Practical tools for measured work
Irregular Hip Roof Calculator for Unequal Pitches
Calculate the shifted plan angle, true hip length, face-specific backing bevels and jack differences for unequal roof pitches.
Calculate the layout, check the diagram, then print the result for the shop or jobsite.
Horizontal eave-to-intersection run, perpendicular to eave A.
At 600 mm spacing, theoretical jack-length differences are 1006.2 mm on roof A and 500.0 mm on roof B.
How it works
How to use it: enter both pitches and one horizontal run on roof A. The calculator finds the roof B run that reaches the same height at a square (90-degree) eave corner.
Geometry. The roof planes are z = slope A × x and z = slope B × y. Their intersection fixes the hip plan line. True length combines both plan runs and the rise. Each backing bevel is the roof slope seen in a vertical section perpendicular to that hip line.
Current-input example
The result above uses these exact values. This snapshot is included when the page is printed so the output can be checked against the original measurements.
- Roof A pitch rise
- 6
- Roof A pitch run
- 12
- Roof B pitch rise
- 9
- Roof B pitch run
- 12
- Roof A reference run
- 3600 mm
- Jack spacing along eaves
- 600 mm
Primary result: True hip length: 4686.1 mm.
Before using the result
- Measure from the datum or reference edge described by this tool, and do not mix inside, outside and centerline dimensions.
- Keep inputs in the displayed units and preserve more precision than the final cutting or purchasing tolerance requires.
- When the result is close to a limit, verify it with a test piece, field measurement, manufacturer drawing or qualified project professional.
Limitations
This assumes straight eaves meeting at 90 degrees and pitches rising from the same eave elevation. Values are theoretical face-line geometry with no ridge thickness, overhang, birdsmouth, timber-width, housing, or connection deductions. Backing bevels are referenced from level across the member. Verify conventions and a test cut locally. This is not structural sizing or code approval.
Frequently asked questions
Why is the hip not 45 degrees in plan?
With unequal pitches, the steeper roof needs less horizontal run to reach the same height, so the intersection shifts away from the equal-pitch diagonal.
Are the two backing bevels supposed to differ?
Yes. Each side follows a different roof plane, so an irregular hip generally needs a different bevel on each face.
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