Section 20.6.1/Concrete Cover for Reinforcement
ACI 318-19 Section 20.6.1 specifies minimum concrete cover based on exposure condition, member type, and bar size.
Minimum concrete cover is the distance from the nearest surface of the concrete to the outermost surface of the reinforcing bar. For cast-in-place concrete not exposed to weather or in contact with ground, the minimum cover is 1.5 inches for walls and slabs with No. 11 bars and smaller, and 0.75 inches for slabs with No. 5 bars and smaller. Concrete exposed to weather requires 1.5 inches for No. 5 bars and smaller and 2 inches for No. 6 through No. 18. Concrete cast against and permanently in contact with ground requires 3 inches minimum. Prestressed concrete has separate cover requirements in Section 20.6.1.4.
Why this section exists
Concrete cover protects reinforcing steel from corrosion. When cover is insufficient, moisture and chlorides penetrate to the steel, causing rust. Rust occupies more volume than steel, generating internal pressure that spalls (chips off) the concrete surface. This exposes more steel, accelerating the cycle. Inadequate cover is the leading cause of concrete deterioration in bridges, parking garages, and buildings exposed to weather or deicing chemicals. The cover requirements are calibrated to the exposure severity.
What plan reviewers look for
Plan reviewers check the structural details and general notes for concrete cover dimensions. They verify the cover matches Table 20.6.1.3.1 for the exposure condition and bar size. They pay special attention to members exposed to weather (balconies, parking garages, retaining walls) and members cast against ground (footings, grade beams). They check that the cover accounts for the outermost bar (including stirrups and ties), not just the main reinforcement.