Foundation depth

[VLADIMIR LEVIN]

Code says foundation shall extend below the frost line, which in NY is 42".
My drawings always indicate "...min 42" to top of footing", which places the footing below the frost line.
I had contractor question me and say they always do it to the bottom of the footing. And some Code officials say the same thing.
But 42" to the bottom of the footing would place the footing above the frost line.

Any one have any thoughts about this?

 

[steveray]

Footing bears below frost depth typically

 

[VLADIMIR LEVIN]

Footing bears below frost depth typically

So you agree with what I said that at least some portion of the footing must be below the frost line, and 42" to bottom of footing is not code compliant?

 

[steveray]

So you agree with what I said that at least some portion of the footing must be below the frost line, and 42" to bottom of footing is not code compliant?

42 and a 1/16th is…

 

[bill1952]

Everything I read says first line in NYS is 48". Certainly is where I live in NY. I have to ask how thick are the footings?

 

[VLADIMIR LEVIN]

Everything I read says first line in NYS is 48". Certainly is where I live in NY. I have to ask how thick are the footings?

42" or 48" is not the point of the question... My footing are typically 10-12"

 

[VLADIMIR LEVIN]

42 and a 1/16th is…

in theory, not in practice

 

[steveray]

Our frost depth is 42” and I couldn’t tell you the last time we had 36” of frost….

 

[bill1952]

Our frost depth is 42” and I couldn’t tell you the last time we had 36” of frost….

Well yes I was using code value for frost depth, not reality.

 

[bill1952]

42" or 48" is not the point of the question... My footing are typically 10-12"

I agree bottom of footing is required to be at or below frost depth. I local code say 42", then that is to bottom of footing.

You refer to "my drawings". I don't know if you're a designer, owner, contractor, or enforcer. I'd really have to see the whole drawing and I owe the local code. I found places in NYS where local code says 36". I read there are places that say 60". If a designer showed 6" min footings with code frost depth of 48", and said top of footing at 42" min below grade, I don't see a problem staying it that way. It achieves the same result.

 

[VLADIMIR LEVIN]

I agree bottom of footing is required to be at or below frost depth. I local code say 42", then that is to bottom of footing.

code doesn't say foundation to be "at or below" frost depth, it says "extend below".
So the bottom of footing at frost depth is not below frost depth

 

[bill1952]

code doesn't say foundation to be "at or below" frost depth, it says "extend below".
So the bottom of footing at frost depth is not below frost depth

Obviously you just want to argue. Good bye.

 

[VLADIMIR LEVIN]

Obviously you just want to argue. Good bye.

I dont want to argue. This is a discussion board, and that little nuance is at the heart of my question

 

[SDS]

pictorially speaking...all my 2021 code footing diagrams that are referencing/dimensioning frost line show it dimensioning to the bottom of the footing...

 

[ajesaitis]

Code states below the frostline so bottom of the footing is not below. I agree with top of the footing is at frostline. This complies with code

 

[Sifu]

IMO Bottom. If the footing EXTENDS below the frost line then it is doing what the code says. Both the IRC and IBC use extend.

IRC 403.1.4.1
1. Extended below the frost line specified in t301.2.1(1)

IBC 1809.5
1. Extending below the frost line of the locality.

 

[VLADIMIR LEVIN]

I asked NYS Code Official. This is their response:

Your question (paraphrased):
Residential Code requires foundations to "extend below the frost line" as indicated in R403.1.4.1.
If the frost depth is 42" below grade and the bottom of a footing is at 42" below grade, does that meet the code requirement?

Our response:
Based on the information provided and my review of the 2020 Residential Code of NYS; no; as per section R403.1.4.1 if the frost line is determined to be 42”, then the bottom of the footing must extend beyond that point to prevent the possibility of heaving.

 

[Yankee Chronicler]

So you agree with what I said that at least some portion of the footing must be below the frost line, and 42" to bottom of footing is not code compliant?

No. 42 inches to bottom of footing is compliant. Or, as steveray posted, 42" + 1/16th is "below."

There's nothing wrong with doing it your way, and if your drawings call for the top of the footings to be 42 inches below grade, that's what a contractor is obligated to build.

 

[VLADIMIR LEVIN]

No. 42 inches to bottom of footing is compliant.

There's nothing wrong with doing it your way, and if your drawings call for the top of the footings to be 42 inches below grade, that's what a contractor is obligated to build.

What is your rational for saying that 42" to the bottom is code compliant?

 

[Yankee Chronicler]

Code states below the frostline so bottom of the footing is not below. I agree with top of the footing is at frostline. This complies with code

Yes, placing the top of footing at the frost depth complies, but it goes beyond complying and costs someone (the contractor and thus, ultimately, the owner money that doesn't need to be spent.

2021 IRC:



From the 2021 IRC Commentary:



So, in a very technical sense, placing the bottom of footing AT the frost depth arguably doesn't extend "below" frost depth. However, as steveray commented, 1/16th of an inch below is "below." I can tell you that I have been a licensed architect for 51 years, and I started my first job as a drafter in an architects office 58 years ago. I have been through eight state building inspectors. In all that time, I have not seen a single design that called for bottom of footing to be below the code-mandated frost depth.

If you want to be conservative, add two inches and set the bottom of footing at 44" below grade. Placing the entire footing below the frost depth is just wasting money.

 

[Yankee Chronicler]

The illustration in the IRC Commentary aren't enforceable, but they are there for guidance:

 

[BN4537]

The other fact is that the "frost line" is a conservative number. The frost never actually reaches the "frost line". The frost will not be heaving anything at frost line. It probably won't heave anything for a few inches above the frost line either. They build that leeway in.

 

[ICE]

If a something extends past a point, that something commences at the point where the extension began. With a footing and a frost line, the frost line is the point from which the footing will extend.
Arbitrary dimensions provided for the supposed extension are as low as 1/2" while others are generous with 2".
Shirley Prudence would demand satisfaction of the reason behind the intent. If such minute extensions were enough, the code should probably just ask that the footing start at the frost line and rise from there.

 

[Inspector Gadget]

42 and a 1/16th is…

A gawdawful way to measure something when the metric system exists and solves all those fractional foulups with a nice decimal solution.

code doesn't say foundation to be "at or below" frost depth, it says "extend below".
So the bottom of footing at frost depth is not below frost depth

I would agree. The language of your code would be a "greater than"

FYI, Canadian code states "minimum depth," which is a "greater than or equal to"....