construction of the nave and side erections of the building for the Exhibition of 1862; and also for some of the passages, &c., of the Horticultural Society, where they still exist, and deserve examination. It is also adopted for temporary sheds of large spans. 2052a. This work by De Lorme deserves the study of every one that seeks to be an architect, though in these unfortunate days for the art the reward of study and reading is very doubtful. A 20526. Since the period of De Lorme, another system, arising out of it, has been extensively adopted for large buildings. Colonel Emy, having been called upon in 1819 to design a roof of 60 feet span, succeeded in composing one in which, while timbers of a greater length might be used, the necessary solidity, with the lightness and economy of the system of De Lorme, might be combined. This he carried out in 1825 and 1826. The workmanship is less than in De Lorme's roofs, as the wood is all in straight pieces, and is within the power of the ordinary carpenter. An arch is composed of a series of long and thin planks, laid flatways, the flexibility of which permits them to be easily and quickly bent without the aid of heat; and their rigidity, properly regulated, maintains the form given and destroys the thrust. Fig. 701a is a portion of the base of one arc, which will illustrate the system. The details are best learnt from Emy's own work, as it would require much space to do justice to them. The vertical pieces A are 7 inches thick, and placed about 4 inches from the wall. The three first radial pieces B are prolonged beyond the uprights, and enter recesses in the wall to steady the frames. The plates C, breaking joint well with one another, compose the arc, and are 13 inch thick, 5 inches broad, and about 40 feet long, bolted together, the bolts being driven tightly into accurately made holes, and are further firmly tied together by iron straps; the bolts are inch diameter, and about 2 feet 6 in. apart; the principal rafters are 54 in. thick; the trusses are placed 9 feet 10 in. apart. Fig. 701a. B 2052c. Upon an experiment that was made by Emy to test the strength and thrust of this arch, he found it necessary to add a supplementary plate to a part of the extrados, and two plates to a part of the intrados. The following is the proportion of the number of plates and their width, which he adopted as a rule: From the springing to radial (B) No. 1 - Nos. 6 and 7 From this tie to radial No. 6 From radial No. 9 to the king-post 7 plates, ft. in. These supplementary plates were of oak, and of the same thickness as the others. These roofs are also given with sufficient detail in Newlands' work above-mentioned. 2052d. MEDIEVAL ROOFS.-In the south of France the few Romanesque roofs did not differ from the common king-post roof, except in two points, viz., that the tie-beam and the king-post were stop-chamfered; and the strain of the purlines upon the principal rafter was counteracted by a nearly upright strut from the tie-beam. This system left the principal rafter with a false bearing, if the walls were not extremely thick in proportion to the width of the apartment which they enclosed. As a remedy, the late Romanesque builders tenoned the purline into the principals, and, moreover, laid it with its wider side to the rafters, in order that the backs of the common rafters should be flush with those of the principal rafters (similarly to fig. 692.). The next step was to put proper struts from the foot of the king-post. At the present day the purline is placed on edge for economy of material. A CO**** Fig. 7016. 2052f. In the north of France there was difficulty in roofing over the vaulting; either the main walls had to be carried as high as the ridge-rib, or else the frame of the roof had to be similar in principle to that shown in fig. 701b. Experience proved that the latter scheme resulted in letting the principal rafters draw the tenons of the braces, and so destroy all idea of a tie connecting the two walls; hence the medieval builders were obliged to raise the walls sufficiently high to allow the tie-beams to pass over the back of the ridge-rib, as would be the case at A. This was expensive, and, moreover, it was scarcely practicable where the walls were little thicker than was necessary for the backing to the formerets of the vaulting over the arches of windows. It is to these facts, rather than to any influence of climate, that may be attributed the adoption of the high-pitched roof, a system which required neither great width of footing nor large scantling of timber, for the purlines were discarded, and the weight was distributed among the rafters and trusses of each bay. The details of such a roof are simple. Two plates A (fig. 701c.) are placed with their widest sides on the wall, and are strutted between from E the feet of the trusses to the centre of the bay. Upon these plates, tassels or short hammers B, are cocked down at intervals between the tie-beams, which are cocked down and dove-tailed, to take not only the feet of the common rafters, but also the nearly upright stud or ashlar