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Roofing - Past and Present
Baker, M. C.; National Research Council of Canada. Associate Committee
on the National Building Code
N21t2 nr.
191-e . 2 BI;DG
This publication is one of a series being pro-duced by the Division of Building Research of the National Research Council as a contribution towards better building in Canada. It rnay therefore be reproduced, without arnend-rnent provided only that the Division is advised in advance and that fult and due acknowledgrnent of this original publi-cation is always rnade. No abridgrnent of this report may be published without the written authority of the Dlvision. Extracts ,may be published for purposes of review only.
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CANADA
DIVISION OF BUILDING RESEARCH
ROOFING P.&ST AATD PRESENT by
C . B a k e r
A N A L Y Z E D
Technical Paper No. 191 of the
Division of Building Research
OTTAWA F e b r u a r y 1 9 5 5 M .
PREFACE
Mernbers of the Division of Building Research are frequently called upon to deliver talks to professional groups a n d v a r i o u s a s s o c i a t i o n s . T h i s p a p e r b r i n g s t o g e t h e r e x c e r p t s frorn four talks dealing with roofing and principally biturninous roofing on flat roofs given by Maxwell C. Baker, a Civil
Engineer and Architect with the construction section of the D i v i s i o n .
The talks which forrn the basis of this report are: Talk given to Architects and Engineers of the Federal Departrnent of Pubtic Works at Ottawa, Ontario, 6 D e c e r n b e r 1 9 6 3 .
Paper presented at the Annual Meeting of the Alberta Roofing Contractors Association at CaLgary, Alberta, 2l Novernber 1963, entitled t'Dignity and Respect in the Roofing Industty. r,
Paper presented at a rneeting of the Master Sheet Metal Contractors Association of British Colurnbia a t V a n c o u v e r , B . C . , 26 Novernber 1963, entitled i l R e s e a r c h
a n d R e c e n t D e v e l o p m e n t i n R o o f i n g . r ? Paper presented at the Annual Meeting of the
Newfoundland Association of Architects at St. Johnrs, Nfld. , 2l January 1964, entitled ilThe Architect and t h e D e s i g n o f R o o f i n g . r r
THE HISTORY OF. ROOFING R o m a n c e o f R o o f i n g . .. B i t u m i n o u s R o o f i n g . . .
A s p h a l t . . . . .
Felts
Construction Industry Today . . . The Roofer Today
THE ARCHITECT
C r i t i c i s m o f A r c h i t e c t s
Changes in tsuilding practice Related to Roofing DESIGN CONSIDERATIONS - ROOFING SYSTEN4S
Building Movement Insulation of Roofs
Condensation of Water Vapour
Page i I I
z
4 56
7
9
9
l lt z
t 3
L 4 l 6 DESIGN CONSIDERATIONS COVERINGSChoice of Materials for
- BITUMINOUS ROOF Bituminous Roofing. . . . l 8 l 8
z?.
2 3 DrainageR o o f T e m p e r a t u r e s and Surface Treatments Flashings
( i )
TABr.Ii OF CONTENTS (contrd) Application of Materials S u m m a r y o f F a c t o r s t h a t U s u a l l y A s s u r e S a t i s -factory Roofing T H E D 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 . . . . 2 9 C o n s t r u c t i o n S e c t i o n . . 3 0
Organic Materials Section 30
A s p h a l t D u r a b i l i t y . . . 3 I R o o f T e m p e r a t u r e s 3 2 L o w T e r n p e r a t u r e P r o p e r t i e s .. 3 4 E n g i n e e r i n g P r o p e r t i e s 3 5 Combined Heat and Moisture Flow 36
Related Work of the Division 36
NEW MATERIAI.S AND SYSTEMS 3 7
b y M . C . B a k e r
HISTORY OF ROOFING
W h e n w e s p e a k o f r o o f i n g t o d a y , w e are usually refer-r i n g t o b i t u refer-r n i n o u s refer-r o o f s , as sorefer-rne forefer-rrefer-rn of biturefer-rninous refer-rnaterefer-rial is i n v o l v e d f o r a n e s t i r n a t e d 85 to 90 per cent of the entire annual r o o f i n g c o v e r a g e i n c a n a d a and the united states. This type of r o o f i n g h a s n o t a l w a y s g i v e n good service and in recent years con-c e r n o v e r p r o b l e r n s h a s b e e n e > < p r e s s e d by a r con-c h i t e con-c t s , o w n e r s r m a n u f a c t u r e r s a n d t r a d e s l T r e n . orie of the oft-quoted reasons why b u i l t - u p r o o f i n g h a s n o t given satisfactory service is lhe difficulty of obtaining good workmanship. That this is a problern is pointed up by the fact that one of ,the stated objectives of canadian Roofing c o n t r a c t o r s A s s o c i a t i o n s i s t h e u p g r a d i n g of the roofing tradesmen a n d t h e u p g r a d i n g o f t h e r o o f i n g industry. T h r o u g h t h e y e a r s t h e r e h a s b e e n a c e r t a i n s t i g m a in connection with roofing tradesrrren - a t e n d e n c y t o c o n s i d e r t h a t they are in a category lower than other t y p e s o f t r a d e s m e n . A t a r o o f e r s r m e e t i n g i n eaLgary in 1962, the i d e a w a s e x p r e s s e d b y a canadian rnember of a panel that children w e r e n o t a l w a y s p r o u d of the fact that father was a roofer, and t h e r e a p p e a r e d t o b e a feeling that roofing is not an industry in which anyone can operate with respect and dignity. It is inieresting to consider how this situation has corne about, by exarnining what has happened in roofing, what the situation is today, and what will probably happen in the future.
Romance of Roofing
S u r e 1 y r o o f i n g m u s t h a v e b e e n one of the'earliest crafts i n t h e w o r l d . s h e l t e r h a s b e e n o n e o f t h e p r i m a r y needs of rnan, and frorn the beginning he had to protect hirnself against the
r e l e n t l e s s f o r c e s o f n a t u r e . w e c a n i r n a g i n e i n t h e b e g i n n i n g that r o o f s w e r e m e r e a c c i d e n t s , overhanging branches of trees for the t r e e - m e n , p e r h a p s L a t e r t i e d t o g e t h e r , and overhanging rock
l e d g e s f o r t h e c a v e - m e n , perhaps ]ater filled in at tttu
" i a . s w i . t h s t o n e a n d m u d t o e x c l u d e the elements. perhaps pit dwellings c a m e n e x t , w h e r e a c i r c u l a r p i t w a s d u g i n t o t h e g r o u n d a n d .
r o o f e d o v e r w i t h b r a n c h e s and leaves. It must be assumed that s o m e w h e r e i n t h e m a r c h of evolution rnan discovered the
water z water
-s h e d d i n g q u a l i t y o f l e a v e -s w h i c h o v e r l a p p e d each other, and thi-s u n d o u b t e d l y l e d t o t h e u s e o f stone slabs and other local materials f o r r o o f s , l a i d i n o v e r l a p p i n g fashion. when such roofs leaked, t h e 3oints were probably stuffed with rnoss. As it was a living a n d g r o w i n g p l a n t , t h e m o s s f i l l e d the joints and forrned an e f f e c t i v e e x p a n s i o n j o i n t and water barrier. w h e r e s t o n e w a s s c a r c e , a s i n E g y p t , c l a y h a d to be considered for building, and b u i l d i n g b l o c k s a n d t i l e w e r e invented. The first clay roofing t i l e s a r e s a i d t o h a v e b e e n moulded by hand and shaped on the t h i g h s o f w o m e n a r t i s a n s . s o m e s p a n i s h t i r e e v e n t o d a y h a s t h i s c h a r a c t e r i s t i c s h a p e , w i d e a t o n e e n d a n d n a r r o w a t t h e o t h e r . T h e h i s t o r y o f t i l e , s l a t e , thatch and other roofing rnaterials is e x t r e m e l y i n t e r e s t i n g and the rooferrs craft with these rnaterials i s s t i l l a l i v e i n c e r t a i n parts of the world.
one thing com'''on to all these materiars is that their u s e e x t e n d s b a c k o v e r hundreds of years. clay tile was used by t h e e a r l y E g y p t i a n s , and terra-cotta tile has been found in Greek r u i n s d a t i n g a t h o u s a n d y e a r s before christ. s r a t e w a s b e i n g u s e d f o r o t h e r b u i l d i n g p u r p o s e s only a little later, and probably also f o r r o o f i n g . T h e r e a r e s l a t e r o o f s i n E n g l a n d that have been in s e r v i c e f o r o v e r 1 0 0 0 y e a r s . Records indicate that thatch for r o o f i n g w a s i n c o n s i d e r a b l e use in England seven or eight centuries
a g o , b u t i t s u s e p r o b a b l y originated much earlier. T h e r e a r e p l e n t y o f p r a c t i c a l rules, based on experience, to guide the c r a f t s m e n , a n d w i t h w e l l - e s t a b l i s h e d a p p t i c a t i o n p r o c e d u r e s n o d i f f i c u l t i e s a r i s e .
