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.
155. In building the roof on a house, the rafters are nearly always carried beyond the front of the plate from 10 to 24 inches, in order that the drip from the eaves may fall clear of the wall of the house. Fig. 67 shows the method of cutting the rafters where they so project, and also a method of finishing and enclosing the rafters, and of forming a standing gutter.
A rafter abefdc is notched over the plate g at cd and projects beyond the plate at df. The portion of the rafter below df is cut away to lighten the appearance of the eaves, and the line on which to cut the rafter for it is shown at mlr, Fig. 65. At h is a tie-beam, which is spiked to the ends of the rafter on each side of the building, and, in this case, forms, also, the ceiling beam of the upper story and rests on the plate g. From the top of the tie the rafter is closely boarded with 1-inch boards k, the lower one of which is allowed to project about half its width beyond the end of the rafter at e i. The end of the rafter is cut on the line ef, which is parallel to the plumb-cut at the ridge, and the soffit, or plancher, j on the bottom of the rafters has its outer edge beveled to the same angle, as is, also, the top of the facia /, which finishes the ends of the rafters. A crown molding m is then secured in place by nailing it to both the projecting roof-board k and the front of the facia /. This gives a finish to the projecting eaves, and the under side is completed by the insertion of the molding o between the soffit j and the frieze, or top casing, n. This finish is usually called a box cornice, in that it is formed by a boxing, or casing, of wood. Over the roofing boards, and outside the line of the front of the building, a bedplate p is nailed securely to each rafter, to form the gutter, as will be explained further on.
156. Roofs are variously covered with wood shingles, steel shingles, slate, tin, lead, zinc, corrugated iron, copper, or tiles. A flat roof should always be covered with tin, copper, or other material which is practically one piece, as water will run back between the joints of shingles, slates, or tiles, and thereby get into the interior of the building. A pitched roof may be covered with any of the above materials, but generally shingles, slate, or tiles are used.
157. Shingles are laid on the roof of the house, either upon sheathing boards, as shown at k, Fig. 67, or upon shingle laths, as shown at v. The latter method is preferable, as it gives better ventilation to the under side of the shingles and prevents the accumulation of moisture there. When boards are used as a roof covering upon which shingles are to be laid, they should not be laid close, as at k, except over the eaves. Shingle laths, shown at v, are usually 11/4 in. X 2 in., or 1 1/4 in. X 3 in., and are laid at right angles to the rafters, and from 4 inches to 8 inches on centers, according to the exposure of the shingles to the weather. The amount of this exposure also determines the length of shingles which can be used with the greatest economy of material consistent with first-class work.
Shingles vary in length, and can be obtained in regular sizes of 16 inches, 18 inches, 24 inches, and 27 inches in length, and from 4 inches to 7 inches in width. The size to be used in each case should be about 3 inches longer than three times its exposure to the weather.
The first course of shingles is laid at the eaves, and is laid double with broken joints, as at u, Fig. 67, in order that water finding its way through the joints of the upper layer, may not readily percolate through the lower layer and rot the roofing boards, facia, etc.
When the first course is laid, each shingle is nailed with two nails about 2 inches above the upper line of its exposure; the amount of exposure is then measured back from the lower, or butt, edge of the shingles, and a line is struck by means of a chalked cord, to which line the butts of the next course are laid, as at w. This protects the nails driven in the previous shingles by the 2-inch lap shown at z w, and the nails of the second course pass, also, through the upper ends of the first course, as at z'.
158. After the shingling is completed up to the gutter plate p - which, in this case, requires but two courses - the gutter face board q is set in place with its lower edge beveled to fit the top of the shingles; a plinth e' a cap member c', and bed mold d', may now be nailed in place.
In lining the gutter with copper or tin, it is well to nail a strip of hoop iron along the edge of the cap c', allowing the lower edge to project below the cap. To this edge the metallic lining may be clasped, from which point it extends across the bed of the gutter to b' and up as far as a'.
In starting the course of shingles above the gutter, care must be taken that the butts are placed somewhat higher than the overflow of the gutter, so that they will be clear of the water when the gutter is choked; it is well to have the metallic lining extend for 5 or 6 inches under the shingles. When the first course of shingles above the gutter is laid, the course is doubled for the same reason that it is at the eaves, and the remainder of the roof from here up to the ridge is shingled, one course at a time, as explained above.
159. Another form of gutter is shown in Fig. 68, where the end of the rafter is cut out at a bc, and a short piece of timber d is spiked on the side of the end, as shown, to form the front edge of the gutter depression, while the back of the gutter is formed with a piece of 1 1/8-inch plank spiked on the end of the rafters at a b.
The lining of the gutter or flashing fgh is then bent in place and turned over the roof-board m and around the fillet of the molding /, where it is held in place by being clasped to the edge of a strip of hoop iron, previously attached to the fillet. The back of the lining is turned under the shingles at /"and the first course of shingles n. is laid so that the butts project 1 inch to 1 1/2 inches over the edge of the gutter.