Snow load observations at B stations 1958-59

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Snow load observations at B stations 1958-59 Peter, B. G. W.; Thorburn, H. J.

NATIOXAI, RESEARCH COmTCIL CANADA

DIVISIOIV OF BUILDING RESEARCH

SNOW LOAD OBSEEVATIONS AT B S!i?ATIONS

1958-59

by B.G.V. P e t e r and

H.J.

!I!horburn ANALYZED I n t e r n a l R e p o r t No. 189 o f the Division o f B u i l d i n g R e s e a r c h OTTAWA December 1959

PREFACE

This r e p o r t h a s been s p e c i a l l y prepared f o r t h e information of a l l those who a r e k i n d l y a s s i s t i n g t h e Division of Building Research of t h e National Research

Council with i t s country-wide survey of snom l o a d s on r o o f s by t a k i n g observations a t what a r e c a l l e d ( f o r convenience) t h e B S t a t i o n s .

Although t h e v a l u a b l e information s o obtained i s i n c o r p o r a t e d i n t o t h e Annual Reports on t h e survey a s a whole (DBR Reports 163 and 1 8 4 ) , i t was thought t h a t t h e

o b s e n r e r s a t t h e B S t a t i o n s might each l i k e t o s e e how h i s o m work f i t t e d i n w i t h t h a t of h i s f e l l o w observers.

IChis r e p o r t h a s t h e r e f o r e been prepared w i t h i n t h e Building S t r u c t u r e s S e c t i o n of DBR

(W.R.

Schrievor, Head) under t h e g e n e r a l guidance of H.J. Thorburn, t h e compilation being c a r r i e d o u t by B.W.G. P e t e r , an undergraduate i n

c i v i l engineering from t h e Nova S c o t i a Technical College who s p e n t t h e summer of 1959 working w i t h t h e Division.

With each copy going t o t h e B-Station o b s e r v e r s goes a l s o t h e thanks of t h e Division f o r t h e i r ready a s s i s t a n c e and a n assurance t h a t t h e i r e f f o r t s , s o o f t e n c a r r i e d o u t i n inclement weather, a r e c o n t r i b u t i n g most u s e f u l l y t o t h e n a t i o n a l fund of knowledge of r e a l snow l o a d s on b u i l d i n g s , informatioil t h a t w i l l e v e n t u a l l y be r e f l e c t e d i n improved snow l o a d requirements i n t h e National B u i l d i n g Code of Canada.

Ottawa

December 1959

R. P. Legget D i r e c t o r

STTOB LOAD 0BSERVli.TIOPSS AT B STAITIOPSS, 1958-59

---

.---

----

B.G.W. P e t e r and B . J . Thorburn During t h e 1958-59 w i n t e r , o b s e r v e r s t a k i n g p a r t i n 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 l s s u r v e y o f a c t u a l snow l o a d s on r o o f s completed t h e second w i n t e r o f f~711 s u r v e y o b s e r v a t i o n s . !These o b s e r v e r s , Borne 50 a c r o s s Canada, measured tile d e p t h o f snow or1 many d i f f e r e n t r o o f s a n d on t h e ground s u r r o u n d i n g t h e s e r o o f s . Soine a l s o measured t h e d e n s i t y of t h e snow.

Depending on t h e t y p e s o f rneas~lrernents made a n d t h e t y p e o f r o o f s o b s e r v e d t h e s e o b s e r v a t i o n s t a t i o n s were

d i v i d e d i n t o t h r e e g r o u p s . Those a - t which d e p t h and d e n s i w on r e s i d e n t i a l s i z e r o o f s a r e measured a r e c a l l e d A S t a t i o n s , t h o s e whore o n l y d e p t h was measured on r e s i d e r ~ t i a l s i z e r o o f s a r e c a l l e d B S - t a t i o n s , a n d t h o s e at; which d e p t h and d e n s i t y on v e r y l a r g e r o o f s l o c a t e d a - t RCAP b a s e s a r e c a l l e d C S t a t i o n s . A f t e r e a c h w i n t e r t h e o b s e r v a t i o n s a r e summarized i.n an a n n u a l p r o g r e s s r e p o r t which p r e s e n t s i n g r a p i i i c a l , t a b u - l a r , a n d p i c t o r i a l form t h e r e s u l t s of t h e o b s e r v a t i o n s a n d d i s c u s s e s i n d e t a i l any t r e n d s and u n u s u a l f e a t u r e s . To deterrtline t h e l o a d s a c c u r a t e l y i t i s n e c e s s a r y t o know b o t h t h e d e p t h a n d d e n s i t y o f t h e snow a n d , i n g e n e r a l , h a v e a d e t a i l e d a c c o u n t o f t h e snow l o a d c o n d i t i n t i s . F o r t h i s r e a s o n t h e a n n u a l r e p o r t d e a l s p r i m a r i l y w i t h t h e o b s e r v a t i o n s made a t A a n d C S t a t i o n s and g i v e s summary t r e a t m e n t o n l y

