| Primary value | 30 mm (Moderate exposure) (20 Mild · 30 Moderate · 45 Severe · 50 Very-Severe · 75 Extreme) |
| Applies to | All RCC members designed to IS 456 · Selection of cover when neither code-specific nor fire-rated requirements govern |
| Exceptions | Mild — protected from weather → 20 mm |
| Moderate — sheltered, exposed to rain → 30 mm | |
| Severe — alternate wetting / drying → 45 mm | |
| Very Severe — coastal, marine spray → 50 mm | |
| Extreme — tidal, sulphate, sewage → 75 mm | |
| Footing — minimum cover → 50 mm (always) | |
| Fire rating may govern over exposure → See IS 456 Cl. 26.4.3 | |
| Measured as | Nominal cover from the outermost surface of concrete to the face of the nearest reinforcement (including links / stirrups, not just the main bar). |
| Source | IS 456 — Table 16, Clause 26.4.2 ✓ Verified |
68 related items across IS codes, knowledge articles, design rules, maps and tools
Concrete cover is the primary durability barrier — it protects the steel from carbonation and chloride ingress. The exposure-based progression reflects measured chloride / carbonation depths over a 50-year design life: every step up adds another decade of corrosion protection. Reducing cover saves a few millimetres of section but costs decades of service life.
Indian projects default to 25 mm cover in slabs (mild + a 5 mm buffer), 40 mm in beams (moderate + 10), 50 mm in columns (severe), 50–75 mm in footings. Coastal projects (Mumbai, Chennai, Vizag) bump everything one class up to handle the chloride spray.