Page 39
JKOC 16
Inch
INCR 1
Feet
9-3/16
Inch
6. Find regular incremental jack adjustment and Regular Jack lengths:
JK1 4
Feet
0-5/16
Inch
JK2 2
Feet
3-1/8
Inch
PLMB 30.26˚
LEVL 59.74˚
7. Find Regular Jack plumb, level and cheek cut angles:
CHK1 48.81˚
IRREGULAR HIP/VALLEY AND JACK RAFTERS - JACKS MATE AT THE HIP
Example: A roof has a 7/12 Pitch and a span of 16 Feet (run = 8 Feet). The Irregular Pitch is 9/12. The
Jacks must mate at the Hip. 16 Inches is the most On-center spacing allowed. Determine the sizes
(smallest to biggest) of the Jack Rafters, as well as their respective Plumb, Level, and Cheek cut angles.
PLMB 33.69˚
LEVL 56.31˚
5. Find Irregular Jack plumb, level and cheek cut angles:
CHK1 41.19˚
KEY INPUT & DISPLAY
0
FRAC 0-1/16
Inch
*
1. Select Preferences until you reach “Jack Descend”:
*(If fractional setting not at 1/16, press until 1/16 is displayed)
Cont’d on page 41
STORED
JK3 0
Feet
5-15/16
Inch
Jack
JK4 0
Feet
0
Inch
Jack
JACK dESCEnd
Set Preference to “Jack Ascend”:
JACK ASCEnd
IRJK OC-OC
IRJK JAC-JAC*
Set Preference to “Jacks Mate”:
*Note: After completing this example, you may need to reset the Preferences back to “IRJK OC-OC” if
this is not the way you would normally calculate jack rafter measurements.
PTCH 7
Inch
RUN 8
Feet
0
Inch
2. Calculate the common rafter length:
DIAG 9
Feet
3-1/8
Inch
Jack
Jack
Jack
Jack
Jack
Jack
Jack
Jack
Jack
Jack
On/C On/C
(Prefs)
Conv Stor
+
StorStorStor StorStorStor
+
Stor
+
Run
Diag
Feet
Inch
7
Pitch
8
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