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In light frame construction, a birdsmouth joint or bird's beak cut is a
In light frame construction, a birdsmouth joint or bird's beak cut is a woodworking joint
Joinery is a part of woodworking that involves joining pieces of wood, engineered lumber, or synthetic substitutes (such as laminate), to produce more complex items. Some woodworking joints employ mechanical fasteners, bindings, or adhesives, ...
that is generally used to connect a roof rafter
A rafter is one of a series of sloped structural members such as Beam (structure), steel beams that extend from the ridge or hip to the wall plate, downslope perimeter or eave, and that are designed to support the roof Roof shingle, shingles, ...
to the top plate
A plate or wall plate is a horizontal, structural, load-bearing member in wooden building framing.
Timber framing
A plate in timber framing is "A piece of Timber upon which some considerable weight is framed...Hence Ground-Plate...Window-plat ...
of a supporting wall. It is an indentation cut into the rafter which consists of a "seat cut" (the face of which rests on the top plate) and a "heel cut" or "plumb cut" (the face of which lies parallel to the supporting wall), forming a shape resembling a bird's mouth. The indentation should not extend unsupported on the interior in order to maintain the structural integrity of the rafter because the unsupported section can split along the grain of the wood. The joint is generally fastened with nails by toenailing the rafter from the side into the top plate below.
The depth of a rafter cut varies according to local building code differences in different locations. As a general rule, no more than one third of the depth of the rafter should be removed, in order to maintain structural integrity.
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