13S 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



devoted, nnd here we do not recognize that masterly arrangement, 

 that perfect equilibration, which should at once proclaim it to be 

 "By its own weight made steadfast and immoveable," a line that may 

 be applied to Westminster Hall, with equal truth, force and beauty. 



In the present instance a considerable thrust is exerted laterally 

 upon the walls, rendering buttresses necessary to its stability. Still 

 there is much ingenuity in the frame work, and the pressure is made 

 to exert itself at an angle of about 70°, being as near to a vertical 

 direction as the scheme of the roof would perhaps admit of. The 

 principal rafters may be said to partake of the property of an arch, 

 and being concealed, their ruder construction does not form a very 

 material disadvantage. 



The forces are made to exert themselves upon the hammer beam ; 

 but with respect to the manner in which this timber is supported, a 

 marked difference is observable ; a difference, indeed, that causes a 

 complete change in the constructive principle and ultimate transmis- 

 sion ot the load. At Westminster we have seen the great arched rib 

 proudly spanning the entire width of the hall, and forming the grand 

 support of the whole roof. The hammer beam, as has been shovvn, is 

 poised with the greatest precision upon a point in the arch, and the 

 weight thrown perpendicularly on the walls at the springing ; but at 

 Hampton Court this principle is not carried out, for the hammer 

 beams with their struts support the arch ! In estimating the lateral 

 thrust of such a piece of framing, the simplest method seems to be 

 to compose the forces acting on the hammer beam, and draw the re- 

 sultant, A B, through the bracket and the walls to the ground. We 

 thus liave the elements of a lever, the external edge of the wall bein? 

 the fulcrum or prop. The weight of the wall collected at half its 

 thickness from the fulcrum, as the resistance to be overcome, and the 

 point where the resultant cuts the ground, shows the position of the 

 counteracting force. 



In this point of view the ancient massive rubble wall had certain 

 advantages over the light and compact mural works of the modern^. 

 In conveying the forces from the hammer beam to the wall, the 

 bracket is presumed to be of adequate strength ; but it ought to in- 

 clude a straight (or more strictly a parabolic) line from the bottom of 

 the queen-post to the corbel, to prevent a cross strain, and the line of 

 the composed forces should pass en the outside of the corbel, other- 

 wise the hammer beam would be liable to be depressed. The form 

 ot these brackets being just the reverse of that which the mathema- 

 tician would prescribe, the introduction of the bolt, an object which is 

 regarded by the carpenter with extreme jealousy, became an act of 

 only due precaution. 



[April, 



Roof of Wisstminsler School.— {Fig. 13.) 

 This exhibits very closelv the anatomy of such as Hampton Court, 

 and was selected by Tredgold as a general type of these works. The 

 deflexion of the hammer beams and derangement of the queen-posts 

 consequent on an excessive loading of the inner ends of the brackets, 

 is quite apparent. The hammer beams of the opposite sides are 

 now connected by bars of iron, a most unsightly and I fear equally 

 ineffectual remedy. ^ 



King's College Chapel.— {Fig. 10.) 

 This roof, which has been very accurately delineated by Mr. Mac- 

 kenzie, is curious, from the degree of care bestowed on its form and 

 finish, considering its destination as a mere covering to the very 

 beautiful masonry beneath. It illustrates the practice of first roofing 

 m buildings to be vaulted with stone. "There are," savs Rickman, 

 " buildings in which, though the upper roof is shown, there is pre- 

 paration for an inner roof; such is Chester Cathedral, where only the 

 lady chapel and the ailes of the choir are groined, and the whole of 

 the rest of the church is open; but on the top of the shafts is the com- 

 mencement of the springing of a stone roof. 



It is in perfect consistency with the usual order of events to suppose 

 that roofs were constructed with principals of a simple arched rib 

 antecedently to those of more complicated forms and grander dimen- 

 sions; and at Conway Castle (12S4) (Fig. 7) there are appearances 

 which have induced me to suppose that the purlins and other timbers 

 were supported by a series of stone arches and gables, serving the 

 purposes of principals. 



Guard Room, Lamhelh Palace, 1450.— (Fig. 4.) 

 This is a very elegant roof of a simple wooden arch, but its precise 

 aate is not recorded. It has the lofty two-centred and bold tracery 

 ot early perpendicular work, and there is in Braylev's illustrations a 

 memorandum under the date 1452, that on accmint of the great in- 

 firmity ot Archbishop Kemp a convocation was adjourned from St. 

