Snow loads on roofs 1962-63: seventh progress report

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Snow loads on roofs 1962-63: seventh progress report Allen, C. M.; Peter, B. G. W.

DIVISION OF BUILDING RESEARCH

SNOW LOADS ON ROOFS 1962-63

SEVENTH PROGRESS REPORTｾＮ

BY

C.M. ALLEN AND B.G.W. PETER

ANAL

VZED-Internal Report No. 279 of the

Division of Building Research

OTTAWA

PREFACE

The specification of roof snow loads in building codes in Canada is of considerable importance because the heaviest load

that will be imposed on many roofs is the snow load. The prediction

of roof snow load is difficult because, in addition to variations in snowfall, factors such as wind, local shelter, roof shape and heat loss have a great influence on the magnitude and distribution of this load.

Some building designers believe that the design snow load values in the National Building Code of Canada 19"0 are too

conservative and point out that, in practice, these loads are reached

on very few roofs. There are, on the other hand, . many cases of very

heavy snow loads which, in some instances, have resulted in collapse. V!hat is needed, therefore, is a better understanding of snow loads to provide a basis for rational adjustment of design snow loads.

It is the purpose ｯｾ this report, the seventh of a series

of snow load reports, to provide information so that further

refinements of the design roof snow loads can be made'in the National

Building Code of Canada. It also presents the results of the 1962-63

survey in the form of graphs, tables, and photographs and includes a discussion of the various factors affecting roof snow loads and a number of interim conclusions.

The Division of Building Research wishes to express again its appreciation to all those observers whose active participation

made possible the survey of the 1952-53 winter. In particular,

grateful appreciation is recorded to A-station observers of the Meteorological Branch of the Department of Transport at Goose Bay and Gander, the National Parks Branch of the Department of Northern Affairs and National Resources at Glacier, B.C. and P.E.I. National

Park , Ecole Polytechnique Otontreal) ｾ Macdonald College (Ste. Anne de

.Bellevue), Queen's University (Kingston), University of Toronto,

University of Manitoba (WinnipeG), University of Alberta (Edmonton), University of Waterloo, Aluminum Company of Canada at Arvida,

Mr. L.A. Holbrook at Inuvik, and the Atlantic, Prairie. and

B.C. Regional Stations of the Division. Sincere thanks are also

expressed to the Chief of the Air Staff, Air Force Headquarters, Ottawa, and to the RCAF personnel at the C Stations at Comox. Lancaster, Cold Lake, Winnipee, North Bay, Ottawa and Goose Bay, and to the building inspectors and individuals who made B station observations.'Vithout all this willing co-operation this survey could not have been carried out.

This report was prepared by C.M. Allen, of Queen's University, a summer worker with the Building Structures Section, and B.G.W. Peter, research officer with the Section. under the direction of W.R. Schriever.

Ottawa

INTRODUCTION

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SURVEY PROCEDURES OF 1962-63 OBSERVATIONS • • • • • • • • • • • • e 2

A Stations

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RESULTS OF THE 1962-63 OBSERVATIONS

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PRESENTATION OF RESULTS

SUMMARY OF THE RESULTS

B Stations C Stations WEATHER A stations B stations C Stations GENERAL DISCUSSION

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3 3 3 4 5 5 8 9 9 10 Drifts on Canopies

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Large Flat Roofs Wind Sloped Roofs

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10 11 12 12

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Roof to Ground Snow Load Sheltered 'Roofs

INTERIM CONCLUSIONS REFERENCES

Ratios for Exposed and

13

14

15

S1'1O"! LOADS ON ROOFS 1962-63

Seventh Progress Report by

C.M. Allen and B.G.W. Peter

This progress report is a continuation of the

survey of snow loads on roofs which was begun in 1956

by the Division 0:[' Building Research with" the aim of' improving

the design snow loads given in the National Building Code of

Canada (NBC) (1). The 1962-63 survey was carried out on

various types of roofs all across Canada. In most cases the

same roofs were used as in previous years. This report

describes the observations of snow loads for the winter of

1962-63 as well as conditions of maximum wind speed, average

daily temperature and accumulation of snowfall so as to analyze better the various factors that affect snow loads. The report also discusses trends and unusua] features of the

observations, and correlates the results with the interim conclusions of previous reports (2-8).

Snow loads should be of considerable concern to

designers. In many of the More populated areas of Canada,

the basic design snow load is in the ranGe of 40 to 60 psf.

For most ｳｴｲｵ｣ｴｵｲ･ｳｾ therefore, the load due to the weight of

the r oor system and positive wind pressures is. much less than

the design snow load. Thus there is considerable concern as

to the value of the de sLrm snow load to be used. If' it is

too high, there will be needless extra expense and, if it is

too small, the p.robabi Ltt y of structural failure may become

excessive.

The J"ollowing is a summary of the developments

concerning design snow loads that have taken place during the

last 20 years. In the 1941 lJational Building Code. the snow

load 'was determined from

-L

=

S + H

where

S

=

sum of the average snowfa Tl.s in January, Pebz'uary

and ｾ｡ｲ｣ｨ over a numher of years, and

R = sum of the average rainfall, in inches, in Janrnry,

February and Earch (9).

For many cities, including Vancouver, ''linnipeg and Halifax, the

results given ｬｾｾｲ this formula wer e inadequate.

In the 1:;53 ITBC, the minimum design load was ba sed, for

the first tine. on the snow depth on the ｾｲｯｵｮ､Ｎ This value of

depth of snow in the 1941-50 period together with the estimated maximum amount of rainfall that might fall into

the snow cover in 24 hours (10). A specific gravity of 0.2

was used for the snow. The minimum design load applied to

flat roofs and to roofs with slopes up to 20 deg. For roofs

with slopes greater than 20 deg the following formula was used:

=

L [} - 0.0233 (x-20I]

where

L

=

minimum design load for a flat roof, and

x

=

slope of the roof in degrees

Thus, in the 1953 Code, consideration was made for the effect

of roof slope and for the ｾ｡ｴ･ｲ content in the snow but no

consideration 'Nas given for wind, which perhaps is "the most serious factor.

In the 1960 1ffiC allowance was made for conditions

produced by wind (1). The basic ground load was based on the

maximum snow load in a 30-year period. The design roof

snow load was taken as 80 per cent of this basic ground snow load and was reduced for various slopes of roofs starting at

30 deg. In addition, the desiGn roof snow load was increased

by 50 per cent in areas where there would likely be drifts. Even the 1960 Code, however, may be in need of improvement in

certain aspects. RooIs exposed to the wind usually have loads

much lower than the 80 per cent of the ground load used in

the 1960 Code. Thus the reason for further snow load studies

becomes apparent. By accumulating information on the behaviour of snow on roofs in comparison with the snow on the ground, further amendments to the Code are possible so as to produce more reasonable and, at the same time safer design snow loads for roofs.

SURVEY ｐｒｏｃｽｾｄｕｈｅｓ OJ? 1962-63 OBSEHYATIONS

The survcv procedures used at the A, Band C Stations for the 1962-63 winter season were the same as those us ed in

the previous ve a r-s (2, 11, 12). An additional "local" survey ,

(now included in the B stations) was made on a number of roofs in the Ottawa arca(This was done for the first time in the

1961-62 survey). 8ighty-eight roofs were observed.

A Stations

As in other years, detailed observations of snow depth and density on the ground and on roofs were recorded

3

-A Stations, at least one flat roof and one eable roof were

observed. Snow depth and density measurements were taken

in the same manner as in previous years.

The A Stations at Revelstoke and Fort Churchill,

Manitoba were discontinued in the 1962-63 winter. Two

additions to the A Stations were at D.E.I. National Park

and at Glacier. Forty-one roofs were observed at the

seventeen A Ｇｾ｡ｴｩｯｮｳ (Table I).

B Stations

In the past, most observations at the B 'Jtations

were carried out on a ｶｯｬｵｮｴ｡ｾｊ basis by building inspectors.