rafter F, which serves to give a wider base to the principal and to the rafter. All these vertical pieces are doubletenoned and pinned into the other portions of the work. 2052g. The racking motion to which large roofs are liable, soon showed that this was not the manner in which to make them secure. The purlines had been discarded, but the need of their service remained; the necessity was obviated by erecting a sort of trussed partition under the ridge. If the king-post was not carried by the tie-beam, the whole roof depended upon the strength of the head of the king-post, into which the ridge was tenoned, and the manner in which it was connected with the ends of the principal rafters. It therefore appears to be more probable that the king-post was supposed to be carried by the tie-beam; indeed, examples occur of trussed partitions (fig. 701d.) to ridges, supported by king-posts A, which stand upon tie-beams that ride in queen-stirrups, B, where the stirrups are hung from the principal rafters at three-quarters of the height of the roof. Care has been given D Fig. 701c. C B E D to this detail of the practice, because it seems to have been entirely mistaken by Viollet le Duc, Dict.: for example, the braces C, to the collars D, are supposed by him to exercise a favourable effect in preventing the flexure of the rafter outwards, whereas the fact would seem to be that the brace has to hold up the collar D and with it the stirrup B, and with them the tie-beam E, for the collar is tenoned into the king-post and rafter. That author defers dating the period of the perfection of medieval carpentry (as well as of joinery) until the end of the 15th and the beginning of the 16th century. 2052h The framing of cradle roofs, with king-posts carried upon (not carrying, as Viollet le Duc sup poses) the tie-beams, became a practice that in France was general from the latter part of the 12th until the end of the 16th century, and which continued the same peculiarities of construction that are above indicated. The distinction between the stirrup and the post is less easy in the truss shown in fig. 701e., but still it must be reckoned as a post; this example from the préfecture, formerly the episcopal palace, at Auxerre, covers a hall which is 30 feet wide; the trusses are placed 13 feet apart from centre to centre. The scantlings are as follows:- King-posts, 5 by 5, and principal rafters 54 by 4; the common rafters, 5 by 43. are shown in fig. 701f, and are trussed in a different manner; they are placed nearly 2 feet apart. The roof appears to be boarded on the inside to the circular form. Fig. 701d. AT AUXERRE. 2052i. Although Viollet le Duc is of opinion that the tie-beams to the fine cradle roof, 57 feet 3 inches span, constructed at the beginning of the 16th century, over the great hall of the Palais de Justice, at Rouen (fig. 247. ), have been cut away, it may not be unfair to suggest that the work might have stood as well if, in its construction, it had resembled the older and fine roof of the château at Sully-sur-Loire, which he so well illustrates, but which want of space prevents our also doing. The student has, perhaps, no cause for regret, as its construction can scarcely be recommended for imitation in the present day. It is about 36 feet span. 2052k. The absence of a ridge roll and the position of the ridge-piece in the majority of medieval roofs deserve notice. 635 As soon as the purlines were discarded, it seems that builders relied upon the king-post to carry a ridge-piece upon which rested the ends of the rafters; these were halved and spiked together above it. Excepting in a few cases the ridge-piece was rather a purline at the top of the roof than an abutment. Much of the bolt and strap work applied in the visible frames of roofs is not always the most judicious as regards the conversion of construction into decoration. For example, if it were calculated that a tie-beam would sag, instead of increasing its scantling, or of trussing it, the medieval carpenter would very probably hang it up to his truss, as in figs. 701g. and 701h. At a later period (say the 14th century) with some spikes. Fig. 701k. illustrates the method of forming the junction of post, beam, and strut in a roof; and fig. 7011. that of beams and posts in the timber framing of houses. 20521. It will be at once perceived, by fig. 701c., that the hammer-beam BB′ takes the place of the tie-beam, the middle part of which may have been cut away. The tinted por. tion shows the foot of the rafters in a cradle roof; and the lighter portion the position and form of the hammer-beam, the outer end of which is tenoned and pinned on to the wall Fig. 701g. Fig. 701h. Fig. 701i. Fig. 7011. Fig. 701k. plates A, and the inner end supported by a curved brace C, which starts from the bottom of the wall piece D, the whole being pinned together at the ends. Sometimes a corbel receives the foot of the wall piece and brace. Thus the whole length of the hammer beam may be said to have a solid bearing equal to supporting the roof rising above it, by the ashlar rafter or strut E, and