Jack Rafter Function

Common, 45° Hip/Valley and Jack Rafters Tutorial Video

Calculates the Regular or Irregular Jack rafter length. Finds the descending Jack rafter sizes for regular pitched roofs, based on the stored On-center spacing and previously entered or calculated right triangle/rafter values (e.g. pitch, rise, run).

For Irregular Side Jacks (Ir/Jack) pitched side, calculates the rafter length.

Note: You may set your calculator to display the Jack Rafter lengths in either ascending or descending order from the Preferences screen.

Note: You may set your calculator to "mate up" with the Jack Rafters, rather than using the entered or default On-center spacing for both sides from the Preferences screen.




Related functions:

Examples:

1. A roof has a 9/12 Pitch and a run of 6 Feet 9 Inches. Find the incremental jack adjustment, jack rafter lengths, and cut angles at 18-inch (versus 16-inch) On-center spacing. The On-center spacing is used for both Regular and Irregular calculations.

Keystroke Display
[Clear] [Clear] 0.
9 [Inch] [Pitch] Pitch
9 INCH
6 [Feet] 9 [Inch] [Run] Run
6 FEET 9 - INCH
18 [Inch] [Store] [5] On-Center Spacing STORED
18 INCH
[Jack] Jack Rafter O-C Spacing STORED
18 INCH
[Jack] Incremental Jack Adjustment
1 FEET - 10 1/2 INCH
[Jack] Jack Rafter 1 Length
6 FEET - 6 3/4 INCH
[Jack] Jack Rafter 2 Length
4 FEET - 8 1/4 INCH
[Jack] Jack Rafter 3 Length
2 FEET - 9 3/4 INCH
[Jack] Jack Rafter 4 Length
0 FEET - 11 1/4 INCH
[Jack] Jack Rafter 5 Length
0 FEET - 0 INCH
[Jack] Plumb Cut
36.87°
[Jack] Level Cut
53.13°
[Jack] Cheek Cut 1
45.00°


2. You're working with a 7/12 Pitch, and half your overall span is 4 Feet. The irregular pitch is 8/12, and 16-Inch On-center spacing is maintained on both sides. Find the Irregular incremental jack adjustment and Irregular Jack rafter length and cut angles, then find the Regular incremental jack adjustment, Regular Jack rafter length and cut angles.

Step 1: Find Common rafter length.

Keystroke Display
[Clear] [Clear] 0.
7 [Inch] [Pitch] Pitch
7 INCH
4 [Feet] [Run] Run
4 FEET - 0 INCH
[Diag] Diagonal
4 FEET 7 9/16 INCH


Step 2: Enter the On-center spacing.

Keystroke Display
16 [Inch] [Store] [5] (o.c.) On-Center Spacing STORED
16 INCH


Step 3: Find Irregular Hip/Valley rafter length and cut angles.

Keystroke Display
8 [Inch] [Conv] [Hip/V] (Ir/Pitch) Irregular Pitch
8 INCH
[Hip/V] Irregular Hip/Valley Rafter Length
5 FEET - 9 11/16 INCH
[Hip/V] Plumb Cut
23.70°
[Hip/V] Level Cut
66.30°
[Hip/V] Cheek Cut 1
41.19°
[Hip/V] Cheek Cut 2
48.81°


Step 4: Find irregular incremental jack adjustment and Irregular Jack lengths.

Keystroke Display
[Conv] [Jack] (Ir/Jack) Irregular Jack Rafter O-C Spacing STORED
16 INCH
[Jack] Irregular Incremental Jack Adjustment
1 FEET - 4 13/16 INCH
[Jack] Irregular Jack Rafter 1 Length
2 FEET - 9 5/8 INCH
[Jack] Irregular Jack Rafter 2 Length
1 FEET - 4 13/16 INCH
[Jack] Irregular Jack Rafter 3 Length
0 FEET - 0 INCH


Step 5: Find the Irregular Jack plumb, level, and cheek cut angles.

Keystroke Display
[Jack] Plumb Cut
33.69°
[Jack] Level Cut
56.31°
[Jack] Cheek Cut 1
41.19°


Step 6: Find regular incremental jack adjustment and Regular Jack lengths.

Keystroke Display
[Jack] Jack Rafter O-C Spacing STORED
16 INCH
[Jack] Incremental Jack Adjustment
1 FEET - 9 3/16 INCH
[Jack] Jack Rafter 1 Length
2 FEET - 10 3/8 INCH
[Jack] Jack Rafter 2 Length
1 FEET - 1 1/4 INCH
[Jack] Jack Rafter 3 Length
0 FEET - 0 INCH


Step 7: Find Regular Jack plumb, level, and cheek cut angles.

Keystroke Display
[Jack] Plumb Cut
30.26°
[Jack] Level Cut
59.74°
[Jack] Cheek Cut 1
48.81°


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