Common rafter layouts use the Pythagorean Theorem to determine the length of the rafters needed for building a roof at a given pitch. Calculate rafter lengths and design a workable rafter layout for a certain roof pitch with instructions from an experienced builder in this free video on carpentry.
Rafter layout; one of the most interesting parts of construction. I'm Robert Markey, I've been doing instruction, especially framing and rafters, for many years. I'm going to talk about common rafter layout. Okay, we'll assume that you know your roof pitch which is something and twelve. Let's say it's nine and twelve. And we'll assume you know your rafter length, okay. And your rafter length; if you don't have it and you just know your height and your horizontal distance it's the Pythagorean Theorem, A squared plus B squared equals C squared. It gives you your common rafter length, okay. In order to lay it out well you can just use a framing square, but if you have these nice little brass thingies it makes it much easier. So, we've got em' set at nine and twelve, put the top of our rafter. It's our ridge, and actually you want to cut that first so you got somethin' nice to hook your tape on, and then you measure your rafter length to the outside of your top plate. And let's assume it's a seventy two inch rafter, so we now make a mark there from the top, come down, okay. So, this is this is your length. Now, once you have this, the rafter tail, the bird's mouth needs to be dealt with if you're using two by four walls say, or let's say two by six cause' we want more insulation you could come over five and a half inches. If you got plywood on the outside you'd come over six, but let's just work it this way. Here's your bird's mouth right there, so the rafter sits, the rafter's going to sit like this for your rafter tail, and then it depends very much on what your what your trim work, what your corners work is like. And you may come over here and you may cut this this way, you may cut it straight. You may come back here and straight up for for something like that, and that's all in the design work, but the essential mathematical piece of laying out the rafters; here we got it. I'm Robert Markey, and we've been talking about common rafter layout.