Zinc and other Metallic Roofs.
Additions are made every year to the number of contrivances for forming metallic roofs, among which is one now the subject of a patent, for the use of galvanized iron. In this case the aid of the electric agent is employed to give iron sheets an amount of durability which they do not possess in their natural state.
Zinc has been much employed within the last few years as a material for roofs. Its availability for this purpose rests partly on its superior lightness as compared with lead, and its superior condition under the action of the atmosphere as compared with iron. The latter quality arises thus; after the zinc has been covered with a thin film of oxide by the action of the atmosphere, it suffers no further change from long exposure; so that the evil of rust checks itself. At the temperature of boiling water, zinc sheets, which are brittle when cold, become malleable, and their availability for roofs is thereby increased. The property which zinc has, however, of taking fire at a temperature of about 700° Fahr., rather detracts from its value as a material for roofs.