Snow loads on roofs 1959-60: fourth progress report

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Snow loads on roofs 1959-60: fourth progress report Watt, W. E.; Thorburn, H. J.

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NATIONAL RESEARCH COUNCIL CANADA

D I V I S I O N O F B U I L D I N G RESEARCH

SNOW LOADS ON ROOFS

1959-60

F O m H PROGRESS REPORT W. E. Watt and

H.

J. T h o r b u r n

I n t e r n a l

R e p o r t No. 204 o f t h e D i v i s i o n of B u i l d i n g R e s e a r c h OTTAWA N o v e m b e r

1960

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PREFACE

A s t h e l o a d due t o snow i s u s u a l l y t h e c r i t i c a l l o a d f o r which r o o f s i n Canada must be d e s i g n e d , t h e e f f e c t of t h e magnitude and d i s t r u b u t i o n of t h e d e s i g n snow l o a d on t h e s a f e t y of t h e s t r u c t u r e and on t h e c o s t of c o n s t r u c t i o n

is

c o n s i d e r a b l e . Hence t h e r e i s a need f o r g r e a t e r r e f i n e m e n t

i n

t h e magnitudes of t h e snow l o a d s s p e c i f i e d i n t h e N a t i o n a l

B u i l d i n g Code. Such r e f i n e m e n t c a n come o n l y f r o m . t h e o b s e r - v a t i o n of a c t u a l snow l o a d s on r o o f s and

it

i s f o r t h i s purpose t h a t t h e s u r v e y of snow l o a d s on r o o f s i s b e i n g c a r r i e d out by t h e D i v i s i o n of B u i l d i n g Research.

S i n c e t h e s t a r t of t h e s u r v e y i n 1956, t h e r e s u l t s of each w i n t e r ' s o b s e r v a t i o n s have been r e c o r d e d i n a n n u a l p r o g r e s s r e p o r t s and

it

i s t h e purpose o f t h i s f o u r t h r e p o r t t o p r e s e n t t h e r e s u l t s of t h e 1959-60 o b s e r v a t i o n s . A s b e f o r e , u s e i s made of g r a p h s , t a b l e s and photographs i n p r e s e n t i n g t h e r e s u l t s , and t h e t r e n d s and u n u s u a l f e a t u r e s of t h e o b s e r - v a t i o n s a r e d i s c u s s e d i n d e t a i l . Because of t h e s t a t i s t i c a l n a t u r e of snow l o a d s , , o n l y i n t e r i m c o n c l u s i o n s can be drawn a f t e r b u t f o u r winte-rs of o b s e r v a t i o n s .

The D i v i s i o n of B u i l d i n g Research wishes t o e x p r e s s once more i t s a p p r e c i a t i o n t o a l l t h o s e o b s e r v e r s whose a c t i v e p a r t i c i p a t i o n made t h e s u r v e y of t h e 1959-60 w i n t e r p o s s i b l e . I n p a r t i c u l a r , t h a n k s a r e e x p r e s s e d t o t h e many b u i l d i n g

i n s p e c t o r s , p r i v a t e companies and i n d i v i d u a l s who made B - S t a t i o n o b s e r v a t i o n s , and a l s o t o t h e RCAP p e r s o n n e l a t t h e C S t a t i o n s and t h e i r o r g a n i z e r s i n Ottawa. G r a t e f u l a p p r e c i a t i o n i s

recorded a l s o t o A-Station o b s e r v e r s of t h e M e t e o r o l o g i c a l Branch of t h e Department of T r a n s p o r t a t Goose Bay and Gander, t h e Department of N a t i o n a l Defence a t P o r t C h u r c h i l l , Ecole

Polytechnique ( M o n t r e a l )

,

IlIacdonald College ( S t e

.

Anne de

B e l l e v u e ) , Q u e e n ' s U n i v e r s i t y ( K i n g s t o n ) , U n i v e r s i t y of Toronto, U n i v e r s i t y of Manitoba (Winnipeg), U n i v e r s i t y of A l b e r t a (Edmonton), Aluminum Co. of Canada a t Arvida, t h e F e d e r a l Day School a t

I n u v i k , and t h e A t l a n t i c , P r a i r i e , and B.C. Regional S t a t i o n s of t h e D i v i s i o n .

Ottawa

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TABLE OF CONTENTS Introduction

...a

1 Summary of 1959-60 Observations

...

1

...

Description of 1959-60 Survey 2 Weather

...

2 ( a ) A S t a t i o n s

...

4 ..

( b )

B

S t a t i o n s

:...e...

6

( c ) C S t a t i o n s

...

6 ...

General Discussion

7 ...

( a ) Snow Loads from a Single Large Snowfall

7

( b ) Height of Roof above Ground

...

8

...

( c ) Snow Loads on Large F l a t Roofs 8

...

( d ) Depth of Concentrations 8 Interim Conclusions

...

9

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SNOW. LOADS ON ROOFS 1959-60 Fourth Progress Zeport

W.

E. Watt and H. J. IChorburn

During t h e w i n t e r of 1959-60 t h e Division of B u i l d i n g

Research continued i t s country-wide'survey of snow l o a d s on

r o o f s with o b s e r v a t i o n s of snow depth and d e n s i t y on a l a r g e number of r o o f s and on t h e ground. This f o u r t h p r o g r e s s r e p o r t d e s c r i b e s t h e s e o b s e r v a t i o n s , d i s c u s s e s t h e i r t r e n d s and unusual f e a t u r e s and r e c o n s i d e r s , i n t h e i r l i g h t , t h e i n t e r i m c o n c l u s i o n s drawn on t h e b a s i s of p a s t observations.

The survey, which was s t a r t e d i n 1956 a t t h e r e q u e s t of

t h e Associate Committee on t h e National B u i l d i n g Code, i s being

c a r r i e d out t o provide information on which t o base more r a t i o n a l snow load s p e c i f i c a t i o n s i n f u w r e e d i t i o n s of t h e Code. I n t h e c u r r e n t e d i t i o n of t h e Code ( 1 9 5 3 ) , t h e l o a d s a r e based on measurements of snow depths on t h e ground and on t h e assumption t h a t t h e s e

depths w i l l a l s o qccur on f l a t o r low-slope r o o f s . Casual obser-

v a t i o n s i n d i c a t e , h o w e v ~ r , t h a t t h i s assumption i s n o t e n t i r e l y c o r r e c t and t h a t

it

t e n d s t o make t h e s p e c i f i e d l o a d s c o n s e r v a t i v e . One of t h e prime o b j e c t i v e s of t h e survey, t h e r e f o r e , i s t o s t u d y t h e r e l a t i o n between roof and ground snow l o a d s and t h e f a c t o r s t h a t a f f e c t t h i s r e l a t i o n s h i p . This s t u d y was s t a r t e d w i t h a

p i l o t i n v e s t i g a t i o n d u r i n g t h e w i n t e r of 1956-57 and h a s continued a s a f u l l survey d u r i n g each subszquent w i n t e r . A f u l l d e s c r i p t i o n

of t h e background and r e s u l t s of t h e s e p a s t survey a c t i v i t i e s

i s

presented i n f i v e DBR i n t e r n a l r e p o r t s (1 t o 5 ) . It i s expected t h a t t h e survey w i l l continue f o r s e v e r a l more w i n t e r s .

