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Two king post trusses linked to support a roof. Key:1: ridge beam, 2: purlins, 3: common rafters. This is an example of a "double roof" with principal rafters and common rafters. A timber roof truss is a structural framework of timbers designed to bridge the space above a room and to provide support for a roof.
A truss roof with tongue and groove sheathing. The gap in the sheathing at the ridge is the space designed to allow natural ventilation. Pre-manufactured roof trusses come in a wide variety of styles. They are designed by the manufacturer for each specific building. Timber trusses also are built in a variety of styles using wood or metal joints.
The king post is the central, vertical member of the truss. Crown posts in the nave roof at Old Romney church, Kent, England. A king post (or king-post or kingpost) is a central vertical post used in architectural or bridge designs, working in tension to support a beam below from a truss apex above (whereas a crown post, though visually similar, supports items above from the beam below).
This type of truss is seen in a framed roof consisting of rafters and a ceiling joist, [14] and in other mechanical structures such as bicycles and aircraft. Because of the stability of this shape and the methods of analysis used to calculate the forces within it, a truss composed entirely of triangles is known as a simple truss. [ 15 ]
A hammer-beam 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 purlins are the large beams perpendicular to the rafters; from this shot, it appears that there are three purlins on either side of the roof. The sheathing boards are sometimes called the roof deck and are painted white. A purlin (or historically purline, purloyne, purling, perling) is a longitudinal, horizontal, structural member in a roof.
Arched rafter: Of segmental form in an arched roof. Knee (crook, kneeling, cranked) rafter: A rafter with a bend typically a few feet from the foot used to gain attic space like adding a kneewall. Rare in America. Barge rafter: The outermost rafter on a gable end, sometimes forming a roof overhang.
A 10-panel truss requires counter-braces in every panel but the end panels, and these should be at least one-half as strong as the braces. A Howe truss bridge can be strengthened to achieve a live load to dead load ratio of 2-to-1. If this ratio is 2-to-1 or greater, then a six-panel truss must have counter-braces and these must at least one ...