t o B - S t a t i o n o b s e r v a t i o n s . !The i m p o r t a n c e o f t h e B - S t a t i o n o b s e r v a t i o n s l i e s , hovfever, m a i n l y i n t h o f a c t t h a t t h e y a r e u s e d p r i m a r i l y t o p r o v i d e 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- a n d C - S t a t i o n o b s e r v a t i o n s , a f e a t u r e t h a t w i l l have g r e a t e r i m p o r t a n c e i n t h e o v e r - a l l a n a l y s i s o f t h e complete s u r v e y . B - S t a t i o n o b s e r v a t i o n s a l s o s u p p l y i n f o n n a t i o n on t h e slow l o a d s i n t h e a r e a s beixieen t h e A a n d C S t a t i o n s which a r e l i m i t e d i n number. I n a d d i t i o n t o t h e a b o v e , t h e snow l o a d r e p o r t s r e c e i v e d f r o n B - S t a t i o n o b s e r v e r s o f t e n c o n t a i n p e r t i n e n t a n d u s e f u l comments on slow l o a d s which, a l t h o u g h t h e y do n o t a p p e a r d i r e c t l y i n t h e a n n u a l p r o g r e s s r e p o r t , f o n u p a r t o f t h e body o f i n f o r n l a t i o n t h a t i s b e i n g c o l l e c t e d .

Although c o n s i d e r a b l e u s e i s made of B - S t a t i o n

o b s e r v a t i o n s i n t h e s e a n n u a l p r o g r e s s r e p o r t s , it i s t h o u g h t t h a t -Lhcy deserve g r e a t e r and w i d e r c i r c u l a t i o n . It i s

t h e r e f o r e t h e purpose o f %he p r e s e n t r e p o r t t o g i v e a d e t a i l e d account of t h e o b s e r v a t i o n s made a t B S t a t i o n s

d u r i r q t h e 1958-59 w i n t e r . I t d e s c r i b e s b r i e f l y t h e r e s u l t s o b t a i n e d a t each s t a t i o n , sometimes quoting t h e o b s e r v e r , and concludes w i t h a s h o r t d i s c u s s i o n of t h e r e s u l t s . The r e s u l t s a r e a l s o s u ~ m a r i z e d i n Table I ; t h e l o c a t i o n s of t h e s t a t - i o n s a r e shown

i n

Pig. 1. RESULTS General Note

-

In

d e t e r m i n i n g t h e l o a d s observed a t B S t a t i o n s it was n e c e s s a r y t o e s t i m a t e t h e d e n s i t y of t h e snow. I n t h e past, i n c l u d i n g t h e N a t i o n a l B u i l d i n g Code (1953) ( N B C ) , a d e n s i t y of 0.2 grn/cc was assumed r e g a r d l e s s of t h e a g e of t h e siiow. Snow d e n s i t y . however. does n o t remain c o n s t a n t

_{- .}

t h r o u g h o u t t h e w i n t e r . A graph of d e n s i t y v o r s u s t i m e ,

which was p l o t t e d f o r t h e snow on t h e r o o f s of a l l A S t a t i o n s , i n d i c a t e d t h a t t h e mean d e n s i t y i n c r e a s e d from 0.15 g / c c

on 1 December t o 0.35 gm/cc on 31 I.!arcl?. The s c a t - t e r of t h e p o i n t s was 0.05 gm/cc. On t h e b a s i s of t h i s p l o t t h e f o l l o w i n g d e n s i t i e s were used f o r d e t e r m i n i n g B-S-tation l o a d s . From To Density (gm/cc) 1 December 1 5 J a n u a r y 0.20 1 6 January

1 5

February 0.25 1 6 February 31 TbTz.rcli 0.30 K i t i m a t , B.C. O b s e r v a t i o n s by M r . R.K. J e n s e n Loads (ab/sq f t )

Ground Roof Roof

Roof NBC Max Avg L1ax Avg Max D r i f t

F l a t 60 75 40

-

The maximum l o a d s o c c u r r e d i n January. The mean t e m p e r a t u r e s f o r J a n u a r y were b e l o n noimal and 12.6 i n . of p r e c i p i t a t i o n o c c u r r e d . It i s i n t e r e s t i n g t o n o t e t h a t t h e ground l o a d exceeded t h e NBC d e s i g n ~ 1 1 0 1 ~ l o a d , t h e

accumulation b e i n g 72 i n . of d r y snow. D r i f t i n g o c c u r r e d on t h e roof and it can be s a f e l y assumed t h a t t h e l a r g e d i f f e r e n c e between roof and ground l o a d s i s due p r i m a r i l y t o wind and perhaps h c a t l o s s e s .

