Floors

Bridging.

Floor frames are "bridged" in much the same way as was described for the walls, and for much the same purpose, namely, to stiffen the floor frame, to prevent unequal deflection of the joists and to enable an overloaded joist to get some assistance from the pieces on either side of it. Bridging is of two kinds, "plank bridging" and "cross bridging," of which the first has already been shown in connection with the partition supports. Plank bridging is not very effective for stiffening the floor, and cross bridging is always preferred. This bridging is somewhat like the diagonal bridging used in the walls, and consists of pieces of scantling, usually 1X3 inches or 2X3 inches in size, cut in diagonally between the floor joists. Each piece is nailed to the top of one joist and to the bottom of the next; and two pieces which cross each other are set close together between the same two joists, forming a sort of St. Andrew's cross, whence we get the name "cross bridg ing" or "herringbone bridging" as it is some times called. The arrange ment is shown in Fig. 160, and the bridging should be placed in straight lines at intervals of S or 10 feet across the whole length of the floor. Each piece should be well nailed with two eightpenny or tenpenny nails in each end. If this is well done there will be formed a continuous truss across the whole length of the floor which will prevent any overloaded joist from sagging below the others, and which will greatly stiffen the whole floor so as to prevent any vibration. The bridging, however, adds nothing to the strength of the floor.

Porch Floors. A word might be appropriately inserted at this point in regard to floors of piazzas and porches. These may be supported either on brick piers or on wood posts, but prefer ably on piers, as these are much more durable than posts.

If piers are used, a sill, usually 4X6 inches in size, should be laid on the piers all around, and light girders should be inserted between the piers and the wall of the house, in order to divide the floor area into two or three panels. The joists may then be framed parallel to the walls of the house, and the floor boards laid at right angles to these walls. The whole frame should be so constructed that it will pitch outward, away from the house at the rate of 1 inch in 5 or 6 feet, thus bringing the outside edge lower than the inside edge and giving an opportunity for the water to drain off.

Stairs. The stairs are built on frames called "stringers" or "carriages," which may be considered as a part of the floor framing. They consist of pieces of plank 2 to 3 inches thick and 12 or more inches wide, which are cut to form the steps of the stairs and which are then set up in place. There are usually three of these stringers under each flight of stairs, one at each side and a third in the center, and they are fastened at the bottom to the floor and at the top to the joists which form the stair well. This subject is taken up more fully under "Stair Building." Unsupported Corners. An interesting place in a floor framing plan is where we have a corner without any support beneath it, as at the corner A in Fig. 161. This corner must be supported from the three points B, C, and D, and the figure shows how this is accom plished. A piece of timber E is placed across from B to C, and another piece starts from D and rests on the piece B C, projecting beyond it to the corner A. This furnishes a sufficiently strong sup port for the corner.