# How to Calculate the Angle of a Gambrel Roof Truss

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#### Things You'll Need

• Graph paper

• Protractor

A gambrel style is often called a barn roof. Its double, or sometimes triple, slopes on each side of a peak provide more space inside the roof, which is attractive to homeowners too. A gable roof has only two rafter or truss chord angles, a top cut at the peak and a bottom cut at the walls. A gambrel has four angles, at the peak, at the wall and where the two rafters or truss chords connect. There are three ways to calculate angles for gable trusses, which are rafters built with internal braces and installed as a unit.

## Step 1

Calculate gambrel angles with graph paper and a protractor. Draw a semi-circle on the graph paper, mark a center peak at the top and draw two lines on each side in the shape desired for the gambrel roof. Use the protractor to measure those angles, at the peak, the walls and the point where the two lines intersect on the top side of the roof.

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## Step 2

Determine a pitch for the top slope of the gambrel roof, the rise in inches per foot from the midpoint connection to the peak; 7/12, or a rise of 7 inches per foot, is a common top gambrel pitch. Reverse that for the bottom angle; make that pitch 12/7, a drop of 7 inches per foot from the connection to the wall. Draw a scale plan on graph paper and measure the rise to figure the pitch.