Publisher’s version / Version de l'éditeur:
RSI-Roofing, Siding, Insulation, 38, 4, pp. 1-24, 1964-10-01
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Roofing research in Canada
Jones, P. M.; Baker, M. C.
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ROOFING
RESEARCH
IN CANADA
BY
P . M . J O N E S A N D M . C . B A K E R
R E P R I N T E D F R O M R O O F I N G . S I D I N G . I N S U L A T I O N v o L . 3 8 . N O . 4 . A P R T L 1 9 6 4 , P . 2 4 v o | . . 3 4 , N o . 5 , M A Y t 9 6 4 , P . e O T E C H N I C A L P A P E R N O . I 9 O O F T H ED I V I S I O N O F B U I L D I N G R E S E A R C H
OTTAWA
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A N A ! - Y Z E D
N R C 6 t 9 9 P R I C E I O C E N T S-s64( (
T h i s p u b l i c a t i o n is being distributed by the Division
o f Building Research of the National Research Council.
I t
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-s i o n o f t h e o r i g i n a l p u b l i -s h e r .
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o f t h e canadian
G o v e r n r n e n t Spe cifications Board.
I Roofing research is a relatively new branch of organized applied science. As roofing is an important component in the satisfactory perfor-mance of a building, in most countries it is dealt with as a part of building research. Building research itself is a relatively new branch of applied sci-ence; all but one of the national build-ing research establishments have been founded in the last 20 years.
Interest in rooflng and its accom-panying problems is world-wide. These problems will differ from place to place because of local conditions with respect to climate, design and materi-als. This paper will try to present the picture of the Canadian roofing indus-try against an appropriate background. This means a quick look at the land that is Canada, for the pattern of Ca-nadian industry, commerce, and re-search can only be fully appreciated against such a background.
Perhdps climate is the biggest single factor in determining the performance of roofing. In Canada, the climate varies from place to place and season to season in a way that is very similar to that of corresponding adjacent areas of the northern United States. This is Lrecause over all of North America there is a constant struggle between cold air that attempts to surge down from the north and warm air trying to flow up from the south. This pro-duces high and low pressure areas with a weather front usually characterized by cloud precipitation and generally poor weather.
If orie asked for the weather
fore-Roofing Research in Ganada
B y P . M . J O N E S
q n d M. C. BAKER
cast in Canada this year the answer would be - just about anything. Since we hear so much about the weather perhaps some of the unusual historical facts of Canadian climate would be of interest. On July 28,1903, Southern Alberta had a sizzling 115 degrees F -the highest temperature recorded in Canada, yet the same province has experienced a temperature of-78 de-grees F, which is 5 dede-grees lower than the lowest in Ontario of -73 de-grees F. The City of Toronto in one July had temperatures of 100 degrees or better for six consecutive days and no rain for three weeks.
The weather can change rapidly-one day in Portage, LaPrairie it was 94 degrees, the next day it fell 50 degrees in 2 hours. ln 1945, around Christmas, all of Canada was enjoying reasonable temperatures in the 20's when cold air swept out of the Arctic across to Newfoundland and in three days created sub-zero temperatures all across Canada.
Apart from these extremes, the largest difference between the climate in Canada and in the United States is the length of duration of cold weather. Thus, winter construction, including roofing, is an economic necessity in Canada.
As in the United States, the Can-adian roofing industry can be divided into two groups-prepared roofing products and built-up roofing. There were 2Vz million squares of asphalt shingles produced in 1962 and l1/z million squares of smooth and min-eral-surfaced roll roofing. In the same year approximately I1,b million squares of asphalt and coal-tar pitch built-up roofing was prepared. This last figure may be compared with a figure of 9 million squares for the United States. The roofing industry
in Canada is at present faced with a variety of roofing defects some of which are:
1. Faulty design.
2. Improper drainage on dead level decks.
3. Lack of a vapor barrier where one is needed.
4. Insufficient insulation to prevent interior surface condensation. 5. Application of roofing in
inclem-ent weather.
6. Improper storage of felts and insulation.
7. Overheating oI bitumen. 8. Faulty flashings.
Many causes of these failures have been proposed which are no doubt familiar to everyone in the roofing industry. Many of these "causes" are suggested without any supporting evi-dence. It is reasonable to assume, how-ever, that many of the more recent roofing faildres are related to changes that have recently taken place in building practice.
Since World War Il rhere has been a large increase in the roofing market with a corresponding development of new roof-deck materials. Prior to this, two types of roof decking predomi-nated: cast-in place concrete and wood plank or wood sheathing. At pr3sent there is in use an ever-increasing var-iety of multiple-unit-type roof decks of lightweight aggregate ccncrete, steel and asbestos-cement, to mention only a few. Some of these materials have insulating properties but addi-tional insulation is usually specified.
