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.
In finishing against open valleys, care should be taken to cut the shingles parallel to the line of the tilting fillet, or the result will be a wavy line.
In constructing close valleys, the shingles are interwoven with metal sheets (see Fig. 33), and are mitered in the angle. The shape of these sheet flashings will vary with the pitch of the roof, if it is desired to make the lower edges of the sheets parallel with the butts; but this is not necessary, as square sheets will serve the same purpose, provided they are properly lapped.
The general manner of constructing this valley is as follows: A row of shingles should be laid each side of the valley, aclear space of 1/2 inch being kept between the miter edges as shown at b, to allow for expansion. The gauge should then be measured, and the flashing set, as shown at c, to the line so obtained; the next course of shingles, as shown at d, covers the metal entirely, and each ascending flashing will be covered in like manner. This gives a tight valley and is used more on account of appearance than durability; for the snow and rain keep the shingles damp, consequently causing them to rot before the rest of the roof.
36. This method, applied to the hips of roofs, is shown in Fig. 34, a being the flashing laid in with the shingles. While not prolonging the life of the shingles, this no doubt makes the most weather-proof hip except a metal roll. The roll, however, never looks well, and on that account should be avoided.
37. The method known as the Boston hip is very effective and neat, and under ordinary conditions, especially on a very steep roof, is sufficiently weather-tight for all purposes. Shingles of a uniform width of, say, 5 inches, should be selected. A chalk line is snapped on either side of the hip, about 4 1/2 inches from its center and parallel to it. See a, Fig. 35.
The slope shingles should be carried up to this line, stepping back to allow the hips to be laid last. Lay a shingle on the roof with its edge at, and parallel to, the hip line, and the lower corner of its butt just touching the butt of the shingle below it, as shown at b. Across it, and at right angles to the eaves, draw a line for the vertical side cut, as at c. Slightly taper the side d to heighten the effect of a hip roll, and to allow the next hip shingle above to slightly project over and cover the end of the vertical side cut. Fit the slope shingle to the side or vertical cut, and nail the hip shingle in place. Now repeat this from the other side, laying the edge of the shingle flush with the upper and outside edge of the first shingle, obtaining the side and butt cuts in the same manner as before; the third shingle is laid on the same side as the first, with the hip edge flush with the outside edge of the second, and the fourth from the side of the second; continue thus, laying alternately, until the hip is completed.
One of the chief advantages of this method is, that the grain of the wood runs with the hip, and the tendency to curl is taken away from the line of the hip to the side of the shingle.
The appearance of the roof may be improved, and the drip over the gables may be stopped, by putting a tilting fillet up the rake, running the shingles up on it as at a, Fig. 36, and cutting the ends of the shingles at an angle of 45° to the side joint, as shown at b.
38. There are three methods of finishing the ridge of the roof. The first consists of laying over the last row of shingles but one, a metal flashing, as at a, Fig. 37, which extends on each side of the ridge to the depth of the last row, after which the last row of shingles may be laid and the ridge capped with a ridge saddle of white pine 1 1/4 inches thick. The first side c is put on flush with the ridge and opposite side of the roof, and the finished piece is put on with a lap of about 1/2 or 3/4 inch, as shown at d.
The second method [see (a) Fig. 38] consists of the two ridge pieces a, a, one being the thickness of the board wider than the other, laid over two pieces just the thickness of the shingles, which are first nailed to the roof-boards, and against which the shingles abut. The top of the ridge piece is capped with a wooden roll b, Fig. 38. No metal flashing is required, as the roll effectually covers the joint. The third method [see(b), Fig. 38] is similar to the second, except that the wood roll is covered with a galva-nized-iron or copper roll and wings pushed over it. Galvanized nails are driven into the roll, near the wings, to keep it in place; lead is also used for the same purpose.
39. The second method of laying shingles is that of laying them on boards, which cover the entire surface of the roof. The boards should not be set close together, as they would then prevent the passage of air, stop ventilation, and cause the shingles to rot. This process of rotting arises from the warm air of the rooms below condensing when it comes in contact with the roof, making it wet, or resulting in what is called "sweating." It is also caused by capillary attraction acting through the butt ends of the shingles.
40. The third method of laying shingles (see Fig. 39) is on matched boarding a covered with roofing felt b; the lath c is then nailed on, the same as in the first method, and the shingles are laid on the lath.
This method makes a very good roof, when the spaces between the ends of the lath are left open at the gables for ventilation; but when closed, as is usually the case, makes the poorest roof of all, as the closed air space only increases the condensation and hastens the destruction of the roof.
41. In laying shingles on a roof, the best results are obtained, and their endurance, which is the chief point, is vastly increased by setting the shingles from 3/16 to 1/2 inch apart. This allows the water to drain off rapidly, dries the roof quickly, and also allows for expansion and prevents buckling. Where narrow shingles are used, the joints should not be less than 1/8 inch; while for shingles over 5 inches in width, from 1/4 to 1/2 inch joints should be allowed.
42. For covering conical roofs, the shingles should be selected in three or four widths, the largest butts being 5 inches at the gutter, and the smallest, 2 inches at the top. (See a, b, c, d, Fig. 40.)
To keep the shingles true to the radial lines, and the butts in line with the horizontal curves or courses running around the tower, a nail is driven into the center of the apex post e, to which a cord is attached. The starting course is laid horizontal with the eaves, the next gauge is laid off, and a shingle g is tacked in place. The cord is held to a joint of the first course under the tacked shingle, and a line is drawn through the center of the shingle g vertically; the cord is then moved to the outside corner of the butt, first on one side h, and then on the other side z: the side or taper lines h j and i k being drawn will be radial to the center of the apex, as shown by the plan l. The shingle, cut to the lines marked, will form a templet for the first course. The shingles with 5-inch butts should be laid first, then the 4-inch, and so on until each lot is used, making a new templet as often as the joints begin to come too close.
This mode of application should be continued until the base of the finial is reached, when the apex should be flashed with tin if a wooden cap is to be used. If, however, a sheet-metal finial is required, the flashing may be omitted.
43. The gauge, or exposure to the weather, of a shingle is obtained by subtracting the lap from the length and dividing the difference by 3. Thus, for a shingle 18 inches long, and with a 3-inch lap, the exposed length will be 18 inches - 3 inches = 15 inches, which divided by 3, will give 5 inches. The number of inches exposed to the weather multiplied by the average width of a shingle gives the area of the exposure; dividing 14,400 (the number of square inches in 100 square feet) by the area of the exposure gives the number of shingles required to cover 100 square feet of roof. The average width of a shingle is, for example, 4 inches, and if exposed to the weather 4 inches, the area of exposure is 16 square inches; now 14,400 square inches divided by 16 gives 900, the number of shingles required per square.
44. The following table is arranged for shingles from 16 to 27 inches in length, and based on a given exposure to the weather: