Geometric Models of
Square Fascia intersects Main Roof

Main Roof Ridge and Dormer Ridge intercept = 90°

Elevations of Dormer and Main Roof
Section Views

Purlin/Square Tail Fascia intercepts Plane of Main Roof
Square Fascia extracted from Model of Reciprocal Dormer Pitch

Fascia Wedge nested on Main Roof Wedge
Tetrahedron modelling Square Fascia nested on 7/12 Main Roof Wedge

Square Cut Fascia Wedge removed from Main Roof Wedge
Model of Square Fascia

Square Cut Fascia Wedge equivalent to section removed from Hip Roof
Extracted Section of Irregular Hip Roof
equivalent to model of Square Fascia Angles
Backing Angle = arcsin (sin Common Rafter Pitch Angle × cos Plan Angle)
Jack Rafter Side Cut Angle = arctan (cos Common Rafter Pitch Angle ÷ tan Plan Angle)
Sheathing Angle = arctan (tan Plan Angle ÷ cos Common Rafter Pitch Angle)

Square Cut Fascia Wedge equivalent to section removed from Hip Roof
Dimensioned Model of Square Fascia

Solution of Fascia Bevel and Miter Angles
Working directly from the model dimensions:

Solution of Fascia Miter Angle and Angle on the Fascia
Square Fascia Miter and Bevel Angles
Joe Bartok
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