What is the allowable MINIMUM specified compressive strength for concrete in foundations NOT exposed to weather?

The minimum specified compressive strength for concrete used in foundations that are not exposed to weather is typically set at 2,500 psi. This strength is sufficient for typical foundation applications, such as footings and walls, where the concrete is protected from environmental factors like moisture and freeze-thaw cycles.

This strength ensures that the concrete has adequate durability and load-bearing capacity to support the structures built on top of it. It is a balance between ensuring structural integrity and managing costs, as higher compressive strength generally leads to increased material costs.

By specifying 2,500 psi, building codes provide a standard that is effective for common construction practices while based on years of performance data and engineering principles. This allows contractors and engineers to design foundations confidently, knowing that they meet safety and performance requirements without overspending on unnecessary strength when the concrete is not subjected to the elements.