Jerry Peck
07-11-2008, 11:45 AM
I know we started to discuss this once, then got side tracked, but ...
I was just looking through a 1939 4 volume set of Audels Carpenters & Builders Guide (only the 'Old Farts' here will remember those things) and came across the 'roof slope vs roof pitch' chart.
slope - pitch
2/12 - 1/12
4/12 - 1/6
6/12 - 1/4
8/12 - 1/3
10/12 - 5/12
12/12 - 1/2
14/12 - 7/12
16/12 - 2/3
18/12 - 3/4
20/12 - 5/6
22/12 - 11/12
24/12 - 1
You will notice that "pitch" is based on rise versus 2run.
With run = 12, that means "pitch" is rise vs 2run or 24
6/12 slope = 6/24 pitch = 1/4 pitch
This was based on the assumption that the roof started at the wall, rose to the ridge, then went back down to the other wall (2 runs for 1 rise).
If the roof rose 6 feet to the ridge, the ridge was 12 feet from the wall, then went back down 6 feet to the other wall 12 feet further, you had a rise of 6 feet over a run of 24 feet, or 6/24, reduced to the lowest common denominator = 1/4.
Remember, early buildings had roofs which were simple triangular structures, gable on one end, gable on the other, roof the same from gable to gable. Symmetry was the simplest and strongest way to build a roof.
I was just looking through a 1939 4 volume set of Audels Carpenters & Builders Guide (only the 'Old Farts' here will remember those things) and came across the 'roof slope vs roof pitch' chart.
slope - pitch
2/12 - 1/12
4/12 - 1/6
6/12 - 1/4
8/12 - 1/3
10/12 - 5/12
12/12 - 1/2
14/12 - 7/12
16/12 - 2/3
18/12 - 3/4
20/12 - 5/6
22/12 - 11/12
24/12 - 1
You will notice that "pitch" is based on rise versus 2run.
With run = 12, that means "pitch" is rise vs 2run or 24
6/12 slope = 6/24 pitch = 1/4 pitch
This was based on the assumption that the roof started at the wall, rose to the ridge, then went back down to the other wall (2 runs for 1 rise).
If the roof rose 6 feet to the ridge, the ridge was 12 feet from the wall, then went back down 6 feet to the other wall 12 feet further, you had a rise of 6 feet over a run of 24 feet, or 6/24, reduced to the lowest common denominator = 1/4.
Remember, early buildings had roofs which were simple triangular structures, gable on one end, gable on the other, roof the same from gable to gable. Symmetry was the simplest and strongest way to build a roof.