Practical tools for measured work
Unequal-Pitch Valley Rafter Calculator
Calculate internal valley centerline geometry, separate backing bevels and side-specific jack differences for two unequal roof pitches.
Calculate the layout, check the diagram, then print the result for the shop or jobsite.
Perpendicular from its eave to the valley's high endpoint.
Jack common differences at 400 mm eave spacing: main side 693.3 mm; intersecting side 300.5 mm. Bevel direction is inward for a valley.
How it works
How to use it: describe the two roof planes forming an internal valley. Enter the main roof run; the calculator matches the intersecting roof to the same vertical rise.
What is distinct here. Unlike an equal-pitch hip/valley calculator, this reports the shifted valley plan angle, separate backing bevels and a separate jack common difference for each roof side.
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.
- Main roof pitch rise
- 5
- Main roof pitch run
- 12
- Intersecting roof pitch rise
- 8
- Intersecting roof pitch run
- 12
- Main roof horizontal run
- 4200 mm
- Jack spacing along eaves
- 400 mm
Primary result: True valley length: 5252.9 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 is an internal-corner interpretation of the same plane-intersection geometry used by irregular hips. It assumes a 90-degree plan corner, common eave elevation and no offsets. It does not deduct ridge, valley-board or plate details, size members, or verify drainage, loading or code. Confirm which face and bevel direction your saw or framing convention references.
Frequently asked questions
Can I use hip-rafter numbers for this valley?
The centerline geometry is shared, but a valley is concave: bevel direction, support and detailing differ. Use these values as layout geometry and verify the physical joint.
Why are there two jack differences?
The pitches and the valley's plan angle differ on each side, so equal spacing along each eave does not create the same change in rafter length.
Related tools
Irregular Hip Roof
Calculate the shifted plan angle, true hip length, face-specific backing bevels and jack differences for unequal roof pitches.
Advanced Hip/Valley/Jack
Calculate hip, valley and jack rafter seat cuts and compound cheek (side) cuts, beyond length and plumb angle alone.
Baluster Spacing Calculator
Enter the railing opening, baluster width and maximum gap you intend to use to calculate an equal-spacing layout.
Fence Picket Spacing
Lay out fence picket spacing across a run, with a live diagram of the finished fence section.