Herramientas prácticas para trabajos de precisión
Calculadora de Corte de Boca de Pájaro y HAP del Cabio
Convierta la pendiente del techo y el ancho de la solera en el asiento de la boca de pájaro, la profundidad de la muesca y la altura sobre la solera (HAP).
Example: 0.3333 means one third
The result stays within the user-entered notch fraction. That is not a structural approval.
How it works
How to use it: enter roof pitch, actual rafter depth, wall-plate width and the notch limit you intend to check. The calculator translates pitch into seat length, vertical notch depth and height above plate (HAP).
Formula. Angle = atan(rise / run). The horizontal seat bearing equals the entered plate width. Vertical notch depth = plate width x tan(angle). HAP = rafter depth - notch depth.
Worked example. At 4 in 12 pitch with an 89 mm plate, vertical notch depth is 89 x (4/12) = 29.67 mm. A 184 mm rafter retains 154.33 mm HAP.
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.
- Pitch rise
- 4
- Pitch run
- 12
- Rafter depth
- 184 mm
- Wall plate width
- 89 mm
- Your maximum notch fraction
- 0.3333
Primary result: Horizontal seat bearing: 89.0 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 cut geometry only. It does not size the rafter, account for ridge and overhang cuts, or certify a notch under any building code. Accepted notch limits and bearing details vary. Enter your own limit and have structural work checked locally.
Frequently asked questions
What is HAP?
Height above plate is the vertical amount of rafter material remaining above the wall plate after the birdsmouth is cut.
Why is the notch limit editable?
Rules and framing details differ. The tool should compare against your confirmed requirement, not present one rule of thumb as universal.
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