Spike's Calculators
Construction Math
Solving Unknown Lengths and Angles # II Dual Pitched Roof
Solving for length's aa and abSolving it Spikey style!!
Before you can find the angles and different lengths you first need to solve for length's aa and ab to find where the roof peak is located in relation to the side walls.
To do that: add the values of both rises from the pitches together.An example:
What is Known:
Roof pitch no 1 = 9/12
Roof pitch no 2 = 5/12
length a = 20'
Adding the two rise values together: 9 + 5 = 14
Divide "length a" by this number:
20 / 14 = 1.4285714286, this becomes the multiplier
To solve for "length aa" take the rise of the opposite pitch, pitch #2 = 5 and multiply it with the multiplier:
Length aa = 5 * 1.4285714286 = 7.14285714' = 7' 1 11/16"
To solve for length ab take the rise of the opposite pitch, pitch #1= 9 and multiply it with the multiplier:
length ab = 9 * 1.4285714286 = 12.8571428' = 12' 10 5/16"