at the same time forming a part of that structure. When the whole is put together securely, it has been considered almost impossible for hammerbeam roofs to spread, as from the stiffening action of the braces, it would require a very heavy force to push out the walls. But the absence of that curved brace which distinguishes the Westminster example, makes these roofs much more likely to exert a thrust upon the walls, and, accordingly, it is notorious that in very many cases this has occurred. In the fine example at Croxton, the strain was so great as absolutely to break short off the perfectly sound heart of oak pins, nearly an inch in diameter, with which it was held together; and it is to be feared that many of the finest of these examples are similarly in a dangerous condition.” So writes Mr. Street, in his English Woodwork, read at the Institute of British Architects in 1865, a paper which should not be neglected by the student. The principle of the construction of these roofs has perhaps not yet been satisfactorily elucidated. 2052m. The timber roofs in England may be divided into five classes: -I. Roofs with tie-beams; II. Roofs with trussed rafters, or single framed roofs; III. Roofs with braces with or without collars; IV. Roofs framed with hammer beams; and V. Aisle roofs. The first are more general and better treated in France. The others are more peculiar to England, in which country elaborate examples of these forms are to be found, especially on the hammer-beam system. 2052n. Pitch. These roofs are for the most part acutely pitched, though this was by no means their invariable characteristic. An angle of 90° was perhaps the ordinary elevation of Norman roofs, and in the early English period, though generally acutely pointed, roofs are nevertheless found of an equilateral pitch or angle of 60°, though this is of rare Occurrence. In this and the succeeding style, examples are found of so low a pitch as to equal the flattest specimens of the perpendicular period. The roof, of the decorated style, over the larger south aisle of St. Martin's Church, Leicester, has a span of 21 feet, with a rise of only 4 feet. (See par. 2040b.). 20520. I. The tie-beam bears the whole weight of a low pitched roof. The roof over the south chapel of Kiddington Church, Oxfordshire, is of rather a steeper pitch than that at Leicester. The under side of the beam is well moulded, and is connected with the wall-pieces by moulded curved braces forming a very obtusely pointed arch; the purlines rest directly on the beam, and the ridge is supported on it lv a post, and by short curved braces, the whole of the space above the tie-beam being filled up so as to give it the appearance of a solid triangular shaped beam. The naves of Raunds and of Higham Ferrers Churches, Northamptonshire, the latter of decorated date, and of Wimmington Church, Bedfordshire, present good and differing examples. The tie-beam is rarely left perfectly horizontal; the collar-beams and even the hammer-beams will be found to incline upwards. Tie-beams were sometimes employed quite independently of the other timbers, being simply laid across the building from wall to wall, notched down, and pinned to the wall plates. They were never entirely discarded, as they are to be met with in each of the four usually accepted divisions of the style. At Southfleet Church, Kent, the tie-beam is beautifully moulded; whereas, at Northfleet, it is left in almost its natural roughness, while the roof itself, which is one of the trussed rafter kind, is panelled, and has moulded ribs with carved bosses at the intersections. 2052p. An example of a strongly cambered tie-beam, with an ornamented king-post, is seen in Swardestone Church, Norfolk, and it is by no means uncommon in the counties of Kent Fig. 701m. NORTH WALSHAM, NORFOLK. and Sussex. The tie-beam of the roof over the aisle of North Walsham Church, Norfolk (fig. 701m.), passes through the nave wall, the end forming a corbel for the wall pieces of the nave roof. This roof also presents a practice which became almost universal in roofs of later date, viz., an intermediate truss between the tiebeams, in consequence of the extreme width between the main trusses, to support the ridge and purlines, by the adoption of double rafters on each side, strongly united and framed together, springing from a small hammer Fig. 701. 21.9 WIMBOTSHAM, NORFOLK. beam over the apex of the arches. In roofs of high pitch, various endeavours were made to retain the arched shape in conjunction with the tiebeam. At Pulham Church, Norfolk, and Morton Church, Leicestershire, the beam divides the arch into two. with a bad result. 