93. TUMBLING in a joist, is to frame a joist between two timbers, of which the sides, which ought to be vertical or square to the upper edges, are oblique to these edges.

Figure 5 shows the method of fitting-in a joist between the sloping sides of two others. The first thing done, is, to turn the upper edge of the joist upon the top of the two pieces into which it is to be fitted, and brought over its proper place. The next thing is to turn the joist on its under edge, so as to lie over its place; then apply a rule, or straight edge, ac, upon the side of the one piece where the shoulder of the joist is intended to come; then slide the joist until the line, previously drawn on the upper edge, come to the straight edge of the rule so applied; then draw a line by the edge of the rule. Do the same at the other end, and the two lines thus drawn will mark the bevel of the shoulder of the tenon at each end.

94. It frequently happens, in modern houses, that the flues are so numerous as not to leave space for the insertion of binding or trimming-joists, without either placing them too far apart, or too near to the flues. To avoid this difficulty, we have generally put iron ends to the joists, as shown in figs. 6 and 7, plate XIII. Fig. 7 shows the plan of a joist with the iron plates bolted to it, one on each side; the iron ends, aa, resting upon a short iron plate, bb, inserted in the wall. The wooden joist is cut off so as not to touch the wall. A mortise is made in the joist on each side at c, fig. 6, and each plate is cast with a nob upon it, to insert in these mortises. Fig. 8 shows the inner side of one of the plates. The reasons for placing the bolts, and forming the plate, as shown in the figures, will be understood by considering that the bolt, d, and the ledges bear the whole weight; and that the bolt d being in its place, the one at e is to prevent the plates descending, or turning round on the bolt d: hence, the nearer the bolt d is to the end of the beam the better, and there should be as much distance between the bolts as the nature of the case will allow of.

The same method is sometimes applied to secure the decayed ends of girders, and renders the expensive process of renewing large girders unnecessary.

95. The plans of the floor-timbers for a house, which is called a first-rate house, according to the dimensions specified in the London Building-Act, are shown in plate XIV. Fig. 1 is the plan of the ground-floor, a is the space for the staircase, ce the spaces trimmed for the hearths; the joists, ƒgh and i, are supported by the partitions and the front and back walls. Fig. 2 is the plan of the first floor, fig. 3 the plan of the bed-room floor, and fig. 4 the plan of the attic floor. These plans will afford the Carpenter a tolerable idea of the slight and cheap system of constructing floors adopted for the London houses.

Trussed Girders.

96. It has been shown, in Art. 60, that to render a girder effective without increasing its depth, it must be trussed with a stronger material than wood; and, in plate XV. we show various methods of trussing girders with iron.

Fig. 1 No. 1, shows the arrangement of a truss, consisting of two truss-pieces, a king-bolt, and a tie. The truss-pieces should not be fitted too tightly into the parts of the beam. No. 2 is the plan of a girder trussed in this manner. The sides should be firmly bolted together.

Fig. 2 shows a girder trussed with queen-bolts, the truss being in three parts. When the span exceeds 23 or 24 feet, this species of truss is much to be preferred to the preceding. No. 2 shows the plan.

In all trusses of this kind the tie should be of wrought iron, and the extremities of the truss should extend on to the wall-plates, as shown in these figures; then the floor will remain firm, though the ends of the girder be partially decayed.

Figure 3 is a section of either of the preceding girders at the abutments to a large scale, with one of the bolts. Fig. 4 shows the abutment-bolt, with part of the tie, and of the truss-pieces. Fig. 5 is the king-bolt and part of the truss-pieces to fig. 1.

97. Where there is depth for the purpose a light truss may be framed, as in fig. 6, connected by bolts. The principles of framing trusses have been explained in Art. 63, and plates VII. and VIII.

98. In order further to illustrate this interesting subject, we have procured a drawing of the girders used for the large room over the Riding-School of the Horse Bazaar, King Street, Portman Square; the span being esteemed the largest in Britain. Fig. 1, plate XVI, shows the arrangement of this truss; and its parts, to a larger scale, are shown by the other figures. The span is 46 feet, and the floor is supported by eight of these girders, and the roof, with its three large lanthorn lights, is supported by girders of the same kind. They were designed expressly for the purpose, by Mr. Tredgold, and, according to his recommendation, each girder was proved before it was fixed in its place; the first one was proved by a load of six tons distributed over the middle part of the girder.

The tie TT is a double bar of wrought iron, each part 3 inches by 1 inch, and thicker where it is bent round the foot of the abutments; see fig. 5. For convenience, it was formed in lengths, and joined by gibs and wedges, as shown in fig. 6.

The truss-pieces B, B, are of cast iron, 3 inches in thickness, and 6 inches deep in the middle, and 4 inches deep at the ends.

The middle stretcher, A, is also of cast iron, 3 inches in breadth, 9 inches deep in the middle, and 6 inches deep at the ends, its section in the middle resembling the letter I, and is shown in fig. 4. The straps, E, fig. 3, are of wrought iron, 5 inches by an inch, and bent round the joints, as shown in fig. 4. The wooden beams, DD, rest on the edges of the ties, and are firmly bolted together. On these the binding-joists, CC, are notched; and the bridging and ceiling-joists, as shown in fig. 4. The enlarged parts are drawn to a scale of half an inch to a foot.

99. The framing to support the galleries of churches and chapels should be strong and secure, as they are frequently much crowded with people. In order to illustrate this part of our subject, we give the framing of the galleries of Camden-Town Chapel, near London, as executed by Messrs. Inwood, Architects. The following detail of the scantlings of the timbers, with references to them by letters, will render them still more useful to the reader, as it rarely happens that such minute detail can be procured.

Figure 1, plate XVII, the Truss to the Gallery at the west end, bearing on the Tower wall. Its scantlings are:

H, Strut, 8 inches by 6 inches.

J, Trimmer, 9 in. by 6 in.

K, Small Strut, 5 in. by 4 in.

Figure 2, the Trusses of the Side Galleries.

A, Bressumer, 10 inches by 8 inches.

B, Girder, 10 in. by 8 in.

C, Binder, 13 in. by 34 in.

D, Bridging-joints, 4 in. by 3 in.

E, Truss, 6 in. by 4 in.

F, Carriage, 8 in. by 4 in.

G, King-post (oak), 4 inches by 4 inches.
H, Binders to ceiling-joists, 7 in. by 5 in.
J, Ceiling-joists, 3 in. by 2 in.

K, Plate, 8 in. by 5 in.

L, Wall-plate, 12 in. by 6 in.