Slope vs pitch confusion in roof inspection training

The training explains the difference between pitch and slope, which I thought I understood. However, in the Underlayment portion of the training, it states “the angle of slope is described by the number of inches the roof rises in each horizontal foot. So, a roof that rises 4 inches in every 12 inches of horizontal is said to have a 4:12 (or “4 &12”) pitch” Shouldn’t this have said “slope”? A 4 feet rise over a 12 foot run has a slope of 4 in 12 or 4:12. BUT a 4 foot rise over a 24 foot span, would be a pitch of 4 feet over 24 feet or a 1:6 pitch???

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Slope is the incline of the roof expressed as a ratio of the vertical rise to the horizontal run, where the run is some portion of the span. This ratio is always expressed as inches per foot.

Pitch is the incline of the roof expressed as a fraction derived by dividing the rise by the span, where the roof span is the distance between the outside of one wall’s top plate to another.


The summary of Marcel’s link helps to understand the difference (at least to me):


Pitch and slope do not mean the same thing. Slope is the ratio measured in inches per foot. Because slope affects how water is shed from a roof surface and determines the limits for using asphalt shingles, understanding how to measure the slope of a roof may be valuable to a home inspector.

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Think they slipped up and worded it incorrectly , most people would say 4-12 " pitch" instead of “slope” although technically, as Im sure you’ve heard Ben say over and over, they are different.

Absolutely right. Anyone who knows anything about roofs uses the term “pitch” and any inspector who describes the roof angle of slope as a percentage is going to be looked at as if he is clueless by everyone but his mother, and anyone who knows anything about roofs who is involved in the transaction is going to tell everyone else that the inspector doesn’t know what he’s talking about… and he’ll be right.

Forget the term “slope”


I agree, Kenton.

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can someone just tell me that simplest way to find out what the pitch of a roof is for example 4 X 12 or something like that

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You probably mean a slope, not a pitch. Level and a ruler, there are also gadgets and phone apps. Youtube it.


thank you. I just thought it would be something like length times width to get square footage

Are you suggesting I use the word pitch to mean slope and ignore the use of the actual pitch calculation all together as if the span is not relevant for inspectors representing roof specifications?

I’m currently going through InterNACHI’s pool of 2100 study questions and I’ve noticed a clear preference for slope over pitch. There are at least 28 questions about slope and only 6 questions about pitch, however all the pitch questions seem to be using pitch to mean slope, which is what I suspect you are suggesting.

  1. Roofs with a pitch of between 4:12 and 6:12 are considered _____ roofs.

  2. Where a portion of a roof having a steep pitch meets a portion of the roof having a lower pitch, the valley that’s created may be especially vulnerable to _____.

  3. The minimum required height of a hot-water heater vent on the high side of a roof with a pitch of 6:12 or less is _____ inches.

… ignore 4 and 5 …

  1. Roll roofing on flat roofs having a pitch of 2:12 or more must be overlapped at least _____ inches.

If I “forget” the term slope as you suggest then I can foresee a problem of always having to clarify every mention of pitch. I would think it would be easier to simply include both, just to make sure there’s never any confusion, however, I don’t want to come across as “the inspector [who] doesn’t know what he’s talking about” or to be looked at as “clueless by everyone but [my] mother.” These are very heavy cautions that I take quite seriously, as a noob in this profession. So I might need some hand holding before I feel confident that I’m not going to be ostracized before I get started. Anyone want to mentor me?

The more I learn the more questions I have, but I’m hoping my questions get less stupid.

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Pitch Gauge - app Measures and takes a picture and mails it to yourself to add to report.

I don’t have 5.2 on my framing square. LOL


Hi, Lionel. If you (or anyone) ever sees an error in an online course, please email or We’ll fix, and send you a nice gift.

Where did you see this “pitch” term used incorrectly?

And in relation to underlayment, the 2018 IRC TABLE R905.1.1(2) UNDERLAYMENT APPLICATION uses “roof slope” correctly.

In the 2018 and 2021 IRC, the definition of “Pitch” is “See Slope.”

Nope. Bad advice, and I disagree.

Home inspectors should use the term “slope” particularly when referring to the roof-covering or the roof assembly, including underlayment.

The IRC uses the term “slope” 170 times in Chapter 9 Roof Assemblies ( and “pitch” only 10 times. And all ten are incorrectly used. That’s okay. We know better.

2021 IRC defines “Pitch” as “See Slope.”

The National Roofing Contractors Association (NRCA) uses and defines “slope” and not “pitch”. Glossary - NRCA

The 2021 International Building Code IBC doesn’t even define “pitch”, but instead defines “slope” when referring to roofs. “STEEP SLOPE. A roof slope 2 units vertical in 12 units horizontal (17-percent slope) or greater.”

Kenton Shepard’s article “Mastering Roof Inspections: Accessing the Roof, Part 1” uses “slope” and not “pitch.” Mastering Roof Inspections: Accessing the Roof, Part 1 - InterNACHI®. Kenton writes, “The purpose of the series “Mastering Roof Inspections” is to teach home inspectors, as well as insurance and roofing professionals, how to recognize proper and improper conditions while inspecting steep-slope, residential roofs. This series covers roof framing, roofing materials, the attic, and the conditions that affect the roofing materials and components, including wind and hail.”

Screen Shot 2021-06-01 at 3.20.31 PM


Nor do I but the calculator with the app still figures out how many squares (you need to add width and length of roof). Round the number works fine for inspection.

Nope. I disagree. Home inspectors should use “slope.”

Kenton explains slope and underlayment limitations correctly in InterNACHI’s free, online Inspecting Asphalt Shingle Roofs Course:

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I have been using this book for years, and there is no mention of slope. This is what I will go by.
IMG_0340 (1)


Scott, in that book, the author actually is referring to pitch correctly in that it is the height in relation to the span. That’s the entire span of the gable roof (from wall to wall). That’s pitch. Pitch is the incline of the roof expressed as a fraction derived by dividing the rise by the span, where the roof span is the distance between the outside of one wall’s top plate to another. And that’s what the author of that book is referring to.

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Scott, I think my book is a little older and got more abuse. LOL

Although I understand the Pitch and the Slope, growing up in this as a kid with my Father, we always called it Pitch. It is just one of those things that get used interchangeably.
Look at the date and price of the book. LOL


I agree with Scott and Marcel.

One learns different things in different areas of the country and the locals, and others, understand that.