Johnson Level & Tool Mfg. RAS-1 - Manual (Page 10)

8
FIG. 3 The Common Rafter.
Then the run is found by dividing in half the building width.
When a ridge board is being used, deduct 1/2 its thickness
from the run.
STEP 2. OBTAIN ROOF RISE: Find the distance you wish the
roof ridge to be above the wall (in feet) by measuring, calcu-
lating or obtaining it from the blueprints (see Figure 2).
INCH RISE PER
FOOT RUN
RISE X 12
RUN
RAFTER
LENGTH
RUN 2 + RISE 2
OR
USE TABLES
= =