rafter (the hypotenuse). Any part of the triangle can be computed if the other two parts are known.

Use the following equation:

The square of the hypotenuse of a right triangle is equal to the sum of the squares of the two

sides. In roofing terms--

Rafter length2 = run2 + rise2

b. Bird's Mouth. A bird's mouth is a cutout near the bottom of a rafter, that fits over the top

plate. The cut that fits the top of the plate is called the *seat*; the cut for the side of the plate is called

the *heel *(see Figure 3-26).