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RE: ICF Shear Wall in SDC C

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Folks doing residential design with ICF's should probably check out the new PCA 100-07: Prescriptive Design of Exterior Concrete Walls for One- and Two-Family Dwellings. It updates the current design methods and tables (reflected in the IRC) to ACI 318-05 and ASCE 7-05. It is referenced in the about-to-be-released 2009 IRC. Link to purchase here:

I'm not intimately familiar with its provisions and where (or if) they may diverge from some of ACI 318's minimums. I know the PCA committee had some of the same folks as the ACI 332 residential concrete committee, and some of the usual residential seismic gurus.


Gary J. Ehrlich, PE 
Program Manager, Structural Codes & Standards 
National Association of Home Builders (NAHB) 
1201 15th Street, NW, Washington, DC 20005 
ph: 202-266-8545  or 800-368-5242 x8545 
fax: 202-266-8369 
Attend the 2010 International Builders' Show 
January 19-22, 2010, Las Vegas, NV

-----Original Message-----
From: Scott E Maxwell [mailto:smaxwell(--nospam--at)] 
Sent: Thursday, February 26, 2009 8:54 PM
To: seaint(--nospam--at)
Subject: Re: ICF Shear Wall in SDC C

Forgive me as I don't have my codes with me, so I am going from memory.

The Vu<phi*Vc/2 to my knowledge is NOT a seismic requirement, but rather a
general shear requirement.  Thus, to my knowledge, it applies to ALL
reinforced concrete elements in shear whether there is seismic or not as
long as it is an "engineered" solution (i.e. per IBC/ACI 318).  The IRC is
a prescriptive code and generally speaking ACI 318 does not really apply.

Thus, if you design it per the IBC, then you are into the ACI 318
requirements, which would include he Vu<phi*Vc/2 bit.  If you design per
the IRC, then you would not need to follow any ACI 318 provisions unless
they are specifically called for in the IRC.


Adrian, MI

On Thu, 26 Feb 2009 11:24:34 -0700, "Joseph R. Grill"
<jrgrill(--nospam--at)> wrote:
> I am working on a residence in a SDC C using an ICF concrete form which
> gives a 6" thick concrete wall.  IBC 2006 says that seismic design is not
> required in a SDC C.  ASCE 7-05 says that a plain concrete shear wall is
> not
> allowed in a SDC C ( a seismic requirement) and an "ordinary reinforced
> structural wall" would be required.  It appears that most if not all the
> shear walls will be subject to a shear Vu<phiVc/2.  The IRC allows
> horizontal reinforcing less than the .0020 Ag required in chapter 11 of
> ACI for ICF walls.
> My thought boils down to this.  Since seismic design is not required for
> residence in a SDC C the minimum horizontal reinforcing requirements of
> chapter 11 are not required, and I can use (if the numbers work out for
> applied shear to the walls) the minimum reinforcing allowed by the IRC,
> which I think is #4@48" o.c. if the shear Vu does turn out to be less
> phi Vc/2.
> Agree?
> Joseph R. Grill, PE
> Verde Valley Engineering, PLLC
> email: VVEng(--nospam--at)

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