How to Calculate the Riser Length for the Ridge Board

A building's roof is angled to shed rainwater away from the home. When building such a structure, some basic mathematics is used to determine the ridge board riser length. The ridge board is the horizontal member that rests at the peak of the roof. The length of the ridge board varies according to the type of roof you want to build. For a gable roof it is simply the length of the building plus the overhang on each end. A hip style roof is slightly more difficult to calculate.

Instructions

1. • 1

     Divide the width of the building by two. The result is the center of the ridge.

   • 2

     Divide the width of the ridge board by two. This is typically 1 1/2 inches divided by two, equaling 3/4 inch. Subtract the result from the width of half of the building.

   • 3

     Multiply the result from Step 2 by two and subtract this result from the total length of the building. The answer is the length of the ridge board on a hip roof.