Also known as the king rafter. In a regular hip end, the standard common rafters that form the bulk of the roof continue along the wall plates on a repeating layout, typically 400mm centres, starting at the position of the last common rafter. This rafter is identical in length to a common rafter. Its special name is given due to its specific location within the roof, more specifically at the beginning of the hip end. This last common rafter forms part of the intersection that receives the top of the hip, and marks the beginning of the layout of the jack rafters on the wall plate. The position of the last common rafter is easy to calculate, following a simple formula in relation to the crown rafter.  

The position of the outside face of the last common rafter on the wall plate is half the span of the hip back from the corner of the plate, less half the thickness of the crown rafter. This principle is demonstrated very clearly when framing or drawing a modern 2” timber roof. As we’ve looked at, the geometric centre of the hip end is half the span of the end back from both corners of the roof. The crown rafter sits centrally over this point at the end of the roof. If both the crown rafter and the last common rafter are 2” timbers, then the last common rafter will also be sat centrally over this geometric centre. Hence, the position of the last common rafter is half the span of the hip end, less half the thickness of the crown rafter. In a regular hip end roof, this concept is very easy to understand. That being said, more complex shapes of hip end exist, which we will look at shortly. To understand the layout of these roofs, we must remember this basic formula now.

If the position of the last common rafter is incorrect, all of the calculated cuts made on the jack, hip, and crown rafters are going to be incorrect. If the last common rafter is too far forward towards the end of the plates, the crown rafter will be too long. Cutting it down to fit will solve the problem temporarily, but the geometric centre of the hip top cut intersection will have shifted off of the true 45 degree course. The hip will end up too short on plan, with the jack rafter cuts being open as they receive into the side of the hip. This overall cock up will result in the end plane of the roof being steeper than desired, as well as a shoddy overall look.  

If the last common rafter is too far away from the end of the plates, then the crown rafter will be too short. Lengthening it will rectify that issue, but again, the hip will drift off of its true plane, receiving into the intersection at a shallower angle than desired, whilst also being longer than planned. Again, the jack cuts will not fit nicely against the hip rafter.  

Some roofs feature intentional changes in pitch as they return around a hip end, but there are special methods of calculating the positions of all of the components properly. We will also look at these later.  

In some scenarios, most often when installing a hand cut hip onto a truss roof, a plywood saddle board is installed on the outside face of the last truss. This may also be the case on a regular cut roof. The purpose of the plywood saddle board is to provide additional bearing and fixing points on the outside pair of rafters, as the hip rafters themselves are typically deeper than the regular rafters. If the hip timbers are particularly deep, or the common rafters or trusses are less deep in comparison (as is the case with common 4” trusses), the addition of the board provides stability to the lower portion of the hip rafters.  

Speaking again geometrically, the introduction of a timber saddle board alters the specific position of the last common rafter. Following the previously mentioned calculation for the position of the last common rafter, the thickness of the saddle board must also be considered, pushing the last common rafter back. This ensures that the correct 45 degree geometric intersection is still achieved for the hip rafter top cut. The introduction of a saddle board does not affect the length of the crown rafter, as it still receives into a timber fixing where the last common rafter would be if there were not a saddle board.