On t h e whole t h e o b s e r v a t i o n s of t h e 1959-60 w i n t e r were n o t u n l i k e t h o s e of 1958-59 and t h e r e s u l t s of t h e survey a r e t h e r e f o r e s i m i l a r . Again, t h e average roof l o a d s were

g e n e r a l l y low compared t o c u r r e n t design v a l u e s , i n s p i t e of t h e f a c t t h a t t h e snowfall i n many a r e a s of Canada was above normal. Avera e l o a d s v a r i e d from almost n e g l i g i b l e v a l u e s , such a s o s e r v e d a t Sasiratoon and Fort C h u r c h i l l , t o t h e maximum of 32

-b--g

psf observed on a s h e l t e r e d P l a t roof a t Ottawa. Maximum l o a d s ,

on t h e o t h e r hand, were a g a i n q u i t e high

i n

c e r t a i n c a s e s . The 1959-60 o b s e r v a t i o n s d i d , however, provide con- s i d e r a b l e evidence i n support of t h e t r e n d s t o b s e r v e d i n p a s t w i n t e r s . A s b e f o r e , t h e average l o a d s on r o o f s were g e n e r a l l y found t o be s u b s t a n t i a l l y l e s s t h a n t h e corresponding !loads on

t h e ground, w i t h t h e d i f f e r e n c e s being q u i t e v a r i a b l e and dependent on many f a c t o r s . Wind, combined w i t h s h e l t e r , shape, and o r i e n t a -

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t i o n of t h e roof a g a i n appeared t o be t h e foremost of t h e s e f a c t o r s . Concentrations sometimes exceeding t h e ground. load were once more observed i n t h e expected l o c a t i o n s such a s n e a r

p a r a p e t w a l l s and on t h e lower l e v e l s of s p l i t - l e v e l r o o f s .

Generally, t h e magnitudes of t h e s e c o n c e n t r a t i o n s remain d i f f i c u l t t o p r e d i c t although some means f o r d.oing t h i s suggested themselves.

3

DESCRIFTION OF THE 1959-60

SURVEY

The survey was c a r r i e d out i n e s s e n t i a l l y t h e same way a s i n t h e previous two w i n t e r s . Measurements were a g a i n made a t t h r e e t y p e s of o b s e r v a t i o n s t a t i o n s , a s f o l l o w s :

A-Station observers continued, i n most c a s e s , t o make h e t a i l e d observations of snow depth and d e n s i t y on one f l a t and. one pitched roof of r e s i d e n t i a l s i z e , and on t h e surrounding ground. These measurements, which were made weekly and a f t e r every heavy snowstorm, were c a r r i e d out a s d e s c r i b e d i n DBR Technical Note 233 ( 6 ) .

B-Station obse&ers made p e r i o d i c measurements of only depth u s u a l l y on one roof and on t h e surrounding ground. Additional measurements were made on o t h e r r o o f s a t t h e time when t h e snow l o a d s were a t a maximum f o r t h e w i n t e r . C-Station observers made -the e q u i v a l e n t of A-Station

o b s e r v a t i o n s on l a r g e r o o f s l o c a t e d a t RCAP bases a c r o s s Canada. A t each s t a t i o n two o r more of t h e f o u r s t a n d a r d C-Station r o o f s were observed, t h e f o u r being t h e Unit

Supply Depot roof ( f l a t ) , t h e c a n t i l e v e r hangar roof ( f l a t ) , t h e Nechanical Equipment Garage roof ( f l a t , s p l i t - l e v e l ) , and t h e a r c h hangar roof ( c u r v e d ) .

Observation r e p o r t s f o r t h e 1959-60 w i n t e r were r e c e i v e d from a t o t a l of 53 s t a t i o n s . F i f t e e n A S t a t i o n s , i n c l u d i n g t h e new s t a t i o n a t Arvida, Quebec, r e p o r t e d o b s e r v a t i o n s on

4 1

r o o f s , 3 2 _B _{S t a t i o n s r e p o r t e d on 4 5 r o o f s and 6}_C _{S t a t i o n s r e p o r t e d on} 15 r o o f s f o r a t o t a l of 101 r o o f s . The l o c a t i o n s of a l l s t a t i o n s a r e given i n Figs. 1 and 2,

The w i n t e r of 1959-60 was i n many r e s p e c t s s i m i l a r t o t h a t of 1958-59. Por example, snowfall i n western Canada was a g a i n below normal p a r t i c u l a r l y i n B r i t i s h Columbia, Alberta and s o u t h e r n Manitoba. Other p a r t s of Canada experienced s n o w f a l l s up t o 135 p e r c e n t above normal. A l l of t h e s t a t i o n s f o r which r e c o r d s a r e a v a i l a b l e experienced c l o s e t o normal winds except H a l i f a x where t h e monthly wind mileage v a r i e d from

1 5

t o 33 p e r

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October, November and March, c l o s e t o normal i n January and A p r i l , and above normal i n December and February. Most of Canada r e c e i v e d l e s s t h a n normal sunshine d u r i n g October and Pebruary and normal amounts o r g r e a t e r d u r i n g t h e remainder of t h e w i n t e r .

5. RESULTS

A s i n previous p r o g r e s s r e p o r t s , A-Station r e s u l t s a r e given i n d e t a i l f o r each roof by means of a graph i n which t h e average ground l o a d , t h e maximum, average and minimum roof l o a d s and, where r e q u i r e d , t h e maximum load on a canopy o r l e a n - t o roof a r e p l o t t e d a g a i n s t time. Accompanying t h e graphs f o r

each s t a t i o n a r e r e c o r d s of wind, temperature and sunshine a s w e l l a s drawings g i v i n g t h e gauge p o s i t i o n s and b a s i c dimensions

of each r o o f . These d e t a i l e d r e s u l t s , which a r e given i n Figs.

3 t o 1 6 , a r e summarized i n Table I and i t s g r a p h i c a l e q u i v a l e n t ,

Pig, 22.

B-Station r e s u l t s a r e presented i n t h e same manner a s

i n DBR Report 184. %igure 2 g i v e s B-Station l o c a t i o n s a s w e l l

a s " s t i c k t ' graphs of maximum average roof and ground l o a d s a t t h e s e l o c a t i o n s . Table I1 shows t h e roof d e t a i l s and l o a d i n g i n f l u e n c e s f o r each r o o f .

With t h e exception of t h e g r a p h i c a l surnmary, C-Station r e s u l t s a r e presented i n t h e same form a s A-Station r e s u l t s . The load-time curves f o r each roof a r e given i n Pigs. 17 t o 21, and t h e r e s u l t s a r e summarized i n Table 111.

Snox load o b s e r v a t i o n s d u r i n g 1959-60 showed t h a t t h e average roof l o a d s were g e n e r a l l y s u b s t a n t i a l l y l e s s t h a n t h e

corresponding average ground l o a d s . Indeed, only 17 p e r c e n t

of t h e r o o f s observed had l o a d s exceeding 75 p e r c e n t of t h e

ground load. Once more it was found t h a t a l a r g e proportion of

t h e r o o f s w i t h high roof-load t o ground-load r a t i o s were l o c a t e d i n a r e a s where t h e maximum snow l o a d s r e s u l t e d from one o r a few snowstorms a s opposed t o t h o s e a r e a s where t h e l o a d s accumulated throughout t h e w i n t e r .

