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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]
If built using dimensioned timber, each rafter is usually jointed into the previous one. More commonly, these roofs are constructed with roundwood poles where each rafter is laid upon the previous one. In both of these approaches, the roof is assembled by installing a temporary central support that holds the first rafter at the correct height.
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.
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 simple rafter roof consists of rafters that the rafter foot rest on horizontal wall plates on top of each wall. [3] 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.
Eaves must be designed for local wind speeds as the overhang can significantly increase the wind loading on the roof. [ 7 ] The line on the ground under the outer edge of the eaves is the eavesdrip , or dripline, and in typical building planning regulations defines the extent of the building and cannot oversail the property boundary.
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.