![]() ![]() The overhang is 6.5 inches past the plumb cut (8 inches minus 1-1/2 inch subfascia), so mark that plumb cut. Collectively, this triangle notch is called a bird’s mouth. The rafter should sit on the full width of the wall, so square a line off the plumb line that is six inches long this is the seat cut. The speed square in the video is one of the small ones that fit in your nail bags, but you can buy bigger ones for laying out wide rafters.Īfter making the plumb cut, hook the long point and measure along the top of the rafter to 16’ 8-7/16” and mark that plumb line. Rotate the square until the edge of the rafter lines up with the 6 on the common rafter scale and scribe the edge. You can use the degree scale along the outer edge, but the common rafter scale is much faster and easier. Use a speed square to draw the correct angle. In order to measure the rafter accurately, you’ll need to make the plumb cut on the upper end so that you can hook your tape on it. That’s the calculator part, now comes the saw part. gives us the rafter length (excluding tail): 16’ 8-7/16” Marking and Cutting a common gable roof rafter So how do you get from expensive new lumber on the saw horses to a perfect fit on top of the walls? A 6/12 roof rises 6 inches for every 12 inches of run. The first number is the rise the second is the run. Pitch is shown on the plans and is indicated as a fraction, usually with 12 being the denominator. ![]() That’s the run, 14 feet, 11-3/16 inches in this case. Hook the outside of the building with your tape and measure to the inside of the ridge. It doesn't always make it up to the top of the wall plates when someone is pulling numbers for rafter measurements. And don't forget to include the exterior plywood wall sheathing in the dimensions. So, after marking the center line, also mark each edge of the ridge. In reality, you’ll need to subtract half the ridge from the measurement. If there were no ridge, the run would be half the width from the center to the outside of the wall. The overhang (8-inchers, including the subfascia).To lay out the common rafters, we will need to know How to calculate the length of a common rafter You can calculate that with a pencil and some OSB, but because we’re paying you by the hour, you’d better use a construction calculator, which you can download on your phone. The Pythagorean theorem (a 2 + b 2 = c 2) describes the relative lengths of a right triangle. We can measure the run, and the roof pitch is noted in the plans, b ut we need to figure out the rise and the rafter length. The rafter is the hypotenuse of a right triangle. So it all boils down to laying out one rafter. The gable roof frame is a series of identical rafters spaced equally for the length of the house held together with sheathing.įor a simple regular gable roof, the rafters on the left side are identical to the rafters on the right. Reducing roof framing geometry to framing lumber with a calculator, a speed square, and a circular sawĪ gable roof is almost the simplest roof you can frame aside from a shed roof, which is basically half of a gable roof. ![]()
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