A much better way is to use two joists far enough apart to project a little on each side of the partition, as shown at AA in Fig. 144, and thus afford a nail ing for the finished flooring. These joists must be large enough to support the weight of the partition without sagging any more than do the other joists of the floor, and, therefore, joists 3 or even 4 inches thick should be used. They should be placed about 6 or 7 inches apart on cen ters, and plank bridging should be cut in between them at inter vals of from 14 to 20 inches, as shown at E in Fig. 144, in order to stiffen them and make them act together. This plank bridging should be made of pieces of joist 2 inches thick and of the same depth as the floor joists, and should be so placed that the grain will in every case be horizontal.
A partition, supported as described above, is bound to settle somewhat as the 10 or more inches of joist beneath it shrinks in seasoning, and the settlement may cause cracks in the ing at the corner between the partition and an outside wall. In order to prevent this ment, partitions running allel with the floor joists are often supported on strips which are secured to the under side of the floor joists, as shown at A in Fig. 145. These strips can not be allowed to project into the room below, and so they must be made as thin as is consistent with safety. Strips of iron plate about inch thick and wide enough to support the partition studs are, fore, used for this purpose, and are fastened to the joists by means of bolts or lag screws. Partitions which run at right angles to the floor joists can also be supported in this way. If a partition runs at right angles to the joists near the center of their span, the tendency for the joists to sag under it will be very great, and they must be strengthened either by using larger joists, or by placing them closer together. If the span of the floor joists is large and the partition is a heavy one, it may be necessary to put in a girder running at right angles to the joists to carry the partition. In this case the partition stud will set directly on the girder, which may be a large timber, or in some cases, a steel I-beam.
Headers and Trimmers. Another case where a girder may be necessary in a floor above the first, is where an opening is to be left in the floor for a chimney or for a stair well. The timbers on each side of such an opening are called "trimmers," and must be made heavier than the ordinary joists; while a piece called a "header" must be framed in between them to receive the ends of the joists, as shown in Fig. 146. The trimmers may be made by simply doubling
up the floor joists on each side of the opening, or, if necessary, I-beams or heavy wood girders may be used. In most cases these trimmers may be built up by spiking together two or three joists, and the header may be made in the same way.
Joist Connection. With Sill.
Joists are also "gained" into the sill, as shown in Fig. 94, in which case a mortise is cut in the sill and a corresponding tenon is cut in the end of the joist. The mortise was illustrated and described in connection with the sill, while the end of the joist is cut as shown in Fig. 94, the tenon being about 4 inches deep and gained into the sill about 2 inches. This brings the bottom of the joist flush with the bottom of the sill, and the top of the joist somewhat above the top of the sill, according to the depth of the joist. The top of a 10-inch joist would come 4 inches above the top of a 6-inch sill, and the joist would rest partly on the masonry wall, thus relieving the connection of a part of the stress due to the weight of the loaded joist. A common but very bad method of framing the joist to the sill is simply to "cut it over" the sill without mortising the latter, as shown in Fig. 147. This does not make a strong con nection even when the joist rests partly on the masonry wall; and if it is not so supported it is almost sure to fail by splitting, as shown in Fig. 14S, under a very small loading. In fact, it would be much stronger if the joists were turned upside clown. Frequently the joist is cut as shown in Fig. 149, where the tenon is sunk into a mortise cut in the sill, thus bringing the top of the joists flush with the top of the sill; but in this case the bottom of the joists will almost invari bly drop below the bottom of the sill and the wall must be cut away to make room for it, as shown in Fig. 140. It is also weak in the same way as is the connection shown in Fig. 14S.
With Girders. The framing of the joists into the girders may be accomplished in several ways, according to the position of the girder. The placing of the girder is quite an important point. The top of the floor, on which rest the sole-pieces of the cross-partitions, must remain always true and level, that is, the outside ends of the joists must be at the same level as the inside ends. Otherwise the doors in the cross-partitions will not fit their frames, and can not be opened or shut and the plastering is almost sure to crack.