There are basically seven different types of roof rafter designs used to create a roof: common, hip, hip jack, valley, valley jack, cripple jack and flying hip. While the most common gable roof can be constructed using only one type of roof rafter, the most complex roof designs can use a combination of all seven roof rafter types. While the rafter can be assembled on site from raw materials, the most common method of building a roof uses a pre-made rafter delivered to the job site by a lumber distributor who will also place the rafters on the roof with a boom truck.
The common rafter is used to create the basic gable roof. This type of rafter runs from an exterior wall and continues up to the ridge board or the peak of the roof. The common roof rafter is used to determine the height of the roof and to place the ridge board. Once the ridge board has been set, the roof is ready for the next type of rafter.
The hip rafter runs on a 45-degree angle to the common rafter. The hip rafter is placed on the corner of the wall or foundation and runs up to the ridge board. This type of rafter is used in finishing off the end of the roof where it meets the end of the building. The hip jack rafter sits on the building's wall and runs up to the hip jack. The hip jack runs in line with the common rafters and lines up with the common rafters on the hip rafter.
Valley rafters are used anywhere there is an inside corner on the roof. Placed at 45-degree angles to the common rafters, the valley roof rafter runs from the ridge board to the outside wall of the building. Valley jack rafters run from the valley rafter up to the ridge board and are in line with the common rafters. The cripple jack rafter is used to span the distance from a valley rafter to a hip rafter when they are located very close to each other.
The flying hip rafter is used on multiple level roofs when there are multiple roof ridge boards at different heights. The flying hip rafter runs from the area where a valley rafter meets up with a ridge board and runs to the end of a higher ridge board. The flying hip roof rafter is also known as a mystery hip rafter. When building a roof it is likely that a combination of several types of rafters may be used in order to complete the finished roof.