The approved design shows this interior bearing wall delivering 1,800 pounds per linear foot down to the footing, and the soils report gives a presumptive load-bearing value of 2,000 pounds per square foot. The contractor has formed the thickened footing 12 inches wide. Does that width carry the wall load?
- ANo, the required width works out to about 43 inches
Forty-three inches comes from dividing the wall load by 500 pounds per square foot, a very weak soil value that the soils report does not support. Reaching for a remembered default instead of the reported value is the error.
- BNo, the required width works out to about 21.6 inches
Twenty-one and a half inches results from dividing by 1,000 pounds per square foot, half the reported bearing value. It is the arithmetic slip of halving the soil capacity rather than using the number given.
- CNo, a footing under any bearing wall must be at least 16 inches wide regardless of the calculation
There is no blanket 16-inch minimum for footings under interior bearing walls. Minimum dimensions in the code are tied to what the footing supports, and substituting a remembered minimum for the calculation defeats the point of the soils report.
- Yes, the load calls for about 10.8 inches of width, so a 12-inch footing is adequate
Why D is correct
Dividing 1,800 pounds per linear foot by 2,000 pounds per square foot yields 0.9 foot, which is 10.8 inches of required bearing width. The 12-inch footing exceeds that, and the reverse check confirms it: 12 inches of width at 2,000 pounds per square foot carries 2,000 pounds per foot against a demand of 1,800.
What this question is testing
Whether the candidate can convert a linear wall load into a required bearing width using the reported soil value, and can verify the answer by the reverse calculation. It also tests resistance to substituting a remembered default for reported data.
On the job
Interior bearing walls landing on slab-on-grade are where builders economize, and a thickened section poured at the crew default width is often the only thing under a wall carrying a full floor and roof. The inspector who runs the division in the field can approve a 12-inch thickening with confidence, or reject the same 12 inches under a heavier load, instead of guessing. On poor soils the identical wall can need twice the width.
Memory technique
Load over pressure equals width, every time.
Exam tip
Pounds per linear foot divided by pounds per square foot gives you feet of width; check the units and the answer follows.
Where to look it up
IRC Chapter 4 footing provisions and the presumptive load-bearing values table, read together with the bearing wall load path in Chapter 6.