For the 1962-63 winter season, there were only six reports

sent in from locations outside the Ottawa. area. As in the

previous winter, B-Station observations in the Ottawa area

were made by the staff ｯｦﾷｾｨ･ Ｇｾｲｵ｣ｴｵｲ･ｳ Section of the Division

of Building Research, National Research Council. These

observa"tions were made on 22 roofs, of a var-Lety of shapes

and sizes. Most of the B Stations, including roofs in the

Ottawa area, were observed only once since the observations

on the roofs of "the B ｾｴ｡ｴｩｯｮｳ were to be taken only after a

very heavy snowfall or after an occurrence of structural failure due to snow load.

C Stations

The observations on large roofs at airports were carried out by RCAF personnel in the same manner as at the

A Stations. Observations were taken onca a week and after

every heavy snowfall. Because the roofs being observed were

very large, the standard snow depth gauges were not used. The buildings used were: arch hangars, mechanical equipment

6arages, cantilever hangars and unit supply depots. The roof

shapes of these buildings are shown in Figures 19 to 24

inclusive. rfuerepossible, canopies attached to these buildings

were observed. ｾｶ･ｮｴｹＭｴｷｯ roofs were observed at the eight

C ':;tations. WEATHER

In contrast to the 1961-62 season, normal to

below-normal snowfalls occurred west of Toronto, except at Glacier. East of Toronto, normal to above-normal sncwfalls occurred, except at Ottawa.

In general, the mean te:n pe ra trure s were below normal in Eastern Canada and ab ov e no.rmaL in 'Vestern Canada during

the winter season. January was an exception to this.

Tempera-tures were 5 to 9 deg b e Low normal on the Prairie Prov i.nc e s

Winds were normal throughout most of Canada except

for the Atlantic Provinces. ｊ｡ｮｵ｡ｾｲ and ｆ･｢ｲｵ｡ｾｲ brought very

strong winds to the Atlantic Provinces. PRESENTATION OF RESULTS

As in previous snow load progress reports, results

from A Stations arc given in detail for each roof by means of

graph on whLch the ground load, the minimum, maximum and

average roof load, and in some cases, the maximum canopy load

are plotted against time. There are also glBphs of the

accumulated fresh snowfall" in inches, the maximum daily wind speed with direction of wind, and the mean daily temperature

plotted against time. Plan and elevation views of the roof

are drawn so as to show the size and shape of the roof and the

locations of snow Gauges. These graphs are contained in

Figures 3 to 18 inclusive, and are summarized in Table I, and Figure s 1 and 2.

B-Station results are given in Tables II and IV.

Table II gives the results of the observations made by bUilding

inspectors at B Stations. Table IV gives the results of the

observations made on the roofs in ｴｨｾ Ottawa area.

C-station results are presented in a similar manner

as the A Stations (Pigures 19 to 2 ,"r ) and are aurnrrarized in Table

III and Figure 1. Table V presents the comparison of the roof/

ground load ratio for the large [lat roofs of A and C Stations.

The Graphs showing the snow loads and weather records

for A and C ｾＩｴ｡ｴｩｯｮｳ (Figures 3 to 24), give both the normal

snowfall and the total snowfall within a stated period of the

winter. Values of normal snowfalls were obtained from the

Meteorological Branch of the Department of Transport. (On

previous reports the normal snowfall was taken from 1921 to

1950. j"1any stations did not have the reqUired information

for this period, however, and so the usefulness of reporting

these normal snowr'a l l s be carnc doubtful). The 1941-60 averages

'were used, therefore, as these 20-year averages were available

for most of the" stations. 1ne only exception to this was at

Cold Lake, Alberta, where the ave ra ge sn owf'aL'l from 1953 to

1962 was used as the normal snowfall.

Variations in snow loads in Ottawa due to factors such as roof shape and shelter arc shown in Figures 27 to 32.

In Fi[':ure 25, the ratio of maximum average roof

load (for exposed roofs) to the maxi.mum averaee ,c:round load

is plotted ｡ＬｾＧ｡ｩＺＺＱＮｳｴ the slope of the roo:f. ＱＱＧｩｾｵｲ･ 26 shows

the sane ｲ｣ｬ｡ｴｩｯｾｳｨｩｰ 8S in FiGure 25, but for sheltered roofs

instead

0::

expo s c d roofs. ｾｲｨ｣ Lntormatl on shown in }i'isures

25 and 26 was taken from all proryCSS reports on A Stations

f _rom +,_",1C Joe"7 ,'n t I e ' ' ) ,",.; t ' """ (" ｾ 7 0 d g)

5

-RSi3TJLTij 05 '['HE 1962-63 OBSEl1VATIONS

For all roofs observed, the average roof load was

lower than the 1950 ITJC minimum design snow load for roofs (13). Twelve roofs bad max'i murn snow loads in exccss of the Code values.

Some of these hie-h na xi nu-n roof loads wouLd ba ve be en covered

｢ｾｲ the use of the 1960 Code " sh8pe" factors. Seven roofs or

canopies had maxf.mum loads that exceeded even the values ,'jiven

by the 1960 Code shape factors. These occurred on the ｍＮｾｯ

garage and cantilever hanga r at Lanca st e r , Alberta, on ｴｬｾ･ M. E.

carase and canopy of the supply depot at Goose Bay, Labrador,

on a flat roof in Gander, "Newfoundland, and on a gable roof

and a canopy in Ottawa.

Only Ha Li.tax and Arvida reported roofs with average

roof loads [jreater than the reported [round load. These roofs

were sheltered so that the wind could not blow off the snow.

Thirteen of 25 A and C Stations reported roofs with ｭ｡ｸｩｭｵｾ

roof loads greater than the ground loa d. As Ln other years,

drifts occurred along parapets, at the junction of split level

roofs, at extending walls, and at any other object which would act as a snow fence.

Mast of the B-Station roofs observed in the Ottawa

area were in well-sheltered locations. This resulted in a

very uniform snow load on the roofs whLch was almost equal to

the ground load. In other parts of O-ttawa, there was a great

deal of drif"ting on the roofs. Thus the prediction of snow

loading become s very di.ff'Lcu I t since snow loa ding on roofs

changes even within a city due to the various conditions of

shelter and wind.

The ｦｯｬｬｭｾｩｮｧ presents a marc detailed discussion

of individua1 A Stations.

A Stations

V:.mcouver, B.C. - l''lc:asurcments of snow loads on

-roofs were not taken because the snowfall was very small and did not accumulate on the roofs.

ｾ . 1 'T ,or rn I 1 t' f

l.TIl.1VL(, 1'.• •1.. - n genera ｾ De average r oof sriow

loads were not high. An exposed rable roof had maximum snow

loads greater than the ground snO'7 loads, but the maximum

｡ｶ･ｲ｡ｾ･ roof snow load reported was only j8 per cent of the NBC

desiGn roof ｳｮｾｶ load.

Glacier Park, B.C. - 'i:l18 snowfall was almost 11 per

cent above norr:mi ':lith a total of- a Lnost 4UO in. of' snowJall

reported. rehis is the ｲｩｲｾＳｴ year t:1at ob ae rvatnons have been

made on this fLat roof' . e a r t of' the rooi' ＢＧｖ｡ｾＳ heated, but only

the unhea-'ced section of the roof' nas observed. From sketches

of the snow on the roof it [l.l'pc::ars that there '''!88 ver:r little

evenly distrib1rted on the unheated section of the roof

throughout the winter. The hcat ed section of the roof

accumulated very little snow. The maximum roof snow load

was 75 per cent of the lillC des ib'TI roof snow load.

''linnipep;, LI:::m.• - ';rinnipeg's snowra Ll. was about

normal. The ground load was ver"jr low and, for the most part,

the roof ｬｯ｡､ｾ were less than the ground loads. In March,

however, snowdriftinp; caused a maximum roof load of 10 psf

in comparison with a Ground load of only 3 psf. This roof

load was considerably below the 35 psf roof load specified

by the 1960 Code.

ｋｩｮｾｳｴｯｮＬ Onto - Although the snol\ffall was almost

17 per centiabovc normal, the roof snow loads never exceeded

the NBC value :for the design roof snow load. As in previous

years, the maximum snow Load on the roof of ﾷＬＧﾷｾ｣ｎ･ｩｬｬＮ House

exc ceded the ground snow load, at one point by nearly 180 per

cent. These maximum snow loads were the result of snowdrifting

at the parapets.

