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1 Presentation 27: HIP JACK THEORY AND LAYOUT
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Presentation 27:
HIP JACK THEORY AND LAYOUT
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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.
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Hip Jack Rafters
Hip Rafter
Ridgeboard
Common Rafters
Hip Jack Rafters
``
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Hip and Common Rafter Run
Run is the horizontal under the rafter.This is true for all rafters.The red lines represent the run for each rafter.
This applies to jack rafters too.
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Hip Jack Rafter Run
The red distances here are the same length.Therefore a square is formed under each pair of jack rafters.
This applies to jack rafters too.
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Hip Jack Rafter Run
The jack rafter run is equal to the jack’s distance from the corner.
RunDistance from the corner
They are the same measurement.
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Common Difference
A square is formed
Hip run is at a 45° angle with the building line.
45°
All red distances are equal
OC Jack Rafter Spacing
Adjacent jack rafters have a difference in run that is equal to the OC spacing.
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Common difference LENGTH of jack rafters
Common Difference
OC Jack Rafter Spacing
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.
45° Common difference in RUN of jack rafters
All red distances are equal
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CDL = OC (terms of feet) x Unit length
Common Difference
Common difference in length (CDL) may be calculated.
OC Jack Rafter Spacing
CDL
Or may be found on the third and fourth line on a rafter square.
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Hip Jack Tails
• Since hip jacks are shortened OC rafters, the tails are laid out the same.
• Use the common rafter pattern.
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Hip Jack Upper End
• Hip jacks are shortened and have side cuts in the same fashion as hip rafters.
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Hip Jack Layout for Hip
• Draw plumb line.
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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.
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Hip Jack Layout for Hip
Usually
3/4″
Usually 1 1/16″
• Side cuts are made by measuring ½ the jack thickness.
• Draw angled line over the top.
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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.
