# What is proper grade slope? There are so many different answers to this question

I’ve found several different answers that are significantly different from each other so I don’t know how to answer the question planely. I think the most popular answer to this question is 6 inches within the first 10 feet as shown in this question:

which is repeated here:

and here:

But here it starts to get really confusing. Could someone explain to me how this next one can be reconsiled with 6 inches in 10 feet?

That would work out to 12 inches in 10 feet, exactly double the slope of the previous three questions/answers.

This next one is even more strange. The first two options are functionally the exact same answer but only one of them is correct. How can that be possible?

So, what’s the difference between the first and second option?

• 1 inch per foot for every 2 feet
• 1 inch per foot for every 6 feet

One inch per foot is not affected by the “every 2 feet” or “every 6 feet”. It will still be one inch per foot for however many feet you want. So what’s the difference? And one inch per foot works out to 10 inches in 10 feet which is not the same as 6 inches in 10 feet or 12 inches in 10 feet. So we have 3 different possilbe answers here so far and I’m not sure I’ve found them all.

3 Likes

For the most part the InterNACHI education is great and I get a lot out of it but what OP brings up here is my biggest (and really only) frustration with it. There are many, many “rules” that seem to be made up and vary depending on which class or section of that class you’re in you can be incorrect. Ultimately, there are enough ridiculously easy questions that it makes up for the inconsistencies.

4 Likes

My issue is the questions are read and regurgitate. The right answer is whatever the prior reading said. That may have no bearing on what one does when visiting an actual house.

4 Likes

@bnesbitt I don’t mind different options applying in different areas and situations and all that changing over time, really. I expect that. I just need to know which answer will be expected on my license exam.

The correct answer is 6" within the first 10 feet. So I would go with that for your test.

1 Like

Yes, that’s also my conclusion but not all of these questions give me that option. The most common response I get to my questions about these study questions is “just choose the best answer” even if the correct one is not available. So, my concern is if I also have to memorize these other possible answers just in case the “correct” answer is not an option.

This is stated in IRC, look it up Beyond IRC, your milage may vary based on locale.

2 Likes

R401.3 Drainage. Surface drainage shall be diverted to a
storm sewer conveyance or other approved point of collection
that does not create a hazard. Lots shall be graded to
drain surface water away from foundation walls. The grade
shall fall not fewer than 6 inches (152 mm) within the first 10
feet (3048 mm).

Exception: Where lot lines, walls, slopes or other physical
barriers prohibit 6 inches (152 mm) of fall within 10 feet
(3048 mm), drains or swales shall be constructed to ensure
drainage away from the structure. Impervious surfaces
within 10 feet (3048 mm) of the building foundation shall
be sloped not less than 2 percent away from the building.
3 Likes

Thank you. I’ve never seen that line before.

1 Like

The most important “rule of thumb” is the grade that “works”.
Is the house located at the bottom of a canyon?
How well does the water drain away from the roof system? etc.

2 Likes

That might make sense for practical purposes but I’m studying for my license exam and I’d like to know which option to choose if the options are 1:10 inches or one inch per foot for however many feet.

1 Like

1 inch per foot for every 2 feet = 5 inches for every 10 feet most correct answer
1 inch per foot for every 6 feet = approx. 1.7 inches for every 10 feet
1 inch per yard for every 12 feet = 4 inches for every 12 feet

(someone check my math)

A 5% slope usually is fine which is 5" in 10’.

1 Like

But the IRC says… so 5 inches must be illegal…according to another post…You want him to do “TIME!” LOL

1 Like

The problem is that the question asks for appropriate slope but uses 1" per foot for 2 of the answers. So the slope for both answers is the same

2 Likes

You are right. 1" per foot is 1" per foot no matter how far you go.
vs
1" per 2 feet or 1" per 6 feet.

Thanks for checking my math

2 Likes

You betcha! It’s just a copy and paste error. Honestly, having just finished the CPI courses a year ago, the curriculum is full of them. You just got to figure them out. NACHI should probably have someone comb through them and fix/update but that is no small task.

2 Likes

In a 10 foot run would be 6 1/4" fall. 4% would equate to 5" fall. More than adequate regardless.

2 Likes

Yes, my bad. .05 X 10 = .5

1 Like

Most of you need some level of remedial math. A 5% slope is exactly a 6 inch drop in 10 feet which is what the IRC calls for (R401.3). There are apps to figure this if you need one, but the biggest problem seems to be non-common factors. If you use feet, both measurements must be in feet (.5 feet over 10 feet) if you use inches both must be inches (6 inches over 120 inches). See you in class!

3 Likes