Spanning 23 feet with doubled 2x8 floor joists might be possible depending on the specific load requirements and the building codes in your area. However, it's essential to consult a structural engineer or a qualified professional to determine the appropriate size and spacing of floor joists for your specific situation.
The ability of 2x8 floor joists to span 23 feet without additional support will depend on several factors, including:
Live Load: The weight of people, furniture, and other movable items that the floor needs to support.
Dead Load: The weight of the floor structure itself, including the joists, subfloor, and any additional layers like underlayment and flooring.
Building Codes: Local building codes and regulations dictate the minimum requirements for floor joist sizes and spans to ensure structural safety.
Deflection Limits: The amount of acceptable floor deflection or bounce, which can impact the comfort and usability of the floor.
Species and Grade of Lumber: Different wood species and grades have varying load-carrying capacities.
Spacing of Joists: The distance between each joist (commonly 16 or 24 inches on center).
Additional Supports: The use of support beams, columns, or load-bearing walls to help distribute the load.
Given the considerable span of 23 feet, it's likely that additional support will be necessary to prevent excessive floor deflection and ensure a safe and stable structure. This could involve using larger joists, increasing the number of joists, or incorporating support beams or columns.
Again, I cannot stress enough the importance of consulting a structural engineer or a qualified professional to assess your specific requirements and ensure that your floor system is designed and built to meet all necessary safety standards. They will be able to perform load calculations and provide you with the most appropriate and safe design for spanning 23 feet.