POLICY
STUDIES
HOUSING
The Impact of
Economy and Technology
Edited by
Oktay Ural
Professor and Director
International Institute for Housing and Building
Florida International University
Miami, Florida, U.S.A.
Robert Krapfenbauer
Baurat h.c. o Professor
Pötzleinsdorfer Strasse 94, A-1184 Vienna, Austria
Pergamon Press
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Copyright © 1981 Pergamon Press Inc.
Library of Congress Cataloging in Publication Data
International Conference on Housing: the Impact of
Economy and Technology (1981 : Vienna, Austria)
Housing : the impact of economy and technology.
(Pergamon policy studies on urban and regional
affairs)
Proceedings of the conference presented by the Inter-
national Association for Housing Science, in coopera-
tion with the Florida International University et al.
1. Housing policy-Congresses. I. Ural, Oktay.
II. Krapfenbauer, Robert Johann. III. International
Association for Housing Science. IV. Florida Inter-
national University. V. Title. VI. Series.
HD7286.I5123 1981 363.5'8 81-15326
ISBN 0-08-028066-8 AACR2
All Rights reserved. No part of this publication may be reproduced,
stored in a retrieval system or transmitted in any form or by any means:
electronic, electrostatic, magnetic tape, mechanical, photocopying,
recording or otherwise, without permission in writing from the
publishers.
Printed in the United States of America
PREFACE
The theme of the World Congress emphasizes two major concepts which are
closely related to the provision of decent shelter to the population of our
planet: Economy and technology, and their impact on the housing industry.
The lack of decent housing affects the lives of every family in every
country. The population growth has complicated, and will continue to compli-
cate, the search for a solution. According to United Nations studies, the
world's population will increase by four billion people in the next thirty
years. This translates, in real life, to 20 million new houses per year for
the next three decades.
Cities are growing at a frightening pace. In 1900 there were eleven
cities of more than a million people each. Today, in 1981, there are 191
cities with populations exceeding a million, and one hundred of these cities
are in the Third World Nations. It is predicted that by 1985 the number of
"million cities" will reach 275. This is an increase of 265 "million cities"
in 85 years.
Today there are about one billion people in the world who do not earn
enough to own a shelter, any kind of a shelter. They are the cause of squatter
settlements which become economic and social burdens to the nations. Cities
under the unexpected and unscheduled demands from squatters cannot succeed in
the provision of community services.
The limited resources of the world are causing economic and social
dilemmas to almost all nations. The accustomed life-styles are changing; poor
nations are developing very slowly.
The housing situation around the world, obviously, is not good at all.
It is rather alarming. However, it is not a hopeless case. Through technology
transfer and adaptation, with the support of a wise economic plan, we ca npro-
vide better shelter to more people.
The Proceedings include many outstanding manuscripts prepared by com-
petent, dedicated individuals. They cover a wide range of problems associated
with housing technology and economy. It is fair to say that the future of our
world and society will greatly depend on what will be done on the implementa-
tion of ideas presented in this document.
We have to convey our sincere appreciation to all the authors who have
prepared these excellent manuscripts, and to colleagues who supported our
efforts. Thanks to Linda Shuflin and Antonia San Jorge for their excellent
work in the preparation of this book.
Oktay Ural
Robert Krapfenbauer
September 1981
Miami, Florida
Vienna, Austria
xi
CONSTRUCTION PRACTICES IN BITUMINOUS
BUILT-UP ROOFING
Herbert W. Busching
Department of Civil Engineering
Clemson University
Clemson, SC 29631
USA
ABSTRACT
Bituminous built-up roofing membranes are widely used on low-
slope roofs in North America. While the cost of low-slope roofs
constitute approximately 2-5 percent of the total building cost,
roofing failures account for an inordinately high percentage of
litigation. This paper reviews some of the materials and con-
struction practices that are currently used in built-up bituminous
roofing. A brief summary is provided on the following topics:
membrane materials, adhesion, joints, construction equipment and
post-construction evaluation.
INTRODUCTION
The most widely used roofing system for low slope roofs in North
America is the built-up bituminous membrane. While the cost of these roofs
constitutes approximately 2-5 percent of the cost of the building, roofing
cases account for nearly 50 percent of litigation involving construction
failures.
Analysis of litigation in building failures in the United States indi-
cates roofing, building fascades and foundations to be the most frequently
litigated cases with roofing cases the most prevalent. It has been noted
that almost 50 percent of the lawsuits suffered by building designers in-
volve defective or inadequate roofing systems. In general, bituminous roof-
ing membranes are replaced every 10-20 years depending on severity of service,
design and maintenance.
