The "Tie-beam Roof" is the earliest form of which there is any record, and the simplest in construction, being merely two rafters pitching one against another with the tie- beam inserted, holding their lower portions to counteract the outward thrust on the walls. This was probably the only form known at the Norman period, and it was never entirely discarded by mediaeval builders, being used in every succeeding style. In the early examples, the beam is merely pinned to the wall-plate at either end and unconnected with the rafters. Various methods were afterwards adopted in order to make the truss harmonize well with other features. The tie beam was rarely straight, being cambered or curved; in the later examples this camber governed the pitch of the roof, the purlins resting immediately on it, as at Wellingborough Church. Curved braces were often inserted, connecting the tie-beam with wall-pieces, the whole being framed together and giving the favourite form of the arch, as at Outwell Church.

In roofs of steeper pitch the open space above the tie-beam was filled in with perpendicular strutting or carved open work, as at Outwell Church, Norfolk. A pillar or king-post and struts were often supported on the tie-beam to strengthen the rafters, which gave a pleasing effect, as at Swardstone Church and also as shown in the illustratiomn. This is an inversion of the use of king-post and tie-beam as adopted in modern roofs, in which the former acts as a suspending piece. A timber arch was sometimes introduced, springing from a wall-piece below the tie-beam, but as the tie-beam always intersected this the result, as seen at Morton Church, Lincolnshire, and elsewhere, was not satisfactory. [pp. 290-92]

Open Timber Roofs of the Middle Ages

References

Fletcher, Banister, and Banister F. Fletcher. A History of Architecture on the Comparative Method for the Student, Craftsman, and Amateur. 5th ed. London: B. T. Batsford, 1905.


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