C o n n e c t e d w i t h e a c h o f t h e s e materials there is a great deal of romance. what could be rnore rornantic than the s l a t e r t s t r a d e w h e r e t h e s l a t e r w o r k s w i e h E m p r e s s e s , p r i n c e s s e s , D u c h e s s e s , C o u n t e s s e s , L a d i e s , e u e e n s , R a g s , and peggies, w h i c h a r e s o m e o f t h e names used to describe specific sizes of s l a t e . A n d w h o i s n o t f a s c i n a t e d b y the beauty, real or irnagined, of thatched roof cottages found in the willages throughout the c o r n - g r o w i n g c o u n t i e s o f E n g l a n d , and which have come to be a c c e p t e d a l l o v e r t h e w o r l d as an essential part of the English c o u n t r y s c e n e r y . T h e r e a r e o v e r 8 0 0 f u l l - t i m e t h a t c h e r s in E n g l a n d a n d w a l e s still practicing this fascinating craft, rnain-t a i n i n g a n d r e n e w i n g old roofs, and rnain-tharnain-tching new houses.
Bituminous Roofing
How is it then that the trade of the tar or asphalt roofer i s n o t c o n s i d e r e d a dignified craft? For the answer to this
q u e s t i o n , i t i s n e c e s s a r y to look back to the introduction of b i t u m i n o u s r o o f i n g , a n d what has happened in the roofing
i n d u s t r y s i n c e t h a t t i m e . T h e w a t e r p r o o f i n g , p r e s e r v a t i v e a n d c e r n e n t i n g q u a l i t i e s o f natural biturninous materiars was an
e a r l y d i s c o v e r y o f a n c i e n t p e o p l e s a n d , b e c a u s e o f t h e s e q u a l i t i e s , b i t u m e n s h a v e b e e n u s e d in various applications since earliest t i m e s . T h e i r i n t r o d u c t i o n i n t o roofing involves one of those
a r n a z i n g b u s i n e s s s u c c e s s stories based on circurnstance and o p p o r t u n i t y w h e r e an impressive nationar enterprise grew from s r n a l l , l o c a l i z e d , a n d b a r e l y r e c o r d e d b e g i n n i n g s . T h e s e b e g i n n i n g s w e r e I i t t l e r n o r e than I00 years ago.
I n 1 8 4 4 , S a r n u e l D . W a r r e n is reputed to have s t a r t e d a r o o f i n g b u s i n e s s in cincinnati, ohio, using paper and p i n e t a r f o r c o v e r i n g almost flat roofs. To soften ttre pine tar h e e x p e r i m e n t e d w i t h c o a l tar and later used only coal-tar pitch. I n 1 8 5 4 , i n c h i c a g o , s a m u e r E . B a r r e t t s e t u p a roofing business t h a t t o d a y i s t h e B a r r e t t Division of Allied chernical c&poration. H e h a d b e e n s e l l i n g pine tar and paper roofing for a short time before starting his own company. At this tirne, individuar sheets o f p a p e r w e r e i m r n e r s e d in Lhe saturant, and the excess was s c r a p e d o f f b y h a n d . B a r r e t t switched to coal tar pitch
e x c l u s i v e l y a n d s e t up a continuous process of roofing-felt rnanu-f a c t u r e , , u s i n g p a p e r r o l l s 2 6 i n . w i d e , and a laundry hand
w r i n g e r t o s p e e d u p production. I n i t i a l r y h e p u r c h a s e d roofing rnaterials frorn the pioneer w-arren chernical Manufacturing
c o m p a n y , w h i c h was an offshoot of the original warren business. A l i t t l e e a r l i e r A m e r i c a had taken rapidly to the idea of coal gas i l l u m i n a t i o n , a n d g a s p l a n t s p r o d u c i n g gas frorn coal had
" p " * g u p n e a r a l l t h e l a r g e r cities. The more gas that was produced, t h e m o r e c o a l t a r piled up in the gas plants. Gas companies were running into trouble with the rnunicipal authorities con-c e r n i n g t h e d i s p o s a l of the waste and the fouring of rivers and s e w e r s w i t h c o a l t a r , and were having to employ haulers to dump t h e r n a t e r i a l . T h e y w e r e h a p p y , t h e r e f o r e , lo puy roofing
c o m p a n i e s s u c h as Barrettrs to dispose of the annoying problem. T h e d i s a s t r o u s f i r e o f l g ? l i n C h i c a g o d e s t r o y e d 1 7 , . 4 3 0 b u i l d i n g s i n c l u d i n g the Barrett plant; darnage amounted to $ I 6 8 r n i l l i o n . T h e p o s t - f i r e r e b u i l d i n g p r o g . " * c r e a t e d a
t r e m e n d o u s m a r k e t f o r buirding and rooiing materials. T h e
b u i l d i n g i n d u s t r y w a s required to create a new city in an extremely s h o r t t i r n e . E c o n o m y in rnaterials and labour was necessary, a n d m o s t o f t h e n e w buirdings, which were of a[ types, rr"aii"t r o o f s . A s a r e s u l t o f t h i s catastrophic fire, built-up roofing frorn
4 -p a -p e r a n d c o a l - t a r -p i t c h a n d t h e B a r r e t t b u s i n e s s g o t a b o o s t w h i c h a s s u r e d t h e i r f u t u r e . T h e B a r r e t t c o m p a n y e > r p a n d e d i t s b u s i n e s s a c r o s s t h e c o u n t r y d u r i n g t h e e a r l y I 9 0 0 r s , i n c l u d i n g C a n a d a i n 1 9 0 6 , a n d A l l i e d C h e m i c a l w a s f o r m e d in 1 9 2 0 . T h e B a r r e t t D i v i s i o n o f A l l i e d C h e r n i c a l n o w p r o d u c e s a w i d e r a n g e o f b u i l d i n g r n a t e r i a l s a n d i s a leading developer of c h e r n i c a l - b a s e d b u i l d i n g p r o d u c t s .
The foregoing rnight indicate that Barrett was the o n l y r o o f e r i n t h e e a r l y d a y s . T h i s w a s f a r f r o m t h e c a s e , as i t w a s n o t l o n g b e f o r e t h e r e w a s a large group of reputable r o o f e r s , a n d a s u s u a l a f e w i r r e s p o n s i b l e o p e r a t o r s . B y t h e e a r l y l 9 0 0 r s , t h e i n d u s t r y w a s c o n s i d e r e d t o b e i n an unhealthy state because of questionable application methods and skirnping o f m a t e r i a l s b y s o r r e r o o f e r s . T h e B a r r e t t c o r n p a n y m a d e a n atternpt to rernedy this situation by introducing roofing
s p e c i f i c a t i o n s a b o u t 1 9 0 6 a n d t h e s y s t e m of bonding roofs in 1 9 1 6 . T h i s w a s a f o r w a r d s t e p at the time and helped tre-mendously to standardize procedures and upgrade the quality o f w o r k m a n s h i p . T h e s y s t e m i t s e l f h a d f a u l t s , h o w e v e r , a n d these forced the abandonrnent of the bonding system in Canada in
r 9 6 0 .
