Bird's mouth cut
A birdsmouth or bird's mouth cut is a carpentry or timber roofing term for a small triangular cutout from a beam either at the end or along one side. It is made up of two cuts to remove a triangular piece of timber, the cuts are at 90 degrees to one another but their angle to the edge of the timber being cut will vary depending on the angle of the roof.
Birdsmouths are cut in to roofing rafters at the top to hang onto and be fixed to the ridge beam as well as lower don the rafter on one side to hang over the edge of the wall plate, making the top of the wall frame or lying on top of the wall if masonry of brick. The combination of the two cuts allows the rafter to sit at an angle to the horizontal beams creating the roof pitch.
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