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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.
The top ends of the rafters often meet at a ridge beam, but may butt directly to another rafter to form a pair of rafters called a couple. Depending on the roof covering material, either horizontal laths , battens , or purlins are fixed to the rafters; or boards, plywood , or oriented strand board form the roof deck (also called the sheeting or ...
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.
English: Detail of a steel truss, like it is build nowadays, it uses welds and bolds due to the fact it is at site joint, where two parts get connected at site (see Plan of the tuss). It is a part of a Plan (File:Det JoKa008-Model.pdf), which shows three details of a truss (File:Fachwerkplan.pdf)
The rafters are the beams of wood angled upward from the ground. They meet at the top of the gable at a ridge beam , which has extra bracing to attach it to the rafters. 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.
Because of these very strong and rigid joints, some of the bending moment in the rafters is transferred to the columns. This means that the size of the rafters can be reduced or the span can be increased for the same size rafters. This makes portal frames a very efficient construction technique to use for wide span buildings.
A knee wall is a short wall, typically under three feet (one metre) in height, used to support the rafters in timber roof construction. In his book A Visual Dictionary of Architecture, Francis D. K. Ching defines a knee wall as "a short wall supporting rafters at some intermediate position along their length."
A birds-mouth joint in a rafter, set upon a double top plate. Shown are the two cuts of the joint: the seat cut and the heel cut. In light frame construction, a birdsmouth joint or bird's beak cut is a woodworking joint that is generally used to connect a roof rafter to the top plate of a supporting wall. [1]