run would give a pitch of 4:12, 6:12, or 8:12. There are two methods of indicating pith.
(1) Method 1. The pitch is indicated as a ratio of the rise to the span of a roof, stated in
fractions (3/4, 5/8, 1/2, and 5/12). The units of span and rise must be the same (inches or feet), and
the faction is reduced to its lowest common denominator (see Figure 3-11, page 3-8).
To obtain the unit rise, multiply the pitch by 24. For example, if the pitch is given as
1/3, multiply 1/3 by 24 (1/3 x 24 = 8). Therefore, the unit rise is 8 inches per foot (8-12
pitch).
If the pitch is given as 5/12, multiply 5/12 by 24 (5/12 x 24 = 10). Therefore, the unit
rise is 10 inches per foot (10-12 pitch).
(2) Method 2. The pitch is stated as the ratio of rise (in inches) per 1 foot of run (12
inches). Using this method, 4, 6, or 8 inches of rise per foot of run would give a pitch of 4-12, 6-12, or
8-12. A roof with 1/2 pitch can be said to have a 12-12 pitch. Remember 1/2 x 24 = 12.
l. Rise. The rise of a rafter is the vertical (or plumb) distance that a rafter extends upward
from the plate.
m. Plumb Line. The line is the line formed by the cord on which the plumb bob is hung (see
Figure 3-28).
Figure 3-28. Roof pitch
n. Plate. The plate is the wall-framing member that rests on the top of the wall studs (see
Figure 3-8, page 3-4).
o. Ridge. The ridge is the highest horizontal roof member. It ties the rafters together at the
upper end (see Figure 3-8).
3-21
EN5156
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