Minimum nominal concrete cover protects reinforcement from corrosion and fire. Cover depends on exposure condition (Table 16) and required fire resistance (Table 16A). Always use the larger of the two.
Quick Lookup — By Exposure
Mild Moderate Severe Very Severe Extreme
30 mm Min M25
Sheltered from severe rain, indoor RCC
Cover for Fire Resistance (Table 16A of IS 456)
Fire rating in hours — use the larger of durability cover and fire cover
Member 0.5h 1h 1.5h 2h 3h 4h Slab (simply supported) 20 20 25 35 45 55 Slab (continuous) 20 20 20 25 35 45 Beam (simply supported) 20 20 20 40 60 70 Beam (continuous) 20 20 20 30 40 50 Column 40 40 40 40 40 40 Wall (load-bearing) 20 20 25 25 25 25
Practical Notes
• Nominal cover = clear cover to nearest surface of the outermost reinforcement (including stirrups)
• Cover to main bar ≥ bar diameter (Clause 26.4.1)
• For bundled bars, cover ≥ equivalent diameter of the bundle
• Cover blocks (spacers): use PCC cover blocks, NOT stone/brick pieces
• Maximum cover should not exceed 75mm unless designed for fire resistance
• In aggressive environments (coastal, industrial), consider additional 10mm beyond code minimum
• For precast elements, cover may be reduced by 5mm per IS 456 Clause 26.4.2
• Tolerance on cover: +10mm, −0mm (cover must never be less than specified)
• Always check both durability and fire requirements — use the LARGER value