Common Rafter Common Rafter

A common rafter is used to construct many different kinds of roofs and it extends from the top of the wall to the ridge. When you are building a common rafter it is very important that you get the exact dimensions of it right. Many construction workers like to use the Pythagorean Theorem (a2 + b2 = c2) to figure out the length of the common rafter.

  • Figure out the height of the roof, this represents a. Start at the crest of the roof an measure straight down to where the roof stops.
  • The run of the building must be measured out in inches and represents b. This will be measured from the center of the floor below where the common rafter will be, to the wall.
  • Square a, and then square b. Squaring is to multiply the number by itself.
  • Add together a squared and b squared and you will get c squared.
  • To find the length of your common rafter you have to find the square root of this number.

Using the Pythagorean Theorem to Find A Common Rafter Length

If you don't use this method often it is best to double check your work and have someone look it over before you cut the common rafter. Some calculators will let you slip in the numbers and it will calculate it for you, but a regular calculator is capable of doing the work the long way.

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