ｏｴｾ｣｡ｷ｡Ｌ Ont. - Ottawa's snowfall was about 30 per

cent below normal. As in previous years,all of the roofs,

except for the flat roof of the Division of Building Research, had roof snow loads that were below the Ground load.

The maximum roof snow load on the flat roof of the DER buildinC was ["reater than the ground load throughout most

of' the wtrrt er , A',though the maximum roof load (33 paf )

exceeded the [round load by 180 per cent, it was still below

the 48 psf ape c i.fLe d by the 1960 N:3C. The maximum roof load

occurred at the parapets and was caused by high winds which

were either from the east or west. As soon as the mean daily

temperature reached the vicinity of 32°P, which was in

mid-March, the roof loads, including the maximum roof loads caused by drifts, decreased rapidly.

The well-she1tored roof at Pairhaven ｾＧＡ｡ＭＺｲ had a high

average roof load which was just slightly less than the ground load for most of the winter.

Ste. Anne de 3cllevue. P.Q. - As in the 1961-62

season, the sn cwf'aI l wa s about 10 per cent above normal. Unlike

the previous year, however, the rround load was very much

hieher, r'e achtng a maxi mun value of 55 psi' ( the depth of

snow ｾｾｳ

43

in..). This barely exceeds the

rmc

design ground

snow load of 55 psf.

The averaｾ［｣ roof snow load was very much be10'1"1 the

ground S110rf load, reac'1ing a hiGh of' onLv 9 psr • This was

7

-roof load reached a peak of 44 psf. This occurred on the

cast end on the hip roof

(45

deG slope) of the poultry

bUildinG of Eacdonald College, i'or which the design roof

Gnaw load of the 1960 ｾｭ｣ would be 26 psf.

Montreal, P.Q. - The snowfall was almost 10 per

cent greater than normal and because the mean daily temperature

was below 32°F for most of the winter, the ground load reached

a high of

55

psf. Because of the high wihds, however, which

were mostly in the easterly and westerly directions, the roof loads were comparatively low, the maximum roof load reaching a peak of 21 psf.

p.E I. National Park - The sn owf'aLL was 65 per cent

above normal. The reportpd maxi.raum ground. load near tVIJO of

the three roofs was below the IJTlC design Fround snow Loa d :

ncar the third roof it was 59 per cent above the NBC design

c;round sriow load. This high value appears to have been caused

by the severe snowdrifting around this particular building and should therefore be disreGarded.

One of the roofs had a drift roof load of 56 psf. This was five times larger than the average roof load and

exceeded the design roof snow load by 6 per cent. This high

roof load occurred in the lee of the gable roof whose top

was 6 ft above the flat roof observed. This maximum roof snow

load would have been covered by the NBC under the conditions

of driftinB snow at locations of shelter.

Tne exposed gable roof and the other flat roof had

very low average and maximum roof loads.

Halifax z N.S. - The snrylfall in Halifax was about

normal. There was very little accumulation of snow, however,

as the mean daily temperature was very close to 32°F throughout

the winter. In spite of this, the maximum roof snow loads

were very often greater than the average ground snow loads .because of the very high winds which caused considerable

drifting.

(ioose nay, Nfld. - Although the sn owfa TI 'N8S only

15 per cenG"oove normal, the reported maximum ground snow load was 175 psf which wa s "/1 per cent above the design ground

snow load of the NBC and therefore seems unusual. The density

of the snow was reported to be inthe 0.60 to 0.70 gm/cc range. These very hiGh densities could be attributed partly to mild

weathe r . Several time s during December, ,January and Tilarch,

and durins most of April, the mean daily temperature was higher

than 32°J:il. This would cause considerable melting of the sn ow

and hence high snow densities. The reported snow depths were also unusually hieh, perhaps as a result of the severe drifting

hifh ground loads do not appear to represent the average ground

snow load for the Goose Bay area. It was therefore decided

to use the ground load of the C Station at Goose Bay for the purpose of this report.

The roof loads were very low considering the amount of snow on the [round, reaching a maximum of only 15 psi'. This was the result of the high winds which appear to be common in the Goose Day area and the exposure of. the roofs used for the observations.

Gander, Nfld. - Although the snowf'aLl. was about 68

per cent above normal, the Ground snow load did not exceed

35

psf' , Surprisingly this is about half the -vaLue obtained in

the previous year when the snowfall was only 50 per cent above

normal. It must be assumed that the ground snow load was

reduced by frequent thaws. As in previous years, the roof

loads were very 10VI, the ITlaximum roof snow load being only 11

psi. The roof snow load remained low due to tDe very high

winds which reached maximum values over 50 mph several times in Janua ry.

Other A Stations - Ho unusual characteristics were observed at the other A Stations not mentioned above (Edmonton,

Saskatoon, Arvida, ｾｾｩ｡ｴ･ｲｬｯｯ and Toronto).

D Stations

ｾｾｨ･ｲ｣ were v ex-; few reports from building inspectors

conc e rrn.ne unusual roof snow loads. Of the three. roofs which

had appreciable snow loads, two had avc ra ge roof snow loads

less than the ground load blrt the third had an average roof

snOVI load 30 per cent greater than the ground load. -'There

vverealso large drifts in the lee of a, wall of another building.

Strong wt.nds appeared to have been the rna jor influence.

Interesting results were obtained from the roofs

observed in the Ottawa area. ｉＧＮｾｯｳｴ of the roofs cbs erved

during the winter of 1961-62 were house roofs in well-sheltered locations and many had average roof loads almost equal to the

ground loads. This contrasted Greatly with the obs ervations

made in the previous year in en adjacent housing development, in which most of the roofs were exposed and severe drifting

was common. On one she 1tered roof", a maximum roof snow load

of 105 psf 17/8S reported. This occurred on the cave of the

roof wher e ice had a c cumuLa't c d , ':11Cre .rocrs were more exposed,

the averaze roof snow load was fa! below the cround ｳｾｯｷ load.

On the roof of a larGe sinzlc-storcy inoustrial

building, large drifts accumulated at ｯ｢ｳｴｲｵ･ｴｩｯｾｳ on the roof

while the expbscd parts of the roof were swept clear of the

9

-the basic design load by 8 per cent. On the same building.

a canopy had a maximum load of 117 psf 1'Ihich is 63 per cent h i.ghc r than the value allowed in thelTBC ior canopies in the Otrtawa area.

C Stations

Otta'Na. Ont. - The ave ra ge roof snow loads of all three roofs were below the ground load. but on two of the roofs, the maximum roof snow loads were Greater than the NBC

desi8u roof snow load of 48 psf. The arch hanEar had a

maximum roof snow load of 65 psi' and the mechanical equipment

ga ra gc bad a maximum roof snow load of 53 psf , Neither of

these loads exceed the ｾｭ｣ design snow load for drifting.

Goose Bay, Lab. - The C Station reported

approxi-mately the same dep

ch

of' snow as the A Station but the dens i ty

measurements were in the range of 0.20 to 0.40 Gm/cc. ｔｨｾ

resulted in a maximum ground snow load of 100 psf.

The roof of the supply depot had 10'J'l snow loads. The snow load on the canopy, however, was 144 psi which is

17 per cent higher than the design snow load of 123 PSI

specified in the National Duilding Code for a canopy in Goose

Bay. In a similar ｾ｡ｮｮ･ｲＬ drifting on the mechanical

equip-ment garage produced a maximum roof snow load of 150 psf viliich is 22 per cent greater than the NBC design snow loa d allowed for driftiu,::-.

Other 0 Stations - The average roof snow loads of

the other C Stations (Lancaster, Cold Lake, '1innipcg, and

North ｂ｡ｾｊＩ were below the ground snow loads. As in previous

years, drifting occurred where there was local shelter on

the roof. The roofs at Comox, B.C. and Toronto, Onto had no

snow throughout the winter.

