For a concrete slab on ground, which thickness is acceptable for two-family dwellings?

The acceptable thickness for a concrete slab on ground for two-family dwellings is typically 4 inches. This is based on standard building practices and codes that ensure proper structural support and load-bearing capacity. A slab of this thickness provides adequate strength to support the weight of the building and the various loads it may encounter, including occupants, furniture, and other live loads.

A 3-inch slab may not provide sufficient strength or durability over time, particularly in residential applications where floors need to withstand significant use. Similarly, a 3.5-inch slab, while slightly thicker, still falls short of the commonly recommended minimum for structural integrity and may lead to issues such as cracking or structural failure. Choosing a 5-inch thickness could be excessive for typical residential use; while it may provide extra strength, it might not be necessary for standard two-family dwellings and could increase construction costs unnecessarily.

Therefore, while the other options present may not fully comply with general building standards for two-family dwellings, a 4-inch thick slab is deemed acceptable because it balances structural integrity, durability, and cost-effectiveness.