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Frost Protection of Foundation/Footing

jar546

jar546

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Below is the code section from IRC 2009.

If a municipality deems the frost depth to be 36". Does that mean that the foundation wall must extend below 36" or just the bottom of the footer?

It is our interpretation that the foundation wall must extend below the frost depth of 36" which means the top of the footer can never be any shallower than 36" to the top of it. The thicker the footer, the deeper you must go.

How do you interpret this?

R403.1.4.1 Frost protection. Except where otherwise

protected from frost, foundation walls, piers and other

permanent supports of buildings and structures shall be

protected from frost by one or more of the following methods:

1. Extended below the frost line specified in Table

R301.2.(1);

2. Constructing in accordance with Section R403.3;

3. Constructing in accordance with ASCE 32; or

4. Erected on solid rock.

Exceptions:

1. Protection of freestanding accessory structures

with an area of 600 square feet (56m2) or less, of

light-frame construction, with an eave height of

10 feet (3048mm)or less shall not be required.

2. Protection of freestanding accessory structures

with an area of 400 square feet (37 m2) or less,

of other than light-frame construction, with an

eave height of 10 feet (3048 mm) or less shall

not be required.

3. Decks not supported by a dwelling need not be

provided with footings that extend below the

frost line.

Footings shall not bear on frozen soil unless the frozen

condition is permanent.
 
We take it to the bottom of the footing, or pier, or whatever.....because the footing is the support for the wall...if everything is smooth nothing should be "grabbed" and heaved by the frost, and it should not get under the footing...
 
"Bottom @ Footing" is how it is enforced here, and how every structural engineer I have ever worked with specifies the frost-protection for footings. Not to say that just because everybody else does it this way, that it should be that way, but even the ICC engineers I have worked with view it this way.
 
But,

The code specifically says Foundation Wall and ....extend below the frost line.

How can a foundation wall extend below a frost line if the top of the footer is above the frost line?
 
From the 2009 IRC, Table R301.2(1): The frost line depth may require deeper footings than indicated in

Figure R403.1(1). The jurisdiction shall fill in the frost line depth column with the minimum depth of

footing below finish grade.



Your jurisdiction will have to define the depths that they want to be used.

Has your AHJ done this?

.
 
Some foundation walls don't even need footings. Piers don't have footings. The point is, the bottom of the built system should be low enough to prevent frost from getting underneath.
 
Yankee said:
Some foundation walls don't even need footings. Piers don't have footings. The point is, the bottom of the built system should be low enough to prevent frost from getting underneath.
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Grade beams come to mind.

Hopefully this will help some, from the 2006 IBC Commentary, Section 1805.2.1 (Frost Protection): "...A common method of accomplishing this is my placing the footing bottom below the frost line." (P 18-12)
 
Yankee said:
Some foundation walls don't even need footings. Piers don't have footings. The point is, the bottom of the built system should be low enough to prevent frost from getting underneath.
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Yes, Foundation walls without footings must be below the frost depth, the code specifically says that piers must extend below the frost depth.

The point is that the language of the code requires that foundation walls extend below the frost depth. So when you have a footer, the top of it must be below frost depth.

It does not matter what is "customary" in your area if you have adopted the codebook as written. It says what it says.
 
Here the frost line depth is set at 24",(meaning thats a safe depth before frost becomes an issue). So when asked by Mr. contractor; "How deep do the footings have to be"? They are not talking about the walls, they want to know how deep to make their trench to the bottom of the trench.

12" high footing (table R403.1) + a 24" frost depth requirement (established by code and approved by ordinance) = a 36" deep trench, this is the contractors answer.

We have a general rule in our area if your live near US36 Highway, your frost depth is 36" which works out so far. Most spread footings here are 8" thick and 12" wide.

pc1
 
jar546 said:
It does not matter what is "customary" in your area if you have adopted the codebook as written. It says what it says.
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In your experience, is frost protection a bearing issue? In my limited experience, a foundation wall bearing on a footing, the bottom of which is below the frost line, is not at risk of heaving...unless there are significant climate changes due in the near future. The code also says that foundations shall be built on undisturbed, compacted fill material or CLSM. It doesn't say they can be built on footings. ;)

In addition, the Figure 1805.4.6 of the 2006 IBC indicates the bottom of footing below the frost line, not the top of footing, or bottom of foundation.
 
Got to go with Papio on this one, even though he is being self depreciating with the whole limited experience stuff. The footing is apart of a load bearing system and so long as it is below the frost depth all is well.
 
It specifically states that foundation walls must extend below the frost depth. There is a foundation wall and most times, there is a footer. If it says the foundation wall must extend below the frost depth then the top of the footer must be below it too.
 
jar546 said:
They need to change the verbiage of the code then....................
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I couldn't agree more. I will write the code change and you submit it(insert smiley faced emoticon with arrow sign denoting "I AGREE")!
 
jar546 said:
It specifically states that foundation walls must extend below the frost depth. There is a foundation wall and most times, there is a footer. If it says the foundation wall must extend below the frost depth then the top of the footer must be below it too.
Click to expand...
Isn't a footing (if present) the permanent support for a foundation wall?
 
jj1289 said:
The code also says other permanent supports. The footing is a permanent support.
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Yes, and it should extend below the frost depth just like the foundation wall has to. BUT, in order for the foundation wall to extend below the frost depth, the entire footer must be below it too.
 
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