The maximun l o a d s , i n t h e form of d r i f t s and concen-

t r a t i o n s , o f t e n exceeded t h e ground l o a d s and were observed i n much t h e same p l a c e s a s i n t h e previous w i n t e r . Again t h e most f r e q u e n t examples occurred a t t h e junction of t h e l e v e l s of s p l i t - l e v e l r o o f s ( F i g . 2 3 ) , on porch r o o f s and canopies and a l o n g p a r a p e t w a l l s . Others occurred on t h e "leeward" s i d e of p i t c h e d r o o f s and n e a r l a r g e chimneys ( P i g . 2 4 ) . Although t h e l o c a t i o n s of many of t h e s e c o n c e n t r a t i o n s can now be p r e d i c t e d w i t h a f a i r degree of c e r t a i n t y , t h e same cannot be s a i d f o r t h e i r magnitudes which were a g a i n found t o be extremely v a r i a b l e .

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Some of t h e f o l l o w i n g comments on i n d i v i d u a l A-Station o b s e r v a t i o n s w i l l p o i n t o u t t h e v a r i a t i o n s i n t h e roof-load t o ground-load r a t i o s and c o n c e n t r a t i o n s mentioned above.

( a ) A S t a t i o n s

Vancouver.- No measurements were t a k e n a t t h i s s t a t i o n

because of t h e very l i g h t snowfall. The maximum snowstorm pro-

duced only 3 t o 4 i n . with l e s s e r amounts f a l l i n g on f o u r o t h e r occasions. I n a l l c a s e s t h e snow melted soon a f t ' e r it f e l l .

Inuvik.

-

Although t h e snowfall was only 11 p e r c e n t

above norm-uvik, a s i n 1958-59, experienced h i g h e r snow

l o a d s t h a n would be expected. For t h e second consecutive w i n t e r ,

t h e maximum average load on t h e ground exceeded t h e 35 psf l o a d s p e c i f i e d by t h e NBC. Loads on t h e r o o f s , however, were l e s s t h a n t h i s , w i t h t h e two gable r o o f s accumulating 22 and 25 psf o r

45 and 50 p e r c e n t of t h e load on t h e ground. Due t o t h e pre-

v a i l i n g NW wind, d r i f $ i n g occurred on t h e leeward s i d e s of t h e

two gable r o o f s . These c o n c e n t r a t i o n s , which were maximum a t

t h e r i d g e and minimum a t t h e eaves, were most pronounced on t h e

exposed gable roof and reached a maximum of

4 1

p s f . On t h e f l a t

r o o f , however, wind and t h e degree of exposure were observed t o have kept t h e average load t o 7 psf ang produced only s l i g h t c o n c e n t r a t i o n s .

Saskatoon.

-

A w i n t e r of average snowfall d i d n o t l e a d

t o any o u t s t a n d i n g o b s e r v a t i o n s a t t h i s s t a t i o n ; t h e l a r g e s t

average roof load was 8 p s f , t h e l a r g e s t average ground load was

18 p s f , and t h e average roof load ranged between 17 and 62 p e r

c e n t of t h e ground load. What i s of n o t e , however, i s t h e

o b s e r v a t i o n s , t a k e n f o r t h e f i r s t t i m e , on t h e gymnasium roof a t

t h e U n i v e r s i t y of Saskatchewan. This f l a t r o o f , approximately

225 f t by 160 f t , has a s l i g h t s l o p e towards one s i d e which

r e s u l t s i n t h e parapet w a l l s v a r y i n g i n h e i g h t from 2 t o z e r o f t

a l o n g t h e a d j a c e n t s i d e s . Although t h e b u i l d i n g i s bordered on two s i d e s by evergreen t r e e s , 20 t o 30 f t i n h e i g h t , i t s r o o f ,

being almost 40 f t above ground, can be considered exposed. With

t h e s e c h a r a c t e r i s t i c s it i s somewhat s u r p r i s i n g t h a t t h e load on t h e roof was among t h e h i g h e s t observed a t Saskatoon,

P o r t C h u r c h i l l .

-

A s i n t h e two previous w i n t e r s , t h e r o o f s a t P o r t C h u r c h i l l a g a i n demonstrated t h e e f f e c t of extreme

exposure i n an a r e a of f r e q u e n t h i g h winds. Even w i t h a snowfall

135 p e r c e n t above t h e normal 40 i n . , which produced an average ground load of 34 p s f , t h e l a r g e f l a t roof was c o n t i n u a l l y swept b a r e while t h e gable roof accumulated only a small amount, mostly

on t h e leeward slope. A s would be expected, t h e l e a n - t o roof of

b u i l d i n g P-2 r e c e i v e d a s i z a b l e load of 37 p s f . The t h r e e i d e n t i - c a l c o r r i d o r r o o f s , two of which a r e o r i e n t e d a t r i g h t a n g l e s t o

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t h e t h i r d , a g a i n i l l u s t r a t e d t h e e f f e c t o f o r i e n t a t i o n . Being o r i e n t e d i n t h e d i r e c t i o n most conducive t o removal of t h e snow by t h e wind, t h e t h i r d roof had average l o a d s which were only

1 / 4

t o 1/6 of t h o s e on t h e o t h e r two r o o f s . The d i f f e r e n c e

between t h e observed maxima was even g r e a t e r .

Toronto.

-

Snowfall which exceedsd t h e normal 55 i n . by 50 p e r c e n t produced average l o a d s of 7 psf on t h e gable r o o f , 1 3 psf on t h e f l a t r o o f , and 1 7 psf on t h e ground. The most s i g n i f i c a n t f e a t u r e of t h e s e l o a d s i n t h e h i g h r o o f - l o a d t o ground-load r a t i o o f 77 p e r c e n t . This i s t o be expected, however, because of Toronto's moderate c l i m a t e i n which t h e maximum load w i l l u s u a l l y r e s u l t f r o m one o r t w o snowstorms r a t h e r t h a n a n accumulation throughout t h e w i n t e r .

Ottawa.

-

Snow l o a d s observed i n Ottawa were s l i g h t l y lower t h a n T i E Z of 1958-59 i n s p i t e of 10 i n . more snowfall. The 34 p e r c e n t above normal f a l l of 110 i n . produced a n average load on t h e ground of s l i g h t l y more t h a n 40 psf. The average roof load m o s t n e a r l y approaching t h i s a g a i n occurred on t h e s h e l t e r e d f l a t roof . a t Fairhaven Way where a l o a d o f 32 psf was measured. This roof a l s o accumulated t h e l a r g e s t c o n c e n t r a t i o n , a l o a d of 57 psf a d j a c e n t t o t h e r a i s e d s e c t i o n . The o t h e r l e s s s h e l t e r e d f l a t r o o f s had much lower l o a d s w i t h 1 5 psf o c c u r r i n g on t h e one w i t h p a r a p e t w a l l s and 1 4 psf o c c u r r i n g on t h e o t h e r . Both gable r o o f s were loaded f a i r l y uniformly t o a maximum average l o a d o f 1 0 p s f .

Ste. Anne de Bellevue.

