A continuous footing is formed 26 inches wide and 8 inches thick, centered under an 8-inch-thick concrete foundation wall. Judging only the geometry of the footing, what should the inspector conclude?
- AIt is acceptable, because the projection on each side is well above the 2-inch minimum.
The 2-inch value is only the lower bound; this projection fails the upper bound tied to footing thickness.
- BIt is acceptable, because a wider footing always spreads the load more conservatively than a narrow one.
Extra width without extra thickness overhangs the wall and puts the concrete into bending it cannot carry.
- It is unacceptable, because each side projects 9 inches, which is more than the 8-inch thickness of the footing.
- DIt is unacceptable, because a footing projection may never exceed 6 inches under any wall.
No fixed 6-inch cap exists; the ceiling on projection is the thickness of the footing itself, which varies.
Why C is correct
Projection equals half of the footing width minus the wall thickness: 26 minus 8 is 18, and half of that is 9 inches. The code allows a projection of at least 2 inches but no more than the footing thickness, which is 8 inches here. Nine is greater than eight, so the geometry fails and the footing must be deepened to 9 inches or trimmed to 24 inches wide.
What this question is testing
Applying a two-sided limit rather than a single minimum, and computing projection correctly by subtracting the wall thickness first and then halving. It also checks whether the candidate resists the intuition that more concrete is automatically safer, which is the trap built into the wrong choices here.
On the job
This one shows up whenever a trench gets sloppy and the crew simply forms wider than the plan. Widening looks harmless and even generous, so it rarely gets questioned by anyone on site. The inspector who knows the projection rule reads it as a thickness problem instead: a 26-inch footing needs 9 inches of depth, and adding an inch of concrete depth is cheap while a cracked overhang discovered after backfill is not. Expect to see it most on soft-soil lots where the plan already calls for a wide footing.
Memory technique
Projection lives between two and the thickness: never stubby, never longer than the footing is deep.
Exam tip
Sketch the footing and wall in cross section before you compute; the halving step is the one candidates skip.
Where to look it up
IRC Chapter 4, the minimum size paragraph under R403.1 where footing width, thickness and projection are defined together.