in architecture, is the external covering on the top of a building; sometimes of stone, but usually of wood overlaid with slates, tiles, lead, etc. The form and construction of the timber work of roofs differ materially according to the nature of the building on which it is to be placed, and any attempt to notice all the varieties would far exceed the limits of this work. The main portions of the framing, which in most cases are placed at regular intervals, are each called a truss, principal, or pair of principals. These, in ornamental open roofs, are the leading features, and in some ancient roofs are contrived with an especial view to appearance. The accompanying diagrams of two of the simplest kinds of modern roofs will serve to explain the names of the most important timbers: a king-post roof has one vertical post in each truss, a queen-post roof has two.
Mediaeval roofs vary so much in their structure, on account of the ornamental disposition of the pieces, that it is not easy to establish a universal nomenclature for them. Many names of beams and timbers occur in old contracts of which the original application is often uncertain.
The Hammer-beam roofs contain most of the peculiarities of structure that distinguish the mediaeval roofs from the modern roofs, and the following nomenclature may be adopted in describing them: Sometimes one hammer- beam is repeated over another, forming, as it were, two stories. It is then called a double hammer-beam roof, and the nomenclature runs: lower hammer-beam, upper hammer-beam, lower hammer-brace, upper hammer-brace, lower side-post, upper side-post, etc.
It must be remembered that all upright pieces may be called posts, with an epithet, if necessary, e.g. Pendant-post. Inclined pieces, if not rafters, are braces, and commonly derive their epithet from the piece under which they are placed, or which they principally stiffen, as collar-brace. Ashlar pieces are fixed to every one of the rafters in most mediaeval roofs. but they are sometimes concealed by cornice — moldings and frieze — boards. The example from Dorchester shows the hammer-beam construction with collar-brace, side post, etc.
Of the construction of the wooden roofs of the Ancients very little is known, but it was probably of the most inartificial kind, and judging from the form of their pediments, the pitch of them was low. Some small buildings still retain their original roofs of marble, as the Tower of the Winds, and the Choragic Monument of Lisicrates at Athens. The Mausoleum of Theodoric at Ravenna has a domed roof, formed of a single block of stone, nearly thirty-six feet in diameter.
Saxon roofs were elevated, but to what degree we have no certain account; neither is there satisfactory evidence of their internal appearance. The illuminations in manuscripts seem to represent them as often covered with slates, tiles, or shingles.
Norman roofs were also raised, in some cases to a very steep pitch; but in others the elevation was more moderate, the ridge being formed at about a right angle. It does not appear that at this period the construction was made ornamental, although, doubtless, in many cases the framing was open to view. The covering was certainly sometimes of lead, but was probably oftener of a less costly material.
Early English roofs were generally, if not always, made with a steep slope, though not universally of the same pitch. Sometimes the section of the roof represented an equilateral triangle, and sometimes the proportions were flatter. A few roofs of this date still exist, as on the nave of Hales Owen Church, Shropshire: this originally had tie beams across it, and under every rafter additional pieces of timber are fixed, which are cut circular, so that the general appearance is that of a series of parallel ribs forming a barrel vault. This seems to have been a common mode of improving the appearance of roofs in this style before any important ornaments were applied to them. The additional pieces under the rafters were usually either quite plain or only chamfered on the edges. A molded rib sometimes ran along the top, and a cornice next the wall plate, both of which were generally small. The tie beams also were frequently molded.
When first the approach of the Decorated style began to exercise an influence, the roofs, though still of the same construction, became somewhat more ornamental. There are also roofs existing of this date, and some probably earlier, in country churches, the insides of which are formed into a series of flat spaces, or cants. They are usually quite plain, with the exception of the tie beam and cornice, which are frequently molded, and the king post, which is commonly octagonal, with a molded capital or base. Of a later period, roofs of this kind are extremely common in some districts, but they are generally to be distinguished from the earlier specimens by being arranged in seven cants instead of six. Of the older description good examples remain at Chartham Church, Kent, and on the south aisle of Merrow Church, Surrey. Most of these roofs are now ceiled, but probably many of them were originally open.
As the Decorated style advanced, the leading timbers of the principals were often formed into an arch by the addition of circular braces under the tie beams, the beams themselves being also frequently curved. The spandrels formed by these braces were very usually filled with pierced tracery, and the timbers generally were more molded and enriched than in the earlier styles. Where the lines of moldings were interrupted, they very commonly terminated in carved leaves or other ornaments. Sometimes, the tie beams were omitted in roofs of high pitch, but the principals were generally arched. The roofs of domestic halls, in the Decorated style, appear to have been more enriched than those of churches: that of Malvern Priory had a variety of cross braces above the tie beams cut into ornamental featherings; that of the archbishop of Canterbury's palace at Mayfield, Sussex, was supported on stone arches spanning the whole breadth of the room (about forty feet). This kind of construction is also partially used in the hall at the Mote, Ightham, Kent. This kind of construction, a wooden roof supported on stone arches instead of the large timbers necessary for the principals, seems to have been more common than is generally supposed, and at all periods.
In the Perpendicular style hammer-beam roofs were introduced (one of the finest specimens of which is that on Westminster Hall), and, together with them, most numerous varieties of construction for the sake of ornament. These are far too manifold to be enument. These are far too manifold to be enumerated; many specimens exist in churches and halls, some of which are extremely magnificent, and are enriched with tracery, featherings, pendants, and carvings of various kinds, in the greatest profusion. Many roofs in this style were nearly or quite flat; these, when plain, had the timbers often exposed to view, and molded; in other cases they were ceiled with oak and formed into panels, and were usually enriched with bosses and other ornaments of similar description to those of the higher roofs; good examples remain at Cirencester Church, Gloucestershire. On halls hammer-beam roofs were principally used, but on churches other kinds of construction were more prevalent. There are some mediaeval buildings, principally vestries, apses, and portions of churches, which are entirely roofed with stone. They are generally of high elevation, and often have ribs answering to the rafters in a wooden roof. They occur at all periods, and in some cases may have been erected for protection against fire; in other cases, when the material was suitable, perhaps from economy.
The name of roof is often applied to what are, in fact. ceilings having an external coverings or outer roof, distinct from that which is seen. Vaulted roofs are also frequently spoken of, but a vault usually has an outer roof over it, and is more properly a vaulted ceilings See Parker, Gloss. of Architect. s.v.; Chambers's Encyclop. s.v.; Walcott, Sac. Archoeol. s.v.