Understanding Rafter Cuts
Rafters require several precise cuts to properly fit and support the roof structure.
-
Types of Cuts
- Plumb Cut: At ridge board connection
- Bird's Mouth: Seat on wall plate
- Tail Cut: At rafter overhang
-
Bird's Mouth Guidelines
- Maximum depth: 1/3 rafter depth
- Minimum seat: 3 inches
- Position: Inside edge of wall
Technical Specifications
Common Rafter Sizes
- 2x4: Light loads, short spans
- 2x6: Standard residential
- 2x8: Longer spans
- 2x10/12: Heavy loads
Recommended Overhangs
- Minimum: 12 inches
- Standard: 16-24 inches
- Maximum: 36 inches
Design Formulas
Rafter Length
L = √(rise² + run²)
Where:
- L = Rafter length
- Rise = Vertical height
- Run = Horizontal distance
Ridge Height
H = (span × pitch) / 24
Where:
- H = Ridge height
- Span = Building width
- Pitch = Rise per foot
Bird's Mouth Depth
Maximum depth = Rafter depth / 3
Factors to consider:
- Rafter size
- Roof pitch
- Load requirements