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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."
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 ...
Cross bracing between joists or rafters strengthens the members by preventing sideways deflection. This bracing is known by many names such as herringbone strutting, blocking, bridging, and dwanging. Cross bracing on a bridge tower. In construction, cross bracing is a system utilized to reinforce building structures in which diagonal supports ...
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]
A view of a roof using common purlin framing. The purlins are marked in red. This view is from the inside of the building, below the roof. 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.
Sometimes rafters may be attached directly to the poles. The roof pitch of pole buildings is usually low and the roof form is usually gable or lean-to. Metal roofing is commonly used as the roofing and siding material on pole buildings. The floor may be soil, gravel, concrete slab, or framed of wood.
Bent rafters were formed from 1x3 or 1x4 inch boards. Un-surfaced boards were preferred because rough-sawn boards created more friction when laminated. For barns up to 30 feet (9.1 m) wide, rafters were commonly made from four pieces of 1x3 (actually 3/4 inches thick) random length boards with end joints of at least two feet apart nailed ...