I understand that the slope of a roof is measured by the amount of inches it rises by the run measurement. So for every 4" rise for every 12" run would be 4:12.
The pitch is: A roof that rises 8 feet over a 24-foot span was said to have a “1 to 3” pitch. If the rise is 4 feet over a 24-foot span, then the roof pitch was said to be “1 to 6.”
I dont understand how they are getting 1/3" pitch or 1/6" pitch? Why is a pitch described in feet and the slope is described in inches?
TYIA Candi
If you’re referring to a Nachi course, could you supply the link to the specific page or pages?
Yes sorry:
1:3 and 1:4 are ratios. 1/3 and 1/4 are fractions but also ratios. The long way of describing them is the denominator (bottom number of a fraction) is 3 or 4 times the numerator (top number in a fraction always 1 for a ratio) 1 inch in three inches is the same as 1 foot in three feet, 1 yard in 3 yards or even 1 mile in three miles. The ratio is always the same…
1 inch in three inches = 12 inches in 36 inches = 1 foot in 3 feet = 5280 feet in 15840 feet.
If you think of 4:12 as a fraction (4/12) right away you realize it is reduced to 1/3.
This is perfect Thank you!
Your welcome and best of luck!
Also don’t be a stranger here, lots of knowledgeable people in here.
I literally just learned about the forum page this week, very excited to have this connection! 
The Nachi course makes a big deal of a supposed difference between slope and pitch, and muddies the water with examples in different units.
A ratio is not in inches, feet or anything else.
Your 8 feet over 24 feet can be expressed as 8:24 or 4:12 or 1/3 pitch. It’s all exactly the same:
8 ÷ 24 = .333333…
4 ÷ 12 = .333333…
1 ÷ 3 = .333333…
8:24 = 1/3 = 4:12 pitch = 4/12 pitch = 18.43 degrees = 4 & 12 or just “4 pitch”.
To say it again, a ratio (the relationship of two numbers) is not inches, not feet, it does not have a unit at all.
See also Slope vs pitch confusion in roof inspection training
2021 IRC defines “Pitch” as “See Slope".
This is great! Thank you so much!
