Creeper calculations, Rafter shortening and Pattern Rafter Oblique Hip Creeper calculations, Rafter shortening and Pattern Rafter M.S.Martin June 2005 Reviewed Feb - 2008

We can do this by looking at it as a ratio 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

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

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

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

Rafter Shortening distances & Set out of Pattern Rafter

The next slide shows this at the gathering point of a roof 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

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

Note shortening for first creeper This will be different for Hip A and Hip B

Pattern Rafter