Hip Rafter Calculator – Guide & Formulas
Calculate hip and valley rafter lengths, backing angles, and jack rafter offsets based on main pitch and run.
Calculate hip and valley rafter lengths, backing bevel angles, cheek cut angles, and jack rafter progressive offsets. Perfect for framing compound sloped roof structures.
Key Takeaway
Use the free Hip Rafter Calculator to calculate hip and valley rafter lengths, backing angles, and jack rafter offsets based on main pitch and run. Get instant results with step-by-step explanations.
How to Use the Hip Rafter Calculator
- Enter the span of the building (or horizontal run of the common rafter).
- Input the roof pitch ratio (e.g. 6/12).
- Provide overhang depth and structural ridge thickness to isolate exact rafter lengths.
The Formula
Variable Definitions
- L_hip: Lineal length of the hip or valley rafter
- Run: Horizontal run of the common rafter
- Rise: Vertical rise height of the ridge
Hip Rafter for a 10ft Common Run
Find the hip rafter length for a roof with a common run of 10 feet and a rise of 5 feet (6/12 pitch ratio).
- Step 1: Calculate run square: 10² = 100. Double it: 200.
- Step 2: Add rise square: 5² = 25. Total = 225.
- Step 3: Solve square root: √225 = 15 feet.
- Step 4: The hip rafter length is exactly 15.00 feet before adding any sloped tail overhang.
Frequently Asked Questions
Why is a hip rafter longer than a common rafter?
Because a hip rafter runs at a 45-degree angle relative to the building walls, extending diagonally from the corner to the ridge, whereas common rafters run at a 90-degree angle straight up.
What is a backing angle on a hip rafter?
It is the bevel angle cut along the top edge of the hip rafter so the roof sheathing sits flat across both intersecting planes of the hip.
What is jack rafter offset?
It is the progressive difference in length between consecutive short rafters (jack rafters) that intersect the hip rafter at regular spacings.