This section is from the book "A Treatise On Architecture And Building Construction Vol2: Masonry. Carpentry. Joinery", by The Colliery Engineer Co. Also available from Amazon: A Treatise On Architecture And Building Construction.
This form of gutter is generally invisible from the ground and permits an uninterrupted slope to the roof from the ridge to the eaves, so that accumulated snow may slide off without hindrance, and free the roof of its weight and dampness. It is objectionable, however, in some cases where the eaves project considerably, as will be shown further on, and if it is built up closer to the plate, or above the plate, it materially weakens the rafter. The necessary slope, or fall, of the gutter, in order to cause the water to flow towards the leader end, is accomplished, in this case, by cutting each succeeding rafter slightly deeper than the preceding one.
160. The lining of a gutter should be of the best quality of material, with all the joints properly folded, if of tin, and well soldered. It should be painted on both sides and well fitted to the gutter. The gutter plate p, Fig. G7, is made of a varying width so that the gutter has a gradual pitch towards the leader, or outflow pipe, which is located at the lower end. This leader is usually made of tin, corrugated galvanized-iron, or copper pipe from 2 inches to 6 inches in diameter, according to the size of the roof it must carry the water from; and where the roof area is very great, more than one leader may be necessary to carry off the accumulation of water during a heavy rain. A liberal allowance is to provide 1 square inch of leader section for each 75 square feet of roof area; but never to use a leader less than 2 inches in diameter. Even that size is liable to become choked and clogged with dirt or leaves, if in a wooded section of country, and should be used only for veranda, porch, bay window, and other small roofs.
The leader is inserted through the bottom of the gutter and its metallic lining, and must be well soldered to the latter, while its throat, or inlet, should be countersunk, and protected with an open iron grating-, or wire screen, to prevent foreign substances from entering with the water.
161. Flashing is a term given to all sheet-metal work used in connection with roof covering to insure a watertight condition at joints and angles. Flashings are required on hips, valleys, ridges, and eaves, around scuttles, skylights, gables, flanks of dormer-windows, etc.
162. On hip roofs, where angle rolls are not used, pieces of flashing are laid on the hip over each course of shingles or slate in the same manner that a shingle or slate itself would be laid, if it could be bent to fit around the corner as shown at a, Fig. 69. For, while the joints between the various pieces of roof covering may be broken, or alternated, as at b, in the main flat slopes, the hips must have a continuous row of joints from the eaves to the ridge, as at c, and the insertion of flashings under the shingles, at these points, prevents the water that would work its way beneath the covering from getting into the interior, and carries it to the flat slopes, where it may harmlessly run off.
163. In valleys the means adopted are different, as the conditions are in some respects reversed. On the hip of the roof there is no accumulation of water at any time, and what little may fall there is immediately drained off by the pitch; but in the valley we have a depression between two slopes, and all the water falling on each of them is immediately carried to the valley.
The valley, therefore, acts in the capacity of a gutter, and is flashed accordingly. The tin is joined, generally at the ends, to form a continuous gutter in the depression, and its edges are turned up under the shingles about 6 inches. The shingling is not carried down to the intersection of the slopes, but is stopped about 5 inches from the valley rafter, and the gutter, thereby, is left open. The flashing of all such situations will be treated in detail in Sheet-Metal Work.
164. Along the ridge the roof is rendered water-tight by a number of different methods, two of which are illustrated in Fig. 70, (a) and (b). At (a) is a method used on a shingle roof and requires no flashing, while at (d) a metal flashing is used on a slate, or flat tile, roof. At (a) the ridge plate a is carried above the line of the shingle lath b and the top of the shingles d, and its top is beveled off to conform with the general pitch of the roof. After the shingling is complete, the top of the ridge is finished off to form a continuation of the top surface of the last course of shingles, and the ridge boards c are nailed to it and to each other in the position shown. Before the ridge boards are nailed in place, there should be a layer of two-ply roofing felt folded over the ridge, on top of which the ridge boards may be firmly nailed; this will tend towards making a thorough water-tight job. These ridge boards are usually from 1 inch to 1 1/8 inches in thickness, and from 5 1/2 to 9 inches. in width, according to the amount the shingles are exposed to the weather. The ridge roll e is formed from a single piece of wood, is from 2 1/2 to 3 inches in diameter, and is rebated, or rabbeted, at fgh to fit the angle at the top of the ridge boards; this V-shaped groove, or rabbet, should be deep enough to permit the edge of the roll h to lap well over the joint between the two ridge boards c.
At (b) the slating of the roof m is carried up to the beveled end of the ridge plate k, butting against it as the shingles do in (a), and the wooden ridge roll / is rabbeted over the joints formed at the ridge and the ridge plate. This roll is held in place by long spikes p driven through its top into the upper edge of the ridge plate, and over it is sprung the galvanized-iron covering n, which has been previously shaped to fit the roll and catch the under edge of the last course of slates, as at o.
Ridges, like hips, are very slightly subject to leakage, and, as little water falls on them, and practically none remains after it has fallen, we do not require the same precautions with flashings at these points as we require elsewhere.
165. Around skylights and dormer-windows, where the sill rests on the slope of the roof, flashing is applied so that it extends under the roof covering which is adjacent to the sill, and turns up and over the sill itself in such a manner as will prevent any possibility of water working its way between the sill and the slate or shingles. The sides of a dormer, where they intersect with the roof pitch, are flashed in the same manner as are the valleys, except that the shingling or other covering may be carried up close to the finished sides.
166. Great care must be observed along the eaves of a roof, especially where that roof is over a well heated room, as the interior heat will, during the winter, cause the snow on the roof to melt and run to the eaves, where, relieved from the effects of the high temperature, it freezes and builds up a dam of ice, and the accumulated water backs under the shingles and gets into the house. Under these conditions it is sometimes desirable to build the gutter above the line of the plate, in order that the same heat that melts the snow may sufficiently warm the gutter to prevent it from freezing up when its services are most needed.
Unless the pitch of a roof is at least 45 degrees above the horizontal, there is much danger of leakage during windy weather, as a high wind will drive the water under the shingles and through the first crevice that presents itself. Hence, the importance of exercising the greatest care with all the flashings, and of securing broken joints in each course of shingles.
Shingles with loose knots or open knot holes within half their length of the butt, or shingles that are split, or shaky and liable to split, should be rejected, and rejected shingles should be broken or cut through with the hatchet, lest some other workman, with less precaution, be inclined to use them. The slight apparent waste thus caused is nothing compared with the expense and inconvenience of a leaky roof.