V i c t o r i a , B.C. O b s e r v a t i o n s by M r . Alex J. James Loads ( l b / s q f t )

Ground Roof Roof

Roof NBC Max Avg Max Avg Max D r i f t

F l a t 30 4

3

5

L i g h t s n o w f a l l s and w a r m w e a t h e r d i d n o t a l l o w snow t o accumulate o v e r t h e w i n t e r . Measurements were t a k e n on a s i x - s t o r y f l a t r o o f b u i l d i n g which i s exposed b u t has a penthouse and p a r a p e t w a l l . D r i f t i n g o c c u r r e d o n t h o r o o f b u t none o f t h e drifts were v e r y deep.

Dawson Creek, B.C. O b s e r v a t i o n s by M r . Harry G i l e s Loads ( l b / s q f t )

Ground Roof Roof

Roof NBC

Max

Avg Max Avg Max D r i f t

F l a t 40 25 20 20

O b s e r v a t i o n s were made on a f l a t r o o f which h a s a b o u t a 5 O s l o p e . The b u i l d i n g was n o t h e a t e d o r s h e l t e r e d

by t r e e s and b u i l d i n g s . The maximum l o a d o c c u r r e d a f t e r a l o n g p e r i o d o f a c c u m u l a t i o n and very l i t t l e d r i f t i n g t o o k p l a c e even though t h e snow was l i g h t and d r y .

Kamloops, B.C. O b s e r v a t i o n s by M r . O.D.E. R o b e r t s

-

Loads ( l b / s q f t )

Ground Roof Roof

Roof KBC Max Avg Max Avg Max R r i f t

F l a t 40 5 4 5

-

Gable 40 5 5 8

There w a s v e r y l i t t l e s n o w f a l l o v e r t h e w i n t e r .

A t no t i m e d u r i n g t h e w i n t e r was t h e r e more t h a n

5

i n . o f snow

i n

any exposed area. !he g a b l e r o o f

i s

l o c a t e d a t B a r r i e r e which i s 40 m i l e s n o r t h o f Kamloops. When t h e

o b s e r v a t i o n w a s made b o t h f l a t and p i t c h e d r o o f s had t h e same amount o f snow a n d t h e r e was v e r y l i t t l e d r i f t i n g . P e n t i c t o n , B.C. O b s e r v a t i o n s by M r . George E. Corbin

Loads ( l b / s q f t )

Ground Roof Roof

Roof NBC

Max

Avg Max Avg Max Drift

The snow i n this a r e a

was

v e r y wet and n e v e r l a s t e d f o r more t h a n a few days. Tho r e s u l t of t h i s w a s t h a t

d r i f t i n g d i d n o t occur and both t h e r o o f and ground d e p t h s were t h e same.

T r a i l , - B.C. Observations by M r . !P.

N.

S t r e t t o n

Loads ( l b / s q f t )

Ground Roof Roof

Roof NBC Max Avg BlaxAvg M a x D r i f t

F l a t 70

-

25

33

Severe d r i f t i n g d i d n o t occur. The t o t a l f r e s h s n o w f a l l f o r t h e p a s t w i n t e r was 98.5 i n . w i t h t h e maximum s n o w f a l l o c c u r r i n g i n January.

! b e h e a v i e s t s n o w f a l l e v e r r e c o r d e d i n T r a i l w a s i n 1951 when t h e t o t a l s n o w f a l l amounted t o 141.6 i n .

During that w i n t e r snow had accumulated i n drifts u p t o 5 and 7 f t ( 6 O t o 90 l b / s q f t ) and it had t o be removed from t h e r o o f s .

Nelson, B.C. Observations by M r .

D.

E. Smuin Loads (lb/sq f t )

Ground Roof Roof

Roof NBC Max Avg

Max

Avg Max Drift

Gable 40 37 22 25

Snow d i s t r i b u t i o n on t h e r o o f s was v e r y uniform. !this was i n d i c a t e d v e r y c l e a r l y by photographs t h a t showed t h e roof covered e n t i r e l y by an even b l a n k e t of snow. Snow depth was g r e a t l y i n f l u e n c e d by i n s u l a t i o n . No o t h e r r o o f s a t t h e same e l e v a t i o n had l a r g e r snow l o a d s .

