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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 find the point-to-point length of of the common rafter.
Then find the plumb and level cuts.
Note: The common rafter length does not include any overhange or ridge adjustment.
KEY INPUT & DISPLAY
1. Find the point-to-point length of the common rafter (same as finding the diagonal):
On/C
On/C
7
Inch
Pitch
1
6
6
Feet
Run
Diag
2. Find plumb and level cuts:
Diag
Diag
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
Find Diagonal and Pitch:
On/C
On/C
8
1
0
Feet
1
6
8
Feet
Diag
Pitch
Pitch
16' 6" Span
8' 3" Run
÷
=
2
Inch
1
/
2
Rise
Inch
Inch
Run
Page 35
0
PTCH 7
Inch
8
3
Feet
Inch
RUN 8
3
Feet
Inch
DIAG 9
6-5/8
Feet
Inch
PLMB 30.26˚
LEVL 59.74˚
0
RISE 8
10-1/2
Feet
Inch
RUN 16
8
Feet
Inch
DIAG 18
10-9/16
Feet
Inch
PTCH 6-3/8
Inch
PTCH 28.04˚
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