But this is the story of coal-tar pitch, which in many a r e a s o f C a n a d a a n d t h e U n i t e d S L a t e s h a s b e e n d i s p l a c e d entirely by asphalt. How did this corne about? coal-tar pitch built-up r o o f i n g w a s b o r n o f w a s t e m a t e r i a l s f r o r n t h e g a s i n d u s t r y , and asphalt built-up roofing was born of waste rnaterials frorn the p e t r o l e u m i n d u s t r y . N e i t h e r s c i e n c e n o r r e s e a r c h p l a y e d m u c h p a r t i n t h e u s e o f t h e s e m a t e r i a l s and it is perhaps stretching a point to say that their use for roofing was an art.
Asphalt
A s p h a l t f r o m n a t u r a l l y o c c u r r i n g s e e p a g e s and deposits w a s b e i n g u s e d f o r i t s p r e s e r v a t i v e and cernenting qualities three o r f o u r t h o u s a n d y e a r s b e f o r e c h r i s t . A l a r g e s o u r c e o f n a t u r a l a s p h a l t , a n a s p h a l t l a k e , w a s d i s c o v e r e d i n Trinidad by
christopher columbus and sir walter Raleigh. Both of them reported on this, after stopping there and caulking their ships w i t h t h e m a t e r i a l . T h e w o r k i n g o f a s p h a l t f r o m n a t u r a l sources, o f w h i c h r r i n i d a d L a k e w a s t h e p r i n c i p a r o n e , d i d n o t b e c o m e commercially practical until the advent of the automobile in the latter half of the lgth century. The autornobile needed srnooth
r o a d s a n d a s p h a l t w a s used for road paving. Native asphalt was v e r y h a r d a n d n e e d e d a flux to soften it. The petroleurn industry w a s h a v i n g a p r o b l e r n disposing of the residue reft from the
d i s t i l l a t i o n o f p e t r o l e u m . F o r r n a n y y e a r s e n o u g h o i l s were left in t h e r e s i d u e t o y i e l d a fruid product which could be used as a flux f o r n a t i v e a s p h a l t , and rnosl of it was disposed of in this rnanner a n d f o r J . a y i n g d u s t o n d i r t roads.
I n i t i a l l y i n t h e p e t r o l e u r n industry kerosene was the m o s t i m p o r t a n t p r o d u c t , and the gasoline and heavy oirs were d i f f i c u t t t o d i s p o s e o f . The rapid developrnent of ihe autornobile, h o w e v e r , c h a n g e d t h e ernphasis, and gasorine and rubricating oils b e c a r n e t h e i m p o r t a n t comrnodities. K e r o s e n e s a n d h e a v y o i l s n o t s u i t a b l e f o r l u b r i c a n t s had to be disposed of by the peiroleum i n d u s t r y . T h e r m a l c r a c k i n g o f kero"".r" to produce '',ore gasoline r e l i e v e d t h e s i t u a t i o n w i t h regard to kerosene-type materials, but i n c r e a s e d t h e p r o b l e r n s in Tegard to asphaltic rnaterials, the supply o f w h i c h w a s l a r g e l y in excess of what was required for fluxing n a t i v e a s p h a l t s and for laying dust on dirt roads. The refiners had t o f i n d o t h e r u s e s for the rnaterial, and of course pubric demand f o r b e t t e r s t r e e t s and highways red to its use in road building, e v e n t u a l l y l a r g e l y replacing natural aspharts. Applicatiorr" Jth", t h a n r o a d b u i l d i n g w e r e investigated and, with some alterations in m a n u f a c t u r i n g p r o c e d u r e s , rnateriars were produced for use in r o o f i n g a n d w a t e r p r o o f i n g applications. e y t r r e s t a r t o f w o r l d w - a r I I s a t i s f a c t o r y asphal.ts for road and airfield construction, a n d f o r t h e m a n u f a c t u r e of roofing and roofs, was being produced b y m o s t r e f i n e r i e s . E l e c t r i c i t y h a d d i s p r a c e d g a s f o r t i t r r t i r r g , t o a l a r g e e x t e n t f o r cooking, and to some extent in industry. New u s e s w e r e a l s o b e i n g found for coal and coal-tar in the new chernical i n d u s t r i e s . T h i s n a t u r a l c h a n g e in emphasis on the use of material h a s c o n t i n u e d a n d , since asphalt has sorne advantages over coar-t a r p i coar-t c h a n d i s i n more ample supply, coar-the racoar-tio of usage for roofing in canada is currently about three or four to one in favour of asphalt.
F e l t s
what about the ferts that form the basis of built-up r o o f i n g ? A s o n e r n i g h t suspect, they too are a by_product _ in t h i s c a s e o f t h e p a p e r industry - and utilize rags, wood bark and o t h e r w o o d w a s t e , a n d s c r a p p a p e r . Of course, rags were used i n - p a p e r - m a k i n g long before paper was used to make roofing f e l t s ' T o d a y p a p e r i s manuf""io.ed rnostly from wood pulp, and
6
-only a few companies in Canada and the U. S. still use rags in the manufacture of roofing felt, although the name ttt"g feltrt is
s t i l l c o m m o n l y u s e d t o d e s c r i b e r o o f i n g f e l t . R a g s w e r e u s e d p r i n c i p a l l y b e c a u s e t h e y m a d e t h e f e l t s e a s i e r t o s a t u r a t e a n d allowed them to absorb more saturant. The manufacture of
s a t u r a t e d o r s a t u r a t e d - a n d - c o a t e d r o o f i n g f e l t t o d a y i s e s e e n t i a t l y t h e s a m e o p e r a t i o n a s i n v e n t e d b y B a r r e t t , lut carried out
u n d e r f a i r l y r i g i d f a c t o r y c o n t r o l s .
A s b e s t o s f e l t s , c o n s i s t i n g p r e d o m i n a n t l y o f a s b e s t o s f i b r e s , w e r e d e v e l o p e d i n t h e 1 9 ? 0 t s . I t w a s c l a i m e d t h a t t h e y e l i m i n a t e d t h e p o t e n t i a l d e f i c i e n c i e s o f m o i s t u r e m o v e m e n t a n d decay found in organic fibre felt (rag {elt) and improved the fire r a t i n g o f t h e r o o f . B e c a u s e o f t h e s r n a l l p e r c e n t a g e o f o r g a n i c f i b r e s n e c e s s a r y t o f a c i l i t a t e s a t i s f a c t o r y m a n u f a c t u r e , a s b e s t o s f e l t s a r e n o t e n t i r e l y f r e e f r o r n m o i s t u r e r n o v e m e n t a n d d e c a y a n d , p r i n c i p a l l y b e c a u s e o f h i g h e r c o s t , h a v e n o t b e e n w i d e l y u s e d i n C a n a d a . I n r e c e n t y e a r s g l a s s f i b r e f e l t s h a v e b e e n i n t r o d u c e d i n t o b u i l t - u p r o o f i n g . T h e s e a r e a l m o s t e n t i r e l y f r e e o f d i m e n s i o n a l c h a n g e s f r o r n m o i s t u r e a b s o r p t i o n a n d , o f c o u r s e , a r e c o m p l e t e l y f r e e o f d e c a y . B e c a u s e o f t e n s i l e s t r e n g t h s a n d b r i t t l e n e s s c h a r a c t e r i s t i c s , t h e s i g n i f i c a n c e o f which is not yet fully appreciated, they too have not been corrr-p l e t e l y t r o u b l e - f r e e , d e s p i t e t h e h i g h h o p e s f o r t h e i r p e r f o r m -a n c e .
