Next, I press the Rise key, and write that number down: 1 ft. Be sure to go through all the calculations a few times, clearing the calculator in between.
If all the results match, you can rule out any keystroke errors. First, I attach a set of stair gauges to my framing square, so I can make precise, repetitive marks. I carefully align those measurements along the edge of the rafter material, and then set the gauges.
As a young carpenter (or should I say, “helper”) I was always amazed at the skill of the roof framers.
By drawing it out on a story pole, I find the post elevation, and I can then cut the story pole to post the ridge. The calculator has no idea about the depth of the seat cut, or the size of the rafter material—it’s easiest to measure from the seat cut to the top edge of the rafter I’ve cut, and that is the HAP. In real life (not mathematics), not everything is perfect. more, to allow me to shim the ridge into position perfectly.In time, an older carpenter named Rich Murphy took me up on a roof and helped me lay out and cut a reverse gable using a framing square and his roofer’s pocket reference or “bible.” That experience sent me on the quest to master the art of roof cutting.I can’t say I ever mastered it, but I’ve come a long way since Rich graciously took the time to help me understand what was going on. Today, I use a calculator to find rafter lengths and angles.Before I set my rafters, I like to set the ridge in position first.That’s why I recorded the Rise measurement of our rafter.If you are framing from scratch, and not matching rafter heights (which will be explored in a future article), you will need to decide on what size the seat cut should be. In my model here, and on most of my jobs using 2×4 walls, the seat measures 4 in. With wider plates, you cannot cut into the rafter more than a third of its overall width—this would weaken the structure too much.