Types of Roofs and Cutting Common Rafters Dr. David Agnew Arkansas State University

Types of Roofs: In Agricultural Applications Hip Gothic Combination Uneven span Types of roofs

Types of Rafters

Parts of A Roof…..

Definition of a Rafter Single timber supporting a roof section.

Kinds of Rafters

Parts of a Rafter

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

Calculating Pitch

Procedures for Rafter Layout Three Techniques Stepping method Figuring length using A 2 + B 2 = C 2 Rafter Table

Procedures for Rafter Layout Three Techniques Stepping method # steps= feet of run

Procedures for Rafter Layout Three Techniques A 2 + B 2 = C 2 Example: If A=4, B=3 then what would c=? = 25 then C= sq root of 25 which is 5 A= Run of Roof

Resources Needed to Layout and Cut a Rafter Timber/Lumber (2x4, 2x6, 2x8, etc) Measuring Device-- Tape Measure Marking Pencil Rafter/Carpenter’s Square Saw Sawhorses Note: The class project rafter layout will need some different supplies.

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.

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.

Parts of a Framing or Rafter Square 1.5 inches thick 2inches thick

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.

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.