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IBC/IRC Foundation wall tables

IBC/IRC Foundation wall tables

IBC/IRC Foundation wall tables

(OP)
I have a question regarding the difference between the foundation tables in the IRC/IBC. I am looking at IRC table R404.1.1(1) and R404.1.1(3). Specifically, we have an issue with an existing 12" CMU foundation wall that is 8' in height with 7' backfill.

Table R404.1.1(1) specifies that a hollow 12" CMU wall is adequate for this condition, assuming "GW, GP, SW and SP" soils.
Table R404.1.1(3) specifies that #4 bars at 64" o.c. are required for "GW, GP, SW, and SP" soils.

I'm not understand why these are different. Either you need reinforcement or you don't. Can someone help shed some light on this as to why the two tables have different requirement's for the same wall with same high and backfill?

Thanks

RE: IBC/IRC Foundation wall tables

#4 @ 64" oc hardly qualifies as reinforcing, might as well use WWF. Those tables have never made much sense structurally, I think they just reflect what has historically been adequate in residential construction.

RE: IBC/IRC Foundation wall tables

(OP)
Yes I agree that that reinforcement is not significant. But I'm trying to understand which is correct, or more importantly, which is required by code. It can't be both? Must be one or the other. Based on reviewing the tables seems like both work, which doesn't make sense.

RE: IBC/IRC Foundation wall tables

Table R404.1.1(1) is only the minimum wall thickness. Footnote a notes that hollow units may be used, except where otherwise indicated. Table R404.1.1(3) gives the required reinforcement, which is indicating that hollow units cannot be used. Either way, if you run the numbers and actually engineer the wall, it is probably under reinforced, but that is an entirely different conversation.

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