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COMMON RAFTER LENGTH
Example: You are working in a roof that has a 7 Inch pitch and span of 16 Feet 6 Inches.
Calculate the run (half the span) and use that to nd the point-to-point length of of the common rafter.
Then nd the plumb and level cuts.
Note: The common rafter length does not include any overhange or ridge adjustment.
KEY INPUT & DISPLAY
0
1. Find the point-to-point length of the common rafter (same as nding the diagonal):
PTCH 7
Inch
8
Feet
3
Inch
RUN 8
Feet
3
Inch
DIAG 9
Feet
6-5/8
Inch
PLMB 30.26˚
2. Find plumb and level cuts:
LEVL 59.74˚
IF PITCH IS NOT KNOWN, CALCULATE USING THE ROOF RISE AND RUN
Example: A roof has a rise of 8 Feet 10-1/2 Inches and a run of 16 Feet 8 Inches. Solve for the pitch in
formats of inches and degrees. Then use the pitch to calculate the rafter length using above method.
KEY INPUT & DISPLAY
0
RISE 8
Feet
10-1/2
Inch
RUN 16
Feet
8
Inch
DIAG 18
Feet
10-9/16
Inch
PTCH 6-3/8
Inch
PTCH 28.04˚
Find Diagonal and Pitch:
On/C On/C
Pitch
Run
Diag
Feet
Inch
7
÷
1
=
Inch
2
Diag
Diag
On/C On/C
1 / 2
Rise
Feet Inch
8 1
0
Run
Feet Inch
8
6
1
Pitch
Diag
Pitch
6 6
16’ 6” Span
8’ 3” Run
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