1. What is Rafter Length Calculation?

The rafter length calculation determines the length of roof rafters needed for construction based on the building span and roof pitch. This is essential for proper roof framing in UK building projects.

2. How Does the Calculator Work?

The calculator uses the rafter length formula:

Where:

• \( \text{Span} \) — The horizontal distance between walls (meters)
• \( \text{Pitch} \) — The angle of the roof slope (degrees)
• \( \cos \) — Trigonometric cosine function

Explanation: The formula calculates the hypotenuse of the right triangle formed by half the span and the roof pitch angle, then doubles it for the full rafter length.

3. Importance of Accurate Rafter Length

Details: Correct rafter length ensures proper roof structure, prevents material waste, and maintains building integrity. It affects roof pitch, overhang, and overall aesthetics.

4. Using the Calculator

Tips: Enter the span in meters (wall to wall distance) and roof pitch in degrees (typically between 30°-45° for UK roofs). Ensure pitch is between 0°-90°.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between span and run?
A: Span is the total horizontal distance between walls, while run is half the span (center to wall).

Q2: How does pitch affect rafter length?
A: Steeper pitches (higher degrees) result in longer rafters for the same span compared to shallower pitches.

Q3: Should I add extra length for overhangs?
A: Yes, this calculator gives the basic rafter length. Add additional length for any desired eaves overhang.

Q4: Is this calculation suitable for all roof types?
A: This works for simple gable roofs. More complex roofs (hip, valley) require additional calculations.

Q5: What's the typical rafter spacing in the UK?
A: Standard spacing is 400mm or 600mm centers, but always check building regulations for your specific project.