To calculate the difference for the jacks: traveling back on that ridge 2' to the first rafter, you've created a total height of 14" (2 x the unit rise of 7"). I typically started with the shortest rafter being zero and found the common difference for 2' centers. Typically, I never bothered to calculate the valley although it is a simple pythagorean calculation: Total length of ridge squared, plus minor rafter squared, find the square root for the valley length. Cut this piece to length, holding 8/12 and marking the 12. The answer is the length of the ridge from the inside of the gable to the sheathing. Multiply this by 8" to get total rise.ĭivide the total rise by 7 and multiply by 12". Determine the total rise of the lay-on (above the sheathing) by subtracting the ridge thickness (1.5") from the span. Here's how I did it with a $4.00 calculator. You can calculate for precutting irregulars too. If you prefer marking and cutting the long-points add the rafter thickness to the ridge length first. from the girder then the ridge length can be used and the jack lengths will be to the short-point of the valley bevel miters so just save the ridge length as the new and press the jack button and record the lengths. Layout the ridge so the jacks will break the sheathing from the truss layouts and take the longest layout from the pointy end of the ridge and use that as the starting run for the valley jack rafters. Now press and subtract half the ridge's thickness to solve for the ridge length. Enter that as the of the girder's pitch that you have the CM set to work with, press to solve the sleeper valley length. Instead of marking both sides of the girder, block-mark one side and measure the top cord “Rafter” length of the girder. Some other solves for precutting the saddle style overlay roof calculations. It's easier if someone gives you that first measurement, but after that, it's quite possible to get all of your measurements by yourself. If you use a CM, and you are a thinking man, you can literally cut all parts and pieces without anyone giving you one measurement. If someone thinks it is a problem, then I would suggest building the house square in the first place, then there's no problem. Now, one thing to mention.if your building is not square to begin with, this is not going to come out exactly the way you want it. The edge of your valley board planes with the top surface of your roof (obviously) The top part of the valley boards should meet nice and snug. Lay the two boards down roughly where they are going and line the valley edge with the top face of the girder. The angle on your saw is the main roof pitch (6/12 or 26.57°) This is the angle across your board on the lower end. Your diagonal was your hip/val measurement. Remember, we are just trying to figure your angles. The rise that you punch in, that was your previous run. I wish I had graphics, it would make it so much easier. Picture a large right triangle angled on the surface of your main roof sheathing, where the run is directly underneath where your ridge board is going to go. You already have the numbers, but you need to punch them in differently. Then you need the angles, top and bottom. This is the length of your length valley board. So say your run (not your span) is 11'-5 3/8" Measure from one mark to the other and this is your "span". Wherever the top surface of your block intersects the top surface of your girder, make a mark, and do it on both ends. If you take a block of wood, just a scrap, that is the thickness of your valley board (I'm assuming a 2x), you lay this on the plywood surface near the lower end of where the valley board is going to intersect the girder. It does help getting the measurement that you need. I will use a girder truss for an example.
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