-

With t h e snowfall 40 p e r c e n t above normal t h e average load on t h e ground a t Ste. Anne de

Bellevue reached approximately 35 p s f . Much below t h i s were t h e average l o a d s on t h e two exposed r o o f s , 3 p s f on t h e gable

and 10 psf on t h e f l a t . The d i f f e r e n c e between t h e roof l o a d s can perhaps be a t t r i b u t e d t o t h e l o c a t i o ~ of t h e h i g h e r c e n t r a l s e c t i o n of t h e b u i l d i n g , l o c a t e d a t t h e e a s t end of t h e gable roof and a t t h e west end o f t h e f l a t r o o f . The gable roof had t h e l a r g e s t c o n c e n t r a t i o n a g a i n when i c e accumulated t o a depth o f 18 i n . a t t h e eaves producing a load o f

94

psf.

Arvida.

-

Observations a t t h i s pew s t a t i a n were made on a large-00 sq ft;) f l a t roof which covers a rod r o l l i n g

m i l l a t t h e Arvida Works of t h e Aluminum Company. The m i l l ,

which i s u n s h e l t e r e d except f o r a b u i l d i n g of equal h e i g h t on t h e e a s t s i d e , i s heated b u t t h e roof i s i n s u l a t e d . Although

it has no p a r a p e t w a l l s , t h e roof h a s numerous p r o j e c t i o n s i n t h e form of c y l i n d r i c a l v e n t i l a t o r s which a r e 4 f t i n d i a m e t e r and 6 f t high. The average snow l o a d accumulated by t h i s roof d u r i n g t h e period observed reached only 4 psf while t h e load on t h e ground r o s e t o 25 p s f . Pew and small c o n c e n t r a t i o n s were observed with t h e l a r g e s t producing 1 2 psf.

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H a l i f a x .

-

Although t h e snowfall exceeded t h e normal by 100 p e r c e n t t h e mild weather a t H a l i f a x prevented any s u s - t a i n e d accumulation of snow loads. A s would be expected, t h e maximum load occurred a s t h e r e s u l t of a s i n g l e storm, i n t h i s c a s e , a record 24-hr snowfall of 30 i n . accompanied by 20 t o 25 mph winds and 31 t o 32 deg temperatul-es. The average ground load reached 38 psf (IJBC design load = 40 p s f ) while t h e avera e load on t h e gable roof reached 11 psf and on t h e two f l a t = &

reached 2 1 and 22 p s f . It should be noted t h a t because of t h e s u b s t a n t i a l wind t h e roof-load t o ground-load r a t i o was n o t a s high a s would be expected i n a n a r e a where a s i n g l e snowstorm produces t h e maximum load. The wind can a l s o be considered t h e cause of a

78

psf maximum l o a d which occurred a d j a c e n t t o a

5 - f t - h i g h penthouse on one of t h e f l a t r o o f s . Other p o i n t s t o be noted i n t h e H a l i f a x o b s e r v a t i o n s w i l l be d i s c u s s e d l a t e r .

Gander.

-

With a 1 0 p e r c e n t above normal snowfall of 128 i n . a n ~ t h e o w i e s t March on r e c o r d , t h e average l o a d s on

t h e f l a t and gable r o o f s f a i l e d t o exceed

5

and

7

p s f , r e s p e c t i v e l y . Concentrations were oply 1 psf more t h a n t h e average i n both c a s e s . One s u r p r i s i n g f e a t u r e of t h e o b s e r v a t i o n s was t h e grouiid load. Mild weather and l i g h t snowfall throughout most of February

reduced t h e ground load t o z e r o , b u t a s a r e s u l t of t h e March snowfall it r o s e t o a maximum of 69 p s f .

Other A S t a t i o n s .

-

The l o a d s observed a t A S t a t i o n s n o t a l r e a d y mentioned were r e l a t i v e l y l i g h t and no unusual

accumulations were observed. Roof l o a d s were g e n e r a l l y l e s s t h a n 20 p e r c e n t of t h e corresponding ground l o a d s .

( b ) B S t a t i o n s

Again i n 1959-60 B-Station o b s e r v a t i o n s have provided s t a t i s t i c a l s t r e n g t h t o t h e A-Station o b s e r v a t i o n s . A s i n d i c a t e d by Table I1 and Pig. 2 t h e average l o a d s observed on t h e r o o f s were s i g n i f i c a n t l y l e s s t h a n t h e l o a d s observed on t h e ground.

S i m i l a r l y , c o n c e n t r a t i o n s f a r exceeding t h e grow?<< load were observed on many r o o f s .

( c ) C S t a t i o n s

- _{Observations made a t s i x}_C _{S t a t i o n s d u r i n g t h e 1959-60}

r i n t e g showed, a s i n t h e previous two w i n t e r s , t h a t l a r g e f l a t r o o f s i n exposed l o c a t i o n s do n o t accumulate high average l o a d s . This can be seen i n Table 111 where it w i l l be found t h a t t h e maximum average load on a f l a t roof was 10 psf a s observed on t h e ME Garage r o o f s a t North Bay and Goose Bay. The only average value t o exceed t h i s was t h e accumulation of 23 psf on t h e f l a t wings of t h e a r c h hangar a l s o a t North Bay. Concentrations

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exceeding t h e s e v a l u e s were observed on many of t h e r o o f s , t h e most n o t a b l e examples o c c u r r i n g on t h e lower l e v e l s of

t h e s p l i t - l e v e l ME Garage r o o f s . Others were observed n e a r t h e door housings on t h e c a n t i l e v e r hangar r o o f s and on t h e canopies

of t h e U n i t Supply Depots. Only a few o b s e r v a t i o n s were made on

t h e a r c h proper of t h e a r c h hangar ( t h e v a l u e s given i n Table I11

a r e f o r t h e f l a t wings o n l y ) and t h e s e showed t h a t t h e depth of snow on t h e crown of t h e a r c h was roughly h a l f of t h a t a t a p o i n t h a l f way down t h e a r c h .

GENERAL DISCUSSION

A f t e r one w i n t e r of p i l o t o b s e r v a t i o n s and t h r e e w i n t e r s of f u l l o b s e r v a t i o n s t h e survey h a s - p r o v i d e d c o n s i d e r a b l e i n f o r - mation on t h e s u b j e c t of snow l o a d s on r o o f s . The load p r e d i c t i o n s t h a t can be made on t h e b a s i s of t h i s information a r e , however,

i n many c a s e s q u a l i t a t i v e r a t h e r t h a n q u a n t i t a t i v e . For example, t h e survey has shown t h a t snow l o a d s on r o o f s a r e s u b s t a n t i a l l y l e s s t h a n t h e l o a d s on t h e ground, but by how much under any given s e t of c o n d i t i o n s cannot y e t be p r e d i c t e d , and may never be p r e - d i c t e d a s a c c u r a t s l y a s could be wished. It h a s shown t h a t

maximum l o a d s sometimes exceeding t h e l o a d s on t h e ground accumu- l a t e i n c e r t a i n p o s i t i o n s b u t t o magnitudes t h a t a r e y e t g e n e r a l l y u n p r e d i c t a b l e .

The o r i g i n a l hopes f o r q u a l i t a t i v e answers from t h e

f i r s t few y e a r s of t h e survey now appear t o be dimmed and

it

would seem t h a t q u a n t i t a t i v e d e t a i l s must now come a t a much slower r a t e from o b s e r v a t i o n s of f u t u r e w i n t e r s . A s t h e s e d e t a i l s must a p p a r e n t l y come from a s t a t i s t i c a l approach, t h e number of w i n t e r s t o be observed w i l l depend on t h e s t a t i s t i c a l

s t r e n g t h r e q u i r e d o r d e s i r e d . I n t h e meantime, while t h i s

s t r e n g t h i s being gained, it remains f o r t h e progress r e p o r t s on

each w i n t e r ' s o b s e r v a t i o n s t o p r e s e n t and d i s c u s s , i n a d d i t i o n t o t h e observed l o a d s , t h e r a m i f i c a t i o n s of t h e a l r e a d y known q u a l i t a t i v e f a c t s and o t h e r a s p e c t s of t h e s u b j e c t . This

i s

done i n t h e f o l l o w i n g d i s c u s s i o n .

