How to calculate birdsmouth cut?

Birdsmouth cuts are based on wall thickness and local building codes. The cut allows the rafter to sit properly on the wall plate while maintaining structural integrity.

How to handle valley rafters?

Valley rafters require special calculations as they run at an angle where two roof planes intersect. Use the valley rafter option in the calculator for accurate dimensions.

What about snow load considerations?

Consider local snow load requirements when sizing rafters. Areas with heavy snowfall may require larger rafter dimensions or closer spacing to support the additional weight.

Rafter Length Calculator

Q: What is rafter spacing?

Rafter spacing is the distance between rafters, typically 16-24 inches on center. The spacing affects the load capacity and material requirements for your roof structure.

Q: What affects rafter size?

Rafter size is determined by span length, roof load (snow, wind, dead load), material strength, and local building codes. Larger spans require larger rafter dimensions.

Rafter Parameters

Span

Building width

Roof Pitch

Roof slope

Overhang

Eave extension

Rafter Type

Select rafter type

Calculation Results

Rafter Length Calculator: Your Guide to Roof Framing

Need to calculate rafter lengths for your roof? Our Rafter Length Calculator helps you determine the exact dimensions needed for your roof framing project.

Understanding Rafter Calculations

Rafter calculations are important for several reasons:

Structural Integrity: Proper roof support
Material Planning: Accurate lumber estimates
Cost Control: Budget management
Safety: Load-bearing capacity
Code Compliance: Building standards

How to Use the Rafter Length Calculator

Enter Span: Input building width
Enter Pitch: Input roof slope
Enter Overhang: Input eave extension
Select Rafter Type: Choose rafter style
Click Calculate: Get rafter dimensions

Rafter Length Calculation Formulas

Common Rafter Length:
L = √(S² + (S × P)²) + O

Hip Rafter Length:
L = √(S² + (S × P)²) × 1.414 + O

Valley Rafter Length:
L = √(S² + (S × P)²) × 1.414 + O

Where:
L = Rafter length
S = Span/2
P = Pitch ratio
O = Overhang

Common Rafter Specifications

Common Rafter:
- Use: Standard roof framing
- Spacing: 16-24 inches
- Material: 2x6 to 2x12
- Connection: Ridge and wall plate
Hip Rafter:
- Use: Hip roof corners
- Spacing: 16-24 inches
- Material: 2x8 to 2x12
- Connection: Ridge and corner
Valley Rafter:
- Use: Valley intersections
- Spacing: 16-24 inches
- Material: 2x8 to 2x12
- Connection: Ridge and valley
Jack Rafter:
- Use: Hip and valley fill
- Spacing: 16-24 inches
- Material: 2x6 to 2x12
- Connection: Hip/valley to wall

Real-World Examples

Example 1: Standard Gable Roof

Span: 24 feet
Pitch: 30 degrees
Overhang: 12 inches
Rafter Type: Common
Results:
- Rafter Length: 13.86 feet
- Run: 12 feet
- Rise: 6.93 feet
- Total Length: 14.86 feet

Example 2: Hip Roof Corner

Span: 30 feet
Pitch: 35 degrees
Overhang: 16 inches
Rafter Type: Hip
Results:
- Rafter Length: 19.60 feet
- Run: 15 feet
- Rise: 10.50 feet
- Total Length: 20.93 feet

Frequently Asked Questions

What is rafter spacing?

Typically 16-24 inches on center.

How to calculate birdsmouth?

Based on wall thickness and local codes.

What affects rafter size?

Span, load, and material strength.

How to handle valleys?

Use proper valley rafter calculations.

What about snow load?

Consider local snow load requirements.