U m b e r l e g , B.C. Observations by hk. K e i t h C o l l i e r Loads (lb/sq f t )

Ground Roof Roof

Roof

NBC

Max _{Avg MaxAvg M a x D r i f t}

F l a t Not 20 19

-

Sloped S p e c i f i e d 1 5

-

Sloped 40

-

m r e e r o o f s were observed: (1) F l a t garage r o o f , s l o p e d 5' a t t h e s i d e of a n o f f i c e b u i l d i n g which w a s a 6 o u t 13 f t h i g h e r . !&is roof had p a r a p e t w a l l s of d i f f e r e n t h e i g h t s ,

( 2 ) 45' gable r o o f .

( 3 ) Sloped porch, i n t h e l e e of a two-story house. Snow accunlulerted an t h e r o o f s over a long p e r i o d . The depth on t h e f l a t r o o f w a s even b u t s l i g h t l y l e s s t h a n a t t h e p a r a p e t s and on t h e ground. M r . C o l l i e r thought t h i s w a s because of h e a t l o s s through t h e r o o f . On t h e g a b l e r o o f s heavy i c i c l e formation occurred a t t h e eaves because of c o n t i n u a l thawing and f r e e z i n g of t h e snow. '1210 l e a n - t o roof accumulated t h e most snow (30 i n . ) because i t i s s h e l t e r e d by t h e b u i l d i n g and was n o t a f f e c t e d by h e a t l o s s o r s o l a r r a d i a t i o n a s i t i s on a n o r t h e r n exposure. Calgary,Al.ta.Observations by M r . L. S. Walker

Loads ( l b / s q f t )

Ground Roof Roof

Roof NBC Max Avg MaxAvg M a x D r i f t F l a t 25

-

Others

-

Powdery snow and h i g h winds r e s u l t e d i n t h e r o o f s being swept b a r e . A f l a t roof w i t h 4 f t - 6 i n . p a r a p e t

w a l l s and a 1 2 - f t penthouse was observed weekly. Neverthe- l e s s even w i t h t h e s e l a r g e o b s t r u c t i o n s snow n e v e r accumu- l a t e d i n drifts t o g r e a t e r depths t h a n 1 2 i n . Lower s h e l t e r e d r o o f s were a l s o observed b u t t h e s e d i d n o t accumulate much snow e i t h e r . A newspaper c l i p p i n g from "The ~ l b e r t a n " contained a photograph t a k e n a f t e r a heavy snowstorm on 21 A p r i l 1932. D r i f t s up t o 15 f t occurred on t h e ground b u t p i t c h e d r o o f s i n t h e photographs were completely f r e e of snow. M r . Walker thought t h a t t h e e f f e c t s of h e a t l o s s on snow accumulation were c o n s i d e r a b l e f o r t h e observed r o o f and a l s o t h a t maximum snow l o a d s were l i k e l y t o occur i n t h e e a r l y o r l a t t e r p a r t of t h e w i n t e r when t h e snow i s n o t s o powdery and wind speeds a r e l e s s t h a n i n mid-winter. Lethbridge,A.lta .Observation.s by M r . _{R. Peacock}

Loads (lb/sq f t )

Ground Roof Roof

Rpof NBC Max Avg Max Avg Max D r i f t

F l a t 25 13 9

-

F l a t ( u p p e r ) 25 1 3 7

-

( l o w e r ) 25 1 3 1 4 75

The two observed r o o f s a r e :

(1) F l a t roof w i t h p a r a p e t s on t h r e e s i d e s and a 1 0 - f t v e r t i c a l p r o j e c t i o n of a h i g h e r b u i l d i n g on t h e f o u r t h s i d e .

( 2 ) A s p l i t - l e v e l f l a t r o o f (5' s l o p e ) w i t h no p a r a p e t s .

Snow accumulation r e s u l t e d from a s i n g l e s n o w f a l l and d r i f t i n g d i d n o t g e n e r a l l y occur. On t h e lower l e v e l l o a d s were l a r g e r t h a n on t h e upper l e v e l , w i t h a d r i f t 6 f t deep o c c u r r i n g on t h e lower l e v e l .

Medicine Hat ,Alta. O b s e l v a t i o n s by M r . R. A. P e a r c e

P d r . G.

N.

N u t t a l l who had made o b s e r v a t i o n s f o r t h e p r e v i o u s y e a r s l e f t t h e c i t y l a s t w i n t e r and s o r e c o r d s were n o t k e p t . However, M r . R. A. P e a r c e w i l l be making f u t u r e o b s e r v a t i o n s and h e r e p o r t e d t h a t t h e t o t a l s n o w f a l l f o r l a s t w i n t e r vras 50.7 i n . w i t h November h a v i n g t h e l a r g e s t monthly s n o w f a l l of 22.7 i n .

