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n.1.(Arch.) An interior angle or notch cut across a piece of timber, for the reception of the edge of another, as that in a rafter to be laid on a plate; - commonly called crow's-foot in the United States.
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(B) The notch is called a bird's-mouth. Without a bird's-mouth, the rafter would be resting only on the edge of the top plate.
If the ridge and bird's-mouth cuts fit tight, label one of the rafters as a pattern and use it to mark the remaining 2x4s for cutting.
Note that the rafters have a small "bird's-mouth" cutout at the eave, as shown in Fig.
Calculating the length, angled end cuts and bird's-mouth cut-outs of the roof rafters takes a healthy dose of trial and error (Photo 7 and Fig.