When it is desired to support the rafters of a roof without using trusses, a method of framing, such as is shown in Fig. 89, can often be adopted with advantage. Purlins are placed under the centre of the rafters, and these are supported by braces as shown, and pieces of boards or plank are nailed to the rafters and against the purlins, as at A. The braces should be spaced about 8 or 10 feet apart and the purlins proportioned according to the length of the rafters and distance between the braces. If there are no ceiling joists then tie-beams must be used, spaced the same distance apart as the braces, to keep the plates from spreading, and the plate must be of such width that it will not bend horizontally between the tie-beams. Such construction is well adapted for the roofs of pavilions, depot platforms, etc., when the span is from 30 to 35 feet, and centre posts are not objectionable.