(1) The row of figures in the first line represents the length of common rafters per foot of run (look at the left end of Figure 3-29 ), as the title at the left-hand end of the blade indicates.

(2) Each set of figures under each inch division mark represents the length of a rafter per foot of run, with a rise corresponding to the number of inches over the number. For example, under the 16-inch mark appears the number 20.00 inches. This number equals the length of a rafter with a run of 12 inches and a rise of 16 inches. Under the 13-inch mark appears the number 17.69 inches, which is the rafter length for a 12-inch run and a 13-inch rise.

(1) The figures show that a rafter with a run of 12 and a rise of 4 has 1/6 pitch. A 12 run, 6-inch rise has 1/4 pitch. A 12 run, 8-inch rise has 1/3 pitch.

(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.

(6) The lengths that are given in the rafter table are line lengths. The overhang must be added.

(7) When the roof has an overhang, the rafter is usually cut square to save time. If the roof does not have an overhang, the rafter is cut plumb, but no notch is cut in the rafter seat.

(8) A level cut is made on the rafter long enough to extend across the plate and the wall sheathing. This type of rafter allows very little protection to the sidewalls.