32 STEEL ROOF TRUSSES AND MILL BUILDINGS. CHAP. I. 



it will lay 168 sq. ft. For flat seam roofing, using in. locks, a box of 20 X 28 tin will lay about 

 399 sq. ft., and for standing seam, using f in. locks and turning i j and if in. edges, making i in. 

 standing seams, it will lay about 365 sq. ft. 



TAR AND GRAVEL ROOF. Tar and gravel roofs are called three-, four-, five-ply, etc., 

 depending upon the number of layers of roofing felt. Tar and gravel roofs may be laid upon timber 

 sheathing or upon concrete slabs. For details of a tar and gravel roof see Fig. 23. The following 

 specifications are taken from the author's " Specifications for Steel Frame Buildings." 



Specifications for Five-Ply Tar and Gravel Roof on Timber Sheathing. The materials used 

 in making the roof are I (one) thickness of sheathing paper or unsaturated felt, 5 (five) thick- 

 nesses of saturated felt weighing not less than 15 (fifteen) Ib. per square of one hundred (100) 

 sq. ft., single thickness, and not less than one hundred and twenty (120) Ib. of pitch, and not 

 less than four hundred (400) Ib. of gravel or three hundred (300) Ib. of slag from f to f in. in size, 

 free from dirt, per square of one hundred (100) sq. ft. of completed roof. 



The material shall be applied as follows: First, lay the sheathing or unsaturated felt, lapping 

 each sheet one in. over the preceding one. Second, lay two (2) thicknesses of tarred 'felt, lapping 

 each sheet seventeen (17) in. over the preceding one, nailing as often as may be necessary to 

 hold the sheets in place until the remaining felt is applied. Third, coat the entire surface of this 

 two-ply layer with hot pitch, mopping on uniformly. Fourth, apply three (3) thicknesses of felt, 

 lapping each sheet twenty-two (22) in. over the preceding one, mopping with hot pitch the full 

 width of the 22 in. between the plies, so that in no case shall felt touch felt. Such nailing as is 

 necessary shall be done so that all nails will be covered by not less than two plies of felt; fifth, 

 spread over the entire surface of the roof a uniform coating of pitch, into which, while hot, imbed 

 the gravel or slag. The gravel or slag in all cases must be dry. 



Specifications for Five-Ply Tar and Gravel Roof on Concrete Sheathing. The materials 

 used shall be the same as for tar and gravel roof on timber sheathing, except that the one thick- 

 ness of sheathing paper or unsaturated felt may be omitted. 



The materials shall be applied as follows: First, coat the concrete with hot pitch, mopped 

 on uniformly. Second, lay two (2) thicknesses of tarred felt, lapping each sheet seventeen (17) 

 in. over the preceding one, and mop with hot pitch the full width of the 17-in. lap, so that in no 

 case shall felt touch felt. Third, coat the entire surface with hot pitch, mopped on uniformly. 

 Fourth, lay three (3) thicknesses of felt, lapping each sheet twenty-two (22) in. over the preceding 

 one, mopping with hot pitch the full width of the 22-in. lap between the plies, so that in no case 

 shall felt touch felt. Fifth, spread the entire surface of the roof with a uniform coat of pitch, 

 into which, while hot, imbed gravel or slag. 



Cost of Five-Ply Tar and Gravel Roofing.* The cost of a round house roof in the middle 

 west, based on 1912 prices and containing 500 squares of five-ply tar and gravel roofing, was as 

 follows. 



Cost per square of 100 sq. ft. not including fixed charges or profit ,*not including sheathing. 



Sheathing paper, 5 Ib $o. 12 



Pitch, 155 Ib. at 60 cents per 100 Ib 0.93 



Felt, 85 Ib. at $1.65 per 100 Ib 1.40 



Nails and caps 0.05 



Cleats for flashing 0.05 



Gravel (about one-seventh yard) 23 



Labor, including hauling, board and railroad fare 1.15 



Total cost per square $3-93 



SHOP FLOORS. Floors for industrial plants may be placed on a foundation resting directly 

 on the ground or may be self supporting. Several examples of shop floors that rest on the ground 

 are shown in Fig. 25. Standard specifications for a cement floor and for a wood floor on a tar 

 concrete base follow. 



The following specifications are from the author's " Specifications for Steel Frame Buildings." 



Specifications for Cement Floor on a Concrete Base. Materials. The cement used shall 

 be first-class Portland cement, and shall pass the standards of the American Society for Testing 

 Materials. The sand for the top finish shall be clean and sharp and shall be retained on a No. 30 

 sieve and shall have passed the No. 20 sieve. Broken stone for the top finish shall pass a \ in. 



*Am. Ry. Eng. Assoc., Vol. 14, p. 852. 



