I am studying the roof inspection course and having trouble understanding the roof pitch fraction formula. When I follow the formula stated in the paragraph under the diagram, I come up with a decimal answer. Eg. 2:12 slope can be expressed as 1/12 pitch, where as pitch is a fraction derived by dividing the rise by the entire span. Span = 24ft, rise = 2in. 2÷24 = .08333333. Math is not my strong point here. Any help to understand the appropriate formulation is appreciated.

Morning, John.

Welcome to the forum.

Try this. Slope is the incline of the roof, thus expressed as a ratio of the **vertical rise** Up/down, to the horizontal run, a measure of level line left to right, where the run is some portion of the span. Portion being any way you divide the total. Typically, every foot, 12 inches of rise to the total horizontal distance.

This ratio is always expressed as inches per foot. A roof that rises 4 inches for every 1 foot measured horizontally, or 12 inches of run, is said to have a (“4 in 12” slope.)

Make it easy by using PITCH - SLOPE LOCATOR on the job.

Slope is the only real measurement you will be using. Pitch is very seldom mentioned, as this was typically used with older, simple gable type framing. Now, with newer building practice, you can have ridges all over the place, so pitch doesn’t really apply.

But to answer your question, slope is inches drop/inches rise. So, 4" drop for 12" rise is 4:12.

(I think you already know that one) and that can be used no matter what the length is of the horizontal run you are measuring.

Update: I has to correct myself here-

But pitch is the total span from wall to wall. So if slope was 4:12, and the span was 24’ wall to wall, then the rise was still only 4’ high for the 24’ distance, so 4/24. Or, simplified, is 1/6

I updated my answer above.

You are trying to divide 2 by 24. It’s the other way around.

24 ÷2 is 1/12 pitch

It’s just a matter of simplifying the fraction.

(Sorry for all the updates)

I was going to state that, but your update did it for me.

Thank you Robert for the quick response and the tool reference…

Thank you Daniel. Makes more sense now…

Daniel has helped you with this…