Roofs. Roofs are of various kinds or classes, as " lean-to" or "shed" roof, "span" or "couple" roof, "collar-beam" roof, "king-post" roof, "queen-post" roof, "mansard" or "curb" roof, the "conical" roof, and the "high-pitched" or "Gothic" roof. These we shall illustrate and describe in their order. The simplest form of roof is that we have first named - the "lean-to" or "shed," illustrated in fig. 233 - in which rafters a a are placed parallel to one another - about 14 inches to 18 inches from centre to centre - and rest upon the front wall b at their lower end, and are built into, or rest upon, the brick wall c c at their upper end. In some cases " wall plates," as d and e, are employed upon which to rest the ends of the rafters a a; these wall plates run along the whole length of the wall, being built into the same. This form of roof is used only for narrow spans, and where the roof covering is to be light, as asphalte or tar coating. Fig. 234 illustrates a form of " lean-to " roof a little more complicated, and calculated for wider spans than that in fig. 233; in this a new member is introduced, namely, the " tie beam " a a, resting at its extremities upon the wall plates b b, and to which the lower end of the rafters c c is notched (see Joints of Timber), the upper end resting upon the wall plate d, the gutter being formed at e, behind the parapet / of the front wall. In fig. 235 a still stronger form is shown ; in this four new members are added, namely, the " king post" a, the " brace " or " strut" b, the " purlin " c, and the " common rafter" d. The brace b butts at its lower end against the foot of the rafter a, and at its upper against the under side of the " principal rafter" e e, the upper end of which butts against the upper end of the king post a a, the lower on the tie beam f.f, which again rests upon the wall plates g g, h h being the gutter, or simple form of what is known as the " bridged gutter." Another form of gutter, and the most usually adopted, being that shown at f in fig. 233. The " purlin " c is notched into the upper side of the principal rafter, and runs parallel to the wall plates the whole length of the building, sometimes projecting beyond the gable walls of the same. The office of the purlin is to bear up the pressure of the "common rafters" d d, upon which the boarding or slates and tiles are placed. In fig. 235 we meet with the elements of the "truss," an arrangement by which pressures are sustained. The tie beam runs at right angles to the walls, the principal rafters the same, the purlin and wall plates parallel. These members make up what is called the truss, and which support the common rafters and the roof covering. The "trusses" are placed upon the walls at distances usually of ten feet, as at i i, fig. 235, the common rafters being placed between them, as j, resting on the upper sides, and also borne by the purlin k k, the distances between the common rafters being 14 inches.
In fig. 236 we illustrate a form of "double lean-to roof,' which may be called the " weaving-shed roof," as it is almost universally used for that class of building, the whole length of the side a a being glazed or fitted up with windows to throw the light upon the ranges of looms below, no light being on the side b.
" Span Roof, or Couple Roof" - The simplest form of roof of this kind is shown in fig. 237, in which the rafters a a, b b simply butt against each other at the apex c, and rest upon the wall or wall plates d d. This form of span roof is strengthened by the addition of the member a a, fig. 238, called a "collar beam," hence the roof is named a "collar-beam roof;" of this kind another modification is shown at fig. 239, in which "purlins" a a are used, and a second short collar beam b nearer the apex than the beam c. In fig. 240 another form of span roof is illustrated, in which the " rafters" a a, b b are supported by the " braces " or " struts " c c, which butt at their lower end against the "straining cill" or "straining piece " d d. In place of the rafters at their apex simply-butting against each other, as at/ f, or being crossed, as at g, and nailed together, they usually butt against a flat piece of timber d d, which is called the "ridge pole" or "ridging piece." The rafters, also, in place of simply resting upon the end of " tie beam " h h - another new member in this form of roof - rest upon what are called " pole plates " e e, which are notched into the "tie beam," and run parallel to the wall plates the whole length of the building. In fig. 241 another form of span or " collar-beam " roof is shown, in which the purlins a a, and the "collar beam" b support vertical uprights c c to form a ventilator in the roof. The sketch d shows a method of forming the gutter (see Gutters). We now come to the " king-post" roof, in which the " truss" for the first time is fully exemplified: this is illustrated in fig. 242, in which a a are the 9" side "walls;" b b the "wall plates," 4" x3"; cc the "tie-beams," 9"x4"; d the "pole plates," 4" 4"; ee the "principal rafters," 6" x 3"; f f the "struts" or "braces," 3½ x 2½"; g the "king post," 5" x 3"'; h the "purlin," 8"x 3"; i the "common rafters," 3½" x 2"; j the "ridge pole," 8" x 1½". The tie beam, principal rafters, king post, and struts, form what is called the " truss," and support the common rafters with their roof covering, as of slates, tiles, etc. The trusses are placed in the wall at distances varying from 8 to 12 feet - the average is 10 feet - the spaces between being filled up, as already explained, by the " common rafters," resting partly on the " principal rafters," and between these partly on the "purlins." In fig. 243 we illustrate the "queen-post roof" In this what may be called two king posts, as a b (one only in diagram), are placed some distance apart, so as to afford a space, as c, between them, which space might be used as an apartment; these posts, as a 6, are in this form of roof, however, called "queen posts," they are separated or kept out at the top by the " straining beam" d, and at the foot by the "straining sill" e, f the "struts" or "braces," g the "principal" or "common rafter." In the lower part of the same figure, in A, we give a diagram of a queen-post roof with two queen posts a b, and in diagram B one with three queen posts; the diagram in B will be adapted for a 60 feet span, of which the scantling of the timbers will be as follows: - Principal rafters, 8" x 6"; common rafters, 6" x 3"; purlins, 9f" x 6"; wall plates, 8" x 6"; tie-beams, 15" x 10"; queen posts, 10" x 8"; small do. (b and c), 10" x 4"; straining beam, 11" x 6"; braces, 6" x 3", this being adapted for wider spans than the upper figure. In fig. 244 we illustrate another form of queen-post roof. In