C o n s t r u c t i o n I n d u s t r y T o d a y
What has happened to building during the hundred years or so that built-up roofing has been struggling to become a craft? Looking around any of the large Canadian cities, one c a n s e e h u n d r e d s o f p u b l i c , c o m m e r c i a l , a n d i n d u s t r i a l
b u i l d i n g s r e c e n t l y c o r n p l e t e d o r i n c o n s t r u c t i o n . M o s t a r e o f spectacularly modern appearance. Although the curtain wall tends to give them all a sarrleness, one must admit that b u i l t l i n g h a s g r e a t l y c h a n g e d i n r e c e n t y e a r s , a n d i n a r c h i -t e c -t u r e -t h e r e a r e n e w b u i l d i n g -t y p e s , n e w p r o b l e m s , and new c l i e n t s . A n a b u n d a n c e o f w o r k h a s r e s u l t e d i n t h e w e s t e r n world as a result of an expanding economy and an expanding p o p u l a t i o n . A r c h i t e c t s a n d c o n t r a c t o r s h a v e b e e n v e r y b u s y a n d a l r n o s t c e r t a i n l y w i l l c o n t i n u e t o b e s o , T h e r e i s n o c o m p u l s i o n , t h e r e f o r e , f o r t h e m t o g i v e s p e c i a l a t t e n t i o n t o a n y o n e a s p e c t o f b u i l d i n g s u c h a s r o o f i n g , a n d t h i s w a s p a r t i c u l a r l y t r u e w h e n b o n d i n g o f r o o f s w a s t h e p r a c t i c e .
M o s t o f t h e e l e g a n t n e w b u i l d i n g s are protected f r o m s u m r r r e r s u n a n d w i n t e r storm by a roof surface that is e s s e n t i a l l y t h e s a r n e a s t h e c o v e r i n g developed a century ago f r o r n w a s t e p r o d u c t s , t o r e l i e v e the roof construction problems o f t h e f i r e - d e v a s t a t e d c i t y o f C h i c a g o . It is reasonable to
a s s u m e t h a t r n a n y o f t h e m o r e r e c e n t f a i l u r e s in built-up roofing a r e d u e t o r e c e n t c h a n g e s i n t h e p r a c t i c e of building, which h a v e n o t b e e n t a k e n i n t o a c c o u n t in roofing design and a p p l i c a t i o n . T h e s e c h a n g e s a r e . ' a n y a n d v a r i e d , and are d e s c r i b e d l a t e r i n t h i s p a p e r .
R o o f i n g t o d a y i s o f a c o m p o s i t e construction and one thing about which very little is known is the interaction b e t w e e n t h e s t r u c t u r a l f r a r n e w o r k and the roof decking, or b e t w e e n t h e d e c k i n g a n d t h e insuration and roof covering laid on it. It is known that roof structure rnoverRent is irnportant i n r e l a t i o n t o c o n t i n u o u s r n e m b r a n e s , but the rate and amount o f s t r u c t u r a l m o v e m e n t i n actuar buildings is difficult to fore-c a s t . E v e n i f t h e s e fore-c o u l d b e f o r e fore-c a s t , t h e r e i s v e r y l i t t l e i n f o r m a t i o n a v a i l a b l e o n the engineering properties of built_up r o o f i n g r n e m b r a n e s , w h i c h would enabre designing to arlow for m o v e m e n t s - M o s t c u r r e n t r a b o r a t o r y i n v e s t i g a t i o n s , including t h o s e a t t h e D i v i s i o n o f Building Research, are only involved w i t h t h e c o r n p o n e n t s and it is difficult to relate their isolated b e h a v i o u r t o t h e b e h a v i o u r in cornposite construction. I n
r o o f i n g , p e r h a p s r n o r e t h a n in any other industry, there appears t o b e a g r e a t d e a l o f o f f - t h e - c u f f opinion, unsupported by
k n o w l e d g e o r r e s e a r c h , with half-truths the rule rather than the exception. Research orga'-izations around the world are
d e v o t i n g s o m e e n e r g y t o these problems, and the situation is g r a d u a l l y b e i n g r e m e d i e d .
T h e R o o f e r T o d a y
W h a t c a n t h e r o o f e r s do in the midst of all this? T h e r e i s v e r y l i t t i e t h e y can do about the innovations in
b u i l d i n g p r a c t i c e t h a t have caused some of the problerns, and t h e r e i s v e r y l i t t l e t h e y c a n d o i n t h e a r e a o f r e s e a r c h .
T h e r e a r e a r e a s , h o w e v e r , i n w h i c h r o o f e r s can irnprove t h e i n d u s t r y . R o o f e r s h a v e a l r e a d y taken rong strides in the r i g h t d i r e c t i o n w i t h t h e f o r m a t i o n of roofing associations such a s t h e c a n a d i a n R o o f i n g contractors Association and the
A l b e r t a R o o f i n g c o n t r a c t o r s Association. D i g n i t y a n d r e s p e c t , w h i c h t h e m e m b e r s seek, are synonyrnous with pride of
work 8 work -m a n s h i p o n w o r k p r o p e r l y c a r r i e d o u t . R o o f e r s , t h e r e f o r e , h a v e a j o b t o d o i n t r a i n i n g r o o f i n g p e r s o n n e l i n p r o p e r l y d e f i n i n g s t a n d a r d s o f a p p l i c a t i o n a n d w o r k r n a n s h i p . T h e p u b l i c a t i o n o f t h e C R C A s p e c i f i c a t i o n s M a n u a l i s a n i n d i c a t i o n o f t h e s e r i o u s i n t e n t b y r o o f e r s t o e n s u r e t h a t r o o f i n g i s a d e q u a t e l y specified by a r c h i t e c t s a n d e n g i n e e r s . M a n y r o o f e r s r e a l i z e , h o w e v e r , t h a t t h i s i s n o t e n o u g h . R o o f e r s c a n d o a g r e a t s e r v i c e to the C a n a d i a n c o n s t r u c t i o n i n d u s t r y b y d e f i n i n g g o o d roofing practice s o t h a t m a n u f a c t u r e r s , a r c h i t e c t s , e n g i n e e r s , c o n t r a c t o r s , a n d r o o f e r s c o u l d a l l b e w o r k i n g t o c o r n r n o n s t a n d a r d s . A t p r e s e n t e v e n t h e t e r m s u s e d i n t h e r o o f i n g i n d u s t r y o f t e n h a v e d i f f e r e n t m e a n i n g s t o t h e v a r i o u s p e o p l e i n v o l v e d w i t h r o o f i n g .
The Cornrnittee on Asphalt and Tar Roofing Materials o f t h e c a n a d i a n s t a n d a r d s A s s o c i a t i o n i s w o r k i n g on a code of P r a c t i c e t o c o v e r d e s i g n a n d a p p l i c a t i o n of built-up roofing. T h e s u p p o r t o f t h e R o o f e r s r A s s o c i a t i o n s i s n e c e s s a r y ,
p a r t i c u l a r l y i n r e l a t i o n t o a p p l i c a t i o n , a n d t o a s s u r e t h a t t h i s w o r k i s p u s h e d f o r w a r d b y t h e c o r n r n i t t e e . T h e c o d e o f p r a c t i c e c o u l d f o r m t h e b a s i s f o r p a r t o f a n educational prograrn for r o o f e r s , w h i c h r o o f e r s r e a l i z e i s b a d l y n e e d e d . c r a f t s m a n s h i p has been defined as rrthe quality irnparted to anything in the p r o c e s s o f r n a k i t g , t t a n d a c r a f t s r n a n a s r r o n e w h o p r a c t i c e s a h a n d i c r a f t . I ' B y t h e s e d e f i n i t i o n s t h e r e are few craftsmen in t h e r o o f i n g i n d u s t r y . E v e n r o o f i n g f o r e r n e n o f t e n d o n o t
u n d e r s t a n d o r a p p r e c i a t e w h y c e r t a i n p r o c e d u r e s a r e n e c e s s a r y in roofing application. How many, for instance, know the
f u n c t i o n o f g r a v e l s u r f a c i n g ? E x p e r i e n c e indicates that very f e w a p p r e c i a t e s u c h r n a t t e r s . T h e c a s u a l l a b o u r e m p l o y e d o n most jobs know nothing of the trade. Good workrnanship can usually only be obtained through the art and skill of workmen o r c r a f t s m e n , a n d i f t h e y d o n o t h a v e the art and skill,
s a t i s f a c t o r y a p p l i c a t i o n i s u n l i k e t y t o o c c u r even by chance. It would appear that this is the reason the asphalt roofer d o e s n o t e n j o y t h e r e s p e c t g i v e n t o sorne of the longer estab-l i s h e d r o o f i n g t r a d e s , s u c h as the sestab-later and thatcher in other c o u n t - r i e s . R o o f i n g a s s o c i a t i o n s are very concerned about a n e d u c a t i o n a l p r o g r a m f o r t h e r o o f i n g personnel of the m e m b e r f i r r n s , a n d s t e p s are being taken to implement such tr aining.
