Red Roofing Book and Hip Valley Roofs

So far this week we have been working on simple hip - valley roofs. By using the red roofing book we did an excersise where we had to cut out two opposing common rafters at a specified angle. The angle i received was 31 degrees and fortunately for me, in the book it was listed as 30 degrees and 58 minutes, which is very close to 31 degrees. The rise worked out to be 600mm over every 1000mm run. This way to cut my plumb cut to join onto the ridge i measure down 100mm on the rafter, and then 60mm across the rafter, perpendicular to the 100mm mark. By joining these two lines together, i had made a 31 degree angle. Using the half span and multiplying it by the rafter constant i came up with a rafter length measurement, which was around 1911mm. I hooked the tape on the long end of the plumb cut and ran the tape down the length of the rafter and marked 1911. I then squared it off, and repeated the previous process of the 100mm and 60mm marks to make the plumb cut line. I then used a tape to run down the plumb cut line and marked 110mm and then squared that off perpendicularly. When this triangle is cut out, it creates a notch out of the rafter that allows the rafter to sit on the wall plate. This notch is called the birdsmouth, and because of the 110mm measurement we used to obtain the depth at which it was cut, it is called more specifically, a 110mm birdsmouth.
We also cut a whole bunch of common rafters, two jack rafters and a ridge to length and began nailing them in position ontop of our small stud wall house we had built and used previously. Dan then used the red roofing book to calculate the length of the hip and luckily the hip fitted perfectly, generally hips are just hand measured as sometimes a non-square room can make the red roofing calculations of the hip length wrong.