1
The National Roofing Contractors Association has conducted a survey of
problems associated with low-slope built-up bituminous membranes. The re-
sults of this survey, updated annually, are summarized as part of NRCA's
Project Pinpoint (1). Chief visible characteristics of roof problems re-
ported in 1980 were blistering and splitting. Because these problems are
prevalent on new roofs and on reroofing projects, the emphasis of this paper
is directed to construction procedures and details.
The built-up bituminous membrane used often in clustered housing, and
industrial and commercial buildings consists of 3-5 plies of roofing felt
adhered together, generally over thermal insulation, by hot asphalt cement
or coal tar pitch. The area of built-up roofing constructed each year in
the United States would cover approximately 3 billion ft (280x10° mz) or
108 mi2 (280 km2) (2) .
The built-up roof membrane is generally expected to last approximately
15-20 years. Because an excellent opportunity for conserving energy exists
through retrofitting insulation and roofing, increased emphasis has been
directed to correct construction techniques for roofing. The cost of roofing
bitumen has increased rapidly in the last several years and motivates addi-
tional care in construction of built-up roof membranes.
The conventional built-up bituminous membrane is subjected to widely
varying temperatures during its service life. Figure 1 shows typical summer
and winter temperature profiles through a roof section. Because of these
severe service requirements imposed on the membrane, good construction
practice is needed to maximize membrane life.
WINTER
0°F(-I8°C)
65°F 75°F
(I8°C) (24°C)
INTERIOR TEMPERATURE
FIGURE I. TEMPERATURE PROFILES THROUGH ROOF SECTION
2
MEMBRANE MATERIALS
Membranes are composed of bitumen and felts which are generally of
three types: organic, asbestos, and glass fiber. Organic felts are gener-
ally saturated with asphalt or coal tar pitch and perforated to facilitate
venting of steam and moisture during placement. Organic felts lose strength
rapidly when wet and, consequently, care must be taken to prevent them from
being wetted during storage, during construction and after the membrane has
been constructed. Strength in the longitudinal direction is approximately
twice as large as the strength in the transverse (narrow) dimension.
' Asphalt-saturated asbestos felt has been more widely used in the United
States than in Europe. Asbestos felt is somewhat fire resistant; however,
it has low tensile strength in the transverse direction. Membranes con-
structed of asbestos felt have been prone to failure by splitting (1) es-
pecially over untaped joints of rigid insulation and it has been projected
that the use of asbestos membranes will decline during the 1980fs. Like
organic felt, the tensile strength of asbestos felt is approximately twice
as large in the longitudinal direction as in the transverse direction. The
most recent manual on roofing and water-proofing published by the National
Roofing Contractors Association (NRCA) does not include asbestos membranes
as a generic membrane (3). NRCA has utilized preliminary performance cri-
teria regarding minimum tensile strength (200 lbs/in in the weakest direc-
tion when tested at 0°F) to accept/reject generic membranes.
Preliminary performance criteria for bituminous built-up roofing mem-
branes had been proposed in 1974 by researchers at the National Bureau of
Standards (NBS) to serve as a guide in the production of roofing materials
and the development of new products for membrane roofing (4). Asphalt-
saturated glass fiber felts are used more widely now and are stronger than
organic or asbestos felts. Furthermore, strength of glass fiber felt is not
significantly reduced by moisture and the strengths measured in longitudinal
and transverse directions are nearly equal.
Asphalt or coal tar pitch, roofing felt, thermal insulation and other
materials for flashing are generally stored near the roof to be constructed.
The materials should be stored so that they are not deformed during storage
and they should be stored in a dry condition. Organic and asbestos felts
lose strength when they are wet and even upon subsequent drying do not
regain their original strength.
Fasteners approved by the insulation and felt manufacturer should be
used to attach these materials to the substrate involved. In many instances,
mechanical fasteners are specified and are installed by power tools. Testing
pull-out resistance of these fasteners is advised to verify that the attach-
ment is acceptable and that wind uplift forces will not tear off or damage
the roof.
Wind uplift forces may be estimated by the expression:
q = 0.00256 V2C
where V = wind velocity in mi/hr
2
q = stagnation pressure in lbs/ft
C = uplift coefficient
3
The uplift coefficient for a flat roof is approximately -1.0 except along
the perimeter where the coefficient is -2.4 and at corners where the co-
efficient is -5.0 (5). The attachment required at the roof perimeter is
therefore greater than that in the interior of the roof. On occasion,
mechanical attachment supplements attachment by adhesion.
On conductive substrates such as steel or concrete decks, the hot
bitumen should receive the insulation board as quickly as possible before
the bitumen cools. In no case should the quantity of hot asphalt be applied
at less than 12 lbs/100 ft^. Point-of-application temperatures of roofing
asphalts should fall within the 135-200-centipoise viscosity range (6). The
softening point of asphalt and the application point temperatures are tabu-
lated here.