The inclusion of a vapor barrier to prevent penetration of rvater vapor into the insulation from inside the building is now general practice. This vapor barrier usually consists of one or two layers of rag felt mopped to the top of the deck or, in the case of Jones
a steel deck, a vinyl type film applied with a special adhesive.
Much of the new roofing is used without any intentional slope and consequently has poor drainage. Pre-cast concrete and other multiple-unit roof decks are now widely accepted. Some of these are subject to creep deflections, often in excess of load deflections. This results in permanent deflections and ponding of water on the roof. The importance of adequate drainage is emphasized by the fact that the Division has not had to in-Vestigate a failure on any roof with adequate slope and drainage. Greater thicknesses of lighter insulation are used to achieve better thermal re-sistance, giving a soft underbedding for the roof membrane and subjecting it to greater variations in temperature. The increasing use of vapor barriers, while restricting the entry of moisture into the construction, introduces problems from moisture trapped in the construction. Humidification of buildings in winter is common and this aggravates the problems of mois-ture transfer into the roof compon-ents.
Roofing defects are generally char-acterized by a breakdown of the rooT-ing membrane and wettrooT-ing of the in-sulation, usually indicated by leaking inside the building in late winter. This frequently occurs in the early life of the roofing, from one to six years after construction. The question arises
as to whether the moisture in the in-sulation enters from the inside or from the outside of the building.
For some time now, these diffi-culties have been attributed to vapor diffusion when no vapor barrier is used, but it is often difficult to ac-count for the amounts of water in-volved on this basis except in cases where there is the possibility of wetting by mass air flow around roof pene-trations such as at ducts and pipes, or at joints or cracks in the roof deck. There is a very significant proble'm with moisture trapped in the rooflng during construction. In Canada in re-cent years, there has been a large increase in the amount of rvinter con-struction, leading to the application of roofing under conditions where it may be difficult to meet the
require-ments necessary to obtain good
roof-ing. Protective cover is widely used for other phases of construction, but as yet it is not employed by the roof-ing industry.
Roof construction is subject to many hazards; snow and ice on roof decks, the possibility of wet material from
improper storage, inadequate adhesion
of felts due to the application of ma-terials to cold surfaces, and overheat-ing the bitumen.. Many of the wet finishing operations, such as concret-ing and plasterconcret-ing, release large quan-tities of moisture which can penetrate into the roofing system under certain conditions.
There are two common character-istics of failures: (a) ridging or wrinkling of the membrane over in* sulation joints, and (b) splitting of the membrane across the whole width of the roof. These problems have been observed in all parts of the country regardless of the rvide range of cli-matic conditions.
Failures due to ridge formation in the membrane are most prevalent along insulation joints where insula-tion is applied over a structural deck. Subsequent weathering and mechan-ical damage can lead to breaks in the membrane, wetting of the insulation, leakage, and eventual complete de-terioration of the membrane. This type of failure appears to be confined to flat or low-sloped roofs, and has occurred on roofs, rvith or without vapor barriers, over various types of insulation and is believed to occur only with membranes composed of rag felts.
Membrane splitting is characterized by a complete separation, often /z to 3/+ in. wide often across the complete width of a building and usually along the continuous unstaggered joints of insulation and is accompanied by a corresponding separation of the in-sulation. The splits are usually par-allel to the direction of laying of the felts; they are not confined to any one type of felt (in some cases with rag felts splitting and ridging occur on the same roof).
Improvements in Roofing Technology
Although roofing is part of the larg-est industry in Canada, the construc-tion industry, it is unique by industrial standardS in that there are many hundreds of roofing flrms, which are fairly small individual organizations. The material supplier is the part of the roofing industry that comes closest to the generally accepted view of "in-dustry" and it is to this segment that the customer must look for guidance in roofing material problems. Trade associations are also playing a major role in providing some answers to the problems of the industry. Perhaps the most noteworthy of the contributions from this source in Canada is the ending of the bonding system. This improvement and other steps in the advance of the roofing industry in Canada are as follows:
1. Elimination of bonds.
2. Preparation of specification
man-uals by roofers.
3. Educational programs for roof-ers.
4. Preparation of standard code of practice by C.S.A.
5. Material research by suppliers. 6. Laboratory and field studies by
D.B.R.
The system of bonded roofs was introduced into Canada by the Barrett Company in 1916 at the same time as it was introduced in the United States.
In 1960 the system was abandoned in
Canada because it was believed that it
encouraged inadequate supervision of
workmanship and a lack of concern for design detail by architects and for protective maintenance by owners.
