General Contractor Practice Exam

What is the minimum needed in a concrete basement floor for normal use that is not exposed to weather?

1. 2 inches thick with a 4 mil vapor barrier

2. 3 inches thick with a 6 mil vapor barrier

3. 3 1/2 inches thick with a 6 mil vapor barrier

4. 4 inches thick with a 10 mil vapor barrier

The correct answer is: 3 1/2 inches thick with a 6 mil vapor barrier

The minimum thickness of a concrete basement floor for normal use that is not exposed to weather is vital for ensuring proper structural support, insulation, and moisture control. A thickness of 3 1/2 inches is generally recommended because it offers sufficient strength to handle everyday loads such as furniture, appliances, and foot traffic without cracking or settling. In addition, a 6 mil vapor barrier is appropriate to mitigate moisture migration from the ground into the concrete slab, which is crucial in basement applications where humidity could be higher. This barrier helps prevent issues that may arise from excess moisture, such as mold growth and deterioration of both the concrete and any materials above it. While thinner options might be offered, they would not provide the necessary durability or moisture protection expected in a functional basement. Thicker options might also be available but could lead to unnecessary excess in material use and costs. The combination of the specified thickness and vapor barrier in the correct answer effectively balances performance and efficiency for a basement that experiences normal use while remaining protected from weather-related moisture issues.