Sunday, May 5, 2013

Octagon Roof Framing Using Traditional Layout Geometry

This Octagon Roof Framing  drawing was developed using Traditional Layout geometry. It gets pretty messy with all the construction lines.

The octagon ground plan has:

  1. R1 -- Jack Rafter plumb to earth, perpendicular to plate line with double miter angles at the peak of the jack rafter and sloping tail return angle. (90°)
  2. R2 -- Jack Rafter plumb to earth, perpendicular to plate line with single miter at the peak of the jack rafter and the claw seat at the hip rafter and  sloping tail return angle. 
  3. R3 -- Octagon Hip Rafter with  sloping tail return angles.
  4. R4 -- Purlin rafter with claw tips, purlin lip cut angles.
  5. R5 --  Jack Rafter plumb to earth, offset/skewed from plate line with single miter angle at the peak of the jack rafter and sloping tail return angle.


In this image of the drawing I turned off the construction lines and dimensions layers.


As you can see it gets pretty messy with all of the construction lines.


Here we have  witches cut on the hip rafter. I've label the lines in the order that they should be drawn. Point # 3 is the critical area. If this is not drawn correctly the  bevel angles on top of the hip rafter tail will not be correct.


The claw on the jack rafter seat at the hip rafter is developed from the H1 & H2 dimension that were first developed from the hip rafter plumb line. 


The claws on the purlin are developed from the plan view of the purlin developed from the purlin at the profile rafter.


The Jack Rafter plumb to earth and  offset/skewed from plate line was developed using dimensions from the plan view.




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