HAMMERBEAM ROOF, in architecture, an open timber roof in which the trusses have no true cross ties, but are framed together with a series of horizontal and vertical members bracing the main rafter in triangles, and tied together by curved brackets and braces. The horizontal beams are known as hammerbeams. In the greater number of cases there is an intermediate tie, about one-third of the way down the rafters, and each truss has one hammerbeam on each side with a post extending from its outer end up to the intersection of rafter and cross tie. The hammer beam is supported by a bracket from the wall and the posts tied to the cross tie by curved members which sometimes take the form of a complete pointed arch. In the earliest extant example, which is also one of the largest, that over Westminster hall, Lon don 0395-99, 68 ft. span), an additional complete pointed arch member adds strength to the construction. The hammerbeam truss was frequently used over the naves of parish churches during the 15th and 16th centuries, as in Bacton church, Suffolk, and in March and Knapton churches, where the hammerbeams are carved with angels. This type of roof was also used over manor and other halls. The great hall of Hampton Court palace (1534-35) and that of Eltham palace (16th century), and the halls of Charter house (17th century) and the Middle Temple, London where there are two rows of hammerbeams, are good examples.