Lecture VIII.

Roofs—Continued.

Trussed roofs.—Collar roofs.—King-post truss.—King and queen-post truss.—Iron trussed roofs.—Various examples.—Mansard roof.—Morality of "la Mansarde."—Roof of Houses of Parliament—Charing Cross Station roof.—Albert Hall roof.—Vienna Exhibition dome.—Arched iron roofs.—Difference between stone arches, trussed bridges, and roofs.—Crystal Palace roof.—Derby Market Hall roof.—St. Pancras Station, Midland Railway.—Covering Materials: Thatch: danger from birds—Boarded roofs—Weather boarding—Upright boarding—Painting to be done when dry—Stone should be dry before being oiled.—Tarring bridge planking—Cementitious coverings—Expansion and contraction to be provided for—Cement unsuitable—Asphalte and tar concrete recommended—Hydraulic mortar—Felt—Metallic coverings: lead, tin, zinc, copper, galvanised corrugated iron.—Tiling—Definitions—Principles of tiling and slating—Shingles—Sandstone slabs—Structure of slate—Origin of cleavage—Curved tiles—Greek form—Roman form—pan-tiling—Hips and ridges—Valleys and gutters—Practical suggestions,