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Compass rafter: A rafter curved or bowed on the top (the top surface of a rafter is called its "back") or both the top and bottom surfaces. Curb rafter: The upper rafters in a curb (kerb, gambrel, Mansard roof) roof. Hip rafter (angle rafter): The rafter in the corners of a hip roof. The foot of a hip rafter lands on a dragon beam.
Timber roof truss example. The top members of a truss are known generically as the top chord, bottom members as the bottom chord, and the interior members as webs.In historic carpentry the top chords are often called rafters, and the bottom chord is often referred to as a tie beam.
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 tie in building construction is an element in tension rather than compression and most collar beams are designed to work in compression to keep the rafters from sagging. [ 2 ] [ 3 ] A collar near the bottom of the rafters may replace a tie beam and be designed to keep the rafters from spreading, thus are in tension: these are correctly called ...
By supporting the rafters they allow longer spans than the rafters alone could span, thus allowing a wider building. Purlin plates are very commonly found in large old barns in North America. A crown plate has similarities to a purlin plate but supports collar beams in the middle of a timber-framed building.
For more truss types, see truss types used in bridges. A large timber Howe truss in a commercial building. There are two basic types of truss: The pitched truss, or common truss, is characterized by its triangular shape. It is most often used for roof construction. Some common trusses are named according to their "web configuration".
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 lookout, [1] lookout rafter or roof outlooker [2] is a wooden joist that extends in cantilever out from the exterior wall (or wall plate) of a building, supporting the roof sheathing and providing a nailing surface for the fascia boards. When not exposed it serves to fasten the finish materials of the eaves.