In the Eastern States the ceiling joists under a flat roof are seldom built into or supported by the walls, but are hung from the roof joists in the manner shown in Fig. 184, and carefully leveled as they are put up. It should be noticed that the ceiling joists run at right angles to the roof joists, and if the spacing of the former is different from that of the latter this is necessary. If the spacing of the two sets of joists is the same the ceiling joists may be hung directly beneath the roof joists, using 1x3-inch boards for the suspending pieces. The putting up of this work is generally specified under the head of furring.
When the walls are of brick and the bricks are laid from an outside scaffolding this method of supporting the ceiling is possibly the most economical, but when the walls are laid from the inside, as is the custom in the Western States, the author believes that it is better to build the ceiling joists into the wall and tie them in the same way as the floor joists. Where the span is not greater than 13 feet, 2x6-inch joists will be stiff enough, but for greater spans it will be more economical to use 2X4-inch or 2x6-inch joists and truss them from the roof joists, as in Fig. 185. By trussing each pair of joists the roof may be made very stiff and with less timber than is required by the method shown in Fig. 184, and there is less "kindling wood" in the roof space.* If the ceiling joists are anchored to the wall, as should be the case, they also greatly strengthen the building. Where the ceiling joists are built into the wall they are supported by the interior partitions and another set of studding placed on top of the cap to support the roof joists.
The ceiling joists are also utilized by the brick masons for a scaffold, a temporary partition being set under them about 5 feet from the wall (as shown by the dotted lines) and allowed to remain until the joists are permanently braced. In frame buildings the ends of the ceiling joists may be supported by a false girt. Where the rooms under a flat roof are inhabited a space between the ceiling and the roof adds greatly to the comfort of the rooms, and it is desirable that the average height of this space should be at least 2 feet. This space also affords opportunity for running pipes and wires above the ceiling joists. Of course the greater the height of the air space the greater becomes the expense of suspending the ceiling. In Colorado suspended ceilings are seldom, if ever, seen.
The ceiling joists, whether suspended or built in, are usually cross-furred if the other ceilings are, although this is not really necessary with the suspended ceiling.