CHAPTER XIX. 

 ROOF COVERINGS. 



Introduction. Mill buildings are covered with corrugated steel 

 supported directly on the purlins ; by slate or tile supported by sub- 

 purlins; or by corrugated steel, slate, tile, shingles, gravel or other 

 composition roof, or some one of the various patented roofings sup- 

 ported on sheathing. The sheathing is commonly made of a single 

 thickness of planks, I to 3 inches thick. The planks are sometimes laid 

 in two thicknesses with a layer of lime mortar between the layers as a 

 protection against fire. In fireproof buildings the sheathing is com- 

 monly made of reinforced concrete constructed as described in Chapter 

 XX. Concrete slabs are sometimes used for a roof covering, being in 

 that case supported directly by the purlins, and sometimes as a sheath- 

 ing for a slate or tile roof. 



The roofs of smelters, foundries, steel mills, mine structures and 

 similar structures are commonly covered with corrugated steel. Where 

 the buildings are to be heated or where a more substantial roof cov- 

 ering is desired slate, tile, tin or a good grade of composition roofing 

 is used, or the roof is made of reinforced concrete. For very cheap 

 and for temporary roofs a cheap composition roofing is commonly used. 

 The following coverings will be described in the order given ; corrug- 

 ated steel, slate, tile, tin, sheet steel, gravel, slag, asphalt, shingle, and 

 also the patent roofings ; asbestos, Carey's, Granite, Ruberoid and Fer- 

 roinclave. The construction of reinforced concrete roofing is de- 

 scribed in Chapter XX. 



Corrugated Steel Roofing. Corrugated steel roofing is laid on 

 plank sheathing or is supported directly on the purlins as described in 

 Chapter XVIII. For the cost of erecting corrugated steel roofing see 

 Chapter XXVIII. 



