A hip roof adds architectural lines to the design of the house as a whole and offers protections to walls, doors and windows due overhang used for the roof framing. In addition, its rafters tying off to all walls and corners of the structure and they lend more to the structural integrity of a house. Hip roof faming is a more complex process than gable roof because it has more components than a gable roof, such as the ridge board (not necessarily if the house has all the four walls of the same length that and forms a square), common rafters (same length), hip rafters and jack rafters. In the case of a square house, the roof will be like a pyramid. The length of hip rafters and jack rafters vary and they are determined with the help of a hip calculator or a table book such as “The Full Length Rafter Frames”, and the length of the ridge can be determined by subtracting the width of the building from its length. For instance, if the building is 35x29 the ridge will have a 6 feet length.
In most cases the ridge board is 1 ½” thick, so the ridge length needs to be added 1 ½”, because all common rafters are shortened at half of the roof thickness or ¾” and this allows the top of common rafters to align with the top of the ridge at each end. The common rafters are the first step in the hip roof framing process in order to place the ridge where it needs to be. Up until now, hip roof framing and gable roof framing are very much alike, but from here, there are no more similarities. Common rafters need to bee nailed on one side of the ridge at each end first. After this is done, you need to raise the ridge and nail two rafters on the other side of the ridge, opposite to the position of the first two rafters. Now push the ridge up so the birdsmouth cuts pull in tight to the walls on each side of the structure. Then, the rafters can fit their corresponding locations in relation to the ridge and be nailed to the wall. It is important that you nail the two common rafters to the center of the end walls and to the ends of the ridge board. This way you will lock the ridge in the perfect position.
The rest of the common rafters can be nailed to the wall and ridge board and the next elements that need to be installed are the four hip rafters, nailed on the outside corners of the walls and at the intersection of the first and end common rafter. Thanks to the great alignment of the common and hip rafters, the hip roof framing is creating a very solid and strong roof. The last step is installing the jack rafters, but before this, you must run a string from the plumb cut on the hip rafter to just above the birdsmouth by driving a nail in the center of the hip, tie the string to one nail and secure it to the other by pulling it tight. This way you can ensure that the hip rafter will remain straight during the jack rafter installation process. In addition, the string should be stabilized as the jack rafters are nailed on. In order to keep the hip rafters straight, the jack rafters must be nailed on in pars to both sides of the hip.
Finally, the procedure goes down the hip rafter until all jacks are installed and then, the string must be removes in order to complete the hip roof framing process. Before the roof can be sheathed you must install the collar ties and fascia boards, as these are the basic rules for hip roof framing.