# Minimum Thickness for Frost Wall



## Ryan Schultz (Jun 4, 2015)

I have a PEMB that has an occupancy of A3 in a IBC 2009 jurisdiction.

The steel structure is supported on concrete piers.

Between these piers will be a frost wall with fill on both side.  Slab on grade.

Question, what's the minimum thickness that this frost wall needs to be?  I found minimum thicknesses for foundation walls in table 1807.1.6.2, but this frost wall is really not a foundation, per say, if defined as an element that bears the building load.

Thanks Much, Ryan


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## north star (Jun 4, 2015)

*$ ~ ~ $*



Can you please provide a definition of Frost Wall as it

will be used in your application [ i.e. - what is its intended

purpose if not load bearing, ...lateral bracing, ...retaining

wall, ...other  ] ?........Also, how high will the fill be on both

sides of your Frost Wall ?

Thanks !

*$ ~ ~ $*


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## Ryan Schultz (Jun 4, 2015)

Sorry, it's 4ft below grade with perhaps 6in exposed.  So ~4'-6".

'Frost Wall' is used to satisfy this code:

http://publicecodes.cyberregs.com/icod/ibc/2009/icod_ibc_2009_18_par112.htm

Thanks.


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## Ryan Schultz (Jun 4, 2015)

Here's the back story here for more info and sketches: https://github.com/OpeningDesign/Sports_Complex/issues/44#


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## mtlogcabin (Jun 4, 2015)

I



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If it is non-structural then use a 4" wall or ASCE 32 might let you just insulate  without the concrete


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## north star (Jun 4, 2015)

*= = + = =*

mtlogcabin,

Is the application in your pictures a "prescriptive" application

that can be referenced & applied from the IBC, or does Mr.

Schultz need to get a S.E.  to design & stamp something from

the ASCE ?



*= = + = =*


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## mtlogcabin (Jun 4, 2015)

That is the AHJ call. Look at R403 in the IRC it is taken right out of ASCE 32 It does not really require an engineer to figure out what will be needed.

I suggested Logix forms because I knew you could get them in a 4" width and they are an excellent product.

It also might help address the energy code requirements for slab on grade depending on the Climate Zone the building is in


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## BayPointArchitect (Jun 8, 2015)

I would agree with mtlogcabin.  It is important to clearly distinguish between the  "foundation" and the "non-supporting" concrete elements that also need to extend below the frost line.  I would recommend color-coding the column footings orange as the foundation which supports the structural load.  Then the 4 or 6 or 8 inch thick concrete that spans in between these column footings should be highlighted yellow and called out as "not a foundation wall subject to IBC 1805.2.1".  Essentially that yellow portion of the system is a "skirt" to hold down the slab edge as it would otherwise be subject to frost heave and expansive clay soils.  Unless you are using that ICF wall product recommended by mtlogcabin, that 4 or 6 or 8 inch thickness would be determined by the width of your back hoe.

Unfortunately, some building officials have a hard time conceiving that a "foundation" could be anything other than a perimeter trench footing.  And when their thinking is challenged, they dig in their heals and say "this is how you will do it because this is the only way it has ever been done".

For a perimeter trench that is 6 inches thick and 54 inches deep, the cross section area of steel reinforcement needed to control cracking and shrinkage would be 54 x 6 x .0018 which equals one #4 rebar top, middle, bottom.  Three #4 rebar horizontal total.


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## Paul Sweet (Jun 9, 2015)

It needs to be thick enough to allow the concrete to reach the bottom.  6" might be marginal for a 4'-6" depth, even if both sides are formed.  It might need to be 8" to 12" thick if one or both sides are cast against the dirt.


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## mstehlin (Jun 10, 2015)

BayPointArchitect said:
			
		

> For a perimeter trench that is 6 inches thick and 54 inches deep, the cross section area of steel reinforcement needed to control cracking and shrinkage would be 54 x 6 x .0018 which equals one #4 rebar top, middle, bottom.  Three #4 rebar horizontal total.


I'm curious how you came to this conclusion.  Is this a code requirement or rule of thumb?


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