How to Design the Pitch Slope of a Gambrel Roof

The gambrel style is a distinctive roof design characterized by bent rafters that create four roof planes rather than the two planes that are generally on typical gable roofs. The gambrel roof originated with barn designs because the style creates more storage space that other styles. Designing an attractive and functional gambrel roof and adjusting its pitch slope requires some basic geometry skills.

Instructions

- 1
  Draw an octagon on a piece of paper. Draw a line through the center of the octagon from one corner to an opposite corner. Position the figure so that the line you drew through the center is horizontal in front of you. The four sides of the octagon above the line represent the basic shape of a gambrel roof.
- 2
  Modify the joint angles and rafter lengths of the basic roof to suit your needs. In a basic gambrel roof, all four rafters are the same length, and each of the three joints is 45 degrees. The center rafters are 22 1/2 degrees from horizontal, and the outer two rafters are 67 1/2 degrees from horizontal.
- 3
  Broaden the angles of the two side joints for a wider roof, such as for a barn in which you want a lot of storage but don't want the roof to be too tall. Extend the length of the side rafters to create a taller and narrower gambrel roof.

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