What is the minimum thickness of concrete floor slabs supported directly on the ground?

The minimum thickness of concrete floor slabs supported directly on the ground is typically governed by building codes and standards that seek to ensure structural integrity, durability, and load-bearing capacity. A thickness of 3-1/2 inches for these slabs is generally accepted as the minimum because it provides adequate strength to support typical residential and light commercial loads while also minimizing cracking and other potential damage that can result from the ground's moisture variations and soil movement.

Thicker slabs will help accommodate any stresses and movements due to temperature changes, shrinkage, or soil settlement. Using a thickness of 3-1/2 inches balances material efficiency with the necessary resiliency required for stable flooring. The other thicknesses listed may not provide sufficient strength or durability for various applications, making them inadequate under standard construction practices.