 Fauls Cathedral to the Manor of Lambeth, and held in the High 

 ureal Chamber, (alUl camertl rnajori,) which he supposes to be the 



room in question. It is said to have been the restoration of a still 

 earlier guard room. Though now plastered over there is every reason 

 for concluding that the rafters were originally exposed to view. 



Hall and Chapel, Croydon Palace, 1450.— (Figs. 6 & ] 1.) 

 These furnish examples with the four-centred arch; and at the 

 Moat House, at Igthum, Kent, is a very bold simple arch which 

 when accompanied by spandril tracery, and the upper part occupied 

 by king-posts and the other timbers, must have produced a very fine 

 effect. 



The Roof of the Divinity School, Oxford, may be instanced as a 

 specimen of the arched rib, with pierced tracery in the spandril, sup- 

 porting a ground ceiling with pendants and elaborate tracery. 



In Rick man's work on " Gothic Architecture," is mentioned a roof 

 at Willingham Church, Cambridgeshire, where stone ribs rise like the 

 timber ones, the intervals are pierced, and the slope of roof is of 

 stone ; it is high pitched, and the whole appears of decorated cha- 

 racter (1307 to 1377). 



In smaller examples we often meet with arch-formed timbers serv- 

 ing (otherwise than for ornament) as auxiliaries to the principal 

 ralters, and give no change of direction to the weight. Instances of 

 this are found at South Wraxall (Fig. 12), the Vicar's Hall, Wells, 

 and many other places. 



Nursled Court, Kent, 1330 (Fig. 2.) 



At Nursted Court, situated about four miles due south from Graves- 

 end, is a roof of singular interest, doubtlessly anterior to that of West- 

 minster Hall, and attributed, with great probability, to Stephen de 

 Gravesend, Bishop of London, who became possessed of the manor in 

 1338. In this example the portion of the weight which at Westminster 

 thrown on the inner end of the hammer-beam, is here at once con- 

 veyed by a series of arches and posts to the ground. Mr. Carlos says, 

 "The interior of the hall was distinguished by the singular construc- 

 tion of its roof, which was sustained on pillars standing within the 

 area, in this respect differing from the generality of ancient examples 

 which have reached our day, it is however highly probable that 

 Westminster Hall was originally divided after the same manner. The 

 roof ajipears to have been sustained on a frame work composed of 

 two principal beams and two purlins, and supported by four oaken 

 pillars disposed on two ranges on each side of the area, the beams 

 being converted into arches by the addition to their soffits of arch 

 formed timbers. It is illustrated in the " Gentleman's Magazine," for 

 April, 1 837, where there is a notice of a similar roof at Balsall Temple, 

 Warwickshire. The School House, at Coventry (Fig. 5), is another 

 example. 



Crosbrj Hall, 1470.— (Fig. 14.) 



_ Another class of roofs of considerable antiquity, but perfectly 

 distinct in principle from those yet considered, based on the projierty 

 of the triangle to resist racking or change of form, is met with in 

 several of our colleges, at Crosby Hall, and in many later buildings. 

 It is in roofs of this kind that timbers possessing the nature of a tie, 

 or for which a flexible substance, as a rope or chain, might be sub- 

 stituted, are first advanced in English work, all beams in the former 

 examples being either compressed or subjected to cross strains. This 

 roof was well adapted for the oranamental ceilings of the sixteenth 

 century, when the custom of concealing the timbers prevailed, and 

 formed an easy transilience from the steep inclination of the old roof 

 to the flat unbroken plane of " modern instances." 



Gothic roofs, then, (using the term generically, in contradistinction 

 to those with level ties) admit of an obvious and definite analysis into 

 four classes, to one or other of which any roof may be referred. Three 

 of these have the arch for their basis, and the science of equilibriation 

 is called into direct action; the fourth has in itself a countercheck to 

 lateral pressure. 



The first class comprises roofs with simple arched ribs as at the 

 Guard Room, Lambeth ; the Moat House, Igtham ; Ackwell Manor 

 House, &c. 



The second class comprehends those examples that have a grand 

 arch spanning the entire width with axillary timbers, by which part 

 of the weight is suspended from the intrados as at Westminster, 

 Eltham, Boddington, luxon Hall, Lambeth, &c. 



The third class consists of such as have the arch supported by 

 brackets, as at Hampton Court, Westminster School, &c. 



The fourth class, or angular roofing, includes such as are formed of 

 two intersecting triangular frames, in which the tendency to press out 

 the walls is counteracted by the longitudinal stress upon the connect- 

 ing beams, as at Crosby Hall. 



In this latter class we arrive at a point where it becomes difficult to 



trace the principle of construction, and to determine with exactitude 



( the object of the cross beams. In some instances their use as struts is 



