Hammerbeam roof

A hammerbeam roof is a decorative, open timber roof truss typical of English Gothic architecture and has been called "...the most spectacular endeavour of the English Medieval carpenter." They are traditionally timber framed, using short beams projecting from the wall on which the rafters land, essentially a tie beam which has the middle cut out. These short beams are called hammer-beams and give this truss its name. A hammerbeam roof can have a single, double or false hammerbeam truss.

A hammerbeam is a form of timber roof truss, allowing a hammerbeam roof to span greater than the length of any individual piece of timber. In place of a normal tie beam spanning the entire width of the roof, short beams – the hammer beams – are supported by curved braces from the wall, and hammer posts or arch-braces are built on top to support the rafters and typically a collar beam. The hammerbeam truss exerts considerable thrust on the walls or posts that support it. Hammerbeam roofs can be highly decorated including ornamented pendants and corbels, with church roofs often including carved angels.

A roof with one pair of hammer beams is a single hammerbeam roof. Some roofs have a second pair of hammer beams and are called double hammerbeam roofs (truss).

A false hammerbeam roof (truss) has two definitions:

Possibly the earliest hammer-beamed building still standing in England, built in about 1290, is located in Winchester, in Winchester Cathedral in Pilgrims' Hall, now part of The Pilgrims' School.

The roof of Westminster Hall (1395–1399) is a fine example of a hammerbeam roof. The span of Westminster Hall is 20.8 metres (68 ft. 4 in.), and the opening between the ends of the hammer beams 7.77 metres (25 ft. 6 in). The height from the paving of the hall to the hammerbeam is 12.19 m (40 ft.), and to the underside of the collar beam 19.35 metres (63 ft. 6 in.), so that an additional height in the centre of 7.16 m (23 ft. 6 in.) has been gained. 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 also supported by curved braces rising from the end of the hammerbeam.

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