FLOOR (AS., led. //fir, (ler. nor, Ir., Gael.
Corn. /or, Welsh //o/cr, Bret. tear; ultimately connected with OPruss. plonis, barn-floor, Lill'. Flom's, flat, Lat. pianos, level. Gk. 71-XaZ, plax, level surface). The horizontal partition between the stories of a building; the upper part of which forms the floor of the apartments above, and the lower portion the ceiling of those below. The ground floor of barns and such structures is but slightly raised above the ground level, thus being distinguished from pavements, which are laid solidly on the ground. In its narrowest sense, it is merely the lower visible surface of any interior or even of a bridge, a platform, balcony, etc., without reference to the supporting structure.
Floors are variously constructed, according to their dimensions, to the weight they have to sustain, and to the character of the buildings. The supporting structure may be a vault of masonry, a eomhination of iron beams with brick arches or other non-combustible filling, or a series of parallel wooden beams called joists. The last is the common construction, except for im portant and fireproof buildings. Single-joisted floors are the simplest and most cheaply con structed, and are used for ordinary buildings, where the distance between the bearings does not exceed 20, or, at most, 24 feet.
,Joists are beams laid edge upward, and rest ing, at their ends upon wall-plates built into the walls. Their width should not be less than two inches, for if narrower, they would he liable to split with the nailing of the flooring-boards. They are placed edge upward, in order to econo mize timber, as the strength of a beam to hear a transverse strain varies simply with the breadth and with the square of the depth. When a deep and long joist is used, there is danger of its twisting or turning over; this is prevented by strutting, or cross-bracing, that is. nailing cross pieces of wood between them. or, less effectually, by driving pieces of planking hetween them. Strutting is required when the length of the joists exceeds eight feet. The laths for the ceil ing of the room below are nailed to the bottom of the joists. In good, substantial work, the dis tance between the joists, from centre to centre, is about twelve inches, hut this is usually exceeded in cheaply built houses, where the normal dis tance is sixteen inches.
Double-joisted floors are constructed by laying strong timbers. Killed binding-joists. from wall to wall, at a distance of about six feet :I pa rt. and a double set of joists. one above for the floor, and one below for the ceiling, laid across these, and notched down upon them. latter, When f.ln,s placed, a re cal led bridging joists, as they bridge over the interval between the larger binding-joists. This is adopted when a more perfect ceiling, free from cracks produced by the yielding of the floor, is required, or where there is a difficulty in obtaining a sufficient amount of long timber for single-joisting the whole of the floor. The term doubt. floor is
used of this method as well as of n flooring made of two thicknesses of board or plank. the lower of rough material laid diagonally, the upper of choicer material.
The framed floor is one degree more complex than the double-joisted. Binding and bridging joists are used in the framed floor, but the bind ing-joists cease to be the primary support, as for this purpose strong balks of timbers. called girders, are used. They are laid across, at distances of from eight to ten feet, and the binding-joists aro framed into them by a tusk tenon joint. The bridging-joists are notched to these in the same manner as for double-joisted floors. A bay is the general name for the space between girders; if between a girder and a wall, it is called a toil boy; or between two girders, a ease bay; and the work between is described as a buy of joist lug.
When the space to he spanned is too great for a simple wood girder, trussed or built-up wooden girders or iron girders are used; the latter have, of late, come into extensive use, even whele simple wood girders are sufficient. See OntnER.
With a given quantity of lumber and a mod erate space, the single-joisted flour is the strong est of any. One of its disadvantages is the free communication of sound to the apartment below, unless some additional means of obstructing the sound be adopted. This is partly obviated by the use between the hoards of the double flooring above of felting, heavy building-paper, or the like.
The flooring-boards are usually nailed to the joists, and vary from 1 to 11,/, inches in thickness; for common floors they are from 4 to 8 inches wide, but for better floors a width of only 2 to t inches is used. The advantage of the narrow boards is that the' shrinkage and warping have not so much effect on the spaces between. In all but the commonest houses, the floor is ldind-nailed. This refers to the ordinary deal flooring, used ill modern American domestic buildings. In old English and Continental houses the flooring. in stead of being of thin and narrow matched boards. was of wider heavy plank. The facing of the floor in many old mansions is formed of small pieces of oak carefully inlaid. (See PAR QUETRY. For other kinds of inlaid fancy floors, see MOSAIC: TILE. seetion Encaustic Tiles: ('oN CRETE.) in the old palaces and houses of Italy and many buildings in Frame and 1 k‘rina ny, bricks a re often found in place of wood for all floors, occa sionally replaced by decorative Snell heavy flooring was natural in the Middle Ages. when stone-vaulted rooms were frequent and even concrete floors were used. In fireproof buildings the beams and girders are usually of iron or steel between which are flat arches or brick terra cotta. or concrete slabs on iron plates, bars. or wire netting. See FIREPROOF CONSTRUCTION.