Types of Roofs and Cutting Common Rafters

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Types of Roofs and Cutting Common Rafters

• Dr. David Agnew
• Arkansas State University

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Types of RoofsIn Agricultural Applications

• Hip
• Gothic
• Combination
• Uneven span

Types of roofs
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Types of Rafters
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Parts of A Roof..
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Definition of a Rafter

• Single timber supporting a roof section.

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Kinds of Rafters
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Parts of a Rafter
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Rafter Slope

• Roofs are not flat
• Pros and cons of low or steep roofs
• Cost of steep is higher for materials
• Harder and more dangerous to work on if steep
• Steep roofs have greater ability to withstand
  load
• Pitch
• Expressed as a Fraction ¼, 1/6, 1/8, etc.
• Rise/foot of run
• Example 2 in./ ft.
• Used in more plans today than pitch

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Calculating Pitch
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Procedures for Rafter Layout

• Three Techniques
• Stepping method
• Figuring length using
• A2 B2 C2
• Rafter Table

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Procedures for Rafter Layout

• Three Techniques
• Stepping method

steps feet of run
Ex
10
12
etc.
Step 1
2
3
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Procedures for Rafter Layout

• Three Techniques
• A2 B2 C2

2
C
2
B
A
2
A Run of Roof
Example If A4 , B3 then what would c? 16
9 25 then C sq root of 25 which is 5
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Resources Needed to Layout and Cut a Rafter

• Timber/Lumber (2x4, 2x6, 2x8, etc)
• Measuring Device-- Tape Measure
• Marking Pencil
• Rafter/Carpenters Square
• Saw
• Sawhorses
• Note The class project rafter layout will need
  some different supplies.

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Steps to layout of Rafter Using the Rafter Table.

• Determine Rise or Pitch
• Determine the Span and/or Run
• Using the table for common rafters on the Rafter
  Square Identify the length of rafter per ft of
  run.

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Rafter Layout Continued

• Multiply the run times the number from the table.
  That number is the length of the rafter But you
  are not done yet
• Identify the end of the board that you want to
  make the ridge cut.
• The square has a tongue and a body
• Tongue is the smaller of the two 18 inches long
  and 1 ½ inches wide.
• Body is larger 24 inches long and 2 inches wide.

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Parts of a Framing or Rafter Square
1.5 inches thick
Tounge

1. inches thick

18 "
Body
24 "
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Proper Use of the Square

• Always work from one side of the square (never
  flip it over).
• Remember to either use the numbers from the outer
  edge or inner edge, but do not use both at one
  time.

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Ridge Cut

• Using the appropriate numbers on the square (ex.
  4 and 12) place the square near the end of the
  board where the cut is to be made. See picture
  below.