This section is from the book "A Treatise On Architecture And Building Construction Vol3: Stair Building, Ornamental Ironwork, Roofing, Sheet-Metal Work, Electric-Light Wiring And Bellwork", by The Colliery Engineer Co.. Also available from Amazon: A Treatise On Architecture And Building Construction.
28. Window sills are made of sheet metal to represent cut-stone sills. They should be filled in behind with timber of the proper size. The metal sills are usually slipped over the wood backing and secured to the wall by nailing closely through the flange a, Fig. 16, which extends along the bottom and up the sides. The top flange b is made wider than that at a; it is nailed against the window frame and is bedded in white or red lead to make it watertight. A better plan, however, is to bed the window frame over the metal sill with red or white lead, the metal being flanged and passing up into the groove c. Metal window sills are generally used on galvanized-iron fronts. Copper is seldom used for this work.
29. Window lintels are covered in a similar manner, the chief difference being that the top flange of the lintel is overlapped by the metal siding above it. The soffit of the lintel flanges down against the top of the window frame and is nailed to it. Particular care, however, should be taken to have a well inclined wash on the lintel. Horizontal surfaces, particularly pocketed surfaces, are very objectionable and should always be avoided.
30. The covering of bay windows, architraves, pediments, etc. depends altogether upon the design. An important point to be considered in the line of sheet-metal work for bay windows, pediments, etc., is the provision for lookouts and other projections to which the cornice and other moldings must be attached. Small moldings are usually planted on the flat, sheathed surfaces, while lookouts are required for the cornice and other large projections. It is advisable, on all the work, to provide solid backing for the sheet metal. When wooden lookouts are used, they should be so made that the metal work can be nailed across the grain of the wood, not with it. The expansion and contraction of the metal soon draws out and loosens all nails which are driven in the direction of the grain.
31. Window caps, like all other ornamental parts of sheet-metal work, are made up from stock sizes and shapes of bent or stamped sheet metal. Fig. 17 shows a sheet-metal window composed of an architrave a, a frieze b, and two impost blocks c, c supported by brackets or trusses d. The impost blocks support the pediment e, and a counter-flashing at f makes the top water-tight against the brick wall. If the cap is put on after the walls are up, it is customary to secure it in place against wooden lookouts, as shown at b, Fig. 18. Furring strips a, a are nailed to soft pine plugs, previously driven into the wall, and the lookouts b, Fig. 18, are set about 1 foot apart along the line of the furring strips and nailed to them. Two special lookouts are secured to support the trusses. The sheet-metal cap is then set over the lookouts and is rigidly nailed to them. The metal is extended under the soffit of the lintel and flanged down against the hanging tile of the window frame, and is neatly finished with an angle molding bedded in white lead and well nailed in place. The wash c of the cornice is turned up against the wall and is counterflashed in the usual manner.
If the wall has not been built, it is advisable to use iron lookouts and build them in the brickwork when the wall has been brought up to the proper height. The upper surface of all window caps, sills, and cornices should be carefully protected during the erection of the building. Every window cap, and indeed every other projecting molding or cornice, should be closed water-tight on top with a sloping deck or wash, and should be sufficiently strong for a man to walk along the projection.