( a ) Snow Loads from

a

S i n g l e Large Snowfall.

-

Some

u s e f u l i n d i c a t i o n s a s t o t h e c h a r a c t e r of t h e snow l o a d s which r e s u l t from a s i n g l e severe snowstorm were provided by t h e

record 30 i n c h f a l l i n 24 h r a t Halifax. Observations made

a f t e r t h e storm i n d i c a t e d t h a t t h e l o a d s were oonsiderably lower t h a n might have been expected. On u n s h e l t e r e d f l a t r o o f s , i n p a r t i c u l a r , t h e accumulations were v e r y s m a l l while on p i t c h e d r o o f s i n s i m i l a r s h e l t e r c o n d i t i o n s l a r g e r l o a d s were observed

on t h e leeward s i d e of t h e roof (Fig. 2 5 ) . Unbalanced l o a d i n g

of t h i s type was observed on many r o o f s , even on t h o s e considered t o be i n s h e l t e r e d l o c a t i o n s ( F i g . 26). I n t h e s e c a s e s t h e wind

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removal of t h e snow.

It

was a l s o observed t h a t t h i s unbalanced l o a d i n g was b u i l t up by t h e wind d u r i n g t h e s n o w f a l l and n o t a f t e r w a r d s . Thus t h e r e n e v e r was a uniform l o a d b u t r a t h e r a g r a d u a l b u i l d up t o t h e f i n a l shape. I t w i l l be r e a l i z e d t h a t t h e above c h a r a c t e r i s t i c s a r e l a r g e l y dependent on t h e wind and t h a t i f t h e r e had been no wind d u r i n g t h e s n o w f a l l t h e l o a d i n g p a t t e r n s would have been much more uniform u n t i l reshaped by a subsequent wind.

( b ) Height of Roof above Ground.

-

The p b s e r v a t i o n s made a t H a l i f a x a f t e r t h e r e c o r d s n o w f a n a l s o r e v e a l e d a p r e v i o u s l y overlooked f a c t o r which a f f e c t s t h e r e l a t i o n s h i p between snow l o a d s on r o o f s and snow l o a d s on t h e ground. I t

was observed t h a t t h e l o a d s on t h e r o o f s of two- and t h r e e - s t o r y b u i l d i n g s were c o n s i d e r a b l y l e s s t h a n t h o s e on t h e r o o f s of

s i n g l e - s t o r y b u i l d i n g s . I t i s evid.ent t h a t t h i s i s due t o t h e f a c t t h a t wind speed i n c r e a s e s w i t h t h e h e i g h t above ground. Presumably t h e r e i s a n e l e v a t i o n a t which a r o o f would be k e p t c o n t i n u a l l y b a r e e x c e p t f o r a r e a s of l o c a l i z e d s h e l t e r .

( c ) Snow Loads on Large F l a t Roofs.

-

Because of s e v e r a l i n q u i r i e s r e g a r d i n g snow l o a d s on l a r g e f l a t r o o f s , a number of t h e s e r o o f s were added f o r t h e 1959-60 s u r v e y t o t h o s e a l r e a d y observed. I n a l l , 23 r o o f s w i t h a r e a s g r e a t e r t h a n a b o u t 5000 s q

f t

( a n a r b i t r a r y l i m i t ) were observed. From t h e r e s u l t s , l i s t e d i n Table I V , it i s s e e n t h a t t h e a v e r a g e r o o f l o a d s a r e a l l w i t h i n t h e s u r p r i s i n g l y low range of 0 t o 1 3 p s f . The r o o f - l a a d t o ground-load r a t i o s v a r y from 0 t o 100 p e r c e n t , b u t o n l y v e r y few a r e above 50 p e r c e n t . Excepting t h e s e few, which

occurred on r o o f s w i t h l a r g e p r o j e c t i o n s on them o r on r o o f s i n " s i n g l e s n o w f a l l a r e a s " , it would seem t h a t , i n g e n e r a l , l a r g e f l a t r o o f s have low r o o f - l o a d t o ground-load r a t i o s such a s would be expected i n u n s h e l t e r e d c o n d i t i o n s . I t i s t h e r e f o r e

perhaps r e a s o n a b l e t o assume t h a t r e g a r d l e s s of a d j a c e n t s h e l t e r i n g o b j e c t s t h e s e r o o f s remain exposed by v i r t u e of t h e i r s i z e . Unlike s m a l l e r r o o f s , t h e y a r e l a r g e enough t o extend beyond t h e a r e a of s h e l t e r provided by t h e a d j a c e n t o b j e c t s . Even w i t h o u t t h i s c h a r a c t e r i s t i c , however, l a r g e f l a t r o o f s could be expected t o have low r o o f - l o a d t o ground-load r a t i o s because t h e y o f t e n c o v e r b u i l d i n g s t h a t a r e t h e e q u i v a l e n t of two o r t h r e e s t o r i e s i n h e i g h t and t e n d t o be l o c a t e d on r e l a t i v e l y f l a t l a n d .

( d ) Depth of C o n c e n t r a t i o n s .

-

The magnitudes of t h e l o a d s t o be expected from c o n c e n t r a t i o n s a r e s t i l l l a r g e l y unknown a l t h o u g h e a c h w i n t e r ' s o b s e r v a t i o n s have provided some i n d i c a t i o n s . From p a s t o b s e r v a t i o n s it i s b o w n , f o r example, t h a t t h e lower l e v e l s of s p l i t - l e v e l r o o f s , l e a n - t o r o o f s , and c a n o p i e s t h a t a r e l o c a t e d n o t t o o f a r below t h e main r o o f s u r - f a c e s w i l l accumulate c o n c e n t r a t i o n s up t o d e p t h s e q u a l t o t h e d i f f e r e n c e s i n l e v e l s ( F i g . 2 7 ) . Up t o what maximum d i f f e r e n c e s

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i n l e v e l s t h i s i s t r u e i s n o t y e t known b u t it i s suspected t h a t

it i s governed by s e v e r a l f a c t o r s . One o f t h e s e would obviously

be t h e amount of snowfall, a r e a s of heavy snowfall e x p e r i e n c i n g deeper c o n c e n t r a t i o n s t h a n a r e a s of l i g h t snowfall. Another f a c t o r , one which was suspected on t h e b a s i s of p a s t w i n t e r s ' o b s e r v a t i o n s , was w e l l demonstrated on a roof a t Lethbridge

( P i g . 28). Here

it

was observed t h a t t h e depth of t h e concentra- t i o n was g r e a t l y i n f l u e n c e d by t h e s i z e of t h e main r o o f .

Because of t h e r o o f ' s g r e a t a r e a , a l a r g e amount of snow was a v a i l a b l e f o r t r a n s f e r by wind t o t h e lower roof.. Thus even w i t h only a small depth of snow on t h e ground a v e r y l a r g e con-

c e n t r a t i o n developed. I t can l o g i c a l l y be assumed t h a t t h e s i z e

of a roof w i l l a l s o i n f l u e n c e t h e depth of snow t h a t w i l l accumulate n e a r p a r a p e t w a l l s .