Yorkton,Sask. 0bservation.s by M r . B. W e Harper Loads ( l b / s q f t )

Ground Roof Roof

Roof RBC

Max

Avg Max Avg Max Drift

P l a t 35

Snowfall w a s below normal f o r t h e l a s t w i n t e r . 'The a v e r a g e r o o f depth w a s o n l y h a l f of t h e ground d e p t h and

drifts ( l a r g e r t h a n t h e ground d e p t h ) o o c u r r e d a t t h e e a s t p a r a p e t . Thus t h e d r y snow was blomn from t h e r o o f by t h e wind and accumulated a t t h e 2 - f t p a r a p e t w a l l .

P l i n Pion, -Man. O b s e r v a t i o n s by M r . D. Wright Loads ( l b / s q f t )

Ground Roof Roof

Roof NBC Max Avg MaxAvg M a x D r i f t

F l a t 40

-

20

-

A s u b s t a n t i a l amount of snow f e l l d u r i n g t h e l a s t w i n t e r . U n f o r t u n a t e l y , however, a c t u a l measurements were n o t made, and s o e s t i m a t e s had t o be used. M r . Wright

thought t h a t prolonged heavy wind s t o r m s a r e n o t common

i n F l i n Plon and d r i f t i n g i s t h e r e f o r e n o t a s e r i o u s problem t h e r e . Brandon, Man. O b s e r v a t i o n s by M r . P. R. P e r k i n s T k r . F.R. P e r k i n s h a s o n l y r e c e n t l y been a p p o i n t e d B u i l d i n g I n s p e c t o r f o r t h e C i t y o f Brandon and l e a r n e d a b o u t t h e survey t o o l a t e t o p a r t i c i p a t e i n l a s t w i n t e r ' s o b s e r v a ti oris.

Kenora, Ont. O b s e r v a t i o n s by Mr.

Loads ( l b / s q f t )

Ground Roof Hoof

Roof NBC Max Avg Viax Avg Ylx D r i f t

P l a t 40 35 1 4

-

bIeasurements were made a t t h e c e n t r e o f a f l a t r o o f . The d i s t r i b u t i o n of snow was uniform and d r i f t i n g o c c u r r e d o n l y a l o n g t h e open l a k e s h o r e .

P o r t P r a n c e s , Ont. O b s e r v a t i o n s by M r . R. Readman Loads ( l b / s q f t )

Ground Roof Roof

Roof NBC Max Avg Max Avg Max D r i f t

F l a t 45 F l a t II

Lean-to I t

n a t ( u n h e a t e d )

-

The w i n t e r w a s one o f t h e c o l d e s t on r e c o r d . M r . Readman mado a n e x t e n s i v e survey of t h e main s e c t i o n of t h e town. Snow a o c u ~ n u l a t i o n was o v e r a l o n g p e r i o d and l i t t l e d r i f t i n g was observed. Roofs w i t h no i n s u l a t i o n were b a r e e x c e p t a t t h e e a v e s where l a r g e i c i c l e s o c c u r r e d i n d i c a t i n g h e a t i n g l o s s . The maximum a v e r a g e l o a d of 20 l b / s q f t

i n d i c a t e d by a p h o t o b ~ a p h o c c u r r e d on a n unheated s h e l t e r e d

h u t . The o t h e r f l a t r o o f s t h a t were measured were h e a t e d b u t i n s u l a t e d .

During t h e pas-t w i n t e r s n o w f a l l was e x c e p t i o n a l l y lorn f o r Niarch. L a r g e r snow l o a d s may be e x p e c t e d i n f u t u r e w i n t e r s a s s n o w f a l l s f o r t h i s month a r e u s u a l l y t h e h e a v i e s t .

P o r t W i l l i a m , Ont. O b s e r v a t i o n s by I&. D. Thompson Loads ( l b / s q f t )

Ground Roof Roof

NBC Max Avg Max Avg Max D r i f t

The r o o f l o a d w a s always c o n s i d e r a b l y l e s s t h a n t h e ground l o a d . !this a p p e a r s t o be due t o h e a t i n g l o s s and m i l d weather.

Wawa,Ont. O b s e r v a t i o n s by M r . C a l v i n MacDonald Loads (lb/sq f t )

Ground Roof Roof

Roof NBC Max Avg Max Avg Max D r i f t

Gable 40 65 40 40

Gable 40 65 20 36

BJO g a b l e r o o f s w i t h t h e same s l o p e were observed.

IChe f i r s t roof w a s s h e l t e r e d and t h e snow accumulation was even, whereas t h e o t h e r r o o f w a s exposed t o s t r o n g winds which r e s u l t e d i n a l i g h t e r l o a d b u t heavy d r i f t i n . g . !-This

was t h e o n l y B S t a t i o n t o r e p o r t o f a snow l o a d e q u a l t o t h e NBC r e q u i r e m e n t s . -

-

S a r n i a , On*. (1) O b s e r v a t i o n s by &Ire H e D. Cook

Loads ( l b / s q f t )

Ground Roof Roof

Roof NBC Max Avg Max Avg I h x D r i f t

F l a t 30 7 7

7

The f l a t r o o f observed was s h e l t e r e d on two s i d e s

by h i g h e r b u i l d i n g s . No d r i f t i n g was observed.

