North Carolina Building Contractor License Practice Exam

What is the minimum thickness for a concrete floor slab that is directly supported on the ground?

1. 2 inches

2. 3 inches

3. 3-1/2 inches

4. 4 inches

The correct answer is: 3-1/2 inches

The minimum thickness for a concrete floor slab that is directly supported on the ground is typically 4 inches. A slab that is 4 inches thick offers sufficient strength and durability to withstand normal residential loads and is also compliant with many building codes. This thickness helps in reducing cracking and improves the overall stability of the structure. Additionally, a thicker slab can provide better insulation properties and protection against moisture intrusion from the ground. Concrete slabs that are thinner, such as 2 inches or 3 inches, do not usually meet the structural requirements for load-bearing and durability, particularly in various weather conditions. A thickness of 3-1/2 inches, while closer to the required standard than the thinner options, is still generally considered inadequate in most building practices. Compliance with codes is critical for the safety and longevity of construction projects, emphasizing the importance of adhering to the 4-inch minimum slab thickness.