Tables VII. and VIII. compiled by the author, from a comparison of other tables and formulas, and from the weight of actual trusses, are sufficiently accurate for the purpose of determining stresses. The weights given are probably slightly in excess of the actual weights of average trusses, as the author prefers to have the error, if any, on the safe side. It should be noted that the weights are for each square foot of roof surface, and not for the horizontal area.

 Span. 1/2 Pitch 1/3 Pitch 1/4 Pitch Flat. lbs. lbs. lbs. lbs. Up to 36 ft. 3 3 1/2 3 3/4 4 36 to 50 ft. 3 1/4 3 3/4 4 4 1/2 50 to 60 ft. 3 1/2 4 4 1/2 4 3/4 60 to 70 ft. 3 3/4 4 1/2 4 3/4 5 1/4 70 to 80 ft. 4 1/4 5 5 1/2 6 80 to 90 ft. 5 6 6 1/2 7 90 to 100 ft. 5 3/4 6 3/4 7 8 100 to no ft. 6 1/2 7 1/2 8 9 110 to 120 ft. 7 8 1/2 9 10

* The following are some of the formulas given for weight of steel trusses, W being weight per horizontal square foot, S = span in feet, P = capacity of truss in pounds per horizontal square foot, and A the distance centre to centre of trusses in feet: '

Charles Evan Fowler, C. E., for Fink trusses:

W = .06S + .6 for heavy loads; W= .04S + .4 for light loads.

H. G. Tyrrell, C. E.:

W = .05S+ di_t. centre to centre. C. W. Bryan, C. E.:

W = .04S + 4. M. S. Ketchum. C. E.:

+ For scissors trusses increase one-third.

Table VIII. - Weight Per Square Foot Of Roof Surface For Steel Trusses

 Span. 1/2 Pitch. 1/3 Pitch. 1/4 Pitch. Flat. Up to 40 ft. 5.25 6.3 6.8 7.6 " 50 ft. 5.75 6.6 7.2 8.0 " 60 ft. 6.75 8.0 8.6 9.6 " 70 ft. 7.25 8.5 9.2 10.2 " 80 ft. 7.75 9.0 9.7 10.8 " 100 ft. 8.5 10.0 10.8 12.0 " 120 ft. 9.5 11.0 12.0 13.2 " 140 ft. 10.0 11.6 12.6 14.0