The minimum thickness of a Reinforced Cement Concrete (RCC) slab depends on several factors, including the type of slab, its span, loading conditions, and structural design requirements.

However, some general guidelines are typically followed based on the application:

1. Residential and Commercial Buildings (Slab on Beams)

• Minimum thickness: For residential buildings, the minimum thickness for an RCC slab supported on beams is typically 100 mm (4 inches).
• Common practice: Thicknesses of 125 mm (5 inches) to 150 mm (6 inches) are commonly used depending on the span and load.

2. One-way Slab

• A one-way slab is supported by beams on two opposite sides. The thickness for one-way slabs is usually:
  • Minimum thickness: 100 mm (4 inches), but typically 125 mm (5 inches) or more, depending on the span and load conditions.

3. Two-way Slab

• A two-way slab is supported on all four sides. It generally requires slightly more thickness due to the distribution of loads:
  • Minimum thickness: 125 mm (5 inches) for most residential applications, but it could go higher depending on the span and load.

4. Slab Without Beams (Flat Slab)

• Flat slabs, which are directly supported on columns, often require greater thickness to ensure strength and minimize deflection.
  • Minimum thickness: Typically 150 mm (6 inches), but for larger spans, it can range from 175 mm to 300 mm (7 to 12 inches).

5. Industrial or Heavy Load Slabs

For slabs subjected to heavy loads (e.g., industrial floors, parking garages), the thickness is increased to accommodate higher loads:

• Minimum thickness: 150 mm (6 inches) or more, depending on the load requirements and span.

6. Thumb Rule for Slab Thickness Based on Span

A rough rule of thumb used by engineers is that the slab thickness should be at least:

• Span/30 for simply supported slabs.
• Span/35 for continuous slabs.

Factors Influencing Minimum Thickness

1. Span of the slab: Longer spans typically require thicker slabs.
2. Live load and dead load: Heavier loads demand greater slab thickness.
3. Type of reinforcement: Slabs with higher reinforcement content may require less thickness.
4. Deflection control: To limit deflection, especially for slabs with longer spans, additional thickness may be necessary.
5. Local building codes: Regulations in different regions may specify minimum slab thicknesses based on safety and design standards.

Conclusion

For residential and commercial buildings, the minimum thickness of an RCC slab is typically 100 mm to 150 mm depending on the type and design of the slab. For industrial or heavy-load applications, this could be higher. Always consult local building codes and structural engineers to ensure proper design.