We use inches in this example.Īdditionally, we need to calculate the roof angle by plugging arctangent (6/12) into a calculator.įollowing these recalculations, we have the following: Let’s say you’re building a roof with the following dimensions:įirst, let’s convert all measurements to the same unit. Rafter overhang – The horizontal distance the rafter projects past the outside wall. Roof slope – The roof rise and run, expressed by a ratio that indicates roof steepness.Ĥ. Ridge boards are usually made of 2-by board, so 1.5 inches is typical.ģ.
Ridge board thickness – The thickness of the board where the top ends of the opposite rafters meet. Roof span – Also called the building width or rafter span, this measurement refers to the distance between the outside opposite walls.Ģ. To determine roof rafter length, you need to know the following four measurements:ġ. How Do I Figure Out How Many Rafters I Need? Plug Your Measurements Into the Rafter Length Formula It might trigger traumatic memories of high school math class, but the sheer bliss in knowing that you sized your rafters correctly is well worth it. To put you on par with the experts, we provide the formula carpenters use to figure out common rafter sizing and where to mark cuts.Īll you need is paper, a pencil, and a scientific calculator.
#2X6 RAFTER SPAN HOW TO#
Seasoned framers know how to calculate this crucial measurement no matter the project requirements thanks to millennia-old trigonometry.
Before building a gable roof or hip roof, you need to know your common rafter sizes.
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