🔨 Birdsmouth Cut Calculator
Professional rafter birdsmouth cut calculator with advanced measurements and visual diagrams
Input Parameters
inches
inches
:
Results
Birdsmouth Depth
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Seat Cut Length
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Plumb Cut Angle
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Remaining Rafter Height
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Code Compliance
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Seat Cut Angle
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Visual Diagram
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What is a Birdsmouth Cut?
A birdsmouth cut is a notch cut into the bottom of a rafter that allows it to sit flush on the top plate of a wall. It consists of two cuts:
- Plumb Cut (Heel Cut): The vertical cut that sits against the wall
- Seat Cut (Level Cut): The horizontal cut that rests on the top plate
Building Code Requirements
According to IRC (International Residential Code):
- The birdsmouth depth should not exceed 1/3 of the rafter depth
- Minimum bearing length on the wall plate should be 1.5 inches
- The remaining rafter height must maintain structural integrity
How to Use This Calculator
1. Enter your rafter dimensions (depth and width)
2. Input your roof pitch (typically expressed as rise over 12 inches of run)
3. Select your building code requirements
4. Click Calculate to get your birdsmouth measurements
5. Use the visual diagram to understand the cuts