( 2 ) O b s e r v a t i o n s by Polymer Corp. Ltd. Loads ( l b / s q f t )

Ground Roof Roof

Roof NBC Max Avg Max Avg Max D r i f t

F l a t 30 8 6 1 0

P l a t '50 1 0 8

-

-

27

O t h e r s 6

-

Both observed r o o f s had p a r a p e t s and v e n t i l a t o r s . Snow l o a d s were from a s i n g l e s n o w f a l l and g e n e r a l l y l i t t l e d r i f t i n g o c c u r r e d . A snow storm i n March, however, caused c o n s i d e r a b l e d r i f t i n g a l o n g p r o j e c t i o n s . A l a r g e d r i f t a p p r o x i m a t e l y 30 by 1 5 f t and 1 3 i n . deep (20 lb/sq f t ) o c c u r r e d behind a v e n t i l a t o r ( 6 by 4 f t by 1 2 i n . ) w h i l e o t h e r s e c t i o n s o f t h e c e n t r a l p a r t o f t h e r o o f were b a r e . The a v e r a g e r o o f l o a d when t h i s o c c u r r e d w a s 6 lb/sq f t . London, 0n't. O b s e r v a t i o n s by M r . J. C. Dodd Loads ( l b / s q f t )

Ground Roof Roof

During t h e w i n t e r t h e r e w a s never enough snowfall t o begin B-2 o r B-3 o b s e r v a t i o n s .

O r i l l i a , Ont .Obse.rvations by N r . A. L. P a r r y Loads (lb/sq f t )

Ground Roof Roof

Roof WBC Max Avg Max Avg Max Drift

F l a t 70 40 22 22

IChe maximum roof l o a d occurred i n December a f t e r a three-day snowfall. Winds were v e r y l i g h t and s o t h e r e was no d r i f t i n g .

Pembroke,

Orrt.

Observations by htr. R. C. Cheyne Loads (lb/sq f t )

Ground Roof Roof

Roof NBC Max Avg Max Avg Max D r i f t

Gable

-

-

₃₀

-

P l a t

-

-

-

₇₅

It was n o t p o s s i b l e t o keep r e c o r d s f o r t h e p a s t w i n t e r . However, two p a r t i c u l a r c o n d i t i o n s were r e p o r t e d :

(1) A n unheated p i t c h e d roof had a uniform l o a d of 2 f t of snow on one s l o p e .

( 2 ) A t r i a n g u l a r accumulati.on w i t h a maximum depth of 6 f t occurred a t a 1 0 - f t p r o j e c t i o n on a f l a t a r e n a r o o f ,

Osliawa

,

Ont. Observations by M r . Grahame P i s h Loads (lb/sq f t )

Ground Roof Roof

Roof NBC Max Avg Max Avg Max D r i f t

P l a t 35 14 1 0 1 0

Gable 25 1 4 12 12

The house observed h a s a p i t c h e d roof (30°) and a lower f l a t r o o f . No d r i f t i n g occurred on e i t h e r roof and both r o o f s had about t h e same l o a d .

P e t e r b o r o u g h , kt. O b s e r v a t i o n s by M r . R.E. W h i t e h i l l Loads ( l b / s q f t )

Ground Roof Roof

Roof

NBC

Max Avg Max Avg Max Drift

Gable 40 50 3 3 47

The g a b l e r o o f (37O s l o p e ) c o v e r s a n u n h e a t e d g a r a g e

w i t h one o f t h e g a b l e e n d s b u i l t a g a i n s t a h i g h e r h o u s e ; t h u s p a r t o f t h e r o o f i s s l ~ e l t e r e d . Drifts o c c u r r e d a t t h e peak o f t h e r o o f a n d i n t h e b e g i n n i n g o f March snow h a d t o b e removed from t h e r o o f . However, it i s improbable

t h a t t h e r o o f l o a d would h a v e i n c r e a s e d a f t e r t h a t d a t e s i n c e t h e d e p t h o f snow on t h e ground w a s a maximum a t t h a t d a t e .