7.

INTERIM CONCLUSIONS

On t h e b a s i s of t h e 1959-60 o b s e r v a t i o n s l i t t l e can be added t o t h e i n t e r l m conclusions drawn f r o m p a s t o b s e r v a t i o n s and s e t f o r t h i n DBR I n t e r n a l Reports 163 and 184. They can, perhaps, be r e p e a t e d h e r e , w i t h more c e r t a i n t y .

( i ) The average snow l o a d s on r o o f s a r e s u b s t a n t i a l l y l e s s t h a n t h e load on t h e surrounding ground. ( i i ) The amount by which t h e snow load on t h e roof and

t h e load on t h e ground d i f f e r i s p r i m a r i l y dependent on t h e degree t o which t h e roof i s s h e l t e r e d .

(iii) Concentrations sometimes exceeding t h e load on t h e ground a r e t o be expected on r o o f s i n any a r e a of l o c a l i z e d s h e l t e r , t h e magnitude being dependent on, among o t h e r t h i n g s , t h e snowfall and t h e s i z e of t h e main r o o f .

1. A l l a n , D.E. Snow Loads on Roofs

-

The p r e s e n t requirements and a proposal f o r a survey of snow l o a d s on r o o f s .

National Research Council, Division of B u i l d i n g Research, I n t e r n a l Report No. 106, Sept. 1956. 19 p.

2. A l l a n , D.E. Snow Loads on Roofs 1956-57

-

A Progress Report. National Research Council, D i v i s i o n of B u i l d i n g Research,

I n t e r n a l Report No. 134, Jan. 1958. 7 p.

3. A l l a n , D.E. and T u r k s t r a , C . J . Snow Loads on Roofs 1957-58

-

Second Progress Report. National Research Council, Division of B u i l d i n g Research, I n t e r n a l Report No. 163, Nov. 1958.

6

p.

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4.

Thorburn, H . J . and P e t e r , B.G.W. Snow Loads on Roofs 1958-59

-

Third P r o g r e s s Report. N a t i o n a l Research C o u n c i l ,

D i v i s i o n of B u i l d i n g Research, I n t e r n a l Report No. 184, Nov. 1959. 16 p.

5. P e t e r , B.G.W. and Thorburn, H . J . Snow Load O b s e r v a t i o n s a t

B

S t a t i o n s 1958-59. N a t i o n a l Research Council, D i v i s i o n of B u i l d i n g Research, I n t e r n a l Report No. 189. 1 3 p a

6.

A l l e n , D.E. F i e l d I n s t r u c t i o n s f o r Observers a t "A" S t a t i o n s of Snow Loads on Roofs. N a t i o n a l Research C o u n c i l , D i v i s i o n of B u i l d i n g Research, T e c h n i c a l Note No.

233,

Octm 1957. 11

P.

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!rnmrn: I

SNO'VLOAD:; FOR A STATIONS

Max. Av. Ground ( p s f 1 Max. Av. Roof Cable: Exposed, h e a t e d , i n s u l a t e d 30 Gable: S h e l t e r e d , h e a t e d , i n s u l a t e d 30 F l a t : Exposed, h e a t e d , i n s u l a t e d 3 0 Gable: Not h e a t e d 2 5 F l a t : Heated, i n s u l a t e d 2 5 Edmonton, A l t a

.

S a s k a t o o n , Sask. Gable : Heated, i n s u l a t e d Gable: Heated, i n s u l a t e d F l a t : Heated, i n s u l a t e d P l a t : Heated, i n s u l a t e d F l a t : Heated, i n s u l a t e d Winnipeg, Man. Gable: Heated, i n s u l a t e d F l a t : Heated, i n s u l a t e d F o r t C h u r c h i l l , Man. Toronto, Ont. Gable: He ~ t e d , i n ~ u l a t e d 55 F l a t : Heated, i n ~ u l a t e d 5 5 F l a t ( C o r r i d o r s ) : Heated, i n s u l a t e d 55 Gable: Heated, i n s u l a t e d F l a t : Heated, i n s u l a t e d Kingston, Ont

.

Gable : Heated, i n s u l a t e d F l a t : Heated, i n s u l a t e d

Ottawa, Ont. Gable : Heated, i n s u l a t e d 4 5 4 0

Gable: Heated, i n s u l a t e d 4 5 40 F l a t (No p a r a p e t ) : Heated, i n s u l a t e d 50 4 8 F l a t ( P a r a p e t ) : Heated, i n s u l a t e d 5 0 3 3 F l a t ( F b i s e d s e c t . ) : Heated, i n s u l a t e d 50 4 5 Gable: Heated, i n s u l a t e d F l a t : Heated, i n s u l a t e d S t e . Anne de B e l l e v u e , P.Q. M o n t r e a l , P.Q. Gable: Heated, i n s u l a t e d F l a t : Heated, n o t i n s u l a t e d Arvida, P.Q. F l a t : Heated, i n s u l a t e d

1

55

1

2 5 H a l i f a x , N.S. Gable : Heated, n o t i n s u l a t e d F l a t : Heated, i n s u l a t e d F l a t : Heated, i n s u l a t e d Gander, N f l d . Gable: Not h e a t e d , i n s u l a t e d

F l a t : Not h e a t e d , i n s u l a t e d

I

Goose Bar, Lab. Gable: Heated, i n s u l a t e d 52

F l a t : Heated, i n s u l a t e d

I

a l e a n - t o b

I I I

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1,oc:i t Lon i : i t i m : ~ L , ]I.'.:. V i c t o r i n , ?.I:. P e n t i c t o n , U.C., Vcrnon, B.C. I i e l s o n , 9.C. C a l p n r y , A l t a . T , e t h b r i d c e , A l t a . rq'lat >'la t Pln t F l a t S a b l e ? l a t " a t Y e l l o w k n i f e , N'#T. x x x x x x x Yorkton, Snsk. Norm:r House, binn. J i n n i p e ~ , Mnn. Kenora , Ont. F o r t I;kances, Ont.

F o r t Hope, Ont. Cable Cable Wewa, Ont.

I

C a b l e

1

Gable h'la t S a u l t S t e . M n r i e , Unt.

1

S n r n i a , Ont. ?.and o n , Ont

.

S t r a t f o r d , Ont. Moononec, Ont. t l a m i l t o n , Ont. P l a t L e a n - t o F l a t P l a t x P l s t

I x

x x B e l l e v i l l e , Ont. Pembroke , Ont.

I

C a b l c F l a t F l a t C a b l e Cable x x Cumberland, Ont. P o r t H a r r i s o n , P.Q. L a c h i n e , P.Q. M i s t o s s i n n y , P.Q. C a b l e F l a t Gable M o n t r e a l , P.Q.

I

x F l a t Gable C a b l e ~ r o i a ~ i v i i r e s , P.Q. x F r e d e r i c t o n , N.B. Amherst, N.S. S t . J o h n ' s , N f l d .

