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. 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 be too deep (less than a third of the rafter's thickness) in order to maintain the structural integrity of the rafter. The joint is generally fastened with nails by toenailing the rafter from the side into the top plate below.
- Wagner, John D. (2009). Ultimate Guide to House Framing. NJ: Creative Homowner. ISBN 978-1-58011-443-1.