2052q. 11. Single-framed roofs sometimes have only diagonal braces connecting the rafters. These occur generally where the span is small, as over a porch. In wider spans, even without tie-beams, each pair of rafters was framed with a collar-beam, and was stiffened by braces crossing at times above the collar, and at others the braces being tenoned into its under side; when the latter was the case, a second collar was generally introduced above the first. Such roofs were very frequently boarded underneath, forming thus a polygonal barrel vault, and moulded ribs were applied, dividing the boarding into panels, with carved bosses at the intersections. The above details will be found combined in the examples of the decorated period from the nave of Wimbotsham Church, Norfolk (fig. 701n). The angle of the roof is 78°. The span is 21 feet 9 inches; the rafters and collars are 4 inches by 4 inches. The former are placed 1 foot 9 inches apart between the centres. The nave roof of Reedham Church, Norfolk, 31 feet span, is framed on the same principle. The hall at Sully-sur-Loire is a fine example. 2052r. III. Roofs constructed with braces may be divided into two classes: I. Those with collar-beams and braces; and II. Those without collar-beams. An example of the former is seen in the roof of the nave at Pulham Church (fig. 7010.), which is formed at an angle of 105°, with a span of 20 feet 5 inches. Wall pieces A, are used, pinned into the underside of the principal rafters, descending low down on the wall; the arched brace springs directly from this to the collar-beam, uniting them both with the principal. It is held that it would be impossible for this roof to spread until it had broken the curved braces. The va rious timbers are all effectively moulded. The principal rafters, 12 inches by 10 inches; common rafters, 6 inches by 3 inches; collar-beam, 14 inches by 8 inches; ridge piece, 8 inches by 8 inches; B purline, 8 inches by 6 inches; wall piece, 10 Fig 7010. PULHAM, NORFOLK. Fig. 701p. STARSTON. NORFOLK. inches by 8 inches. Width between centres of trusses, 6 feet 2 inches; and depth of cornice 3 feet 2 inches. Of class II. is the roof over the nave of Starston Church, Norfolk (fig. 701p.). The angle formed is 100°. At the apex of the roof is a strut B, about 9 inches square, which hangs down 2 feet; its four sides are morticed, two to receive the ends of the braces where they are pinned, thus preventing the possibility of its dropping; and the other two on the opposite sides, to receive the arched ridge braces, as shown at C. This arrangement tends to prevent the roof either spreading outwards, or rocking from east to west. The span is 21 feet 10 in. The principal rafters are 10 in. by 9 in.; common rafters, 6 in. by 4 in.; wall piece, 10 in. by 74 in.; purline, 6 in. by 5 in.; and cornice, 11 in. by 10 in. 2052s. IV. Hammer-beam roofs are always double-framed roofs, the rafters being supported by a skeleton framing of purlines and ridge, resting on, or framed into, the principal trusses. Among the many varieties of this description of roof may be noticed:-(1) Those with collar-beams and no struts, the collars, principals, and hammer-beams being united with curved braces; (2) Those in which the collar-beam is omitted, the curved braces being carried up almost to the ridge, and framed at the apex of the arch into a strut, which receives also the upper ends of the principals; (3) Those with no collars or struts, the whole of the truss being connected together and stiffened with curved braces only; in this instance the arched braces are formed of three pieces of timber, one on either side of the roof, tenoned into the hammer-beam and principal, and reaching up as far as the purline, the centre piece forming the apex of the arch, being tenoned into each principal, itself acting as a brace, and to a certain extent as a collar beam; and (4) Those having hammer-beams, collars, and struts, connected together with curved braces. (See par. 20521.) Fig. 7019. 18.3. CAPEL ST. MARY, SUFFOLK. 2052t. An example of the first sort is the roof of Capel St. Mary's Church, Suffolk (fig. 701q.). The angle formed is 87°, and it is very seldom that a hammer-beam roof has a steeper pitch. The span is 18 feet 3 inches. The principal rafter is 10 inches by 8 inches; common rafter, 6 inches by 3 inches; hammer-beam, 10 inches by 8 inches; collarbeam, 10 inches by 8 inches; purlins, 6 inches by 5 inches; ridge piece, 6 inches by 6 inches. The trusses are 6 feet apart from centre to centre. The second sort is shown in fig. 701r., the nave roof of Trunch Church, Norfolk. The intermediate trusses are the same, except that instead of the long wall-piece and brace, the wall-piece is stopped at the crown of the arch of the clearstory window, and a very depressed brace connects it with the hammerbeam. The spandrils are filled in with perforated tracery. The span is 19 feet. The principal rafter is 10 inches by 9 inches; common rafter, 6 inches by 4 inches; hammer-beam, 10 inches by 10 inches; purline, 8 inches by 5 inches; ridge piece, 10 inches by 10 inches. The trusses are 5 feet 6 inches apart. The third sort is shown in fig. 701s., from the nave of Wymondham Church, Norfolk. The hammer-beams project rather more than a quarter the width of the nave, and are carved into figures; the intermediate trusses have also similar figures, but made subordinate to those of the main trusses. At the intersections of the purlines and ridge braces are large carved flowers standing out in bold relief. Of the |