IS 456 concrete cover requirements
Nominal cover is the distance from the outermost reinforcement (including links) to the concrete surface. It protects steel from corrosion and gives fire resistance. IS 456:2000 sets minimum nominal cover by member type and exposure condition.
Nominal cover by member (mild exposure)
| Member | Nominal cover |
|---|---|
| Slab | 20 mm (15 mm for bars ≤ 12 mm in mild exposure) |
| Beam | 25 mm |
| Column | 40 mm (may reduce to 25 mm for columns ≤ 200 mm with small bars) |
| Footing | 50 mm |
Cover by exposure condition (IS 456 Table 16)
| Exposure | Min. nominal cover |
|---|---|
| Mild | 20 mm |
| Moderate | 30 mm |
| Severe | 45 mm |
| Very severe | 50 mm |
| Extreme | 75 mm |
Key points
- For footings cast against earth, provide at least 50 mm cover.
- Higher exposure demands higher concrete grade as well as more cover.
- Cover blocks/chairs on site should match the design cover — a common source of durability defects.
This is a quick reference. The governing values depend on the exposure category, member size and bar diameter for your specific project. The final cover, grade and detailing must be fixed by a licensed structural engineer as per IS 456 and the project specification.
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