I

f a b l e F l a t Hip Gable F l a t a n r a o k e t e d f i g u r e i n d i c a t e s b a s i c iIDC ( 1 9 5 7 ) l o a d . --.-.- -.---- -- --.---*--- -- x

(17)

TABLE

I11

SZOW LOADS FOR C STATIONS ( i n p s f )

Note:

-

i n d i c a t e s roof n o t a v a i l a b l e .

g f i g u r e i n b r a c k e t s i n d i c a t e s maximum on canopy o r l e a n - t o . Comox, B.C.

Lancaster, Alta. Cold Lake, Alta. Winnipeg

,

Illan

.

North Bay, Ont. Goose Bay, Lab.

Cant. Hangar M,E. Garage 'I Max. round 3 25

1 5

6

-

NBC ( B a s i c )

45

25 30 35

55

90 i &lax. D r i f t 0

4 1

9 11 60

4 1

Max. Ground 3 25

1 5

9

19 40 Supply Depot Max. Av. Roof 0 9 6

4 -

-

Max. Av. Roof 0

5

6

5

10 10 Arch Hangar Max. D r i f t 0 35(22)

9 1 4 ( 4 )

-

Max. Ground 3

-

16 9 20

-

Max. D r i f t

-

6 7 ( 2 ) 1 3 ( 2 3 ) " 1 4 ( 2 5 ) Max. Ground

-

1 4

9 1 3 48 Max. Av. Roof

-

5 - 4

7 7 hIax

.

Roof 0

-

8

5

23

-

A v o M a x . D r i f t 0

-

11 9 35

-

(18)

TABLE I V

SNOW LOADS ON

LARGE

PLAT ROOFS

L Location L a n c a s t e r , Alta. Cold Lake, A l t a . Lethbridge, A l t a . Saskatoon, Sask. P o r t C h u r c h i l l , Man. Winnipeg

,

Man. S a u l t S t e . Marie, Ont. S a r n i a , Ont. London, Ont. North Bay, Ont. B e l l e v i l l e

,

Ont. Lachine, P.Q. Montreal, P.Q. Anrida

,

P.

Q.

Gander, Nfld. Goose Bay, Lab.

Roof M.F. Garage Cant. Hangar U.S. Depot M.E. Garage Cant. Hangar Civic Centre Gymnasium Barracks U. S

.

' ~ e p o t M.E; Garage Cant. Hangar F a b r i c a t i n g P l a n t Warehouse Manufacturing P l a n t . Average Roof Load ( psf

1

5 9 5

6

7 8 0 4 5

4

5 3 11 Roof Load

,

100% Ground Load 25 36 36 40 40 100 50 0 44 56 67 31 15 77 37 5 3 35 28

1 5

1 6

9 12 15 25 U. S. Depot M.E. Garage Manufacturing P l a n t 11 1 I t~ TI R o l l i n g M i l l M.E. Roon D-26 U. S. Depot M.E. Garage 7 10 1 3 7 8

4

5

7 1 0

(19)

FIGURE I A 81 C STATION LOCATIONS AND THEIR

- -

(20)

FIGURE

2

B STATION LOCATIONS AND THEIR

(21)

1 I I I

-

NUMBER INDICATES MAXIMUM ON CANOPY

GAUGE LOCATION e--- OR L E A N - T O ROOF OF MAXIMUM \ ETC. \

-

'

GROUND LOAD 0 - MAXIMUM 0 0 LOAD ON 0 AVERAGE MAIN ROOF MINIMUM TIME (DAYS)

(22)

R O O F D E S C R I P T I O N

E - 3 SCHOOL

E - 3 R E S I D E N C E

(SHELTERED HEATED INSULATEOl

E

-

3 R E S I D E N C E

(EXPOSED, HEATED, INSULATED 4 3

F E D E R A L B U I L D I N G

WIND DIRECTIOW

(EXPOSED, HEATED, INSULATED)

F I G U R E 3

SNOW LOAD OBSERVATIONS ON ROOFS Y E A R : 1959/60

(23)

ROOF DESCRIPTION

ADMINISTRATION BLDG.

SECTION " A - A "

MINING STORE SHED

1 SHELTERED, UNHEATED BL DG. I

SNOWFALL

SNOW LOAD OBSERVATIONS ON ROOFS

Y E A R : 1 9 5 9 / 6 0

LOCATION : EDMONTON, ALTA.

(24)

-- ROOF DESCRIPTION

314 LAKE CRESCENT

I EXPOSED, HEATED. INSULATED)

I EXPOSED. HEATED, INSULATED I

OUTDOOR TEST S T A T I O N

NORMAL 1959/60

SNOW LOAD OBSERVATIONS ON ROOFS

Y E A R : 1959 160

LOCATION: SASKATOON, SASK.

(25)

N . R . C . L A B . - -N.R.C. L A B . D E T A I L A I E X P O S E D , H E A T E D , lNSUL A T E 0 I G Y M N A S I U M EXPOSED. HEATED,VENTILATEO 2 ' PARAPETS

SNOW LOAD OBSERVATIONS ON ROOFS

Y E A R : 1959 /60

LOCATION: SASKATOON. SASK.

(26)

ROOF DESCRIPTION

L I B R A R Y S . W I N G

60

EXPOSED, I N S U L A T E D , NOT YEN T I L A T E D , UNHEATED A I R SPACE

A G R I C U L T U R A L E N G . BLDG.

EXPOSED, A T T I C UNHEATED, VENTIL A T E 0 INSULATED

NORMAL 1 9 5 9 / 6 0

SNOW LOAD OBSERVATIONS ON ROOFS

YEAR : 1959 /60

LOCATION : WINNIPEG.

(27)

H E 4 T E D , INSUL 4 T E D , NOT Y E N T l L A T E D

H E A T E D , I N S U L A T E D . V E N T I L 4 T E D

SNOWFALL ( NOM-APRIL1 4 0 '

SNOW LOAD OBSERVATIONS ON ROOFS Y E A R : 1 9 5 9 / 6 0

LOCATION: FORT CHURCHILL MAN.

(28)

3 I D E N T I C A L ROOFS

ALL MAXIMA LIT *4

I HEATED, INSULATED, VENTILATED)

SNOW LOAD OBSERVATIONS ON ROOFS

YE AR : 1959 /60

LOCATION : FORT CHURCHILL

(29)

R O O F DESCRIPTION I I DOUGLAS C R E S . ( S H E L T E R E D H E A T E D I N S U L A T E D 1 21 DOUGLAS CRES. S H E L T E R E D BLDG. H E A T E D A T T I C U N H E A T E D C E I L I N G I N S U L A T E D

SNOW LOAD OBSERVATIONS ON ROOFS

Y E A R : 1959/60

LOCATION: TORONTO, 0 NT.

(30)

SNOW LOAD OBSERVATIONS ON ROOFS

Y E A R : 1959 /60 LOCATION: KINGSTON, 60 ONT.

-

ROOF DESCRIPTION 26 EDGEHILL AVE.

,+

i-

4 0 '

-i

SHELTERED ATTIC NOT HEATED BL DG HEATED INSUL ATE0

M~ NEILL HOUSE

EXPOSED INSUL ATED

A T T I C NOT VENT/L ATE0 ATTIC NOT M A T E D BL DG HEATED PARAPET 2 ' 6 "

(31)

R O O F D E S C R I P T I O N 7 2 B I S H O P BLVD ( E X P O S E D , H E I T E D , I N S U L I TED 2") ( E X P O S E D , HEd T E D . I N S U L I T E D 2") ( E X P O S E D , H E A T E D , I N S U L T E D NO7B:EXPOSED 5i C E l L I N G I N S U L A T E D (47 HEATED BL DG 1 F L A T : 10' TO EAVES FAIRHAVENWAY - -( S H E L T E R E D , H E A T E D , I N S U L A T E D / Y E A R : 1959 /60 SNOW LOAD OBSERVATIONS ON ROOFS LOCP;TION: OTTAWA,

ONT.

