. Principles and practice of plumbing . inlet is clogged with ice or otherwise obstructedthe rain water can over-flow through a scupper tothe ground or to anotherroof surface. If, for in-stance, a leader were locat-ed at the center of a squarebuilding having a flat roof,and the inlet became clog-ged, the water would beretained on the roof form-ing a pool of dangerousweight. In industrial build-ings of the saw-tooth type,it is bad practice to runhorizontal leader mainsunder the roof, takingbranches up to the severalgutters. In this location the pipe becomes heated to thetemperature of the hotte
. Principles and practice of plumbing . inlet is clogged with ice or otherwise obstructedthe rain water can over-flow through a scupper tothe ground or to anotherroof surface. If, for in-stance, a leader were locat-ed at the center of a squarebuilding having a flat roof,and the inlet became clog-ged, the water would beretained on the roof form-ing a pool of dangerousweight. In industrial build-ings of the saw-tooth type,it is bad practice to runhorizontal leader mainsunder the roof, takingbranches up to the severalgutters. In this location the pipe becomes heated to thetemperature of the hottest part of the room, then quicklychilled from a cold rain. Lead-calked joints are liable towork loose under such temperature changes, so if the lead-ers must be installed that way, they had better be of screwpipe. Outside leaders should be provided on the top with aservice box, into which the roof water can discharge. Thisservice box should be set low enough so in case the leaderbecomes stopped with ice, the water can overflow the box. Fig. :;oFlexible Connection for Roof Ontter Digitized by Microsoft® Principles and Practice of Plumbing 43 without backing up on the roof. The principal objectionto outside leaders is that they freeze and burst. In coldclimates outside leaders are a source of worry and expensethat can be avoided by the additional first cost of insideleaders. The bursting of outside leaders from frost can bereduced to the minimum by using corrugated pipe in placeof cylindrical; then, when the water expands upon freezing,the corrugations yield to the pressure without the pipesbursting. Cast iron pipe with lead calked joints nevershould be used for soil waste or leader pipes where exposedto frost. Even though the pipe is usually empty, the oakumused in calking the joints becomes wet from the water flow-ing through the pipe, which, upon freezing, forces the leadout of the joints, causing leaks. Size of Leaders.—The Barrett Company, from theirextensive experience i
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