CHAPTER II. 

 SNOW LOADS. 



The annual snowfall in different localities is a function of the 

 humidity and the latitude and is quite a variable quantity. The amount 

 of snow on the ground at one time is still more variable. In the Lake 

 Superior region very little of the snow melts as it falls, and almost the 

 entire annual snowfall is frequently on the ground at one time; while 

 on the other hand in the same latitude in the Rocky Mountains the dry 

 winds evaporate the snow in even the coldest weather and a less pro- 

 portion accumulates. In latitudes of 35 to 45 degrees the heavy snow- 

 falls are often followed by a sleeting rain, and the snow and ice load 

 on roofs sometimes nearly equals the weight of the annual snowfall. 



From the records of tjie snowfall for the past ten years as given 

 in the reports of the U. S. Weather Bureau and data obtained by 

 personal experience, in British Columbia, Montana, the Lake Superior 

 region and central Illinois the author presents the values given in Fig. 

 4 for snow loads for roofs of different inclinations in different latitudes. 

 For the Pacific coast and localities with low humidity, take one-half 

 of the values given. The weight of newly fallen snow was taken at 5 

 Ibs. and packed snow at 12 Ibs. per cubic foot. 



A high wind may follow a heavy sleet and in designing the trusses 

 the author would recommend the use of a minimum snow and ice load 

 as given in Fig. 4 for all slopes of roofs. The maximum stresses due 

 to the sum of this snow load, the dead and wind loads ; the dead and 

 the wind loads ; or of the maximum snow load and the dead load be- 

 ing used in designing the members. 





