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.
Hips in slate should be finished the same as described for shingle roofs. If a roll is applied, the simple method shown at Fig. 99, with a short flat wing, will serve all purposes and will give a neat finish.
Where a slate roof finishes against a parapet, gable, or other wall of brick or stone, there should be provided both flashings and counterflashings, the flashings to be cut in short lengths, 2 inches longer than the unexposed part of the slate, and to be laid as each course of slate is put on, as shown at a, Fig. 101. This flashing should have a lap on the roof equal to the width of half a slate, and should turn up against the wall at least 4 or 5 inches. The flashing against the wall must not then be nailed, for if the roof settles, the flashing will lift the slate or break them. This flashing is sometimes called a "soaker." The counterflashing b, which covers the soaker flashing, is either let into a raglet cut 1 inch deep in the stone or stepped into the joints, as shown. This stepped counterflashing is secured at the top by wall hooks, and the joints are well pointed up with elastic cement.
When lead is used for flashing instead of tin, zinc, or copper, it should not weigh over 5 or 6 pounds to the square foot, as the thickness will give an uneven appearance to the slate.
124. Colored or ornamental slate should be used with great care, as color never increases the utility of the roof and is more likely to spoil an otherwise respectable roof by a poor and gaudy design, while the cutting of the slate to any shape that tends to carry away the water from the joints, as before described, is the only recommendation for ornamental forms. Colored slate is necessary for certain buildings, but the color should be uniform.
In slating curved surfaces, follow the directions given for shingle roofs, commencing at the lower course, with slate from 6 to 10 inches wide, and gradually taking off until a slate 2 inches in width is reached. This is about the limit that will safely cover a nail hole and keep the weather from affecting it; even with this width the upper courses should be well bedded in slater's cement (which is generally composed of paint skins and refuse lead), as should also all hips, ridges, and joints around chimneys, bulkheads, gables, and parapet walls.
125. The nails used for slating have large, flat heads, so that they may get a good hold on the surface of the slate. The proper length of a nail is twice the thickness of the slate, plus the thickness of the boarding or lathing; this length will give the full amount of hold that can be secured. The nails generally used are threepenny, which are 1 1/8 inches long, and fourpenny, which are 1 3/8 inches long.
126. Slating is calculated by the square of 100 square feet. To ascertain the number of slates of a given size required per square, subtract 3 inches from the length of the slate, multiply the remainder by the width and divide by 2; this will be the number of square inches of roof covered by the gauge of each slate. Then divide 14,400, the number of square inches in a square, by the number of square inches covered by each slate, and the result will be the number of slates required for a "square" of roof.