Wood I-joist floor system with OSB decking
Use of horizontal I-beams from engineered wood products reduce virgin materials and waste disposed by burning or landfills. Joists use material more efficiently when spaced 24 inches apart on center. In some cases, where more support is required, the joists may be closer together. I-joists provide consistent structural performance for residential applications. They can span long distances, offering flexibility. They are simple to install, are dimensionally stable, and are lightweight and easy to handle. When reasons of aesthetics require enclosure of exposed spaces, negative effects are increased because more materials are used, primarily those with higher embodied energy, such as gypsum board. Enclosed cavities around plumbing also increase the potential for mold development affecting indoor air quality.

Citation
APA Website www.apawood.org/level_b.cfm?content=app_bas_floor