girders (fig. 26). The bearings of the joists on the wall also rest on wall plates, so as to get a level bed, and are sometimes notched over them. Wall plates, which are usually 412 in. × 3 in. and are bedded on walls in motar, take the ends of joists and distribute the weight along the wall. The plates bolted on the side of girders are of sizes to suit the width of the flanges.
The medieval floor (fig. 27) consisted of the framed floor with wood girders, binding, bridging and ceiling joists; and the underside of all the timbers was usually wrought, the girders and binders being boldly moulded and the other timbers either square or stop chamfered.
Flooring is strengthened by the use of strutting, either herring-bone (fig. 28) or solid (fig. 29). Herring-bone strutting consists of two pieces of timber, usually 2 in. × 2 in., fixed diagonally between each joist in continuous rows, the rows being about 6 ft. apart. Solid strutting consists of 114 in. boards, nearly the same depth as the joists and fitted tightly between the joists, and nailed in continuous rows 6 ft. apart. Where heavy weights are likely to be put on floors long bolts are passed through the centre of joists at the side of strutting; since this draws the strutting tightly together and does not produce any forcing stress on the walls, it is undoubtedly the best method.
Floors are usually constructed to carry the following loads (including weight of floor):—
Residences, 114 cwt. per foot super of floor space.
Public buildings, 112 cwt. per foot super of floor space.
Factories, 212 to 4 cwt. per foot super of floor space.
Local By-laws.—With regard to floor joists in domestic buildings, the following are required in the Hornsey district, in the north of London. The size of every common bearing floor joist up to 3 ft. long in clear shall be 3 in. × 212 in.; from 3 ft. to 6 ft. in clear it shall be 412 in. × 3 in.; from 6 ft. to 8 ft., 612 in. × 212 in.; from 8 ft. to 12 ft., 7 in. × 212 in., and so on according to the clear span. The Hornsey by-laws with regard to trimmers are as follows:—A trimmer joist shall not receive more than six common joists, and the thickness of a trimming joist receiving a trimmer at not more than 3 ft. from one end and of every trimmer joist shall be 1⁄8th of an inch greater than the thickness for a common joist of the same bearing for every common joist carried by a trimmer. For example, if the common joists are 7 in. × 212 in. and the trimmer has six joists trimmed into same, the size of trimmer would have to be 7 in. × 314 in. The Hornsey council also requires that the floor boards shall not be less than 78ths of an inch thick.
There is little difference in the requirements of the various localities. For example, the regulations of the Croydon council require that every common bearing joist for lengths up to 3 ft. 4 in. in clear shall be 3 in. × 212 in.; for lengths between 3 ft. 4 in. and 5 ft. 4 in., 4 in. × 2 in.; for lengths between 5 ft. 4 in. and 7 ft. 4 in., 4 in. × 3 in.; and so on according to the clear span. The Croydon by-laws with regard to trimmers are as follows:—A trimmer joist shall not receive more than six common joists, and the thickness of a trimming joist shall be 112 in. thicker than that for common joists of the same bearing, and the thickness of a trimmer joist shall be 14 in. thicker for every joist trimmed into same than the common joist. For example, if the common joists are 4 in. × 3 in. the trimming joists would have to be 4 in. × 414 in., and the trimmer joist would have to be 4 in. × 412 in.
Partitions.—Partitions are screens used to divide large floor spaces into smaller rooms and are sometimes constructed to carry the floors above by a system of trussing. They are built of various materials; those in use now are common stud partitions, bricknogged partitions, and solid deal and hardwood partitions, 412 in. brick walls or bricks laid on their sides, so making a 3 in. partition, and various patent partitions such as coke breeze concrete or hollow brick partitions (see Brickwork), iron and wire partitions, and plaster slab partitions (see Plasterwork).
There are two kinds of stud or quarter partitions, common and trussed.
Fig. 30.—Common Partition.
Common partitions (fig. 30) simply act as a screen to divide one room from another, and do not carry any weight. They weigh about 25 ℔ per foot superficial including plastering on both sides, and are composed of 4 in. × 3 in. head and sill and 4 in. × 2 in. upright studs; Common partitions. 4 in. × 2 in. nogging pieces are fitted between the studs to keep them from bending in, and are placed parallel with the head, usually 4 ft. apart. Where door-openings occur in these partitions the studs next the opening are 4 in. × 3 in. Should the floor boards have been laid, the sill of the partition would be laid direct on them, but if the partitions are erected at the time of building the structure the sill should either rest directly over a joist, if parallel with it, or at right angles to the joists; should the position of the sill come between two joists, that is, parallel with them, then short pieces called bridging pieces of 4 in. × 2 in. stuff are wedged between the two joists and nailed to carry the sill.
Fig. 31.—Trussed Partition.
Trussed partitions (fig. 31) are very similar to the last, but they are so built as to carry their own weight and also to support floors, and in addition have braces; the head and sill are larger, and calculated according to the clear bearing and the weight put upon them. Trussed partitions. There are two forms of trussing, namely, queen post (fig. 32) and king post (fig. 33).
Bricknogged partitions are formed in the same manner as the common stud partition, except that the studs are placed usually 18 or 27 in. apart in the clear instead of 12 in., and the 18 and 27 in. widths being multiples of a brick dimension, they are filled in with brickwork 412 in. thick and Brick-nogged partitions. always built in cement. These are used to prevent sound from passing from one room to another, and also to prevent fire from spreading, and are vermin-proof. Another method is to fill the space between the studs with coke breeze concrete instead of brickwork.
Timber partitions have the advantages that they are light and cheap and substantial, and the disadvantages that they are not fire-resisting or sound-resisting or vermin-proof; they should never be erected in damp positions such as the
