Figure 3-30. Actual lengths on the rafter table
(2) To use the rafter table to determine the length of a rafter with a 1/6 pitch (or a rise of
1/6 the width of the building) and a run of 12 feet, find the 1/6 in the table, then follow the same line
of figures to the right until directly beneath the figure 12. The numbers that appear beneath this figure
are 12, 7, and 10, which show the rafter length required and which represent 12, 7, and 10 mean 12 feet,
7 inches, and 10/12 of an inch. Therefore, the length of the rafter required is 12 feet 7 10/12 inches
long.
(3) Using rafter table method 2, assume you have a roof with a 1/2 pitch (or a rise of 1/2
the width of the building) and a run of 12 feet (see Figure 3-30). Find 1/2 pitch on the table. Follow
the same line of figures to the right until directly beneath the figure 12. The numbers that appear
beneath this figure are 16, 11, and 6, which represents 16 feet 11 6/12 inches. The length of the rafter
required is 16 feet 11 6/12 inches long.
(4) When the run is in inches, the rafter table reads inches and twelfths instead of feet and
inches. If the pitch is 1/2 and the run is 12 feet 4 inches, add the rafter length of a 12-foot run to that
of a rafter length of 4-inch run (see Figure 3-30). For a run of 12 feet and 1/2 pitch, the length is 16
feet 11 6/12 inches. For a run of 12 feet and 1/2 pitch, the length is 5, 7, and 11. In this case, the 5 is
inches, the 7 is twelfths, and the 11 is 11/12 of 1/12 (which is nearly 1/12 of an inch). Add the 1/12 to
the 7 to make it 8, making a total of 5 8/12 inches. Add the two lengths together (16 feet 11 6/12
inches + 5 8/12 inches = 17 feet 5 1/12 inches)
(5) If the run of a building is over 23 feet, the table is used as follows: Using a run of 27
feet, with a 1/4 pitch (the framing square blade is 24 inches long), find the length for 23 feet, then find
the length for 4 feet, and add the two. The run for 23 feet with a pitch of 1/4 is 25 feet 8 5/12 inches.
For 4 feet, the run is 4 feet 5 8/12 inches. The total run for 27 feet is 30 feet 2 1/2 inches.
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EN5156
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