Oblique Hip

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Oblique Hip

• Creeper calculations, Rafter shortening and
  Pattern Rafter

M.S.Martin June 2005 Reviewed Feb - 2008
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We need to transfer distance d up to be able to
calculate the true length for creeper reductions
We can do this by looking at it as a ratio
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Follow these calculations in your text

• Unknown side d spacing ½ span side
  offset distance
• d 600 3320 5300
• d 3.320 apply cross multiplication
• .600 5.300
• d x 5.300 .600 x 3.320
• d .600 x 3.320
• 5.300
• d .376 this is the plan length for the creeper
  reduction
• We can now use this measurement like we do with
  the ½ span to find our centre line length on the
  common rafter.
• This time we want to find the true length for
  creeper reduction on the common rafter.
• using the true length per / m for common rafter x
  d
• 1.155 x .376 .434 this is the true length
  creeper reduction for hip A

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Simplify the Formula

• d rafter spacing x ½ span
• side offset
• Then true length per / m x d
• Now apply this to obtain the true length for
  creeper reduction for hip B

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Hip B

• d rafter spacing x ½ span
• side offset
• d .600 x 3.320 .958
• 2.080
• true length per / m x d
• 1.155 x .958 1.106

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Rafter Shortening distances

• Set out of Pattern Rafter

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Rafter Shortening

• For common rafters this is no different to
  another roof, the rafter is shortened by half
  thickness of ridge.
• For the crown end, still shortened by half the
  thickness of common rafter, but measure this so
  it is at right angles to both the plumb cut and
  the edge bevel.

The next slide shows this at the gathering point
of a roof
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Set out of Common Rafter

• At one end of your timber mark the plumb bevel
  common rafter, this is your centre line.
• Measure along the rafter your true length and put
  another plumb bevel C/R for the back of the
  birdsmouth.
• Measure off your eaves overhang put another plumb
  bevel C/R for its full length.
• Now go back to your original plumb bevel (centre
  line) measure off your calculated creeper
  difference (example used 434mm) and mark in the
  plumb bevel.
• Add or subtract creeper correction from this
  point to establish the first creeper long point.
• You can now mark the remaining creepers from this
  point down the length of the rafter
• Mark the crown end reduction at top
• On other side of rafter repeat the creeper
  process for hip B

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Note shortening for first creeperThis will be
different for Hip A and Hip B
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Pattern Rafter