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Calculating
The Shed Roof Line length And Overhang
The
rise and run are used in the Pythagorean Theorem to calculate the
line length and overhang of the shed roof rafter shown in figure 1. The
rafter rise of 500 mm is the
difference between the height of the walls supporting
the rafters.
2500 mm - 2000 mm = 500 mm. The span of 2500 mm is also
the run of
the
rafter. The rafter line length of 2549.5 mm is calculated by taking the
square root of the sum of the rise (500) squared and the run (2500)
squared. The line length lies between WP1 (working point1) and
WP2. Both
working points line up with an exterior surface of a wall. The
overhang of 510 mm at each end of the rafter is calculated
by dividing the line length of 2549.5 mm by the run of 2500 mm and
multiplying the answer by the projection of 500 mm.
Mark WP2 on the rafter. Use the line length and the overhang length to
mark in the WP1 and the overhang tail cut locations on the top
surface of the rafter.
Draw a line, 90 degrees to the rafter sides, through each central
working point and
tail cut location. Extend plumb lines down from each line. See "How
To
Frame Hip Roofs - Figure 3"
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