ｓｭｩｬｬｦｾｒｙ OF ｾｻｅ RESULTS OF 1962-63 OBSERVATIONS

In general the results ｯｾ the 19G2-63 observations

tended to confirm the interim conclusions of the previous

reports. They showed that the snow load on a roof was a

variable quantity which depended greatly on location, wind speed and wind direction, temperature, 8nd the shape and size

of the roof itself. T'Ilere was also further evidence to

indicate that it might be advisable to revise the shape

factors for roof slopes and drifts given ｾｮ the ＱｾｃＮ

More than half the stations observed had above-normal

snowfalls. Of these, P.E.I. National Park (A Station), Gander

(:3 Station), and Lancaster, North Bay and Goose Bay (C Stations),

Even in ottawa, which had ｢･ｬｯｷＭｮｯｲｾ｡ｬ ｳｮｯｾｦ｡ｬｬＬ some of the B-3tation and C-Station roofs had drift loads exceeding the

1960 NnC design. va Lue s ,

The observed average roof loads ranged from 0 to

89 psf. The 89-psf load occurred at Glacier Park on a

sheltered roof. 'I'he maximum drift load obs erved was 150 psf

in Goose Bay, 8casured adjacent to a wall where the wind had

piled up the snow into a large drift. GENERAIJ DISCUS SION

The observations of the 1962-63 survey have

substantiated most of the interim conclusions of previous

reports. Together with earlier observations they provide

an increasing amount of evidence that certain revisions of

the NBC design snow loads are desirable. The 1962-63

obser-vations have also coruLrme'd that, although the Imowledge in

this field has improved greatly over the last few years, an

exact prediction of snow loads is not possible: Statistical

approaches together with enr,ineerine judgment are required as a means of establishing the best possible estimate of the design snow loads. Some dii'ficulties in a statistical approach arise, however, in that the survey to date has only been carried out for seven years on a relatively small number of roofs.

In addition, there are many factors affecting snov loads which can only be assessed by engineering judgment.

Precipitation, temperature and heat loss are obvious in their effect on roof snow loads and will not be discussed

here as they are clearly explained in references 3, 5 and 8.

Further comments on other factors affecting snow loads on roofs are presented in the follOWing paragraphs.

Wind

In previous reports it has been stated that wind

is the major factor affecting snow loads on roofs (9). Wind

conditions are, to some extent, related to geographical locations as shown by the two extreme examples of Glacier

and Fort Churchill. At Glacier, large balls of snow accumulate

on top of coniferous trees because of the lack of winter winds, whereas at Por-t Churchill, at the other end of the scale,

drifting conditions are extreme and almost continuous. Such

effects of geographic locations arc, however, limited to only

a few areas of CDnada. In the majority of the populated areas

of Canada, on the other hand, winter winds wi.Ll, be intermediate

in strength and intermittent. This will make their effect more

difficult to predict. Furthermore, roofs wi.LL hav e various

degrees of' shelter depencling on the surroundings and hence the

11

-example of this is found in Ottawa, where in any given winter some roofs will have very evenly distributed snow loads and others will have no snow at all or heavy drift

loads only. This further illustrates that it is very

difficult to make an exact prediction of roof snow loads due to the variations in exposure to the wind even in one

880graphic location. ｓｾ｡ｴｩｳｴｩ｣ｳ and engineering judgment

must be combined to determine the design snow loads for a

given area and a given roof. This inevitably results in the

desiEn snow loads of many roofs being greater than the actual snow loads since the maximum roof snow load in a 30-year

period, on which the d e s Lgn roof snow load is based, wi.Ll, occur on a limited number of roofs.

Sloped Roofs

There are two thoughts to be presented concerning

sloped roofs. The first c'oncerns the d epos it ion of snow on

sloped roofs compared with that on flat roofs and the second concerns the slope of the roof at which snow will begin to slide off.

Under normal exposed conditions, frequently more

snow collects on sloped roofs than on flat roofs. Theoretically,

with 100 per cent shelter, sloped roof's should collect the

same amount of snow as flat roofs. In exposed locations,

howeve r , there is evidence that Gabled or peaked roofs actually

have hiEher average snow loads than flat roofs. Examples of

this occurred durin8 the 1962-63 winter. The poultry building

at ste. Anne de Bellevue has a flat roof and a gable roof with

slopes of 45 and 34 deg respectively. In 1963, the heaviest

loads occurred on the 45 deg slope and reached a maximum of

44 psf as mentioned earlier in this report. In Gander, during

1963, even wi,th the flat roof unheated and insulated, both the

ave ra ge and maximum roof loads "rere higher on the gable roof. The accumulation of snow on a sloped roof and the formation of an unbalanced snow load on a peaked roof was

confirmed from observations given in a Russian paper concerning

the prevention of drifts on roofs (14). Buildings, by their

nature alone, are obstructions which cause turbulence in the air f'Low which in turn causes a reduction in vlind velocity

behind the obst ruct Lon , 'here there is a reduction in wind

ve l.ocftv , some of the wind-blo''\'ll snow will be deposited. Since

the wake from a peaked roof occurs over the roof whereas the wake from a flat roof occurs mainly over the fround, a peaked

roof will accumulate more wind-blmvn snow during a snowst orm,

Furthermore, a pe ake d roof wi L]. accumulate on one side some

snow bLown from the other side. 1':'1.e 1950 lr3C has provided for

an unbalanced load on peaked roofs. But it is not, as yet,

recognized in the Code that sloped roofs ma v on the whoLe have higher averaGe snow loads than flat roofs.

12

-In most codes reductions are allowed in the design

snow load fo'r sloped roofs. This is presumably based on the

thought that snow loads will be more easily reduced on sloped roofs since the water from melted snow can easily run off and

that, in addition to this, the snow can slide off. In the

1960 National Building Code, reduction of design snow loads

begins with a slope of 30 deg. It now appears that this

reduction is very crude and, in some cases, incorrect. The

roofs of well-constructed modern homes have well insulated ceilings and well ventilated attic spaces and, as a result,

very little melting ｯ｣｣ｵｲｳｾ In addition, the sliding of snow

off the roofs depends a great deal on the roofing material. Although metal roofs will usually shed much of their snow at

quite low slopes shingled roofs viith slopes up to more than

15 clef, will frequently keep their load (Figure 29). The

heavy drift on the 45 deg slope of roof at Ste.Anne de Bellevue did not slide off the roof.

It appears therefore that under ordiDarJ exposed conditions there will not be less snow on gabled roofs than on flat roofs, unless the roof' slope is greater than about 45 deg or unless the roofing material facilitates the sliding of

snor'off'the roof. Large Flat Hoofs

In previous reports (7, 8, 9), results of observations of snow loads on large flat roofs on industrial and public

buildings have been reported. It was observed that the roof

loads were always considerably smaller than the ground loads and that perhaps, by nature of their size alone. laree flat roofs would always be exposed to the wind, resulting in low

average roof loads. In 1963, 24 out of 25 roofs had roof to

ground load ratios below 0.51; the ave rar;e ratio of the 25

roofs was 0.32. All the roofs observed had areas greater

than 5000 sq ft. Some of the roofs ｯ｢ｳ･ｾｲ･､ had parapets

which produced hiGh loads at the edge of the bnilding but did not affect the average load a great deal since the area

affected by the parapet is srna11 compared with the area of

the large roof. It appears then. that there mipht be a

reduc-tion factor for large flat roofs when the design roof snow

load is being determined. Drifts on Canopies

In the 1960 NBC provision was made for drifting on

canopies (and on other roofs in the lee of hifher roofs). In

de s LcnLng canopies, the design roof snow' load is to be increased

by 50 per cent. There is some evid ence t"Cat this factor is

13

-0.80 of the maximum ground load b;r 80 per cent. In Ottawa,

where the snowfall was 20 per cent ccLow normal, the average

snow load on the canopy of one building exceeded 0.80 of the

maximum cround load by 203 per cent. noreover, quite a few

canopy failures have been reported in the past.

Drift loads on flat roof's in the lee of a higher roof have also exceeded the design values for drifting in the

NBC. This occurred in G3nder and Goose Day in 1963. There

was also a report of a recent roof failure in Morrt.reaL due

to this type of' Loadi ng , A drift load o:r appr-oxirna t e'l y 250 psf

(525 per cent of 0.80 of the maximum ground load) occurred in

the Lee of the main roof of the buildin{( which was 12 ft higher

than the roof tihat tailed. lihis main roof hael a very large

area which extended for a length of 300 ft. It appears that

the size of the contributing area as Nell as the height of

the vertical obstruction ｬｾｶ･ some bearing on the amount of

the snow drift.