The bond system was replaced by a gvarantee by the roofer that the roof would perform satisfactorily for two years. The specification and super-vision of the roofing is sometimes done
by a roofing consultant in cooperation with the architect. This consultant also arranges with the owner for main-tenance inspection to insure continu-ing good roof performance. The Can-adian Roofing Contractors Assn. is also improving roofing practices by discussing problems. In addition, they have produced specifications manuals and are in the process of preparing additional roofing manuals. The na-tional organization together with the various Provincial Associations of Roofing Contractors are also consider-ing educational programs for roofers-As members of the Committee on Asphalt and Tar Roofing Materials of the Canadian Standards Assn., they are also working on the preparation of a standard code of practice for roof design and application.
Patt ll
Research on Roofing
o Most of the Canadian material suppliers have modest programs of product evaluation and exposure tests of new and established materials. But very little organized research is under-way to understand and study roofing problems.
The agency in Canada that is con-cerned with the broad range of roof problems is the Division of Building Research of the National Research Council of Canada. These problems are brought to the attention of the Di-vision through inquiries from archi-tects, builders and owners, and are concerned with roof terraces, roof deck construction, insulation, vapor control and the more recently devel-oped roof coatings.
The Division conducts investigations of roof construction practices and roofing failures and tries to keep the construction industry informed on these matters. Before describing the work of the Division of Building Re-search a short historical sketch and de-scription of the National Research Council of Canada will be given, since many of you may be familiar with the work of this organization.
The Division of Building Research was established, in 1947 with a major responsibility of research into the problems of the construction industry. Essentially the main task is to provide information, to those who need it, in design work, construction problems on the job in connection with materials and their properties, or assisting with the analysis of difficulties, poor per-formance, or failures. The' Division does not engage in any consulting architectural or engineering work, and information in answer to inquiries is based on the basic building science in-volved. The interest in failures is re-lated only to the nature and cause of the failure.
Laboratory investigations of build-ing research are carried out by sections such as Organic Materials. This sec-tion and others similar to it can be con-sidered as building science sections. Other sections collect results of labora-tory studies and act as a liaison be-tween the construction industry and re-search. These sections deal with the "building practice" side of building research.
There are, therefore, two sections in the Division interested in
roofing-Or-ganic Materials and Construction-al-though other sections have some inter-est, in particular the Building Services Section, in connection with roof insu-lation. Laboratory activity is princi-pally confined to work on built-up roofing, as is indicated by the following: L Low temperature properties of bitumens.
2. Roof temperature.
3. Engineering studies of roofing membranes.
4. Combined heat and moisture flow.
5. Durability of coating-grade as-phalts.
Low Temperature
Properties of Bitumens
In some preliminary studies on the weathering performance of bitumens it was noticed that occasionally the low temperatures in winter would cause cracking of the materials, without any chemical change. The problem of roof splitting was also observed in roofing investigations.
It was therefore decided that the first investigation would be a study of the low temperature characteristics of built-up roofing. One part of this work is concerned with the brittleness of bitumens at low temperatures which gives some indication of the ductility and the ability of the material to with-stand deformation. The test is a modi-fied form of that devised by Fraass and used in Europe for many years.
An illustration of the test unit is shown in Figure 1. In the test a uni-form thin sample of bitumen is ap-plied to a polyester film and flexed
Figure l-Temperolure fesf unif
once a minute. At the sime time the temperature is decreased at a rate of
1.8 degrees per minute. The tempera-ture at which a crack appears in the asphalt is taken as the brittle point temperature.
This test has been used to study the effects of overheating roofing asphalt and it has been found that the material can withstand heating to 500 degrees for a short period of time in the order
of an hour without any detectable change in the brittle point temperature. The test has also been used to demon-strate self-healing abilities of the bitu-mens. Studies are now in progress to evaluate hardness changes that accom-pany weathering and also to develop a measure of self-healing and to study the change in this property with aging.
Roof Temperatures
In 1960 an outdoor exposure study was started to measure roof tempera-tures and to observe the weathering of roofing asphalts on a variety of built-up roofing systems. At this meeting last year, Bill Cullen of the National Bu-reau of Standards in Washington pre-sented the results of his roof tempera-ture studies. DBR results, which are very similar to those of Mr. Cullen, have shown that:
l A built-up roofing membrane in-sulated from the roof deck will attain appreciably higher temperatures as the result of solar heating than its non-insulated counterpart.
2. tEmissive cooling or night radia-tion of roofing exposed to a clear night sky can reduce the temperature of the roofing below that of the air tempera-ture; with an insulated deck this can be as low as 15 degrees.
3. There are large and rapid fluctua-tions in temperature of built-up roof-ing. Even during a normal sunny day in summer when the temperature of the roof surface can easily reach 150 degrees a heavy rain storm will reduce the temperature to 80 degrees in less than an hour.
