ROOF

the top covering of any building, designed for shelter from the sun, rain, etc., and for protection. Rs. are usually curved, and slope downwards in each direction from a central ridge, though the earliest Rs. were flat, as they still are in rainle countries. There are two main kinds of R., the ‘King-post’ and the ‘Queen-post’; the former has only one main support, to which the rafters are fastened, while the latter has two, and is used for buildings of greater width. The Gothic Rs. were of the former variety, the tiebeam being moulded in the Perpendicular style the tie-beams were cut away in the center, forming what is known. as the hammer-beam R. The R’s of buildings not infrequently form one of their chief beauties from an architectural point of view (see ARCHITECTURE). Rs. are given various names from peculiarities of shape or construction. Thus a Dutch R. is a double-slope R., each side being composed of two planes, the lower of steeper pitch than the upper. <A compa R. is a gable R. which has ties from the foot of each rafter to a point about the center of the opposite one. A pavilion R. slopes equally on all sides, and a saddle R. is an ordinary ridged R. which has two gables. A truncated or cut R. has two slopes which meet in a level surface on top, whilst a mansard R. is a hipped curb R., a R., that is, which is a curb R. on all sides. The roofing over of enormous spans in exhibition buildings, etc., has been rendered po ible by the introduction of iron and steel.