Using 2x6 lumber for floor joists depends on the span and the load-bearing requirements of the floor. In some cases, 2x6 lumber may be suitable, while in others, it may not be adequate. Here are some factors to consider:
Span: The distance between the supports (walls or beams) is critical in determining the size of the joists needed. Longer spans require larger and stronger joists to support the load without excessive deflection.
Load capacity: Consider the intended use of the floor and the expected loads it will need to bear. For residential applications, typical live loads (furniture, people, etc.) and dead loads (weight of the floor itself) are used for calculations.
Building codes: Local building codes specify the minimum requirements for floor joists based on factors like span, loads, and species of wood. Always check your local building codes to ensure compliance.
Species and grade of lumber: Different species and grades of lumber have different load-bearing capacities. For example, #2 or better grade lumber is stronger and less prone to knots and defects than lower grades.
If you're unsure about the appropriate size of the floor joists for your specific project, it's essential to consult with a structural engineer or a qualified building professional. They can perform load calculations and help you determine the appropriate size and spacing of the floor joists to ensure your floor is safe and meets the necessary building codes.