Collar Tie Calculator
A collar tie is a horizontal structural element that connects opposing rafters in a roof structure. It helps to resist the outward thrust at the top of walls, which can occur due to the weight of the roof and external forces like wind or snow loads. This calculator helps determine the appropriate length of collar ties for your roof construction project.
How to Use the Calculator
- Roof Span: Enter the total span of your roof in feet. This is the horizontal distance between the two walls that support the roof.
- Roof Pitch: Enter the pitch of your roof as a slope ratio (e.g., 6/12 means the roof rises 6 inches for every 12 inches of horizontal run).
- Height of Collar Tie: Enter the vertical height from the top plate (the top horizontal member of the wall) to where the collar tie will be installed.
Click "Calculate" to determine the required length of the collar tie.
Formula
The collar tie length is calculated using the Pythagorean theorem:
Collar Tie Length = √((Roof Span/2)² + (Collar Tie Height)²)
Where:
- Roof Span/2 represents half the total roof span
- Collar Tie Height is the vertical distance from the top plate to the collar tie
Importance of Collar Ties
Collar ties are crucial for maintaining the structural integrity of a roof system. They:
- Prevent the roof from spreading outward at the eaves
- Reduce the risk of wall collapse due to outward thrust
- Help distribute roof loads more evenly
- Are especially important in areas with high wind loads or significant snowfall
Example Calculation
For a roof with:
- Roof Span: 20 feet
- Roof Pitch: 6/12
- Collar Tie Height: 4 feet
Calculation:
- Half Span = 20/2 = 10 feet
- Collar Tie Height = (6/12) × 4 = 2 feet
- Collar Tie Length = √(10² + 2²) = √104 ≈ 10.20 feet
The required collar tie length is approximately 10.20 feet.