-

(32)

SNOW LOAD OBSERVATIONS ON ROOFS

YEAR: 1959/60

LOCATION: STE. ANNE

ROOF D E S C R I P T I O N

1

POULTRY BLDG.(WEST WING)

60

EXPOSED, INSUL ATEO, VENTIL ATEO, HEATED

I POULTRY BLDG (EAST WING)

1.9

SECTION A - A

EXPOSED, INSULATED A T T I C VENTILATED ATTIC NOT HEA TED

DECEMBER JANUARY FEBRUARY MARCH APRIL BLOG HEA TED

0 + 5 0 - - - NORMAL 1959/60 DE BELLEVUE, P.Q. u I- 2 - _- - 4 0 - - - L W 1 0 - O f - m I E rn

1

3 z 0 3 0 _i SNOWFALL 89' 124" - - - -

-

FIGURE

I

(33)

ROOF DESCRIPTION 8 4 3 9 BERRl S T 6 0 f E X P O S E D , H E A T E D , NOT INSULATED1 11771 O ' B R I E N BLVD. INSULATED NORMAL 1 9 5 9 / 6 0

SNOW LOAD OBSERVA1-IONS ON ROOFS

Y E A R : 1959/60

(34)

SNOW LOAD OBSERVATIONS ON ROOFS

Y E A R : 1959/60 LOCATION: ARVIDA, P. Q. / - - - 1 ! ! \ \ \ \ ,\,

-

- - /

-

10 6 0 4 0 N +

$

2 0 0 a 0 _I

ALCAN BUDG. No. 6 0

APRIL D I R E C T I O N ROOF DESCRIPTION BLOG. NO. 6 0

-'*-

0 0 . 4 0 Z = 2 5 3

=

SwO

2 0 W P

,x

V) g . 3 A \ \ I - - - I 0 + 5 0 + 32

2

k 0 a B L D G . 62)'

s

,,

DECEMBER

w7E

s

''1

FEBRUARY

,

_I - 7 - 1 1 15. 1 2 0 '

-

JANUARY MARCH ,/WIND I 2 5 3 ' - - _--- - I 0 S u - - NORMAL 1959/60 a . - 2 2 I 1

k

r

-

I

l

3

SECTION A-A

EXPOSED, HEATED. /NSUL ATED

--- u + s - 4 0 LL W Z

z

5

z

5 x V) - - - - - - - -

a

A

-

. " b . , o 14. - 5 *1 - - - -

-

. 9 13. ' 4 9 SNOWFALL - 109"

FIGURE

13 .

BLOG. 3 4 5

(35)

60 ROOF DESCRIPTION 4 0 N.S. TECH. COLLEGE N. S. TECH. COLLEGE A INSUL ATE0 P l R A P E T T O GRADE N. R.C. LAB. ENGINEERING BLDG.

SNOW LOAD OBSERVATIONS O N ROOFS

Y E A R : 1959 /60

LOCATION : HALIFAX, N . S .

(36)

SNOW LOAD O B S E R V A T I O N S ON R O O F S YEAR : 1959/60 LOCATION : GANDER, R O O F D E S C R I P T I O N NFLD. I\ 1 \\, 60 2 9 HAWKER CRES. 1

I SHEL TERED HEATED INSUL A T E D I

MECH. E Q U I P ROOM

9 2 '

H.12'

150'

4

-I NOT SHELTERED EXCEPT FROM EAST NOT HEATED INSULATED I

t 5 0 - a z 0 NORMAL 1959/60 2 9 HAWKER 2 : I - 4 0 g Id ' 0 - CRES. - - -

-

- SNOWFALL 119 " 128 " I E - - - - - / - FIGURE

15

(37)

FLAT ROOF

INSULATED NO PARAPET

EXPOSED, HEATED, /NSUL A TED

SNOW LOAD OBSERVATIONS ON ROOFS

Y E A R : 1959 /60

LOCATION: GOOSE BAY, LAB.

(38)

SNOW LOAD OBSERVATIONS ON ROOFS

YEAR: 1959 /60

LOCATION: RCAF LANCASTER

6 0 ALTA. ROOF DESCRIPTION H ~ 2 6 ' M.E. GARAGE 421' CANT. HANGAR --- NORMAL 1959/60 Y _- SNOWFALL 51.0" 29.5' - 4 0 L L W

=:I

a m 3 2 0 3 I v , - - 10-

1

-

FIGURE

17

0 -

(39)

U.S. DEPOT ARCH. HANGAR M.E. GARAGE --- CANT. HANGAR SNOWFALL -

SNOW LOAD OBSERVATIONS ON ROOFS

Y E A R : 1959/60

LOCATION: R.C.A.F: COLD LAKE A LTA

.

(40)

ARCH. HANGAR U.S. DEPOT M. E. G A R A G ARCH. HANGAR M.E. GARAGE CANT. H A N G A R NORMAL 1959/60

SNOW LOAD OBSERVATIONS ON ROOFS

Y E A R : 1959 /60

LOCATION :R.C.A.F WINNIPEG, MAN.

(41)

ROOF DESCRIPTION U.S. DEPOT ARCH. HANGAR M E. GARAGE NORMAL 1959/60

FIGURE 2 0

SNOW LOAD OBSERVATIONS ON ROOFS

YEAR : 1959 /60

LOCATION :R.C.A.F NORTH BAY ONT.

-

(42)

ROOF DESCRlPTlON

U.S. DEPOT

M.E. GARAGE

NORMAL 1959/60

SNOW LOAD OBSERVATIONS ON ROOFS

Y E A R : 1959 /60

LOCATION: R.C.A.F. GOOSE BAT LAB.

(43)

LOAD IN LB/FT~ I EDMONTON SASKATOON WINNIPEG TORONTO KINGSTON OTTAWA STE. ANNE r m C, DE BELLEVUE m z 0 MONTREAL STE. ANNE

I

15

DE BELLEVU ri;. ", _.E_ROOF HALIFAX ---A GANDER GOOSE BAY

(44)

Fig.

23 Ottawa, Ont. 1 March 1960. Typical Example of

the concentrations which occur on split-level

-

gable roofs.

Fig.

24

Halifax, N.S.

4 February 1960. The locations and

magnitudes of concentrations are frequently

influenced by large chimneys.

(45)

Fig.

25 Halifax,

N.S.

4 February 1960. Unsheltered

pitched roofs accumulated large unbalanced loads.

Pig. 26 Halifax,

N.S.

4 February 1960. Sheltered

(46)

Fig.

27 Ottawa, Ont. 1 March 1960. Canopies l o c a t e d n o t

t o o f a r below t h e main roof w i l l accumulate

c o n c e n t r a t i o n s equal i n depth t o t h e d i f f e r e n c e i n l e v e l s .

Fig. 28 Lethbridge, Alta. 26 A p r i l 1960. The depth of

c o n c e n t r a t i o n s

i s

very much i n f l u e n c e d by t h e s i z e of t h e main roof.