Where cover is measured
ACI 318 Section 20.5 states: "Concrete cover shall be measured from the concrete surface to the outermost surface of the steel to which the cover requirement applies."
That sentence settles three traps:
- Cover goes to the steel's outer surface, not a bar centerline. Measuring to the centerline of the main bars or of the outer layer overstates cover by half a bar diameter.
- The form face is where the concrete surface ends up. It is the starting point of the measurement, not the point it is measured to.
- "Outermost" means whatever steel is closest to the surface.
Stirrups and ties come first
Where stirrups or ties enclose the main bars, the outermost steel is the stirrups or ties (ACI 318 commentary R20.5.1.3). An inspector who measures from the bottom of a beam to the bottom of the main bars has added the stirrup thickness to the reading, so the actual cover is less than measured. This is the common error: cover is not always measured to the main bars.
IBC Table 1808.8.2 sets no number for shallow foundations
In IBC 2021 Table 1808.8.2, the shallow-foundations row reads "In accordance with Section 20.5 of ACI 318." The table gives no value of its own for that row. The traps:
- A fixed 3-inch or 1½-inch cover is not what that row says.
- The table points to ACI 318, not to IRC Section R404. The IBC does not send you to the residential code.
Finding it in your edition
The exam accepts ACI 318-14 or ACI 318-19. The cover provisions sit in:
- ACI 318-19: §20.5
- ACI 318-14: §20.6
If you brought ACI 318-14, looking up §20.5 uses the 2019 number in the wrong book. Two other sections are easy to confuse with cover: §26.12 holds the strength acceptance criteria, and §19.2 covers the specified compressive strength basis. Neither holds cover.