4. Light-colored gravel and liquid surfacing tend to reduce the rise in temperature from solar heating.
5 . O n s m o o t h - s u r f a c e d s a m p l e s , there appears to be greater deteriora-tion of the bitumen for roofins over insulation.
Engineering Properties
of Built-Up Membranes
In order to examine the pheno-menon of membrane splitting a study was begun to assess the eftect of tem-perature on strength and deformation in relation to shrinkage and embrittle-ment.
Very little information is available on stress-strain properties of roofing as it is considered to be non-loadbearing, but there is no doubt that membranes are subjected to strains due to build-ing or roof deck movements and to moisture and temperature changes.
Laboratory studies have been confined to some controlled conditions of pre-paring and testing the membranes. The testing was that of tensile studies at temperatures of 75 degrees and -20 degrees and at two rates of straining on both saturated felt and membranes.
The results indicate that the felt plays a major role in the strength of the membrane at both high and low temperatures. But a.mere value of strength does not give very much in-formation, for it is not loads that are splitting the roofs, but deformations which are imposed on it by structure and climate.
It is therefore of interest to note in Table I the deformation that accom-panies thbse stresses, particularly at low temperatures. In this case it is ap-parent that the bitumen is a rigid mate-rial and has formed a tightly welded structure with the reinforcing felts, consequently failure in the bitumen re-sults in a failure of the membrane. Flow of the bitumen is impossible and no variation in the breaking strain is found for the materials.
The results are difficult Jo relate to splitting of roofs but they do serve to indicate that studies are necessary to assess the strains that occur on actual roofs. The effect of temperature has al-ready been studied by Cullen who re-ports an increase in the coefficient of thermal expansion at the lower tem-peratures. In practice these tempera-tures efiects are complicated by the three-component membrane, fibre, saturant, and the presence of moisture can be a serious factor in changing dimensions upon cooling.
Combined Heating and
Moisfure Flow
This is a study that has been under-way in the Division by the Building Services Section. The object is to de-termine the rate of moisture gain and distribution on this moisture in vari-ous insulating materials when exposed to a temperature gradient. The cold surface is sealed and the warm surface is open to controlled moist air condi-tions.
Durability of Asphalts
This study has been concerned with coating-grade asphalts used in the pre-pared roofing and siding industry. Its purpose was to evaluate the natural and accelerated degtadation of asphalts and to correlate these durabilities with known physical and chemical
para-r o a /o / c a a
LEG
E ND
Y = 2 3 . 1
X + 8 - 4 4 ( R = 0 ' 9 5 )
T W O S T A N D A R D
E R R O R S
O F Y
1 . 0
2 ' o
3 . 0
D U C T I L I T Y ,
C M
Figure 2-This groph shows fhe correlolion of dudility with durobility of ospholfs. The resuhs show fhol duc'tility of ospholt hos o degree of corre-lation with lhe occelerofed weofhering pertormonce ol these moferiols.
80
70
6 0
5 0
40
30
2 0
t 0
.J) lrl J(-)
(-,
u-o o z. j F J CD E. ometers. Results have shown that the ductility of asphalt has a degree of cor-relation with the accelerated weather-ing performance of these materials and are shown in Figure 2.
These brief descriptions of the labor-atory studies may appear somewhat remote from the day-to-day problems of roofers. This is not the case, how-ever, as one of the two sections con' cerned with roofing studies-the Con-struction Section-maintains very close contact with the roofing industry.
Contact is with both the roofing material suppliers through the Asphalt Roofing Technical Committee and with the roofers through the Canadian
4 . 0
Roofing Contractors Assn. The co-op-eration of these associations, together with that from architects, engineers, consultants and rooflng contractors, has enabled the division to examine a large number of roofs across the coun-try, thus providing field investigations to complement the laboratory research. The concern in Canada regarding the problems of roofing is being sup-ported by some studies and action. The program of laboratory research by the Division of Building Research is a modest start at these problems. No rapid and sure answer is anticipated but a better understanding of the
prob-lems is being achieved.
Table l-The deformoiion thot occompanies lhese sfresses, porficulorly in
low temperotures, indicotes fhof the bilumen is o rigid moleria.l ond hos formed a lightly welded sfrucfure with the reinforcing felts. Failure in lhe bilumen resufis in foilure of lhe membrone.
Tensile Froperties of Roofing Membranes at -20 F
Sample Directioo
Breaking Load lblin.
Asphalt - rag lilgthwise crogswlSe
t . 0 5 t . t 8
237 143
Asphalt - glass lengthwise crosswlse
l . t 2 t . l l
t o J /
Coal - tar pitch rag lengthwise crosswrse
o . 6 2 0 . 4 5
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