How to Calculate a Gambrel Roof
Gambrel roofs have two sides that meet in the center to form a raised ridge. Each side is split into two horizontal sections with differing slopes. The upper portion has a smaller pitch to increase available space in the upper floors. The lower roof portions have a steeper pitch that prevents snow and rain accumulation. This split-roof design is commonly found on older barns and 17th and 18th century homes. Does this Spark an idea?
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Instructions
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1
Determine the length of the roof.
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2
Determine the vertical height and horizontal width of one side of the upper roof.
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3
Divide the height by the width of the upper roof.
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4
Use a calculator with tangent functions to apply the inverse tangent (TAN-1 on most calculators) to find the angle of pitch in degrees of the upper roof.
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5
Square the height and width. Add them together.
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6
Find the square root. This is the flat width of the upper roof.
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7
Multiply the width by the length of the roof to find the total area of the upper roof.
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8
Repeat Steps 1 to 7 to calculate the measurements for the lower roof.
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1
Tips & Warnings
Some calculators have a setting for switching between degrees and radians for angle calculations. Be sure to set your calculator to the degree setting for a proper calculation.
References
- Photo Credit Photos.com/Photos.com/Getty Images
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Comments
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Dh Fullington
Dec 27, 2010
After looking for the right formula to determine the lengths of each gambrel roof section, I believe this to be the correct one. If you are going with equal length sides as in an octagon style roof but only using half of the octagon the formula is to determine the maximum width in inches and multiply it by .414214 and this will give you the lengths of your outside roof trusses with a 22.5 degree cut on both ends. It is also the 30 degree 60 degree slope most people refer to as the desired look of the roof angles. Remember these trusses will fit directly on the wall sill plate so if an over hang is desired additional width will have to be added.