Application Temperature for Roofing Asphalts (7)
Softening Point, °F Application Temperature, °F
140-155 340-380
160-175 355-390
185-200 375-400
205-225 410-430
Asphalt should be applied at the equiviscous temperature (EVT) which has
been established for that asphalt and less than the blowing temperature.
Asphalt should not be overheated because that may cause a fall back in vis-
cosity. One generalization that has been widely used is that bitumens should
never be heated above 550 °F.
Cooling rates of hot bitumens are dependent on several environmental
factors including application rate, wind velocity, air temperature, bitumen
temperature, substrate temperature and thermal properties such as thermal
conductivity, density, specific heat, thermal diffusivity and heat capacity.
Rossiter, et_ al., have modeled cooling rates of bitumens placed on a variety
of substrates subject to a variety of environmental factors (8).
Figure 2 shows cooling rates of asphalts placed on various substrates.
Insulation, wherever possible, should be installed in two layers with the
joints staggered. This will reduce heat and moisture leakage that occurs
when straight through joints are used. Moisture uptake by felts at the
joints results in weakened felts and splitting failure. In addition, mois-
ture absorption and related swelling of organic and asbestos felts causes
ridging and wrinkling of the membrane (2).
Hot bitumen may be applied by a felt-laying machine or by hand mopping.
The felt-laying machine should distribute the liquid asphalt in a continuous
layer. The discharge holes should not be clogged. Bitumen which is too cold
will not adher to the felt which will be placed over it and bitumen which is
too hot may flow too readily and not be distributed in sufficient quantity.
In general, the quantity of interply asphalt will generally be in the range
15-25 lbs/100 ft^. Because bitumen has become so expensive, roofing contrac-
tors cannot afford to waste it by placing it in excessive quantities.
4
RODEL — ASPHALT ON VARIOUS SUBSTRATES
S0Ô
SUBSTRATES
T'^TONCRETE """
2 · STEEL
3 · INSULATING CONCRETE
4 - PLVUOOD
5 - FELT/PUF INSULATION
6 - FIBER GLASS INSUL.
7 - PUF INSULATION
1\\2 , 3%4 7 -^..5 6' ·· .
v
300 -i—r—i—'—r—i—i—r
10 20 30 40 50
COOLING TIME, SECONDS
AIR AND SUBSTRATE TEMPERATURES ARE 70 F
UIND SPEED IS 0 HPH
Figure 2. Effect of Substrate on the Asphalt Cooling
Time (8). The Quantity of Applied Bitumen
is approximately 20 lbm/100 ft2 (0.98 kg/m2) .
Hand-mopping is accomplished using cotton mops and buckets of hot
liquid bitumen. The quantity and quality of bitumen coverage obtained using
these methods are quite dependent on the skill of the roof installer. The
felt or insulation must be placed in the hot bitumen quickly after the bitumen
is applied. Often the felt is seated in the hot bitumen by the weight of the
felt roll which is pushed over the bitumen or by brooming the felts into the
bitumen. Figure 3 shows that the time for asphalt placed at 500 °F to cool
to 300 °F is only 5 seconds or less when placed on concrete substrates.
Joints of the insulation should not be placed over gaps or low areas of
corregated metal decking. Rolling equipment over these joints will cause
strain or movement of the partially completed membrane.
Roof slope is important in providing adequate drainage. In general, a
roof membrane slope of approximately 1/4-in per foot is desirable. The
National Roofing Contractors Association recommends a roof slope of 1/4-in
per foot. Water should be completely drained from a roof within 18 hours of
rainfall. The additional cost involved in constructing a roof with adequate
slope compared to a "dead level" roof has been estimated to be approximately
3-6 percent (9).
The effect of membrane defects such as ridging, blistering and splits
is to exacerbate problems caused by ponded water. The ridges and blisters
5
«ODEI — ASPHALT ON CONCRETE
__WIHD_ SPEED
SOLI· · t HP*
DOTTED · 1· WM
DASHED · 2t *PH
DASH/DOT · 3t HPH
÷éêñ.Ë^Ë
I SOLID · Ö ÐÑÇ
4S· - DOTTED · It HPH
DASHED · 2t HP*
DASH/DOT · 3· ËÑÌ
"1
4—
3St
'vl
3tt 1 W ,,'.,,,»,,., » ...,',,.. »
£|J3L ArSÜL. —
SOLID ~ · · ÐÑÌ
DOTTED · It HPH
DASHED - 2t HPH
DASH/DOT · 3· ÐÑÇ
Figure 3. Relationship Between Bitumen Temperature
and Cooling Time for the Two-Component
Model, Asphalt Applied on Concrete. The
Quantity of Applied Bitumen is Approxi-
mately 20 lbm/100 ft2 (0.98 kg/m2) (8).
6