It is apparent then that further studies of drifts on roofs and canopies are required so that a reasonable

re vi s ion of the lTBC on sriow loads can be nad e .

Roof to rrround Snow Load Patios for Exposed and

P,heltered ｬｾｯｯｩＧｳ

T'i[;ure s 25 and 26 show the roof to F::round snow load ratios for exposed and sheltered roofs for the period from

1S157 to 6j. l'Tearl? all the exposed roofs had ratios below 0.70.

Those above 0.70 occurred in areas of Low snow loads. Thus

it appears that -'che present value of O.GO 1J3ed by the 1960

NBC in d et e rml.nLng the design roof sn ow load is rather hie;h

for exposed .roofs , A More suitable value wonLd be in the

l'anse of 0.60 to 0.70. In contrast to ｴｾｩｳＬ accordinE to

Fi[ure 26, a ｳｩ｛ｾｮｩｩＧｩ｣｡ｮｴ percentage (20 per cent) of' the

sheltered roof's had ratios of roof to ground snow load above

0.80. This represents a large number of roofs and cannot be

ignored.

It appears then, that there should be separate design

snow loads for exposed roofs and sheltered roofs. Some difficulty

arises, however, in determining whet.he r a roof is exposed or

not. It can be said, honeve r , that a hLch decree of over-all

shelter, such as that pr-od uo ed by a wooded area all around a

house, is reguirecl to produce roof to ['round load ratios of

over 0.80. In any case, careful consideration of this question

is required before decic:.inr whLch of the roofs or conditions

justifies a cnanre in the roof to ground snow load ratio aI'

14

-IUTERH1 CONCLUSIOnS

The 1952-6) observations have substantiated most

of the interim conclusions of previous reports. These

conclu-sions can be repeated here as follows:

1. The average snow loads on roofs are less than the

load on the surrounding ground.

2. The amount by which the snow load on the roof and

the load on the ground differ depends primarily on the degree to which the roof is sheltered. (The

effects of shelter are, havever, extremely difficult to predict exactly.)

3. Concentrations (drifts), which f re querrtLy exceed

the load on the ground, are to be expected in any roof area of localized shelter, the magnitude of

the load being dependent on, among ｯｾｨ･ｲ things,

snowfall, the size of the roof area which is 'contributary", and the height of the localized

shelter.

4. Because of the complexity and variability of factors

affecting snow loads a statistical approach for

determining the design roof snow Toad becomes

neces-sary.

As a result of further analysis of the other reports

and the 1952-6) observations, further conclustons can be made:

5.

The present requirements for reduction of design

snow loads with ｩｮ｣ｲ｣｡ｳｩｮｾ slope of the roof,· are

not consistent with observed conditions. The slope

of the roof at which the snow will slide off will vary 8reatl:{ with the roofing material and the extent

of insulation of the roof. Also it is possible for

gable roofs to accumulate more snow than a flat roof because of the effects of the wake which occurs over one of the slopes.

6. Drifts on canopies and at vertical projections on

roofs, often exceed the factor of 50 per cent used

in the 1960 liBC design snow loads to provide for

drifting.

7.

There might be a reduction factor in the design

roof snow loads for large flat roofs.

8. If a satisfactory distinction can be made between

exposed and sheltered roofe, it appears that the present roof to ground snow load ratio of 0.80

used in the EnC could be Lcwe r-ed ior expos ed roofs,

F

15

-REFErtENCES

1. National BuildinG Code of Canada 1960. National Research

Council, Associate Committee on the National Building Code, Ottawa.

2. Allen, TI.E. Snow loads on roofs, 1956-57 - A progress

report. National Research Council, Division of BUilding

"Research, Interna 1 Pepor-t No. ＱＳＴﾷｾ Janua ry 1958. 7 p ,

3. Allen, D.E. and C.,I. ｾｵｲｫｳｴｲ｡Ｎ SnOI'lJ' loads on roofs.

1957-58 - Second progress report. National Research Council, TIivision of BUilding Research, Internal

Report No. 163, November 1958. 6 p.

4. Thorburn, ILJ. and B.G.W. Pet er , Snow loads on roofs,

1958-59 - Third progress report. National Research Council, TIivision of Building Research, Interna 1

Report No. 184, November 1959. 16 p.

5. Peter, B.G.1Y. and H.J. ThorbuTI1. Snow load observations

at B Stations, 1958-59. National Research Council,

Division of DuildinE, Research, Internal Report No.

189, December 1959. 13 p.

6. Watt, '·'.E. and H.J. Thorburn. mow loads on roof's,

1959-60 - Fourth progress report. Hational Research Council,

Division of Duilding Research, Internal Report No. 204, November 1960. 10 p.

1. Scott, J.P. and B.G.W.Peter. Snow loads on roofs,

1960-61 - Fifth progress report. National Research Council,

Division of Building Research, Internal Report No. 228, November 1961. 14 p.

8. Hebert, P.A. and ｂＮｇＮｾＮ Peter. Snow loads on roofs,

1961-62 - Sixth progress report. National Research

Council, Division of Building Research, Internal Report No. 260, -Iariua.rv 1963. 11 p ,

9. Thomas, f\'I. K. and D.ＢｾｉＮ Boyd. Computed maximum snow loads.

National Research Council, Division of Building Research, Building Note No. 34, February 1958. 5 p.

10. Thomas, T,T. K. A method of computing maximum snow loads.

Engineering Journal, Vol. 38, No.2, February 1955. p 120-123.

16

-11. Allen, D E. Field instructions for observers at

A Stations of snew loads on roofs. National

Research Council, Division of BUilding Research, Technical Note No. 233, October 1957. 11 p.

12. Allen, D.E. Snow loads on roofs. The present

requirements and a proposal for a survey of snow

loads on roofs. National Research Council,

Division of Building Research, Internal Report No. 106, September 1956. 19 p.

13. Climatic information for building desiGn in Canada

1961. Supplement No. 1 to the National Building

Code of Canada, 1960. National Research Council,

Associate Committee on the National BUilding Code, Ottawa. NRO 6483.

14. Bessonov, V.S. A method of preventing the accumulation

of heavy drifts on roofs of industrial.buildings. Promyshlennoe Stroitel'stvo, No.9, 1962, p. 20-24 translated by W.A. Dalgliesh.

a

TABLE I

SNOvl LOADS FOR A STATIONS 1962-63

NBC Max Max Avg Max

Statlon Roof Roof (pa r ) Ground Roof Observed

/53 /60 (ps r ) ( ps r ) Roof (psI') Inuvlk, N.W.T. Gable: Not heated, sheltered from sroth 30 37

