2 STANDARD SPECIFICATIONS 



4. Purlins. The weight of purlins will average, for each 

 square foot of superficial roof area, as follows: 



Steel purlins ......................... 2-3 Ibs. 



Wooden purlins ...................... 3-5 " 



5. Roof Trusses. The weight of ordinary steel roof trusses, 

 having a pitch of -J- to J, will average, for each square foot of 

 horizontal area, as follows: 



or for the total weight of one truss, 



where W = total weight of truss in Ibs. 



c= weight in Ibs. per sq.ft. on horizontal area carried by 



truss. 



d= distance in feet between trusses, provided that d> 



5 



(Par. 23). 

 L =span in feet of truss. 



6. Snow Load. In latitudes between 40 and 50 the snow 

 load shall be taken per horizontal square foot of roof area as 

 follows : 



Pitch from flat to inclusive .......... 25 Ibs. 



" over to J " .......... 20 " 



" i to 4 " .......... 15 " 



" 4 to 4 " .......... 10 " 



" and more .......... " 



In other latitudes these snow loads should be modified according 

 to local conditions. 



7. Wind Pressure. The wind pressure shall be taken as 

 30 Ibs. per sq.ft., upon the entire exposed area of the steel 

 framework, or upon the vertical projection of sides and ends of 

 roof and building, and as acting horizontally in any direction. 