B e l l e v i l l e , Ont. (1) O b s e r v a t i o n s by M r . G r a n t S t i c k l e Loads ( l b / s q f t )

Ground Roof Roof

Roof NBC Max Avg MaxAvg M a x D r i f t

F l a t 50 1 3 4

-

The f l a t r o o f o f t h e c i t y h a l l a c c u m u l a t e d v e r y l i t t l e snow. Drifts o c c u r r e d a t t h e e d g e s o f t h e r o o f a n d a l s o o n e i t h e r s i d e o f t h e l a r g e b r i c k t o w e r which p r o j e c t s from t h e r o o f . T h i s r o o f d i d n o t h a v e p a r a p e t s . M r . S t i c k l e i n c l u d e d p h o t o g r a p h s o f a v e r a n d a on a wood-frame house which f a i l e d f r o n sn.ow l o a d .

( 2 ) O b s e r v a t i o n s by N o r t h e r n E l e c t r i c Co. Ltd. Loads ( l b / s q f t )

Ground Roof Roof

Roof I W C Max Avg Max Avg Max D r i f t

P l a t 50 3 3 8 60

O b s e r v a t i o n s were made o n a l a r g e (3301 x 4321) f l a t r o o f on which t h e r e were s i x l o n g m o n i t o r s . L i t t l e snow accumula'ted on and between t h e m o n i t o r s w h i l e d r i f t s u p t o 48 i n . o c c u r r e d a l o n g t h e edge o f t h e r o o f a t one end o f t h e m o n i t o r s .

Lachine, P.Q. O b s e r v a t i o n s by Northern E l e c t r i c Co. Ltd. Loads ( l b / s q f t )

Ground Roof Roof

Roof NBC Max Avg Max Avg Max D r i f t

P l a t 50 22 1 2 45

T h i s i s a l a r g e f l a t r o o f (423 by 232 f t ) w i t h v e r t i c a l w a l l s on two s i d e s . !I!he snow on t h e r o o f w a s

g e n e r a l l y even w i t h o c c a s i o n a l d r i f t s p a r t i c u l a r l y a g a i n s t t h e v e r t i c a l w a l l s .

Montreal, P.Q. O b s e r v a t i o n s by N o r t h e r n E l e c t r i c Co. Ltd. Loads ( l b / s q f t )

Ground Roof Roof

Roof

N.B

C Max Avg Max Avg Max D r i f t

F l a t 50 23 3 50

The f l a t r o o f observed w a s on a v e r y h i g h b u i l d i n g (129 f t ) a n d s o i t w a s exposed t o s t r o n g winds, The c e n t r e a r e a s were swept b a r e w h i l e d r i f t s 3 f t deep a n d 20 f t

wide o c c u r r e d a l o n g t h e p a r a p e t s . Accumulation was o v e r a

l o n g p e r i o d .

F r o i s R i v i e r e s , P. Q. O b s e r v a t i o n s by M r . W a l t e r Baucher Loads ( l b / s q f t )

Ground Roof Roof

Roof NBC Max Avg Max Avg Max D r i f t

F l a t 60 7 0 23

8 5

Gable 60 70 2 3 40

Snow accumulated f o r t h e e n t i r e w i n t e r a n d heavy d r i f t i n g o c c u r r e d on t h e f l a t r o o f even though t h e r e were no o b s t r u c t i o n s such a s p a r a p e t w a l l s , The b u i l d i n g s were h e a t e d a n d i n s u l a t e d .

a e d e r i c t o n , N.B. O b s e r v a t i o n s by M r . R e H. Colwell Loads ( l b / s q f t )

Ground Roof Roof

Roof mBC Max Avg Max Avg Max Drift

Gable 65 24 20

-

F l a t 65 22 1 3 20

O t h e r s 65

-

1 0

-

The g a b l e r o o f w a s observed weekly. I t was n o t

h e a t e d . The dis-ti-ibution was g e n e r a l l y even and t h e maximum snow l o a d o c c u r r e d a f t e r a s i n g l e s n o w f a l l .

S a i n t J o h . r ~ , 1T.B. --.- 0bselva.-bions by lulr. \V. J. S i n c l a i r

Loads ( l b / s y f t )

Ground Roof Roof

Roof IJB C 1l"mx _{Avg lJax Avg &'lax D r i f t}

Plz,,t; 50 1 0 1 0 25

Observz-bions w e r e made o n t h e 3- a n d 4 - s t o r y C i t y

H a l l b u i l d i r ! ~ . The h i g h e r r o o f h a s a p e n t h o u s e a n d t h e l o w e r r o o f i s s h e l t e r e d by h i g h e r b u i l . i l i n g s on Imo s i d e s . The

snow was o f t e n w e t a n d h e a v y b e c a u s e o f walm w e a t h e r b u t d r i f t i n g d i d o c c u r sometimes. Snow d e p t h s w e r e a b o u t t h e

same o n t h e h i g h r o o f a s o n t h e low a n d o n o t h e r b u i l d i n g s

i n t h e area.

