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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.