I would be happy to hear from anyone who either agrees or disagrees with the idea of transferring the HAP measurement from the common rafter to the hip rafter as the first step in calculating where the seat cut of the hip rafter bird's mouth goes. My experience of one roof tells me that the calculation for the depth of the heel cut (whether with the "drop hip" option or with the "chamfer hip" option) on the site results in a hip rafter that is too low, whereas the method explained by Joe Fusco (of transferring the measured HAP from the common rafter to the hip rafter and then either increasing the heel cut depth by the "hip drop" amount or chamfering the top of the hip rafter by the same amount) gave me a perfect fit. We cannot at this stage agree on the correct way to do cut the hip rafter bird's mouth cuts.
The slight error in the cheek cut was due to the fact that I didn't realise until after I had complete the cuts, that with a circular saw I should have set the circular saw to a 45 degree angle rather than the angles shown on the site (which would be correct for a manual cut, or a compound mitre saw).īlocklayer and I have had many email exchanges over the past few days. You can see the top of the hip roof in the next photo. I did the following (I already had the common rafters attached to the top plate).ġ) Set the metric framing rafter to 80/283 and drew the plumb building line on the hip rafter.Ģ) Measured down this plumb line from the top of the hip rafter the HAP as measured on the common rafter (along the plumb line from the top of the common rafter to the seat cut of the common rafter) as in the diagram below.ģ) As I was going to chamfer the hip rafter, I cut out this seat line (actually, I also shorted the seat line by a distance of 1/2 the hip rafter thickness, so that I could create a nice pocket for the corner of the top plate).ģ) Determined the "hip drop" measurement by coming in along the hip bird's mouth seat line a distance equal to half the hip rafter thickness, and measuring down to the bottom of the hip rafter.Ĥ) I checked this measurement mathematically (on spreadsheet) using: =0.5 * hip rafter thickness * TAN(RADIANS(hip angle))ĥ) I then chamfered (bevelled) this off the top of the hip rafter. My common rafter rise/run is 400/1000, or 21.8 degrees. I watched several videos online, notably by Joe Fusco, about common and hip rafters, then went out and bought a metric framing square to try this method. It seemed to me that there might be an error in the online calculator. However, the first hip rafter that I made using this calculator sat too low, due to the bird's mouth heel cut being too deep. I made extensive use of 's hip roof online calculator. I still have to put up flashing and asphalt/fibreglass tiles over the painted plyboard roof decking. I recently completed my hip roof over my day bed.