A r c h i t e c t s a n d o t h e r d e s i g n e r s r e c e i v e a great deal o f c r i t i c i s m i n c o n n e c t i o n w i t h i n a d e q u a t e r o o f i n g design and s p e c i f i c a t i o n s , m u c h o f i t d e s e r v e d . Those in the roofing
i n d u s t r y , h o w e v e r , s u r e l y c a n n o t e x p e c t t h e architect to be an e x p e r t r o o f e r . T h e m e m b e r s o f r o o f i n g a s s o c i a t i o n s , a n d t h e i r r o o f i n g p e r s o n n e l , m u s t b e t h e a p p l i c a t i o n experts, the crafts-m e n . R o o f e r s h a v e t o b e c o m p e t e n t a n d r e s p o n s i b l e i n solving j o b p r o b l e m s , advising on the correct solutions to remedy
u n d e s i r a b l e c o n d i t i o n s , t o a s s u r e a first-class job. The asphalt r o o f e r r s t r a d e h a s a l l o w e d i t s e l f t o b e greatly influenced by m a n u f a c t u r e r s , a r c h i t e c t s , a n d c o n t r a c t o r s . R o o f e r s s h o u l d b e t h e o n e s t o d e t e r m i n e , i n c o n s u l t a t i o n and co-operation w i t h t h e o t h e r s , o f c o u r s e , w h e n t h e c o n d i t i o n s on a job are s u i t a b l e f o r r o o f i n g . M o s t r o o f e r s h a v e b e e n i n v o l v e d w i t h j o b s w h e r e the architect or contractor, or both, have insisted on roofing when the roofer was aware that conditions were not suitable. It would be wonderful to be in a position to refuse when such a situation occurs. It would be naive to suggest that this is a l w a y s o r e v e n o c c a s i o n a l l y p o s s i b l e . I t i s i r n p o r t a n t , h o w e v e r , that roofers be more emphatic through their associations in point-i n g o u t t o a r c h point-i t e c t s a n d c o n t r a c t o r s the dangers of roofpoint-ing under u n s u i t a b l e c o n d i t i o n s . C o n f i d e n c e i n r o o f e r s f r o m d e s i g n e r s will o n l y c o m e f r o m h o n e s t a n d straightforward dealings and co-o p e r a t i co-o n co-o v e r a p e r i co-o d co-o f time. Rco-oco-ofers have tco-o be sure co-of what they are doing and actively make this knowledge known.
THE ARCHITECT
C r i t i c i s m o f A r c h i t e c t s
It is a current fad for everyone, including architects, t o c r i t i c i z e a r c h i t e c t s as a group for their failings of one sort o r a n o t h e r . T h e c r i t i c i s m t o w h i c h t h e p r o f e s s i o n is subjected from architects appears to indicate an insecurity and a fear of the future that exists within the profession, but there is no d o u b t t h a t t h i s s e l f - a p p r a i s a l is a good sign, Architects, as p e r h a p s n e v e r b e f o r e , are questioning the system of archi-t e c archi-t u r a l e d u c a archi-t i o n a n d m a n y oarchi-ther previousry acceparchi-ted sarchi-tan- stan-d a r stan-d s o f t h e p r o f e s s i o n , anstan-d are becoming increasingly con-cerned about the public image of the architect. Despite the c o n v i c t i o n o f a r c h i t e c t s t h a t they are the leaders of the con-s t r u c t i o n i n d u con-s t r y , a c o n v i c t i o n not nececon-scon-sarily con-shared by others in the construction industry, architects at the moment a r e o f t e n c o n s i d e r e d t o b e a trnecessary evil, fr what the pro-f e s s i o n c l e a r l y h a s t o guard against is being considered an ttunnecessary evil. It It is quite conceivable that the con-s t r u c t i o n i n d u con-s t r y c o u l d e x i con-s t without profecon-scon-sional architectcon-s, but impossible for architects to exist without a construction i.ndustry.
t 0
-T h e a r c h i t e c t l s l o t i s n o t a n e a s y one, even if one d i s c o u n t s t h e f r u s t r a t i o n s attendant on being an adjudicator, f i n a n c i a l a d v i s e r , d e c o r a t i n g consultant, and guardian of c u l t u r e a n d a e s t h e t i c s . T h e d e s i g n a n d c o n s t r u c t i o n o f a building involves the cornbination of a variety of rnaterials. E v e r y a r c h i t e c t u r a l office is bulging with quantities of trade l i t e r a t u r e , a n d o f t e n p e r h a p s e v e n s t a c k s o f r e s e a r c h r e p o r t s , t h a t d e s c r i b e t h e v i r t u e s and confirm the properties of the ' " a n y m a t e r i a l s a v a i l a b l e for use. To the average layrnan or a n a i v e a r c h i t e c t , d e s i g n i n g a building merely rneans choosing a e s t h e t i c a l l y - p t e a s i n g m a t e r i a l s a n d f i t t i n g t h e m t o g e t h e r .
M o s t a r c h i t e c t s , o f c o u r s e , k n o w that this approach i s q u i t e r i d i c u l o u s , and are aware that rnaterials which have m o s t d e s i r a b l e p r o p e r t i e s i n t h e r n s e l v e s c a n b e c o r n e u n m a n -a g e -a b l e r n o n s t e r s w h e n c o m b i n e d with other seerningly excellent rnaterials to function as building elernents. And yet, earry a n d s e r i o u s r n a l f u n c t i o n and deterioration of sorne of our b u i l d i n g s i n d i c a t e s a lack of appreciation of many of these f a c t o r s . T h e s e f a c t o r s i n v o r v e t h e unchanging raws of physics a n d c h e r n i s t r y , a n d t h e i r effects on sorne of our cornplex a s s e m b l i e s o f b u i l d i n g r n a t e r i a l s - in other words, basic b u i l d i n g s c i e n c e . V a p o u r p r e s s u r e , r n o i s t u r e rnigration, air and heat flow, light and sound transrnission, vorurnetric change a n d e l e c t r o l i t i c a c t i o n a r e n o t r n y s t e r i o u s p h e n o m e n a of
i n t e r e s t o n l y t o e n g i n e e r s a n d s c i e n t i s t s . T h e s e a r e sorne of the rnechanisrns that daily affect the combinations of rnaterials that go to make up our rnodern buildings.
