The world's first Hammerbeam roof
The Hammerbeam roof is the name given to a Gothic open timber roof, of which the finest example is that over Westminster Hall (c.1399).
In order to give greater height in the centre, the ordinary tie beam is cut through, and the portions remaining, known as hammerbeams, are supported by curved braces from the wall; in Westminster Hall, in order to give greater strength to the framing, a large arched piece of timber is carried across the hall, rising from the bottom of the wall piece to the centre of the collar beam, the latter being also supported by curved braces rising from the end of the hammer-beam.
The span of Westminster Hall is 68 ft. 4 in., and the opening between the ends of the hammer-beams 25 ft. 6 in. The height from the paving of the hall to the hammerbeam is 40 ft., and to the underside of the collar beam 63 ft. 6 in., so that an additional height in the centre of 23 ft. 6 in. has been gained.