Lecture on Roof Construction: Rafter Cutting and Building a Roof

Introduction

• Focus on cutting a rafter and building a roof.
• Importance of clear explanation for first-time builders.
• Anna assists to clarify any unclear explanations.

Key Concepts

• Rafters: Boards on a slope to ensure water runoff.
• Roof Pitch: Vital for making accurate cuts.
  • Example: An 8-12 pitch vs. a flatter pitch.

Types of Roofs

• Gable Roof: Two slopes on either side of a ridge; think Snoopy's Doghouse.
• Shed Roof: Single slope to one side.
• Hip Roof: Slopes on all sides like a pyramid.
• Barn/Gambrel Roof: Different configurations often combined in structures.

Common Rafter

• Definition: Runs from the wall up to the ridge.
• In gable roofs, common rafters determine ridge height.
• Other types of rafters: Valley, Hip, Jack.

Cutting a Rafter

• Key Measurements: Run, Rise, and Roof Pitch.
  • Run: Horizontal distance covered by the rafter.
  • Rise: Vertical distance the rafter travels.
  • Example: An 8-12 pitch rises 8 inches per 12 inches of run.
• Span: Full width of the building.
  • Run is half the span.

Tools and Marking

• Framing Square: Essential tool for accuracy.
  • Use either all outside or inside scales, never mix.
• Marking Cuts: Plumb (vertical) and Level (horizontal) cuts.

Measuring Rafter Length

• Methods:
  1. Trigonometry: Using the Pythagorean theorem.
  2. Framing Square: Using square to step off the length.
  3. Rafter Table Book: Pre-calculated lengths and angles (e.g., Roof Framer's Bible).
• Adjustment for Ridge and Tail: Deduct half ridge thickness and add tail length.

Practical Steps

• Step-off Method: Using the framing square to measure length.
  • Issues: Inaccuracies due to cumulative error.
• Using Framing Square Charts: Provides per foot rafter length based on pitch.
• Using Rafter Tables: Comprehensive pre-calculated tables.

Rafter Layout

• Common Rafter Length: Deduction for ridge thickness.
• Seat Cut (Bird's Mouth): Ensure full bearing on wall.
• Overhang and Fascia: Adjustment for fascia and flat soffit.

Conclusion

• Component Parts: Break the roof into sections for easier construction.
  • Solve for each section's run numbers and rafter lengths.
• Complex Roofs: Any roof can be framed with these principles.
• Upcoming video: Building a hip roof.

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Tips:

• Always measure along the top edge of the rafter.
• Use proper tools and methods to ensure accuracy.
• Divide and conquer in roof framing by solving each section individually.