The under floors are generally laid as soon as the joists are in place and bridged, and all bearing partitions are set at the same time, at least enough to support the floor timbers, but all other rough interior woodwork is usually left until the building is enclosed and protected from the weather.
In some sections of the country it is customary to lay a rough under floor in every building having wooden floors, while in other sections under floors are seldom seen except in the very best buildings. The saving in omitting the under floor, however, is usually very slight, while the benefits to the building in having it are considerable. In the first place an under floor, especially if laid diagonally, greatly stiffens the building during the construction, and it is not only a great convenience to the workmen, but also allows the laying of the upper floor to be put off until the building is nearly finished. Moreover, without an under floor it is impossible to have any efficient deafening unless boards are cut in between the joists. For these reasons it is advisable to specify under flooring wherever the limit of cost will permit, even if some ornamentation has to be omitted.
The cheapest kind of lumber may be used (hemlock is generally used in the Eastern and Northern States and native pine in the Western States) so long as it is sound, but the boards should be dressed one side to a uniform thickness, and the narrower they are the better. In the better class of buildings the boards should be laid diagonally with the joists, pieces of scantling being cut between the joists at the walls to support the ends of the boards. It costs a little more to lay under flooring in this way on account of the waste at the ends, but it greatly stiffens the building and gives a much smoother surface to the upper floor, especially when the flooring is matched. The boards should be laid close together, nailed over every bearing with two 8-penny nails, driven through the top, and should extend close to the brick walls or to the outside boarding of a wooden house, and should be cut around the studding.
Preparations for Tile Floors. - When a tile or mosaic floor is to be laid on wooden beams it is necessary to have a good bed of concrete under the tiles, and to support the concrete rough boards are cut in between the floor beams, resting on 7/8 -inch strips nailed to the sides of the beams. The top of the boards should be at least 4 inches below the top of the tiling, and 5 inches is better. The top of the beams should also be beveled on both sides to an edge at the centre. When wooden walls or partitions are to have a tile wainscoting it is customary to lath with expanded metal or some other form of stiff metal lath, and to hold the lath pieces of 2x3 or 2x4-inch scantling should be nailed horizontally between the studding and about 12 inches on centres.