-

4 4

Gable: Heated, lnsulated, exposed 30 37 25 14 30

Flat: Heated, lnsulated, exposed _{35 37} 18 6 9

Vancouver, B.C. 30 27 Practlcally no snow

Glacler, B.C. Flat: Exposed. unheated, no lnsulatlon - 129 119 89 97

Edmonton, Alta. Gable: Unheated, sheltered 25 22 7 4 6

Flat: Heated, lnsulated, exposed 25 22 ₇ 2 6

Saska toon, Sask. Gable: Heated, lnsulated, exposed 33 28 15 1 4

Gable: Heated, lnsulated, exposed 35 28 22 1 5

Flat: Heated, lnsulated, exposed 35 28 11 3 7

Flat: Heated, lnsulated, exposed 35 28 18 3 7

Flat: Heated, lnsulated, exposed 35 28 10 1 2

Wlnnlpeg, Man. Gable: Heated, lnsulated, sheltered 32 36 3 1 10

Flat: Heated, lnsulated, exposed 35 36 3 2 4

Waterloo, Onto Gable: Heated, lnsulated, exposed

-

48 19 1 4

Flat: Heated, lnsulated, exposed

-

48 21 2 6

Flat: Heated, lnsulated, shattered

-

48 21 5 14

Toronto, Onto Gable: Insulated, sheltered 24 26 9 2 2

Flat: Heated, lnsulated, sheltered 35 32 6 5 8

Klngston, Onto Gable: Heated, lnsulated, sheltered 47 40 29 14 21

Flat: Heated, lnsulated, exposed 55 40 16 13 31 2'6" pa.rapet

Ottawa, Onto Gable: Heated, lnsulated, exposed 42 48 28 6 16

Gable: Heated, lnsulated, exposed 42 48 28 6 15

Gable: Heated, lnsulated, exposed 50 48 28 11 16

Flat: Heated, lnsulated, exposed 50 48 28 20 32

Flat: Heated, lnsulated, exposed 50 48 38 15 23

Flat: Heated. lnsulated, exposed 50 48 36 26 37

Ste. Anne de Gable: 8/12 heated, lnsulated,exposed 34 35 _{56 9}

Bellevue P.Q. : 8/8 heated, lnsulated, exposed 21 26 44

Flat: Heated, lnsulated, exposed 50 44 55 9 13

Montreal, P.Q. Gable: Heated, lnsulated, exposed 42 43 55 8 21

Flat: Heated, lnsulated, exposed 50 43 49 9 11

Arvlda, P.Q. Flat: Heated, lnsulated, exposed 55 60 23 3 9

I

P.E.I. Natlonal Gable: Heated, lnsulated, exposed 56 53 20 2 5

Park Flat: Unheated, lnsulated, sheltered 60 53 105 8 11 from east and west

Flat: Heated, lnsulated, sheltered 60 53 44 11 56 from east

Hallfax, N.S. Gable: Heated, not lnsulated, shelmred 34 36 7 4 6

Flat: Heated, lnsulated, exposed 40 36 5 5

_ｩｾ

Flat: Heated, lnsulated, sheltered 40 36 4 13

Gander, Nfld. Gable: Hented, lnsulated, exposed 38 50 35 7 11

Fla.t: Unheated. lnsulated, exposed 45 50 34 4 5

Goose Bay, Lab. Gable: Heated, lnsulated, exposed 78 82 100 10 15

Type Heated. Not Major Influences Loads in psf

Location of and Heated Strong Heat !-lUd NBC Avg. Roof Remarks Roof Insulated Winds Loss Weather roof Ground roof rifts

/5) /60

Fort St. John,

Hii X

-

42 19 17 )8 Snow drifts

B.C. 4 12 behind) ft high

false front

Lloydminster,

-

25 No unusual loads I

Sask-Alta.

I

I

Rosser, Winnipeg X No unusual loads

Man.

Arvida. P.Q. Flat X X 55 60 10 I) )8 Snow drifts in

lee of' building 9' taller than

Dorval. P.Q. X No unusual loads roof observed

Gander. Nf'ld. Flat X X ₄₅ 50 27 6 112 Large drifts on

roof' in lee of'

ｓｎｾｾ LOADS FOR C STATIONS 1962-63 (in psf)

ｾ

Supply Depot Arch Hangar M.E. Garage Cant. Hangar NBC

Max Max avgi Max

Basic Max Max avg Max Max Max avg Max Max Max avg Max Roof Load Station ground roof drift ground roof drift ground roof drift ground roof Idrift 1953 1960

I

I

Comox, B.C. 0 0 0 0 0 0 0 0 ₄₅ 46 Lancaster,

-

-

-

-

-

-

17 7 46 17 17 ₄₄ 25 22 Alta. Cold Lake, 22 6 9 I 22 11 27 20 6 8 21 7 14 30 33 Alta. I i Winnipeg, 0 0 10 5 13 0 0 4 2 8 35 36 Man. _I North Bay, 51 12 20 28 15 46 30 11 74

-

-

-

55 43 Onto Ottawa, Onto

-

-

-

54 26 65 53 14 53 41 16 47 50 48 Toronto, 6 0 0

-

-

-

6 0 0

-

-

-

35 32 Onto Goose Bay, 100 14 20/w

-

-

-

91 20 150

-

-

-

90 82 Lab. 144"" NOTE: TABLE III

- indicates roof not available.

Type Heated Loads in psf

Location of and NBC Avg. Roof Remarks

Roof Insulated

ＯｾｒｯＯｦ Ground Roof Drifts

53 60 14 Kaymar Flat X _{50 48} 27 26 30 17 Kaymar Flat 50 48 27 22 27 17 Kaymar Gable X 50 48 27 20 23 3:12 18 Kaymar Gable X _{50 48} 27 20 23 3:12 9 Kindlecourt Gable X 50 48 27 25 31 3:12

15 Kindle cour t Gable 50 48 27 10 105 Ice accumulated

3:12 along eave.

15 Kindlecourt Flat 50 48 27 25 27

53 Oriole Dr. Flat 50 48 27 27 28

53 Oriole Dr. Gable X _{50 48} 27 22 31 3:12

45 Oriole Dr. Gable X _I 21 29 27 8 16 Unbalanced load

12:12 (16 psf on one ｳｬｯｰｾ

o on the other slopcl

1 Fairhaven Way Flat Part 50 48 35 25 31

Heated

1 Fairhaven Way Flat X 50 48 35 19 25

Davidson Cres. Flat X _{50 48 27} 15 20 12 Briarcliffe Flat X _{50 48 27} 18 24

37 Delong Hip X ₄₇ 48 27 27 44 Load on one end of

5:12 hip roof

Taunton Place Flat 50 48 35 26 35

Taunton Place Gable X _{42 48 35} 28 38 6:12

9 Leroy Gable X _{34 38} 29 1 5 Drifts on leeward

8:12 slope

23 Appleford Gable X _{47 48} 29 2 7

5:12

31 Appleford Gable X _{30 38 29} 2 14 Drifts on leeward

9:12 slope

Shoppers City Flat X _{50 48 17,c 9 52}

Blair Road 36 . _{5 44}

36,H} _{88 117}

M-20 NRC Pro;x;rty Flat X _{50 48 22 17 43} Roof sheltered by

ｾｴｲ･｡ｬ Road higher roof

TABLE V

SNOW LOADS ON LARGE FLAT ROOFS

Average Ground Root' Load

x 100 Location Roof Roof Load Load Ground Load

(psf) (psf) ＨｾＩ

Inuvik, N.W.T. Post Office 6 18 33

Comox, B.C. Arch Hangar 0 0

-M.E. Garage 0 0

-Cant. Hangar 0 0

-Lancaster, Alta. M.E. Garage 7 17 41

Cant. Hangar 17 17 100

Cold Lake, Alta. U.S. Depot 6 22 27

Arch Hangar 11 22 50

M.E. Garage 6 20 30

Cant. Hangar 7 21 33

Saskatoon, Sa s k , Gymnasium ₃ 11 27

Winnipeg, Man. Library 2 3 67

U.S. Depot 0

-

0

Arch Hangar 5 10 50

M.E. Garage 0

_-

0

Cant. Hangar 2 4 50

Waterloo, Onto Main Eng. Bldg. 2 21 10

Eng. Building 5 21 24

North Bay, Onto U.S. Depot 12 51 24

Arch Hangar 15 28 54

M.E. Garage 11 30 37

Toronto, Onto U.S. Depot 0 6 0

M.E. Garage 0 6 0

Ottawa, Onto Arch Hangar 26 54 48

H.E. Garage 14 53 26

Cant. Hangar 16 41 39

Arvida, P.Q. Rolling Mill 3 23 13

Goose Bay, Nfld. D-26 14 100 14

U.S. Depot 14 100 14

M.E. Garage 20 91 22

• .r."'DO-l-/ No A STATIONS I INUVIK 2 GLACIER PARK 3 EDMONTON 4 SASKATOON 5 WINNIPEG 6 WATERLOO 7 TORONTO 8 KINGSTON 9 OTTAWA

10 STE. ANNE DE BELLEVUE

II MONTREAL

12 ARVIDA

13 RE.I. NATIONAL PARK

14 HALIFAX 15 GANDER 16 GOOSE BAY No C STATIONS 17 LANCASTER 18 COLO LAKE 19 WINNIPEG 20 NORTH BAY 21 OTTAWA 22 TORONTO 23 GOOSE BAY

D

Q ｾ '. L. (

"

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ltJE '\

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A

a

C STATION LOCATIONS AND THEIR AVERAGE ROOF

a

GROUND LOADS,( MAXIMA OBSERVED 1962-63)