A c r i t i c i s r n o f t h e p r o f e s s i o n of architecture is that i t r n e r e l y p a y s l i p s e r v i c e t o s c i e n c e a n d r e s e a r c h . A r c h i -t e c -t u r a l s -t u d e n -t s are no-t -taugh-t basic buirding science, and
s u c h e n g i n e e r i n g c o u r s e s a s a r e g i v e n a r e u s u a r l y c o n s i d e r e d a s s o r n e t h i n g a d d i t i o n a l to architectural design, rather than a p a r t o f i t . P r a c t i c i n g architects, although generaly aware o f t h e s c i e n c e p h e n o r n e n a rnentioned, find the effort too great u n d e r t h e s t r e s s o f d a y - t o - d a y p r o b l e m s t o b e c o m e skilled in t h e a p p l i c a t i o n o f t h e s e phenornena to architectural design. T h e r e i s a t e n d e n c y to think of any particurar rnateriar or s y s t e m a s b e i n g g o o d or bad, depending on the architectrs e x p e r i e n c e w i t h i t s p e r f o r m a n c e on an actual building. This approach assus)es that durabirity is a fundarnentar property of the material or systern. Nothing courd be further from t h e t r u t h . T h e p e r f o r m a n c e o f a material or system depends on the environrnent to which it is exposed and the degrading
e f f e c t s o f s e r v i c e . A p r o p e r u n d e r s t a n d i n g o f b u i l d i n g science h e l p s o n e t o r e c o g n i z e t h e pertinent factors affecting the per-formance. It is then possible to anaryze designs systematically a s t o t h e p r o b a b l e p e r f o r r n a n c e , and choose rnaterials or systems t o s a t i s f y t h e v a r i e d requirernents. A s w e l l a s r e m a i n i n g t h e g u a r d i a n o f c u l t u r e and aesthetics, the architect rnust reassert h i m s e l f a s a t e c h n i c a l l e a d e r , and to do this he must know more a b o u t n a t u r e r s l a w s w i t h which he can generally cope, but which h e c a n n o t c h a n g e and is il1-advised to flout.
A r c h i t e c t s h a v e b e e n b r a m e d for buirding problems in many specific areas within the building industry. In con-n e c t i o con-n w i t h r o o f i con-n g , for icon-nstacon-nce, icon-nadequate desigcon-n acon-nd s p e c i f i c a t i o n , a s w e l l as lack of supervision, is usually a t t r i b u t e d t o t h e architect. c e r t a i n l y a l a c k o f c o n c e r n for d e s i g n d e t a i l a n d t h e supervision of workrnanship were encour-a g e d b y t h e s y s t e m of bonding roofs thencour-at existed in cencour-anencour-adencour-a from 1 9 1 6 t o 1 9 6 0 . u n d e r the conJitions of present architectural p r a c t i c e , i t i s r i d i c u l o u s to s'.rggest that the architect should be a n e x p e r t r o o f e r ' an expert carpenter, or an e>cpert in any trade. F o r e v e r y t r a d e , however, the architect is required to have knowledge of the materials used, and the factors that affect their performance. It is also extrernery irnportant for the a r c h i t e c t t o r e c o g n i z e new factors brought auout by changes in b u i l d i n g p r a c t i c e .
C h a n g e s i n B u i l d i n g p r a c t i c e Related to Roofin
I t a p p e a r s t h a t m a n y of the more recent roofing f a i l u r e s m a y b e due to changes that have recenily taken prace in building practice, which have not been taken into account in r o o f i n g d e s i g n a n d application" There has been an increasing u s e o f d e a d - l e v e l roof decks, and consequently poorly drained r o o f s u r f a c e s " P r e c a s t concrete and many other t1ryes of rn-ultiple unit roof decks are now widery accepted. Deflections o f s u c h d e c k s h a v e not been investigated in
" . l " t i o ' t o t h e effect on roofing. The obvious effett of permanent defrection f r o m c r e e p o n roofs intended to be ftat is the ponding of water w h i c h i n c r e a s e s t h e failur e hazard. Greater ihi.to.sses of l i g h t e r i n s u l a t i o n s praced on top of roof decks have been used t o a c h i e v e b e t t e r t h e r m a r resistance, but they provide a soft u n d e r b e d d i n g f o r the roofing rnembrane and subject it to g r e a t e r v a r i a t i o n s in temperature. T h e i n c r e a s i n g u s e of v a p o u r b a r r i e r s , w h i l e r e s t r i c t i n g t h e entry of moisture into
r z
-t h e c o n s -t r u c -t i o n , i n -t r o d u c e s n e w p r o b l e m s caused by rnois-ture t h a t m a y b e t r a p p e d i n t h e c o n s t r u c t i o n . A i r - c o n d i t i o n i n g a n d humidification of rnany buitding tlpes are cornrnon, and these m e a s u r e s a g g r a v a t e t h e p r o b l e r n s o f moisture transfer into the b u i l d i n g c o m p o n e n t s . Y e a r - r o u n d c o n s t r u c t i o n h a s a d d e d t o t h e h a z a r d o f t r a p p e d c o n s t r u c t i o n m o i s t u r e in building materials a n d s y s t e r n s . T h i s i s p a r t i c u l a r l y t r u e i n r e l a t i o n t o r o o f i n g , w h e r e n o p r o t e c t i v e c o v e r i s u s e d , s u c h a s i s e m p l o y e d o n s o m e o t h e r p h a s e s o f b u i l d i n g c o n s t r u c t i o n . A p a r t f r o r n t h e h a z a r d s o f r a i n , s n o w , a n d i c e o n roof decks, and the possibility of wet r n a t e r i a l s f r o r n i m p r o p e r storage, there is great danger of i n a d e q u a t e a d h e s i o n o f f e l t s d u e to application of materials to c o l d a n d w e t s u r f a c e s , o r d u e t o overheating rnaterials to c o u n t e r a c t t h e c o l d . T h e o v e r h e a t i n g rnay also destroy the d e s i r a b l e p r o p e r t i e s o f t h e biturnen. In sorne buildings large q u a n t i t i e s o f m o i s t u r e a r e released into the closed-in building f r o m w e t - f i n i s h i n g o p e r a t i o n s , such as concreting or plastering. u n d e r c e r t a i n c o n d i t i o n s , such rnoisture can penetrate into the r o o f i n g s y s t e m a n d c a u s e subsequent deterioration.
DESIGN CONSIDERATIONS - ROOFING SYSTEMS
I n t h e d e s i g n o f a r o o f i n g system, the rnost important c o n s i d e r a t i o n i s t h e p r o v i s i o n of a watertight or water-shedding c o v e r i n g t o k e e p t h e i n t e r i o r of the building dry. Steeply_ p i t c h e d r o o f s s h e d w a t e r rapidry and a covering of overlapping i m p e r v i o u s u n i t s c a n b e used to achieve this. Flat and low-p i t c h e d r o o f s t e n d t o h o l d water, or shed it very slowly. The c o v e r i n g , t h e r e f o r e , m u s t be jointless and watertight.
T h i s a p p e a r s t o b e v e r y difficult to achieve because o f t h e n a t u r e o f t h e r n a t e r i a l s usually used. organic felts, most cornrnonly used in the built-up biturninous roofing systems, c a n a b s o r b m o i s t u r e w i t h consequent dirnensional changes and d e t e r i o r a t i o n . B i t u m e n s o x i d i z e f r o r n exposure to air,
m o i s t u r e , h e a t a n d u l t r a v i o l e t light, and the oxidation products a r e w a t e r - s o l u b l e a n d v o l a t i l e . T h e y b e c o r n e v e r y b r i t t l e w h e n e x p o s e d t o l o w t e r n p e r a t u r e s , are subject to slurnping at h i g h s e r v i c e t e m p e r a t u r e s , a n d a r e s u b j e c t t o d e t e r i o r a t i o n at t e m p e r a t u r e s o n l y s l i g h t l y above those required for application. T h e q u a l i t y o f t h e f i n i s h e d roofing depends largely on the work-rnanship and the weather conditions during application.
