1. VALLEY JACK THEORY AND LAYOUT
Presentation 23:
VALLEY JACK THEORY AND LAYOUT

2. Jack Rafters Jack rafters are OC rafters that must be shortened.
Valley Jack Rafters

3. Valley Jack Run
Zooming into this portion of the roof will help reveal the valley jack run.

4. Valley Jack Run
Removing some nearby rafters for clarity reveals…

5. Valley Jack Run
Valley jack run is the horizontal distance under the rafter.
The total rise is vertical.

6. Valley Jack Run
Since valley run, like hip run, is at a 45 angle with the side walls, a square is formed under the valley jack.

7. Valley Jack Run
A corner of the square is directly under the three-way intersection of two valleys and the ridgeboard.

8. Valley Jack Run
One side of the square is equal to the distance from the valley jack to the three-way intersection.

9. Valley Jack Run
Thus, a valley jack’s run is equal to its distance from the three-way intersection.

10. Valley Jack Run
This is true of all jacks.

11. Valley Jack Run
This is true of all jacks.

12. Valley Jack Run
This is true of all jacks.

13. Valley Jack Length Lengths are calculated the same as common rafters.
Length = Unit Length x Run.

14. Common Difference
The jack rafters of a roof have a common difference in length from one another.
This is because they are evenly spaced.
Typical rafter spacing is 16″ OC.

15. Common Difference
The difference in run between adjacent jack rafters is the OC spacing.
OC Spacing (ft) x unit length = difference in length

16. Conclusions Jack rafters are OC rafters cut short.
The run under a valley jack is equal to the distance from the jack’s location along the ridge to the end of the ridge.
Difference in run between adjacent jacks is the OC spacing.