What is the typical dimension of a birds mouth notch?

The typical dimension of a bird's mouth notch is 1 1/2 inches. This notch is critical in rafter construction as it allows the rafter to sit snugly on the top plate of the wall, ensuring that it aligns properly with the structure of the building. The 1 1/2 inch measurement generally corresponds to the dimension of standard lumber, specifically the thickness of the top plate, which is usually a 2x4 or 2x6. This dimension helps maintain structural integrity and proper load distribution, aiding in the overall stability of the roof system.