B u i l d i n e M o v e m e n t
F a c t o r s s u c h a s r o o f structure movement, which rnay be u n i r n p o r t a n t o n a s t e e p shingled roof, must be carefully considered i n r e l a t i o n t o a c o n t i n u o u s membrane. I t m a y b e n e c e s s a r y t o p r o -v i d e s u i t a b l e w a t e r p r o o f e d discontinuities in the membrane at places w h e r e t h e r e m a y b e movements greater than the rnembrane can a c c o m m o d a t e . o f c o u r s e , i t m a y a l s o b e n e c e s s a r y t o c o n s i d e r the d e s i g n o f t h e s t r u c t u r e to reduce the amount of movement as rnuch a s p o s s i b l e . T h e r a t e a n d a m o u n t of structurar movement is
difficult to forecast for an actual building. In addition, there is little information available on the engineerir,g properties of built-up r o o f i n g m e m b r a n e s , which have not in the past been considered as l o a d - b e a r i n g " T h e s t r e n g t h o f t h e actuar rndmbrane depends a great deal on workrnanship, and very little is known about the
b e h a v i o u r o f r n e m b r a n e s due to ter.nperature and moisture changes. T h e m e m b r a n e r n u s t , of course, be considered in relation to roof insulation' vapour control, and heat and vapour ventilation of the r o o f s y s t e m - F o r t h e s e r e a s o n s it is difficult to provide positive r e c o m m e n d a t i o n s for practical roof deck and roof membrane design.
It appears certain that a built_up biturninous felt r o o f i n g m e r n b r a n e should not be raid so that it is solidly adhered to two parts of a building which rrrove in relation to each other, e v e n i f t h e m o v e m e n t is very small" This condition occurs w h e r e v e r a r o o f deck meets a verticar surface at a parapet, c u r b , p e n t h o u s e , or wall. The standard procedure in this con-dition is to provide a 4s-degree cant strip with the roofing felts c a r r i e d t o t h e t o p of the strip. Base frashings are then applied to the wall extending out onto the deck over the roofing mlmbrane.
to allow for rnovement. Such n d c a n b e p r o v i d e d easily with a t t a c h e d t o t h e d e c k . C o v e r ame tirne as the roofing to p r e v e n t w a t e r penetrating behind the skirting.
s u c h a c o n d i t i o n also occurs with precast roof deck e l e m e n t s a t e a c h j o i n t between elements. With small units this d o e s n o t s e e r ' ' t o cause many roofing problems, but with rarger u n i t s t r o u b l e w i l l probabry occur unless adequate provision is m a d e f o r m o v e m e n t . T e s t s b y t h e D i v i s i o n of g,'itairrg Research indicate that roofing membranes fail at a strain of approximately o n e p e r c e n t a t - 2 , 0 " F . To avoid fracture of the membrane at s t r u c t u r a l j o i n t s it therefore appears necessary to separate the
1 4
-rnembrane frorn the roof deck at the joint for a sufficient width t o r e d u c e t h e s t r a i n t o a v a l u e o f l e s s t h a n o n e p e r c e n t .
Knowing the amount of possible rnovement at a structural joint, i t i s a s i r n p l e m a t t e r t o c a l c u l a t e t h e f r e e w i d t h o f m a t e r i a l n e c e s s a r y t o a c h i e v e t h i s . A s t r i p o f m a t e r i a l l a i d o v e r the joint will then prevent adhesion of the rnernbrane to the deck for t h e w i d t h r e q u i r e d .
I t i s u s u a l i n b u i l d i n g d e s i g n t o p r o v i d e a n e x p a n s i o n j o i n t i n the roofing only where expansion joints are provided in t h e s t r u c t u r e , a s r e q u i r e d w h e r e t h e r e i s a change in direction o f f r a m i n g , w h e r e w i n g s p r o j e c t f r o r n a main structure, or on a n y r e l a t i v e l y l o n g o r l a r g e s e c t i o n o f a b u i l d i n g o r f o r some o t h e r s t r u c t u r a l r e a s o n . I n r n o s t m o d e r n b u i l d i n g s t h e r o o f a n d w a l l s a r e i n s u l a t e d o u t s i d e t h e s t r u c t u r a l f r a m e , and after the b u i l d i n g h a s b e e n c o n s t r u c t e d a n d i s i n o p e r a t i o n the frame will u s u a l l y b e s u b j e c t e d t o v e r y s r n a l l ternperature differentials. T h e s t r u c t u r a l e n g i n e e r o n t h i s b a s i s r n a y be justified in making r e l a t i v e l y l a r g e s p a c i n g s b e t w e e n e x p a n s i o n j o i n t s . I f c o n -s t r u c t i o n i -s d o n e i n c o l d w e a t h e r , t h e e f f e c t o f rapid warm-up w h e n t h e b u i l d i n g i s c l o s e d i n r n u s t also be carefully considered. T h e s p a c i n g s d e t e r m i n e d f r o m structural considerations alone rnay not be adequate for the roofing mernbrane. It will be sub-j e c t e d t o t h e f u 1 l range of outside ternperatures, and for black s u r f a c e s o v e r i n s u l a t i o n t h e r a n g e m a y b e i n c r e a s e d by at least 1 0 0 F d e g r e e s i n e x c e s s o f t h e r a n g e o f a m b i e n t a i r t e m p e r a -t u r e s . s e a s o n a l t e r n p e r a t u r e d i f f e r e n t i a l s o f 200 F degrees a n d t e r n p e r a t u r e v a r i a t i o n s o f u p t o 8 0 F degrees'in a few hours are possible in rnany parts of. canada. The coefficient of
e x p a n s i o n o f b i t u m i n o u s r n e r n b r a n e s is such that these tempera-t u r e v a r i a tempera-t i o n s , p a r tempera-t i c u l a r l y a t t e m p e r a t u r e s b e l o w 3 0 " F , w i l l t e n d t o c a u s e q u i t e l a r g e m o v e r n e n t s . T h e r e i s v e r y 1 i t t l e knowledge about the rnanner in which such rnovements are r e s i s t e d o r a c c o r n r n o d a t e d b y t h e roofing systern. It can only be suggested at this time that limiting the extent of continuous b i t u r n i n o u s r n e m b r a n e s t o l o 0 t o 150 ft appears to be of sorne help in reducing the incidenc'e of mernbrane splitting.
Insulation of Roofs R o o f s c a n b e i n s u l a t e d i n f o u . r w a y s ( F i g u r e l): A b o v e t h e s t r u c t u r a l d e c k ( t h i s i s u s u a l p r a c t i c e w i t h r i g i d i n s u l a t i o n o n w o o d , con-c r e t e o r s t e e l ) 1 .
By the use of an insulating rnaterial to form t h e d e c k i t s e l f ( a e r a t e d l i g h t w e i g h t concrete o r f i b r e )
Imrnediately beneath the structural deck (poured gypsum or other lightweight material o v e r f o r m b o a r d )
4" On a ceiling below the roof proper, with a loft or attic between the ceiling and the deck (this i s s t a n d a r d p r a c t i c e i n house construction, and i n s o m e i n d u s t r i a l b u i l d i n g s ) .
It is important to be aware of the differences between t h e s e m e t h o d s , and that each invorves speciar problems. K n o w i n g t h e s e d i f f e r e n c e s , it is usually possible to design a roof
con-struction that will give the best performance at the least initial and operating cost for the locar clirnate, and for the anticipated occupancy of the building. The lowest initial cost for insuiation and the lowest operating cost for heating and cooring can be attained better with an insulated ceiting below a ventilated loft space, than with insulation either above, in, or imrnediatery b e l o w t h e d e c k " This design also has cornfort advantages and c a n b e d e s i g n e d to handle occupancies in which very high m o i s t u r e c o n d i t i o n s prevail,
Many of the roof systerns in which the insuLating m a t e r i a l f o r m s the deck,. or where insuration js.placed dirJctly below the deck, are entirely unsuitable for buildings with a high i n d o o r m o i s t u r e content. 'when the roof is to serve as an
interior ceiling, the choice between insulating above, within, or immediately below the deck will be determined by anticipated interior moisture conditions, internar appearance, and rerative cost. If the roof is to carry traffic loads the insuration above t h e d e c k m u s t b e a load-bearing type, but it seems more logical t o c o n s i d e r t h e use of a more efficient non_Ioad_bearing
insulation below the deck or on a ceiring forming a roft space. In all cases careful attention must be given to vapour barriers and their rocation, or to vapour contror by v e n t i l a t i o n , w h e r e v e r the moisture level generated by the o c c u p a n c y d u r i n g periods of cold weather indicates a potentiar. condensation pr oblern.
z .
