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In construction, a bird’s mouth refers to a notch or cutout made at the bottom of a rafter or truss where it rests on the top plate of a wall. This notch allows the rafter to sit securely on the wall, providing support and stability to the roof structure.

The bird’s mouth cutout is typically triangular in shape and is made using a saw or other cutting tool. It is located at the end of the rafter that will be positioned against the top plate of the wall. The depth and angle of the cutout are carefully measured and executed to ensure a snug and secure fit.

The primary purpose of the bird’s mouth is to establish a solid connection between the roof framing members and the supporting walls. By creating a flat surface along the bottom edge of the rafter, the bird’s mouth allows for maximum contact with the top plate, distributing the weight of the roof evenly and preventing any shifting or movement.

Additionally, the bird’s mouth helps to transfer the downward force exerted by the roof load to the walls below, enhancing the structural integrity of the entire building. Without a properly formed bird’s mouth, rafters may not be adequately supported, leading to sagging or failure of the roof system over time.

Bird’s mouths are essential components of traditional roof framing techniques, such as stick-built or conventional framing. They are found at each end of every rafter or truss where it meets the wall, ensuring a secure and stable connection that withstands the forces of gravity, wind, and other external loads.

In summary, a bird’s mouth is a critical feature of roof framing that provides structural support and stability by allowing rafters or trusses to securely attach to the walls of a building.

The carpenters carefully cut bird’s mouth notches into each rafter to ensure a secure attachment to the top plate of the wall.

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