1. HIP JACK THEORY AND LAYOUT
Presentation 27:
HIP JACK THEORY AND LAYOUT

2. Hip Jack Rafters All jack rafters are OC rafters.
They are cut shorter because of the presence of another member.
For hip jacks, this member is a hip rafter.
They are considered special common rafters.

3. Hip Jack Rafters Hip Rafter Ridgeboard Common Rafters Hip Jack Rafters` `

4. Hip and Common Rafter Run
Run is the horizontal under the rafter.
This applies to jack rafters too.
This is true for all rafters.
The red lines represent the run for each rafter.

5. Hip Jack Rafter Run This applies to jack rafters too.
The red distances here are the same length.
This applies to jack rafters too.
Therefore a square is formed under each pair of jack rafters.

6. Hip Jack Rafter Run
The jack rafter run is equal to the jack’s distance from the corner.
They are the same measurement.
Run
Distance from the corner

7. Common Difference Hip run is at a 45° angle with the building line.
A square
is formed
Adjacent jack rafters have a difference in run that is equal to the OC spacing.
45°
OC Jack Rafter Spacing
All red distances are equal

8. Common Difference Hip run is at a 45° angle with the building line.
Adjacent jack rafters have a difference in run that is equal to the OC spacing.
Common difference LENGTH of jack rafters
45°
Common difference in RUN of jack rafters
OC Jack Rafter Spacing
All red distances are equal

9. Common Difference Common difference in length (CDL) may be calculated.
CDL = OC (terms of feet) x Unit length
CDL
Or may be found on the third and fourth line on a rafter square.
OC Jack Rafter Spacing

10. Hip Jack Tails
Since hip jacks are shortened OC rafters, the tails are laid out the same.
Use the common rafter pattern.

11. Hip Jack Upper End
Hip jacks are shortened and have side cuts in the same fashion as hip rafters.

12. Hip Jack Layout for Hip
Draw plumb line.

13. Hip Jack Layout for Hip
Rafter is shortened for the hip ½ the diagonal thickness of the hip.
Usually 1 1/16″
Draw a square line on the top with a center mark.

14. Hip Jack Layout for Hip Usually 3/4″
Side cuts are made by measuring ½ the jack thickness.
Usually 1 1/16″
Usually 3/4″
Draw angled line over the top.

15. Conclusions
Hip jacks are OC rafters with tails the same as common rafters.
Adjacent hip jacks have a common difference in length.
Hip run is equal to the distance the jack is located from the building corner.
Shortening and side cuts may be handled in the same fashion as for hip rafters.