Moncton, B.B. O b s e r v a t i o n s by Mr. R. A. S t e v e n s Loads ( l b / s q f t )

Ground Roof Roof

Roof NRC l h x Avg Xhx Avg Max D r i f t

Plat- 60 1 4 1 2

-

30

O t h e r s 1 2

-

The maximum l o a d o c c u r r e d from an a c c u m u l a t i o n o v e r

a l o n g period-. D r i f t s o c c u r r e d a t t h e p a r a p e t s w h i l e t h e c e n t r e o f t h e r o o f w a s b a r e . C o n s i d e r a b l e d r i f t i n g was

a l s o r e p o r t e d f o r n o t h e r r o o f s i n t h i s a r e a ,

Amherst, N.S. Obsez-vations by M r . 1fl.G. P l e t t Loads ( l b / s q f t )

Ground Roof Roof

Roof BBC lIi3.x Avg Max Avg Max D r i f t

P l a t 55 11 2 2

No snowstorms o c c u r r e d d u r i n g t h e w i n t e r a n d s o t h e l a r g e s t amount o f snow or1 any r o o f w a s 2 i n . on a f l a t

s h e l t e r e d r o o f .

GmTERAL DISCUSSION

O n t h e w h o l e , t h e r e s u l t s o f t h e o b s e r v a t i o n s made

a t B S t z i t i o n s d u r i n g t h e 1958-59 w i n t e r follow a l o n g t h e same l i n e s a s t h o s e o f t h e A S t a t i o n s , The o b s e r v a t i o n s show t h a t a c o n s i d e r a b l e d i f f e r e n c e e x i s t e d between snow l o a d s on r o o f s a n d snow l o a d s on t h e ground. I n most c a s e s t h e r o o f l o a d 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 g r o u n d l o a d s p a r t i c u l a r l y i n t h o s e l o c a l i t i e s nhol-e t h e l o a d s a c c u m u l a t e d t h r o u g h o u t t h e v r i n t e r . I n t h o s e ctl:;es vi11er.u t h e maxirnur,~

a v e r a g e r o o f arid ground l o a d s were r o u g h l y e q u a l t h e l o a d i n g was u s u a l l y produced by a s i n g l e storm. I n a c c o u n t i n g f o r t h e d i f f e r e n c e s bettveen r o o f and ground l o a d s most o b s e r v e r s c o n s i d e r e d wind a c t i o n and h e a t l o s s t o be t h e a c t i v e

f a c t o r s .

Many B - S t a t i o n o b s e r v e r s a l s o r e p o r t e d d r i f t s a n d c o n c e n t r a t i o n s g r e a t e r t h a n t h e ground depths. On main r o o f a r e a s t h e s e were u s u a l l y produced by p a r a p e t w a l l s and o t h e r o b s t r u c t i o n s . S i m i l a r c o n c e n t r a t i o n s were f r e -

q u e n t l y r e p o r t e d on t h e lower l e v e l of s p l i t - l e v e l r o o f s and l e a n - t o and porch r o o f s . T h e b e s t examples of t h i s

were found a t L e t h b r i d g e , Pembroke, a n d T r o i s R i v i e r e s . It i s n o t p o s s i b l e t o draw any c o n c l u s i o n s from t h e B - S t a t i o n o b s e r v a t i o n s a l o n e , b u t when t h e y a r e .combined

w i t h t h e A- and C - S t a t i o n o b s e r v a t i o n s s e v e r a l p r e l i m i n a r y c o n c l u s i o n s can be drawn:

1. m e a v e r a g e snow l o a d on a r o o f i s g e n e r a l l y l e s s t h a n t h a t on t h e s u r r o u n d i n g ground. 2. The amount by which t h e r o o f and ground l o a d

v a r i e s i s a s y e t u n p r e d i c t a b l e b u t p r i m a r i l y i s determined by t h e s h e l t e r of t h e r o o f . 3 . C o n c e n t r a t i o n s t o g r e a t e r t h a n t h e ground d e p t h a r e t o be e x p e c t e d 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 . The l o c a t i o n s of t h e s e a r e a s a r e g e n e r a l l y p r e d i c t a b l e w h i l e t h e magnitude of t h e l o a d t h e y w i l l accumulate i s n o t a s y e t .

Although t h e s e p o i n t s have become much c l e a r e r a f t e r two y e a r s of f u l l survey obsel-vations t h e y r e q u i r e t h e

o b s e r v a t i o n s of s e v e r a l more w i n t e r s b e f o r e t h e y can be confirmed.

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FIGURE

I

B

-STATION LOCATION

.

1958/59

-

( S E E T A B L E I FOR N U M B E R E D L I S T O F S T A T I O N S )