How To Frame Hip Roofs 4

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Adjustment Of The Hip Rafter

The hip rafter is shortened by removing one half the diagonal thickness of the common rafter at 90 degrees to the plumb line.When locating the plumb line, remember that the run of the hip is 45 degrees to the building.

One half the diagonal thickness of the common rafter is number 7, shown in plan view in figure 4. The hip centreline is at an angle of 45 degrees to the ridge and end common. This allows number 8 in figure 4, to represent two equal sides of a right triangle and number 7 to be the hypotenuse. Number 8 = 1/2 FCR and 1/2 ECR. If the common rafter stock is 38 mm thick then the length of number 8 = 19 mm. The square root of 19^2 + 19^2 = 26.87 mm rounded to 27 mm. 27 mm is the length of number 7 and is one half the diagonal thickness of the common rafter at 90 degrees to the plumb line.

The upper end of the hip rafter is shortened by 27 mm measured at 90 degrees to the hip rafter working point plumb line. Mark a plumb line at the new location and extend it squared across the top of the rafter. See number 7 on figure 5.

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Ronald Hunter

All images and text are copyright Ronald Hunter 2005 to 2011