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ROOF, 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. Tlie form and con- struction 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 prmcipals. 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
Queen-post Roof.
A, king:-po9t. B B, queen-posts. G C C C, braces or struts. D D, tie-beams.
E E E E, principal rafters, blades, or backs.
F F, ridge -pieces.
G G G G G G, purlins.
H, collar.
J J J J, common rafters.
K K K K, pole-plates.
L L L L, wall-plates.
of modern roofs will serve to explain the names of the most important timbers : a kinij-post roof has one ver- tical post in each truss, a qiteen-post roof has two. * Mediieval roofs vary so much in their structure, on account of the ornamental disposition of the pieces, that it is not easj' to establish a universal nomenclature for them. Man}' names of beams and timbers occur in old contracts of which the original appplication is often uncertain.
The Hammer-beam roofs contain most of the peculi- arities 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
Ilanimer-beam Roof.
A, hammer-beam. B B, pendunt-pnst. C, hammer-brace. D D, rafter.
E, collar.
F, side-post.
G, collar-brace. H, upper collar.
were, two stories. It is then called a double hammer- beam roof, and tlie nomenclature runs : lover hammei-- beam, upper hammer-beam, lower hammer-brace, upper hammer-brace, lojver 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. Pen- dant-post. Inclined pieces, if not rafters, are braces, and commonly derive their epithet from the piece un- der wliich they are placed, or which they principally stiffen, as collar-brace. Ashlar pieces are fixed to ev- ery one of the rafters in most mediaeval roofs, but they are sometimes concealed by cornice - mouldings and frieze - boards. The example from Dorchester shows the hammer-beam construction with collar-brace, side- post, etc.
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Hammer-beam Roof, North Aisle, Dorchester, Oxfordshire.
Of the construction of the wooden roofs of the An- cients 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 illumina- tions 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 an- gle. It does not appear that at this period the con- struction was made ornamental, althougli, doubtless, in many cases the framing was open to view. The cov- ering wis certainh' 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 imiversally of the same pitch. Sometimes the section of the roof repre- sented an equilateral triangle, and sometimes the pro- portions were flatter. A few roofs of this date still ex- ist, as on tlie 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 i)lain or only chamfered on the edges. A moulded 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 moulded.
AVheii first tlie approach of the Decorated style be-
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South Aitfle, Kifllmgton, Oxfordshire.
gan to exercise an influence, the roofs, though still of the same construction, became somewhat more orna- mental. 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 mouldeti, and the king-post, which is commonly octagonal, with a moulded 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 re- main at Chartham Church, Kent, and on the south aisle of Merrow Church, Surrey. Most of these roofs are now ceiled, but probabh' many of them were orig- inally open.