84 



CAMBRIA STEEL. 



APPROXIMATE WEIGHTS OF VARIOUS 

 ROOF COVERINGS. 



In Pounds per Square Foot. 



Copper Sheeting, B. W. G. No. 22 1} 



Corrugated Iron, B. W. G. Nos. 26 to 16 1-3 



Felt, two Layers 



Felt and Asphalt 2 



Felt and Gravel, % inch thick 6 



Galvanized Iron, B. W. G. Nos. 26 to 16 1-3 



Lath and Plaster Ceiling, Ordinary 6-8 



Sheathing, 1 inch thick, Hemlock 2 



White Pine or Spruce 2 



" Yellow Pine 4 



Shingles, 16 inch, laid 5 1 A inch to weather 2 



Skylight Glass, A to H inch thick 2^-7 



Slates, M to & inch thick, 3 inch double lap 4-7 



Slag Roofing, 4-ply, with cement and sand 4 



Steel Sheeting (See next page) fi-3 



Tiles (See Page 69) 8-20 



Tin 5i-l 



Zinc, B. W. G. No. 20 l 



APPROXIMATE WEIGHT OF ROOFS INCLUDING FRAMING: 



Corrugated Sheets. . . . . 8-10 



Shingle 6-10 



Slate 12-15 



Tar and Gravel 10-12 



Tin 6-8 



Tile 20-30 



If roof is plastered underneath, add to values given above 6 



Weight of Roof Truss with span of 75 feet or less 5 



Snow Load 25 Ibs. per horizontal square foot of roof for all slopes 



up to 20, reduced 1 Ib. for each degree of slope in excess of 20. 



No snow load to be considered for slope of 45 or more. 



WIND PRESSURE ON ROOFS. 



Based on 20 Lbs. per Sq. Ft. on a Vertical Plane. 



1.84 cos a - 1. 

 FORMULA. Normal Pressure per sq. ft. = P sin a 



Pitch 



a) 



Horizontal 



Degrees. Minutes. 



Rise of Roof per Foot. Normal Wind Pressure. 



Inches. 



Pounds per Sq. Ft 



18 - 25 

 26 - 33 

 33 - 41 

 45-0 

 53-7 

 56 - 20 

 63 - 27 



8.4 

 11.9 

 14.6 

 18,1 

 19.4 

 19.7 

 20.0 



