Intersection of Jack Rafter with Hip or Valley Rafter
Study of Chamfer Cut or Square Cut along the Plumb Line


Tetrahedron modeling Chamfer Cut or Square Cut along plumb line of the Jack Rafter
Jack Rafter superimposed on Tetrahedron modeling Chamfer Cut or Square Cut along plumb line of the Jack Rafter
Exploded view of component triangles ... Tetrahedron modeling Chamfer Cut or Square Cut along plumb line of the Jack Rafter
Development of Tetrahedron modeling Chamfer Cut or Square Cut along plumb line of the Jack Rafter
SS ... Common Slope Angle measured from level.

DD ... Plan Angle measured between the Hip run and the eave line, or the Valley run and the ridge line.

R1 ... Hip-Valley Slope Angle measured from level.

A7 ... "Plumb Backing Angle", the angle viewed in section on a backed Hip-Valley rafter if the cutting plane is rotated to plumb through the Hip-Valley Slope Angle R1.

P5 ... Tenon Layout Angle on the jack rafter shoulder set in the surface of the roof to produce a tenon face perpendicular to the side (plumb) face of the Hip-Valley rafter. Also the angle created on the jack rafter by the housing chamfer cut (square cut) for the plumb line (the chamfer to remove the feather edge along miter angle SS).

Cutting the housing to accommodate the jack rafter on the Hip-Valley rafter creates angle 90 A9 on the backed shoulder of the Hip-Valley.

Angles P5 and A9 are produced by a plumb section plane or cutting plane intersecting the backed shoulder of a Hip-Valley rafter, the section plane also following a line at right angles to the Hip-Valley run in plan view.

P5BV ... Saw Blade Bevel to cut the tenon from the upper shoulder of the jack rafter, along the miter line produced by angle P5.

Joe Bartok