It should be noted that the basement wall tables in the IRC have been consistently maintained by either PCA or ACI (I’m forgetting which at the moment), so there is a solid technical basis to them. Ditto the ACI 332 tables. The principal differences are that the IRC & ACI 332 tables use a smaller minimum reinforcement ratio than and a higher limit on reinforcing tensile strength than ACI 318. The relaxations were deemed appropriate based on the observed performance of residential walls, as opposed to the limitations of the more general ACI 318, which has to work for everything from small residential and light commercial structures up to high-rise buildings and industrial/essential facilities.
It’s also worth noting, since the discussion started with ICF’s, that PCA has a new consensus standard (PCA 100-07) for prescriptive design of residential concrete walls, which is referenced in the 2009 IRC. Covers both below-grade and above-grade concrete walls, both traditional walls and ICFs. Complies fully with ACI 332 (or ACI 318 where necessary) and ASCE 7-05. I think they even used ACI 318 Appendix D to calculate ledger attachments and top-of-wall support. (Not without much grumbling, mind you.)
Regards,
Gary
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
gehrlich@nahb.com
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