Different Kinds of Rafters

Common Rafters

• Common rafters are constructed at right angles to exterior wall plates and ridge boards. This system establishes the height of the roof and centers the ridge boards. Common rafters are so named because they are common to all styles of roof and form the foundation for adding on other types of rafters, to create more complex roofs. Exterior wall plates consist of a set of two-by-four boards nailed together to form the skeleton for the outside walls of a house or building. Ridge boards are the single two-by-four wood plank that forms the peak of a roof.

Valley Rafters

• Valley rafters run between the wall plates and ridge beams at a 45 degree angle. They form the dip, or valley, where two section of roof meet at an angle. Valley rafters can be seen in cross gable roofs, at the point where two gables meet.

Jack Rafters

• Jack rafters either connect valley rafters and ridge beams together or connect wall plates to hip rafters. They are cut at 45 degree angles, like common and valley boards. Because they run between the valley and ridge or between the wall and hip rafters, their lengths will vary, depending on the spacing. There are three types of jack rafters. Hip jacks have a notched bottom resting on the wall plate -- like the common rafter -- and extend upward to a hip rafter. Valley jacks join the ridge board with the valley rafters. Cripple jacks are only used with valley and hip rafters that are placed close together on a roof. They span the distance between the valley and the hip rafter.

Hip Rafters

• Hip rafters form the corners of a roof line, running between the wall plate and ridge board, like common rafters. The roof line, at this point, runs at a diagonal to the common rafters and extends over the corners of the building. Unlike an A-frame roof, which has only two slopes, hip roofs have four sloped roof panels. The two shorter roof panels on the sides of the building are triangular in shape, and the the longer roof panels at the front and back of the building form trapezoids.