The manner in which wooden floors for residences should be framed, has been described in Chapter II (Foundations On Compressible Soils)., and the floors in other classes of buildings are often framed and supported in the same way. The floors of stores, warehouses, mills, public buildings, etc., however, require as a rule, larger timbers, and should be supported by posts and girders rather than by partitions.
It is the purpose of the author in this chapter to describe some of the special forms of construction frequently required in buildings other than dwellings; the methods of framing with posts and girders, and what may be designated as "heavy framing."
In modern Protestant churches it is becoming the custom to pitch the floor so that it will be higher at the back of the audience room than in front of the pulpit. For such floors the pitch should not exceed ½-inch to the foot, as a greater inclination is unpleasant to walk over. If the seats are arranged in straight rows the floor should be merely an inclined plane, but if the seats are set on a circle the floor should be "bowled," so that any line drawn on the floor from the same centre that is used in laying out the pews will be level from end to end. Where chairs are used for seating a bowled floor is not absolutely necessary, but with pews it is quite essential. There are two methods of forming a bowled floor, their adoption depending principally upon the use that is made of the space below.
First Method. - If there is a finished story below the audience room, for Sunday school or similar purposes, it is generally necessary to frame the floor for a straight incline, and then form the upper or bowled surface by means of furring strips cut out of plank.
If the girders supporting the incline run the same way as the inclination they should be given the same pitch as the floor, and the joist will then be level from end to end. If the girders run in the opposite direction then they will be level endways, and the joist will be on an incline. Whether the joist or girders shall be inclined depends upon the plan of the room, the openings in the walls and the desired spacing of the columns. In arranging the girders it should be remembered that it is better, and generally more economical, to give the longer span to the joist, and to limit the girder spans to 12 or 13 feet for wood and 16 feet for steel.
The greatest span that should be allowed for wooden floor joists in audience rooms may be found from the tables in Appendix B.
Joists 14 inches deep should not be less than 2 ½ inches thick, as
3-inch joists are apt to fail by buckling, unless bridged every 4 or 5 feet by solid bridging, and such bridging will usually cost more than the extra thickness in the joists.
The furring strips to form the bowled surface should be 2 inches thick, and may either be run across the top of the joists or spiked on top of them lengthwise. When the rise exceeds 8 inches, 2x6 joists may be used for the furring, and these should he supported every 3 feet from the main floor joists.
Second Method. - If the space beneath the audience rooms is not finished, or is used only for such purposes that the position of the piers or vertical supports is not of consequence, the cheapest way to frame the floor is by using short lengths of girders and setting them tangent to a circle struck from the centre used for the seating. By placing the girders at the proper height the joists may be set on top of them in the right position for receiving the flooring, and no furring strips will be required. Fig. 457 shows a floor that was framed in this way. A little fitting of the joists on the girders is required, but the labor and material required for a floor framed in this way is not more than 20 per cent, greater than for a level floor. When the inclination of the bowl is not over ½-inch to the foot the floor boards can be laid in straight lines across the room in the usual way, as the boards will spring sufficiently to fit the floor. The ends of the boards will have to be cut, however, where the bowled surface terminates, unless the bowling is very slight.