40

1

35 30 25 20 15 10 5 ｾ I I

ｾｬ ｾｩ

\ f/

1

_, I 4-A LOAD IN LB/ SQ FT ( 1962-19631 AVG ROOF LOAO (I/AXI / '

ｾ

///)[

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"-LOAD IN LBI FT2 co o en o WATERLOO WINNIPEG TORONTO KINGSTON INUVIK SASKATOON GLACIER OTTAWA STE. ANNE DE BELLEVUE EDMONTON i:--:-:---:::-::::::r--J _ : I -J MONTREAL

ｩｾＺＺＺＺｩ

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j

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I

GOOSE BAY

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5

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MAXIMUM}

AVERAGE LOAD ON

MAIN ROOF MINIMUM

TIME (DAYS)

-ROOF DESCRIPTION

r--"'---

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r

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::11

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11 ,. "7 ,. 1

03

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18' J APRIL

---

---MARCH II -t-ＭＭｾＭＭＭＭＭＭＭＭ］］］ｾ , 7 7 ! ｉｾｾＭＭＭＭ j i I , ...---....----_...---...,."" - ",,/ I

-_,_L , -+ - j +-- +-- + --j E-3 RESIDENCE

GROUND VALUES NOT AVAILABLE

UNIFORlII COVERAGE

----l

OCTOBER NOVEMBER DECEMBER JANUARY FEBRUARY

o 20 60 o 60 40 --MAXIMA AT .. 2 MINIWA AT . , 20 --40ｾＭＭＬ FEOERAL BUILDING o -e 5 20f - - '

T

ｾ｟｟｟

__

-o ｾ __ｾＭＭＭ (Q 9 10 - 9 ｴＭＭＭｾ

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If-

-+I -+- - t -+ ---j

ＢｾＬ ＬＢｾＢＢ ｾＢＢＭＭＭＭＭｉＭＭＭＭＭＫＭＭＭＭＭＯＭＭＭＭＭＭＭＭ

---HOME ECONOMICS ANNEX E - 3 RESIDENCE

IEXPOSEO, HEATED INSULATEDｾＮＩ

1 I I, -' -' ｾ ｾ 80 ｾ ｾ >-ｾ 40 ---ＭＭＭＭＭｬＭＭＭＭＭＭＫＭＭＭＭ｟｟ｩ｟ＭＭＭｾＮＮｌＭＢ］］］ｪ｟］］ｾＭＭＭ｟｟ｩ｟ＭＭＭ｟｟｟ｉ :Oi => u ｾ o

(SHELTERED FROM SOUTH, LOW HEAT)

(NOvEMBER-APRILI ＴＰｾｾｬ］ｅ 2 0 - - s NORMAL 1962 I 63 57" o +50 >- +32 -=! ... "'. 0,,-z:Oi "'... ... >-:Oi FIGURE 3 -40

SNOW LOAD OBSERVATIONS ON ROOFS YEAR: 1962/63

d/;

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BO

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-ｾ

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OClOBER NOVEMBER DECEMBER JANUARY FEBRUARY MARCH APRIL

i I ｾ>25'-0" - - - " " . 1 - 140' O· !

I

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I I I ,. ,.

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GENERATOR _'oi 400 ---.--._. - ---.. _{ROO/ll ,} '" ,. z- _,;,1

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,. -.l 360- - - _ .__.. -Ｍｾ ｾＭＭ ｾ VEHICLE STORAGE

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NOT SHELTERED, NOT HEATED,

1 320

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;!; .: _I .----J , _.. ｾ '" 280 . _

-11

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0 ｾ '" 240 '" .... if I '" , --J =:> I 2 § 200 f--'" !

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160 I

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ｾ

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WINO SPEED NOT AVAILABLE

ｾ 40 --- _..｟ｾｾＭＭ - - - (NOVEMBER· APRIL) NORMAL 1962/63 351· 395" ＭＭｾ f - - -

ＭＭＭＫｾ｟ＮＭ

.32 ---ＭＭＭＭＭＭＭＭＭﾷｴｾ _{ｎＭａｾＭＭ}

_II'"

'Y'W ..1'>.1'..ｾＭ 0 --_. -V v _{FIGURE 4} -40

SNOW LOAD OBSERVATIONS ON ROOFS YEAR: 1962/63

40ｉＭＭＭＭＭｾ｟ＫＭＭＮ ---+---1----+---/ ｾｓｔｒａｔｉｏｎ BLDG. IIIIAQII, AT ". 20ｬＭＭＭＭＭＭＫＭＭｾｾＭＭＭ p"'- ＭＭｾ --.•----._--. o ROOF DESCRIPTION AOM."ISTRATlO.. BLDG. ｲｾＭＭｾ

11'

' 4

j

; -2 _5 fl_ .

..

I ＭｾｾｉＭＭＭｾｾＫＭｾｾＭＫＭｾＭＭＫＭＭｾｾ｟｟ｴ ｾ ｾ • 6 0 1 - - - l - - - , 1 - - - - + - - - T - - - _ _ _ j 40ｌＭＭＭｾＭＭＭＭＭｬＭＭＭＭＭＫＭＭＭＭＫＭＭＭＭｩ

MINING STORE SHED 20ｲＭＭＭＭｾｾＭＭＭＭＱＭＭＭＭＭＫ｟｟ＭＭＭＫＭＭＭ｟ＫＭＭＭ｟｟｟ｪ EXI'OS£D HEATED INS/ILATED '-l)A -l

4'2-Ｈｄｾ

SECTION • A-A-• ｾｬ［ＮＮ /-""""_.-_t ••• __• o

ＭＭＭＭｴｾＮＧｦＭＭＭＭＭＭＭＭＭＭＫＭＭＭＫＭＭＭＭＭＭＭＭＭＭＭｩ

I

NOVEMBER DECEMBER JANUARY FEBRUARY MARCH 120

:I 9'JｌＭＭＭＭｾＭＫＭＭＭＭＭＭＭ｟｟ｬＭＭＭＭＫ｟ＭＭＭＫＭＭＭ｟｟｟ｪ

ｾ

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o

ｾ

MINING STORE

.

SHED

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ｾＬｾ

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( SHeLTERED,IJNHCATED 8L OG)

o ... ｾ_.... :::> '"' :::> u u C( 0"=======1=--'===,---+---- - 1 - - - + - - - \ -40

SNOW LOAD OBSERVATIONS ON ROOFS

t,.OVEIII8ER - .... RCHI

NORMAL 1962/63

39' 40'

FIGURE 5

YEAR: 1962163

o

(EXPOSED. HEATED, INSULATED)

I

314 LAKE CRES. 314 LAKE CRESCENT

(EXP.OSED, HEATED, INSULATEO)·

\ ｾＮｴＭ

FE

. , · s

...

I

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_{I:: ::}

--.1 ,.' ----l " I I II I i I OUTDOOR

ｾｓｔ

STATION

I

i o o '"o ...J

120 NOVEMBER DECEMBER JANUARY FEBRUARY MARCH

60 o I---+---j---I + _ _ _ 40 -

ＭＭｬＭｾＧＭＫＭＭｾＭｉｾ

o ｾ...J ::> ::IE ::> u u '" SNOWFALL NORIIAL 1962/63 26" 31" FIGURE 6(0) (OECEIII8EA - MUCHI ITfI)OtAECTlOIlI I I III

r.

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.+,

s -40 -- +sgf---+----+----+----t---::fi1 +32 -- - - -

---SNOW LOAD OBSERVATIONS ON ROOFS YEAR: 1962/63

I ..j ［ｾ I I .- ｾｉ_-!

..

ｾ _\ OESCRIPTION ROOF , ; ｌｾ <c.> 111'

--

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..

., .s ., ., GYMNASIUM DETAIL A

(EXPOSED, HEATED, INSULATED) I _-o I 60ｴＭＭＭＭＭｾｲ｟Ｍ ＭＭｾＭＭＭ I 20ｉＭＭＭＭＭｾＮＭＭＭＭ｟｟｟ＫＭＭＭＭ｟ＫＭＭＭＭＫ｟｟ＭＭＭ｟｟｟ｉ 0

..

