The Parisian Method of Flooring differs raclicall).• from that generally adopted in other countries. It aims to secure in the solid mass of the walls the support of the girders which sustain the floor, and, while the floor itself is framed, it is said that boarded floors are not to be found in anv of the dwellings of Paris except those of the most costly description. Whether the floors are boarded or not, the flooring joists are as completely COY ered on the upper side with a coating of mortar as the ceiling below is cov ered with a coating of plaster. In the principal portion of the space adja cent to the joists rough battens are placed as close together as they will lie, and on this foundation, which serves a purpose analogous to that served by laths in interior walls, floor-mortar is spread to a thickness of about 3 inches; and, as a compact combination occurs to a considerable extent in the entire mass between the ceiling and top of the floor, it may be said that different stories are separated rather by a wall than by such materials as usually separate the different stories of American buildings. The result of the Parisian system is a firm floor, upon which paving-tiles are generally laid in ordinary dwellings. The safeguards against the communication of fire and of sound are increased by this additional precaution, and an inde structible floor is provided. In applying larg-e quantities of mortar to the foundations of floors, special efforts should be made to guard against the effects of expansion. Modern practice in Paris in reference to floors is to use wrought-iron joists rolled in I-, T-, and I-forms, and to fill in with strong mortar or plaster. Details will be more particularly described in the discussion of iron structures. In some cases, to lighten the aggregate weight of the structure, earthen pots have been placed between the joists, and the spaces filled with mortar.
Roof Construction in word " roof" is used to express the covering that is designed to protect the interior of any building from the weather. In carpentry the term "roof" is restricted to the framework upon which an external coating- is secured, which in large buildings is per haps the highest triumph of applied science displayed in the edifice.
Considerations in Roof means of supporting this outer covering of roofs is the chief consideration in their construction, and in making the plan it is in the first instance necessary to decide upon the general form and the angle at which the surfaces should stand; in the next place should follow the consideration of the construction of the timber work which serves as the support of the covering itself, the boarding, the dimensions, particularly the depth of the building, the dimensions of cer tain of the inner apartments, the position of such inner walls as have a modifying influence, etc. Framework in timber has until the recent sub stitution of iron been almost the only method of forming roofs, and the object has been to arrange the timbers so as to combine the greatest strength and stiffness with the least \\Tight of material, avoiding lateral strain or thrust upon the supporting walls, and so as to present two or more inclined planes for the slopes of the roof over the enclosed space.
Fornzs of in general, notwithstanding the great variety in shape and appearance, may be reduced to two kinds—the lean-to and the saddle roof. The simple form known as the " lean-to," or shed roof, was primarily constructed by merely laying pieces of wood across in the position of an inclined plane, in order to throw off the water. Both of these classes of roof may, however, when presupposing the simple right angled ground-plan, terminate at the sides by gables, or be hipped—that is, sloped—on the narrow sides. Figure 19 (j5/. 3) represents the saddle roof with gables at the sides, the gable in the middle not being- taken into account. The line at the top, which is common to both surfaces, is called the " ridge " of the roof. In Figure 2o is exhibited the example of a sim ple hipped-saddle roof erected upon a right-angled ground-plan. It shows four oblique lines of intersection or hips, besides the ridge. The slopes are triangular surfaces, while the others have the form of the parallel trape zitini. Figure 21 (i5i. 3) ShOWS the pavilion-roof, a special form of the hipped roof suitable for square or polygonal ground-plans. All the connecting roof-surfaces are triangular. Steep roofs of this class, when erected upon towers, are usually called " spires." Figure 22 represents a flat-topped roof which might be described as formed by cutting off a sloped or hipped roof horizontally. All the surfaces have the form of the parallel trapezium. The platform is not made perfectly horizontal, but is provided with a slight fall ou each side; it is used either to lessen the height of the roof without altering the angle of inclination of the surfaces, or, in the case of an irregu lar ground-plan, to conceal that irregularity', which is then communicated to the platform only. Figure 23 shows the simple lean-to roof with no side slopes; this form is generally used in cases where a building stands with its long side close to a party-line. Figure 24 presents a mansard or broken (curb) roof with a hip-slope. The surfaces here appear broken— that is, the lower portion of the roof is considerably steeper than the upper —a moulding or projection being- placed where the two siirfaces meet.
°Mei- Forms of Roofs.—Besides these varieties, there are roofs with curved surfaces, domes being included in this class. There are also com posite roofs, which are erected over more complicated ground-plans, par ticularly plans with projecting angles, every angle occurring in the ground plan having the effect of making a valley in the roof—for instance, such a valley as is seen in Figure P9—arising from a projection of the building.