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.
32. The methods of laying shingles generally in use are: (1), on shingle lath; (2), on boarding without paper or felt; and (3), on matched boarding and lath with felt.
The first method is, no doubt, the best, though generally used only on cheap buildings. In more expensive houses, the requirements usually call for a matched-board roof, which prevents the free passage of air, and causes the shingles to rot.
33. To lay shingles according to the first method, commence at the eaves and lay from one to three hemlock boards 10 inches wide. The advantage of using more than one board is, that, if it becomes necessary to walk on the eaves of the roof to make repairs, the shingles will not be so readily broken. In the valleys formed by the main roof and dormers, where not very long, one board, however, on each side is sufficient. These boards also act as a stop to the wind, and, to a great extent, prevent the rain from being blown over the flashing. The same remark applies to hips and ridges.
Each shingle is secured with 2 fourpenny nails, at a distance of about 2 inches above the upper line of the exposure. The amount of exposure or gauge is measured back from the butt ends of the shingles, and a mark is struck with a chalk line, to which mark the butts of the next course of shingles are laid. The heads of the nails are in this manner protected by the laps, and the shingles are further secured by the nails of each succeeding course passing through the heads of the previous course. If the gutter is built on the surface of the roof, as shown in Fig. 32, the butts of the shingles must be placed well up above the overflow line.
34. Around all chimneys, ventilators, skylights, etc., board the roof to the first rafter on each side; and at the back of all chimneys, build in a saddle, as shown at a, Fig. 30, and nail the boards b at each side and at the front
Along the valleys should be placed tilting fillets a, Fig. 31, over which the flashing is formed. Similar tilting fillets should be placed along the upper edge of the gutter just above the overflow.
Gutter linings may with advantage extend several inches up under the shingles. See b, Fig. 32. The valley lining also extends under the shingles 3 or 4 inches, as shown at b, Fig. 31; likewise, the chimney flashing extends 3 or 4 inches at the back and sides of the chimney, and 5 or 6 inches at the front.