_....... <,

•

80 ｾ .. _--I I 0 I I ｾ 1 : 60 I _I : 40 I I GVMNASIUM i MAXIMA AT:;-5 I MINIMA AT #1,2,9 20 I ! ,"ｾＭ ...ｾ ...'" I _--,..ｾＭ - ---!r...---=' I " . - -!

NOVEMBER DECEMBER JANUARY FEBRUARY MARCH

1 2 0 1 - - - - " " " " ' - - - ' r - - - + - - - - + - - - I EXPOSED, HEATED, vENTILATED

2' PARAPETS o .., .... ... i :> u u ... 80ｉＭＭＭＭＭｾＮ 40 r---o -.-- ..- ..ＭＮＭＮＭＭＭＫＭＭＭＭＭＭＭＭＭＫｾＭＭＭＭＭＭｴＭＭＭ ＭＭＭｾＭ 40ＬＭＭＭｾ

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y y V \tv{\".JJV V SNOWFAll (OEC(YBER - MAACI-I) NORMAL 1962/ 63 26' 31" FIGURE 6 (b) SNOW LOAD OBSERVATIONS ON ROOFS YEAR: 1962/63

20 ! 12' ABOVE ROOF 0 - - - - \ -Ｍｾ --- ... ¢,' I .,

.

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.

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A

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I I , I BLDC, I

i i _I SHELTERED, ATTiC UNHEATED, vENTiLATED, INS/.JI.ATEO

NOVEMBER DECEMBER JANUARY FE8RUARY MARCH

120 1 , i '!' , i ..J

1

I

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ｊｌｾ ｾｉＡＬＬｾ

t

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(NOII[MBER MARCH) ｾ 20 :;:8 _ｾ

W

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lJ

Y I •lJ'IVV:

r

＼ｾ 'V'IJV'VIl I NORMAL 1962/63

Q:i' _{43' 43"} x'"

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ｾ +32

ｾ

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FIGURE 7 "' '" -40

SNOW LOAD OBSERVATIONS ON ROOFS YEAR: 1962/63

ROOF OESCRIPTION 254 SUNVIEW

tEE

• '2

, '

4. " " ." .!. ｾ ｾＶＧＭｾＧ ｾ (HEArEO, INSULATED, EXPOSEOJ

40 e---o - - - _ . o _ ..

(HEATED, INSULATED, EXPOSED)

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I

." I-.'- I m,-I ｾ --- _.L___

,,,-oj

"., L

r

--9 a .1 FIGURE 8 NORMAL 1962/63 45' 37'

(HEATED, INSULATED, EXPOSEO) ENGINEERING BLDG.

-MARCH

I

NOVEMBER DECEMBER JANUARY FEBRUARY

SNOW LOAD OBSERVATIONS ON ROOFS YE AR: 1962/63

II DOUGLAS CRES. IIIIN.... AT - , I

" '-0'.

ＭｾＮｾｾｴｊ

-.'.' .' .'.

",,' "".' 4 .., S . -, , L , 2 • L ' . 0 1 1 = ..l.._. ｟ｾＭ ＭｾＭＭ ... - ... r-..

(SHEL TEREO HEATEO INSULATEDI Zl DOUGLAS CRES 21 DOUGLAS CRES. -i 'I S"'fLTEIOE:D BLDG HEATED ATTIC LlNHEATED

CEll IlliG INSULATED

JANUARY FEBRUARY MARCH

--' fl. 80ｦＭＭＭＭｾ

----f---t----I

-FIGURE 9 NORMAL 1962/63 49" 32" SNOWFALL lOEcelll8ER - .. "RCH) ｾ _ _r l -401--- - ｲＭＭｾＭＭＭＭＫＭｾ ｾＭｾＭｾＭＭｾＫＭｾｾｾＭＭＭＭＭｾＭＭＭＭＭ I i

ｾ

5 ..

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IV

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i

VV

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ｾ ｾｙｉ

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ｾｺＭＭＧｾ ＫＳＲｾＭＭ

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ｾ

s

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'" -40

SNOW LOAD OBSERVATIONS ON ROOFS YEAR: 1962/63

ROOF DESCRIPTION 60 -26 EDGEHILL AVE. " 40 '[7

26 EDGE HILL r--4(l---i

YlNIM__T .5 /'\

ｌＮｾｬ

20 -, '

ｾ

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T"

..

'--;-;-40 " ., ., ,. IIcNEILL HOUSE

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I I I

1

H<40' ..!- _{'\!. I} ., ., ,. 20

ＬｾＮｪ

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I.

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-

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--- A.. EXPOSED I 0 6 INSULATED

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ATTIC NOT HEATED BLDG HEATED PARAPET 2'6"

i!i 120 NOVEMBER DECEMBER JANUARY FEBRUARY MARCH

.s ..J ｾ

'"

0 80 ｾ C ｾ ｾ w /" ....

..

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..,

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NORIIAL 1962/63 ｣ｾ 64" 7S' xU>

..

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Ｍｾ

ｾ

ｾ u..+32

---ｾ

Mr:fV\-...

Co.. z'" 0ＭＮｾＭＭＭ .. w FIGURE 10 w .... '" -40

SNOW LOAD OBSERVATIONS ON ROOFS YEAR: 1962/63

4 0 1 j j + ,

-ROOF DESCRIPTION

ｾｄｄｂｒ

.r.

(EXPOSED, HEATED, INSULATED J

,,[7 72 BISHOP,BlVD

U

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-Ｎ

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t

ＮｉＧｾ

(EXPOSED, HEATEDI INSULATED 2")

40 BARKER BLVD D.B.R MINIMA AT #5

ｾＭＭＭＫＭＭＭＫｉ

I

•

ＮＮＮＮＮＭＭＭＭＭＭＫＭＭＭｉＭＯｾＬﾷＭＭＺ

ﾷ［Ｑﾷ＾ＬｾＧＭＺｴｾＧｾＺＧ

8----; 201---···· 0 40 N.... "-<,

•

20 0 '"0 -' 0

NOVEMBER DECEMBER JANUARY FEBRUARY MARCH

120 oi -' -' BO 1l'

-0 ｾ 0 ₄₀ w .... :3 => 2 § 0 '" 0 40 ｾＥ SNOWFALL _0:

'"

(NO't'[MII£A-IIIlACIt) >-=0 NORMAL 1962/63 ｾｾ a. B3" 5B" ><'" '" 2 >- ="-" , . 0a. z'" 0 "'w FIGURE II(0) w .... '" -40

SNOW LOAD OBSERVATIONS ON ROOFS YEA R: 1962/63

H. 3'

EXPOSED UNHEATED AIR SPACE CElLlN6 INSULATED (47 HEATED BL06. FLAT' 10' TOEAVES +N--,. aii e·.7

..

a-"0 ., ,,' - - - 1 ROOF DESCRIPTION DAVIDSON CRES.

(SHELTERED, HEATED, INSULATED)

L

1"Tl

'7 , ; 10

II

• ｾＴＬ I 6 2 5 a I • .:3 4 I L:.---':.L.1 ｌＧｾｉＧ｟ｩ FAIRHAVEN WAY ...x... AT .14 o >-u, <, • 20f j -o 40 o 40 40A BARKER BLVD, YAXIMA AT .12 I I DAVIDSON CRES. 2 0 1 + -40 A BARKER BLVD

1201---i'---l---+----+---tNOVEMBER DECEMBER JANUARY FEBRUARY MARCH

12 -:-l-<1J ｉﾷｾｃＺ］］ＭＭ --' --' 80I - - - ! - - - + - - - - -- - - t _ ｾ

•

o ｾ c 40} - - - ! - - - + - - - , = J , . - L - - - - + - - - j '" >-« ..J => :E => ｾ Ol---+---+--«

IEXPOSED, HEATED, INSULATED)

SNOW FALL ('tOV£MBEA - ...RCH) 0 40 ｾＺｩ

.'"

,;. ｾ - 0_«", c'"c, xV> « :IE >- :!--« . 0 " , z:IE 0 «'" ",>-:IE -40 NORMAL 83' FIGURE 1962/63 58' 11 (b)

SNOW LOAD 08 SERVATIONS ON ROOFS YEAR: 1962/63