1 6
-The most usual roof construction used in Canada is
the one where insulation is placed directly above a structural
deck, and a vapour barrier is placed directly on the deck. The
insulation used, although usually rigid and with some load-b e a r i n g c h a r a c t e r i s t i c s , i s g e n e r a l l y p o r o u s . M o s t i n s u l a t i n g m a t e r i a l s a r e l a r g e l y a i r - e n t r a p p e d b y c e l l s o r f i b r e s , a n d t h e air content in some insulations may range from 50 to 95 per cent o f t h e r n a s s r I n a d d i t i o n , s o m e m o i s t u r e m a y b e p r e s e n t .
Considerable moisture rnay enter the insulation due to inadequate
storage protection oi inclernent weather during construction.
If rnaterial in this condition is confined between a tight roofing
above and a tight air and vapour barrier below with all edges
sealed, pressures that built up within the systern from solar
heating on the roof surface will certainly cause blistering, and
the better the roofing membrane the more likely it is to blister. That many such roofs have perforrned reasonably well
indicates construction is not tight and the air does escape. If.
air can escape to the inside of the building, a breathing or
purnping action rhay take place. For buildings with a high
rnoisture level occupancy, such breathing action could saturate
the insulation with moisture over a period of time. Wet
insulation has less heat resistance and so will aggravate the
problem and, of course, organic insulations, if wet, will rot
in tirne and fail completely. It appears that a properly designed
roofing of this type must rnake provision for the insulation to
breathe to the outer air, where the vapour pressure is the lowest. Condensation of Water Vapour
If water vapour can penetrate into the roof
con-struction in winter frorn within the building it will condense on
the underside of the cold roofing. This is inevitable unless the
vapour pressures inside are equal to those outside. No dripping
will occur until absorptive insulation and other absorptive
material of the construction are fully saturated. To prevent
this, a vapour barrier may be installed as near as practicable
to the warrn side of the construction. Condensation can be
cornpletely forestalled if this vapour barrier is rnaintained at
a ternperature above the dewpoint of the indoor air. It is
important to understand that the over-a11 heat resistance (U value) of the roof is not the irnportant factor, and, in fact, a t1rye of deck that is a poor insulator requires less insulation to prevent condensation than does a good insulator when the
Consider an exancple in Ottawa of a steel deck and a 3-in. plank deck (Figure 2). Assurne indoor air wilt be kept at 70'F and the relative humidity (RH) at 50 per cent. Using the winter design temperature of +10'tr. for outside air, how much insulation is required to prevent condensation at the vapour b a r r i e r ?
The dewpoint ternperature for 70"F air at 50 per cent RH is 50oF, and therefore the vapour barrier will have to
remain above 50"I. if condensation is to be avoided.
The line A to F in Figure 2 indicates a rate of heat loss which must not be exceeded if condensation is to be avoided f o r t h e s t e e l r o o f d e c k . T h i s r a t e p r o j e c t e d o n a resistance scale graph of temperature gradients indicates that the total r e s i s t a n c e r e q u i r e d o f l h e c o n s t r u c t i o n i s 1 . 8 . s i n c e the con-s t r u c t i o n w i t h o u t i n con-s u l a t i o n p r o v i d e con-s l . l I , o n l y 0 . 6 9 i s r e q u i r e d f r o m t h e i n s u l a t i o n , a n d t h i s c a n b e p r o v i d e d b y 0 . 69/Z.le= 0 . 2 5 i r ' . , that is, t/+ irr.
Line AF in the diagram indicates a tate of heat loss which rnust not be exceeded if condensation is to be avoided for the wood deck. The rate of heat loss is considerably slower because of the resistance of the wood deck. When AB is pro-jected to c it can be seen that the total resistance requiied is
l l . 7 a n d , s i n c e t h e c o n s t r u c t i o n p r o v i d e s 4 . 3 9 , t h e i n s u l a t i o n w i l l b e r e q u i r e d t o c o n t r i b u t e ? . 3 1 a n d t h i s w i l l r e q u i r e 7.31/ 2.78 = 2.63, or approximately Z| in. of insulation.
The U value for the insulated wood deck would be 0. 08 and for the steel deck it would be 0. 56. Obviously more insulation would be used on the steel deck than I /+ in. for reasons other than condensation.
Suppose the insulation used on the wood deck were I i n . T o t a l R w o u l d b e 4 . 3 9 + z . ' 1 8 = 7 . L 7 , a n d t h e t e m p e r a t u r e gradient through the deck would be along line DEA, with the temperature at the vapour barrier 38"F. The room could
support 30 per cent RH under these conditions. If I in. of insulation were used on the steel deck, total R wourd be I.lt + 2 . 7 8 = 3 . 8 9 , a n d t h e t e m p e r a t u r e g r a d i e n t would be along line HJA with temperature at the vapour barrier of 60'F. The room under these conditions could support a relative humidity of 7 0 p e r c e n t .
1 8
-DESIGN CONSIDERATIONS - BITUMINOUS ROOT' COATINGS
Choice of Materials for Biturninsgr Roo:!!3g
The properties of the materials used for built-up
r o o f i n g a r e s e l d o r n u n d e r s t o o d b y d e s i g n e r s o r r o o f e r s . T h e
important properties required of biturnens are imperrneability
t o r n o i s t u r e , g o o d a d h e s i v e a n d c o h e s i v e p r o p e r t i e s , a n d a n ability to deform slowly dnd continuously when subjected to
shearing forces. The bituminous rnaterials chosen for roofing
h a v e t h e s e p r o p e r t i e s t o a g r e a t e r o r l e s s e r d e g r e e . D e s p i t e a g o o d d e a l o f r e s e a r c h i n r e c e n t y e a r s , t h e r e s t i l l r e m a i n s a
considerable lack of knowledge of the behaviour of biturnens
over wide temperature ranges. Although certain standards
h a v e b e e n e s t a b l i s h e d t h r o u g h c o - o p e r a t i v e r e s e a r c h o f t h e
petroleurn and roofing industries, and form the basis of ASTM
and CSA rnaterial specifications, it is still doubtful if the
e m p i r i c a l t e s t s i n v o l v e d a r e a d e q u a t e t o d e f i n e p r o p e r l y t h e b e s t r n a t e r i a l s f o r u s e i n t e r m s o f e n d u s e a n d d u r a b i l i t y .
Bitumen is a generic narne applied to mixtures
of predominantly hydrocarbons. In Canada and the United
S t a t e s , t h e t e r m i s l o o s e l y u s e d t o d e s c r i b e e i t h e r c o a l - t a r p i t c h o r a s p h a l t . C o a l t a r p i t c h e s a r e p r o d u c e d a s a b y
-product of the destructive distillation of biturninous coals in
the rnanufacture of gas or coke. Asphalts result from the
natural or industrial distillation of petroleum. Natural
asphalts ate rately used for roofing ln this country but, frorn the confusing array of petroleum asphalts, two types are
mainly used. Residual, or straight-run asphalt, which is
the residue after the rernoval of gasolines, oils, and other volatile products from crude oil, is often used directly or
with slight air oxidation. Blown asphalts are harder
asphalts produced frorn the sarne residues and strongly a i r - o x i d i z e d .
T w o o f t h e e m p i r i c a l t e s t s u s e d t o d e s c r i b e t h e
properties of biturnen are penetration and softening point.
P e n e t r a t i o n g i v e s a m e a s u r e o f b r i t t 1 e n e s s ; s o f t e n i n g p o i n t gives a measure of flow under controlled conditions.
The temperature interval between the softening
point and the point at which a brittle condition is reached
gives a measure of the ternperature susceptibility of the
